VFS-24, VFS-30, VFS-48, VFS-60 - Single/Dual Digital Voice Compression Server Modules

 
VFS-24, VFS-30, VFS-48, VFS-60 - Single/Dual Digital Voice Compression Server Modules
OPERATION MANUAL
                                                                     INSTALLATION AND
       VFS-24, VFS-30,
        VFS-48, VFS-60
Single/Dual Digital Voice Compression Server
                                    Modules
                  Megaplex-2100/2104 Version 12

                                                  Innovative Access Solutions
VFS-24, VFS-30, VFS-48, VFS-60 - Single/Dual Digital Voice Compression Server Modules
VFS-24, VFS-30, VFS-48, VFS-60
   Single/Dual Digital Voice Compression Server Modules
                         Megaplex-2100/2104 Version 12
                    Installation and Operation Manual

                                          Notice
This manual contains information that is proprietary to RAD Data Communications Ltd. ("RAD").
No part of this publication may be reproduced in any form whatsoever without prior written
approval by RAD Data Communications.
Right, title and interest, all information, copyrights, patents, know-how, trade secrets and other
intellectual property or other proprietary rights relating to this manual and to the
VFS-24, VFS-30, VFS-48, VFS-60 and any software components contained therein are proprietary
products of RAD protected under international copyright law and shall be and remain solely with
RAD.
VFS-24, VFS-30, VFS-48, VFS-60 is a registered trademark of RAD. No right, license, or interest to
such trademark is granted hereunder, and you agree that no such right, license, or interest shall
be asserted by you with respect to such trademark.
You shall not copy, reverse compile or reverse assemble all or any portion of the Manual or the
VFS-24, VFS-30, VFS-48, VFS-60. You are prohibited from, and shall not, directly or indirectly,
develop, market, distribute, license, or sell any product that supports substantially similar
functionality as the VFS-24, VFS-30, VFS-48, VFS-60, based on or derived in any way from the
VFS-24, VFS-30, VFS-48, VFS-60. Your undertaking in this paragraph shall survive the termination
of this Agreement.
This Agreement is effective upon your opening of the VFS-24, VFS-30, VFS-48, VFS-60 package
and shall continue until terminated. RAD may terminate this Agreement upon the breach by you
of any term hereof. Upon such termination by RAD, you agree to return to RAD the
VFS-24, VFS-30, VFS-48, VFS-60 and all copies and portions thereof.
For further information contact RAD at the address below or contact your local distributor.

 International Headquarters                       North America Headquarters
 RAD Data Communications Ltd.                     RAD Data Communications Inc.

 24 Raoul Wallenberg Street                       900 Corporate Drive
 Tel Aviv 69719, Israel                           Mahwah, NJ 07430, USA
 Tel: 972-3-6458181                               Tel: (201) 5291100, Toll free: 1-800-4447234
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© 1988–2007 RAD Data Communications Ltd.                          Publication No. 764-262-10/07
Quick Start Guide

                  If you are familiar with the VF modules, use this guide to prepare the module for
                  operation.

                  1.         Installing the VFS Modules
                  Insert the module in the assigned I/O slot.

Setting the Internal Jumpers

                  VFS-60 Internal Settings
                  Refer to the figure below and set the module jumpers as required.

                  VFS-30 Internal Settings
                  For VFS-30 modules, ignore the jumpers serving link 2.

VFS   MP-2100/2104 Ver. 12                                        Installing the VFS Modules      1
Quick Start Guide                                                                   Installation and Operation Manual

                                                   Link 1 Interface                               Link 1 Jumper JP5
                                                 JP7, JP8, JP9, JP10
                                                          JP9
                                                                                                  NO    Pins 3,6 of RJ-45
                                                                                                        Connector of Link 1
                                                                     120 Ω                              not Connected to
                                        JP7    JP8
                                                                   Balanced                             Frame Ground
                                                         JP10

                                                          JP9                                           Pins 3,6 of RJ-45
                                                                                          YES           Connector of Link 1
                                        JP7    JP8
                                                                     75Ω                                Connected to
                                                                  Unbalanced                            Frame Ground
                                                         JP10

                                                                                                                    JP5

                                                        Link 1 Jumpers                     JP9
                                                                              JP7   JP8
                                                                                           JP10

                                                                                           JP13

                                                        Link 2 Jumpers                     JP14                     JP15

                                                         (VFS-60 only)        JP11 JP12

                                                   Link 2 Interface                              Link 2 Jumper JP15
                                                JP11, JP12, JP13, JP14
                                                                                                  NO    Pins 3,6 of RJ-45
                                                          JP13
                                                                                                        Connector of Link 2
                                                                    120Ω                                not Connected to
                                        JP11   JP12
                                                                   Balanced                             Frame Ground
                                                          JP14

                                                          JP13                                          Pins 3,6 of RJ-45
                                                                                          YES           Connector of Link 2
                                        JP11   JP12
                                                                     75Ω                                Connected to
                                                                  Unbalanced                            Frame Ground
                                                          JP14

                    VFS-48 Internal Settings
                    Refer to the figure below and set the module jumpers as required.

                    VFS-24 Internal Settings
                    For VFS-24 modules, ignore the jumpers serving link 2.

2          Installing the VFS Modules                                                     VFS          MP-2100/2104 Ver. 12
Installation and Operation Manual                                                            Quick Start Guide

                                                                                   Link 1 Jumper JP5

                                                                                   NO    Pins 3,6 of RJ-45
                                                                                         Connector of Link 1
                                                                                         not Connected to
                                                                                         Frame Ground

                                                                                         Pins 3,6 of RJ-45
                                                                             YES         Connector of Link 1
                                                                                         Connected to
                                                                                         Frame Ground

                                                                                                               JP24

                                                             Link 1 Jumper

                                                             Link 2 Jumper
                                                             (VFS-48 only)
                                                                                                               JP25

                                                                                   Link 2 Jumper JP15

                                                                                   NO    Pins 3,6 of RJ-45
                                                                                         Connector of Link 2
                                                                                         not Connected to
                                                                                         Frame Ground

                                                                                         Pins 3,6 of RJ-45
                                                                             YES         Connector of Link 2
                                                                                         Connected to
                                                                                         Frame Ground

                   2.        Connecting the Cables
                   Before starting, refer to the installation plan to determine the cables intended for
                   connection to this VFS module.

Connecting the Balanced E1 or T1 Interface
                   To connect the user’s equipment to the balanced E1 or T1 link:
                   •    Connect the user’s equipment to the prescribed VFS RJ-45 connectors marked
                        LINK1 and LINK2.

Connecting the E1 Unbalanced Interface
                   To connect the unbalanced interface:
                   1. Connect the RJ-45 connector of the adapter cable CBL-RJ45/2BNC/E1 to the
                      prescribed LINK connector.
                   2. Connect the coaxial cables from the user’s equipment to the two BNC
                      connectors at the other end of the adapter cable. Pay attention to correct
                      connection:

VFS   MP-2100/2104 Ver. 12                                              Connecting the Cables                  3
Quick Start Guide                                                        Installation and Operation Manual

                               Connect the cable from the user’s equipment transmit output to the
                               green BNC connector (VFS link receive input)
                               Connect the cable from the user’s equipment receive input to the red BNC
                               connector (VFS link transmit output).

                     3.         Configuration Procedure
                     You can sequentially configure all the VFS parameters using the command
                     DEF CH SS *, where SS is the VFS slot number.

Configuring the Internal Port Parameters
                     Configure each internal port using the command DEF CH SS CC, where SS is the
                     VFS slot number, and CC is the internal port number (IN1 to IN8).
                     The internal port configuration parameters and the allowed range of values are
                     listed below.

                    Parameter          Values

                    Connect            YES
                                       NO

                    Rate               1 to 31

                    Max Bytes in       100 to 1472
                    Multiplex Frame    Default: 450

                    MF Relay           Enable
                                       Disable

                    Min Pulse Width    45 to 300 msec, 60 msec

                    Min Power Level    0 to –35 dBm, -12 dBm

                    Frame Interval     10, 20, 30, …, 90 msec

                    Voice Coding       G7231 6.4 kbps
                                       G7231/5.3 kbps
                                       G729A8
                                       G711 A-law
                                       G711 U-law

                    Type               PTP
                                       AAL2oMPLS

                    Volume             NONE
                                       –6 dB to +6 dB
                    Coding Law         A-Law
                                       U-Law

4          Configuration Procedure                                           VFS   MP-2100/2104 Ver. 12
Installation and Operation Manual                                                           Quick Start Guide

                  Parameter           Values

                  Echo Canceller      Enable
                                      Disable

                  Modem               Enable
                                      Disable
                  S Tandem            Disable

                  Fax Rate            N/A
                                      4.8 kbps
                                      9.6 kbps
                                      14.4 kbps

                  Inband              OFF
                  Management          ON
                  Routing Protocol    NONE
                                      PROPRIETARY RIP
                                      RIP2
                  Dst IP              When operating opposite a Vmux device (Type must
                                      be set to AAL2oMPLS), set the IP address in the
                                      format xxx.xxx.xxx.xxx.
                                      When operating opposite a VFS module (Type set to
                                      PTP), N/A is displayed

                  Src/Dst Bundle ID   The allowed range is 1 to 30 when operating
                                      opposite a Vmux device (Type must be set to
                                      AAL2oMPLS)
                                      When operating opposite a VFS module (Type set to
                                      PTP), N/A is displayed

                  Src IP              xxx.xxx.xxx.xxx
                                      N/A
                                      Default: CL module IP address
                  IP Mask             xxx.xxx.xxx.xxx
                                      N/A
                                      Default: 255.255.255.0
                  Default Gateway     xxx.xxx.xxx.xxx
                                      N/A
                                      Default: 0.0.0.0

                  ML Slot             Megaplex-2100: 1 to 12
                                      Megaplex-2104: 1 to 5

                  ML Channel          The allowed range is 1 to 8, in accordance with the
                                      number of external ports on the main link module.
                                      Default: 1

VFS   MP-2100/2104 Ver. 12                                                Configuration Procedure          5
Quick Start Guide                                                           Installation and Operation Manual

Configuring the Link Parameters
                    To define the parameters of the desired VFS link, type:
                         DEF CH SS CC
                    where SS is the VFS slot number, and CC is the desired link number, 1 or 2 (you
                    may also use EX1 and EX2).
                    The link parameters include two types of parameters:
                    •    External E1/T1 port parameters
                    •    Timeslot utilization parameters, displayed immediately after the external
                         E1/T1 port parameters.
                    The E1 and T1 parameters are described below followed by timeslot utilization
                    parameters.

                    External E1 Port Parameters (VFS-30, VFS-60)

                    Parameter        Values

                    Connect          YES
                                     NO

                    Frame            G.732N
                                     G.732N-CRC4
                                     G.732S
                                     G.732S-CRC4

                    Sig. Profile     1 to 5

                    Idle Code        00 to FF (hexa)

                    Rx Gain          LONG HAUL
                                     SHORT HAUL

                    OOS Signaling    FORCED BUSY
                                     FORCED IDLE
                    Restoration      CCITT
                    Time             10 SECONDS (62411)
                                     1 SECOND (FAST)
                    Inband           OFF
                    Management       DEDICATE PPP
                                     DEDICATE FR
                    Inband           N/A
                    Management       64kbps (for DEDICATE FR and DEDICATE PPP)
                    Rate

                    Routing          NONE
                    Protocol         PROPRIETARY RIP
                                     RIP2

6          Configuration Procedure                                               VFS   MP-2100/2104 Ver. 12
Installation and Operation Manual                                                        Quick Start Guide

                   External T1 Port Parameters (VFS-24, VFS-48)

                  Parameter         Values

                  Connect           YES
                                    NO

                  Frame             SF (D4)
                                    ESF

                  Sig. Profile      1 through 5

                  Idle Code         00 to FF (hexa)

                  FDL Type          RESPONSE
                                    COMMAND

                  Line Code         TRANSPARENT
                                    B7
                                    B8ZS

                  Interface         CSU
                                    DSU

                  Tx Gain           CSU Mode – Attenuation
                                    0 dB
                                    7.5 dB
                                    15 dB
                                    22.5 dB
                                    DSU Mode – Length
                                    000 to 133 FEET
                                    133 to 266 FEET
                                    266 to 399 FEET
                                    399 to 533 FEET
                                    533 to 655 FEET

                  Rx Gain           LONG HAUL
                                    SHORT HAUL

                  OOS Signaling     FORCED BUSY
                                    FORCED IDLE
                  RBMF Sig.         YES
                                    NO
                  Restoration       10 SECONDS (62411)
                  Time              1 SECOND (FAST)
                  Inband            OFF
                  Management        DEDICATE PPP
                                    DEDICATE FR
                  Inband            N/A
                  Management        64kbps (for DEDICATE FR and DEDICATE PPP)
                  Rate

VFS   MP-2100/2104 Ver. 12                                              Configuration Procedure         7
Quick Start Guide                                                           Installation and Operation Manual

                    Parameter       Values

                    Routing         NONE
                    Protocol        PROPRIETARY RIP
                                    RIP2

                     Timeslot Utilization Parameters

                    Parameter       Values

                    Local           N/A
                    Destination     INT01 to INT08
                                    SS:CC:TT

                    Timeslot Type   VOICE
                                    TRANS
                                    MNG
                                    CCS
                                    SS7

                    Connection Id   N/A
                                    1 (EX1:1), …, 31 (EX1:31), 32 (EX2:1), …, 62 (EX2:31)
                                    (the first number indicates the VFS destination, the
                                    number in parentheses indicates Vmux destination)

                     4.         Configuring the Module for Server Operation
                     In the server applications, use the following commands to assign timeslots:
                     •    For the VFS-30 and VFS-24 modules: DEF TS SS IN9
                     •    For the VFS-48 and VFS-60 modules: DEF TS SS IN9 and DEF TS SS IN10.
                     The internal IN9 and IN10 port timeslot utilization parameters and the allowed
                     range of values are listed below.

                     Timeslot Utilization Parameters

                    Parameter       Values

                    Local           N/A
                    Destination     INT01 to INT08
                    Timeslot Type   VOICE

                    Connection Id   N/A
                                    1 (EX1:1), …, 31 (EX1:31), 32 (EX2:1), …, 62 (EX2:31)
                                    (the first number indicates the VFS destination, the
                                    number in parentheses indicates Vmux destination)

8          Configuring the Module for Server Operation                           VFS   MP-2100/2104 Ver. 12
Contents
Chapter 1. Introduction
      1.1   Overview....................................................................................................................1-1
              Product Options......................................................................................................1-1
              Main Features.........................................................................................................1-1
                 Voice Transmission.............................................................................................1-1
                 Automatic Fax and Modem Transmission ............................................................1-2
                 Transparent Transfer of Timeslots ......................................................................1-2
                 Traffic Carrying Capacity .....................................................................................1-2
      1.2   Typical Applications....................................................................................................1-4
              Point-to-Point Applications .....................................................................................1-4
              Point-to-Multipoint Applications..............................................................................1-4
              Server Application...................................................................................................1-5
      1.3   Physical Description ...................................................................................................1-6
      1.4   Functional Description................................................................................................1-8
              Functional Block Diagram ........................................................................................1-8
              TDM Bus Interfaces.................................................................................................1-9
              Routing Matrix on TDM Buses Side ..........................................................................1-9
                 Overview of Internal Routing Method .................................................................1-9
                 Routing Matrix Functions ..................................................................................1-10
              CPU ......................................................................................................................1-10
              DSP Subsystem .....................................................................................................1-10
              Signaling RAM .......................................................................................................1-11
              Link Interfaces ......................................................................................................1-11
                 E1 Link Interfaces (VFS-30, VFS-60)..................................................................1-11
                 T1 Link Interfaces (VFS-24, VFS-48)..................................................................1-11
              Clock Generator and Timing Subsystem .................................................................1-12
                 Link Timing.......................................................................................................1-12
                 System Timing..................................................................................................1-12
              Local Management Subsystem ..............................................................................1-12
              E1 Interface Characteristics (VFS-30, VFS-60) ........................................................1-13
              T1 Interface Characteristics (VFS-24, VFS-48) ........................................................1-13
              Handling of Signaling Information .........................................................................1-14
                 Handling of CAS Signaling.................................................................................1-14
                 Handling of CCS Signaling .................................................................................1-14
                 Handling of SS7 Signaling .................................................................................1-14
              Audio Signal Processing Capabilities ......................................................................1-14
                 Handling of Voice Signals .................................................................................1-15
                 DTMF Processing ..............................................................................................1-15
                 Automatic Fax Processing .................................................................................1-16
                 Handling of Voiceband Modem Signals..............................................................1-16
              Test and Diagnostic Capabilities ............................................................................1-17
      1.5   Technical Characteristics ..........................................................................................1-18

Chapter 2. Installation and Operation
      2.1   Introduction...............................................................................................................2-1
      2.2   Setting the Internal Jumpers .......................................................................................2-1
              VFS-60 Internal Settings..........................................................................................2-1
              VFS-30 Internal Settings..........................................................................................2-2
              VFS-48 Internal Settings..........................................................................................2-3

VFS   MP-2100/2104 Ver. 12                                                                                                                 i
Table of Contents                                                                              Installation and Operation Manual

              VFS-24 Internal Settings..........................................................................................2-4
      2.3   Installing the Module in the Chassis............................................................................2-4
      2.4   Connecting the Cables................................................................................................2-5
              Connecting the Balanced Interface ..........................................................................2-5
              Connecting the Unbalanced Interface ......................................................................2-5
      2.5   Normal Indications .....................................................................................................2-6
              Module Status Indication.........................................................................................2-6
              Link Status Indications ............................................................................................2-6

 Chapter 3. Configuration
      3.1   Overview....................................................................................................................3-1
      3.2   Outline of Configuration Procedure ............................................................................3-1
              Outline of Configuration Procedure .........................................................................3-1
      3.3   Configuration Instructions ..........................................................................................3-2
              Configuring Internal Port Parameters.......................................................................3-2
              Configuring Link Parameters....................................................................................3-5
                 External E1 Port Parameters (VFS-30, VFS-60) ....................................................3-6
                 E1 Timeslot Utilization Parameters .....................................................................3-8
                 External T1 Port Parameters .............................................................................3-10
                 T1 Timeslot Utilization Parameters ...................................................................3-14
      3.4   Configuring the Module for Server Operation............................................................3-15
      3.5   System Timing Considerations ..................................................................................3-16
      3.6   Displaying VFS Information.......................................................................................3-16
              Displaying Status and Configuration Information ...................................................3-17
              Displaying Signaling Information............................................................................3-17

 Chapter 4. Troubleshooting and Diagnostics
      4.1   Introduction...............................................................................................................4-1
      4.2   Performance Monitoring.............................................................................................4-1
              Overview ................................................................................................................4-1
              Internal Port Performance Parameters.....................................................................4-2
      4.3   Test and Diagnostic Functions....................................................................................4-3
              Loopbacks and Tests on External E1/T1 Ports..........................................................4-3
                 Remote Loopback on External E1/T1 Interface ..................................................4-3
                 Local Loopback on External E1/T1 Interface ........................................................4-4
              Loopbacks on Internal Ports....................................................................................4-5
      4.4   Troubleshooting the Modules .....................................................................................4-6
              Troubleshooting New Installations ..........................................................................4-6
              General Troubleshooting Procedure.........................................................................4-7
      4.5   Frequently Asked Questions .......................................................................................4-7
      4.6   Technical Support ......................................................................................................4-8

ii                                                                                                   VFS     MP-2100/2104 Ver. 12
Chapter 1
                  Introduction

                  1.1        Overview
                  VFS-24, VFS-48, VFS-30 and VFS-60 are digital voice/fax compression server
                  modules for the Megaplex-2100 and Megaplex-2104 Modular Integrating Access
                  Nodes.

Product Options
                  The voice/fax compression modules are available in the following versions that
                  differ with respect to the interface type (E1 or T1) and the number of external
                  links installed on the module:
                  •   VFS-30: module with one E1 link, supports 30 channels
                  •   VFS-60: module with two independent E1 links, supports 30 channels per link
                      for a total of 60 channels per module.
                  •   VFS-24: module with one T1 link, supports 24 channels
                  •   VFS-48: module with two independent T1 links, supports 24 channels per link
                      for a total of 48 channels per module.
         Note
                  In this manual, the generic term Megaplex is used when the information is
                  applicable to both the Megaplex-2100 and Megaplex-2104 chassis types, and the
                  term VFS is used when the information is applicable to all the four modules. The
                  complete designation is used only for information applicable to a specific version.

Main Features

                  Voice Transmission
                  The VFS modules connect and compress E1/T1 voice trunks for efficient
                  transmission over TDM or IP networks. The timeslots received from the external
                  E1/T1 trunks or from the VC-4/8/16/4A/8A voice compression modules via the
                  backplane are compressed by the module DSP using one of the following
                  standard algorithms:
                  •   ITU-T Rec. G.723.1 at 6.4 kbps per channel. This enables transmitting up to
                      10 voice channels in one timeslot.
                  •   ITU-T Rec. G.723.1 at 5.3 kbps per channel. This enables transmitting up to
                      12 voice channels in one timeslot.
                  •   ITU-T Rec G.729.A at 8.0 kbps per channel. This enables transmitting up to
                      8 voice channels in one timeslot.

VFS   MP-2100/2104 Ver. 12                                                        Overview          1-1
Chapter 1 Introduction                                                  Installation and Operation Manual

                   Compression methods are user-selectable per bundle.
         Note
                   Every six voice timeslots are handled by a single DSP. Each DSP supports one
                   compression method at any time.

                   The module includes adaptive echo canceling for near-end hybrid echo, for delays
                   of up to 16 msec. The echo canceller enables acceptable voice quality on voice
                   lines with long delay, such as long-distance calls or calls over non-terrestrial
                   (satellite) links.
                   To ensure reliable transmission of DTMF signals, they are always transmitted
                   through the link as digital signals (this is called DTMF relaying), and clean
                   representations are synthesized at the receiving end. The same process is used
                   for the call progress tones that are detected within the T1 trunk timeslots.

                   Automatic Fax and Modem Transmission
                   In addition to voice transmission, the VFS modules also support automatic fax
                   relaying, which allows the transmission of Group III fax (ITU-T Rec. V.17 and V.29)
                   at rates of 2.4 to 14.4 kbps, irrespective of the digitizing rate selected for voice.
                   The modules have automatic rate fallback capability, to automatically switch to
                   the next lower data rate supported by both communicating faxes.
                   Voiceband modem transmissions at all the standard rates up to 14.4 kbps (per
                   ITU-T Rec. V.22bis and V.32bis) are also supported, and are handled in the same
                   way as fax transmissions.

                   Transparent Transfer of Timeslots
                   In addition to timeslots being processed to support voice and fax, it is also
                   possible to transparently transfer selected timeslots of the external trunks,
                   through the Megaplex links, to a remote location, thereby providing support for
                   fractional T1 services together with compressed voice through the same T1 trunk.
                   Another application for transparent transfer of timeslots is support for CCS
                   signaling in any desired protocol or flavor: the timeslot carrying the CCS
                   information can be transferred transparently together with the timeslots carrying
                   the voice channels to the remote Megaplex equipment. This permits restoring the
                   original E1/T1 trunk structure, including the signaling channel, at the external link
                   interface of the remote VFS module.
                   Inband management through dedicated timeslots is also supported. Among other
                   options, this enables extending the inband management links, through the E1/T1
                   interfaces of the module, to the other equipment connected to these interfaces.

                   Traffic Carrying Capacity
                   The advanced digital signal processing (DSP) techniques used by the
                   VFS modules provide voice compression options that meet a wide range of user
                   requirements and enable the transmission of high-quality compressed voice
                   signals while requiring low bandwidth.
                   The number of channels that can be transmitted depends on the percentage of
                   silence the number of simultaneously active calls, and the packet parameters. The
                   number of channels and the approximate bandwidth can be estimated using the
                   following formula:

1-2        Overview                                                          VFS   MP-2100/2104 Ver. 12
Installation and Operation Manual                                                              Chapter 1 Introduction

              [(H e a d e r size x p a cke ts p e r se co n d ) + (# tim e slo ts x size o f

      {   co m p re sse d G .7 3 2 p a cke t x 1 0 0 0 /3 0 x a ctu a l tra n sm issio n tim e (%
                                 n o n -sile n ce ) )] x 8 b yte s p e r b it
                                 1 0 0 0 b its p e r kilo b it
                                                                                                    }      + ra te
                                                                                                         co n ve rte d
                                                                                                          to kb p s

                      You can also use for this purpose the Vmux-110/2100 Bandwidth calculator
                      supplied on the Megaplex Technical Documentation CD.
                      Two companding laws are supported, µ-law and A-law. In accordance with ITU-T
                      Rec. G.711, the A-law should be used on E1 trunks and the µ-law should be used
                      on T1 trunks. However, the user can select the desired companding law, µ-law or
                      A-law, in accordance with the specific system requirements.
                      Since the VFS modules can compress and transmit multiple E1/T1 trunks using
                      minimal bandwidth, the Megaplex units can utilize the remaining bandwidth to
                      provide other required services such as data, Ethernet LANs, ISDN and/or
                      management, all in one platform.
                      With regular voice encoding methods, much bandwidth is wasted during the
                      normal periods of silence in a call. To further reduce the actual bandwidth
                      required for voice transmission, the VFS modules support voice activity detection
                      (VAD) techniques with silence detection and suppression:
                      •   When a silence interval is detected in a channel (timeslot), an indication is
                          sent to the far end, and the transmitting side releases most of the bandwidth
                          normally occupied by the channel traffic.
                      •   The far end fills the interval with noise having characteristics similar to normal
                          background noise (this capability is called comfort noise generation), and
                          therefore the subjective quality of the call is not noticeably affected.
                      This method enables using less bandwidth to transmit the same amount of voice
                      traffic, without degrading the quality of the call.
                      The low-rate digitized voice data packets that are the result of digital signal
                      processing of the payload carried by the external port timeslots are routed to
                      internal ports. The VFS modules support up to 8 internal ports; each internal port
                      can be routed to a different destination through any desired main link port,
                      thereby supporting both point-to-point and point-to-multipoint applications.
                      The user can therefore select the bandwidth (number of timeslots on the main
                      link) that will be allocated per internal port in accordance with the selected
                      compression rate. By considering the statistical distribution of speech and call
                      traffic loads, even higher compression ratios are possible.

VFS   MP-2100/2104 Ver. 12                                                                          Overview         1-3
Chapter 1 Introduction                                                   Installation and Operation Manual

                   1.2        Typical Applications

Point-to-Point Applications
                   Figure 1-1 shows a typical point-to-point application for VFS modules. In this
                   application, a single PBX trunk is connected to a VFS module, and the resulting
                   data stream is routed by means of a single internal port, allocated the desired
                   number of timeslots, to a main link port.
                   The compressed voice data stream is transported through the TDM network to
                   the far end, where it is restored and connected to another PBX. The PBX trunks
                   can use any desired signaling protocol:
                   •     For CAS (robbed-bit signaling), no special arrangements are needed, as this
                         signaling protocol is processed and transferred by the VFS module within the
                         compressed voice data stream.
                   •     For other signaling protocols, for example, protocols using CCS, the timeslots
                         carrying the signaling information can be transparently transferred to the far
                         end in other main link timeslots, and made available to the equipment
                         connected to the far end module.
                   A single Megaplex-2100 unit can be equipped with up to 10 VFS-60/VFS-48
                   modules, and therefore can support up to 20 E1/T1 trunks (600/480 digital voice
                   channels). After compression, this payload can be transmitted using only
                   two E1/T1 links, enabling very efficient utilization of the E1/T1 links.
                   Megaplex-2104 units can be equipped with 4 VFS-60/VFS-48 modules to support
                   up to 8 E1/T1 trunks.

           Figure 1-1. Transport of Compressed Digital Trunks in Point-to-Point Topology

Point-to-Multipoint Applications
                   Point-to-multipoint applications use the multiple internal ports (up to 8)
                   supported by the VFS modules. Each internal port can operate at a different voice
                   encoding rate and/or fax rate. Each internal port can be routed to a different
                   destination by routing it to a different main link port or IP destination.
                   Figure 1-2 shows a typical point-to-multipoint application for VFS modules. In this
                   application, two PBX trunks are connected to a VFS-48 module, and the resulting
                   data stream is routed by means of three internal ports, allocated the desired
                   number of timeslots, to a ML-IP module.
                   The ML-IP module provides independent links to the desired destinations through
                   the IP network.

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      Figure 1-2. Combining Compressed Digital Voice, Analog Voice and Data in Point-to-Multipoint
                                               Topology

Server Application
                    Figure 1-3 shows a typical server application for VFS-24 modules. In this
                    application, the VFS module is used to compress the PCM data for sending it
                    towards the network. The VC-16 module is sending PCM data and signaling
                    towards the backplane. The VFS server takes this information from the backplane,
                    compresses it and sends it via the bundles back to the backplane. At this stage,
                    the main link takes the bundle and sends it towards the remote VFS.

      Figure 1-3. Transport of Compressed Digital and Analog Channels over TDM Network (VFS as
                                        Compression Server)

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                   1.3         Physical Description
                   The VFS modules are 4U-high and occupy one slot in the Megaplex chassis. All the
                   module parameters are configurable by software, except for the selection of the
                   link interface type (balanced or unbalanced) in VFS-30 and VFS-60 modules.
                   The module panels are shown in Figure 1-4. The panels include an RJ-45
                   connector and a group of status indicators for each link, and a module alarm
                   indicator.
                   Table 1-1 explains the functions of the components located on the module
                   panels.

                                      VFS-24              VFS-48               VFS-30            VFS-60
                                        T1                 2T1                   E1               2E1

                                    ALARM               ALARM                ALARM              ALARM

                                         ON                   ON                  ON                ON
                             TST         LINE    TST         LINE     TST         LINE    TST      LINE
                             RED         YEL     RED         YELL     LOC         REM     LOC      REM
                                                                I
                                   S. LOSS             S. LOSS  N           S. LOSS          S. LOSS
                                                                K                                         L
                                             L                  1                                         I
                                             I                                                            N
                                                                                                          K
                                             N                                                            1
                                             K
                                                                                      L
                                                                                      I
                                                                  L                   N
                                                                  I
                                                                 N                    K
                                                              ON K
                                                 TST         LINE 2
                                                 RED      YEL
                                                   S. LOSS
                                                                                                          L
                                                                                                          I
                                                                                                          N
                                                                                                          K
                                                                                                          2
                                                                                                    ON
                                                                                          TST      LINE
                                                                                          LOC      REM
                                                                                            S. LOSS

                              VFS-24              VFS-48               VFS-30              VFS-60

                                                            Figure 1-4. VFS Module Panels

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                                       Table 1-1. VFS Panel Components

 Component                      Description

 ALARM indicator                Lights when a fault has been detected in the module

 ON LINE indicator              Lights steadily when the corresponding link is operating properly and is
                                active (i.e., some of its timeslots are connected to an internal port or
                                bypassed).
                                Off when the corresponding link is defective, or none of its timeslots is
                                connected to an internal port or bypassed

 RED S. LOSS (VFS-24/48)        Lights when the corresponding local link has lost frame synchronization
 LOC S. LOSS (VFS-30/60)
 indicator

 YEL S. LOSS (VFS-24/48)        Lights when a loss-of-frame synchronization indication is received by the
 REM S. LOSS (VFS-30/60)        corresponding link from the equipment connected to that link
 indicator

 TST indicator                  Lights when a test is being performed on the corresponding link

 LINK connector                 RJ-45 connector for connection to the corresponding link interface

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                                                        1.4     Functional Description

Functional Block Diagram
                                                        Figure 1-5 shows the functional block diagram of the VFS modules.

                                                                             Internal                                                  VFS
                                                                              Ports

                                                                                1                          Voice
                                                                                                        Processing
                                                                                                          DSP 1
                                                                                2

                                                                                                                                 Link
                                                                                3                                              Interface        Link 1
                                                                                                                              (Port EX1)

                                                                                4
                                                                 Routing
                                                                  Matrix
                                                                   and          5         CPU
                                                                 TDM Bus                                        VFS-48, VFS-60 Only
                                                                Interfaces
                                                                                6
                                                                                                                                 Link
                                                                                                                               Interface        Link 2
      TDM Bus A

                    TDM Bus B

                                TDM Bus C

                                            TDM Bus D

                                                                                7                                             (Port EX2)

                                                                                                           Voice
                                                                                                        Processing
                                                                                8                         DSP 2

                                                                                 ABCD
                                                                             Signaling RAM

                                                                               Control          To Link Interfaces
       Management
        Channel

                                                                                Local
                                                                             Management

       To CL Module

                  Nodal Timing                                                                    Internal Clock
                                                                                                  & Timing Signals
                  Main Clock                                                   Clock
                                                                              Generator           Receive Clock from
                  Fallback Clock
                                                                                                  Link Interfaces

                                                                               Clock
                                                                              Selection

                                                                      Figure 1-5. Functional Block Diagram

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                   The VFS modules include the following subsystems:
                   •    Routing matrix and TDM bus interfaces
                   •    CPU (including internal ports)
                   •    DSP subsystem
                   •    Link interfaces
                   •    Clock generator and timing subsystem
                   •    Local management subsystem
                   •    ABCD Signaling RAM.

TDM Bus Interfaces
                   The VFS module has four independent TDM bus interfaces, one for each Megaplex
                   TDM bus. Each TDM bus interface is used to connect timeslots from the
                   corresponding bus to the routing matrix of the VFS module, in accordance with
                   the commands received from the CL module.

Routing Matrix on TDM Buses Side

                   Overview of Internal Routing Method
                   To understand the payload routing method used within the VFS module, it is
                   necessary to consider three entities:
                   •    Chassis TDM buses. The flow of payload on these buses is organized in
                        timeslots (31 timeslots per bus). The CL module automatically assigns
                        timeslots on the TDM buses to each connected I/O channel or internal port of
                        the modules installed in the chassis.
                   •    External ports. The external port, which has an E1 or T1 interface, provides
                        the connection to the local user’s equipment. VFS-60 and VFS-48 modules
                        have two independent external E1 and T1 ports, respectively.
                        An external E1 port has a capacity of 31 timeslots. However, since signaling
                        information must always be transmitted, only 30 timeslots can carry voice
                        (one timeslot is always assigned either to CAS or CCS signaling).
                        An external T1 port has a capacity of 24 timeslots. When using CCS signaling,
                        only 23 timeslots can carry voice (one timeslot is then assigned to CCS
                        information).
                   •    Internal ports IN1 to IN8. On the TDM buses side, the timeslots that carry
                        voice and fax payload directed for transmission through the VFS module are
                        formally connected to entities designated internal ports. The
                        VFS modules can be configured to use up to 8 internal ports of this type.
                        Internal ports IN9, IN10. These internal ports are logical ports used to specify
                        the Connection ID and the destination bundle for each analog voice channel.
                        An internal port provides a convenient way to indicate which payload is to be
                        routed to a certain destination, and enables the user to specify associated
                        parameters. For flexibility in routing, the internal ports are located between

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                         two routing matrices: the TDM bus side routing matrix, and the internal ports
                         routing matrix.
         Note
                   In addition to packetized payload, it is also necessary to transparently bypass
                   timeslots to a main link port. Bypassing of timeslots is needed to support
                   fractional E1/T1 service through the module links; it may also be used to
                   transparently transfer the common channel signaling (CCS) information received
                   from the user’s equipment connected to the external port to the remote end of
                   the compressed voice link, where the original frame structure and signaling can
                   be restored.
                   The timeslot carrying inband management traffic may also have to be bypassed.

                   Routing Matrix Functions
                   The routing of the TDM bus side matrix is user-programmable, under the control
                   of the CL module, and enables connecting any timeslot between of its ports. As a
                   result, the matrix can be used to perform the following functions:
                   •     Connect timeslots between main link ports of modules installed in the
                         Megaplex and the internal ports of the VFS module. This is performed by
                         connecting the desired timeslots from the TDM buses to the prescribed
                         internal port.
                   •     Bypass timeslots between the external ports of the VFS module and main link
                         ports (through the internal ports of the VFS module).

CPU
                   CPU is used to route the packetized voice traffic to timeslots that are then
                   connected by the TDM side routing matrix to the TDM buses.
                   The CPU is also used to bypass timeslots between the external ports of the
                   VFS module and main link ports.

DSP Subsystem
                   The DSP subsystem consists of two voice processing DSP groups: DSP 1 and
                   DSP 2.
                   Each voice processing DSP group includes four DSPs for each external port.
                   In the VFS-30 and VFS-60 modules, each DSP processes six timeslots out of the
                   30 payload timeslots that may be carried by an external port. In the VFS-24 and
                   VFS-48 modules, each DSP processes six timeslots out of the 24 payload
                   timeslots that may be carried by an external port.
                   The timeslots processed by each DSP are identified in Table 1-2 for the
                   VFS-30/60 modules and in Table 1-3 for the VFS-24/48 modules.
                   Since the DSP performs the same operations on all of the processed timeslots,
                   the six timeslots must use the same voice coding standard and fax rate. The
                   resulting voice packets are sent to the internal ports routing matrix.
                   Note that the rate at which the DSP exchanges data on the external port side
                   must be locked to the external port timing, whereas the packet data rate on the
                   TDM buses side must be locked to the Megaplex nodal timing.

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                   These two rates need not be synchronized, because it is not necessary to lock
                   the packet timing to the external port timing.

                             Table 1-2. Timeslots Processed by Individual DSPs (E1 Links)

                                               DSP          Processed Timeslots

                                                1        1, 2, 3, 4, 5, 6

                                                2        7, 8, 9, 10, 11, 12

                                                3        13, 14, 15, 17, 18, 19

                                                4        20, 21, 22, 23, 24, 25

                                                5        26, 27, 28, 29, 30, 31

                             Table 1-3. Timeslots Processed by Individual DSPs (T1 Links)

                                               DSP          Processed Timeslots

                                                1        1, 2, 3, 4, 5, 6

                                                2        7, 8, 9, 10, 11, 12

                                                3        13, 14, 15, 16, 17, 18

                                                4        19, 20, 21, 22, 23, 24

Signaling RAM
                   The VFS module can serve voice channels from two sources: either two external
                   E1/T1 ports or DS0 from the TDM backplane. While the DSP is taking care of the
                   DS0 compression, the CPU is reading the signaling from the Framer or from the
                   Signaling RAM, respectively. The CPU combines the compressed voice and its
                   signaling and sends it to the remote equipment.

Link Interfaces

                   E1 Link Interfaces (VFS-30, VFS-60)
                   The VFS-30 module has one link interface, and the VFS-60 module has two
                   independent link interfaces. Each link interface performs the following functions:
                   •    The transmit path of each interface generates the E1 frames in accordance
                        with the framing mode selected by the user, and prepares the resulting data
                        stream for transmission.
                   •    The receive path recovers the receive signal and the associated clock.
                   In addition, the link interface can collect performance diagnostic data (CRC-4
                   block error data) in accordance with the applicable standards.

                   T1 Link Interfaces (VFS-24, VFS-48)
                   The VFS-24 module has one link interface, and the VFS-48 module has two
                   independent link interfaces. Each link interface performs the following functions:

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                   •     The transmit path of each interface generates the T1 frames in accordance
                         with the framing mode selected by the user (SF (D4) or ESF), and prepares
                         the resulting data stream for transmission.
                   •     The receive path recovers the receive signal and the associated clock.
                   In addition, when using ESF framing, the link interface collect performance
                   diagnostic data (CRC-6 block error data) in accordance with the applicable
                   standards.

Clock Generator and Timing Subsystem

                   Link Timing
                   The link receive path always uses the clock signal recovered from the received line
                   signal.
                   The timing of the link transmit path is always derived from the Megaplex nodal
                   timing.
                   Therefore, the user’s equipment must operate with loopback timing, i.e., it must
                   be configured to lock its transmit timing to the clock signal recovered from the
                   VFS transmit signal.

                   System Timing
                   The VFS clock generator and timing subsystem provides the clock signals needed
                   by the local module circuits.
                   In addition, this subsystem can also provide Megaplex nodal main and fallback
                   clock signals, derived from the clock signals recovered from the received line
                   signals by each link interface.
                   Therefore, the Megaplex nodal timing can be locked to the clock signal recovered
                   from the desired E1/T1 receive signal. This mode is used when the E1/T1 link
                   timing must be determined by the user’s equipment connected to the VFS
                   interface.
                   This option is necessary only when timeslots are bypassed from the module links
                   to main link ports, and the user’s equipment cannot be configured to lock its
                   transmit timing to the clock signal recovered from the VFS transmit signal.

Local Management Subsystem
                   The local management subsystem of the VFS module controls the operation of all
                   the module circuits, under the control of the CL module.
                   The management subsystem can also provide an interface between the Megaplex
                   CL module and the external links, to support inband management through a
                   dedicated timeslot when this option is enabled by the user:
                   •     In the receive-from-link direction, the management traffic is extracted from
                         the user-specified timeslot and transferred to the CL module via the
                         Megaplex chassis buses.
                   •     In the transmit to-link direction, the management traffic received from the CL
                         module is inserted in the user-specified timeslot of the link interface, for

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                        transmission to the user’s equipment (when it can be managed using one of
                        the protocols supported by Megaplex equipment).
                   The management traffic can use the PPP or Frame Relay protocols, in addition to
                   the RAD proprietary routing protocol.

E1 Interface Characteristics (VFS-30, VFS-60)
                   The E1 interfaces of the VFS-30 and VFS-60 modules meet the requirements of
                   ITU-T Rec. G.703, G.704, and G.732. The line code is HDB3. Jitter performance
                   complies with the requirements of ITU-T Rec. G.823.
                   Each link can be configured by means of internal jumpers to use either of the
                   following types of interfaces:
                   •    120Ω balanced line interface. The nominal balanced interface transmit level is
                        ±3V.
                   •    75Ω unbalanced interface. The nominal unbalanced interface transmit level is
                        ±2.37V.
                   You can select the maximum line attenuation that can be compensated without
                   degrading the BER performance: 12 dB (similar to a DSU) or 36 dB (as required of
                   an LTU).
                   Each link can be configured to use its own framing mode. The following framing
                   modes are supported:
                   •    G732S (16 frames per multiframe), intended for use with channel-associated
                        signaling (CAS). In most applications, the required signaling mode is CAS: this
                        mode is compatible with the signaling mode used by PBXs.
                   •    G732N (2 frames per multiframe), intended for use with common-channel
                        signaling (CCS) protocols. These protocols exchange the signaling information
                        through a dedicated timeslot and therefore require transparent transmission
                        of the CCS timeslot through the link.
                   You can configure each interface to operate with or without the CRC-4 option.
                   The use of the CRC-4 option allows monitoring the E1 connection to the user’s
                   equipment.

T1 Interface Characteristics (VFS-24, VFS-48)
                   The T1 line interface of the VFS-24 and VFS-48 modules meets the requirements
                   of AT&T TR-62411, ANSI T1.403, and ITU-T Rec. G.703, G.704. Jitter performance
                   complies with the requirements of AT&T TR-62411. The interface has a 100Ω
                   balanced line interface, terminated in an RJ-45 eight-pin connector. The nominal
                   transmit level is ±3V.
                   Each T1 line interface has an integral CSU, which enables operation with line
                   attenuations up to 30 dB. The CSU transmit level can be attenuated by 7.5, 15, or
                   22.5 dB, for compliance with FCC Rules Part 68A. The line interface can also
                   emulate a DSU interface. When configured for DSU emulation, the line transmit
                   signal is user-adjustable for line lengths of 0 to 655 feet in accordance with AT&T
                   CB-119, and the maximum attenuation is 12 dB.

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                   The VFS-24/VFS-48 modules support both the D4 (SF) and ESF framing formats,
                   in accordance with user's selection. Zero suppression over the line is
                   user-selectable (transparent (AMI) coding, B7ZS, or B8ZS). Framing and zero
                   suppression methods are separately selectable for each link interface.

Handling of Signaling Information

                   Handling of CAS Signaling
                   In the CAS (robbed-bit signaling) mode, the signaling information of each channel
                   is processed and transferred in the packets transferred through the internal port
                   serving the corresponding voice channels.
                   In case the link to the remote VFS module is out-of-service, the user can select
                   the state of the signaling information sent in all the channels during the
                   out-of-service period:
                   FORCED BUSY        The signaling information is forced to the busy state during
                                      out-of-service periods.
                   FORCED IDLE        The signaling information is forced to the idle state during
                                      out-of-service periods.

                   Handling of CCS Signaling
                   In addition to CAS signaling, the VFS modules can also support equipment using
                   common-channel signaling (CCS) protocols. These protocols exchange the
                   signaling information through a dedicated channel timeslot and therefore require
                   transparent transmission of the CCS timeslot through the module.
                   The CCS timeslots can be compressed and transmitted to the destination ports in
                   up to 8 logical groups, CCS to CCS. Timeslots are assigned to logical
                   groups manually be the user.

                   Handling of SS7 Signaling
                   Handling of SS7 signaling timeslots is similar to that of CCS.

Audio Signal Processing Capabilities
                   This section explains the audio processing capabilities of VFS modules. The audio
                   processing capabilities, which are performed by the digital signal processors
                   (DSPs), include:
                   •     Voice processing
                   •     Processing of DTMF and call progress tones
                   •     Processing of fax and voiceband modem signals.
                   Each DSP processes its group of timeslots (see Table 1-2, Table 1-3)
                   independently of the other DSPs, in accordance with the parameters selected by
                   the user for that group. However, within each group, the DSP detects the signal
                   type (voice, DTMF, fax, etc.) carried in each timeslot (channel), and automatically
                   selects the appropriate processing method.

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                   Handling of Voice Signals
                   Voice is digitized and compressed using one of the processing algorithms
                   supported by the VFS.
                   The low bit rate voice compression options and data rates supported by the VFS
                   modules are as follows:
                   •    Voice compression using multiple-pulse, maximum likelihood code-excited
                        linear prediction (MP-MLQ) per ITU-T Rec. G.723.1, at a channel data rate of
                        6.4 kbps. When using this option, up to 10 voice channels can be carried by
                        each timeslot sent to the Megaplex TDM buses.
                   •    Voice compression using conjugate structure-algebraic-code-excited linear
                        prediction (CS-ACELP) per Annex A of ITU-T Rec. G.729A, at a channel data
                        rate of 8 kbps. When using this option, up to 8 voice channels can be carried
                        by each timeslot sent to the Megaplex TDM buses.
                   To further reduce the bandwidth needed to transmit the voice, the VFS DSP
                   recognizes “silence” intervals and replaces them with special “silence” packets,
                   that require much less bandwidth than regular voice packets. When “silence”
                   packets are received, the comfort noise generator (CNG) of the remote channel
                   generates background noise to fill the silence intervals and give the remote
                   subscriber the impression of a live line.
                   The resulting channel data stream is packetized for transmission through the
                   network. The user can select two parameters:
                   •    The maximum number of bytes included in each voice coder frame (100 to
                        450 bytes). This limits the size of packets sent to the network.
                   •    The maximum interval between consecutive frames: if this interval expires,
                        the frame is closed and sent, even if the specified maximum number of bytes
                        has not yet been collected. This parameter ensures that the end-to-end delay
                        is not excessive, for example, the additional delay needed to collect timeslots
                        to fill a frame from an internal port that carries a single channel (timeslot),
                        even for the minimum frame length (100 bytes) is approx. 12.5 msec.
         Note
                   Because the DSP sends only data packets toward the Megaplex TDM buses, and
                   packets can be read and transmitted independently of the rate of the incoming
                   E1/T1 stream, in general it is not necessary to lock the timing of the link interface
                   to the Megaplex timing. The timing must be locked only when the module
                   transfers (bypasses) timeslots transparently.

                   To improve the perceived link quality, the DSPs also implement adaptive echo
                   canceling for near-end reflections (echo delay less than 16 milliseconds). The
                   echo canceling performance complies with ITU-T Rec. G.168 requirements.

                   DTMF Processing
                   The waveform of the DTMF signals is very different from speech waveforms,
                   therefore most compression algorithms distort DTMF signals to the point that
                   errors occur in the detection of the dialed digits when the DTMF signals are
                   transmitted as analog signals through a compressed voice channel.
                   To enable reliable transmission of DTMF signals, the VFS module uses DTMF
                   relaying. For this purpose, each DSP detects incoming DTMF signals,

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                   independently for each timeslot, and identifies the dialed digits. The digits
                   detected by the receiving end are digitally transmitted through the link to the
                   remote end, where clean digital representations of DTMF signals are synthesized
                   and inserted into the data stream sent in the corresponding timeslot.
                   While DTMF information is received, the voice path is disconnected, to prevent
                   interference by signals transmitted through the regular processing path.
                   The method used for DTMF relaying is also used to transfer transparently call
                   progress tones.

                   Automatic Fax Processing
                   The processing of audio signals by low bit rate voice compression methods does
                   not enable analog transmission of fax signals. Therefore, when it is possible that
                   fax machines may be connected to a VFS voice channel, it is necessary to enable
                   the automatic fax relaying function on that channel.
                   When automatic fax relaying is enabled, a VFS channel will automatically recognize
                   and transmit fax messages at the standard rates in the range of 2.4 to 14.4 kbps,
                   complying with ITU-T Rec. V.17 and V.29. The maximum fax rate can be selected
                   by the user. The VFS supports automatic fallback capability, that is, it will
                   automatically switch to the next lower data rate supported by both
                   communicating faxes.
                   The whole fax transmission process is handled as a data transmission, with the
                   corresponding DSP providing the fax signal modulation/demodulation functions
                   and the detection and generation of the fax connection set up tones (in digital
                   format), to enable the handshaking necessary to implement the standard fax
                   communication protocol. Fax transmission over the digital network improves
                   transmission quality, while greatly reducing long distance telephone costs and the
                   time needed for freeing the fax machine.
                   To set up a fax connection, the DSP processing the local timeslot (channel)
                   emulates the remote fax machine toward the local machine, and the remote DSP
                   emulates the local fax toward the remote machine. After the fax connection is
                   established, the fax data stream is transmitted as a packetized data stream
                   through the link. This means that the link must have enough free bandwidth to
                   enable sustained transmission of a data stream at the fax data rate (and the
                   additional connection supervision signals).
                   This process enables any standard Group III fax machine to transmit over the link.
                   The only limitation is that the round-trip transmission delay through the link
                   cannot exceed the time-out intervals specified by the fax communication protocol
                   (about 700 msec); otherwise, the handshaking needed to establish a fax
                   connection will fail.
                   Since each VFS channel automatically switches between the fax relay mode and
                   the voice mode in accordance with the type of signal being detected, the VFS
                   modules can serve PBX tie lines or channels serving a combined phone/fax
                   machine.

                   Handling of Voiceband Modem Signals
                   The DSPs can also handle voiceband modem signals, in accordance with ITU-T
                   Rec. V.22bis and V.32bis. The processing method is similar, except that the DSP
                   emulates a voiceband modem instead of a fax modem.

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Test and Diagnostic Capabilities
                   The VFS modules feature the following user-initiated loopback functions:
                   •    External E1/T1 ports. The loopbacks available at the external E1/T1 port level
                        include:
                             Local loopback toward the Megaplex TDM buses
                             Remote loopback toward the user’s equipment connected to the port.
                   •    Internal ports. The internal ports support the local loopback toward the
                        Megaplex TDM buses.

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                   1.5        Technical Characteristics

General               Number of External Ports

                          VFS-30                 One E1 port

                          VFS-60                 Two E1 ports

                          VFS-24                 One T1 port

                          VFS-48                 Two T1 ports

                      Number of Internal Ports   8 ports for regular operation
                                                 2 additional ports for server operation

Voice Encoding        Voice Encoding Technique   • MP-MLQ per ITU-T Rec. G.723.1, at a channel
                                                   data rate of 6.4 kbps or 5.3 kbps
                                                 • Conjugate structure-algebraic-code-excited
                                                   linear prediction (CS-ACELP) per Annex A of
                                                   ITU-T Rec. G.729A, at a channel data rate of
                                                   8 kbps

Fax Support           Fax Data Rates             4.8, 9.6 and 14.4 kbps, selectable per internal
                                                 port

E1 Interface          Voice Channels Supported   Up to 30 (per port)

                      Format                     E1, 2.048 Mbps

                      Standard Compliance        ITU-T Rec. G.703, G.704, G.732

                      Framing                    • G.732N
                                                 • G.732N with CRC-4
                                                 • G.732S
                                                 • G.732S with CRC-4

                      Interface                  • 120Ω, 4-wire balanced
                                                 • 75Ω, coaxial unbalanced

                      Line Code                  HDB3

                      Signal Levels

                          Transmit               • Balanced : ±3V ±10%
                                                 • Unbalanced: ±2.73V ±10%

                          Receive                • 0 to -12 dB for short-haul applications (DSU)
                                                 • 0 to -36 dB for long-haul applications (LTU)

1-18       Technical Characteristics                                       VFS   MP-2100/2104 Ver. 12
Installation and Operation Manual                                              Chapter 1 Introduction

                      Jitter Performance         Per ITU-T Rec. G.823

                      Timing Mode                • Transmit clock derived from Megaplex nodal
                                                   clock
                                                 • Receive clock recovered from the receive
                                                   signal, can be selected as timing reference for
                                                   Megaplex nodal clock

                      Connectors                 • Balanced: 8-pin RJ-45
                                                 • Unbalanced: Two BNC coaxial connectors, via
                                                   adapter cable

T1 Interface          Voice Channels Supported   Up to 24 (per port)

                      Format                     T1, 1.544 Mbps

                      Standard Compliance        AT&T TR-62411, AT&T Pub. 54016, ANSI T1.403,
                                                 and ITU-T Rec. G.703, G.704

                      Framing                    • SF (D4)
                                                 • ESF

                      Interface                  100Ω, 4-wire balanced

                      Line Code                  AMI

                      Zero Suppression           • Transparent (no zero suppression)
                                                 • B7ZS
                                                 • B8ZS

                      Signal Levels

                        Transmit Levels          • DSU emulation: ±3V ±10%, software
                                                   adjustable, measured at 0 through 655 ft
                                                 • CSU mode: 0, -7.5, -15, -22.5 dB
                                                   software-selectable

                          Receive                • 0 to -12 dB for short-haul applications (DSU)
                                                 • 0 to –36 dB for long-haul applications (CSU)

                      Jitter Performance         Per AT&T TR-62411

                      Timing Mode                • Transmit clock derived from Megaplex nodal
                                                   clock
                                                 • Receive clock recovered from the receive
                                                   signal, can be selected as timing reference for
                                                   Megaplex nodal clock

                      Connectors                 8-pin RJ-45

VFS   MP-2100/2104 Ver. 12                                        Technical Characteristics     1-19
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