AXE Platform →
AXE Platform →
AXE Platform EN/LZT 101 1513 R4A – 43 – 2 AXE PLATFORM This chapter is designed to provide the student with basic knowledge about the group switch in AXE 810 The access network connects users, for instance telephone subscribers, to a unit, switch. When two subscribers connected to for example different exchanges, speak to each other the speech has to be transmitted between them. This transmission is done in digital form and that means that the analog signal from a subscriber has to be converted to a digital one. The conversion from analog to digital or the opposite can be done in different ways using different methods.
Switching means that incoming digital information is forwarded to a specific outgoing connection. Different subsystems in AXE can perform switching. The Group switch Subsystem, GSS, performs for example switching between access network and trunk network. The main switching function in a local exchange is to interconnect timeslots to and from the subscriber access network and the trunk (transport) network. AXE 810 performs switching according to T-S method, compared to previous AXE versions that use T-S-T method.
The structure of the new GS890 in AXE 810 and the new clocks CL890 are described and the new subracks required by AXE 810 are mentioned. When different exchanges will cooperate it is necessary to synchronize them. The procedure to update GS from previous AXE versions to GS890 is presented.
2 AXE Platform EN/LZT 101 1513 R4A – 45 – AXE PLATFORM SWITCHING ACCESS NETWORK Access network Access network Access network Figure 2-1 Access network The main function of the access network is to connect users, for instance telephone subscribers, to a unit, switch, that can set up a path for exchange of information between two or more users. The main switching function in a local exchange is to interconnect timeslots to and from the subscriber access network and the trunk (transport) network. The connections between the users and the switch form the access network. Remote subscriber multiplexer In the access network multiplexers are used to digitize the analogue signal and this makes it possible to increase the distance between the subscriber and the exchange.
Remote subcriber switch Multiplexer Remote subcriber switch Multiplexer Figure 2-2 An example of an access network
AXE Survey – 46 – EN/LZT 101 1513 R4A A remote subscriber multiplexer for 30 analogue subscriber connections performs pulse code modulation of the speech to and from the subscribers. The digitized speech samples are multiplexed so that one digital link carries 32 timeslots of 64 kbps each with speech samples. The bit rate of the link is then 2.048 Mbps, a so-called PCM (pulse code modulated) link. One time slot is used for signaling, one for synchronization and 30 for speech. Each subscriber has a dedicated timeslot on the link towards the local exchange.
Remote subscriber switch In the access network a larger number of subscribers can be con- nected to a concentrator, a remote subscriber switch (RSS). Some switching functionality is moved out from the local exchange to the remote subscriber switch. The RSS is connected to the local exchange via 2.048 Mbps links or PCM connections. Since the RSS works as a concentrator there are no dedicated timeslots for the connected subscribers. Though physically separate from the local exchange the RSS is under complete control of that exchange. RSS brings all of the functions and services of the AXE local exchange closer to the subscriber.
Calls between two subscribers connected to the same RSS, detached from an AXE local exchange, can be switched within the RSS. Calls between one local subscriber and one subscriber connected to another exchange are switched through the group switch in the AXE local exchange Access to AXE Access will be covered in chapter 8, but in order to better understand the switching concept a sort reference is done here. The connections to an AXE local exchange can either be direct from the individual subscriber or through some intermediate equipment. The direct connections to the AXE local exchange from an ordinary PSTN subscriber is normally on an analogue subscriber line.
Another connection from a subscriber could be on a 2B+D digital subscriber connection for ISDN Basic Access.
2 AXE Platform EN/LZT 101 1513 R4A – 47 – This access gives the subscriber two 64 kbps channels (B- channels) and one 16 kbps channel (D-channel). They can be used simultaneously from the subscribers network access point. The two B-channels can be used for telephony, fax, data communication etc. The D-channel is used for signaling or for packet switched services. Access Products The AXE Local Exchange supports a range of integrated access products, which can be deployed by network operators to meet the service, bandwidth and mobility requirements of subscribers as economically and flexibly as possible.
Such products are: • Fiber in the loop (FTTL) • Radio in the local loop (RLL) • Free set cordless telephony system • DIAMUX flexible access system • AXE Access 910 • MD110 Trunk network In the trunk network different intermediate equipment is also possible such as add/drop multiplexers and digital cross connects. Add/drop multiplexers Add/drop multiplexers make it possible to add or take out circuits of various bit rates from for instance a 620 Mbps SDH connection. Digital cross connects Digital cross connects make it possible to handle circuits of different bit rates, for instance 155 Mbps, 620 Mbps, 2 Gbps and 10 Gbps. Between these circuits it is possible to switch information for instance multiplexed 2 Mbps circuits. The Ericsson digital cross connect AXD 4/1 -2 supports this service.
AXE Survey – 48 – EN/LZT 101 1513 R4A SWITCHING IN GENERAL The International Telecommunication Union Telecommunication Standard Sector (ITU-T) states that the main function of switching is to, on demand, establish a connection from a desired inlet to a desired output. Two general types of switching are used for the connection of subscribers: • Circuit switching • Packet switching. Circuit switching Packet switching A- subscriber B- subscriber Circuit switching Packet switching A- subscriber B- subscriber Figure 2-3 Switching in general Circuit switching Circuit switching means traditionally that the public switched telephone network allocates a circuit between the A-subscriber and the B-subscriber for the duration of the whole call. Packet switching Packet switching may be considered as a form of time division multiplexing on demand. Transmission is only requested when sufficient data to fill a packet is available at the transmitter. At other times the transmission medium may be used to transmit packets between other sources and destinations.
2 AXE Platform EN/LZT 101 1513 R4A – 49 – Digital switching 6 6 7 7 7 7 8 8 8 8 9 9 9 9 Time switch switch 6 6 7 7 7 7 8 8 8 8 9 9 9 9 Time switch switch Figure 2-4 Time switch and space switch The two principles of digital switching are: • Time switching • Space switching Time switching is based on time division multiplexing (TDM) systems for example pulse code modulation (PCM). A PCM link can be shared in time by a number of speech channels. Each channel's share of this time is known as a time slot, and each time slot carries a speech sample. Analogue to digital Digital to analogue A E B F C G D H A B C D Analogue to digital Digital to analogue A E B F C G D H A B C D A B C D Figure 2-5 Need for switching In Figure 2-5 the speech samples from subscribers A, B, C and D are transmitted in a fixed order and are received in the same order. This allows speech connections to be set up between subscribers, A to E, B to F, C to G, and D to H.
AXE Survey – 50 – EN/LZT 101 1513 R4A What is required is a method whereby any subscriber on the left hand side can be connected to any subscriber on the right hand side. This is achieved by utilizing a control store (a data store containing control information) to switch the connections in the required order. The control store manipulates the order in which information is read out of the speech store (a data store containing speech information). A simple time switch is made up of: • A speech store for temporary storage of the speech samples • A control store which controls the reading out from the speech store In Figure 2-6 the speech samples are read into the speech store in a fixed order A, B, C, D. The values in the control store (that is, 3, 1, 4, 2) determine the order in which the speech samples are read out, (that is, C, A, D, B). The result is that the following speech connections, C-E, A-F, D-G and B-H, are established. AB C D BD A C 3 1 4 2 1 2 3 A B C D 1 2 3 4 4 Analogue to digital A B C D Digital to analogue E F G H Speech Store Control Store AB C D AB C D BD A C BD A C 3 1 4 2 1 2 3 A B C D 1 2 3 4 A B C D 1 2 3 4 4 Analogue to digital A B C D Digital to analogue E F G H Speech Store Control Store Figure 2-6 Basic time switch operation Space switch Space switching is used to switch timeslots from an incoming PCM system to an outgoing PCM system.
The space switch is composed of a matrix of cross points (electronic gates). To connect a timeslot in an incoming PCM system to a timeslot in an outgoing PCM system an appropriate
2 AXE Platform EN/LZT 101 1513 R4A – 51 – cross point of the space switch is operated for a defined period (an internal timeslot). Switching functions in AXE ESS GSS SSS ESS GSS SSS Figure 2-7 Subsystems performing switching functions The switching functions in AXE are performed by the following subsystems • Group Switching Subsystem (GSS) • Subscriber Switching Subsystem (SSS) • Extended Switching Subsystem (ESS) GSS functions are used for selecting, connecting and disconnecting paths through the group switch. SSS functions are used in the access network to connect subscribers to the local exchange ESS functions are used for announcement of recorded messages and for simultaneous connection of more than two subscribers. GS INTRODUCTION In all AXE systems that connect two or more subscribers to one another, the Group Switch is the dominant feature, and is generally seen as the core around which the system is built. The Group Switching Subsystem, GSS, has the following basic functions: • Selection, connection and disconnection of speech or signal paths passing through the Group Switch.
• Supervision of hardware in the subsystem by continuous, periodic and traffic-dependent supervision, for example through-connection tests. • Supervision of DL, Digital Link, interfaces connected to the switch.
AXE Survey – 52 – EN/LZT 101 1513 R4A • To maintain a stable and accurate clock frequency for network synchronization purposes. The mechanical structure of the AXE system is based on the packaging system or the BYB structure. The BYB structure offers a high degree of flexibility and contributes to easy handling during design, manufacture, documentation and installation. Different versions of Group Switch are available dependent on the hardware in use. The older version of Group Switch is based on BYB202 hardware, still available in many places around the world. In BYB501 structure, the hardware was minimized and it was possible to put more functions in one board. As it was named in the previous chapter the APT is used to describe hardware and software related to telephony.
The first version of BYB501 hardware was used for APT 1.3 and 1.4 The latest version of BYB501 is used with APT1.5 in AXE 810.
2 AXE Platform EN/LZT 101 1513 R4A – 53 – GS IN PREVIOUS AXE VERSIONS GS in previous versions of AXE is based in BYB202 and BYB 501 with APT1.3 and APT 1.4 In the group switching subsystem, GSS, a number of functions are implemented. For example switching functions, management functions, adaptation functions that are used in order to connect different types of hardware to the group switch, network synchronization functions, subrate switching functions if the group switch will be used in mobile applications, test path functions etc.
SNT MAN TESTPATH SRS GSBASE NETSYNC GSS SNT MAN TESTPATH SRS GSBASE NETSYNC GSS Figure 2-8 GSS Set of parts A number of blocks are needed in order to implement the different functions. All these blocks needed in order to implement a specific function build what we call a “set of parts” Core switching functions CLT TSM CLT TSM Figure 2-9 Function blocks in set of parts GSBASE
AXE Survey – 54 – EN/LZT 101 1513 R4A The set of parts GSBASE consists of both hardware and software. Two function blocks in GSBASE are time switch module (TSM) and clock pulse generation and timing (CLT). Switch core TSM SPM SNT TSM DLMUX TSM Regional SW Central SW DIP TSM SPM SNT TSM DLMUX TSM Regional SW Central SW DIP Figure 2-10 Function block TSM DIP Digital path DLMUX Digital link multiplexer SNT Switching network terminal SPM Space switch module TSM Time switch module The time switch module (TSM) function block is implemented in hardware and regional and central software The hardware units in TSM are digital link multiplexer (DLMUX), time switch module (TSM) and space switch module (SPM).
The TSM function block performs the following functions • Traffic functions within and towards the hardware • Controls the traffic queues and timeslots in the switch • Functions for supervision of TSM, SPM, SNT and digital path (DIP) • Functions for test of TSM and SPM hardware • Administrative functions for TSM and SPM
2 AXE Platform EN/LZT 101 1513 R4A – 55 – The TSM, the DLMUX and the SPM are duplicated in two planes, plane A and plane B. The DLMUX was introduced in BYB501 and its goal is to put together several 2 Mbit/s PCM connections to the group switch. In BYB 202 the 2 Mbit/s PCM connections are directly connected to the Group switch and more specific to TSM. Internal clock frequency CLM-0 CLM-1 CLM-2 8 kHz 4,096 Mhz Regional SW Central SW CLM-0 CLM-1 CLM-2 8 kHz 4,096 Mhz Regional SW Central SW Figure 2-11 Function block CLT CLM Clock module The clock pulse generation and timing (CLT) function block is implemented in hardware and regional and central software The CLT function block performs the following functions: • Clock pulse generation • Clock pulse distribution to units in the group switch • Frequency and phase locking of the three clock modules towards each other • Frequency and phase locking of optional clock module towards external clock references, utilized by the network synchronization function The hardware units in CLT are the clock modules (CLM), voltage controlled crystal oscillators.
AXE Survey – 56 – EN/LZT 101 1513 R4A The CLM unit is triplicated for reliability and maintenance reasons. The CLM generates one 8 kHz and two 4.096 MHz signals which are distributed to all TSMs and SPMs in the group switch network. In some exchanges reference clocks can be implemented to support the CLMs with more stable and accurate clock frequencies. Adaptation functions PCD ETC SNTPCD SNTPCDM SNTET Connection and disconnection Connection, disconnection and fault handling Fault handling SNT PCD ETC SNTPCD SNTPCDM SNTET Connection and disconnection Connection, disconnection and fault handling Fault handling SNT Figure 2-12 Function blocks in set of parts SNT ETC Exchange terminal circuit PCD Pulse code modulation device SNTET Switching network terminal administration and maintenance of ETC SNTPCD Switching network terminal PCD administration SNTPCDM Switching network terminal PCD maintenance The switching network terminal (SNT) has the function of supervising the digital paths (DIP) connected to the group switch. These links connect switching network terminals (SNTs) such as exchange terminal circuits (ETCs) and pulse code modulation devices (PCDs) to the group switch.
The SNT concept is utilized to create a standardized operation and maintenance interface towards the operator for all equipment that can be connected to the group switch. An SNT is a unit, which can be connected to the group switch via one or more of 2048 kbps or 1544kbps digital connections.
2 AXE Platform EN/LZT 101 1513 R4A – 57 – The SNT consists of only central software. Three of the function blocks in SNT are: Switching network terminal PCD administration (SNTPCD), which connects and disconnects the PCD Switching network terminal PCD maintenance (SNTPCDM), which can manually block and deblock the PCD Switching network terminal administration and maintenance of ETC (SNTET), which can connect/disconnect and manually block/deblock the ETC Subrate switching functions The subrate switching (SRS) implements in hardware and software functions for the subrate devices. The subrate module is duplicated and is regarded as a switching network terminal (SNT).
A subrate switch can be interconnected as an add-on to the group switch. The subrate switch enables switching functions to operate more effectively at subrate levels (8 kbps). This function is primarily used in the digital GSM application. The subrate module lowers the switching rate from 64 kbps to 8 kbps. Accordingly, up to eight times as many cellular calls may be handled during the same time span. The subrate switching offers a possibility to switch bit rates of n * 8kbps, where n = 1 to 7. The subrate switch is not required by exchanges for the fixed telephone network.
Group switch hardware The group switch is duplicated in two planes, A-plane and B- plane. Both planes switch speech samples from the same timeslot. The processor takes a decision what plane to use for the outlet connection. The speech sample that is transferred on a serial circuit outside the switch is transferred in parallel in the switch. Two extra bits are then added. One for parity check and one for plane select, A- plane or B-plane, for the outgoing link. The switching is implemented in GSS by the:
AXE Survey – 58 – EN/LZT 101 1513 R4A • Time switch modules (TSM) which implement time switching • Space switch modules (SPM) which implement space switching CLM-2 RP RP CP RP CLM-1 RP RP CP RP CLM-0 SPM SNT TSM DLMUX A A A A B B B B DLMUX TSM SPM Group switch CLM-2 RP RP CP RP CLM-1 RP RP CP RP CLM-0 SPM SNT TSM DLMUX A A A A B B B B DLMUX TSM SPM Group switch Figure 2-13 Overview of group switch hardware CLM Clock module CP Central processor DLMUX Digital link multiplexer RP Regional processor SNT Switching network terminal SPM Space switch module TSM Time switch module Time switch module (TSM) In the group switch, the time switch module (TSM) handles the transmission and reception of speech samples. In the previous section on time switching we used only one speech store. In the AXE we utilize two speech stores for two-way speech, see Figure 2-14 • Speech store for temporary storage of incoming speech samples (SSA) • Speech store for temporary storage of outgoing speech samples (SSB)
2 AXE Platform EN/LZT 101 1513 R4A – 59 – TSM SSA SSB CSAB CSC 511 511 511 511 From devices To devices 16 PCM-links TSM SSA SSB CSAB CSC 511 511 511 511 From devices To devices 16 PCM-links Figure 2-14 Time switch CSAB Control store AB CSC Control store C SSA Speech store incoming SSB Speech store outgoing TSM Time switch module Speech samples are written into the SSA in a fixed order from the incoming PCM links, but when they are being read out, the order is determined by settings in the control store AB (CSAB). SSA SSB CSAB 0 0 0 511 511 511 510 510 510 Speech store Speech store Control store MUP MUP Internal timeslot MUP MUP MUP MUP MUP MUP MUP MUP MUP MUP MUP MUP SSA SSB CSAB 0 0 0 511 511 511 510 510 510 Speech store Speech store Control store MUP MUP Internal timeslot MUP MUP MUP MUP MUP MUP MUP MUP MUP MUP MUP MUP Figure 2-15 Layout of speech and control store
AXE Survey – 60 – EN/LZT 101 1513 R4A CSAB Control store AB MUP Multiple position SSA Speech store incoming SSB Speech store outgoing TSM Time switch module CSAB controls both the reading of speech samples from SSA and the writing of speech samples into SSB. It contains the addresses of the speech samples for reading from SSA and writing to SSB. TSM also has a control store C (CSC) that is used to control the operation of electronic gates in the space switch module (SPM) to transfer speech and data through the group switch. Each TSM in the group switch has 512 inputs and outputs, that is, its speech stores (shown in Figure 2-15 as SSA and SSB) each have 512 multiple positions (MUP) with addresses 0-511 to which calls can be connected. The control store or CSAB also has 512 positions, internal timeslots (see Figure 2-16). Speech store transmit Speech store receive Control store Control store Control store Control store Time switch module Space switch module Inlet Outlet PCM 322 511 1 1 1 2 2 2 3 127 127 127 Crosspoint Speech store transmit Speech store receive Control store Control store Control store Control store Time switch module Space switch module Inlet Outlet PCM 322 511 1 1 1 2 2 2 3 127 127 127 Crosspoint Figure 2-16 Matrix of cross points in a 64 K group switch PCMPulse code modulation Space switch module (SPM) Space switch modules (SPM) enable connections to be set up in the group switch between subscribers connected to different TSMs and between subscribers within the same TSM.
2 AXE Platform EN/LZT 101 1513 R4A – 61 – Each cross point (electronic gate) can be enabled or disabled by a control store (Control Store C or CSC in TSM). By interconnecting a number of SPMs we can form a large space matrix. Each SPM can have up to 32 TSMs connected to it. Digital link multiplexer (DLMUX) The digital link multiplexer (DLMUX) works as a multiplexer between the SNTs and the TSMs, see Figure 2-13. The DL3 interface towards the time switch module in the switch core operates at 49 Mbps carrying 512 timeslots per frame. Existing switching network terminals with a DL2 interface are connected to the switch core by means of a DLMUX. Digital link multiplexers can either multiplex 16 DL2s to one DL3 or demultiplex one DL3 to 16 DL2s.
Connections to the group switch ETB ETC JTC PCD-D PCD ST RSS CSS LSM LSM Analogue device Group Switch ETB ETC JTC PCD-D PCD ST RSS CSS LSM LSM Analogue device Group Switch Figure 2-17 Overview of connections to the group switch CSS Central subscriber switch ETB Exchange terminal board ETC Exchange terminal circuit JTC Junctor terminal circuit LSM Line switch module PCD Pulse code modulation device PCD-D Pulse code modulation device digital RSS Remote subscriber switch ST Signaling terminal Besides narrowband connections, 8 or 64 kbps, the group- switching network is also capable of handling wideband on demand connections.
AXE Survey – 62 – EN/LZT 101 1513 R4A The wideband on demand connections are circuit switched connections using a number of 64 kbps channels in a 32 channel system. This is a so-called n*64kbps switched service or a multi- slot connection with a bit rate up to 1984 kbps. The equipment that connects the timeslots to the group switch are with a common name called switching network terminals (SNT). • SNTs connected to the group switch are for example • Exchange terminal circuits (ETC) connecting the PCM links from a remote subscriber switch • Exchange terminal circuits (ETC) connecting the PCM links to the trunk network • Junctor terminal circuit (JTC) connecting the line switch modules in the central subscriber stage • Pulse code modulation device (PCD) connecting analogue devices • Pulse code modulation device digital (PCD-D) connecting digital devices working with lower bit rates than 2 Mbps, for instance a signaling terminal Configuration of the group switch TSM TSM TSM TSM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM 0-31 32-63 64-95 96-127 65,536 multiple positions 49,152 multiple positions 32,768 multiple positions 16,384 multiple positions TSM TSM TSM TSM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM SPM 0-31 32-63 64-95 96-127 65,536 multiple positions 49,152 multiple positions 32,768 multiple positions 16,384 multiple positions Figure 2-18 Logical view of a 64 K group switch TSM Time switch module SPM Space switch module
2 AXE Platform EN/LZT 101 1513 R4A – 63 – The group switch can be configured for different capacities. Each time switch module can connect 16 PCM links carrying 512 timeslots. One space switch module can handle 32 time switch modules. That is the structure of a 16 K group switch with a capacity of 16 384 multiple positions (MUPs). 1 K is equal to 1024. The multiple positions (MUP) are data areas for storage of the speech samples in the speech stores. One unique multiple position is needed for each subscriber in each call. A 16 K group switch, complete with regional processors, fits in a single subrack for each plane.
64 K group switch The 64 K group switch consists of 128 TSMs and 16 SPMs with a total capacity of 65 536 multiple positions. A 64 K switch fits in four subracks for each plane. Plane A 16K Plane A 16K Plane B 16K Plane B 16K Plane B 16K Plane B 16K Plane A 16K CLM RCM Plane A 16K Plane A 16K Plane A 16K Plane A 16K Plane B 16K Plane B 16K Plane B 16K Plane B 16K Plane A 16K CLM RCM Plane A 16K Plane A 16K Plane A 16K Plane B 16K Plane B 16K Plane B 16K Plane B 16K Plane A 16K CLM RCM Plane A 16K Plane A 16K Plane A 16K Plane A 16K Plane B 16K Plane B 16K Plane B 16K Plane B 16K Plane A 16K CLM RCM Plane A 16K Figure 2-19 Cabinet assembly for a 64 K group switch CLM Clock module RCM Reference clock module 128 K group switch The maximum number of multiple positions in the group switch is 131 072, a 128 K group switch.
AXE Survey – 64 – EN/LZT 101 1513 R4A 16K 16K 16K CLM RCM 16K 16K 16K 16K CLM RCM 16K Figure 2-20 Cabinet assembly for a 128 K group switch CLM Clock module RCM Reference clock module The 128 K group switch is made up of eight 16 K group switch subracks per plane. Each plane is housed in two cabinets. The possible configurations of the AXE group switch are regarding the capacity of multiple positions • 16 K (16 384 MUPs) • 32 K (32 768 MUPs) • 48 K (49 152 MUPs) • 64 K (65 536 MUPs) • 128 K (131 072 MUPs) T-S-T The GS implemented in previous AXE versions is using the T-S- T method, Time-Space-Time both when BYB202 and BYB501 packaging is used.
In AXE 810 The Group switch is designed differently Speech path through the group switch From before we know that speech stores are used to store speech samples. CSAB is used to store the read (from SSA) and write (to SSB) addresses of these speech samples. And CSC is used to connect TSMs.
2 AXE Platform EN/LZT 101 1513 R4A – 65 – Now we will see how a speech path is established through the group switch. The speech path is established simultaneously in both directions, that is, from the A-subscriber to the B-subscriber and from the B-subscriber to the A-subscriber. We first look at the set-up of a call from A to B. SSA SSS SSS SSA SSB SSB CSAB CSAB CSC CSC 511 299 511 299 299 511 511 511 511 511 511 SPM H0 V7 A B SSA SSS SSS SSA SSB SSB CSAB CSAB CSC CSC 511 299 511 299 299 511 511 511 511 511 511 SPM H0 V7 SSA SSS SSS SSA SSB SSB CSAB CSAB CSC CSC 511 299 511 299 299 511 511 511 511 511 511 SPM H0 V7 A B Figure 2-21 Speech path from A-subscriber to B-subscriber CSAB Control store AB CSC Control store C H Horizontal SSA Speech store incoming SSB Speech store outgoing SPM Space switch module SSS Subscriber switching subsystem TSM Time switch module V Vertical The CSC of each TSM controls the connection of a horizontal row of cross points to a vertical row of cross points in the SPM. In Figure 2-21, SC in TSM-7 operates a cross point between horizontal 0 (from TSM-0) and vertical 7 (from TSM-7). Speech samples are read out from SSA in TSM-0 on to horizontal path 0 through the SPM and on to vertical path 7 to SSB in TSM- 7.
AXE Survey – 66 – EN/LZT 101 1513 R4A In Figure 2-22 we see the speech path in the B to A direction. CSC in TSM-0 connects horizontal 7 (from TSM-7) to vertical 0 (from TSM-0) in the SPM. Speech samples are read out from SSA in TSM-7 on to horizontal path 7 through the SPM on to vertical path 0 to SSB in TSM-0. SSA SSS SSS SSA SSB SSB CSAB CSAB CSC CSC 0 0 511 299 511 299 7 511 511 511 511 511 511 511 SPM H7 V0 A B SSA SSS SSS SSA SSB SSB CSAB CSAB CSC CSC 0 0 511 299 511 299 7 511 511 511 511 511 511 511 SPM H7 V0 A B Figure 2-22 Speech path from B-subscriber to A-subscriber
2 AXE Platform EN/LZT 101 1513 R4A – 67 – SYNCHRONIZATION All digital switches require some form of clocking that is timing signals or clock pulses. The clock rate determines the rate at which samples are read from or written into the speech stores. The clock frequency is controlled through one or several clock signals, which can be generated by • Local equipment • A digital path from another exchange • External equipment. Synchronization network The synchronization of a digital network is essential to ensure fault free transport of information between nodes. A slip is loss of information due to discrepancies of frequencies between two adjacent nodes in the network. A slip means loss of a whole PCM frame (32 time slots).
Bits in outgoing timeslot Read frequency = fb Fb > fa duplication = slip fb fa duplication = slip fb
AXE Survey – 68 – EN/LZT 101 1513 R4A Plesiochronous synchronization means that the nodes generate their signals independently of other clocks but the internally located clock. Master and slave synchronization Master exchange has a clock (RCM) with long-term stability Slave exchanges are adjusted to the incoming frequency Master RCM CLM Slave CLM Slave CLM Master exchange has a clock (RCM) with long-term stability Slave exchanges are adjusted to the incoming frequency Master RCM CLM Slave CLM Slave CLM Figure 2-24 Master - slave synchronization CLM Clock module RCM Reference clock module Master and slave synchronization means that a master node generates a long-term stable clock frequency. The slaves obtain their clock rates from the master. The benefit is that all slaves have the same rate as the master.
Mutual single ended network synchronization 2 CLM CLM CLM A B C F A F + A FB F B FC F = C F C All clocks are of equal quality Frequency in the exchanges according to average of incoming frequencies 2 CLM CLM CLM A B C F A F + A FB F B FC F = C F C All clocks are of equal quality Frequency in the exchanges according to average of incoming frequencies Figure 2-25 Mutual single ended synchronization CLM Clock module
2 AXE Platform EN/LZT 101 1513 R4A – 69 – In the mutual single ended network synchronization method several nodes mutually control each other. Each node receives a clock rate, which is the average of a value of the rate from several (up to a maximum of 10) clock references. Single ended means that the internal clock frequency is controlled by the node, and used only in the node. The International Telecommunication Union Telecommunication Standard Sector (ITU-T) specifies that international connections are to work plesiochronically with a slip rate, which is less than one slip in 70 days during normal conditions. This means that an international node must have access to a clock reference with a very reliable clock rate, and with an accuracy of +–10-11 .
Function blocks in NETSYNC NS NSC NS CCM ICM RCM NS NSC NS CCM ICM RCM Figure 2-26 Function blocks in set of parts NETSYNC CCM Cesium clock module ICM Incoming frequency conversion module NS Network synchronization NSC Network synchronization commands RCM Reference clock module The parts network synchronization (NETSYNC) is implemented in both hardware and software. The function blocks that build the NETSYNC are network synchronization (NS), and network synchronization commands (NSC). The function block NS is located in central software and hardware. The NS hardware consists of: • Reference clock module (RCM) • Cesium clock module (CCM)
AXE Survey – 70 – EN/LZT 101 1513 R4A • Incoming frequency conversion module (ICM) Reference clock module (RCM) The reference clock module (RCM) is a reference oscillator with high precision and stability. It is used mainly in transit exchanges and provides an 8 kHz signal. Cesium clock module (CCM) The cesium clock module (CCM) can support international exchanges with the clock frequency needed for international con- nections. It provides very high accuracy. Incoming frequency conversion module (ICM) The Incoming frequency conversion module (ICM) is used for synchronization from other equipment, other exchanges or for example a building clock.
2 AXE Platform EN/LZT 101 1513 R4A – 71 – GS890 IN AXE 810 The new group switch in AXE 810, which is referred to as GS890, is a completely new switch. In earlier AXE modernization, the group switch structure has been the same but the hardware has been modified and extended to 128K, which make it possible to establish more connection through the Group switch. This time, the release of the GS890 introduces a new version of the AXE Group Switch for the APT1.5 architecture. Figure 2-27 A 64K GS890 Group Switch.
Figure 2-27, shows a 64K GS890 Group Switch. The switch is packed with features making this new Group Switch generation well adapted to the current and the future needs of telecommunication businesses. The GS890 Group Switch generation introduces: • A new switch core, the XM. • A new clock, the CL890, • A new DL34 interface for the efficient connection of devices to the Group Switch. Notable features are: • Significant reductions in foot-print, internal cabling, and power consumption
AXE Survey – 72 – EN/LZT 101 1513 R4A The GS 890 provides adaptation for connection of devices implemented in older GDM subracks, Generic Device Magazines. The switch plays a major role in the new GEM (Generic Ericsson Magazine) concept. SUBRACK/ MAGAZINE The terms subrack and magazine are extensively used through the book in a similar way. Subrack is the term used in BYB501 instead of magazine that was used in BYB202. The subrack term is more flexible since plug-in-units of various sizes can be used in one and the same subrack.
THE GEM SUBRACK The GEM subrack is one of the cornerstones in the new APT hardware. GEM, which stands for Generic Ericsson Magazine, is the main building block in APT and it can hold many important and fundamental APT functions: • Group Switch • ET155 • Transceivers • Echo Canceller • Interfaces to GDM subracks This means that the majority of hardware devices will be located in the GEM subracks. Hardware not included in GEM is located in the GDM, which is an older type of magazine. The main principle of GEM can be seen in the figure below. Figure 2-28 GEM is the basic building block in AXE 810
2 AXE Platform EN/LZT 101 1513 R4A – 73 – THE SUBRACK AND INTERFACES Each GEM subrack is a generic piece of hardware which holds some mandatory boards but has 22 generic positions which can be used to house any type of board which is adapted to the GEM size and back plane. This creates flexible solutions with many alternatives. The mandatory boards are: • Two maintenance processors, which take, care of maintenance functions inside the subrack. The board is referred to as SCB- RP, Support and Connection Board with Regional Processor, RP.
• Two group switch boards with a capacity of 16K ports of 64 kbit/s Figure 2-29 The mandatory and free slots in GEM Beside these 4 boards, there are 22 positions that are free for usage. The connection of devices to the group switch is done via the back plane. The interface is a new type of group switch interface with the name “DL34”. This interface is a flexible interface with a capacity of 128-2096 time slots of 64 kbit/s in steps of 128 MUPs. The bit rate is 222.2 Mbit/s. The multiple positions (MUP) are data areas for storage of the speech samples in the speech stores. One unique multiple position is needed for each subscriber in each call. An ET155 board, which terminates up to 63 x 2.048 Mbit/s = 2016 time slots, can be connected via the DL34 interface. Devices with lower bit rate can of course also be connected, as the number of channels is flexible.
AXE Survey – 74 – EN/LZT 101 1513 R4A Figure 2-30 Interfaces to the group switch inside the GEM magazine All devices supporting the DL-34 interface can be “more or less” freely mixed in the GEM. The maximum capacity of each GEM is 16 kMUPs, which, for example, corresponds to eight ET155-1. Physically, there is space for 22 device boards in the GEM. The DL34 is connected to the Group switch via the back plane. GEM EC DL-34 GS 890 16 K TRA ET 155-1 OC-3 ET 155-1 STM-1 Clock module Other devices GEM EC DL-34 GS 890 16 K TRA ET 155-1 OC-3 ET 155-1 STM-1 Clock module Other devices Figure 2-31 The APT 1.5 system equipped only with pure APT 1.5 devices When switch sizes larger than 16 kMUPs are required, or when the number of devices exceeds 22, additional GEM(s) must be added. The configuration of these additional GEM(s) may be
2 AXE Platform EN/LZT 101 1513 R4A – 75 – made while the system is processing traffic, that means no traffic disturbances will be caused as a result of this action. APT 1.5 is “linearly” expandable. Maximum switch size is 512 kMUPs at normal rate (for example, 64 kb/s) or 128 kMUPs at subrates (that means, n x 8 kb/s) Subrate switch is used in connection to mobile telephony. The processing power for the device boards is supplied by the on- board integrated RPs. In the backplane of the GEM subrack, there are several busses. From a control point-of-view, the following two are the most interesting: • a duplicated RP bus (serial RP bus) • a 100 Mbit/s Ethernet for future use. The figure above shows the control structure inside the subrack as well as the Ethernet connection that can be used by future applications. The boxes inside the boards represent the new regional processors that are integrated on the board, the RPI. The bus with number 1 is a duplicated serial RP bus in the back plane of the GEM subrack. The RP bus terminates in the RP Handler subrack of the Central Processor. Figure 2-32 the control structure inside GEM The bus with number 2 in the figure is the duplicated 100 Mbit/s Ethernet bus which will be used by future applications. The SCB- RP has an Ethernet switch as well as one 1Gbit/s and one 100 Mbit/s Ethernet interface to the front of the board. It will be used by future functions in AXE.
AXE Survey – 76 – EN/LZT 101 1513 R4A CONNECTION OF GDM AXE equipment inside the older GDM subracks (GDM stands for Generic Device Magazine) must in some way be able to co-exist with the new GEM magazines. This is achieved by means of duplicated interface boards called DLEB inside the GEM magazine. These boards interface the DL3 interface from the GDM subrack. The DL3 interface is a 34 Mbit/s interface, which was used as the main interface to the old 128K-group switch in APT HWM 1.3 and 1.4. The figure below shows the main principles.
DLEB stands for “Digital Link multiplexer for Existing equipment Board” and DLHB stands for Digital Link Handling Board. Figure 2-33 Connection of GDM subracks to GEM Each DLEB board can connect up to 4 DLHB boards (up to 4 GDM subracks) and there is always a need for two DLEB board, one for each plane in the group switch. The GDM consists of one pair of RP4s, one pair of DLHB boards and sixteen slots for device boards. They are connected to duplicate DLEBs via duplicate DL3 interfaces. RP4s are connected to the CP via a serial RP bus. Reliability Just as with previous group switches from Ericsson, the whole switch is duplicated. The two parts are referred to as A-plane and
2 AXE Platform EN/LZT 101 1513 R4A – 77 – B-plane. Each device is connected to both planes and the system will not be disturbed for single hardware faults. MAIN FEATURES Some of the most important features of the new GS890 are. • Distributed architecture The switch is located in every GEM, Generic Ericsson Magazine and each board has a switching capacity of 16 KMUP. The MUP, Mulriple Position, represents a 64 kbit connection to the group switch. • Subrate switch up to 128K The size of the subrate switch can be extended up to 128K. The subrate is used in mobile applications. The implementation of the subrate switch differs from earlier GS hardware. Maximum subrate capacity (n x 8 kb/s) is 1 M x 8 kbit/s ports, scalable in steps of 128K x 8 kbit/s ports. • Duplicated GS, meaning that single faults do not affect traffic. • Switch expansion may be performed without any adverse traffic disturbances.
• Switch structure allows large flexibility in cabinet configuration. • Built-in network synchronization functionality employing high-performance clocks. • The BYB 501 equipment practice ensures conformance with strict Electro Magnetic Compatibility (EMC) requirements. • Time-Space architecture The old AXE group switch had a time-space-time (TST) architecture. This new one has a time-space (TS) architecture creating better characteristics. • Maximum size of 512K The switch can be scaled up to 512K multiple positions (64 kbit/s channels). This means that the switch can have more than 250 000 calls established at the same time The switch is strictly non-blocking
AXE Survey – 78 – EN/LZT 101 1513 R4A The old group switch in AXE was not strictly non-blocking as each inlet could be loaded to about 80%. The new architecture with time-space structure gives this advantage. • Reduced cabling The cabling has been reduced to about 1/12 if compared with the old switch (GS12). • Reduced power consumption The power consumption has been reduced to 1/6 of the old switch’s power consumption for the same switch size (GS12). • Reduced space The floor space is reduced significantly, as a 16K subrack now is one circuit board. If compared with the old BYB 202 based switch, the changes are enormous, as one 16K switch needed 32 TSM magazines occupying several cabinets. • Device protection without waste of multiple positions. For ET155, protection switching is an option. In that case, the interface to the group switch can connect two ET155:s without wasting multiple positions.
Subrate switching is supported to facilitate the efficient usage of scarce network resources such as transmission capacity, transcoders and signaling terminals. This feature is included in the three nodal types: Trancoder,TRC, Base Station Controller BSC and TRC/BSC. These are nodes used in mobile telephony, GSM. . HARDWARE The main hardware when it comes to switching is the XDB board (X means switching and DB stands for “distributed board”). The XDB board has a switching capacity of 16K and there are two in each GEM subrack, one for the A-plane and one for the B-plane. On the XDB board, there are three ASICs (application specific integrated circuit) that implements the 16K switch. One ASIC is a multiplexer and two are holding the speech stores (SS) and control stores (CS).
The SS are used for storage of speech in the forward and backward direction between the subscribers while the CS is used for controlling the transmission between the incoming and outgoing side of the GS.
2 AXE Platform EN/LZT 101 1513 R4A – 79 – XDB XDB SCB-RP SCB-RP 22 DEVICE SLOTS XDB XDB SCB-RP SCB-RP 22 DEVICE SLOTS Figure 2-34 The XDB boards in GEM One integrated Regional Processor (RPI) is also on the XDB board. The devices in the magazine are connected to the XDB boards via the back plane, while connection to other XDB boards are done via cables connected at the front of the board. The figure below shows the XDB board. Figure 2-35 Circuits on the XDB board
AXE Survey – 80 – EN/LZT 101 1513 R4A STRUCTURE If you only have a 16K group switch, it is enough to have just one XDB circuit board. However, in case of larger switches, the XDB boards have to be inter-connected by means of so-called horizontal and vertical connections. The horizontal and vertical connections are best explained if you imagine all XDB boards put in a matrix. The figure below shows the main idea. Figure 2-36 A matrix of switch boards. Each board has a capacity of 16K so the maximum capacity in the switch is 4 rows x 8 columns x 16K = 32 x 16 = 512K. Horizontals and Verticals The inter-connection of the boards in the switch is done by two different types of connections: • Horizontals These connections connect all switch boards in a row to each other. The connection is “all to all” meaning that all boards in a row have direct connections to all other boards in the same row.
• Verticals These connections connect all switchboards in a column to each other. Also these connections are “all to all”. Showing all cables from all switchboards in a 512K switch is difficult but the figure shows the entire cabling going to and from the first board (0-0) in the switch matrix.
2 AXE Platform EN/LZT 101 1513 R4A – 81 – Figure 2-37 Cabling from one switch board (note that all cables are not shown in the figure) CABLING By studying the front of the board, that is quite easy to see as there are 3 vertical connections and 7 horizontal connections. The board also has 2 connectors for connection of clocks (timing information from CLMs). The figure below shows the front of the XDB board. Figure 2-38 Front of XDB board
AXE Survey – 82 – EN/LZT 101 1513 R4A The Switching In order to understand how switching is made, the figure must be simplified even more. Figure 2-39 A switch matrix with horizontals and verticals (simplified, as verticals are only shown from row 0) As all switch boards within the same row are inter-connected by horizontals, and all switch boards within the same column are inter-connected by verticals, the figure could be drawn like the one below. The principle of switching is as follows: 1. A speech sample comes in on a horizontal and is then copied to all speech stores on that row. The horizontals take care of that.
2. The time switching takes place in the speech store of the correct column and the speech sample is sent on the vertical to the correct board. 3. On the destination board, a multiplexer takes the correct speech sample from the vertical. The switching in the other direction works according to the same principle but that will take another path. The figure below shows the main principle of switching between two switchboards in a part of the switch.
2 AXE Platform EN/LZT 101 1513 R4A – 83 – Figure 2-40 Switching in both directions. It can be seen that the samples take different paths. The rule is always to copy the speech sample to all speech stores on the same horizontal (in the same row) and then switch to the correct vertical. Subrate In order to switch traffic more effectively when used in connection with mobile telephony applications, the switch may be used as a subrate switch (n x 8 kbit/s, n=1-8) and allow one 64 kbit/s channel to include more than one call. As the name indicates, the subrate lowers the rate at which switching is performed –from the normal 64 kbit/s to 8 kbit/s. Subrate switching is non-blocking and is based on the time-space switching concept. Its maximum capacity is 1 M x 8 kbit/s. Any other capacity of the sub-channel, up to 64 kbps, can be switched while maintaining timeslot-frame integrity.
Subrate is used in mobile applications (for example in the BSC in GSM) to. For example, most mobile systems code speech to less than 8 kbit/s, which means that one 64 kbit/s channel, can send 8 calls. To be able to switch these subrate channels, the group switch must be designed in a special way. In the “old” group switches, the subrate switch was a “back pack” solution with a special subrack implementing the switch. The
AXE Survey – 84 – EN/LZT 101 1513 R4A maximum capacity was 4K in all-earlier version of AXE. The figure below shows the main principle of the old subrate solution. Figure 2-41 Subrate in the old group switch The subrate solution in the new GS890 is implemented in the first row of the switch. This row has the capacity of 128K and the same hardware can be used for both subrate and normal rate. However, if the subrate function is used, the maximum size of the switch is limited to 128K. This size should be enough for any type of BSC implementation. The figure below shows the part of the switching matrix where subrate can be used. Figure 2-42 Subrate can only be used in the first row of the group switch.
Wideband Wideband means that the group switch hardware can be used to set-up several 64 kbit/s channels that are kept together. For
2 AXE Platform EN/LZT 101 1513 R4A – 85 – example, an ISDN subscriber using both B channels for Internet access, must have 2 x 64 kbit/s switched though the exchange. The new GS890 can handle wideband in the same way as previous switches; it can establish up to 31 x 64 kbit/s through the switching hardware with the order kept of the channels. Wideband is supported for both the normal and subrate modes of the switch. SWITCH CORE AND DEVICE CONNECTION The GS 890 Hardware structure is shown in Figure 2-43. Here, two GEMs and a 32K switch are shown.
The switching network terminal (SNT) has the function of supervising the digital paths (DIP) connected to the group switch. These links connect switching network terminals (SNTs) for example exchange terminal circuits (ETCs) to the group switch. The SNT is used in order to describe in a uniform way the connection of different types of equipment to the GS. Besides the physical connections to the GS, the GS software needs to know, what equipment is connected to the GS and where. The SNT concept is used for that purpose.
CLM DLEB DL3 SNT SNT DL34 GEM XDB A B Switch Module MUX5 DL5 Up to 8 DLEB pairs can be connected to one pair of XDB boards Up to 22SNT devices can be connected to one pair of XDB boards Links connecting all switch modules within one plane DLEB SNT SNT DL34 GEM XDB A B Switch Module MUX5 DL5 DL3 CLM Figure 2-43 Hardware structure of a 32K Group Switch
AXE Survey – 86 – EN/LZT 101 1513 R4A The SNT concept is utilized to create a standardized operation and maintenance interface towards the operator for all equipment that can be connected to the group switch. It consists of only central software and its name indicates what type of connections / equipment it refers to. The planes of the GS890 switch are duplicated and both planes are housed in the same GEM. Up to 32 GEMs may be included in a distributed switch representing 512KMUPs. Each GEM includes two switching boards (XDBs) - one for each plane. The GEM also contains the clock functions and the DLEB. The Distributed Switching Board (the XDB) implements XM switching functionality (16K switch module) as well as the multiplexing function (MUX5).
Switching functionality is constructed using 16K modules that can be connected only by keeping a rectangular shape - the reason being that only modules (switch boards) in the same row or in the same column are connected (see Figure 2-43). Multiplexing functions are implemented whereby DL compatible equipment may be connected to the Group Switch. These provide DL34 interfaces to the GS890 GS core and a combination of lower order DL interfaces to the devices that are connected to the GS. MUX5 implements the distribution of timeslots to the DL5 interfaces (a multiplexed link carrying 512 DL2s) which in turn interfaces with the switch module and the DL34 interfaces (a multiplexed link carrying 4 to 84 DL2s) and eventually the devices.
All devices with DL34 termination are placed in a GEM. 22 DL34 interfaces per plane are provided from the switch core in each GEM. However, the capacity provided by a switch board places constraints on the number and types of devices that can be configured in one GEM: in particular up to 8 ET155-1 are allowed in one GEM. One PBA per plane – DLEB, is used to multiplex/demultiplex between one DL34 interface from each plane and five DL3 interfaces. One of the five interfaces is used for protection (1:4 protection). One DLHB is included per plane. The DLHB is used to multiplex/demultiplex between one DL3 interface (included in the DLHB’s plane) and up to 16 DL2 or DL1 interfaces.
2 AXE Platform EN/LZT 101 1513 R4A – 87 – Figure 2-44 shows the connection of a GS890 with SNTs in the GEM via DL34 interfaces, and via DL3 interfaces to devices implemented in GDM magazines. Switch core CLM DLEB DLHB SNT SNT DL2 DL3 SNT SNT DL34 GEM (XDB) A B 2 x 5 x DL3 ET155 Magazine (1:4 protection) DLEB First-Generation BYB 501 devices Figure 2-44 Devices connection with a GS890 Group Switch. The GS890 supports the migration of existing nodes based on GS64 (BYB202), GS10, and the GS12 including existing devices. Migration methods are named NNRP-3 and NNRP-4. A special variation of the switching board, the XNB, is needed in this case. EXPANDING THE GS 890 Switch expansions that do not affect the working mode of the switch may be performed disturbance-free (that means, without traffic interruption).
As described in the previous chapters, the GS890 switch is built up of switching modules that are each 16K large all housed in one GEM magazine. Due to the cabling structure considerations, the matrix may only grow in a rectangular pattern. This means for example, that if a switch consists of 8 GEMs in the first row, it can only be expanded by the addition of a completely new row. This means an expansion step of 8 GEMs. Switch increments are possible as long as the switch matrix is kept rectangular. Some expansion examples:
AXE Survey – 88 – EN/LZT 101 1513 R4A • Expansion of a 1 GEM (16K) switch - recommended target- size is 128K. Expansion after 128 k is performed in steps of 8 GEMs, see Figure 2-45. • Expansion of a 4 GEM (64K) switch, recommended target- size is 512K, see Figure 2-46. • Expansion of a 2 GEM (32K) switch, recommended target- size is 256K. Expansion beyond 128k, is performed in steps of 4 GEMs, see Figure 2-47. • The subrate case, which is a special switch matrix that is expandable up to 1 M x 8 kbit/s ports, see Figure 2-48. Note - the numbers in the figures below indicates the order in which expansion steps may be carried out, not how they are to be performed.
GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM 9 10 11 1 2 3 4 5 6 7 8 GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM Figure 2-45 Switch Matrix expandable up to 512 KMUP. Expansion in steps of 1 GEM up to 128k, after which in steps of 8 GEMs per expansion.
2 AXE Platform EN/LZT 101 1513 R4A – 89 – GEM GEM GEM GEM GEM GEM GEM GEM 1 2 3 4 5 6 7 8 GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM Figure 2-46 Switch Matrix expandable up to 512 KMUP. Expansion in steps of 4 GEMs. GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM 1 2 3 4 9 10 5 6 7 8 GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM GEM Figure 2-47 Switch matrix expandable up to 512 KMUP. Expansion in steps of 2 GEMs up to 128K, after which in steps of 4 GEMs per expansion.
GEM 1 GEM 2 GEM 3 GEM 4 GEM 5 GEM 6 GEM 7 GEM 8 Figure 2-48 Switch matrix expandable up to 128 KMUP. Expansion in steps of 1 GEM up to 128k. This is the subrate case.
AXE Survey – 90 – EN/LZT 101 1513 R4A CL 890: THE EXCHANGE CLOCK SYSTEM One of the main functions included in the Group Switch is the exchange clock system, which distributes clock and synchronization signals to the switch core. The main components of the exchange clock system are the clock modules, CLMs that provide the switch with accurate timing. The CLMs are duplicated for maximum timing distribution reliability. Figure 2-49 illustrates the clock architecture ETC ET155 CLM (CGB_1) ICF (IRB) RCM (LRB) ICF (IRB) Synchronization signal to Switch Core plane A External Synchronization references Switch Core plane B CLREF (up to 6) Stand Alone Clock (for ex. CBC) MV CLM (CGB_0) MV External synchronization references (GPS receiver is integrated in the CBC) Stand Alone Clocks Slave Master RCM (LRB) 2 Mbit /s 8 KHz ETC ET155 CLM (CGB_1) ICF (IRB) RCM (LRB) ICF (IRB) Synchronization signal to Switch Core plane A Synchronization signal to Switch Core plane A External Synchronization references Switch Core plane B Switch Core plane B CLREF (up to 6) Stand Alone Clock (for ex. CBC) MV CLM (CGB_0) MV External synchronization references (GPS receiver is integrated in the CBC) Stand Alone Clocks Slave Master RCM (LRB) 2 Mbit /s 8 KHz Figure 2-49 Clock distribution in the GS890 Group Switch. A new synchronization system is developed for the GEM magazine and the new hardware in the group switch. The exchange clock system is called CL890. The Clock Module (CLM) is now duplicated and located in the GEM magazine (or in different GEM magazine). Inside the CLM, there are two clocks for reliability. From the two CLMs, timing information is distributed to all XDB boards in both planes. This means that there are two CLMs and not three as in earlier versions. The CLM function is implemented as a Clock Generation Board (the CGB).
For switches larger than 16K, a number of Clock Distribution Boards (CDB) are required for the distribution of timing signals to all the XDBs that make up the switch core.
2 AXE Platform EN/LZT 101 1513 R4A – 91 – The CLMs are synchronized in a master-slave arrangement and can provide a quality duplicated exchange clock in accordance with the ITU specifications. For network synchronization purposes, the exchange clock system contains interfaces for the connection of incoming clock reference signals. This function is referred to as ICF. External synchronization of a node in a network must be possible in different ways. The exchange clock system in CL890 supports the following: • A local reference clock in case of interrupt of external timing information. The function is referred to as Reference Clock Module (RCM) and the hardware is called Local Reference Board (LRB). This gives better long-term stability that just having the CLMs.
External references from incoming PCM lines or external sources from other vendors. These references are connected via one or two Incoming Reference Board (IRB), which converts the incoming source to 8 kHz. The ICF receives external signals called CLREFs that are converted into a suitable format and distributed to the CLMs. The CLREFs can be different types for example an 8 kHz signal derived from a traffic link originating in the ETC: • Stand-alone clocks like the Ericsson Central Building Clock (CBC) or the GPS System Clock (GSC). GPS (Global Positioning System) Three ICF functions are housed in an IRB board. A maximum of 6 CLREFs can be connected to the system - three on each IRB. The converted signals are distributed from the IRB to the CGB.
The RCM is implemented on a single board, Local Reference Board, LRB, with conforming to the quality requirements specified by the ITU-T specifications. CLOCK CONFIGURATION If more than one GEM is used, the CGBs are to be placed in different GEMs in order to improve the reliability of the system. For switches with target sizes larger than 128K, the clock functions will be housed in two separate magazines. These are
AXE Survey – 92 – EN/LZT 101 1513 R4A specifically used for the synchronization function in order to provide timing distribution for the entire switch. These magazines are referred to as CDMs (Clock Distribution Magazines). In total there are three different clock configuration cases depending on the size of the switch: a single-GEM switch, a switch having a target size of 128K (up to 8 GEMs) and a switch having a target size of 512K (up to 32 GEMs). Clock Distribution for GSs consisting of 1 GEM For switches with only one GEM, all clocks may be housed in the same GEM (see Figure 2-50). It should be noted that the solutions in which all devices (including clocks) are housed in the same magazine couldn’t be considered as preferred solutions for systems with extremely high reliability requirements. XDB XDB SCB-RP SCB-RP 8 DEVICE SLOTS IRB IRB CGB_0 CGB_1 8 DEVICE SLOTS XDB XDB SCB-RP SCB-RP 8 DEVICE SLOTS IRB IRB CGB_0 CGB_1 8 DEVICE SLOTS Figure 2-50 GEM optimized for 16K A GEM configured with external clock distribution is used when the Group Switch is configured with more than one GEM and the clock needs to be distributed to several GEM magazines (up to 8 GEMs in this configuration).
2 AXE Platform EN/LZT 101 1513 R4A – 93 – (CGB_1) XDB XDB SCB-RP SCB-RP 8 DEVICE SLOTS IRB CGB_0 CDB 9 DEVICE SLOTS CDB (CGB_1) XDB XDB SCB-RP SCB-RP 8 DEVICE SLOTS IRB CGB_0 CDB 9 DEVICE SLOTS CDB Figure 2-51 GEM with one clock board It is a magazine housing two XDBs, two SCBs, one CGB, two CDBs, one IRB and contains 16 available device slots (see Figure 2-51). The switch requires two of these magazines since the switch always requires two clock boards (CGBs). Clock configuration for GSs with a target size of 128K Clocks will be housed in two different GEMs for GSs having a target size of 128K (that is up to 8 GEMs). Clock configuration for GSs with a target size higher of 128K Two clock magazines, Clock Distribution Magazine (CDMs), must be used for switches having a target size larger than 128K (that is larger than 8 GEMs). Each magazine will contain one Clock Generation Board (CGB) and a maximum of 8 Clock Distribution Boards (CDB).
AXE Survey – 94 – EN/LZT 101 1513 R4A Note: the LRB is optional CDB CDB SCB-RP SCB-RP IRB CGB_0 CDB CDB CDB CDB LRB CDB CDB SCB-RP SCB-RP IRB CGB_1 CDB CDB CDB CDB CDM 1 CDM 2 CDB CDB CDB CDB LRB Note: the LRB is optional CDB CDB SCB-RP SCB-RP IRB CGB_0 CDB CDB CDB CDB LRB CDB CDB SCB-RP SCB-RP IRB CGB_1 CDB CDB CDB CDB CDM 1 CDM 2 CDB CDB CDB CDB LRB Figure 2-52 CDM Magazines Both CDMs will be connected to every GEM from a CDB-pair. This means that every GEM is connected to four different CDBs. 32 GEMs may be connected if there are 8 CDBs in every CDM. COMPARISON BETWEEN GS IN BYB501 VS GS890
2 AXE Platform EN/LZT 101 1513 R4A – 95 – GS890 Capacity 1 1 Volume 1 1/6 Power 1 1/4 Figure 2-53 16K group Switch comparison Capacity 1 : 1 Cabinets 10 : 2 Power 4 : 1 • Distributed GS, Integrated RP, • Mixed high speed devices 128 K GS890 GS16M-1 Plane A GS16M-4 Plane A GS16M-5 Plane A GS16M-0 Plane A GS16M-3 Plane A GS16M-6 Plane A GS16M-7 Plane A GS16M-2 Plane A CL128M 1800 mm GS16M-1 Plane B GS16M-4 Plane B GS16M-5 Plane B GS16M-0 Plane B GS16M-3 Plane B GS16M-6 Plane B GS16M-7 Plane B GS16M-2 Plane B 128 K GS12 GEM2 GEM3 GEM4 GEM1 GEM6 GEM7 GEM8 GEM5 Figure 2-54 128K group switch comparison
AXE Survey – 96 – EN/LZT 101 1513 R4A MIGRATION OF EXISTING NODES Network Node Renewal Process NNRP refers the various methods available for the extension of existing nodes to include APT 1.5 products and facilities. The GS890 supports migration from existing nodes based on GS64 (BYB202), GS10, and the GS12 including the retaining of existing devices. Migration methods are referred to as NNRP-3 and NNRP-4. NNRP-3: Upgrade/expansion of BYB 202 core to include GS890 & devices (APT1.5). NNRP-4: Upgrade/expansion of BYB 501 core (pre-APT 1.5 generation) to include GS 890 & devices (APT 1.5). NNRP – driving forces NNRP-3: • A group switch larger than 64k is needed because of changes in the network structure (operators are decreasing the number of switches in the network for cost reduction) • A subrate switch in the group switch is needed which is larger than 4k.
• To get access to the new GEM based hardware such as ET155, transcoders and echo cancellers. These devices have significantly better price/performance than hardware available in BYB 202. NNRP-4: As above for the NNRP-3, plus the following: • A group switch larger than 128k is needed larger switches are used in the network. • A subrate switch in the group switch is needed which is larger than 4k. • To get access to the new GEM based hardware such as ET155- 1, transcoders and echo cancellers. These devices have significantly better price/performance than hardware available in BYB 501 (pre AXE 810).
• Further cost of ownership reduction.
2 AXE Platform EN/LZT 101 1513 R4A – 97 – PROCEDURES The main procedure is the same for NNRP3 and NNRP4. The whole idea is to change the existing TSM or GS16M subrack into a multiplexer and insert new interface boards in these magazines. The interfaces connect the old group switch to the new GEM subracks and the actual switching takes place in the new switch. The figure below shows the main principle for the NNRP4. Figure 2-55 NNRP4 upgrade To be able to do this during traffic handling, the two planes of the group switch and the two CP sides are utilized. The main principle is to separate the CP and load the separated CP side with new group switch software. At the same time, the hardware connected to the separated side is updated while traffic is executed in the executive CP controlling the old group switch hardware. The procedure is described step by step. • Step 1: The CP pair is separated. On the executive CP side, one plane of the existing switch core is defined as working while the opposite plane is defined as manually blocked. • Step 2: Upgrade the TSMs (in the case of NNRP-3) or the GS16M subrack (in the case of NNRP-4) within the manually blocked plane of the existing switch core to multiplexers. The multiplexers are then physically connected via either DL3 links (NNRP-3) or DL5 links (NNRP-4) to the same plane of the new switch core.
• Step 3: The upgraded plane is then to be defined by the operator as working while the opposite plane is defined as manually blocked in the standby separated CP side. The executive CP side and the existing switch’s working plane will carry the traffic. The opposite plane of the new switch core, related to the standby CP, is now active. • Step 4: A side switch is used to bring the plane of the upgraded multiplexers and the new switch core into a traffic- processing state.
AXE Survey – 98 – EN/LZT 101 1513 R4A • Step 5: Following exchange verification, the CPs are brought into parallel operation. The remaining manually blocked TSMs/GS16M subracks of the existing switch core are upgraded to multiplexers and connected to the corresponding plane of the new switch core. • Step 6: Both planes are now operating with the existing switch core (that has been converted to multiplexers) connected to the new switch core. After the change, the switch can be “cleaned up” as the CLMs and all the CLM cables of the old switch can be removed. The old part is now synchronized from the new GS890 via the DL3/DL5 interfaces. Also the back plane HWH cables can be removed as well as the SPIB boars.
2 AXE Platform EN/LZT 101 1513 R4A – 99 – EXTENDED SWITCHING SUBSYSTEM, ESS Main functions The extended switching functions can be implemented in subsystem ESS in an ordinary existing source system environment (XSS) or in the subsystem ESS-R in the resource module platform (RMP). Broadcast messages to several subscribers at the same time Conference calls Interactive voice services Group Switch Broadcast messages to several subscribers at the same time Conference calls Interactive voice services Group Switch Figure 2-56 ESS main functions ESS Extended switching subsystem The extended switching subsystem includes the following main functions • Broadcast (BC) is a platform that is used by other functions such as mass announcement (MA) for allowing several subscribers to listen to the same message at the same time • Multi junctor (MJ) for simultaneous connection of more than two subscribers to one call • Announcement system (ANS) to support interactive voice services such as recorded messages to subscribers SET OF PARTS The different functions broadcast, multi junctor and announcement system form the sets of parts in ESS. The broadcast (BC) is software only. It includes a number of function blocks for traffic administration, command handling etc. for the broadcast function
AXE Survey – 100 – EN/LZT 101 1513 R4A CCD AST BC MJ ANC Broadcast MultiJunctor Conference call device Announcement system Announcement sevice terminal CCD AST BC MJ ANC Broadcast MultiJunctor Conference call device Announcement system Announcement sevice terminal Figure 2-57 ESS set of parts Multi Junctor The MJ contains is both software and hardware. It includes func- tion blocks for handling of the hardware for the multi junctor functions. The MJ are primarily used for monitoring, traffic observation, conference call, broadcast, call waiting, enquiry, three party call and for different OPS functions, that is functions for connection of more than two parts in a call.
The user interfaces towards MJ give a number of possible services. Over one of the interfaces it is possible to handle calls with up to 31 participants. The multi junctor hardware is the conference call device (CCD). Announcement system The ANS contains both hardware and software. It includes func- tion blocks for handling of the hardware for announcement system functions. ANS is used to send recorded announcements about network conditions, changed numbers or used together with supple- mentary services to guide subscribers. ANS also includes functions that make it possible for subscribers to record their own messages on line.
The hardware for the ANS are the announcement service terminals (AST). There exist different announcement service terminals with a possibility to compose messages consisting of up to 32 phrases.
2 AXE Platform EN/LZT 101 1513 R4A – 101 – FUTURE DEVELOPMENT APT A large step was taken when AXE 810 was developed. The new GEM subrack and the distributed group switch creates a flexible platform with very high traffic capacity. However, life does not stop here and the development continues. Here are some of the most important plans for the near future (1-2 years): • A general adaptation of AXE towards the server – gateway architecture (which is called “ENGINE” for the fixed part). This includes many different functions where system • Structure, signaling protocols, ATM interfaces are some of them.
• A second generation ALI interface (ATM interface) will be developed which has higher capacity and smaller foot print. • RPP will be developed so it can be included in the GEM subrack. RPP will then be the main signaling platform and some applications from RPG will be moved to RPP. Remember that RPP is already today working as a signaling terminal for the high-speed signaling links (HSL). • Some applications from AST and PDSPL will be moved to the generic RPP platform. APZ Also APZ will be further developed in the future. The key words here are capacity and reliability. Here are some important events in the near future: • A new CP will be released in late 2001 called 212 40. That will be the first CP ever from Ericsson built with a commercial microprocessor. The basis will be an Alpha processor from Compaq.
• The APZ in AXE will evolve towards a multi-processor solution. There are two tracks that will be worked on: one with functional distribution of software (different CPs run different parts of the software), and one with replicated distribution (every CP can work with call handling). The latter gives highest total processing power. The goal is to have a system at the end of 2002, which has 30x the power of an APZ 212 30. • A Gbit Ethernet will replace the RP bus. The GEM hardware (and the SCB-RP) is already prepared for this.
AXE Survey – 102 – EN/LZT 101 1513 R4A Intentionally Blank