Fixed Access Network Sharing
                                     Kenneth J. Kerpez, John M. Cioffi, Peter J. Silverman, Bruno Cornaglia, and Gavin Young

                                                       Abstract                                                 slice. The access node is generalized terminolo-
                                                                                                                gy for a digital subscriber line access multiplex-
                                     Deep fiber deployments for ultrafast broad-                                er (DSLAM), optical line terminal (OLT), cable
                                 band are both technically and economically chal-                               modem termination system (CMTS), and so on.
                                 lenging. Fixed access network sharing (FANS)                                   The aggregation node aggregates traffic.
                                 offers a highly enhanced form of virtual unbun-                                    As fiber penetrates deeper, physical unbun-
                                 dling of broadband access networks, enabling                                   dling gives way to virtual unbundling, and FANS
                                 cost sharing and the dynamics of a competitive                                 provides the means to continue a vibrant compet-
                                 landscape. Data, control, and management inter-                                itive ecosystem supporting economically viable,
                                 faces are automated and harmonized among                                       differentiated, and innovative services. FANS is
                                 wholesale infrastructure providers and retail vir-                             synergistic with the software-defined access net-
                                 tual network operators. Standardized FANS inter-                               work (SDAN) concept [5, 6].
                                 faces can greatly decrease OPEX while increasing
                                 customer satisfaction. When FANS is implement-
                                 ed, network slicing logically partitions and isolates                               Current Multi-Operator Landscape
                                 network resources among the VNOs, and such                                     Competition today on copper infrastructure
                                 sharing can split the cost of network upgrades                                 is often via facilities-based physical unbundling,
                                 among several entities. FANS works with virtu-                                 with competitive providers deploying their own
                                 alization, where control plane functions are                                   access nodes and leasing copper loops from InPs.
                                 migrated from dedicated network equipment into                                 Physical unbundling allows a retail operator to
                                 software running on commodity hardware, with                                   essentially run all their own operations and inde-
                                 FANS providing network as a service. This article                              pendently offer services. Physical unbundling is
                                 describes the drivers behind FANS, several archi-                              very popular in some areas (e.g., Europe) and has,
                                 tectures supporting FANS, and emerging stan-                                   arguably, led to very low-cost and very high-speed
                                 dards supporting FANS.                                                         service to consumers.
                                                                                                                    There is also some “virtual unbundling,” which
                                                  Introduction                                                  has two flavors: bitstream and virtual unbundled
                                 Fixed access network sharing (FANS) applies                                    local access (VULA). Bitstream is generally provid-
                                 when an infrastructure provider (InP) controls                                 ed by giving each VNO access to their customers
                                 a physical access network that supports virtual                                at the IP layer and is simple resale of the service
                                 unbundling to virtual network operators (VNOs)                                 provided by the InP. Bitstream usually is offered in
                                 [1]. FANS provides interfaces [2, 3] that allow                                a way that does not support differentiation of ser-
                                 diagnostics and status data to be disseminated                                 vices between VNOs. VULA is generally provided
                                 from the InP to VNOs, and FANS allows a VNO                                    at the Ethernet layer, and can enable layer 2 class
                                 to request or perform changes in network con-                                  of service differentiation and sometimes multicast.
                                 figuration and control their own virtual network.                              Generally, the management, backhaul, and other
                                 These FANS interfaces enable automated oper-                                   operations are opaque to the VNO with current
                                 ations spanning the InP and VNO domains. An                                    virtual unbundling, although there are limited
                                 objective of FANS is to enable VNOs to perform                                 exceptions [7].
                                 operations with virtual unbundling similar to their
                                 operations with physical unbundling [4].                                              Fiber-Deep Ultrafast Broadband
                                     Not only is the physical access network provid-                            Vectored VDSL2 and coordinate the sig-
                                 ed by the InP and shared with FANS, but manage-                                nals across all the copper pairs emanating from
                                 ment data and configuration are also shared. With                              an access node. Therefore, physical unbundling
                                 FANS, network management is a shared respon-                                   is technically unattractive with fiber to the node
                                 sibility, with some management being performed                                 (FTTN) using vectored very high rate DSL 2
                                 by the InP and some by VNOs. There may be dif-                                 (VDSL2), and with fiber to the distribution point
                                 ferent levels of data sharing, distinguished by both                           (FTTdp) using because multi-operator vec-
                                 the data shared between VNO and InP, and by                                    toring is not yet standardized. Physical unbun-
                                 the resolution and accuracy of the shared data.                                dling with fiber to the premises (FTTP)/fiber to
                                     Figure 1 shows how a single network and its                                the home (FTTH) using passive optical network
                                 equipment is administered by an InP, and a net-                                (PON) technologies could be possible using
                                 work sharing system logically divides the physical                             an overlay network or separate wavelengths.
                                 network resources between a number of VNOs,                                    However, for all these new ultrafast broadband
                                 each of which has their own virtual network                                    deployments, physical unbundling is generally
Digital Object Identifier:
10.1109/MCOMSTD.2017.1600001ST              Kenneth J. Kerpez, John M.. Cioffi, and Peter J. Silverman are with ASSIA Inc.; Bruno Cornaglia and Gavin Young are with Vodafone

1                                       ISSN 2471-2825/17/$25.00 © 2017 IEEE                                                  IEEE Communications Standards Magazine • March 2017
economically unattractive. This is because phys-
ical unbundling would require many operators                                      Access                                   VNO 1
to each run fiber in the outside plant to each of                                 node                      Aggregation
many small nodes, install all these small nodes,                                                               node
and deploy equipment at each of these small
nodes. Much of this fiber and equipment would                                                                              VNO 2
be redundant with other operators’ deployments
and be underutilized.
    The existence of multi-operator environments                                           Shared network
will depend on virtual unbundling. Basic resale is                                           InP domain                    VNO 3
insufficient; an ecosystem supporting innovative
service offerings from multiple operators depends      Figure 1. Network sharing data plane, showing network slices in different
on a platform that allows retailers to perform           colors.
operations in a way that is nearly indistinguishable
from physical unbundling. For example, FANS can            Using an active sharing approach is more con-
enable multicast or real-time service variations       venient than the passive one, mainly because of
such as turbo-boost, bandwidth reservation for         the extra cost in the passive approach for each
video streams, and real-time charging. Moving          operator to install and connect its own equip-
forward, FANS is especially desirable in its ability   ment. On the other hand, active sharing without
to encourage such competitive innovation and           using FANS limits the capability of the operator to
differentiation, and to drive economic growth of       differentiate its offer from others, so active sharing
broadband services at lower cost and lower oper-       can be less attractive. FANS extends active shar-
ational complexity.                                    ing to encompass management and control func-
                                                       tions. With FANS the solution implemented is a
                 FANS Benefits                         “virtual unbundling,” so each operator has similar
Deploying superfast broadband networks is quite        capability to implement its own access network,
costly in terms of both upfront investment and         which is why FANS is an appealing option.
resources needed for design and implemen-
tation. Multiple parallel networks covering the                          Use Cases
same areas can lead to low take rate and long          With current bitstream or VULA, operations “inter-
return on investment. Operators should therefore       faces” between InP and VNO are often manual.
share their own infrastructure in order to reduce      In conjunction with appropriate business arrange-
upfront investments and operational resources.         ments, FANS can assist in automating operations
The International Telecommunication Union (ITU)        interactions between InPs and VNOs; including
Commission for Sustainable Growth and the Euro-        fault, configuration, performance monitoring, and
pean Commission have recognized that sharing           optimization. In particular, standardized FANS
infrastructure can speed broadband rollouts. In        interfaces allow efficient data exchange between
some countries, including Portugal, Spain, and the     all parties. This can lower operation expenditure
United Kingdom, regulatory bodies have taken           (OPEX) costs, improve customer satisfaction by
into account this consideration and have created       enabling rapid response times, and increase the
rules for sharing existing passive infrastructures.    number of customers.
Operators also create their own agreements for             FANS can enhance competitiveness with com-
sharing the access network.                            peting broadband media. Multiple companies can
    Two types of sharing are possible, as shown        share the costs of infrastructure and its upgrades.
in Fig. 2: passive and active sharing. With pas-       The InP can offer enhanced product offerings to
sive sharing, only the passive infrastructure is       the VNOs, with enhanced value for providing
shared, including ducts, poles, and cabling; and       access to automated data and control interfaces.
each operator installs its own access node equip-      FANS use cases include:
ment with a fiber tree connecting it to the opti-          Performance monitoring and optimization
cal distribution frame (ODF) in the central office     is enabled. Each VNO can have automated real-
(CO). For PON, passive sharing leads to a cost         time access to performance and fault monitoring
increase above a single infrastructure because         data. This is useful for VNOs’ network monitoring
multiple parallel connection trees have to be built.   as well as repair and troubleshooting operations.
In the case of active sharing, both passive infra-     Customer relationship management (CRM) can
structure and access node equipment are shared;        improve. VNOs can optimize the configurations
the drawback is that the VNO connects via bit-         of their lines. Further, multi-line optimizations can
stream. Active sharing with bitstream has limited      be performed across multiple operators’ lines by
customer management and service differentiation        a centralized sharing system, which can increase
capabilities, which sometimes make active sharing      performance of all lines [4].
unattractive. Passive sharing can give around 30           Fault correlation can be performed using
percent savings, while active sharing can lead up      shared data to correlate multiple faults across mul-
to 40 percent savings, compared to deploying           tiple lines and multiple service providers; and this
multiple parallel networks.                            can further be used to help coordinate dispatches.
    To overcome this situation, active sharing with    For example, pooled data across multiple VNOs
FANS uses VULA and virtualization concepts to          and/or InPs can be used to identify a fault that
allow slicing the network elements so as to assign     occurs in a single shared cable section. A single
dedicated resources to each operator. In this          dispatch to fix that cable section is much better
case the cost of the passive infrastructure remains    than dispatching to each troubled line separately.
the same, but new slicing capabilities have to be          Configuration can be automated, so a VNO
developed.                                             can rapidly turn up service. VNOs can offer ser-

IEEE Communications Standards Magazine • March 2017                                                                                2
The centralized sharing                                                        Passive sharing
                                                                   CO                                           Shared           Apartment/home
system may be adminis-                                                                                           fiber
                                                          Operator 1
tered by the InP, a VNO, or                                                     Shared       Shared
                                       Operator 1                                fiber       ODF
a third party. The central-
ized management system                                                                                       Shared
itself could be provided               Operator 2
by multiple parties either                                Operator 2
via shared or open source
software, or via APIs                                                           Active sharing
between proprietary sys-
                                                                   CO                                           Shared           Apartment/home
tems. With shared or open                                                                                        fiber
                                                          Operator 1            Shared       Shared
source software, the cost              Operator 1                                fiber       ODF
of the software is split
                                                                        ODF                                  Shared
across multiple parties.                                                                                     fiber
                                       Operator 2

                                  Area 1

                              Figure 2. Passive sharing and active sharing approaches, and their relative 10-year TCO per operator.

                              vices with different quality of service (QoS) levels,       • Runs and redesigns customized systems in its
                              for example, to maximize speed or stability, or to            own virtual network, such as diagnostics and
                              minimize delay or power usage. Data sharing can               optimization and DSM/DLM systems [10]
                              help ensure that the lines can support the neces-           • Provides specific and customized service
                              sary QoS attributes.                                          through its own area network
                                  Services innovation can flourish; for example,          • Utilizes the network resources provided by
                              VNOs can provide different types of assured ser-              the InP to provide its services
                              vices, business class services, sponsored services,         • Obtains revenue by selling services to end
                              and so on. This can build on basic broadband                  users
                              offerings to grow the pie for all entities.
                                  Network planning can be enhanced with net-                          Centralized Sharing System
                              work topology and capacity data. Lines in a small           FANS is generally instantiated around a central-
                              geographic area should all have about the same              ized sharing system, as shown in Fig. 3. The cen-
                              performance, so neighborhood data can be ano-               tralized sharing system has southbound interfaces
                              nymized by a sharing system to provide line per-            to equipment and northbound interfaces to VNO
                              formance projections to VNOs.                               systems. The centralized system performs certain
                                  A single operator can exploit FANS for their            functions, such as authentication, authorization,
                              company and segment their network among dif-                and accounting (AAA), and arbitration of requests
                              ferent operation teams for business customers,              for resources, data, and control. The centralized
                              consumer broadband, and/or mobile backhaul                  sharing system can perform operations such as
                              connectivity. Moreover, FANS can also facilitate            diagnostics, configuration, and optimization for
                              mergers and acquisitions because operations can             the VNO, as shown in Fig. 3 for VNO A; or the
                              initially be run separately but with an integrated          external interface to the centralized sharing sys-
                              network.                                                    tem can enable these functions to be performed
                                                                                          by a VNO itself, which is the case for VNO B
                                           FANS Components                                in Fig. 3. The centralized sharing system may be
                                                    Actors                                administered by the InP, a VNO, or a third party.
                              FANS defines interfaces between an InP (aka                 The centralized management system itself could
                              wholesaler) and multiple VNOs (aka retailers).              be provided by multiple parties via either shared
                              The InP operates the physical network, while the            or open source software, or application program-
                              VNOs interface to broadband consumers.                      ming interfaces (APIs) between proprietary sys-
                                 The InP is responsible for deploying and man-            tems. With shared or open source software, the
                              aging the physical network; the InP:                        cost of the software is split across multiple parties.
                              • Enables physical resource slicing and carries                 The centralized sharing system implements
                                out the slicing                                           multi-tenancy, although the functionality may be
                              • Provides an interface to the VNO for data                 distributed among multiple systems or locations.
                                and control                                               Aspects of FANS could be implemented without
                              • Gets revenue from resource leasing                        a centralized sharing system, for example, with a
                              The VNO leases resources from the InP, and                  distributed architecture simply having interfaces
                                the main VNO functions are:                               between the various players. In any event, the
                              • Operates, controls, and manages its own vir-              centralized sharing system conceptually glues
                                tual area networks                                        FANS together.

3                                                                                                     IEEE Communications Standards Magazine • March 2017
                                                                                                       management systems
                                                       VNO A                                                 Configuration
                                                 management systems
                                                  External interface                                        External interface

                                                                Standard sharing interface                             Standard sharing interface
                                                  External interface                                        External interface
                      Monitoring,                    Diagnostics
                     performance,                                                     AAA
                                                    Configuration                                                                                     Control
                      diagnostic,                                             Resource management                  Central                               and
                      status, and                   Optimization
                                                                                                                  database                          configuration
                    other state data

                                                                                     interfaces                 Centralized sharing


                                                                       Aggz                                    Aggz                 BNGz

                                                                                         Aggy                                                                       Internet
                                                                                                    Aggy                     BNGy


Figure 3. Centralized sharing system.

    The components in Fig. 3 are part of the infra-                       • The business support system (BSS) inter-
structure that supports FANS:                                                face supports ordering and billing functions
• The “hypervisor” manages authentication                                    between InP and VNO. The BSS includes a
   and authorization to use the centralized                                  catalog of offers and resources, an ordering
   sharing system, and manages resources. The                                interface, inventory (of physical and virtu-
   hypervisor here oversees the virtualization                               al components, equipment, outside plant,
   or slicing of the network, not the compute                                admissible configuration settings, etc.),
   infrastructure.                                                           and revenue. The resource catalog should
• AAA: Authentication, authorization, and                                    include physical resources, virtual resources,
   accounting verifies user credentials, admits                              and services.
   requests and limits access, and maintains                              • Test and diagnostics interface. This invokes
   transactional records for billing and other                               specific test actions to provide diagnostics
   purposes.                                                                 data beyond what the equipment can pro-
• Resources management includes assignment                                   vide during normal operation. It provides
   of network bandwidth, equipment interfac-                                 outside plant and network test data, and may
   es, equipment computational resources, and                                provide analyses of these data. Test may be
   management interface bandwidth/frequency                                  abstracted to hide details of the network
   of admissible requests.                                                   equipment capabilities and to provide results
• Southbound equipment management inter-                                     in terms of the virtual services provided. The
   faces typically utilize the existing manage-                              interface may issue commands for request-
   ment capabilities of network elements or                                  ing tests.
   their management systems.                                              • Logical inventory. This includes equipment,
• The northbound sharing interface should be                                 interfaces, virtual ports and their assign-
   standardized. This interface provides moni-                               ments, equipment configuration settings, and
   toring, performance, diagnostics, status, and                             virtual functions inventory.
   other state information from the network to                                Messaging across the southbound interface
   the VNOs, and also relays or interprets con-                           from the centralized sharing system may be imple-
   trol and configuration requests from VNOs                              mented by an abstraction layer or an adaptation
   to the network.                                                        layer. An abstraction layer hides the details of
    There are additional interfaces between InPs                          equipment interfaces to present a simplified inter-
and VNOs that may or may not involve the cen-                             face toward management systems. An adaptation
tralized sharing system:                                                  layer directly translates signals from one format to

IEEE Communications Standards Magazine • March 2017                                                                                                                            4
another format, and usually has a different adapt-       The management system supports multi-tenancy,
Management system shar-     er for each type of interface.                           where each VNO is a separate tenant.
ing separates the manage-                                                                Management system sharing separates the
                              Resources Management and Security                      management plane from the data plane, with
ment plane from the data
                            Resources must be assigned carefully, to control         sharing and network slicing performed by the
plane, with sharing and     access permissions, arbitrate conflicts, ensure cor-     management systems. The data plane can remain
network slicing performed   rect or fair resource utilization, and guarantee reli-   unchanged, and data-plane functions such as
                            ability for the underlying physical infrastructure.      packet forwarding continue to be performed in
by the management           Resources need to be assigned, with data access          the network elements. Aspects of the control
systems. The data plane     and control separated, for the access network,           plane may also support sharing and network slic-
can remain unchanged,       equipment, and computing infrastructure. A VNO           ing functions.
                            cannot be allowed to access private data about               The centralized management system could
and data-plane functions    another VNO’s customers. Sharing of resources            provide functionalities that include the following:
such as packet forwarding   must be managed to ensure that resources are             • Security, which includes authentication to
                            properly allocated among the competing VNOs,                verify user credentials, authorization to admit
continue to be performed    and that any particular VNO cannot either impair            requests and limit access, and accounting to
in the network elements.    another VNO’s service.                                      maintain transactional records for billing and
Aspects of the control          Computing resources, including CPU, memo-               other purposes
                            ry, and virtual network, can be shared between           • Fault correlation, particularly for faults that
plane may also support      any or all of the actors. Managing computing                occur on lines or equipment that impact
sharing and network slic-   infrastructure resources is particularly important          multiple VNOs
                            for virtual functions.                                   • Inventory maintenance of the physical plant
ing functions.                                                                          and equipment, as well as the virtual assign-
                                                Backhaul                                ment of resources
                            The backhaul network extends from the access             • Data maintenance needed to access VNOs
                            node to whatever point the traffic is handed off to         and equipment such as addressing
                            a VNO or service. Traffic on the backhaul broad-         • Support of an automated data clearinghouse
                            band network needs to be segregated between                 that allows automated operations
                            different operators and services. Backhaul segre-        • Providing data to assist VNOs with network
                            gation can use VLANs, MPLS tunnels, or software             planning and to assist in development of
                            defined networking (SDN) approaches. An inter-              innovative services and differentiated ser-
                            esting new VLAN approach is to use a new “oper-             vices
                            ator VLAN” (O-VLAN) tag, which may be a third            • Multi-line optimization across multiple VNOs
                            VLAN tag in addition to C-VLAN and S-VLAN tags               Management system sharing allows a VNO
                            of IEEE 802.1ad Q-in-Q. This allows the VNO to           to choose to perform the following operations,
                            manage two levels of VLANs (S+C VLAN) for its            among others:
                            service configurations, while the InP only assigns       • Services provisioning
                            the O-Tag for each operator.                             • Fault and performance management
                                A VNO may wish to use its own backhaul               • Configuration of the network elements
                            network. In this case, data traffic may be handed        • Testing and gathering of diagnostic data
                            off from InP to VNO at various reference points,         • Line optimization
                            including the V-interface to the regional broad-         • Call center operations to answer trouble calls
                            band network or the A10 interface to service pro-            Unlike virtual node sharing, management-sys-
                            vider network(s) as defined in TR-101 [8]. The           tem-based sharing can be implemented with cur-
                            handoff could be at a broadband network gate-            rently deployed equipment.
                            way (BNG), in the aggregation network, or even
                            in the outside plant at a cabinet location.                          Virtual Node Sharing
                                                                                     Virtual node sharing is based on the concept of
                                     FANS Architectures                              equipment slicing. Virtual node sharing is per-
                            Two types of virtualization are emerging [1]:            formed within equipment, including access nodes,
                            • Equipment slicing, where network resourc-              aggregation nodes, and virtual port mappers. This
                              es are virtualized with slicing to support             may require the equipment to host a common
                              multi-tenancy. Separate tenants perform sep-           execution environment for sharing, such as a
                              arate functions on logically separate parts            segmented space running a version of Linux. A
                              of the equipment. This is most aligned with            hypervisor controls the life cycle and resources of
                              virtual node sharing.                                  virtual machines (VMs). Equipment slicing allows
                            • Full virtualization, where network functions           interchangeable functions to be hosted similar to
                              migrate from equipment to being hosted on              the way a data center can host virtual network
                              cloud infrastructure platforms. This is most           functions (VNFs). This concept is part of the virtu-
                              aligned with management-system-based shar-             al OLT (vOLT) in the Central Office Re-architect-
                              ing.                                                   ed as a Datacenter (CORD) initiative. FANS can
                                                                                     be considered a use case of CORD.
                               Management-System-Based Sharing                           The virtual access node model performs equip-
                            The centralized sharing system in Fig. 3 is the          ment slicing on physical access nodes to abstract
                            core of management-system-based sharing. With            them into multiple virtual access nodes, where
                            this sharing technique, a management system              each VNO accesses a logically separate virtual
                            performs the network slicing at the management           access node. Separate access node functions can
                            system level and not directly in the equipment           be sliced independently, and as shown in Fig. 4
                            itself. The management could be virtualized and          some functions may also be fully virtualized and
                            hosted in the cloud or at other operator locations.      hosted on cloud virtualization infrastructure.

5                                                                                             IEEE Communications Standards Magazine • March 2017
SDN controllers for the
                                                      Virtual access Virtual access Virtual access       Virtualized node         access network can also
                                                      node (VNOx) node (VNOy) node (VNOz)                    functions
                                                                                                     on top of the equipment     be virtualized. There may
                                                                  Access node (InP)                                                  be a hierarchy of SDN
                                                                                                                                 controllers, with an end-
                Access node (InP)        FANS                                                                                    to-end SDN controller on
                                                                                                                                    top of domain-specific
                                                                                                                                SDN controllers. Network
           Function-specific equipment                Virtual access Virtual access Virtual access
                                                      node (VNOx) node (VNOy) node (VNOz)                Virtualized node      SDN control can be divided
                                                                                                             functions         between the InP, having an
                                                                                                      on top of high-volume
                                                                  High-volume server                     server platforms       infrastructure controller,
                                                                                                                                and the VNOs, having vir-
Figure 4. Deployment scenarios for virtual access node functions.                                                                          tual controllers.

Some functions may also be fully virtualized, as                      functions and other VNFs and network services
shown in the bottom half of Fig. 4. VNFs imple-                       (NS); this can be thought of as fixed access net-
ment some of the functions that traditionally                         work as a service (NaaS). Here, the NFVI and
reside in the access node or the BNG.                                 MANO support multi-tenancy, where each VNO
    A virtual access node element represents the                      is a tenant, and they are logically separated. For
whole set of characteristics of a physical access                     a given function, each VNO would have separate
node. A centralized sharing system is still present                   VNFs, NSs, and VMs, thereby using the under-
and is involved as part of virtual node sharing.                      lying NFV components to allocate resources,
The centralized sharing system described earlier                      ensure privacy, perform life cycle management,
performs orchestration, and monitors and scales                       and so on.
virtualized and physical network resources.                               SDN controllers for the access network can
    Other network nodes can similarly use virtual                     also be virtualized. There may be a hierarchy of
node sharing, including virtual aggregation nodes                     SDN controllers, with an end-to-end SDN con-
(e.g. Ethernet aggregation switch, multiprotocol                      troller on top of domain-specific SDN controllers.
label switching [MPLS] router, SDN switch) [1].                       Network SDN control can be divided between
    The port mapper concept is part of virtual                        the InP, having an infrastructure controller, and
node sharing. A port mapper maps a disparate                          the VNOs,a having virtual controllers.
set of physical ports into a logical set of ports                         The following are among the fixed access net-
assigned to each VNO. The port mapper is a                            work functions that may be virtualized:
virtual entity used to map logical ports over the                     • VLAN translation/addition/removal: The
host physical ports. The virtual ports are iden-                         access node would focus on basic con-
tified through virtual port IDs. For example, as                         nectivity, whereas additional VLAN tagging
shown in Fig. 5, an access node may assign each                          could be performed in the NFVI.
user-facing port to a separate VNO, and then the                      • Virtual inventory management performs
VNO references the port through its virtual port                         assignments of physical assets.
ID. The port mapper may be combined with a                            • Per subscriber QoS enforcement (e.g., polic-
virtual switch, which can intelligently forward data                     ing or shaping) enforces QoS policy, and
by inspecting packets before passing them on,                            allocates QoS and class of service (CoS) lev-
ensuring traffic isolation. The port mapper more-                        els.
over facilitates the customer migration as the end                    • Port-based access control/authentication is
customer maintains the same physical ID and only                         performed, for example, by using a central-
changes the virtual port ID when moving from                             ized 802.1x agent
one operator to another.                                              • Traffic is managed, filteried, and shaped, and
                                                                         flow is controlled.
                Full virtualization                                   • Forwarding, traffic steering, load balancing,
Full virtualization moves functions into cloud                           and SDN control are virtualized.
platforms/data centers. Virtualization generally                      • Application awareness, deep packet inspec-
follows the architecture of the European Telecom-                        tion (DPI), and services-aware networking
munications Standards Institute (ETSI) Industry                          are virtualized
Specification Group (ISG) for Network Functions                       • There can be virtual gateway functions, resi-
Virtualization (NFV). Here, the NFV infrastruc-                          dential and business.
ture (NFVI) runs a system such as OpenStack or                        • Control and configuration: Each VNO con-
CloudStack, and the VNFs run on this infrastruc-                         trols and configures their own virtual access
ture. Management and orchestration (MANO)                                node dataset of configuration objects.
are controlled by a system such as Open Platform                      • Diagnostics and state information: Each VNO
NFV (OPNFV), Open Source MANO (OSM),                                     accesses virtual functions providing test,
Open Orchestrator (Open-O), or a proprietary                             diagnostic, performance, and status informa-
system.                                                                  tion.
    FANS with full virtualization can extend man-                     • Dynamic rate allocation (DRA): This function
agement-system-based sharing to include control                          controls traffic scheduling, such as dynami-

IEEE Communications Standards Magazine • March 2017                                                                                                       6
Physical deployment                                                                                 OSS/NMS logic network view
                                 ONU1                                                                                                     OLT
                                                 Slot 1
            Physical port ID
                                      P1                                                                                                     vAN1
    CPE 1                             P2                                                                          Virtual port ID
                                      P3                                                                                                P1
    CPE 2                             P4                                                                CPE 1
                                                           Slot 2                                                                       P2
                                      P1                                                                CPE 3                           P4
                                                                                       OLT                                                   vAN2
                                                                                                                  Virtual port ID
                                      ONU2                                                                                              P1
            Physical port ID                                                                                                            P2
                                                                                                        CPE 2                           P3
    CPE 3                                                           Splitter                                                            P4
                                      P3                                                                                                P5
                                      P4                  Slot 1                                                                        P6
    CPE 4                                                                                                                               P8
            Physical port ID
                                     P1                                                                          Physical port ID
                                     P3              Slot 1
                                                                                                        CPE 4
                                                                                                                                    InP port mapper
                                                                               Management IP address

Figure 5. Port mapper [1].

                                      cally varying the asymmetry ratio, or                     purpose of DSM in DSL environments. Sharing
                                      configuring PON dynamic bandwidth alloca-                        data on cable plant and DSL configuration and
                                      tion (DBA).                                                      performance allows DSM level 2 and 3 multi-line
                                 •    Dynamic resource assignment can be virtu-                        optimizations and DSM level 1/DLM single-line
                                      alized (e.g., access and backhaul bandwidth                      optimizations [10] to enhance the performance
                                      assignment).                                                     of all lines.
                                 •    There can be virtualized dynamic spectrum                           Figure 6, from ND1518, shows a somewhat
                                      management (DSM) and dynamic line man-                           complicated view of data sharing interfaces,
                                      agement (DLM) [10].                                              including interfaces for DSM/DLM, BSS/ordering,
                                 •    Power control entity (PCE), cross-layer                          plant inventory, and plant test and repair. Three
                                      low-power mode control, for There                        entities comprise the InP: two access node opera-
                                      are a number of thresholds and other settings                    tors (ANOs), and a transmission path facility (TPF)
                                      that can be varied to configure low-power                        provider.
                                      mode on individual transceivers, and these
                                      settings and primitives can be determined in                       Broadband Forum DSL Data Sharing
                                      a virtualized power control entity and com-                      Broadband Forum TR-349 [3] describes and
                                      municated to the transceivers.                                   defines data sharing for managing DSL. DSL data
                                 •    VDSL/ vectoring control and manage-                        sharing architectures are described, with cen-
                                      ment: Virtualized functions can control part                     tralized and distributed architectures presented.
                                      of the vectoring configuration, and could                        High-level use cases are defined and requirements
                                      even calculate vectoring coefficients [9].                       presented for these use cases. The data and con-
                                                                                                       trol parameters applicable to each use case are
                                                          Standards                                    identified, and most parameters are common to
                                 An initial effort at standardizing part of FANS for                   all use cases. Two types of DSL data sharing inter-
                                 DSL was undertaken in the U.K. Network Interfac-                      face are defined in detail: profile-level (general)
                                 es Coordinating Committee (NICC) [4]. This then                       and parameter-level (specific). The parameter syn-
                                 fed into the definition of an interface for DSL data                  tax is defined in YANG data models for and
                                 sharing in the Broadband Forum [3], and now a                         for VDSL in Broadband Forum TR-355.
                                 larger project on FANS is underway in the BBF
                                 [1, 2] to define FANS architectures, requirements,                                   Broadband Forum
                                 interfaces, and so on.                                                         Fixed Access Network Sharing
                                                                                                       The Broadband Forum has embarked on a pro-
                                       NICC ND1518, Data Sharing for DSM                               gram to specify FANS. This is to investigate tech-
                                 The NICC specification ND1518 [4] describes                           nical aspects associated with FANS that involve
                                 the use of sharing data between operators for the                     the access network, including access nodes and

7                                                                                                                 IEEE Communications Standards Magazine • March 2017
aggregation nodes. The Broadband Forum FANS
project should generate several specifications,                                    VNO A                         VNO B
the first of which is FANS — Architecture and                                                                      DSM/DLM
Nodal Requirements [1]. This document identifies
architectures and interface points for FANS. Both
management-system-based sharing and virtual-ac-
cess-node-based sharing are included. Require-                                                                                    Centralised system
ments are included, and operation, administration,                                                                                   AAA
and maintenance (OAM) and other operations                                                        Data and control                 DSM/DLM
are also described.
    A project has also been started in the Broad-                                                                                      Inventory DSM,
band Forum to specify FANS access network shar-                                                                                           MPF data
ing interfaces [2]. Further specifications, which
have not yet been started, include access network                InP 1                            InP 2                           MPF provider
virtualization and SDN-enabled FANS.                                      DSM/DLM                                                         Test

                      Summary                                              Inventory and
                                                                             DSM data
                                                                                                            Inventory and
                                                                                                              DSM data                      MPF data
Ultrafast fiber-deep broadband deployments are
changing the competitive landscape. With current            Figure 6. Simplified view of data sharing [4].
bitstream or VULA virtual unbundling, operations
interfaces between InPs and VNOs are often not              [3] Broadband Forum TR-349, “DSL Data Sharing,” 2016.
real time, and VNOs provide simple resale with lit-         [4] NICC ND1518, “Data Sharing for DSM,” 2015.
tle or no differentiation. Sharing network resourc-         [5] K. Kerpez et al., “Software-Defined Access Networks,” IEEE
                                                                Commun. Mag., vol. 52, no. 9, Sept. 2014, pp. 152–59.
es and management interfaces will allow virtual             [6] K. Kerpez and G. Ginis, “Software-Defined Access Network
unbundling to be economically and operationally                 (SDAN),” CISS 2014: The 48th Annual Conf. Info. Sciences
efficient, and enable vibrant competition based                 and Systems, Mar. 19, 2014.
on differentiation of offered services between pro-         [7] W. Schramm, “NGA Regulation in Austria,” TNO DSL Sem-
                                                                inar, June 2013.
viders.                                                     [8] Broadband Forum TR-101i2, “Migration to Ethernet Based
    FANS extends virtual unbundling to unbundle                 DSL Aggregation,” 2011
management and control functions, with network              [9] J. Cioffi, “FULLY Unbundled Vectored DSLs: It Is Absolutely
sharing and data sharing. FANS opens up man-                    Possible!” Summit May 2016.
                                                            [10] Broadband Forum TR-197i2, “DQS: DSL Quality Manage-
agement and control interfaces such that VNOs                   ment Techniques and Nomenclature,” 2014.
can perform the same operations as they would
with physical unbundling, where they own and                                       Biographies
operate their own network elements. Much as the             Kenneth J. Kerpez [F’04] ( received his
Internet offers a platform for innovative applica-          Ph.D. from Cornell University in 1989. He worked at Bellcore
tions, so FANS can offer a platform for innovative          and Telcordia for 20 years, and he now works at ASSIA. He
                                                            became an IEEE Fellow in 2004 for his contributions to DSL
broadband services.                                         technology and standards. He has many years of experience
    Standardized interfaces and a central manage-           working on networks of all sorts, including DSL, fiber access,
ment system are keys to enabling FANS in the                home networks, wireless systems, Wi-Fi, broadband service
near term. In the longer term, virtual nodes, SDN           assurance, IPTV, IP QoS, triple-play services, and virtualization.
control, and full virtualization will all feed into         John M. Cioffi ( received his elec-
enabling FANS. Resource control, AAA, securi-               trical engineering in 1978 from the University of Illinois, and his
ty, and configuration control must be carefully             Ph.D. in electrical engineering in 1984 from Stanford. He was
administered with FANS to ensure privacy and                with Bell Laboratories, 1978–1984; IBM Research, 1984–1986;
                                                            and has been a professor of electrical engineering at Stanford,
avoid harm to the network.                                  1986–present, now Emeritus. He founded Amati Com. Corp in
    FANS offers many benefits, both to InPs and             1991 and was officer/director from 1991 to 1997. He currently
VNOs:                                                       is chairman and CEO of ASSIA, Inc. His specific interests are in
• Automated interfaces lower operational costs              the area of high-performance digital transmission. He has been
                                                            the recipient of numerous highly prestigious awards, has pub-
   relative to manual interfaces, both for the              lished over 600 papers, and holds over 100 patents.
   InP and the VNOs.
• Fault correlation across multiple operators’              Peter Silverman ( is director, Stan-
   lines is enabled, again lowering operations              dards and Technical Marketing at ASSIA Inc. Prior to employ-
                                                            ment at ASSIA he was employed at Bell Laboratories, Ameritech,
   costs.                                                   3Com, and Valo Inc. before taking his current position at ASSIA
• Multi-line, multi-operator optimizations are              in 2005. He has edited numerous international telecommunica-
   enabled, which increases performance of all              tions standards, and is a co-author of two books, Understanding
   lines.                                                   Digital Subscriber Line Technologies (Prentice-Hall, 1999) and
                                                            DSL Advances (Prentice-Hall, 2003) and 10 patents.
• Multiple companies can share the costs of
   network upgrades to superfast broadband.                 Bruno Cornaglia ( received
• It enables enhanced service levels, services              his Degree in electronic engineering from Politecnico di Torino
   differentiation, and innovation.                         in 1990. He worked at CSELT, the research center of Telecom
                                                            Italia Group, Omnitel, which then became Vodafone Italy, and
• The InP can offer FANS as an enhanced ser-                now at Vodafone Group Services. His main areas spread from
   vice to the VNOs.                                        microwaves, where he developed the concept and solution of
• The VNOs can offer enhanced services to                   microwave Ethernet with adaptive modulation;, satellite, where
   the broadband customers (e.g., enterprises).             he worked on defining new SDH payloads to be used in satellite
                                                            links; and now fixed broadband, including copper, cable, and
                                                            fiber technologies, where he is working on different innovative
                      References                            approaches, like distributed architecture for cable, NG-PON2 in
[1] Broadband Forum WT-370, “Fixed Access Network Sharing   fiber, and full access virtualization. He is an author or co-author
    — Architecture and Nodal Requirements.”                 of more than 20 papers.
[2] Broadband Forum WT-386, “FANS Access Network Sharing
    Interfaces.”                                            Gavin Young [M] ( received his

IEEE Communications Standards Magazine • March 2017                                                                                                     8
B.Sc in electrical and electronic engineering from the University
of Wales, Swansea, in 1985 and his M.Sc. in communications
engineering from the University of London (Imperial College
of Science and Technology) in 1986. He is head of the Fixed
Access Centre of Excellence within Vodafone, where his inter-
ests include technology strategy, architecture, innovation, and
performance of broadband networks spanning copper, cable,
and fiber technologies. He is a Fellow of the IET and Distin-
guished Fellow of the Broadband Forum.

9                                                                   IEEE Communications Standards Magazine • March 2017
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