Software Defined Access Networking (SDAN) - Assia-inc

White PaperThe first scenario is that of a network owned by a singleoperator, where a single entity serves as PIP, i.e. controllingthe outside plant and the access hardware, and also as anetwork operator, i.e. providing services to consumers.This scenario is representative of many current networksin which there is no virtualization of the access network.In this scenario, a management system centrally controlsand manages all lines connected to the access hardware.Control functions include the optimization of the physicallayer configuration of the broadband connection, forexample changing parameters such as data rates andpower levels. Management functions include networkanalytics that drive maintenance operations and marketingcampaigns. Centralizing these functions enables the useof advanced algorithms delivering the highest gains,and it also allows for homogeneous, vendor-agnosticmanagement of the access hardware.Next, a scenario in which multiple VNOs deliver servicesto end-users over a single infrastructure is considered.The outside plant and the access hardware are controlledby one or more PIPs, who may themselves be VNOs. Thisscenario applies to current networks where regulatoryprovisions for competition via local-loop-unbundling(LLU), sub-loop-unbundling (SLU) or bit-stream accessexist2. This scenario is especially common in regionswith facilities-based competition or where Layer 2competition is mandated by regulators. In this case, amulti-tenant management system enables the VNO tomaintain substantial control of services, while providingfor determinacy in the operation and performance of theunderlying physical network.Finally, the third scenario is a complete softwaredefined access network that extends beyond the accesssegment, and includes the in-home network and possiblyapplication platforms. In this case, a cloud-based systemreceives data on end-to-end broadband access andapplication performance. The data is collected by agentsin the network, and is used to guide the optimizationand diagnostics engines of the broadband network’smanagement system.2. Single Operator SDANThis section describes the first SDAN scenario. Typicallyin this scenario, a single entity serves both as the PIP(controlling the outside plant and the access hardware)and as the VNO providing services to consumers.2.1. Access Network ControlAccess network control is necessary for configuring theaccess network to support the delivery of broadbandservices to consumers. Configuration changes areapplied to the access nodes, which affect physical layerconfiguration parameters such as data rates, transmittedpower and spectrum, coding schemes, resilience tonoise, and latency. For DSL, a predefined set of suchconfiguration parameters is called a profile.2.1.1. Traditional Access Network ControlTraditional access network control relies on the use ofdefault profiles. These profiles, also known as goldenprofiles, have a one to one correspondence with a serviceproduct, and they are applied to all newly provisionedlines with a given service product. However, there isvast diversity in the transmission characteristics oflines in the access network, either because of the noiseenvironment (e.g. interference in the home and outsideplant), or because of the transmission medium (e.g.variation in the quality of the channel, differences in linelengths, bad contacts or splices, and imperfections ofthe copper or fiber). The application of a golden profileto such a mixed population of lines results in poorperformance for a substantial portion of these lines.The traditional remedy to the limitations of using goldenprofiles is the introduction of maintenance profiles. Suchmaintenance profiles are applied to lines that are foundto suffer from poor performance. This typically occursin reaction to customer complaints, or as technicianswork to correct issues in the field. This means that amaintenance profile is applied only after the customerhas experienced a poor service, and after the providerhas incurred significant customer support expenses.Finally, the manual application of maintenance profilesgreatly complicates the enforcement of a network-wideprofile policy. Contact center agents and technicianscan be inconsistent in following established guidelines,or follow their own preferred practices. As a result,maintenance profiles are improperly or inconsistentlyused in the network. This weakens the enforcementof a network-wide profile policy, and results in poorcustomer experience and higher operational costs.2.1.2. SDAN ControlThe modern approach for access network controlincludes the use of software-based profile optimization.Each service product is assigned a set of allowed2 In the case of bit-stream access, VNOs are often called resellers.Software Defined Access Networking (SDAN) 5

White Paperprofiles3, and software applies to every line in the networkthe profile for that line’s service product that best matchesthe line’s specific transmission characteristics. Thesoftware algorithms performing this profile optimizationrely on historical and current data about the line,and account for the line’s service product. The profileoptimization process is performed for newly provisionedlines, and for lines that are performing poorly or belowtheir full potential. Mutually interfering lines are alsooptimized for improved coexistence4. In this way, theaccess network is automatically and continuouslyadapting to evolving conditions without requiringmanual intervention. Additionally, profile optimizationcan be invoked in real time by contact center agents orby technicians. The principle of profile optimization isillustrated on the right-hand side of Figure 2.The above methodology ensures that all profile changesin the network follow a set of rules established by theoperator and are embedded in the configuration of theprofile optimization software. As a result, software-based profile optimization enables centralized policymanagement for access. The operator controls howresources are allocated to obtain the desired outcomesin terms of service reliability, throughput rates, powerconsumption, and network crosstalk (specifically forDSL). The operator has freedom to define a diversefamily of service products (thus increasing consumerchoice), and to apply on each line the optimal policy foreach such product.This practice of SDAN control has strong similaritieswith the fundamental principles of SDN. SDN separatesthe data plane from the control plane for routing andswitching equipment. The control plane is then logicallycentralized and made programmable. Applicationsinterface only with the control plane, and are notconcerned with the forwarding elements that comprisethe data plane. Similarly, SDAN control separates thedata transmission layer from the control layer. Thecontrol layer contains the logically centralized softwarethat implements the operator’s policy. The policy isFigure 2: Software-defined Diagnostics (left-hand side) and Profile Optimization (right-hand side)3 Older equipment limits the number of profiles that can be stored toas few as 40. Newer equipment allows much larger numbers of profiles,and allows the definition of sub-profiles for even higher flexibility.4 The process of joint optimization of profiles of multiple lines is calledvector profile optimization. It applies to mutually interfering DSLs, butalso to shared media such as GPON and coaxial cable access systems.Software Defined Access Networking (SDAN) 6

White Paperapplied homogeneously to the entire access network,which can include any mix of access equipment frommultiple vendors.rely on hardware, they are difficult to enhance, and theyare isolated from other network functions.2.2. Access Network DiagnosticsThe modern alternative to traditional access networkdiagnostics is the migration of analysis functionality toserver infrastructure, while keeping only the necessaryraw test-data capture functionality on the access node(or on specialized test hardware). The advantages of thisapproach are explained below.Access network diagnostics is the analysis of data collectedfrom the access network for resolving service issues,for qualifying customers for services, and for planningnetwork maintenance and upgrades. Data are collectedfrom the access nodes, and may additionally be collectedfrom test equipment connected to the outside plant (forexample, specialized hardware for DSL metallic testing, orfor optical time-domain reflectometry (OTDR)).2.2.1. Traditional Access Network DiagnosticsTraditional access network diagnostics rely heavilyon hardware systems, for example on specialized testheads for DSL metallic testing, or on handheld devicescarried by technicians. Such hardware systems havehigh costs for deploying and for operating, and oftenrequire replacement or expensive upgrade programs forsupporting newer generations of access technology. Theyare used for performing invasive tests, which typicallycause service disruption, and must therefore include theprior consent of the affected customer.More recently, access equipment manufacturers havebuilt access nodes that integrate data transmissionfunctionality with testing capabilities (e.g. metallic looptesting (MELT), and single-ended loop testing (SELT),in DSL; or OTDR in GPON). But the results delivered bysuch equipment are still physical media diagnostics withlimitations similar to those of specialized test hardware.The use of isolated diagnostics data from specializedtest hardware or from access nodes is problematic inseveral ways:a. Data from a test performed at a given time may fail toidentify intermittent issues.b. Results from one type of test cannot be combinedwith other results to improve accuracy andconfidence.c. Results cannot take into account the “context” ofthe connection, for example, whether a line fault isperformance-affecting for the current service product,such as Internet access or IPTV.2.2.2. SDAN Diagnostics and RecommendationsSDAN-based diagnostics enable the combined use of rawtest-data from multiple sources. For instance, data canbe combined from sources such as access nodes, servicemanagement platforms, and specialized hardware.Also, different types of test data can be combined, e.g.SELT, MELT and Double-Ended Loop Testing (DELT)data in DSL. Finally, the analysis can take into accounthistorical data to better analyze time-varying effects. Theend results are improved accuracy for diagnostics andimproved identification of the root causes of degradation.A software-based framework allows for the expansionof diagnostics functionality for further inclusion inrecommendation functions. Recommendations mayinclude the identification of upsell opportunities, basedon analysis of the following:a. the current service of a consumer,b. the capacity of the line for a higher-tier service, andc. the historical broadband usage of the connection.Other types of recommendations or analytics can includethe identification of customers with high risk for churn,or the prioritization of certain areas for proactive outsideplant maintenance. All of the above functions benefitfrom network-wide learning, and can easily be adaptedto the needs of each operator. The principle of SDANbased diagnostics and recommendations is illustrated onthe left-hand side of Figure 2.SDAN-based diagnostics and recommendationsare a virtualized network function (VNF). They areimplemented on commodity server infrastructure, theyrely on an abstraction layer for the underlying testinghardware, and they can be flexibly defined and updatedto meet the evolving needs of operators.In summary, traditional access network diagnostics canbe characterized as a static network function: They heavilySoftware Defined Access Networking (SDAN) 7

White Paper3. Multiple Operator SDANThis section discusses the scenario in which a network isused by multiple operators. In this scenario, there are atleast two VNOs that are providing services to consumers.The outside plant and the access hardware are controlledby an entity, the PIP, which can either be one of the VNOsor a third party.3.1. Access Network SharingAccess network sharing is imposed by regulation ina number of broadband markets, e.g., LLU, SLU andbit-stream access, or it can be the result of voluntaryoperator collaboration. Subsection 3.1.1 describes theprinciples of traditional access network sharing, whilesubsection 3.1.2 explains how the individual needs ofoperators for configuration, diagnostics and remediationof connections in the access network can be supported foreach VNO using a multi-tenant management platform.3.1.1. Traditional Access Network SharingTraditional access network sharing often relies onregulations for LLU. In the vast majority of markets,physical wire connections between local exchangesand customer premises are owned by incumbentproviders. LLU regulations require that competingproviders be granted access to these connections. Thecompeting providers lease the wire connections from theincumbents to deliver services to their customers andinstall their own access hardware.In recent years, copper wire connections have beenshortened by installing fiber connections betweenlocal exchanges and cabinets in the outside plant. Theshortening of the wires enables newer access technologiesthat deliver higher-speed services. In such cases, SLUregulations require that competing providers be grantedaccess to the sub-sections of wires between cabinets andcustomer premises. The competing providers must againlease the wire sub-section and install their own accesshardware at the cabinet location.Both LLU and SLU have been applied to DSL networks.In LLU and SLU, competitive operators deploy their ownequipment in a central office or cabinet, and regulationsspecify rules for the physical layer characteristics ofeach provider’s operations on the wire connections. Asan example, transmission power and spectra rules areimposed to minimize performance-limiting interference5 The practice of allowing only one provider deploy a vectoredDSLAM at a given site has been described as the “Highlander (ThereCan Only Be One)” approach.among wires. Such rules are traditionally designedfor the worst case scenario that can be encounteredin the network with the assumption that there can beno coordination among operators’ uses of the lines.Consequently, access network performance may notbe optimum. As discussed in sections 3.1.2 and 3.2.2,performance can be optimized by using a multi-tenantmanagement platform to virtualize the networkingequipment.Traditional access network sharing is applied throughbit-stream access in some jurisdictions. This is a form ofvirtual unbundling, where the competing providers aregranted access not to the wire connections but to Layer 2connections between the competing providers’ networkhardware and the customer premises equipment (CPE).Bit-stream access mainly applies to DSL networks at thistime, but its principles can also be used for fiber-based orfor coax-based access.Bit-stream access is often advertised as preferable fordeployments of vectored VDSL. This is because thegains from using vectored VDSL rely on coordinationamong the ports of all equipment at a given cabinet.However, competing providers have expressed concernsthat bit-stream access limits their ability to offerdifferentiated access services. Some have claimed thatthis approach essentially re-monopolizes the accessnetwork and returns complete control to the incumbentprovider, thereby reducing meaningful competition5. TheBroadband Forum has recently released two documentsthat present a broad industry consensus on best practicesfor mitigating the effects of un-cancelled crosstalk onvectored VDSL2, so that facilities-based competition andvectoring performance gains can be realized in vectoredenvironments [9][10].3.1.2. SDAN Network SharingThere are cases where operators have an incentive forimplementing access network sharing in a way thatgoes beyond the LLU/SLU/bit-stream access models.This is the case when certain broadband infrastructureinvestments require a high consumer take rate forservices provided over that infrastructure to make theinvestments economically justifiable.In this case, the physical network is partitioned intovirtual networks corresponding to the customers of eachof the VNOs. Virtualization provides an abstractionmapping the physical access hardware (e.g.Software Defined Access Networking (SDAN) 8

White PaperBroadbandNetworkGateway(Operator A)BroadbandNetworkGateway(Operator B)AggregationSwitchDSLAMVirtual NetworkOperator ABroadbandNetworkGatewayVirtual NetworkOperator ualDSLAMVirtualDSLAMFigure 3: Mapping of Physical Access Network to Virtual Access NetworksDSLAMs or optical network terminals) to virtualhardware. The physical access hardware is mapped tovirtual hardware as shown in Figure 3 for the case ofDSL, while the virtual hardware can be controlled andmanaged by each VNO.The great advantage of this approach is that the virtualhardware can be controlled and managed by the VNOsin a way that provides for determinacy in the operationand performance of the underlying physical network.As explained further in subsection 3.2.2, the VNO hasinformation about and control over the access network,almost as though the VNO owned its own hardware. Asopposed to the use of bit-stream access, this model letsthe VNO design its own competitive service productsand make real-time changes on the network. Variantsof bit-stream access, such as virtual unbundled localaccess (VULA) aim to deliver services “with a degree ofcontrol that is similar to that achieved when taking overthe physical line to the customer” [11]. However, existingimplementations of VULA fall short of such promise.Finally, enabling VNOs to share with each othersome information about their own network, globaloptimization across lines served by different VNOsbecomes possible. Such a capability can greatly improvenetwork performance because the multi-user nature ofmost access channels can make any form of independentmanagement of lines sub-optimal. When all lines areSoftware Defined Access Networking (SDAN) 9

White Papervectored, the channels become decoupled. In this case,VNOs can independently manage lines.3.2. Configuration, Diagnostics and RemediationFunctions for Shared Access PlantsEvery provider managing access lines must haveprocesses for configuring these lines to support theservices delivered, for knowing the line performanceand diagnosing issues, and for responding to remedyissues. Performing these functions within a sharedaccess infrastructure presents additional challenges. Thetraditional and SDAN approaches for implementingthese functions are described below. VULA is assumedfor traditional access network sharing, given that it ismost often presented as appropriate for next-generationaccess technologies such as vectored VDSL and G.fast.3.2.1. Traditional Functions for Shared Access PlantsIn practice, VULA gives competing providers very littlecontrol over line configuration. Typically, the providercan choose from a limited menu of services for the accesssegment. These services are characterized by a data-raterange, but have little or no differentiation in terms ofquality of service. Data collection schedules, quality ofservice definitions, service qualification rules, and profileoptimization rules are not within the control of thecompeting provider.Competing providers also have limited visibilityinto access network performance. Although someVULA implementations include functionality for theprovider to retrieve a pre-defined set of performancequantities and test parameters for a given line, thetypical implementation does not include functionsto enable the provider to independently diagnose thetype or the location of a fault. Providers often resort totheir collection of data from their customers’ CPEs—and even that may not be possible—to quantify thespeed and the quality of the connections. This lack ofvisibility on behalf of the competing providers oftenleads to miscommunication, waste, and even conflict,when coordination with the PIP is required to addresscustomer complaints. Also, competing providers arenot able to share information to assist in diagnosing thesource of performance issues (e.g. identifying a coppercable integrity problem that causes degradation onmultiple DSLs used by different providers).Finally, VULA greatly restricts providers in terms ofactions that they can take to remedy access problems. Thecompeting providers are entirely dependent on the PIPfor correcting any access problem, and have no way toreact or give information to their customers in real time.3.2.2. Multi-Tenant Platform for Shared Access PlantsAccess network virtualization enables the definitionof a customized set of VNFs for each of the competingproviders operating on a shared physical infrastructure.Figure 4 shows a multi-tenant platform that providesVNOs with access network virtualization and withmanagement VNFs. The configuration of such VNFsmeets the netwo

Virtualization (NFV) and Software-Defined Networking to the edge of the network, including access segments and subscriber premises, offers enormous gains in flexibility and control of broadband access services. This concept is described here as "Software Defined Access Networking" or SDAN. SDAN virtualizes access-network control and