1、Report No. 51 A Technical ReportonSeptember 1996 Changes in the NetworkAccess ModelPrepared byT1A1.3Working GrouponPerformance of DigitalNetworks and ServicesCommittee T1 is sponsored by the Alliance for Telecommunications Industry SolutionsAccredited by the American National Standards InstituteCopy
2、right 1996 by Alliance for Telecommunications IndustrySolutionsAll rights reserved.No part of this publication may be reproduced in any form,in an electronic retrieval system or otherwise, without theprior written permission of the publisher.A Technical Report onCHANGES IN THE NETWORKACCESS MODELABS
3、TRACTThis Technical Report discusses the impact of the access network breakup into multipleproviders, e.g., competitive access providers. Until standards are written to address thenew architecture, all providers are expected to maintain satisfactory service and qualitylevels.Document T1A1.3/96-004r3
4、Prepared byT1A1.3Working Group on Performance of Digital Networks and ServicesiForewordThis Technical Report was initiated in the T1A1.4 Working Group on Digital Service Performance. TheWorking Group recognized that recent legislation and FCC rulings regarding alternate service providers andlocal ex
5、change carriers (LEC) service offerings are leading to complexity in the network and that joint effortsfor service establishment and repair will be even more complex. It was felt that a high level document detailingthe extent of this complexity would be generally useful to the technical community. A
6、fter reorganization ofTechnical Subcommittee T1A1 (Performance and Signal Processing) the report was completed in the T1A1.3Working Group on Performance of Digital Networks and Services. At the time this report was completed, theWorking Group had the following members:R. S. Bloomfield Ralph E. Jense
7、nDick Bobilin James LiouDavid Brady Dave MilneAmy Breitenbach Jim MuiterLorence Brown Mark NeibertMichael Brusca Mike OsbornE. Mel C. Celi John RoquetC. Anthony Cooper Richard J. SchweizerGarry Couch Neal B. SeitzDave Curtis Henri SuyderhoudLarry Delss Sangamesh VinayagamvrthyGeoffrey Garner Robert
8、B. WallerKenneth C. Glossbrenner Bernard WorneCannon T. M. Hwu W. R. WycoffiiiiiTable of ContentsForeword. i1.0 Purpose and Scope12.0 Background.13.0 Acronyms14.0 Current Network Models25.0 Ongoing changes 26.0 Impact .46.1 Performance .46.2 Support Responsibility.47.0 Recommendation4Annex A5List of
9、 FiguresFigure 1 Historical Network Model .1Figure 2 Current Simplified End User-to-End User Network Model 2Figure 3 Functional Access Model Dedicated Services2Figure 4 Functional Transit Model Dedicated Services3Figure 5 Functional Access Model Switched Services .3Figure 6 Functional Transit Model
10、Switched Services .4iv11.0 Purpose and ScopeThe purpose of this Technical Report is twofold:1. to recognize that recent legislative and regulatory actions (e.g., the Telecommunications Act of 1996) willhave an important effect on the development of ANSI standards that are used in achieving satisfact
11、ory end-to-end performance for telecommunication services cooperatively offered by multiple providers, and2. to provide particular information on the evolving aspects of the access component (e.g., unbundling of thelocal exchange).To meet the purpose, the Technical Report provides examples of possib
12、le associated changes that may berequired to the access portion of the network model used in specifying and apportioning performance objectivesfor telecommunications services provided in accordance with the following standards:ANSI T1.506-1990 ANSI T1.510-1994ANSI T1.506a-1992 ANSI T1.514-1995ANSI T
13、1.508-1992 ANSI T1.517-1992.ANSI T1.508a-19932.0 BackgroundThe historical (since divestiture in 1984) Network Model consisted of three portions (figure 1). Recentregulatory rulings are fragmenting the local access portion that connects the end user (EU) to the interexchangecarrier (IC).End UserPC/CP
14、EAccess Network Transit Network Access NetworkNI INI INI NIEnd UserPC/CPEFigure 1 Historical Network Model3.0 AcronymsAP Access Provider. Generic term for LEC and any alternate service connection providerIC InterLATA CarrierNI Network InterfaceINI Inter-network InterfaceLATA Local Access Transport A
15、reaPC/CPE Personal Computer/Customer Premises Equipment, e.g., telephoneSWC Serving Wire Center. Building traditionally used to interconnect a loop to interofficefacilities (for dedicated services) or to provide dial tone for switched servicesTECHNICAL REPORT NO. 5124.0 Current Network ModelsArrange
16、ments in which multiple providers are used to provide the access segment are increasing. Anexample of a simple end user-to-end user network model showing functional piece parts and probableinter-network interface (INI) points is shown in figure 2.End UserPC/CPEEnd UserPC/CPELoopFunctionIntraLATATran
17、sitInterLATATransitNI NIINI INI INI INILoopFunctionIntraLATATransitFigure 2 Current Simplified End User-to-End User Network Model5.0 Ongoing changesUnbundling of the local exchange to offer switch ports and loops as separate elements will complicatethe interface question, e.g., demarcation of respon
18、sibilities. Figures 3, 4, 5, and 6 provide examples ofthe complexity of what might occur for dedicated and switched connections respectively. Examples ofalternate providers could include wireless and cable TV service providers. In addition to federalregulation, many individual states have differing
19、regulations. There are ongoing efforts to adapt nationalstandards to meet the new regulatory and industry needs.Figures 3 and 4 provide a simple depiction of the functions involved in connecting two end usersthrough an interLATA (Transit) carrier for a dedicated connection.AP “A“AP1AP2AP1AP2Loop Cro
20、ss Connect Inter OfficeAP3AP4AP3AP4AP3AP4AP3AP4TransitCarrier(figure 4)INI*INI* Normally provided at the SWC location.AP “B“End UserPC/CPEFigure 3 Functional Access Model Dedicated ServicesTECHNICAL REPORT NO. 513INIINI*INITransitCarrierTransitCarrierTP1 TP2AccessProvider(figure 3)AccessProvider(fig
21、ure 3)* INI if more than one carrier provides transit.Figure 4 Functional Transit Model Dedicated ServicesFigures 5 and 6 offer examples of complexity for switched services, where various access and transitproviders operate different portions of the network.= Switch (Dial Tone)AP “A”AP “B”AP1AP2AP1A
22、P2AP3AP4AP3AP4AP3AP4AP3AP4ToTransit Carrier,IC Tandem,orAP Tandem(AP 7)(figure 6)LOOP Inter Office Inter OfficeSWC orX-connectAP5AP6NIINI INIINIINIEnd UserPC/CPEFigure 5 Functional Access Model Switched ServicesIf a local transport AP and IC combine to provide access and dial tone, it is possible th
23、at the dial tonesource could be outside the LATA, e.g., AP“B“ AP2 AP4 AP6.From this diagram it may be observed that the traditional access provider may no longer be directlyresponsible for dial tone or other key elements of the connection.TECHNICAL REPORT NO. 514INIINI*INITP1 TP2AccessProvider(figur
24、e 5)AccessProvider(figure 5)TP3 TP4TP5 TP6* INI if more than one carrier provides transit.= Transit provider switchFigure 6 Functional Transit Model Switched Services6.0 Impact6.1 PerformanceThe current network model has a network interface (NI) and an inter-network interface(INI) on eitherside of t
25、he “transit“ carrier. With the changes that have been discussed, there are many INIs. Ifperformance objectives are established similar to existing ones, there would be various combinations ofNI-to-INI and INI-to-INI. This is a complex and time consuming issue.6.2 Support ResponsibilityUnbundling of
26、the loop and dial tone raises many issues, one of which is subscriber trouble resolution.Today with a single AP there can be difficulties in quickly resolving troubles between premisesequipment, the loop, and the switch for local service. Considering figure 5; when the loop is furnishedby AP “A”, th
27、e dial tone originates from AP3, the interconnection between AP“A“ and AP3 is providedby AP2, and AP6 provides “Interoffice“ connections towards a long distance carrier (AP7 or an APTandem) and a similar multiplicity of APs at the far end; resolution of customer troubles will beextremely difficult.7
28、.0 RecommendationAll service providers must work together to ensure that currently defined overall service performancerequirements are met. It is recommended that the existing access segment performance requirementsdocumented in ANSI standards listed in Annex A - Bibliography should continue to be m
29、et, even thougha specific allocation methodology is not available. The establishment of a well-defined set ofboundaries and interfaces between the IntraLATA access providers will be a key element in ensuringsatisfactory service.TECHNICAL REPORT NO. 515Annex ABibliographyANSI T1.506-1990, Telecommuni
30、cations - Switched Exchange Access Network TransmissionSpecifications.ANSI T1.506a-1992, Telecommunications - Network Performance - Transmission Specifications forSwitched Exchange Access Network (Absolute Round-Trip Delay ) (Supplement to ANSI T1.506-1990).ANSI T1.508-1992, Network Performance - Lo
31、ss Plan for Evolving Digital Networks.ANSI T1.508a-1993, Network Performance - Loss Plan for Evolving Digital Networks (Guidelines forthe Delay of Ring Architectures) (Supplement to ANSI T1.508 -1992).ANSI T1.510-1994, Network Performance Parameters for Dedicated Digital Services - Specifications.ANSI T1.514-1995, Network Performance Parameters and Objectives for Dedicated Digital Services -SONET Bit Rates.ANSI T1.517-1995, Performance Parameters and Objectives for Integrated Services Digital Network(ISDN).
