The overall frame relay network architecture is defined in ANSI TJ. 606, Frame Relay Bea-re-r Se-rvice-A-rchitectural F-ramewo-rk and Se-rvice DescrzjJtion. 1 Access is provided by the frame relay interface, which is defined in various Al'JSI stan dards for both permanent and switched virtual cir cuits. ANSI Tl. 618, DSSJ -Co-re A spects of Frame P-rotocol fo-r Use with Frame Relay Bea-re-r Se-rvice
contains a definition of the protocol for exchanging
Frame Relay Netwo-rks
frames across the interface, as well as annexes concerned with local management (e .g., notifica tion of PVC status).' Although all implementations to date have focused on a PVC-based interface,
svc
access is defined in ANSI TJ. 61 7, DSSJ -Signaling Specification fo-r Frame Relay Bea-rer Service. 8 E ach of these T l S l standards has an equivalentcenT
recommendation, as shown in Table 1 .Other Current Activities
The Internet Engineering Task Force (IETF) is developing specifications for RFCs related to the frame relay technology. A specification called Multiprotocol Interconnect over Frame Relay defines an encapsulation mechanism for support ing multiple protocols over frame relay networks. To allow use of the simple network management protocol (SNMP), an experimental management information base
(MIB)
for frame relay DTEs is also under development.To promote the frame relay technology, a Frame Relay Forum has been set up in both North America and Europe. A technical committee bas been estab l ished to address issues related to the technology in terms of its interoperability and evolution in multi vendor environments. This committee actively par ticipates with the standards bodies and develops implementation agreements and interoperabil ity test procedures. Work continues to define a network-to-network control interface, multicast ing capabilities, multiple protocol encapsu lation, and interworking with other technologies, such as
Table 1 Cu rrent Status of Frame Relay Standardization
Standard ANSI Status
Arch itecture T1 .606 Standard
and SVC Description
Congestion Addendum Standard
Management to T1 .606 Pri nciples Data T1 .61 8 Standard Transfer - Core Aspects Access T1 .61 7 Standard Signaling for SVCs
Management I ncluded Standard
Procedu res in T1 .61 7
for PVCs Annex D
Digital Technical Journal Vol. 5 No. 1 Winter 1993
CCITT Status Remarks
1.233 Standard Replaces 1.222
1.370 Standard
0.922 Standard Most important
(
Annex A frame relaycorresponds standard
to T1 .61 8
)
0.933 Stan dard
I ncluded Standard Concepts
in 0.933 accepted
Annex A in CCITI
DECnet Open Networking
the sw itched m u lti megabit data service
(SMDS)
defined by Bell Commun ications Research, Inc. 1 ' The c e l l swi tch i ng adopted by StrataCom within their network is expected to change over time toconform with emerging CCITT recom mendations f()r broad band
ISDN J6
These recommendations cover asynchronous transfer mode (ATM), which defines a standard ce l l structure and ATM adaptation l ayers (AALs) for particular higher-level fun ctions.Summary
Frame relay is a simpl ified form of packet-mode swi tching that, at least i n theory, provides access to h igh bandwidth on demand, d i rect connectivity to a J I other points in the network, and consump tion of only the bandwidth actually used . Thus, to the customer, the frame relay technology offers a red uction in the cost of transmission l i nes and equi pment and imp roved p erformance and response time.
Rou ters con nected to a frame relay network can consider the mult iplexed , PVC interface as a set of point-to-point I inks. The special characteristics of a frame relay network require that special care be taken i n sel ecting the data l in k protocols and in hand I ing congestion.
Acknowledgments
The authors than k StrataCom, Inc. for provi ding significant input on cell switch ing technology and its use in t heir IPX FastPacket equ ipment. The authors would also l i ke to ackn owledge Cl iff Didcock of the Computer I ntegrated Telephony Development Group who consu l ted in Digit a l 's ini tial frame relay implementation .
References
1 . ANSI TJ. 606: Fra me Relay Bearer Serl'ice
Arc/.Jitectural Fra mework and Seruice
[)escriptimz
(New York: American NationalStandards Institute, I nc . , 1990).
2. CUTT Recomm endation X.25: InteJfa.ce between Data Terminal Equipment (DTL) and Data Circuit-terminating Equipment
(lXI:)
fo r Tenninals Operating in the Packet /Vlode and Connected to Public Data Net tmrks !Jy Dedicated Circuit (Geneva: Interna tiona l Telecommunications Union, 198R).3. Fmme Relay ,�jJecijication with Extensions,
Ret•ision
1 0, C i sco Systems, Digital Equ ip ment Corporation, Northern Telecom. Inc . , and StrataCom, Inc. (September 1990).[ ()(i
4. ccrrr Recommendation V35: Data Tmns mission at 48 Kilobits per Second U�ing 60- 108 kHz Group Band Circuits (Geneva: International Telecommun ications Union, 1976)
'5. A NSI T/. 618: DSS1-Core Aspects of frame Protocol fo r Use with Frame Relay Bearer Seruice (New York: American National Stan dards Institute, Inc., 1990).
6.
CC./7T
Recommendation Q.922: ISDN User Network Interface Layer 3 Spenfication for Basic Call Control (Geneva: I nterna tional Telecom munications Union, 1991).7.
COTT
Recommendation Q.931: ISDN Data Link Lc�ver Specification for Frame Mode Bearer Services (Geneva: International Telecom mun ications Union, I991 ).8.
ANW
Tl. 61 7. DSSJ -S(!{naling Speet
ficatiun j()r Frame Relay Bearer Service (New York:American National Standards Institu te , I nc . ,
1990).
9. CC/Tf' Draft Recommendation Q.
933:
ISDN Signalling Specification for Fra me Mode Bearer Serv ices (Geneva: I nternational Te lecomm u n ications Union, 1991 ).10. Point-to-Poin t Protocol for the Transmission of fi!Iulti-protoco! Datagrams over Point-to Point Links, I n ternet Engineering Task Force RFC 1 331 (May 1992).
1 1 . The
PPP
Internet Protocol Control Protocol(JPCP),
Internet Engineeri ng Task Force RFC1 352 ( May 1992).
1 2 . Point-to-Point Protocol EYtensiunsfor Bridg ing, I nternet Engineering Task Force R.FC 1220
(April 1991 ) .
1 3 . PPP DECnet Phase w Control Protocol (JJNCP), I nternet Engineering Tas k Force
RFC
1 376 (November 1992) .
14. PPP OS! Network Layer Control Protocol (OSI NLCP), Internet Engineering Tas k Force RFC
1377 (November 1992).
1'5. Betlcore TR-TS V-000772, Generic System Requirements in Support of Switched Multi Megabit Data Seruice, Bel l Com m u n ications Research, Inc. (May 1991 ) .
16.
CCJ7T
Drajt Recom mendation I. 121: Broad band Aspects of ISDN (Geneva: I nternational Telecommunications union, 1991 ) .David