Frame Relay

1
Frame Relay

• Raj Jain Professor of Computer and Information
  SciencesThe Ohio State UniversityColumbus, OH
  43210
• jain_at_acm.org
• These slides are available at http//www.cse.ohio
  -state.edu/jain/cis777-00/

2
Overview

• What is Frame Relay?
• Why not leased lines or X.25?
• Frame formats and protocols
• Signaling

3
Problems with Leased Lines

• Multiple logical links ? Multiple connections
• Four nodes ? 12 ports, 12 local exchange carrier
  (LEC) access lines, 6 inter-exchange carrier
  (IXC) connections
• One more node ? 8 more ports, 8 more LEC lines, 4
  more IXC circuits

Router
Router
LEC
IXC
Router
Router
4
Solution X.25/Frame Relay

• Four nodes 4 ports, 4 LEC access lines, 6 IXC
  circuits
• One more node 1 more port, 1 more access line,
  4 more IXC circuits
• Share leased lines ? Virtual Private Networks

Router
Router
LEC
IXC
Router
Router
5
X.25

• In-band signaling. VC setup and clearing
  messages in the same channel as data.
• Three layer protocol. Third layer for
  multiplexing.
• Flow control
• Error control
• ? 16 messages for one packet transfer
• Only 8 messages without flow control and error
  control

6
X.25 Exchange
DCE
DCE
12
14
5
3
4
6
DTE
DTE
11
2
15
16
7
8
9
10
1
Destination
Source
7
Frame Relay Exchange
2
3
7
6
8
1
4
5
Source
Destination
8
Frame Relay Key Features

• X.25 simplified
• No flow and error control
• Out-of-band signaling
• Two layers
• Protocol multiplexing in the second layer
• Congestion control added? Higher speed
  possible.X.25 suitable to 200 kbps. Frame relay
  to 2.048 Mbps.

9
Relay vs Switching

• Switching Relaying Ack Flow control
  Error recovery loss recovery
• Switching X.25
• Relay Unreliable multiplexing service

10
Datalink Control Identifiers

• DLCI Similar to Logical Channel Numbers in X.25

Router
Router
1
1
2
FR
2
FR
3
FR
1
Router
Router
11
Data Link Control Identifier

• Only local significance
• Allows multiple logical connections over one
  circuit
• Some ranges preassigned
• DLCI 0 is used for signaling

12
ISDN Reference Model
Management
Control
User
7
6
5
4
3
2
1
13
Frame Relay UNI Architecture

• UNI User-network Interface
• LAPF Link Access Protocol - Frame Mode Services
• LAPD Link Access Protocol - D Channel

14
Control Plane

• Signaling over D channel (D Delta Signaling)
• Data transfer over B, D, or H (B Bearer)
• LAPD used for reliable signaling
• ISDN Signaling Q.933 Q.931 used for signaling
  messages
• Service Access Point Identifier (SAPI) in LAPD
  0? Q.933 Q.931 Frame relay message

15
User Plane

• Link Access Procedure for Frame-Mode bearer
  services (LAPF)
• Q.922 Enhanced LAPD (Q.921) LAPD
  Congestion
• LAPF defined in Q.922
• Core functions defined in Q.922 appendix
• Frame delimiting, alignment, and flag
  transparency
• Virtual circuit multiplexing and demultiplexing
• Octet alignment ? Integer number of octets before
  zero-bit insertion
• Checking min and max frame sizes

16
User Plane (Cont)

• Error detection, Sequence and non-duplication
• Congestion control
• LAPF control may be used for end-to-end signaling

17
LAPF-Core Frame Format

• LAPF is similar to LAPD Flag, bit stuffing, FCS
• No control frames in LAPF-Core ? No control field
• No inband signaling
• No flow control, no error control, no sequence
  numbers
• Logical Link Control (LLC) may be used on the top
  of LAPF core

18
LAPF Address Field

• 2 Octet

Upper DLCI
EA 0
C/R

• 3 Octet

DLCI
EA 0
DE
FECN
BECN
Lower DLCI or DL-Core control
EA 1
D/C
Upper DLCI
EA 0
C/R

• 4 Octet

DLCI
EA 0
DE
FECN
BECN
DLCI
EA 0
Lower DLCI or DL-Core control
EA 1
D/C
19
LAPF Address Field

• Address length 2, 3, or 4 bytes
• Data Link Control Identifier (DLCI) 10, 16, 17,
  or 23 bits
• Address Extension (EA) bits 0 ? More bytes
• D/C Remaining bits for DLCI or for core control
  protocol (No use for core control has been
  defined)
• C/R Command/response (not used)
• FECN Forward Explicit Congestion Indication
• BECN Backward Explicit Congestion Indication

20
Local Management Interface (LMI)

• Extension designed by a group of vendors
• To overcome problems observed in early
  implementations
• May be standardized by both ANSI and ITU-T
• Status Enquiry (SE) message from user to network
• Status (S) message from network to user
• Uses HDLC UI frames (with sequence numbers)
• Uses protocol ID00001001, DLCI1023

21
LMI Operation
User
Network
SE, S 4, R 3
S, S 3, R 5
SE
FS (All PVCs)
SE
S (New PVCs)
22
DLCI Extensions

• Global DLCI ? DLCI points to the same
  destination at all time and points (OK for
  small networks)
• Multicasting
• One-way multicasting 1 to N
• Two-way multicasting 1 to N and N to 1
• N-way Multicasting N to N

23
Network-to-Network Interface (NNI)

• Developed by frame relay forum FRF 92.08R1, FRF
  92.62
• Working draft of ANSI T1S1.2
• Adding/deleting PVCs between networks
• Diagnosing PVC failures

24
Major NNI Operations

• Notification of adding a PVC
• Notification of deleting a PVC
• Notification of UNI or NNI failures
• Notification of a PVC segment availability or
  unavailability
• Verification of links between frame relay nodes
• Verification of frame relay nodes

25
Summary

• X.25 designed for unintelligent devices over
  error-prone networks ? Slow
• Frame relay Simplified X.25
• Higher data rates than X.25
• Developed for ISDN but runs in non-ISDN
  environments
• Two layer protocol architecture

26
Homework

• Read Section 7.2 of McDysans book

27
Additional References

• Chapter 11 of Stallings ISDN and Broadband
  ISDN with Frame Relay and ATM
• P. Smith, Frame Relay Principles and
  Applications, Addison-Wesley, 1993.
• U. Black, Frame Relay Networks, 2nd Ed.,
  McGraw-Hill, 1995
• C. A. Heckart, The Guide to Frame Relay
  Networking, Flatiron Publishing, 1994
• Frame Relay Forum, http//www.frforum.com

28
Thank You!
29
ITUT Recommendations

• D.225 (10/96) Charging and accounting principles
  to be applied to frame relay data transmission
  service I.122 (3/93) Framework for frame mode
  bearer services
• I.233 Frame mode bearer services
• I.233.1 (10/91) ISDN frame relaying bearer
  service Published with I.233
• I.233.1 Annex F (7/96) Frame relay multicast
• I.233.2 (10/91) ISDN frame switching bearer
  service Published with I.233

30
ITUT Recommendations (Cont)

• I.365.1 (11/93) Frame relaying service specific
  convergence sublayer (FR-SSCS)
• I.370 (10/91) Congestion management for the ISDN
  frame relaying bearer service
• I.372 (3/93) Frame relaying bearer service
  network-to-network interface requirements
• I.555 (11/93) Frame relaying bearer service
  interworking
• I.620 (10/96) Frame relay operation and
  maintenance principles and functions

31
ITUT Recommendations (Cont)

• Q.922 (2/92) ISDN data link layer specification
  for frame mode bearer services
• Q.933 (10/95) Signalling specifications for frame
  mode switched and permanent virtual connection
  control and status monitoring
• Q.933 bis (10/95) Abstract test suite -
  Signalling specification for frame mode basic
  call control conformance testing for PVCs
• Q.2119 (7/96) B-ISDN ATM adaptation layer -
  Convergence function for SSCOP above the frame
  relay core service

32
ITUT Recommendations (Cont)

• Q.2727 (7/96) B-ISDN user part - Support of frame
  relay
• Q.2933 (7/96) Digital subscriber signalling
  system No. 2 (DSS 2) - Signalling specification
  for frame relay service
• X.33 (10/96) Access to packet-switched data
  transmission services via frame relaying data
  transmission services
• X.36 (4/95) Interface between DTE and DCE for
  public data networks providing frame relay data
  transmission service by dedicated circuit

33
ITUT Recommendations (Cont)

• X.36 Amd. 1 (10/96) Switched virtual circuit
  (SVC) signalling and refinements of permanent
  virtual circuit (PVC) signalling
• X.37 (4/95) Encapsulation in X.25 packets of
  various protocols including frame relay
• X.76 (4/95) Network-to-network interface between
  public data networks providing the frame relay
  data transmission service
• X.144 (4/95) User information transfer
  performance parameters for data networks
  providing international frame relay PVC service

34
ITUT Recommendations (Cont)

• X.145 (10/96) Performance for data networks
  providing international frame relay SVC service
• X.222 (4/95) Use of X.25 LAPB-compatible data
  link procedures to provide the OSI
  Connection-mode Data Link service
• X.222 Amend. 1 (10/96) Frame relay mapping
• X.328 (10/96) General arrangements for
  interworking between public data networks
  providing frame relay data transmission services
  and Integrated Services Digital Networks (ISDNs)
  for the provision of data transmission services

35
ANSI Standards

• ANSI T1.513-1997, Frame Relay Data Communication
  Service - User Information Transfer Performance
  Parameters
• ANSI T1.617-1991 (R1997), Signaling Specification
  for Frame Relay Bearer Service for Digital
  Subscriber Signaling System Number 1 (DSS1)
• ANSI T1.617a-1994, Signaling Specification for
  Frame Relay Bearer Service for Digital Subscriber
  Signaling System Number 1 (DSS1) (Protocol
  Encapsulation and PICS)

36
ANSI Standards (Cont)

• ANSI T1.618-1991 (R1997), Signaling Specification
  for Frame Relay Bearer Service for Digital
  Subscriber Signaling System Number 1 (DSS1)
  (Protocol Encapsulation and PICS)
• ANSI T1.633-1993, Frame Relaying Bearer Service
  Interworking
• ANSI T1.634-1993, Frame Relaying Service Specific
  Convergence Sublayer (FR-SSCS)
• ANSI X3.228-1993, X.25 Data Transfer Phase (DTP)
  Procedures for Operation with Frame Relay

37
Implementation Agreements

• Available from Frame Relay Forum,
  http//www.frforum.com
• User-to-Network (UNI) Implementation Agreement,
  FRF.1.1, January 1996
• Frame Relay Network-to-Network (NNI)
  Implementation Agreement Version 2.1, FRF.2.1,
  July 1995
• Multiprotocol Encapsulation Implementation
  Agreement (MEI), FRF.3.1, June 1995
• Switched Virtual Circuit Implementation Agreement
  (SVC), FRF.4, n/a

38
Agreements (Cont)

• Frame Relay/ATM Network Interworking
  Implementation Agreement, FRF.5, December 1994
• Frame Relay Service Customer Network Management
  Implementation Agreement (MIB), FRF.6
  (FRFTC93.111R3), March 1994
• Frame Relay PVC Multicast Service and Protocol
  Description, FRF.7, October 1994.
• Frame Relay / ATM PVC Service Interworking
  Implementation Agreement, FRF.8, April 1995.
• Data Compression Over Frame Relay Implementation
  Agreement, FRF.9, January 1996.

39
Agreements (Cont)

• Frame Relay Network-to-Network SVC Implementation
  Agreement, FRF.10, September 1996.
• Voice over Frame Relay Implementation Agreement,
  FRF.11.1, May 1997, Annex J added March 1999.
• Frame Relay Fragmentation Implementation
  Agreement, FRF.12, December 1997
• Service Level Definitions Implementation
  Agreement, FRF.13, August 1998
• Physical Layer Interface Implementation
  Agreement, FRF.14, December 1998

40
RFCs on Frame Relay

• RFC 1586, Guidelines for Running OSPF Over Frame
  Relay Networks. March 1994.
• RFC 1604, Definitions of Managed Objects for
  Frame Relay Service. March 1994.
• RFC 1973, PPP in Frame Relay. June 1996.
• RFC 2115, Management Information Base for Frame
  Relay DTEs Using SMIv2. September 1997.
• RFC 2427, Multiprotocol Interconnect over Frame
  Relay. September 1998.

41
References Books

• W. Stallings, "ISDN and Broadband ISDN with Frame
  Relay and ATM," Prentice Hall, 1995, 581 pp.
• U. Black, "Frame Relay Networks," McGraw-Hill,
  1994, 234 pp.
• M. Miller, "Analyzing Broadband Networks," MT
  Books, New York, 1994, 522 pp.
• B. Kumar, "Broadband Communications,"
  McGraw-Hill, 1995, 512 pp.
• D. Minoli, "Enterprise Networking Fractional T1
  to SONET, Frame Relay to BISDN," Artech House,
  1993, 736 pp.

42
References Papers

• B. Lisowski, Frame Relay What it is and How It
  Works, A Guide to Frame Relay, Supplement to
  Business Communications Review, October 1991.
• S. Taylor, Plain Talk About Frame Relay,
  Networking Management, January 1992, pp. 72-78.
• I.M. Ali, Frame Relay in Public Networks, IEEE
  Communications Magazine, March 1992, pp. 72-78.
• E. Garciamendez-Budar, The Emergence of Frame
  Relay in Public Data Networks,
  Telecommunications, May 1992, pp. 24-32.

43
References Papers

• C. Finn, DataCom Buyers Guide - Frame Relay,
  Network World, February 3, 1992, pp. 31-37.
• J.T. Johnson, Special Report-Frame Relay
  Products, Data Communications, May 1992, pp.
  69-86.
• S. Hume and A. Seaman, X.25 and Frame Relay
  Packet Switched Technologies for Wide Area
  Connectivity. 3TECH - the 3COM Technical
  Journal, Winter 1992, pp. 33-45.
• J.P. Cavanagh, Applying Frame Relay Interface to
  Private Networks, IEEE Communications Magazine,
  March 1992, pp. 48-64.

44
References Papers

• J. Brown and S. Fry, Designs Make or Break Frame
  Relay Switches, Network World, September 14,
  1992, pp. 39-60.
• J. Merritt, The Future of Frame Relay, TEM,
  January 1, 1992, pp. 33-45.
• N. Lippis, Frame Relay Redraws the Map for Wide
  Area Networks, Data Communications, July 1990,
  pp. 80-94.

45
Packet Service Technologies
46
Frame Relay vs Cell Relay (ATM)

• Frame relay is defined up to 2 Mbps. ATM defined
  for T1 and higher.
• Frame relay uses a variable length frame. ATM
  uses 53 byte cells.
• 10-bit DLCI vs 24-bit VPI/VCI
• CIR vs GCRA

47
X.25 vs Frame Relay
48
(No Transcript)
49
X.25 vs Frame Relay

• Fig 11.6, page 362, Stallings

50
LAPD vs LAPF

• Frame relay was originally planning to use LAPD
  but LAPD was complete and was missing certain
  features
• SAPI and TEI fields of LAPD replaced by DLCI
• Certain values of DLCI are reserved so as not to
  be confused for SAPI when LAPD and LAPF are used
  on the same D channel
• LAPF core LAPF without the control
  fieldNetwork does not worry about
  controlControl is left to the user
• C/R field, even though in the middle of DLCI, is
  not used by network and is treated as payload
• The command/response bit is coded differently in
  LAPD in network-to-user and user-to-network
  directions. In LAPF the coding is symmetric
  (same) in both directions.

51
Q.931 Message Format

• DSS1 Digital Signaling System 1

52
Information Elements
Information Element
1
2
3
4
5
6
7
8
9
10
11
Protocol discriminator
X
X
X
X
X
X
X
X
X
X
X
Call reference
X
X
X
X
X
X
X
X
X
X
X
Message type
X
X
X
X
X
X
X
X
X
X
X
Cause
X
X
X
X
X
Bearer capability
X
Channel identification
X
X
X
X
Data link connection ID
X
X
X
X
Progress indicator
X
X
X
X
X
Network specific facilities
X
Call state
X
Display
X
X
X
X
X
X
X
X
X
X
X
End to end transit delay
X
X
53
Info Elements (cont)
Information Element
1
2
3
4
5
6
7
8
9
10
11
Packet binary parameters
X
X
Link core parameters
X
X
Link protocol parameters
X
X
Calling party number
X
Called party number
X
Called party subaddress
X
Connected number
X
X
X
X
Connected subaddress
X
X
X
X
Transit network selection
X
Repeat indicator
X
Low layer compatibility
X
X
High layer compatibility
X
User-User
X
X
X
X
X
X
54
LMI Message Format
55
NNI Messages

• Status Enquiry (SE) Request status of a PVC or
  link, or request verification of a link
• Status (S) Response to SE
• Full Status (FS) Report on status of all PVCs
• NNI messages are encapsulated in HDLC UI frames
  with sequence number field added. Sent
  periodically on DLCI 0.

56
Multiprotocol Operation Over Frame Relay

• RFC 1294 specifies using Q.922 Annex A frame
  format
• NLPID Network layer Protocol ID 80H ?
  Subnetwork Access Protocol (SNAP) gt OUI
  EtherType

Flag
Q.922 Address/Control
HDLC ControlUI
Optional PAD
NLPID
Data
FCS
Flag
Flag
Q.922 Address/Control
HDLC ControlUI
Optional PAD
NLPID80
Data
FCS
Flag
OUI
EtherType
57
TCP/IP over Frame Relay

• Frame relay provides most of the routing
• TCP requires IP

A
P
S
T
TCP
N
IP
IP
Frame Relay
D
P
Frame relay protocols
58
Signaling

• Permanent Virtual Circuit (PVC) Initially
• Switched Virtual Circuit (SVC) added later
• Q.933 used for FR connections over PVC or SVC?
  Q.933 is a subset of Q.931
• Message Types Alerting, call proceeding,
  connect, connect ack, progress, setup,
  disconnect, release, release complete, status,
  status inquiry
• Frame relay forum has proposed to simplify Q.933
  by deleting progress, connect ack, and alerting.
  Also delete many information element. Add SVC.

59
Connection Control Messages

• Call establishment
• 1. Alerting
• 2. Call proceeding
• 3. Connect
• 4. Connect Acknowledge
• 5. Progress
• 6. Setup
• Call clearing
• 7. Disconnect
• 8. Release
• 9. Release Complete

60

• Miscellaneous
• 10. Status
• 11. Status Enquiry

61
Signaling Example
NT
Frame Relay
NT
Setup
Setup
Call Proceeding
Call Proceeding
Connect
Connect
Connect Ack
Connect Ack
Disconnect
Disconnect
Release
Release
Release Complete
Release Complete
62
Physical Layer Options

• Both ANSI and ITU-T define frame relay on ISDN
• Frame relay forum's implementation agreements
• Metallic interface at DS1 1.544 Mbps (ANSI
  T1.403)
• Leased lines at 56 kbps (V.35)
• Metallic interface at E1 2.048 Mbps (G.703)
• Synchronous interface at E1 2.048 Mbps (G.704)
• X.21 interface for synchronous transmission
• MCI offers frame relay at 56 kbps, 64 kbps,
  fractional T1, N 56 or N 64 kbps.

63
Signaling Example
NT
ISDN
Frame Relay
NT
D-ChannelQ.931 exchange to establish B-Channel Ci
rcuit switched Connection
Setup
Setup
Connect
Connect
Connect Ack
Setup
B-Channel Q.933exchange to establish B-Channel
frame-mode connection
Setup
Connect
Connect
Connect Ack
Connect Ack
64
Signaling Example (cont)
NT
ISDN
Frame Relay
NT
B-Channel Q.933exchange to release B-Channel
frame-mode connection
Disconnect
Disconnect
Release
Release
ReleaseComplete
ReleaseComplete
Disconnect
D-ChannelQ.931 exchange to release B-Channel Circ
uit switched Connection
Disconnect
Release
Release
ReleaseComplete
ReleaseComplete