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Frame Relay

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6 inter-exchange carrier (IXC) connections ... Status Enquiry (SE) message from user to network. Status (S) message from network to user ... – PowerPoint PPT presentation

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Title: 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
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