Cisco S4C6

Frame Relay

WAN Technologies

• PPP• ISDN• Frame Relay CCITT standard that defines a process for

sending data over a public data network Connection Oriented single path, reserved resources,

sequential

Network Considerations

• Carrier-provided public network or private network

• Can be computers, servers, etc.

• Can be switches, routers, CSU/DSU

Frame Relay Terms

• Access Rate – clock spped• DLCI – Data Link Connection Identifier –

number that ids end point – significant only to local network – switch maps DLCIs between routers to form virtual circuit

• LMI – signaling standard between CPE device and Frame Relay switch that manages connections and maintains status

Frame Relay Terms 2

• CIR – Committed Information Rate – guaranteed rate in bits per second

• Committed Burst – maximum number of bits switch agrees to transfer during a time interval

• Excess burst – max number of uncommitted bits switch attempts to transfer beyond CIR

• FECN - a bit that notifies DTE congestion avoidance procedures should be initiated; congestion has occurred

• BECN – same but transmit rate will be reduced by 25%• DE –set bit that drops packets on priority number

Standards

• No standards for connecting equipment inside Frame Relay network exist

• Traditional circuit and packet switching can be used

• Speeds can range from 56 kbps to 2 Mbps<

PVC Identification

• DLCIs are assigned to represent a simplified addressing scheme

• Users can share bandwidth at reduced cost• Permanent virtual circuits are administratively

configures and managed in Frame Relay netowkr• Provides way to multiplex many logical data

conversations• Complete path to destination is established before

first frame is sent

Frame Relay Frame

• Flag• Address (includes DLCI, FECN, BECN, and DE

bits)

1024 DLCI addresses can be created

Cisco LMI supports 16-1007• Data• FCS• Flag

Standardization Attempt

• 1990 –Cisco, StrataCom, Northern Telecom, and DEC

• Extended Frame Relay protocol – extension is called LMI (Local Management Interface)

Determines operational status of PVCs

Transmits keepalice packets

Tells router what PVCs are available

Types are ansi, cisco, and q933a

Extensions

• Virtual Circuit status (common) provides communication and synchornizationbetween network and user device

• Multicasting (optional) single frame sent to multiple recipients

• Global (optional) resembles LAN• Simple flow control (optional) Xon/Xoff

LMI Frame Format

• Flag

• LMI DLCI

• Unnumbered Information Indicator

• Protocol Discriminator

• Call Reference

• Message Type

• Information Element, FCS Flag

LMI Features

• Global addressing• Multicasting• Inverse ARP Builds a frame relay map Learns DLCIs in use and sends an Inverse

ARP to each DLCI for each protocol Router next hop resolved to Frame Relay

DLCI

Frame Relay Switching Tables

• Four Entries – two for incoming port and DLCI and two our outgoing port and DLCI

Port reference can change but DLCI does not change

Subinterface

• Multiple logical interfaces can be cereated from one physical interface making Frame Relay more versatile and less costly

• Each PVC is configured as point to pont connections which allows subinterface to act as a dedicated line

• Allows single router interface to service many remote locations through individual unique subinterfaces

Split Horizon

• Available with Frame Relay

• No different in how it works

• Connection types

Point to point

Multipoint

Frame Relay Configuration

• Select Interface and go into configuration mode

• Configure a network layer address

• Select encapsulation type – cisco or IETF

• Specify LMI type (11.1 or earlier) – ansi, cisco or q933a

Frame Relay Commands

• Show interfaces serial

• Show frame-relay pvc

• Show frame-relay map

• Show frame-relay lmi

Configuring the Serial Interface

• Int s0

• Encapsulation frame-relay

• No shutdown

Configuring subinterfaces

• Select interface• Remove network-layer addresses assigned

to interface• Configure Frame Relay encapsulation• Select subinterface to configiure and

identify as multipoint or point to point• Configure local DLCI for subinterface• frame-relay interface-dlci NUMBER