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%
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