CHABOT COLLEGE CISCO NETWORKING ACADEMY
Chabot College
Frame Relay
Part 1
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Frame Relay Overview
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Frame Relay Operation
Many other WAN technologies (PPP,
ATM) can be used inside the FR cloud.
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Frame Relay Uses PVCs
PVCs have ID numbers called DLCIs.
DLCI - Data Link Control Identifier
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DLCIs Identify Connections
Frame Relay provides a means for statistically
multiplexing many logical data conversations
(referred to as virtual circuits) by assigning each
pair of DTEs connection identifiers.
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DLCI
A number that identifies the logical circuit
between the source and destination device.
The FR switch maps the DLCIs between
each pair of routers to create a PVC.
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DLCIs
• Can have “local only” significance.
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Local Access Rate
The clock speed (port speed) of the
connection (local loop) to the Frame Relay
cloud. It is the rate at which data travels
into or out of the network.
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Local Management Interface
A signaling standard between the CPE
device and the FR switch that is
responsible for managing the connection
and maintaining status between the
devices.
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Possible LMI Functions
• keepalive mechanism, which verifies that
data is flowing
• a multicast mechanism which can provide
the network server with its local DLCI
• multicast addressing
• the ability to give DLCIs global (whole
Frame Relay network) significance
• a status mechanism
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Flavors of LMI
Different flavors have different features.
Currently, ansi is the most common:
 cisco—LMI type defined jointly by Cisco,
StrataCom, Northern Telecom, and DEC
 ansi—Annex D defined by ANSI standard
T1.617
 q933a—ITU-T Q.933 Annex A
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LMI Configuration
Remember to configure your router’s
interface to use the same LMI type that the
FR provider’s equipment is using.
(config-if)#frame-relay lmi-type cisco
(config-if)#frame-relay lmi-type ansi
(config-if)#frame-relay lmi-type q933a
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CIR - Committed Info Rate
The rate, in bits per second, that the Frame
Relay switch agrees to transfer data.
Excess Burst—The maximum number of
uncommitted bits that the Frame Relay
switch will attempt to transfer beyond the
CIR.
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DE - Discard Eligibility
When the router detects network
congestion, the FR switch will drop packets
with the DE bit set first. The DE bit is set
on the oversubscribed traffic; that is, the
traffic that was received after the CIR was
met.
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FECN and BECN
Forward explicit congestion notification:
When a Frame Relay switch recognizes
congestion in the network, it sends an
FECN packet to the destination device
indicating that congestion has occurred.
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FECN and BECN
Backward explicit congestion notification:
When a Frame Relay switch recognizes
congestion in the network, it sends a
BECN packet to the source router
instructing the router to reduce the rate at
which it is sending packets.
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FECN and BECN
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DLCIs
• Can be a number between 16-1007.
illegal
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LMI - Types
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Frame Relay Encapsulation
• The router must be configured to choose
which Frame Relay encapsulation will be
used.
 IETF Encapsulation Type
(Most common)
 Cisco Encapsulation Type
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IETF Frame Relay Frame
variable
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Inverse ARP
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Inverse ARP
The Inverse ARP mechanism allows the
router to automatically build the Frame
Relay map. The router learns the DLCIs
that are in use from the switch during the
initial LMI exchange. The router then
sends an Inverse ARP request to each
DLCI for each protocol configured on the
interface if the protocol is supported.
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The Frame Relay Map
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Frame Relay Operation
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Frame Relay Operation
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B.S. - Before Subinterfaces
Network 7777
Network 8888
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Subinterfaces
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Subinterfaces
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Multipoint Subinterfaces
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Point-to-Point Subinterfaces
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11.2 + Autodetects LMI type
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FR Verification