Frame Relay
Mozafar Bag-Mohammadi
Frame Relay Standards and Equipment
 Frame Relay
 A packet switching and encapsulation technology
 A communications technique for sending data over high-
speed digital connections
 Originally designed for use across ISDN
 Provide connection between the data terminal
equipment (DTE) and the data communications
equipment (DCE) via virtual circuit
 Switched virtual circuits (SVC)
 Permanent virtual circuits (PVC)
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Before Frame Relay
After Frame Relay
Frame Relay Standards and Equipment
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Frame Relay Terminology
Frame Relay Standards and Equipment
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DLCI
 Frame relay connections identify virtual circuits by
Data Link Connection Identifier (DLCI) numbers
 A DLCI number associates an IP address with a specific virtual
circuit
 DLCI numbers have only local significance
 DLCI numbers are usually assigned by the Frame Relay
provider
 Most likely not the same on either side of the Frame Relay switch
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Frame Relay Map
 Frame Relay map
 A table in RAM that defines the remote interface to which a
specific DLCI number is mapped
 The definition will contain a DLCI number and an interface
identifier
 Which is typically a remote IP address
 The Frame Relay map can be built automatically or statically
depending on the Frame Relay topology
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Frame Relay Map
 Subinterfaces
 Virtual interfaces associated with a physical interface
 Created by referencing the physical interface followed by a
period and a decimal number
 For the purposes of routing, however, subinterfaces are
treated as physical interfaces
 With subinterfaces, the cost of implementing multiple Frame
Relay virtual circuits is reduced
 Because only one port is required on the router
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LMI
 LMI basically extended the functionality of Frame Relay by:
 Making the DLCIs globally significant rather than locally
significant
 Creating a signaling mechanism between the router and
the Frame Relay switch, which could report on the status
of the link
 Supporting multicasting
 Providing DLCI numbers that are globally significant makes
automatic configuration of the Frame Relay map possible
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Inverse ARP
 In multipoint configurations
 Routers use the protocol Inverse ARP to send a query
using the DLCI number to find a remote IP address
 As other routers respond to the Inverse ARP queries, the
local router can build its Frame Relay map automatically
 To maintain the Frame Relay map, routers exchange
Inverse ARP messages every 60 seconds by default
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Encapsulation Types
 Cisco routers support these types of LMI encapsulation:
 cisco
 ansi
 q933a
 Cisco routers (using IOS Release 11.2 or later) can
“autosense” the LMI type used by the Frame Relay switch
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Basic Multipoint Configuration with Two
Routers
• LMI will notify the router about the available DLCI numbers
– Inverse ARP will build the Frame Relay map dynamically
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Basic Multipoint Configuration with Two
Routers (continued)
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Multipoint Configuration Using a
Subinterface (continued)
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Point-to-Point Configuration Using
Subinterfaces
 Point-to-point Frame Relay configurations do not support
Inverse ARP
 You will have to configure each subnet separately
 Use the frame-relay interface-dlci command to associate the
DLCI numbers with a specific subinterface
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Monitoring Frame Relay
 You can check your Frame Relay configuration by using show
commands
 These commands allow you to verify that the commands you
previously entered produced the desired effect on your router
 The most common show commands for monitoring Frame
Relay operation are:
show
show
show
show
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interface
frame-relay pvc
frame-relay map
frame-relay lmi
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