1. 1

2. E0
192.168.1.150
E0
192.168.3.150
LAN - 192.168.1.0/24
LAN - 192.168.3.0/24
HYDERABAD OFFICE
BANGLORE OFFICE
E0
192.168.2.150
LAN - 192.168.2.0/24
CHENNAI OFFICE
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3. Frame Relay
• Frame Relay is a data link layer
packet-switching protocol that uses digital circuits.
• It is used for medium to longer distances and for
longer connectivity.
• Leased lines also provide longer connectivity but a
physical circuit is used to make connection between
2 sites and the same circuit path is used always.
• Frame Relay connections use logical circuits to make
connections between 2 sites. These logical circuits are
referred to as Virtual Circuits(VCs).
• Multiple VCs can exist on the same physical
connection.
• VCs are Full duplex.
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4. Advantages of Frame Relay
• VCs overcome the scalability problems of
leased lines by providing multiple logical circuits
over the same physical connection.
• Only one serial interface of a router is needed to
handle the VC connections to multiple sites Whereas
using leased lines multiple serial interfaces are needed
to connect to multiple sites.
• VCs provide full connectivity at a much lower price
compared to leased lines.
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5. Frame Relay Terminology
• Sub-interfaces
• Uses Shared bandwidth
• Local Management interface(LMI):
– used between the Frame relay DTE(eg.Router) and the
Frame Relay DCE(eg. Frame Relay switch)
– Defines how the DTE interacts with the DCE
– Locally significant
– Provides VCs status information(a keep-alive
mechanism)
– LMI standards : Cisco, ANSI, Q933a
The DTE and DCE must have the same LMI signaling type
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6. Frame Relay Terminology
• Data Link Connection Identifier(DLCI) :
– used to identify each VC on a physical interface
(i.e.) Each VC has a unique local address called a DLCI
number.
– switch will map to the destination depending on the
DLCI number
– Inverse ARP is used to map DLCIs to next hop
addresses.
– Mapping can also be done manually.
– Its Locally significant.
– These numbers are given by the Frame relay
service providers, Service providers assign DLCIs in
the range of 16 to 1007.
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7. Frame Relay Terminology
• Virtual circuits are of two types:
– Permanent Virtual Circuits – PVCs
– Switched Virtual Circuits –SVCs
• Permanent Virtual Circuit :
– similar to a dedicated leased line , permanent
connection.
– used when constant data is being generated.
• Switched Virtual Circuit :
– also called as Semi-permanent virtual circuit
– similar to a circuit switched connection where the
VC is dynamically built and then torn down once the
data has been sent.
– used when data has to be sent in small amounts
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and at periodic intervals.

8. Frame Relay Terminology
• Committed Information Rate(CIR) :
– Average data rate measured over a fixed period
of time that the carrier guarantees for a VC.
– committed bandwidth
• Burst Rate(BR) :
– Average data rate provider guarantees for a VC.
– Excess bandwidth
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9. Frame Relay Terminology
• FECN and BECN :
– Forward Explicit Congestion Notification
– Backward Explicit Congestion Notification
• When congestion occurs switch marks the FECN and
BECN bits in the frame header.
• FECN is sent to the destination
• BECN is sent to the source
• Thereby notifying both source and destination
about the congestion.
• FECN = 0 and BECN =0 implies no congestion.
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10. Frame Relay Terminology
• FECN and BECN :
– Forward Explicit Congestion Notification
– Backward Explicit Congestion Notification
• When congestion occurs switch marks the FECN and
BECN bits in the frame header.
• FECN is sent to the destination
• BECN is sent to the source
• Thereby notifying both source and destination
about the congestion.
• FECN = 0 and BECN =0 implies no congestion.
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