frame relay
TRANSCRIPT
Computer networks
FRAME RELAYFRAME RELAY CONTENTSCONTENTS DEFINITIONDEFINITION ADVANTAGESADVANTAGES DISADVANTAGESDISADVANTAGES VIRTUAL CIRCUITSVIRTUAL CIRCUITS FRAME RELAY SWITCHFRAME RELAY SWITCH FRAME RELAY STRUCTUREFRAME RELAY STRUCTURE USE OF FRAME RELAYUSE OF FRAME RELAY CONGESTION CONTROLCONGESTION CONTROL
introductionintroduction
Frame relay is a relatively high-Frame relay is a relatively high-speed protocol that can provide speed protocol that can provide some services not available in some services not available in other WAN technologies such as other WAN technologies such as DSL, cable TV, T-lines. It is quite DSL, cable TV, T-lines. It is quite popular. popular.
Frame relay provides:Frame relay provides:
Higher data rate at lower costHigher data rate at lower cost
Bursty dataBursty data
Less overheadLess overhead
LANLAN
LANLAN
LANLAN
15 T-LINES
a.) Using T-lines
HIGHER DATA RATE AT LOWER COST
LAN
LAN
LAN
LAN
LANLAN
Frame relay
network
6 T-lines
b). Using frame relay
Frame relay is a way to transmit data across a leased line
Data rate
0 1 2 3 4 5 6 7 8 9 10
Total data sent:15.44mbps
1.54
4 M
bp
s
seconds
a. Fixed-rate data
BURSTY DATA V/S FIXED RATE DATA
b. Bursty data
6 M
bp
s0 1 2 3 4 5 6 7 8 9 10
Total data sent:15:44mbps
12 MB
seconds
Data rate
3.44MB
3.44
mb
ps
LESS OVERHEAD
Data from the network layer sent in data link layer
source
data data
Frame relay traffic
destination
Routers
Routers
Routers Bridges
Advantages of Frame RelayAdvantages of Frame Relay
It operates at a It operates at a higher speedhigher speed (1.544 (1.544 Mbps & 44.376Mbps)Mbps & 44.376Mbps)
It operates in physical & data link It operates in physical & data link layerlayer
It allows It allows bursty databursty data
It allows It allows frame sizeframe size of 9000 bytes, of 9000 bytes, which can accommodate all LAN which can accommodate all LAN framesframes
Less expensiveLess expensive than other WANs than other WANs
Disadvantages of Frame Disadvantages of Frame RelayRelay
Not highNot high enough for protocols with enough for protocols with even even higher data rateshigher data rates
It allows variable-length frames. This It allows variable-length frames. This may may create delayscreate delays for different users for different users
Frame relay is not suitable for Frame relay is not suitable for sending sensitive datasending sensitive data
Virtual CircuitsVirtual Circuits
The Frame Relay frame is transmitted to The Frame Relay frame is transmitted to its destination by way of virtual circuits to a its destination by way of virtual circuits to a destination point.destination point.
A VC in frame relay is identified by data A VC in frame relay is identified by data link connection identifier (DLCI)link connection identifier (DLCI)
When a VC is established, a DTE is When a VC is established, a DTE is given DLCIgiven DLCI to send frames to remote DTE.to send frames to remote DTE.
Permanent Virtual Circuit Permanent Virtual Circuit (PVC)(PVC)
I
II
III
IV
A PVC connection is established between two DTEs.
The two DTEs are permanently connected through a virtual connection.
The same virtual circuit is provided between two users
Switched virtual circuit Switched virtual circuit (SVC)(SVC)
A virtual circuit is created whenever it is A virtual circuit is created whenever it is needed & exists only for duration of the needed & exists only for duration of the specific exchangespecific exchange
Single route exists for the duration of Single route exists for the duration of transmission, although the network transmission, although the network could pick an alternate routecould pick an alternate route
Switched virtual circuitSwitched virtual circuit
I
II
III
IV
a. Connection establishment I
II
III
IV
c. Connection release
I
II
III
IV
b. Data transfer
Frame relay switchFrame relay switch
Each switch in a frame relay network has a table to route
The table matches an incoming interface –DLCI combination with an outgoing interface-DLCI combination 1.
2.
3.
DLCI:121DLCI:124
DLCI:041
DLCI:112
Incoming
Interface DLCI DLCIInterface
11
121124
23
041112
Outgoing
Frame structureFrame structure
Frame relay layersFrame relay layers
Frame relay has only physical and data link layers
CongestionCongestion
When the Frame Relay switch recognizes congestion, it sends a FECN message to the destination router.
This message tells the router that congestion was experienced on the virtual circuit.
In addition, the switch sends BECN message to the transmitting, or source, router.
The router's reaction to the BECN should be to reduce the amount of traffic it is sending.
Thus, during times of congestion, the router can discard DE frames in order to provide a higher, more reliable, service to those frames that are not discard eligible.