Semester 4
CHAPTER 5
Secció de Telemàtica
`Content
• Frame Relay concepts
• Configuring Frame Relay
FRAME RELAY CONCEPTS
`Frame Relay Operation
`Frame Relay Switches
The Frame Relay WAN is a mesh of
interconnected switches.
switches Customer DTEs
connect to the switches by leased lines.
`Terminology
• Th
The connection
ti th
through
h the
th Frame
F
Relay network between two DTEs is
called a virtual circuit (VC).
• Vi
Virtual
t l circuits
i
it may be
b established
t bli h d
dynamically by sending signaling
messages to the network. In this case
y are called switched virtual
they
circuits (SVCs).
• Permanent
P
t Virtual
Vi t l Ci
Circuits
it (PVCs)
(PVC )
`Frame Relay communications
•
The data
data-link
link connection identifier (DLCI) is stored in the Address
field of every frame transmitted
•
DLCI have local significance only!!
•
DTE sends frames to DCE Æ The Frames move from switch to
switch to the remote DCE
`Local Significance of DLCIs
The data-link connection identifier ((DLCI)) is
stored in the Address field of every frame
transmitted.
DLCI have local significance
g
only
y – the same
number on a different link indicates a different
VC, and has a different DLCI on each end
`Frame Relay Stack Layered
Support
`Frame Relay Functions
• Frame Relay receives a packet from a
network layer protocol such as IP
• Frame Relay warps it with an address
field ((which contains the DLCI)) and a
checksum
• E
Encloses
l
th
the package
k
iin flflag fifields
ld
(01111110)
• And passes it to the physical layer for
deli er as bits on the wire
delivery
ire
`Bandwidth and Flow Control
• CIR (Commited Info
Info.
Rate) Æ rate at which
the service provider
agrees to accept bits on
the VC
• CIR=Bc/Tc
– Bc Æ Commited Burst
– Tc Æ Commited Time
• EIR Æ Excess Info.
Rate Æ Be
– DE Bit active
• Bc + Be Æ Frame
discarded
`Flow Control
• FECN Bit Æ Forward Explicit
p
Congestion
g
Notification for downstream deviced
• BECN Bit Æ Backward Explicit Congestion
Notification for upstream devices
– Back to DTEs althoutgh is not their fault!
`Full
Full--Mesh Topology
Full Mesh Topology – 5 nodes require 10 links
`Frame Relay Mesh
Mesh Topology
p gy – each DTE has one p
physical
y
link carrying 4 VCs
`LMI (Local Management Interface)
• Three types of LMIs are supported by Cisco routers:
– Cisco — The original LMI extensions
– Ansi — Corresponding to the ANSI standard
T1.617 Annex D
– q933a
q
— Corresponding
p
g to the ITU standard Q933
Annex A
`Stages of Inverse ARP and
LMI Operation
CONFIGURING FRAME RELAY
`Configuring Basic Frame Relay
`Configuring a Static Frame Relay Map
`Reachability Issues with Routing
Updates in NBMA
By
y default,
de au t, a Frame
a e Relay
e ay network
et o p
provides
o des
nonbroadcast multiaccess (NBMA) connectivity
between remote sites. An NBMA environment is
treated like other multiaccess media environments,
where all the routers are on the same subnet.
`Frame Relay Subinterfaces
`Configuring PointPoint-toto-Point
Subinterfaces
`Verifying Frame Relay
• Th
The show
h
interfaces
i t f
command
d displays
di l
information regarding the
encapsulation
l ti and
d Layer
L
1 and
d Layer
L
2
status. It also displays information
about the following:
– The LMI type
– The LMI DLCI
– The Frame Relay data terminal
equipment/data circuit-terminating
equipment (DTE/DCE) type
`The show frameframe-relay lmi Command
`show frame
frame--relay pvc
`show frame
frame--relay map
`Review
• Frame Relay concepts
• Configuring Frame Relay