Wan and ppp

1. Chapter 6
Frame Relay

2. Chapter 6
 Frame Relay is a connection oriented, standard NBMA layer
2 WAN protocol
 Frame relay is a Multi-access WAN connection service
 Frame relay allows one router to access more than one router
using a single physical link (access link)
 Connection in frame relay are provided by virtual circuits.
 Virtual circuits are multiple logical connection on same
physical connection.

3. Chapter 6
Frame Relay

4. Chapter 6
 Frame Relay virtual connection types
PVC
SVC
 PVC(Permanent virtual connection)
 Permanent connection is used.
 When constant data has to be sent to a particular
destination.
 Always use the same path.
 SVC (switched virtual connection)
 Virtual connection is dynamically built when data has to
be send and torn down after use.

5. Chapter 6
 Using a virtual connection (virtual circuit) to each site, the
router will be able to communicate with sites over a single
link
 A virtual connection to a site has an address known as Data
Link Connection Identifier (DLCI)
 When the router sends to a site, it tags packets with the
proper DLCI address which represents the connection to
this site

6. Chapter 6
Frame Relay virtual connection

7. Chapter 6
Frame Relay Operation
The connection between a DTE device and a DCE device
consists of both a physical layer component and a link layer
component:
The physical component defines the mechanical, electrical,
functional between the devices.
The link layer component defines the protocol that establishes
the connection between the DTE device (router), and the DCE
device (switch).

8. Chapter 6

9. Chapter 6
 Packet Switching Across Frame Relay Network
 Frame relay switches at the service provider network are
configured to forward received frames with certain DLCIs to
the appropriate output interface with its DLCIs

10. Chapter 6
 Frame Relay Encapsulation
 Frame Relay takes data packets from a network layer
protocol, such as IP or IPX, encapsulates them as the data
portion of a Frame Relay frame, and then passes the frame
to the physical layer for delivery on the wire.

11. Chapter 6
There are two types of frame relay encapsulations
 CISCO (default and cisco proprietary)
 IETF (when different vendor routers are used)
RouterA (config-if)#encapsulation frame-relay ?
IETF
<cr>

12. Chapter 6
 DLCI (data link connection identifier):
 Address of virtual connections
 every VC there is one DLCI number.
Inverse ARP (address resolution protocol) is used to map
local DLCI to a remote IP
Unique identifier <16-1007>
Router(config-if)#frame –relay interface –dlci 18

13. Chapter 6
 Frame Relay Topologies

14. Chapter 6
 Local Management Interface (LMI)
LMI allows DTE(router) to send status messages to DCE(frame
relay switch) to exchange status information about the virtual
circuits devices.
LMI is used between the router and its frame relay switch to
discover each other using keepalive messages

15. Chapter 6
 Frame relay LMI types:
 CISCO (default)
 ANSI
 Q933A
Router(config-if)#frame –relay lmi-type ?
Cisco
Ansi
Q933a

16. Chapter 6
Frame Relay Address Mapping
 Before a router is able to transmit data over Frame Relay, it needs
to know which local DLCI maps to the Layer 3 address of the
remote destination.
 This address-to-DLCI mapping can be accomplished either by
static or dynamic mapping
 Static Mapping
 To map between a next hop protocol address and DLCI
destination address
 You want to control broadcast traffic across a PVC
 You want to have different Frame Relay encapsulations across

17. Chapter 6
Router(config-if)#frame –relay map {protocol} {destination
address} DLCI source broadcast{cisco ! ietf}

18. Chapter 6
 Dynamic mapping
 Frame relay map is created dynamically using Inverse-
arp protocol
 Inverse-arp operates after receiving LMI PVC status
response messages that explain PVCs, their status, and
DLCIs
 When the router receives a PVC active with its DLCI, it
creates an Inverse-arp message contains its IP address to
be sent over this PVC
 The router can then map the IP address in the message
with its local DLCI

19. Chapter 6
Router (config-if)#frame –relay map inverse-arp source DLCI
RouterA (config-if)#frame –relay map inverse-are 100
RouterB (config-if)#frame –relay map inverse-are 200

20. Chapter 6
Split horizon can cause problems in NBMA environments.
Solution: subinterfaces
A single physical interface simulates multiple logical interfaces

21. Chapter 6
 Configuring Frame Relay Subinterfaces
 Point-to-point
 Subinterfaces act like leased lines.
 Each point-to-point subinterface requires its own subnet.
 Point-to-point is applicable to hub-and-spoke topologies.
Multipoint
 Subinterfaces act like NBMA networks, so they do not
resolve the split-horizon issues.
 Multipoint can save address space because it uses a single
subnet.
 Multipoint is applicable to partial-mesh and full-mesh
topologies

22. Chapter 6
Configuring Frame Relay Point-to-Point Subinterfaces

23. Chapter 6
Configuring Frame Relay Multipoint Subinterfaces

24. Chapter 6
 Committed information rate(CIR)
 Is the line speed
 CIR: Lower speed guaranteed for a certain time.
 Congestion :
indicates traffic problem in the path when more packets are
transmitted in one direction
congestion notifications
1.FECN 2.BECN 3.DE
 DE
 The descent speed of receiving and sending to CIR

25. Chapter 6
 FECN
 Indicates congestion as frame goes from source to destination
 Used this value inside frame relay frame header in forward
direction
 FECN=0 indicates no congestion
 BECN
 Used by the destination(and send to source) to indicate that there
is congestion
 Used this value inside frame relay frame header in backward
direction
 BECN=0 indicates no congestion