1. CAPÍTULO III Frame Relay
M. En C. Juan Antonio Guerrero Ibáñez
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

2. M.C. Juan Antonio Guerrero Ibáñez
Objectives
Describe the operation of Frame Relay
Describe the functions of DLCIs in Frame Relay
Describe Cisco’s implementation of Frame Relay
Describe the process for configuring and verifying Frame Relay
Describe the Frame Relay subinterfaces
Describe how Frame Relay uses subinterfaces to solve the problem of split horizon
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

3. Frame Relay Technology Overview
Frame Relay Terminology
Frame Relay Operation
Frame Relay Multiplexing
Frame Relay Frame Format
Frame Relay Addressing
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

4. M.C. Juan Antonio Guerrero Ibáñez
What Is Frame Relay?
Frame Relay is a packet-switched, connection-oriented, WAN service.
FR defines the interconnection process between a
router and the service provider’s local access switching equipment.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

5. M.C. Juan Antonio Guerrero Ibáñez
What Is Frame Relay?
Frame Relay uses a subnet of the HDLC protocol called LAPF (Link Access Procedure for Frame Relay)
Originally FR was designed to allow ISDN equipment to have access to a packet-switched service on a B channel
FR is now a stand-alone technology
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

6. Connection-Oriented Service
Connection-oriented protocols use an acknowledgement
process between source and destination.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

7. Frame Relay stack layered support
Takes data packets from a network layer protocol, such as IP or IPX
Encapsulates them as the data portion of a Frame Relay frame
Passes them to the physical layer for delivery on the wire
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

8. M.C. Juan Antonio Guerrero Ibáñez
Terminology
VC can be:
established dynamically by sending signaling messages to the network. (SVC)
Preconfigured by the carrier (PVC)
The switching information for a VC is stored in the memory of the switch.
FR provides no error recovery mechanism because it was designed to operate on high-quality digital lines.
The FRAD or router connected to FR network may have multiple virtual circuits connecting it to various end points.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

9. M.C. Juan Antonio Guerrero Ibáñez
LMI and Local Access
The DLCI (Data Link Channel Identifier)value identifies the
logical connection that is multiplexed into the physical channel.
LMI (Local Management Interface)
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

10. M.C. Juan Antonio Guerrero Ibáñez
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

11. Frame Relay Terminology #1
Local access rate
The maximum physical media speed of the link used by the Frame Relay interface. Frame Relay may or may not use this full bandwidth, but cannot exceed it
Common local access rates include T1 (1.544 Mbps) and 56 Kbps – could be up to T3 ( Mbps).
Committed information rate (CIR)
The transmission rate that the frame relay provider guarantees without frame drops
Any frames sent above this rate has the DE bit set to one allowing them to be dropped if congestion occurs.
Monthly service charge is based heavily on this rate.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

12. Frame Relay Terminology #2
Committed burst
The maximum number of bits per second that the Frame Relay provider agrees to transmit during any CIR measurement time interval.
While in most contracts, generally isn’t used very much .
Excess burst
The maximum bits that the Frame Relay switch will attempt to transfer beyond the CIR. Can not exceed the local access rate .
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

13. Frame Relay Terminology #3
Oversubscription
A link is oversubscribed when the combined traffic rate of all VCs (often customers) exceeds the local access link speed. The bursty nature of data traffic allows some VCs to burst while others are idle.
Port speed
The maximum burst rate in bits per second. Basically, CIR is what you’re guaranteed, port speed is what you can burst up to, and local access rate is the capacity of the physical interface to the cloud.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

14. M.C. Juan Antonio Guerrero Ibáñez
BECN and FECN
A Frame Relay switch sends FECN and BECN packets to reduce congestion.
FECN packets are sent to the destination device, BECN packets are sent to
the source device.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

15. Frame Relay Traffic-Control Functions
Error Control with Frame Relay
Relies on upper-layer protocols to provide retransmission of damaged or missing frames. This is a concession to increase speed, but it works only because the quality and reliability of the underlying circuits.
Flow/Congestion Control with Frame Relay
Pseudo flow-control capability via the FECN, BECN, and DE bits in the protocol frame’s address field. Not true flow control because upper-layer protocols are still required to actually carry out the task of reducing transmission rates
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

16. M.C. Juan Antonio Guerrero Ibáñez
Frame Relay Operation
Interconnection of Frame Relay
switches and routers.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

17. M.C. Juan Antonio Guerrero Ibáñez
Frame Relay DLCIs
The end devices at two different ends of a connection can use
different DLCI numbers to the same connection. DLCIs are
locally significant.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

18. Frame Relay Frame Format
Flag - Beginning and the end of the Frame Relay frame ( )
Address - Contains the following information:
DLCI VALUE – First 10 bits: Indicates the DLCI value.
Congestion CONTROL - Last 3 bits control congestion-notification mechanisms. These bits are:
FECN (forward explicit congestion notification)
BECN (backward explicit congestion notification)
DE (discard eligible)
Data - Contains encapsulated upper-layer data
FCS - Frame check sequence
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

19. Frame Relay Addressing
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

20. M.C. Juan Antonio Guerrero Ibáñez
LMI Operation
LMI provides for management of connections. Includes
operational status of PVCs, transmit keepalives, and tell the
router the available PVCs.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

21. M.C. Juan Antonio Guerrero Ibáñez
LMI Frame Format
Flag
DLCI - Defined in the specification as DLCI = 1023.
Unnumbered information indicator - Same format as LAPB unnumbered information (UI) frame indicator, with the poll/final bit set to 0.
Protocol discriminator - Value indicates LMI.
Call reference - Always filled with 0s.
Message type - Two message types:
Status messages (respond to status-enquiry messages). Examples:
Keepalives
Status message of each DLCI defined for the link
Status-enquiry messages
Together help verify the integrity of logical and physical links
Information element (IE) - Consists of one or more: 1-byte IE identifier, an IE length field, and 1 or more bytes containing actual data.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

22. M.C. Juan Antonio Guerrero Ibáñez
LMI States
LMI Connection States. There are three:
Active–Connection between two end routers is up and capable of transmitting data.
Inactive–Connection between the local router and local Frame Relay switch is operational, but the remote router’s link is not operational.
Deleted–Indicates a failed link between the local router and local Frame Relay switch.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

23. Multicasting and Inverse ARP
The router learns the DLCIs from the Frame Relay switch and sends
an Inverse ARP request to each DLCI.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

24. Multicasting and Inverse ARP
Multicast groups are designated by a series of four reserved DLCI values (1019 to 1022). Frames sent by a device using one of these reserved DLCIs are replicated by the network and sent to all exit points in the designated set.
The Inverse ARP allows the router to automatically build the Frame Relay map. The router learns the DLCIs from the switch during the initial LMI exchange. The router then sends an Inverse ARP request to each DLCI. The return information is used to build the Frame Relay map.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

25. M.C. Juan Antonio Guerrero Ibáñez
Frame Relay Mapping
Responses to Inverse ARP requests are entered in an
address-to-DCLI mapping table on the router or access server.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

26. Frame Relay Switching Tables
Routers use Inverse ARP to find the remote IP address and create a
mapping of local DLCIs and their associated remote IP addresses.
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

27. Basic Frame Relay Configuration
Verifying Frame Relay Operation
Configuring the Serial Interface for a Frame Relay Connection
Verifying Frame Relay Configuration
Configuring Subinterfaces
Configuring Optional Commands
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

28. Frame Relay Configuration Steps
Enabling Frame Relay Encapsulation
Router(config-if)#encapsulation frame-relay [cisco|ietf]
Default is Cisco; IETF is the standard.
Specifying the LMI Type
Router(config-if)#frame-relay lmi-type [ansi|cisco|q933a]
Not necessary since Cisco IOS Release 11.2.
Configuring the Link Bandwidth (Optional)
Router(config-if)#bandwidth Num kbps
Default on serial links is 56 kbps.
Enabling Inverse ARP
Router(config-if)#frame-relay inverse-arp [protocol] [dlci]
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

29. Configuring a Static Map (Parameters)
When not using inverse ARP to dynamically map DLCIs to protocol addresses, you must create a static mapping. The syntax:
Router(config-if)#frame-relay map protocol protocol-address dlci# [broadcast] [ietf|cisco]
Protocol - Protocol used on the interface
protocol-address - Protocol address of remote router interface
dlci# - Local DLCI used to reach the remote router
Broadcast - Permits the forwarding of broadcasts
ietf|cisco - Frame Relay encapsulation type
Overrides the encapsulation frame-relay command choice
Cisco is the default
Examples
RTA(config-if)#frame-relay map ip broadcast
RTA(config-if)#frame-relay map ip broadcast
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

30. Basic Configuration Example
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

31. Verifying and Troubleshooting Frame Relay
The show interface serial Command
The show frame-relay lmi Command
The show frame-relay pvc [interface interface [dlci#]] Command
The show frame-relay map Command
The debug frame-relay Command
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

32. The show interfaces serial Command
Lab-B#show interfaces serial
Serial 2 is up, line protocol is up
Hardware type is MCI Serial
Internet address is , subnet mask is
MTU 1500 bytes, BW 1544 Kbit, DLY usec, rely 255/255,load 1/255
Encapsulation FRAME-RELAY, loopback not set, keepalive set (10 sec)
multicast DLCI 1022, status defined, active
source DLCI 20, status defined, active
LMI DLCI 1023, LMI sent 10, LMI stat recvd 10, LMI upd recvd 2
Last input 7:21:29, output 0:00:37, output hang never
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

33. The show frame-relay lmi Command
Router#show frame-relay lmi
LMI Statistics for interface Serial1 (Frame Relay DTE) LMI TYPE = ANSI
Invalid Unnumbered info Invalid Prot Disc 0
Invalid dummy Call Ref Invalid Msg Type 0
Invalid Status Message Invalid Lock Shift 0
Invalid Information ID Invalid Report IE Len 0
Invalid Report Request Invalid Keep IE Len 0
Num Status Enq. Sent Num Status msgs Rcvd 0
Num Update Status Rcvd Num Status Timeouts 9
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

34. The show frame-relay pvc Command
Router#show frame-relay pvc 100
PVC Statistics for interface Serial5/1 (Frame Relay DTE)
DLCI = 100, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0.1
input pkts output pkts in bytes 154
out bytes dropped pkts in FECN pkts 0
in BECN pkts out FECN pkts out BECN pkts 0
in DE pkts out DE pkts 0
out bcast pkts out bcast bytes 0
pvc create time 00:35:11, last time pvc status changed 00:00:22
Bound to Virtual-Access1 (up, cloned from Virtual-Template5)
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

35. The show frame-relay map Command
Router#show frame-relay map
Serial 1 (up): ip
dlci 177 (0xB1,0x2C10), static, broadcast, CISCO
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez

36. The debug frame-relay Command
Serial0(i): dlci 500(0x7C41), pkt type 0x0800, datagramsize 24
Serial0(i): dlci 1023(0xFCF1), pkt type 0x309, datagramsize 13
Copyright 2004
M.C. Juan Antonio Guerrero Ibáñez