Compressing Frame Relay Data with Maps

Problem

You want to configure your router to do Frame Relay compression with map statements.

Solution

The same Frame Relay compression options that we discussed for subinterfaces are also available with map statements. You can turn on FRF.9 compression by simply adding a few additional keywords to the frame-relay map statement as follows:

Central#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Central(config)#interface Serial0
Central(config-if)#description Frame Relay to branches
Central(config-if)#ip address 192.168.1.1 255.255.255.0
Central(config-if)#encapsulation frame-relay
Central(config-if)#frame-relay map ip 192.168.1.10 101 payload-compression frf9 stac
Central(config-if)#exit
Central(config)#end
Central#

Or you can opt to use Cisco's proprietary packet-by-packet compression instead:

Central#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Central(config)#interface Serial0
Central(config-if)#description Frame Relay to branches
Central(config-if)#ip address 192.168.1.1 255.255.255.0
Central(config-if)#encapsulation frame-relay
Central(config-if)#frame-relay map ip 192.168.1.10 101 payload-compression packet-by-packet
Central(config-if)#exit
Central(config)#end
Central#

The map configuration also supports TCP header compression:

Central#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Central(config)#interface Serial0
Central(config-if)#description Frame Relay to branches
Central(config-if)#ip address 192.168.1.1 255.255.255.0
Central(config-if)#encapsulation frame-relay
Central(config-if)#frame-relay map ip 192.168.1.10 101 compress
Central(config-if)#exit
Central(config)#end
Central#

Discussion

As we discussed in Recipe 10.7, Cisco routers are able to compress the data payload of packets before sending them through Frame Relay circuits. This recipe simply shows how to do the same thing using map statements instead of subinterfaces. Note that the header compression example shown in Recipe 10.7 applies to the physical interface. So the configuration for header compression is identical, whether you are using maps or subinterfaces.

You can combine the payload compression option with the other options we discussed in Recipe 10.3 by specifying all of the required options on the same command line:

Central(config)#interface Serial0
Central(config-if)#encapsulation frame-relay
Central(config-if)#frame-relay map ip 192.168.1.10 101 ietf broadcast payload-compression frf9 stac 
Central(config-if)#end

Note that you can specify these keywords in any order, as long as the compression options are last. However, you cannot combine the different compression options with one another.