Cisco IOS Wide-Area Networking Configuration Guide - Free Books

Customizing Frame Relay for Your NetworkConfiguring Frame RelayStep 3Step 4CommandRouter(config-subif)# frame-relay map protocolprotocol-address dlci [payload-compression data-streamstac [hardware-options]]Router(config-subif)# frame-relay ip tcpheader-compression [passive]orRouter(config-subif)# frame-relay ip rtpheader-compression [passive]PurposeDefines the mapping between a destinationprotocol address and the DLCI used to connect tothe destination address on an interface that usesCisco-proprietary encapsulation.Configures an interface to ensure that theassociated PVCs carry outgoing TCP headers incompressed form.Enables RTP header compression on the physicalinterface.Verifying Payload CompressionFor an example of data-stream compression and IP header compression configured on a multipointsubinterface, see the section “Data-Stream Hardware Compression with TCP/IP Header Compression ona Multipoint Subinterface Example” later in this chapter.For an example of data-stream compression and IP header compression configured with FRF.12fragmentation, see the section “Data-Stream Hardware Compression with RTP Header Compression andFrame Relay Fragmentation Example” later in this chapter.To verify that payload compression is working correctly, use the following privileged EXEC commands:CommandRouter# show compressRouter# show frame-relay pvc dlciRouter# show traffic-shape queuePurposeDisplays compression statistics.Displays statistics about PVCs for Frame Relayinterfaces, including the number of packets in thepost-hardware-compression queue.Displays information about the elements queued ata particular time at the DLCI level, including thenumber of packets in the post-hardwarecompressionqueue.Configuring TCP/IP Header CompressionTCP/IP header compression, as described by RFC 1144, is designed to improve the efficiency ofbandwidth utilization over low-speed serial links. A typical TCP/IP packet includes a 40-byte datagramheader. Once a connection is established, the header information is redundant and need not be repeatedin every packet that is sent. Reconstructing a smaller header that identifies the connection and indicatesthe fields that have changed and the amount of change reduces the number of bytes transmitted. Theaverage compressed header is 10 bytes long.For this algorithm to function, packets must arrive in order. If packets arrive out of order, thereconstruction will appear to create regular TCP/IP packets but the packets will not match the original.Because priority queueing changes the order in which packets are transmitted, enabling priorityqueueing on the interface is not recommended.46