This chapter describes how to configure Compressed Real-Time Protocol (CRTP) header on serial lines using Frame Relay, High-Level Data Link Control (HDLC), or Point-to-Point Protocol (PPP) encapsulation. You can also use CRTP over Integrated Services Digital Network (ISDN) interfaces.
To locate documentation of commands that appear in this chapter, use the command reference master index, or search online.
To configure CRTP header, perform the tasks in the following sections. Either one of the first two tasks is required.
CRTP is supported on serial lines using Frame Relay, HDLC, or PPP encapsulation. It is also supported over ISDN interfaces.
You should configure CRTP if the following conditions exist in your network:
Enabling compression on both ends of a low-bandwidth serial link can greatly reduce the network overhead if it carries a lot of RTP traffic. Although the MBONE-style RTP traffic has higher payload sizes, compact encodings such as Compressed Encoding for Linear Prediction (CELP) can also help considerably.
Before you can enable RTP header compression, you must have configured a serial line that uses either Frame Relay, HDLC, or PPP encapsulation, or an ISDN interface. To configure RTP header compression, perform the tasks in the following sections.
To enable CRTP header for serial encapsulations HDLC or PPP, use the following command in interface configuration mode: (You must enable compression on both ends of a serial connection.)
ip rtp header-compression [passive]
Enable RTP header compression.
If you include the passive keyword, the software compresses outgoing RTP packets only if incoming RTP packets on the same interface are compressed. If you use the command without the passive keyword, the software compresses all RTP traffic.
To enable CRTP header with Frame Relay encapsulation, use one of the following commands in interface configuration mode:
frame-relay ip rtp header-compression [passive]
Enable RTP header compression on the physical interface and all the interface maps will inherit it. Subsequently, all maps will perform RTP/IP header compression.
frame-relay map ip ip-address dlci [broadcast] rtp header-compression [active | passive]
Enable RTP header compression only on the particular map specified.
frame-relay map ip ip-address dlci [broadcast] compress
Enable both RTP and TCP header compression on this link.
By default, the software supports a total of 16 RTP header compression connections on an interface. To change that number, use the following command in interface configuration mode:
Specify the total number of RTP header compression connections supported on an interface.
You can display specific statistics such as the contents of IP routing tables, caches, and databases. Information provided can be used to determine resource utilization and solve network problems. You can also display information about node reachability and discover the routing path your device's packets are taking through the network.
To display various routing statistics, use the following commands in EXEC mode:
show frame-relay ip rtp header-compression [interface type number]
Display Frame Relay RTP header compression statistics.
show ip rtp header-compression [type number] [detail]
The following example enables RTP header compression for a serial, ISDN, or asynchronous interface. For ISDN, you also need a broadcast dialer map.
interface serial 0 :or interface bri 0 ip rtp header-compression encapsulation ppp ip rtp compression-connections 25
The following example for Frame Relay encapsulation enables RTP header compression on the specified map:
interface serial 0 ip address 220.127.116.11 255.0.0.0 encapsulation frame-relay no keepalive clockrate 64000 frame-relay map ip 18.104.22.168 17 broadcast rtp header-compression