Specifications

Configure Real-Time Transport Protocol Header Compression

Configuring Serial Interfaces IC-75

Conﬁgure Real-Time Transport Protocol Header Compression

Real-time Transport Protocol (RTP) is a protocol used for carrying packetized audio and video trafﬁc

over an IP network. RTP is described in RFC 1889. RTP is not intended for data trafﬁc, which uses

TCP or UDP. RTP provides end-to-end network transport functions intended for applications with

real-time requirements, such as audio, video, or simulation data over multicast or unicast network

services.

For information and instructions for conﬁguring RTP header compression, refer to the “Conﬁguring

IP Multicast Routing” chapter in the Network Protocol Conﬁguration Guide, Part 1.

Conﬁgure the CRC

The cyclic redundancy check (CRC) on a serial interface defaults to a length of 16 bits. To change

the length of the CRC to 32 bits on an FSIP or HIP of the Cisco 7500 series only, use the following

command in interface conﬁguration mode:

Use the NRZI Line-Coding Format

All Fast Serial Interface Processor (FSIP) interface types on the Cisco 7500 series routers and the

PA-8T and PA-4T+ synchronous serial port adapters on the Cisco 7000 series routers with RSP7000,

Cisco 7200 series routers, and Cisco 7500 series routers support nonreturn-to-zero (NRZ) and

nonreturn-to-zero inverted (NRZI) format. This is a line-coding format that is required for serial

connections in some environments. NRZ encoding is most common. NRZI encoding is used

primarily with EIA/TIA-232 connections in IBM environments.

The default conﬁguration for all serial interfaces is NRZ format. The default is no nrzi-encoding.

To enable NRZI format, use one of the following commands in interface conﬁguration mode:

Enable the Internal Clock

When a DTE does not return a transmit clock, use the following interface conﬁguration command

on the Cisco 7000 series to enable the internally generated clock on a serial interface:

Command Purpose

crc size Set the length of the CRC.

Command Purpose

nrzi-encoding

nrzi-encoding [mark] (

Cisco 7200 series

routers and Cisco 7500 series routers)

Enable NRZI encoding format.

Command Purpose

transmit-clock-internal Enable the internally generated clock on a serial

interface.