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| 8.8 |  | QoS using Low Speed Links |
| 8.8.6 |  | Configuring cRTP |

cRTP is a hop-by-hop compression scheme. cRTP must be configured on both ends of the link, unless the passive option is configured. To configure cRTP, use the following command at interface level:

> Router(config-if)#ip rtp header-compression [passive]

> Note: When the command ip rtp header-compression is used, the router adds the command ip tcp header-compression to the configuration by default. This is used to compress the headers of TCP/IP packets. Header compression is particularly useful on networks with a large percentage of small packets, such as those supporting many Telnet connections. The TCP header compression technique is supported on serial lines using HDLC or PPP encapsulation.

To compress the TCP headers without enabling cRTP, use the command:

> Router(config-if)#ip tcp header-compression [passive]

cRTP is not required to ensure good voice quality. It is a feature that reduces bandwidth consumption. Configure cRTP after all other conditions are met and the voice quality is good. This procedure can save troubleshooting time by isolating potential cRTP issues.