D-Link DI-1750 Reference Manual page 415

9.3.7 Configuration Examples
The following example showes how to configure the CRTP on serial lines using Point-to-Point Protocol
(PPP) encapsulation:
interface serial 1/2
ip rtp header-compression
ip rtp compression-connections 25
encapsulation ppp
9.4 Configure CTCP (TCP/IP Header-Compression Protocol)
This section briefly describes how to configure TCP/IP header-compression protocol on serial link using
PPP. Please refer to the command description of TCP/IP header-compression for details.
9.4.1 CTCP Configuration Steps
There are a few steps to configure CTCP:
♦ Enable CTCP On A Serial Interface
♦ Change The Maximum Number Of CTCP Connections
♦ Display CTCP Compression Information
♦ CTCP Debugging
Note: You must configure CTCP on both ends of a serial connection, otherwise the CTCP is
unavailable.
9.4.2 About CTCP
Currently the CTCP can only support the serial link encapsulated as PPP, and it can expand to Frame
Relay、HDLC encapsulation and ISDN interface. We need to configure CTCP in these cases:
♦ Slow serial links
♦ The serial links need to save bandwidth
Supposing operating on a communication link that need abundant TELNET, each time of click from
client end need to be loaded by a TCP message, and if the size of IP, TCP header without options are
totally 40 bytes but payload is only 1 byte, so the efficiency is quite lower.
If you choose to carry the same message with CTCP, you need only 4 byte header (TCP/IP
head-compression standard stimulated by rfc2507), or 3 bytes (TCP/IP head-compression standard
stimulated by rfc1144).
Note: CRTP should not be used on links greater than 2 Mbps.
9.4.3 Enable CTCP On A Serial Line
To enable CTCP header for serial encapsulations PPP, use the following command in interface
configuration mode: (You must enable compression on both ends of a serial connection.)
Command
ip tcp header-compression
[{ cisco-format | iphc-format
| passive}]
The optional parameter cisco-format is a default value, which specifies IPCP to adopt packets with
cisco format when the IPHC format CRTP is applied to PPP links, else the IPCP packet format is
RFC1144; If you include the passive keyword, the software compresses outgoing RTP packets only if
incoming RTP packets on the same interface are compressed, when the CRTP is applied to PPP links,
IPCP will adopt the cisco format packet if CRTP is IPHC format, else the IPCP will adopt RFC1144
format packet; the key word iphc-format specifies IPCP to adopt packets with RFC2509 format when
Model Name
Purpose
Enable CTCP.
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