Huawei v200r001 user manual Iphc Configuration, Overview of Iphc

User Manual - Configuration Guide (Volume 3)	Chapter 5
Versatile Routing Platform	IPHC Configuration

Chapter 5 IPHC Configuration

5.1 Overview of IPHC

IPHC (IP Header Compression) is the method to classify and compress packet such as IP, TCP and UDP, according to a series of header compression algorithms specified in relevant RFC documents, so as to enhance the transmission rate of voice, video and large packet over low-speed network. Currently, IPHC is mainly applied to the serial links running such protocols as PPP, FR and HDLC and carrying large amount of voice information.

As described in RFC2507, the packets need to be compressed can be classified into the following categories:

1)IP header + TCP header

2)IP header + UDP header

3)IP header + UDP header + RTP header

Among them, (RTP) Realtime Transmit Protocol is an application layer protocol lies above TCP/UDP, which is mainly used to transmit audio, video and simulated data information.

The implementation of IPHC depends on the various existing compression algorithms, whose main concepts are to compress the header since many fields of the headers do not change or change regularly in the course of one-time connection. It divides header into TCP and NON_TCP type, and further divides them into smaller categories. Extracting the unchanged fields or the fields that change regularly from the header of the same packet type, it does not transmit or only transmit the changed values of those fields, thus achieving the purpose of compressing the length of the whole packet.

IPHC defines the two ends of the link as compressor and non-compressor end respectively. The packet processing procedure is described as below:

Compressor: According to the classification method in RFC2507 document, after it classify and compresses the packets, the compressor notifies the decompressor through different packet protocol numbers and makes the decompressor perform different compression in accordance with the corresponding protocol number. If the compressor receives fault-reporting packet CONTEXT_STATE sent from the decompressor, it will mark some location digits in the context storage table according to the information in the packet to identify the faulty packet flow and will performs faulty processing accordingly. For example, when the next packet arrives, it will transmit packets to the decompressor in the complete format to help the latter update context storage table and to implement re-synchronization, etc.

Decompressor: It performs decompression according to the different types of packets transmitted from the compressor, and restores them into complete packets. If it finds that there is fault in packet decompression process, it will either discard the faulty packet or generate CONTEXT_STATE fault-reporting packet according to the actual conditions.

By using IP header compression on low-speed serial link, it can implement:

zEnhance the packet Interactive Response Speed

zReduce the transmission cost of header, enabling small packet to achieve high link transmission quality and saving bandwidth resource

zReduce the packet discard rate on lossy links

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