1. Introduction

2. Center for TeleInFrastructure 2 Introduction  2G (GSM) is voice dominated  3G (UMTS) is IP based  large IP overhead  link bandwidth is limited (25 billion Euro for frequencies)  idea: use header compression to reduce IP overhead  header compression has to be robust  3GPP has chosen Robust Header Compression (ROHC)  open question: Quality of Service?

3. Center for TeleInFrastructure 3 Why do we need header compression?  Large IP overhead for real time services  voice service  audio services  video service  Smaller packets have smaller delays  Smaller packets are less error-prone on the wireless link

4. Center for TeleInFrastructure 4 Wireless Channel  Characteristic  Limited bandwidth  Wireless link is very error prone, BER as high as 1e-3  High error rates are tolerated in order to allow efficient usage of radio resources

5. Center for TeleInFrastructure 5 IP Protocol Suite

6. Center for TeleInFrastructure 6 RTP/UDP/IP Overhead

7. Center for TeleInFrastructure 7 Multiple Description Coding (MDC)

8. Center for TeleInFrastructure 8 MDC with Overhead

9. Center for TeleInFrastructure 9 AMR Speech Codec

10. Center for TeleInFrastructure 10 Finding the redundancy  Redundancy between header fields of the same packet (e.g. RTP/UDP/IP) are referred to as intra packet redundancy  Redundancy between parts of header between different packets (RTP) are referred to as inter packet redundancy  The redundancy changes with the IP version: IPv4/6

11. Center for TeleInFrastructure 11 Header Fields RTP/UDP/IPv4

12. Center for TeleInFrastructure 12 Header Fields RTP/UDP/IPv6