Frank Fitzek,Tatiana K. Madsen, and Patrick Seeling IP Header Compression Enabling High Quality Consumer-Oriented Communications Aalborg University, Denmark Arizona State University, USA

Center for TeleInFrastructure 2 Content  Introduction  Potential savings due to Header Compression  Header Compression schemes  Activities in the field of Header Compression  Tools and voice/ video quality evaluation  Conclusions – why HC should be applied

About the Tutorial

Center for TeleInFrastructure 4 Presenters  Prof. Dr. Frank Fitzek Head of Future Vision group Dept. of Communication Technology Aalborg University, Denmark  Dr. Tatiana K. Madsen Dept. of Communication Technology Aalborg University, Denmark  Patrick Seeling Department of Electrical Engineering Arizona State University USA

Center for TeleInFrastructure 5 Acknowledgements  Prof. Martin Reisslein, ASU, US  Stephan Rein, TU Berlin, Germany  Stefan Hendrata, Carmeq, Germany  acticom GmbH, Germany

Introduction

Center for TeleInFrastructure 7 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?

Center for TeleInFrastructure 8 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

Center for TeleInFrastructure 9 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

Center for TeleInFrastructure 10 IP Protocol Suite

Center for TeleInFrastructure 11

Center for TeleInFrastructure 12 Multiple Description Coding (MDC)

Center for TeleInFrastructure 13 MDC with Overhead

Center for TeleInFrastructure 14 AMR Speech Codec

Center for TeleInFrastructure 15 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

Center for TeleInFrastructure 16 Header Fields RTP/UDP/IPv4

Center for TeleInFrastructure 17 Header Fields RTP/UDP/IPv6

Potential savings due to Header Compression

Center for TeleInFrastructure 19 Potential Savings for Voice/Audio Services  Four example voice/audio codecs  LPC  GSM  G.711  AMR  These values does not depend on the content (no silent detection)

Center for TeleInFrastructure 20 Voice mean bitrateIPv4 savings IPv6 savings codec[kbps][%] LPC GSM G

Center for TeleInFrastructure 21 Voice AMR mean bitrateIPv4 savings IPv6 savings codec[kbps][%] AMR Mode AMR AMR

Center for TeleInFrastructure 22 Potential Savings for Video Services  H.26L video coder  These values does depend on the video content as well as the codec settings  Different video sequences  Different video quality  QCIF video format

Center for TeleInFrastructure 23 Frame Size Trace For Star Wars II  Star Wars II  CD 1  955 kbit/s  Star Wars II  CD 2  880 kbit/s

Center for TeleInFrastructure 24 Video Format/Quality  QP values 1, 31, 51 QP 1 QP 31 QP 51

Center for TeleInFrastructure 25 P. Seeling and M. Reisslein and F.H.P. Fitzek and S. Hendrata. Video Quality Evaluation for Wireless Transmisison with Robust Header Compression

Center for TeleInFrastructure 26 P. Seeling and M. Reisslein and F.H.P. Fitzek and S. Hendrata. Video Quality Evaluation for Wireless Transmisison with Robust Header Compression

Header Compression Schemes

Center for TeleInFrastructure 28 Different Header Compression schemes  Compressed TCP – Van Jacobsen RFC 1144  only for TCP/IP  for wired networks  Perkins  improvement for of CTCP  IPHC  only for IP protocol  no feedback

Center for TeleInFrastructure 29 General Structure of Header Compressors  Two entities: compressor and decompressor  Compressor sends initial base  Base is used by compressor and decompressor  Compressor removes redundancy  Decompressor adds removed information  Proposed solution differ in a possible feedback channel N N Base Compressor Decompressor Base N*

Center for TeleInFrastructure 30 CTCP (Van Jacobsen)  TCP/IP header compression  Using delta compression  Designed for wired networks  Not robust against error-prone links  Base update with each new incoming packet

Center for TeleInFrastructure 31 Loosing synchronization  Synchronization loss = decompressor’s copy of the base is different from the compressor’s copy  Synchronization is lost any time a packet is dropped  Detection: using detection of TCP retransmissions. All retransmissions are sent uncompressed

Center for TeleInFrastructure 32 Performance of VJ scheme in case of random errors  When synchronization is lost, the decompressor starts to toss packets  base update more often than needed S. J. Perkins and M. W. Mutka, Dependency Removal for Transport Protocol Header Compression over Noisy Channels Kbytes/s Throughput of bulk data transfers File sizes of 344K, 328K, and 550K

Center for TeleInFrastructure 33 Perkins – Refinement of CTCP  Perkins & Mutka – improvement of CTCP in case of noise presence  Differentials are sent against a base that changes infrequently  packet loss does not cause endpoints to loose synchronization  All packets refer to the first packet of the frame  the same mechanisms can be used to detect loss of synchronization

Center for TeleInFrastructure 34 Perkins – Refinement of CTCP  Base refresh (sending uncompressed header) – to combat overflow problems  Robustness introduced by periodically repetition of full base information each N packets  N packets define a frame  Larger overhead  Less compression due to higher delta values  Additionally, 1 byte of CID (connection identifier) is transmitted

Center for TeleInFrastructure 35 Performance of Perkins scheme S. J. Perkins and M. W. Mutka, Dependency Removal for Transport Protocol Header Compression over Noisy Channels Throughput of bulk data transfers File sizes of 344K, 328K, and 550K

Center for TeleInFrastructure 36 IP Header Compression (IPHC)  Provides extensions to VJ  Support UDP, IPv6,  Additional TCP features  Uses delta encoding

Center for TeleInFrastructure 37 TWICE algorithm  TCP header compression reduces throughput over lossy links  Bandwidth is wasted when unharmed segments are retransmitted after a timeout  Possible solutions:  Perkins algorithm  TWICE algorithm

Center for TeleInFrastructure 38 TWICE algorithm  Decompressor can detect loss of synchronization by using TCP checksum  Motivation: totally lossless HC is not possible, make an educated guess  If inconsistency is due to a single lost segment + lost segment increments the compression state in the same way   Apply TWICE the delta of a current segment

Center for TeleInFrastructure 39 Compressed RTP (CRTP)  Compressed RTP (RFC 2508)  Compresses 40 byte header to 4 or 2 bytes  First-order changes Expected changes in the fields that can be predicted, no transmission of differences needed  Second-order changes Changes that have to be compressed  Enhanced Compressed RTP (RFC 3545)  Refinement of CRTP in presence of packet loss, reordering and long delays  Local retransmissions and repeated context updates are used

Center for TeleInFrastructure 40 Robusr Checksum-based Compression (ROCCO)  Refinement of CRTP  Includes checksum over uncompressed header  facilitation of local recovery of the synchronization  Targeted to cellular usage

Center for TeleInFrastructure 41 Robust Header Compression  RTP/UDP/IP  UDP/IP  IP  uncompressed

Center for TeleInFrastructure 42 ROHC Modes

Center for TeleInFrastructure 43 States of Compressor and Decompressor

Center for TeleInFrastructure 44 Unidirectional

Center for TeleInFrastructure 45 Optimistic

Center for TeleInFrastructure 46 Reliable

Center for TeleInFrastructure 47 Decompressor

Activities in the field of header compression

Center for TeleInFrastructure 49 ROHC working group RFC 3095 ROHC (Framework + RTP. UDP, ESP, uncompressed) RFC 3242: LLA profile - ”0 byte” RFC 3408: 0-byte for R-mode RFC 3241: ROHC over PPP RFC 3816: ROHC MIB RFC 3843: ROHC for IP RFC 3220: SigComp

Center for TeleInFrastructure 50 Link-layer Assisted ROCH (0-byte)  Purpose is to efficiently match existing applications to existing link technologies  Air interfaces, as GSM and IS-95, will be used in all-IP networks, but their radio bearers are optimized for specific payload size.  Adding even 1 byte of ROCH header is costly  Header-free packet format

Center for TeleInFrastructure 51 LLA ROCH  Lower layers provide the necessary information  Care should be taken of  Packet type identifier  Sequence number  CRC 1 byte Smallest header in ROCH RTP Smallest header in LLA NHP (No Header Packet) Header field functionality provided by other means

Center for TeleInFrastructure 52 LLA ROCH  Zero-byte operation for U/O modes (RFC 3242)  Zero-byte operation for R-mode (RFC 3408)  Periodic context verification is performed  CSP (Context Synchronization Packet) contains only header information, no payload

Center for TeleInFrastructure 53 Interfaces towards the Assisting Layer ROCH RTP LLA profile Interface ROCH to AL Link technology ROCH RTP LLA profile Interface ROCH to AL Link technology channel

Center for TeleInFrastructure 54 Signaling Compression (SigComp)  Motivation  3GPP R5 introduces IP Multimedia subsystem (IMS) that uses Session Initiation Protocol (SIP) for call signaling and session setup  SIP is text-based. SIP message is from a few hundreds bytes up to two thousand bytes. On average 500 bytes  For cellular networks large message size is problematic  introduce delays  Compression of signaling messages is desirable

Center for TeleInFrastructure 55 Signaling Compression (SigComp)  SigComp RFC 3320  Requirements for Signaling Compression  Efficient compression 1:8 – 1:15  Compress any text based protocol  For bidirectional application protocol, the choice to use SigComp is independent in both directions  Transport independent

Center for TeleInFrastructure 56 SigComp Architecture Local application Transport layer Compressor dispatcher Compressor dispatcher Decompressor dispatcher Decompressor dispatcher Compressor 1 Compressor 2 State handler State 1 State 2 Decompressor (UDVM) Decompressor (UDVM) SigComp layer SigComp message SigComp message Application message and Compartment identifier Compartment identifier Decompressed message

Tools

Center for TeleInFrastructure 58 Tools  NetMeter  AudioMeter  VideoMeter

Center for TeleInFrastructure 59 Netmeter Tool Bandwidth w/o ROHC Bandwidth with ROHC Header compression Overall compression

Center for TeleInFrastructure 60 VideoMeter Tool  PSNR calculation is standard metric for objective video quality measurements  Freezing for lost frames  VideoMeter tool for visualization

Center for TeleInFrastructure 61 ROHC testbed

Center for TeleInFrastructure 62 Metrics  Peak Signal to Noise Ratio (PSNR) for quality comparison

Center for TeleInFrastructure 63 VideoMeter Setup

Voice Quality Evaluation for Wireless Transmission with ROHC S. Rein and F.H.P. Fitzek and M. Reisslein Voice Quality Evaluation for Wireless Transmission with ROHC in International Conference on Internet and Multimedia Systems and Applications (IMSA 2003), pages Honolulu, USA.

Center for TeleInFrastructure 65 GSM Encoder RTP UDP IP ROHC link GSM Decoder RTP UDP IP ROHC link IPRTPGSMUDP ROHCGSM Original voiceTransmitted voice Communication System UMTS link error simulation Protocol suite with ROHC

Center for TeleInFrastructure 66 Methodology for ROHC evaluation Communication System with ROHC Communication System without ROHC Original speechDistorted speech Predict ROHC speech quality Predict speech quality Calculate gain for ROHC

Center for TeleInFrastructure 67 Voice quality evaluation framework  Usually expensive software required (state of the art PESQ software available for U.S.$)  Alternative methodology: used a set of elementary objective metrics to predict the subjective voice quality  Metrics represent sensible engineering trade off to networking studies  Performance of the metrics is usually verified by a correlation analysis

Center for TeleInFrastructure 68 Voice quality metrics: Correlations to subjective quality Segmental SNR0.77 Inverse linear spectral distance0.63 Delta form spectral distance0.61 Log area ratio0.62 Energy ratio0.59 Log likelihood0.49 Cepstral distance0.93 Why use an array of metrics for predicting the subjective voice quality?

Center for TeleInFrastructure 69  Every metric covers different distortion types  Coding and noise distortions in the time and frequency domain  Good reliability by including metrics verified by different authors

Center for TeleInFrastructure 70  Varying delay with IP packet voice  Reference and transmitted voice file have to be synchronized  Developed segmental cross correlation (SCC) algorithm in the time domain  SCC makes elementary metrics usable for modern communication systems

Center for TeleInFrastructure 71 missing samples wrongly inserted Segmental Synchronization

Center for TeleInFrastructure 72 Results: Delay jitter measurements

Center for TeleInFrastructure 73 Results: SNR measurements

Center for TeleInFrastructure 74 Results: voice quality

Center for TeleInFrastructure 75 Results: voice quality

Center for TeleInFrastructure 76 Results: Mean Opinion Score

Center for TeleInFrastructure 77  On top of bandwidth savings: Voice quality is improved  ROHC roughly cuts bandwidth for voice transmission in half  ROHC is a very useful complement to third generation mobile systems

Video Quality Evaluation for Wireless Transmission with Robust Header Compression P. Seeling and M. Reisslein and F.H.P. Fitzek and S. Hendrata Fourth International Conference on Information, Communications & Signal Processing Fourth IEEE Pacific-Rim Conference On Multimedia December 2003, Meritus Mandarin Hotel, Singapore

Center for TeleInFrastructure 79  Video services over wireless networks are gaining more and more interest  Services are needed that convince customers to buy new equipment (3GPP)  3GPP networks support video services such as the IMS and the MBMS entities  Problem: Video services need much more bandwidth than voice calls, which makes them hard to sell Video services

Center for TeleInFrastructure 80 Serving Sara (560x304 pixels)

Center for TeleInFrastructure 81 Motivation  Video services are transmitted over IP networks using the RTP/UDP/IP protocols  Video is encoded efficiently, but the protocol stack overhead is not  The protocol overhead comprises a large portion of the traffic (even more for small video formats as for the mobile phones)  Therefore: Compression of the protocol overhead needed

Center for TeleInFrastructure 82 Methodology  Uncorrelated bit errors as recently found for UMTS channels  Simulated with and without ROHC implementation  O-Mode

Center for TeleInFrastructure 83 ROHC Results

Center for TeleInFrastructure 84 Insights  Protocol header compression can be achieved by using ROHC  Higher compression ratios for smaller video formats and higher quantization  Lower fraction of packets comprised of actual video data (i.e., payload)  Lower error probability and state changes within ROHC

Center for TeleInFrastructure 85 ROHC Results

Center for TeleInFrastructure 86  ROHC is an efficient header compression scheme for multimedia in wireless environments  Compression achieved depends on video format and video content  Utilization of ROHC for multimedia streaming does not introduce additional losses in terms of perceived video quality (PSNR)

Cooperative Header Compression F.H.P. Fitzek and T. K. Madsen and P. Popovski and R. Prasad and M. Katz. Cooperative IP Header Compression for Parallel Channels in Wireless Meshed Networks. In IEEE International Conference on Communication (ICC). 2005

Center for TeleInFrastructure 88 Scenario: multiple channels between terminal and cellular network

Center for TeleInFrastructure 89 HC Approach Single Channel

Center for TeleInFrastructure 90 HC Approach Multiple Channels

Center for TeleInFrastructure 91 HC Approach Multiple channels with channel errors

Center for TeleInFrastructure 92 More Robust HC Approach by Exploiting Multiple Channels

Center for TeleInFrastructure 93 HC Approach: Possible Implementation

Center for TeleInFrastructure 94 Error healing

Center for TeleInFrastructure 95 AICs construction for three cooperative channels

Center for TeleInFrastructure 96 Packet Error Probability vs Channel Error Probability

Center for TeleInFrastructure 97 Efficiency vs Channel Error Probability

Center for TeleInFrastructure 98

Center for TeleInFrastructure 99 Cooperative HC  Advantageous of the proposed scheme  Exploit cooperative behavior of parallel channels  Bandwidth efficiency  Low memory consumption and low complexity  Robustness  No need for feedback channel (can be used for multicasting)  Only a small number of cooperative channels are needed to perform efficiently  Analogy: FEC

Why HC should be applied!

Center for TeleInFrastructure 101 Network Provider’s view  Increased quality of service for the user  Delay (web pages, download)  Bandwidth  Cost (?)  Capacity  Installed cells can support more users  $  Cells that will be installed with larger coverage, which results  $

Center for TeleInFrastructure 102 Network Capacity  How can a network provider calculate its potential saving?  A very simplified view  Thumb rule

Center for TeleInFrastructure 103 Notation  P = mean payload size  H_u = uncompressed header  H_c = compressed header  RR = Ratio = no. of users with HC / total number of users.  G: Capacity gain. Capacity gain can be defined e.g. how much more users in percent we can serve if some of them will activate HC (total number of users with HC activated / total number of users without header compression)

Center for TeleInFrastructure 104 Equation

Center for TeleInFrastructure 105 Some examples

Center for TeleInFrastructure 106 Some examples

Center for TeleInFrastructure 107 Some examples

Center for TeleInFrastructure 108 Some examples

Center for TeleInFrastructure 109 Some examples

Center for TeleInFrastructure 110 Some examples

Reference List

Center for TeleInFrastructure 112 Reference List  F.H.P. Fitzek, S. Hendrata, P. Seeling and M. Reisslein. Chapter in Wireless Internet -- Header Compression Schemes for Wireless Internet Access. CRC Press  V. Jacobson, Compressing TCP/IP headers for low-speed serial links, RFC 1144, February  M. Degermark, B. Nordgren and S. Pink, IP header compression, RFC 2507, February  S. J. Perkins and M. W. Mutka, Dependency Removal for Transport Protocol Header Compression over Noisy Channels. In Proc. of IEEE International Conference on Communications, Canada, June 1997, pp  M. Degermak, M. Engan, B. Nordgren, and S. Pink, Low-loss TCP/IP header compression for wireless networks. In Proceedings of ACM MobiCom’96. October 1997, pp

Center for TeleInFrastructure 113 Reference List  C. Perkins and J. Crowcroft, Effect of interleaving on RTP header compression, in Proceedings of IEEE Infocom 2000, Tel Aviv, Israel, 2000, pp  K. Svanbro, H. Hannu, L.-E. Jonsson, and M. Degermark, Wireless real- time IP services enabled by header compression, in Proceedings of the IEEE Vehicular Technology Conference (VTC), Tokyo, Japan, 2000, pp  C. Bormann, C. Burmeister, M. Degermark, H. Fukushima, H. Hannu, L.-E. Jonsson, R. Hakenberg, T. Koren, K. Le, Z. Liu, A. Martensson, A. Miyazaki, K. Svanbro, T. Wiebke, T. Yoshimura, and H. Zheng, Robust Header Compression (ROCH): Framework and four profiles: RTP, UDP, ESP, and uncompressed, RFC 3095, Tech. Rep., July 2001.

Center for TeleInFrastructure 114 Reference List  L-E. Jonsson and G. Pelletier, ROCH: A Link-Layer Assisted Profile for for IP/UDP/RTP, RFC 3242, Tech. Rep., April  R. Price, C. Bormann, J. Christoffersson, H. Hannu, Z. Liu, and J. Rosenberg, Signaling Compression (SigComp), RFC 3320, Tech. Rep., January  T. Koren, S. Casner, J. Geevarghese, B. Thompson and P. Ruddy, Enchanced Compressed RTP for Links with High Delay, Packet Loss and Reodering, RFC 3545, Tech. Rep., July 2003.

Center for TeleInFrastructure 115 Reference List  F.H.P. Fitzek and T. K. Madsen and P. Popovski and R. Prasad and M. Katz. Cooperative IP Header Compression for Parallel Channels in Wireless Meshed Networks in IEEE International Conference on Communication (ICC).  P. Seeling and M. Reisslein and F.H.P. Fitzek and S. Hendrata. Video Quality Evaluation for Wireless Transmisison with Robust Header Compression in Proceedings of the IEEE Fourth International Conference on Information, Communications & Signal Processing and Fourth IEEE Pacific-Rim Conference On Multimedia (ICICS-PCM 03), pages Singapore.  S. Rein and F.H.P. Fitzek and M. Reisslein. Voice Quality Evaluation for Wireless Transmission with ROHC in International Conference on Internet and Multimedia Systems and Applications (IMSA 2003), pages Honolulu, USA.