Robust Header Compression (RoHC) over Multiprotocol Label Switching (MPLS) Networks

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1 Computer Science Mohammad Ahsan Chishti / Shaima Quershi / Ajaz Hussain Mir Robust Header Compression (RoHC) over Multiprotocol Label Switching (MPLS) Networks

3 Bibliographic information published by the German National Library: The German National Library lists this publication in the National Bibliography; detailed bibliographic data are available on the Internet at This book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorized distribution or use of this text may be a direct infringement of the author s and publisher s rights and those responsible may be liable in law accordingly. Imprint: Copyright 2016 GRIN Verlag, Open Publishing GmbH ISBN: This book at GRIN:

4 Mohammad Ahsan Chishti, Shaima Quershi, Ajaz Hussain Mir Robust Header Compression (RoHC) over Multiprotocol Label Switching (MPLS) Networks GRIN Publishing

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6 Robust Header Compression (RoHC) over Multiprotocol Label Switching (MPLS) Networks by: Mohammad Ahsan Chishti Shaima Qureshi Ajaz Hussain Mir i

7 Abstract Due to the rapid evolution of Internet as well as services over the Internet, including high bandwidth consuming applications like audio and video streaming, it has become need of the day to enhance the Internet infrastructure for bandwidth efficiency. One of the present day biggest challenges of networks is the audio/video transmission in real time. Developed by the Internet Engineering Task Force, Multiprotocol label Switching (MPLS) allows networks to offer several services on the single network architecture with improved forwarding speed of routers by solving the problem of longest prefix match in IP networks. Internet Protocol datagram encapsulates payload received from above layer and adds to its own header information. Thus each protocol layer adds its own header with the information related to the layer. This is a disadvantage of a bigger packet header size such as IPv4/UDP/RTP header of 40 bytes compared to the payload size which leads to excessive overhead in case of real-time multimedia applications. Bandwidth can be conserved by reducing the amount of redundant IP header transmitted with every packet for the same packet stream through header compression techniques. The header compression mechanisms have several short comings such as a problem that they work on hop-by-hop basis. The packet is compressed by the compressor and decompressed by the decompressor and for header compression to work; these are connected directly not through any intermediate node, not even a layer 3 device such as a router. In addition to this, there is a limit in the number of compressed flows that a router can take. The objective of this book is to propose header compression technology which can be implemented over MPLS and used as a bandwidth conserving technology. This will solve the problems of hop-byhop compression/decompression as the compression of packets is not hop-by-hop rather the compression is per Label Switched Path (LSP) of MPLS network from ingress to egress Label Switched Routers. This will also handle packet reordering in addition to allowing numerous flows at the same time. The current work in the area, both standardized as well as ongoing research has been discussed in detail. This approach also increases the bandwidth efficiency as well as processing scalability with respect to the maximum number of simultaneous flows. ii

8 Table of Contents 1.1 Introduction Motivation ROHC over MPLS Background Multi Protocol Label Switching (MPLS) Header Compression Header Compression Techniques Van Jacobson Header Compression (VJHC) Space Communication Protocol Specification (SCPS) Internet Protocol Header Compression (IPHC) RTP Header Compression Extended Compressed Real Time Protocol (ECRTP) Robust Header Compression (ROHC) Header Compression over MPLS RObust Header Compression (ROHC) Analysis of Protocol Headers IP Header Fields UDP Header Fields RTP header fields Complete IPv4/UDP/RTP Header Functional Analysis of ROHC Compressor and decompressor finite state machines Compressor states Decompressor states Modes of Operation Unidirectional Mode (U-mode) Compressor states and logic (U-mode) Decompressor states and logic (U-mode) Bidirectional Optimistic (O-mode) Compressor states and logic (O-mode) iii

9 Decompressor states and logic (O-mode) Bidirectional Reliable mode (R-mode) Compressor states and logic (R-mode) Decompressor states and logic (R-mode) Mode Transitions Data structures, Parameters and Profiles Per-channel parameters Per-context parameters ROHC Profiles Encoding Methods Least Significant Bits (LSB) Encoding Window-based LSB (WLSB) Encoding Scaled RTP Timestamp Encoding Timer-based RTP Timestamp Encoding IPv4 Identifier (IP-ID) Offset Encoding Chapter Conclusion Robust Header Compression over MPLS Flow Chart for Compressor and Decompressor MPLS Pseudo Wires MPLS Header Compression Pseudowire Setup, Negotiation and Signaling Packet Reordering References iv

10 1.1 Introduction The basis of Internet at the beginning was to have interconnection between different universities, however it lead to a paradigm change and evolved into interconnection of Government organizations, business institutions, academics etc. Present day Internet has seen a rapid increase in data which is mostly multimedia (Audio/Video) in nature and thus putting a great pressure on the available bandwidth [1]. This type of traffic requires good bandwidth with minimum delays and negligible network congestion [2]. The major resource of a channel is its bandwidth and multimedia streaming can tolerate packet loss to some extent but timely and orderly delivery is very important in transmission of audio/video streams. Services like voice over IP (VoIP) will drive the future of communication which is being deployed over the packet switched networks. However, the most common issue faced by users is not having enough bandwidth to support the channel which results in coherent delays in the data network by which the audio/video quality over the internet is affected badly [3]. Also, the multimedia streams face another issue over the internet that is of packet reordering [4]. Since the packet switched networks break the information into packets and then these packets are transmitted, it can happen that each packet takes a separate route to the destination from the source resulting in the additional delay in reaching the receiver. The receiver ignores this packet as it has already received the packet which is next in sequence, thereby causing poor audio and video quality. In addition to this, to provide better Quality of Service to the users, the network has to provide minimum error rates [5]. Defined in RFC 791, Internet Protocol (IP) [6] is the routing layer datagram service of the TCP/IP (Transmission Control Protocol/Internet Protocol) suite. TCP/IP is the basic protocol of the Internet of which IP is one of the constituent. TCP is involved in assembling and reorder of packets in addition to the connection oriented service on the internet using the client server model over internet. The TCP/IP protocol suite helps nodes in communication over Internet by defining the protocols of how the data is to be packaged, addressed, routed and distributed to the exact destination [7]. Internet started using Internet Protocol version 4 (IPv4) which is a 32 bit IP addressing schema. Apart from addressing, IP handles the routing as well as error detection. It is a 1

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