Chapter 3 Internetwork Layers Networking in the Internet Age by Alan Dennis 1st Edition Copyright 2002 John Wiley Sons Inc 1 Copyright John Wiley Sons Inc All rights reserved Reproduction or translation of this work beyond that named in Section 117 of the United States Copyright Act without the express written consent of the copyright owner is unlawful Requests for further information should be addressed to the Permissions Department John Wiley Sons Inc Adopters of the textbook are granted permission to make back up copies for their own use only to make copies for distribution to students of the course the textbook is used in and to modify this material to best suit their instructional needs Under no circumstances can copies be made for resale The Publisher assumes no responsibility for errors omissions or damages caused by the use of these programs or from the use of the information contained herein 2 Chapter 3 Learning Objectives Be aware of four transport network layer protocols Be familiar with segmenting and linking to the application layer Be familiar with reliable delivery Be familiar with addressing Be familiar with routing Understand how TCP IP works 3 Chapter 3 Outline Introduction Internetwork Protocols TCP IP IPX SPX X 25 Systems Network Architecture Transport Layer Functions Linking to the Application Layer Packetizing Addressing Assigning Addresses Address Resolution Routing Types of Routing Routing Protocols Multicasting TCP IP Example Known Addresses Same Subnet Known Addresses Different Subnet Unknown Addresses TCP Connections 4 Introduction 5 Introduction The Network and Transport Layers The transport layer is responsible for end to end delivery of messages The transport layer sets up virtual circuits when needed and is also responsible for segmentation breaking the message into several smaller pieces at the sending end and reassembly reconstructing the original message into a single whole at the receiving end The network layer is responsible for addressing and routing of the message The network and transport layers also perform encapsulation of message segments from the application layer passing them down to the data link layer on the sending end and passing them up to the application layer on the receiving end see Figure 3 1 6 Figure 3 1 Message transmission using layers 7 Internetwork Protocols 8 Transport and Network Layer Protocols Currently the most commonly used protocol suites are TCP IP IPX SPX X 25 SNA 9 Transmission Control Protocol Internet Protocol TCP IP TCP IP was created in 1974 by Vint Cerf and Bob Kahn as part of Arpanet a U S Department of Defense networking research project Arpanet has since evolved into the Internet making TCP IP the protocol suite used by the Internet Almost 70 of all backbone metropolitan and wide area networks use TCP IP In 1998 TCP IP surpassed IPX SPX to become the most common protocol on local area networks 10 Transmission Control Protocol 3 2 TCP performs packetization segmentation that is breaking up the message into smaller pieces numbering the segments and reassembling them at the destination end of the transmission TCP also ensures that the segments are reliably delivered TCP segments have a 192 bit 24 byte header Header fields include source and destination port identifiers and a packet sequence number used in message reassembly 11 Figure 3 2 Transmission Control Protocol packet 12 Internet Protocol Figures 3 3 and 3 4 IP is responsible for addressing and routing of data packets Two versions in current in use IPv4 IPv6 IPv4 uses a 160 bit 20 byte header and 32 bit addresses IPv6 was mainly developed to increase IP address space due to the huge growth in Internet usage during the 1990s IPv6 uses a 320 bit 40 byte header and 128 bit addresses Header fields include source and destination addresses packet length and packet number 13 Figure 3 3 Internet Protocol packet version 4 Figure 3 4 Internet Protocol packet version 6 14 Internetwork Packet Exchange Sequenced Packet Exchange IPX SPX IPX SPX was developed by Xerox during the 1970s IPX SPX today is mainly used by Novell networks Novell has since replaced it with TCP IP however Similar to TCP IP SPX performs transport layer functions packetization packet numbering ensuring reliable delivery and packet reassembly IPX performs network layer functions addressing and routing 15 X 25 X 25 was developed by ITU T for use in wide area networks Seldom used in North America but has been widely used in other parts of the world especially in Europe X 25 transport layer protocol called X 3 performs packetization Packet Layer Protocol PLP is the network layer protocol It performs routing and addressing LAP B is usually used as the data link layer protocol ITU recommends packet size of 128 bytes but X 25 can support packet sizes up to 1024 bytes 16 Systems Network Architecture SNA SNA was developed by IBM in 1974 and used on IBM and IBM compatible mainframes such as Amdahl mainframes Based on non standard proprietary protocols so it is difficult to integrate with non SNA networks Routing messages between SNA and non SNA networks require special equipment gateways IBM now offers TCP IP on its networks so SNA will likely disappear over time 17 Transport Layer Functions 18 Linking to the Application Layer An important transport layer job is knowing which application layer program to send a message to This is done using source and destination port numbers located in the first two TCP header fields Applications sending outgoing messages give TCP both port numbers Incoming messages also provide port numbers Port addresses are 2 bytes long Usually standard port numbers are used Web servers use port number 80 FTP servers use port number 21 Telnet port number 23 SMTP uses port 25 Nonstandard port numbers are also possible but TCP must be specially configured to use them 19 Segmenting The application layer sees a message as a single block or stream of data Another transport layer job is breaking large messages into smaller pieces segmentation and putting them back together at the destination reassembly The transport layer also decides whether to deliver incoming packets as they arrive as with Web pages or to wait until the entire message arrives as with e mail 20 Transmission Efficiency Fig 3 5 Each communications protocol has both information bytes and overhead bytes Information bytes convey the user s meaning such as the URL of a Web page Overhead bytes carry control data such as the