Chapter 1 Introduction to Internetworking (Recommended reading: Comer, Vol 1, Chapters 1, 3)

1. Chapter 1Introduction to Internetworking(Recommended reading: Comer, Vol 1, Chapters 1, 3) • Motivation for Internetworking • What is internetworking? • Connect multiple networks of one or more organizations into a large, uniform communication system. • The resulting system is called an internetwork or internet. • notion of an unified internet • Why internetworking? • There are many existing networks located at different places. It is desirable to connect them together for global communication and information exchange. • In the future, there will still be multiple types of networks, because no single network technology can fulfill all the needs. It is necessary to connect them for communication. • E.g, multinational companies have high speed optical connections, whereas some other companies located in older buildings still use traditional thin-wire or twisted pair Ethernet connections. Dr. Y.W. Leung

2. User’s point of view: a set of application programs that use the underlying network to carry out useful communication tasks, e.g., World Wide Web, email, ftp, remote login. • Interoperability: the above applications can run on different types of computers. • Different networks may not be compatible. Internetworking requires: • additional hardware to interconnect the networks, • additional software on all the attached computers to execute a common set of internetworking protocols to ensure that these computers can communicate. • One vendor’s email program may talk to another vendor’s email program. • Internet Architecture • Different networks may use different technology and methodology. • different transmission media, addressing scheme, packet format, and etc. • No single network hardware can satisfy all constraints of different users/networks. • Physically, two networks can only be connected by a computer that attaches to both of them. Dr. Y.W. Leung

3. Routers (or gateways) are used to connect the heterogeneous networks. • A router is a special-purpose computer having processor, memory, and I/O interface. • A router performs protocol conversion in order to transmit packets between different networks. Example: • The router captures packets from Net1 that are destined for Net2, and transfers them. • In practice, each router needs to know about the topology of the internet beyond the networks to which it connects. Dr. Y.W. Leung

4. Different routers can connect different number and different types of networks. Example: • An internet consists of a set of networks interconnected by routers. • Each intermediate network must agree to handle transit traffic in exchange for the right to send traffic throughout the internet. • Internetworking Protocols • In an internet, all the computers and routers must agree on acommon set of internetworking protocols. • Even if these computers and routers are attached to different networks, they can still communicate. Dr. Y.W. Leung

5. What is a protocol? • A set of syntactic and semantic rules for communication. • details of message formats • How a computer should respond when a message arrives. • How a computer handles errors or other abnormal conditions. • Independent of lower layers or hardware • The protocols should be transparent, hiding the details of each network and the interconnection of these networks. • The users and application programmers are not required to know these details. They see the internet as a single, large network. • Users' view on the internet: Dr. Y.W. Leung

6. Actual view: • TCP/IP is the most widely used internetworking protocol suite. • TCP: Transmission Control Protocol. • IP: Internet Protocol. • TCP/IP is now the defacto standard for internetworking protocols. • TCP/IP reference model: • Network Access Layer: Specify the protocols being used in the underlying networks. Dr. Y.W. Leung

7. TCP/IP reference model (cont.) • Internet Layer: Define a common packet format and the internet protocol for packet delivery. • Transport Layer: Define transport protocols (transmission control protocol (TCP) for connection-oriented transport, and user datagram protocol (UDP) for connectionless transport). • Application Layer: Define application protocols such as file transfer (FTP), email (SMTP), and virtual terminal (TELNET). • Possible protocols in each layer of the TCP/IP reference model: Dr. Y.W. Leung

8. TCP/IP reference model versus the OSI model: • Epilogue • “Internet" or "internetwork" is composed of a collection of interconnected networks. • "Internet" is the single global internet that operates under the TCP/IP protocols. • "Intranet" is a private internetwork owned by an organization. It may be connected to the Internet through firewalls (we shall study firewalls later). Dr. Y.W. Leung

9. Tutorial Problems • How would your study be affected if there were no Internet? • List some networks that you have learnt from COMP 2330. • There are many different types of networks. Why? • A student argues that it is better to have only one type of networks because this can avoid the overhead of protocol conversion in internetworking. Do you agree? • What are the major functions of a router? • Many routers are available in the market and they have different prices. What factors would determine the price of a router? • If a router can connect to at most K networks, how many routers are required to connect N networks? Dr. Y.W. Leung