1. CS448 Computer Networking Chapter 1 Introduction to Computer Networks Instructor: Li Ma Office: NBC 126 Phone: (713) 313-7028 Email: malx@tsu.edumalx@tsu.edu Webpage: http://itscience.tsu.edu/ma Department of Computer Science Texas Southern University, Houston September, 2005

2. Fall 2005by Li Ma, TSU - CS448 What is Internet? – Components End systems or Hosts –PC, workstation, laptop, cell phone, PDA, security system, etc. Communication links –Coaxial cable, copper wire, fiber optics, radio spectrum, etc. Packet switches –Routers – network-layer –Switches – link-layer

3. Fall 2005by Li Ma, TSU - CS448 What is Internet? – Physical media Route or path –The sequence of communication links and packet switches traversed by a packet through the network Packet switching –Allow multiple communicating end systems to share a path, or part of a path, at the same time End systems access Internet through Internet Service Providers (ISPs) –Local telephone/cable company

4. Fall 2005by Li Ma, TSU - CS448 What is Internet? – Protocols Protocols control the sending and receiving of information within the Internet –Transmission Control Protocol (TCP) deals with loss and delay of packet transmission –The IP protocol specifies the format of the packet Internet standards is developed by Internet Engineering Task Force (IETF) –Requests for comments (RFCs) defines the standards

5. Fall 2005by Li Ma, TSU - CS448 What is Internet? – service description Internet allows distributed applications running on its end systems to exchange data –Web surfing, instant message, email, etc. Two kinds of services –Connection-oriented reliable service – Transmission Control Protocol –Connectionless unreliable service – User Datagram Protocol

6. Fall 2005by Li Ma, TSU - CS448 What is Internet? – protocol A protocol defines the format and order of messages exchanged between communication entities, and the actions taken upon transmission and/or receipt of a message –An analogy: how to start to ask for time

7. Fall 2005by Li Ma, TSU - CS448 Clients and Servers End systems are also referred to as hosts –Clients: user’s machines for applications –Servers: more power machines that store and distribute applications A client program is a program running on one host that requests and receives service from a server program running on another host – distributed applications

8. Fall 2005by Li Ma, TSU - CS448 TCP and UDP Connection-oriented service – TCP –Connection is established by three-way handshaking –Reliable data transfer, flow control, congestion control Connectionless service – UDP –No handshaking procedure –Data can be delivered sooner

9. Fall 2005by Li Ma, TSU - CS448 Network Core – Switching Strategies Circuit switching –dedicated circuit: resources are reserved –send/receive a bit stream –FDM/TDM: wasteful –the ubiquitous telephone networks Packet switching –store-and-forward: resources are used on demand –queuing delay, packet loss –send/receive messages (packets) –today’s Internet

10. Fall 2005by Li Ma, TSU - CS448 Virtual Circuit Networks Typically wait full RTT for connection setup before sending first data packet While the connection request contains the full address for destination, each data packet contains only a small identifier, making the per-packet header overhead small If a switch or a link in a connection fails, the connection is broken and a new one needs to be established Connection setup provides an opportunity to reserve resources

11. Fall 2005by Li Ma, TSU - CS448 Datagram Networks There is no round trip time delay waiting for connection setup; a host can send data as soon as it is ready Source host has no way of knowing if the network is capable of delivering a packet or if the destination host is even up Since packets are treated independently, it is possible to route around link and node failures Since every packet must carry the full address of the destination, the overhead per packet is higher than for the connection-oriented model