CS448 Computer Networking

Chapter 1 Introduction to Computer Networks

Instructor: Li Ma

Office: NBC 126Phone: (713) 313-7028Email: malx@tsu.edu

Webpage: http://itscience.tsu.edu/ma

Department of Computer ScienceTexas Southern University, Houston

September, 2005

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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

Fall 2005 by 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