Transcript Lecture 1 - Department Of Computer Science

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