COMP361 by M. Hamdi1 COMP 361, Fall 2000 Computer Communication Networks I Dr. Mounir Hamdi [email protected]

COMP361 by M. Hamdi 1

COMP 361, Fall 2000

Computer Communication Networks IDr. Mounir [email protected]


How Important is COMP 361?

• Computer Networking is the backbone of the information technology

• Information technology is having and will be having a tremendous impact on our social lives, the economy, and the way we work

• The knowledge of this class, COOMP 361, is a key factor to be an active and productive member of the information technology


You Will Learn

• Networking Terminology• Communication basics

– Media and signals– Data transmission characteristics

• asynchronous and synchronous communication

• serial and parallel transmission• bandwidth, throughput and noise• multiplexing


You Will Learn [continued]

• Networking and Network Technologies– Packet Switching, Circuit/virtual Switching– Protocols and Layering– Network Addressing– Interconnection (bridges, switches,

routers)– Local Area Networks (star, ring, bus, mesh)– Routing– Flow, Error and Congestion Control– State-of-the-art in networks


You Will Learn [continued]

• Applications and Network Services– Network Programming– Client-server communications– Hierarchical naming (DNS)– File transfer (FTP)– Remote login (TELNET)– Email (SMTP, POP, IMAP)– Web technologies (HTTP, HTML, Java)– Network Security


I’ll Do My Part

• Help you learn and enjoy the course

• Answer email promptly

• Be fair and impartial

• Encourage discussion and questions


You Do Your Part

• Have the drive to learn and work hard• Be present and attentive• Don’t wait until the last minute• Contribute in discussions• Ask questions


Grading

• Homework/Quiz 20%

– 2 homeworks and 2 quizes (best 3 out 4)

• Midterm Exam 25%

• Final Exam 30%

• Labs programming/project 25%


Tentative Schedule - Lecture

• Week 1: Introduction

• Week 2: Physical Layer

• Week 3-4: Data Link Layer

• Week 5-7: Local Area Networks

• Midterm Exam

• Week 8-10: Network Layer

• Week 11: Transport Layer

• Week 12: Application Layer

• Week 13-14: State-of-the-art in Networking


Tentative Schedule - Lab

• Week 1: No lab

• Week 2: General Introduction

• Week 3: Introduction to Network Application Programming Interface (API)

• Week 4: Introduction to Socket Programming

• Week 5-6: Example Application of Socket programming

• Week 7: Advanced Concepts of Socket Programming

• Week 8-12: More Advanced Concepts of Socket Programming and the start of a more advanced network programming project

• Week 13: Presentation/Demonstration of Projects


Lecture/Lab Time/Venue

• Lecture: T-Th: 9:00 - 10:20 LTE

• Labs: 1A - Wed: 9 - 9:50 Lab: 4214 1B - Wed: 10 - 10:50 Lab: 4214


FAQ for this Class

• Grade depends on the rest of the class (there is a curve)

• Late homework must be pre-approved

• No copying on homework/labs please

• Midterm/final sample exam will be available one week prior

• Watch course home page for latest material and announcement


How to Contact Us

• Instructor: Mounir Hamdi [email protected]

• Office Hours– Mondays 10:00 - 12:00 p.m.– Wednesdays: 11:00 - 12:00 p.m.– ...and by appointment


How to Contact Us

• Lab TA: Pun Kong Hong - [email protected]

• Course TA: Zhang Lei - [email protected]

• Office Hours

– To be given later


Textbook

• Andrew Tanenbaum, “Computer Networks” Prentice Hall, 1996, ISBN: 0-13-349945-6

• W. R. Stevens, UNIX Network Programming Vol. 1,

2nd ed., Prentice-Hall, 1998.• See course home page for other recommended texts

– Computer Networks - Peterson and Davie– Computer Networks and Internets - Comer– An Engineering Approach to Computer Networks - Keshav– TCP/IP Illustrated - Stevens– Interconnections - Perlman– Internetworking with TCP/IP - Comer– Data and Computer Communications - Stallings– Routing in the Internet - Huitema


Who Am I?

• Associate Prof. Of Computer Science and Co-Director of Computer Engineering– Have been at HKUST since 1991– Spent last year at Stanford University

• Current interests: High-Speed Switching and Routing, Optical Networks, Network Management, Quality-of-Nervice Networking, Network Application (VoIP and Video Conferencing)


Who Are You?

• Computer Engineers/Scientist

– You’re very familiar with computers and the Internet

– Very interested in networking

– Eager to learn new things

• What else?


Introduction


Communication Networks

• Problem: Given a set of devices that want to exchange information. (Device = telephone, computer, terminals, etc.)

• Simple Solution: Connect each pair of devices by a dedicated point-to-point link



• The simple solution is sufficient if the number of devices is small.

• With large number of devices it is not practical to connect each pair of devices.



• A communication network provides a general solution to the problem of connecting many devices:– Connect each device to a network node– Network nodes exchange information and carry

the information from a source device to a destination device

– Note: Network nodes do not generate information



• A generic communication network:

Other names for Device: station, host, terminalOther names for Node: switch, router, gateway




HKUST Campus Network


Classification of Communications

• Communication networks can be classified based on the way in which the nodes exchange information:

• Communication Network– Switched Communication Network

• Circuit-Switched Communication Network• Packet-Switched Communication Network

– Datagram Network– Virtual Circuit Network

– Broadcast Communication Network


Broadcast Communication Networks

• Broadcast Communication Networks do not have intermediate switching nodes:– Each station has a

transmitter/receiver that communicates over a medium shared by other stations

– Transmission from any station is received by all other stations


Broadcast Network Examples

Packet RadioNetwork

SatelliteNetwork

Bus LocalNetwork


Switched Communication Network

• A switched communication network consists of an interconnected collection of nodes. Data are transmitted from source to destination by being routed through the nodes

• The switching method describes how data are processed and routed in the network

• The basic switching methods are:– Circuit Switching– Packet Switching

• Datagram Packet Switching• Virtual-Circuit Packet Switching


Circuit Switching

• In a circuit-switched network, a dedicated communication path is established between two stations through the nodes of the network

• The dedicated path is called a circuit-switched connection or circuit

• A circuit occupies a fixed capacity of each link for the entire lifetime of the connection. Capacity unused by the circuit cannot be used by other circuits

• Data is not delayed at the switches Circuit Switching


Circuit Switching

• Circuit-switched communication involves three phases:– 1. Circuit Establishment– 2. Data Transfer– 3. Circuit Termination

• Busy Signal if capacity for a circuit not available.• Most important circuit-switching networks:

– Telephone networks– ISDN (Integrated Services Digital Networks)


Circuit Switching

• A node in a circuit-switching network:


Circuit Switching


Timing in Circuit Switching


Packet Switching

• Data are sent as formatted bit-sequences, so-called packets.

• Packets have the following structure:

Header and Trailer carry control information


Packet Switching

• Each packet is passed through the network from node to node along some path (Routing)

• At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks)

• No capacity is allocated for packets


Packet Switching


Datagram Packet Switching

• Packets are called datagrams• The network nodes process each packet independ

ently: If Host A sends two packets back-to-back to Host B over a datagram packet network, the network cannot tell that the packets belong together. In fact, the two packets can take different routes.

• Implications of processing packets independently:– A sequence of packets can be received in a different order

than it was sent– Each packet header must contain the full address of the d

estination


Exercise: Datagram Packet

• Exercise: Most network applications (think of email and file transfer) require that data is received in sequence. For such applications a datagram network appears to be inappropriate, since packets may need to get reordered.

• Question: What are advantages of datagram networks?

• The main example of a datagram packet-switching network is the Internet


Datagram Packet Switching


Timing of Datagram Packet Switching


Virtual-Circuit Packet Switching

As the name suggests:• Virtual-circuit packet switching is a hybrid

of circuit switching and packet switching• All data is transmitted as packets• All packets from one packet stream are

sent along a pre-established path (=virtual circuit)

• Guarantees in-sequence delivery of packets• However: Packets from different virtual

circuits may be interleaved



• Communication with virtual circuits (VC) takes place in three phases:– 1. VC Establishment– 2. Data Transfer– 3. VC Disconnect

• Note: Packet headers don't need to contain the full destination address of the packet


Examples

• X.25– X.25 networks have been around since the

1970s– It is used in many public packet switching

networks

• ATM (Asynchronous Transfer Mode)– Developed in the 1980s– For transmission of voice, video, and data in a

single network

• Others– SNA (Systems Network Architecture) by IBM




Timing of Virt. Circ. Packet Switching


Comparison

Circuit Switching Datagram Packet Switching VC Packet Switching

Dedicated transmission pathContinuous transmissionPath stays fixed for entireconnectionCall setup delayNegligible transmission delayNo queueing delayBusy signal overloadednetworkFixed bandwidth for eachcircuitNo overhead after call setup

No dedicated transmissionpathTransmission of packetsRoute of each packet isindependentNo setup delayTransmission delay for eachpacketQueueing delays at switchesDelays increase in overloadednetworksBandwidth is shared by allpacketsOverhead in each packet

No dedicated transmissionpathTransmission of packetsPath stays fixed for entireconnectionCall setup delayTransmission delay for eachpacketQueueing delays at switchesDelays increase in overloadednetworksBandwidth is shared by allpacketsOverhead in each packet

Documents

COMP361 by M. Hamdi1 COMP 361, Fall 2000 Computer Communication Networks I Dr. Mounir Hamdi [email protected]