CS/ECE 438, CSE 425Communication Networks

Nikita BorisovECE Department, UIUC

8/25/06 UIUC - CS/ECE 438, Fall 2006 2

Course Information

Instructor Prof. Nikita Borisov Office Hours:

460 CSL, 244-5385 10-12 Tuesdaysnikita@uiuc.edu or by appointment

TA Monika Battala, battala2@uiuc.edu Office hours TBA

Webpage http://www.cs.uiuc.edu/class/fa06/cs438

Newsgroup class.cs438 on news.cs.uiuc.edu

8/25/06 UIUC - CS/ECE 438, Fall 2006 3

Acknowledgments

Slides are adapted from Prof. Kravets Some material contributed by Profs.

Luo, Lumetta, Hajek, Vaidya Some material from Larry Peterson &

James Kurose & Keith Ross

8/25/06 UIUC - CS/ECE 438, Fall 2006 4

Prerequisites

C Programming (CS241) Pre-req for ECE students is ECE290, but

ECE391/398SSL or C experience highlyrecommended

Probability and Statistics (MATH461,463 or ECE 413)

8/25/06 UIUC - CS/ECE 438, Fall 2006 5

Textbook

Computer Networks: A Top-Down ApproachFeaturing the Internet, by Kurose & Ross,3rd Edition

We will be covering this text out of order Ch 1 Ch 5 + some of 6 Ch 4 Ch 3 Some of Ch 2

8/25/06 UIUC - CS/ECE 438, Fall 2006 6

Recommended Text

UNIX Network Programming,Volume 1, by Stevens

There are 3 editions Second & third edition more up-to-date First edition (1990) contains more

background on general UNIXprogramming

8/25/06 UIUC - CS/ECE 438, Fall 2006 7

Grading Policy

Homework 15% 7 homework assignments

Mid-term Exam 20% Oct 12

Programming Projects 35% 4 Programming projects 2% off per hour late

Final Exam 30%

8/25/06 UIUC - CS/ECE 438, Fall 2006 8

Homework and Projects

Homeworks: Due Wednesdays at 2:00 in class. General extension to Thursdays at 2:00pm (hard

deadline). No questions to TA or on newsgroup after class

on Tuesday. Projects:

Project 1: 5%, Projects 2- 4: 10% Due Fridays at 9:00pm.

8/25/06 UIUC - CS/ECE 438, Fall 2006 9

Academic Honesty

Your work in this class must be your own. Penalties for excessive collaboration and

cheating are severe Sharing strategies and small code

fragments (5-10 lines) OK Sharing homework answers and large

sections of code forbidden Don’t post these to newsgroup!

If in doubt, ask the professor

8/25/06 UIUC - CS/ECE 438, Fall 2006 10

One Unit Students

Graduate students MAY take an extra unitproject in conjunction with this class Graduate students

Register for 4 credits Write a survey paper in a networking research area of

your choice. Project proposal with list of 10+ academic references

(no URL’s) due September 22 Paper due last day of class

Undergraduates may not take this project course

8/25/06 UIUC - CS/ECE 438, Fall 2006 11

Course Objectives

At the end of the semester, you should beable to: Identify the problems that arise in networked

communication Explain the advantages and disadvantages of

existing solutions to these problems in thecontext of different networking regimes

Understand the implications of a given solutionfor performance in various networking regimes

Evaluate novel approaches to these problems

8/25/06 UIUC - CS/ECE 438, Fall 2006 12

Programming Objectives

At the end of the semester, you shouldbe able to Identify and describe the purpose of each

component of the TCP/IP protocol suite Develop solid client-server applications

using TCP/IP Understand the impact of trends in

network hardware on network softwareissues

8/25/06 UIUC - CS/ECE 438, Fall 2006 13

Course Contents

Overview UNIX Network Programming Direct Link Networks Multiple Access Packet Switched Networks Internetworking Reliable Transport Congestion Control, QoS & Fair Sharing Performance Analysis and Queueing Theory

8/25/06 UIUC - CS/ECE 438, Fall 2006 14

Connectivity

Building Block Links: coax cable, optical fiber, … Nodes: workstations, routers, …

Links: Point-to-point

Multiple access …

8/25/06 UIUC - CS/ECE 438, Fall 2006 15

Indirect Connectivity

Switched Networks Internetworks

Recursive definition of anetwork Two or more nodes

connected by a physicallink

Two or more networksconnected by one ormore nodes

8/25/06 UIUC - CS/ECE 438, Fall 2006 15

Indirect Connectivity

Switched Networks Internetworks

Recursive definition of anetwork Two or more nodes

connected by a physicallink

Two or more networksconnected by one ormore nodes

8/25/06 UIUC - CS/ECE 438, Fall 2006 15

Indirect Connectivity

Switched Networks Internetworks

Recursive definition of anetwork Two or more nodes

connected by a physicallink

Two or more networksconnected by one ormore nodes

8/25/06 UIUC - CS/ECE 438, Fall 2006 16

Network Problems

8/25/06 UIUC - CS/ECE 438, Fall 2006 16

Network Problems

What must a network provide? Connectivity Cost-effective Resource Sharing Functionality Performance

8/25/06 UIUC - CS/ECE 438, Fall 2006 17

Addressing

Addressing Unique byte-string used to indicate which node

is the target of communication Routing

The process of determining how to forwardmessages toward the destination node based onits address

Types of Addresses Unicast: node-specific Broadcast: all nodes on the network Multicast: subset of nodes on the network

8/25/06 UIUC - CS/ECE 438, Fall 2006 18

Effects of Indirect Connectivity

Nodes receive data on one link and forward it onto thenext -> switching network Circuit Switching

Telephone Stream-based (dedicated circuit) Links reserved for use by communication channel Send/receive bit stream at constant rate

Packet Switching Internet Message-based (store-and-forward) Links used dynamically Admission policies and other trafficdetermine bandwidth

8/25/06 UIUC - CS/ECE 438, Fall 2006 19

Cost-Effective Sharing ofResources

Physical links and switches must be sharedamong many users

Common multiplexing strategies (Synchronous) time-division multiplexing (TDM) Frequency-division multiplexing (FDM)

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

time

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 20

Circuit Switching: FDM and TDM

FDM

frequency

timeTDM

frequency

time

4 usersExample:

8/25/06 UIUC - CS/ECE 438, Fall 2006 21

Statistical Multiplexing

Statistical Multiplexing (SM) On-demand time-division multiplexing Scheduled on a per-packet basis Packets from different sources are

interleaved Uses upper bounds to limit transmission

Queue size determines capacity per source

8/25/06 UIUC - CS/ECE 438, Fall 2006 22

Statistical Multiplexing in aSwitch

Packets buffered in switch until forwarded Selection of next packet depends on policy

How do we make these decisions in a fair manner?Round Robin? FIFO?

How should the switch handle congestion?

…

8/25/06 UIUC - CS/ECE 438, Fall 2006 23

Functionality

Support For Common Services Goal

Meaningful communication between hosts on anetwork

Idea Common services simplify the role of applications Hide the complexity of the network without overly

constraining the application designer Semantics and interface depend on applications

Request/reply: FTP, HTTP, DNS Message stream: video-on-demand, video

conferencing

8/25/06 UIUC - CS/ECE 438, Fall 2006 24

Channels

Channel The abstraction for application-level communication

Idea Turn host-to-host connectivity into process-to-process

communication

8/25/06 UIUC - CS/ECE 438, Fall 2006 24

Channels

Channel The abstraction for application-level communication

Idea Turn host-to-host connectivity into process-to-process

communication

Host

Host Host

HostHostChannelChannel

8/25/06 UIUC - CS/ECE 438, Fall 2006 24

Channels

Channel The abstraction for application-level communication

Idea Turn host-to-host connectivity into process-to-process

communication

Host

Host Host

HostHostChannelChannel

APP

APP

8/25/06 UIUC - CS/ECE 438, Fall 2006 24

Channels

Channel The abstraction for application-level communication

Idea Turn host-to-host connectivity into process-to-process

communication

Host

Host Host

HostHostChannelChannelChannelChannel

APP

APP

8/25/06 UIUC - CS/ECE 438, Fall 2006 25

Channel Implementation

Question Where does the functionality belong?

Middle (switches)? Telephone system

Edges (end hosts)? Internet

8/25/06 UIUC - CS/ECE 438, Fall 2006 26

Inter-process Communication

Problems typically masked bycommunication channel abstractions Bit errors (electrical interference) Packet errors (congestion) Link/node failures Message delays Out-of-order delivery Eavesdropping

Goal Fill the gap between what applications expect

and what the underlying technology provides

8/25/06 UIUC - CS/ECE 438, Fall 2006 27

Performance

... and to do so while delivering “good” performance. Bandwidth/throughput

Data transmitted per unit time Example: 10 Mbps Link bandwidth vs. end-to-end bandwidth Notation

KB = 210 bytes Mbps = 106 bits per second

8/25/06 UIUC - CS/ECE 438, Fall 2006 28

Performance

8/25/06 UIUC - CS/ECE 438, Fall 2006 28

Performance

Latency/delay

8/25/06 UIUC - CS/ECE 438, Fall 2006 28

Performance

Latency/delay Time from A to B

8/25/06 UIUC - CS/ECE 438, Fall 2006 28

Performance

Latency/delay Time from A to B Example: 30 msec (milliseconds)

8/25/06 UIUC - CS/ECE 438, Fall 2006 28

Performance

Latency/delay Time from A to B Example: 30 msec (milliseconds) Many applications depend on round-trip time (RTT)

8/25/06 UIUC - CS/ECE 438, Fall 2006 28

Performance

Latency/delay Time from A to B Example: 30 msec (milliseconds) Many applications depend on round-trip time (RTT) Components

Transmission time Propagation delay over links Queueing delays Software processing overheads

8/25/06 UIUC - CS/ECE 438, Fall 2006 29

Performance Notes

Speed of Light 3.0 x 108 meters/second in a vacuum 2.3 x 108 meters/second in a cable 2.0 x 108 meters/second in a fiber

Comments No queueing delays in a direct link Bandwidth is not relevant if size = 1bit Software overhead can dominate when distance is small

Key Point Latency dominates small transmissions Bandwidth dominates large

8/25/06 UIUC - CS/ECE 438, Fall 2006 30

Delay x Bandwidth Product

channel = pipe delay = length bandwidth = area of a cross section bandwidth x delay product = volume

8/25/06 UIUC - CS/ECE 438, Fall 2006 30

Delay x Bandwidth Product

channel = pipe delay = length bandwidth = area of a cross section bandwidth x delay product = volume

8/25/06 UIUC - CS/ECE 438, Fall 2006 30

Delay x Bandwidth Product

channel = pipe delay = length bandwidth = area of a cross section bandwidth x delay product = volume

Bandwidth

8/25/06 UIUC - CS/ECE 438, Fall 2006 30

Delay x Bandwidth Product

channel = pipe delay = length bandwidth = area of a cross section bandwidth x delay product = volume

Bandwidth

Delay

8/25/06 UIUC - CS/ECE 438, Fall 2006 31

Delay x Bandwidth Product

Example: Transcontinental Channel BW = 45 Mbps delay = 50ms bandwidth x delay product

= (45 x 106 bits/sec) x (50 x 10–3 sec)= 2.25 x 106 bits

Bandwidth x delay product How many bits the sender must transmit before

the first bit arrives at the receiver if the senderkeeps the pipe full

Takes another one-way latency to receive aresponse from the receiver

8/25/06 UIUC - CS/ECE 438, Fall 2006 32

Bandwidth vs. Latency

Relative importance 1-byte: Latency bound

1ms vs 100ms latency dominates 1Mbps vs 100Mbps BW 25MB: Bandwidth bound

1Mbps vs 100Mbps BW dominates 1ms vs 100ms latency

8/25/06 UIUC - CS/ECE 438, Fall 2006 32

Bandwidth vs. Latency

Relative importance 1-byte: Latency bound

1ms vs 100ms latency dominates 1Mbps vs 100Mbps BW 25MB: Bandwidth bound

1Mbps vs 100Mbps BW dominates 1ms vs 100ms latency

25MB

1 Mbps

1b

1Mbps

1ms

100 Mbps 1Mbps

100ms

8/25/06 UIUC - CS/ECE 438, Fall 2006 33

Bandwidth vs. Latency

Infinite bandwidth RTT dominates

Throughput = TransferSize / TransferTime TransferTime = RTT + 1/Bandwidth x

TransferSize

Its all relative 1-MB file to 1-Gbps link looks like a 1-KB

packet to 1-Mbps link

8/25/06 UIUC - CS/ECE 438, Fall 2006 34

Network Architecture

Challenge Fill the gap between hardware capabilities and

application expectations, and to do so whiledelivering “good” performance.

Hardware and expectations are movingtargets.

How do network designers cope withcomplexity? Layering Protocols Standards

8/25/06 UIUC - CS/ECE 438, Fall 2006 35

Abstraction through Layering

Abstract system into layers: Decompose the problem of building a network into manageable

components Each layer provides some functionality

Modular design provides flexibility Modify layer independently Allows alternative abstractions

8/25/06 UIUC - CS/ECE 438, Fall 2006 35

Abstraction through Layering

Abstract system into layers: Decompose the problem of building a network into manageable

components Each layer provides some functionality

Modular design provides flexibility Modify layer independently Allows alternative abstractions

Application programs

HardwareHost-to-host connectivity

Request/reply channelMessage stream channel

8/25/06 UIUC - CS/ECE 438, Fall 2006 36

Protocols

Definition A protocol is an abstract object that makes up

the layers of a network system A protocol provides a communication service

that higher-layer objects use to exchangemessages Service interface:

To objects on the same computer that want to use itscommunication services

Peer interface: To its counterpart on a different machine. peers

communicate using the services of lower-level protocols

8/25/06 UIUC - CS/ECE 438, Fall 2006 37

Interfaces

Host 1 Host 2

8/25/06 UIUC - CS/ECE 438, Fall 2006 37

Interfaces

Host 1 Host 2

Lower-levelProtocol

(IP)

Lower-levelProtocol

(IP)

8/25/06 UIUC - CS/ECE 438, Fall 2006 37

Interfaces

Host 1 Host 2

Peer-to-peerinterface

Lower-levelProtocol

(IP)

Lower-levelProtocol

(IP)

8/25/06 UIUC - CS/ECE 438, Fall 2006 37

Interfaces

Host 1 Host 2

Higher-level

protocol(TCP)

Higher-level

protocol(TCP)

Peer-to-peerinterface

Lower-levelProtocol

(IP)

Lower-levelProtocol

(IP)

8/25/06 UIUC - CS/ECE 438, Fall 2006 37

Interfaces

Host 1 Host 2

Service interfaceHigher-

levelprotocol

(TCP)

Higher-level

protocol(TCP)

Peer-to-peerinterface

Lower-levelProtocol

(IP)

Lower-levelProtocol

(IP)

8/25/06 UIUC - CS/ECE 438, Fall 2006 38

Terminology

Term “protocol” is overloaded specification of peer-to-peer interface module that implements this interface

8/25/06 UIUC - CS/ECE 438, Fall 2006 39

Layering Concepts

Encapsulation Higher layer protocols create messages and

send them via the lower layer protocols These messages are treated as data by the

lower-level protocol Higher-layer protocol adds its own control

information in the form of headers or trailers Multiplexing and Demultiplexing

Use protocol keys in the header to determinecorrect upper-layer protocol

8/25/06 UIUC - CS/ECE 438, Fall 2006 40

Encapsulation

Applicationprogram

Request/Reply

Host-to-Host

DATA

RRP HDR DATA

Applicationprogram

Request/Reply

Host-to-Host

DATA

RRP HDR DATA

HHP HDR RRP HDR DATA

8/25/06 UIUC - CS/ECE 438, Fall 2006 41

OSI Architecture

Open Systems Interconnect (OSI)Architecture International Standards Organization

(ISO) International Telecommunications Union

(ITU, formerly CCITT) “X dot” series: X.25, X.400, X.500 Primarily a reference model

8/25/06 UIUC - CS/ECE 438, Fall 2006 42

OSI Protocol Stack

Application

Presentation

Physical

Transport

Session

Data Link

Network

Application: Application specific protocols

Presentation: Format of exchanged data

Session: Name space for connection mgmt

Transport: Process-to-process channel

Network: Host-to-host packet delivery

Data Link: Framing of data bits

Physical: Transmission of raw bits

8/25/06 UIUC - CS/ECE 438, Fall 2006 43

OSI Protocol Stack

Application

Presentation

Physical

Transport

Session

Data Link

Network

Physical

Data Link

Network

Application

Presentation

Physical

Transport

Session

Data Link

Network

Host

User-Level

Host

OS

Kernel

Router

8/25/06 UIUC - CS/ECE 438, Fall 2006 44

Internet Architecture

Internet Architecture (TCP/IP) Developed with ARPANET and NSFNET Internet Engineering Task Force (IETF)

Culture: implement, then standardize OSI culture: standardize, then implement

Popular with release of Berkeley SoftwareDistribution (BSD) Unix; i.e., frees software

Standard suggestions debated publicly through“requests for comments” (RFC’s) We reject kings, presidents, and voting. We believe in

rough consensus and running code. – David Clark

8/25/06 UIUC - CS/ECE 438, Fall 2006 45

Internet Architecture –Hourglass Design

FTP

TCP

ModemATMFDDIEthernet

IP

UDP

VoIPDNSHTTP

8/25/06 UIUC - CS/ECE 438, Fall 2006 46

Internet Architecture

Features: No strict layering Hourglass shape – IP is the focal point

Application

NetworkIP

UDPTCP

8/25/06 UIUC - CS/ECE 438, Fall 2006 47

Protocol Acronyms

(T)FTP - (Trivial) File Transfer Protocol HTTP - HyperText Transport Protocol DNS - Domain Name Service SMTP – Simple Mail Transfer Protocol NTP - Network Time Protocol TCP - Transmission Control Protocol UDP - User Datagram Protocol IP - Internet Protocol FDDI - Fiber Distributed Data Interface ATM - Asynchronous Transfer Mode

8/25/06 UIUC - CS/ECE 438, Fall 2006 48

Summary

Goal Understanding of computer network

functionality, with experience building and usingcomputer networks

Steps Identify what concepts we expect from a network Define a layered architecture Implement network protocols and application

programs

8/25/06 UIUC - CS/ECE 438, Fall 2006 49

Assignments

Homework 1 Due Wednesday September 6 at

2:00pm. Project 1

Due Friday September 8 at 9:00pm. Both will be on website by end of

day today.