ECS152B Xin Liu

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ECS 152BComputer Networks

Fall 2003

Prof. Xin Liuwww.cs.ucdavis.edu/~liu/152B/152b.html

ECS152B Xin Liu

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Highlights• prerequisites:

ECS150 and ECS152A

• make sure to follow up the newsgroup messages

ucd.class.ecs152bucd.class.ecs152b.d

• grading• Projects 40% • Midterm 20%• Homework 10%• Final 30%

ECS152B Xin Liu

3Road Map

I. Introduction• Computer Networks Overview

• Layered architecture

II. IP Protocols • Internet Protocol

• Routing protocols

• ICMP and IGMP

III. Transport Layer• UDP• TCP

ECS152B Xin Liu

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Road Map

IV. Transport Layer Interfaces • Socket • Socket related system calls • I/O Multiplexing

V. Networking Applications • Network Library Routines • File Transfer Protocol (FTP) • HyperText Transfer Protocol

(HTTP) • Telnet / Remote Login • Domain Name System (DNS)• Remote Procedure Calls (RPC)

V. Other Topics

ECS152B Xin Liu

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Computer Networks

local network

localnetwork

Core network

internet: network of networks

ECS152B Xin Liu

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Protocols

• A protocol defines: – the format and the order of the messages exchanged– the actions on receipt/transmission of a message

host

Network Adapter

host

Network Adapter

ComputerNetwork

ECS152B Xin Liu

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Protocol Example

hello

yes?

2:30pm

time?

Time request:

TCP connection request

TCP connection reply

index.html

get http:www.cs.ucdavis.edu/~liu/

URL request:

(not necessarily typical:)

ECS152B Xin Liu

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Protocols

• Why use a protocol?

– to provide a common language

• There are so many protocols!

• Rules:

– must be unambiguous and followed exactly

• e.g., TCP/IP, IP (Internet Protocol)

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The Protocol Stack

Physical

Transport

Network

Link

Presentation

Session

Application

Old Saying: If you know what you are doing, four layers is enough; if you don’t seven won’t help.

Physical

Transport

Network

Link

Presentation

Session

Application

TCP, UDP

IPv4, IPv6

Ethernet…

HTTP, FTP…

OSI - 7 layers TCP/IP Suite – 4 layers

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Internet Protocol Suite• Layers provide information hiding

doesn’t matter what lower level layers use as long as higher layers use the same protocol

Link

Transport

Network

Application

Link

Transport

Network

Applicatione.g., supports network applications

e.g., transports application-layer messages

e.g., routes datagrams from one host to another

e.g., transmits individual bits within the frame

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Link Layer: review

• Transfer datagram from one node to adjacent node over a link

• Involves device driver in OS and network interface card

• Physically connecting hosts: encoding, framing, error detection/correction, reliable delivery, access control

• Example: Ethernet, token rings, etc.

“link”

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Network Layer

• Transport packet from sending to receiving hosts

• Network layer protocols in every host, router

• IP (Internet protocol): addressing, routing, forwarding

• Best effort, unreliable

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

application

transportnetworkdata linkphysical

application

transportnetworkdata linkphysical

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Transport Layer• provide logical

communication between app processes running on different hosts

• transport protocols run in end systems

– segments, reassembles

• more than one transport protocol available to apps

• Internet: TCP and UDP

application

transportnetworkdata linkphysical

application

transportnetworkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysical

networkdata linkphysicalnetwork

data linkphysical

logical end-end transport

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Household analogy

• 12 kids sending letters to 12 kids

• processes = kids

• app messages = letters in envelopes

• hosts = houses

• transport protocol = Alice to Bob

• network-layer protocol = postal service

ECS152B Xin Liu

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Protocol Layers

Network

Link

Transport

Network

Link

Application

Transport

Network

Link

Application

HostA router HostB

• Simplifies implementationsegmentation/reassembly, error control, flow control,multiplexing, connection setup in different layers

• There also are some potential disadvantages

may duplicate functionality may need info in a non-adjacent layer (e.g., timestamp)

Network

Link

router

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Encapsulation

source destination

original message

Transport

Network

Link

Application

Transport

Network

Link

Application

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Demultiplexing

source destination

original message

Transport

Network

Link

Application

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The Internet Protocol Stack

source

original message

Transport

Network

Link

Application

Protocol Data Units

(PDU)

message

frame

segment

datagram

software

networkinterface card

software

mixed

Implementation

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Client-Server Model

server client

client = host that initiates the session (e.g., asks for a Web page; browser) server = host that gives the requested service

A typical network has two components: client and server

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Client-Server Model

• Client-server model:– Web, email, file transfer, remote login, news

group, p2p, etc.

• SETI@home project– SETI: Search for ExtraTerrestrial Intelligence– 3 million participants

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Our Class

• Upper layer protocols– Internet protocols– Transport protocols– Transport layer interface– Networking application

• Hands-on experience

Transport

Network

Application

clientserver

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Acronym

• Standardization – Internet Society (ISOC)– Internet Architecture Board (IAB)– Internet Engineering Task Force (IETF)– Internet Research Task Force (IRTF)

• RFC – Request for comments

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Suggested Reading

• TCP/IP Illustrated, Vol. 1, Chp. 1

• Review ECS 150, 152A