CS 3214Computer Systems

Godmar Back

Lecture 23

Announcements

• Project 5 due Dec 8• Exercise 10 handed out• Exercise 11 coming before Thanksgiving

CS 3214 Fall 2010

NETWORKINGPart 1

CS 3214 Fall 2010

Some of these slides are substantially derived from slides provided by Jim Kurose & Keith Ross. Copyright on this material is held by Kurose & Ross. Used with permission. The textbook is Computer Networking: A Top Down Approach Featuring the Internet Jim Kurose, Keith Ross, Addison-Wesley, July 2004

CS 3214 Fall 2010

The Internet: “nuts and bolts” view

• millions of connected computing devices: hosts = end systems

• running network apps

• communication links– fiber, copper, radio,

satellite– transmission rate = bandwidth

• routers: forward packets

local ISP

companynetwork

regional ISP

router workstation

servermobile

CS 3214 Fall 2010

The Internet: “nuts and bolts” view• protocols control sending,

receiving of msgs– e.g., TCP, IP, HTTP, FTP, PPP

• Internet: “network of networks”– loosely hierarchical– public Internet versus private

intranets– Internet vs internet

• Internet standards– RFC: Request for comments– IETF: Internet Engineering

Task Force

local ISP

companynetwork

regional ISP

router workstation

servermobile

CS 3214 Fall 2010

Network Virginia

Source: Sean Gillespie

CS 3214 Fall 2010

“Real” Internet delays and routes

> traceroute www.titanic-magazin.detraceroute to www.titanic-magazin.de (62.75.228.90), 30 hops max, 38 byte packets 1 Gates-rtr.Stanford.EDU (171.64.72.1) 0.523 ms 0.339 ms 0.304 ms 2 bbr2-rtr.Stanford.EDU (171.64.1.161) 0.401 ms 0.346 ms 0.334 ms 3 border2-rtr.Stanford.EDU (171.64.1.148) 4.288 ms 1.070 ms 1.458 ms 4 g1.ba21.b003123-1.sfo01.atlas.cogentco.com (66.250.7.137) 5.231 ms 7.975 ms 9.097 ms 5 g1-1.core02.sfo01.atlas.cogentco.com (66.28.6.13) 11.364 ms 16.192 ms 16.961 ms 6 p14-0.core01.dca01.atlas.cogentco.com (66.28.4.210) 85.497 ms 84.084 ms 80.291 ms 7 p2-0.core01.iad01.atlas.cogentco.com (154.54.2.202) 89.268 ms 88.548 ms 90.046 ms 8 lambdanet.iad01.atlas.cogentco.com (154.54.11.162) 156.812 ms 200.935 ms 157.819 ms 9 LON-2-pos210.uk.lambdanet.net (81.209.156.29) 159.647 ms 159.709 ms 166.504 ms10 DUS-2-pos700-0.de.lambdanet.net (82.197.136.18) 176.365 ms 163.668 ms 165.177 ms11 DUS1-5029.de.lambdanet.net (217.71.104.30) 171.229 ms 173.782 ms 171.486 ms12 titanic.luka.de (62.75.228.90) 172.654 ms 183.307 ms 173.239 ms

traceroute: from host in Silicon Valley (keeda.stanford.edu) to host in Frankfurt, Germany (www.titanic-magazin.de)

CS 3214 Fall 2010

The Internet: a service view• communication

infrastructure enables distributed applications:– Web, email, games, e-

commerce, file sharing

• communication services provided to apps:– Connectionless unreliable– Connection-oriented reliable

CS 3214 Fall 2010

A closer look at network structure:

• network edge: applications and hosts

• network core: – routers– network of

networks• access networks,

physical media: communication links

CS 3214 Fall 2010

The network edge:• end systems (hosts):

– run application programs– e.g. Web, email– at “edge of network”

• client/server model– client host requests, receives

service from always-on server– e.g. Web browser/server; email

client/server

• peer-peer model:– minimal (or no) use of

dedicated servers– e.g. Gnutella, KaZaA

CS 3214 Fall 2010

Connection-oriented service

Goal: data transfer between end systems

• handshaking: setup (prepare for) data transfer ahead of time– Hello, hello back human

protocol– set up “state” in two

communicating hosts• TCP - Transmission

Control Protocol – Internet’s connection-

oriented service

TCP service [RFC 793]• reliable, in-order byte-

stream data transfer– loss: acknowledgements

and retransmissions

• flow control: – sender won’t overwhelm

receiver

• congestion control: – senders “slow down sending

rate” when network congested

CS 3214 Fall 2010

Connectionless service

Goal: data transfer between end systems– same as before!

• UDP - User Datagram Protocol [RFC 768]: – connectionless – unreliable data transfer– no flow control– no congestion control

• TCP-friendliness

App’s using TCP: • HTTP (Web), ssh

(remote login), SMTP (email),Bittorrent (file-sharing), XMPP (instant messenging)

App’s using UDP:• streaming media,

teleconferencing, DNS, Internet telephony

CS 3214 Fall 2010

The Network Core

• the fundamental question: how is data transferred through net?

– circuit switching: dedicated circuit per call: telephone net

– packet-switching: data sent thru net in discrete “chunks”

• How are the network’s resources shared?

CS 3214 Fall 2010

What’s a protocol?a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

TCP connection req

TCP connectionresponseGet http://www.awl.com/kurose-ross

<file>time

CS 3214 Fall 2010

Services vs Protocols

(horizontal component)• Layer k may interact with peer layer k only via

protocols

CS 3214 Fall 2010

messagesegment

datagram

frame

sourceapplicatio

ntransportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

destination

application

transportnetwork

linkphysical

HtHnHl M

HtHn M

Ht M

M

networklink

physical

linkphysical

HtHnHl M

HtHn M

HtHnHl M

HtHn M

HtHnHl M HtHnHl M

router

switch

Encapsulation

CS 3214 Fall 2010

TCP/IP Reference Model

CS 3214 Fall 2010

TCP/IP Reference Model

See: http://www.isc.org/store/logoware-clothing/isc-9-layer-osi-model-cotton-t-shirt

CS 3214 Fall 2010

TCP/IP Hourglass View

UDP

Ethernet

IP

WirelessATM

TCP

NFSDNS FTPHTTP

Host-To-Network

Internet

Application

Transport

CS 3214 Fall 2010

Typical Implementation

may cross

multiple

boundaries!

User App

Socket

Network Device

IP Layer

TCP Layer

user

Kernel:“top-half”

Kernel:“sw interrupt”

Kernel:“hw interrupt”