cse 3214: computer network protocols and applications · 2017-01-08 · 1/8/2017 cse3214 - s.datta...

1/8/2017 CSE3214 - S.Datta 1

CSE 3214: Computer NetworkProtocols and Applications

Suprakash Dattadatta@cse.yorku.ca

Office: LAS 3043Phone: 416-736-2100 ext 77875

Course page: http://www.cse.yorku.ca/course/3214

These slides are adapted from Jim Kurose’s slides.

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AdministriviaCourse webpage:

http://www.cse.yorku.ca/course/3214

Lectures: Tue-Thu 10:00-11:30 pm(PSE 321)

Exams: midterm (30%), final(40%)

Homework (30%): Assignments.

Slides: should be available themorning of the class

Office hours: Tuesday, Thu:12:30-2:30 pm or byappointment at LAS 3043

Computer Networking: A Top DownApproach Featuring the Internet, 6th

edition.Jim Kurose, Keith Ross; Pearson.

Textbook:

1/8/2017 CSE3214 - S.Datta 3

Administrivia – contd.

n Cheating will not be tolerated. Visit the webpage for moredetails on policies etc.

n Be careful not to misuse packet sniffing software.n I would like to have a 2-hour midterm. Your cooperation is

greatly appreciated.n TA: F. Yasmeen

1/8/2017 CSE3214 - S.Datta 4

Course objectives

n Understand the full TCP/IP architecture.n Become familiar with “advanced topics” - P2P systems, multimedia communication (including VoIP), network

security, wireless sensor networks.n Learn about active research areas.

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Major differences with 3213

n Top-down approach.n More algorithmic (less math!)n More hands-on – TCP/IP programming.

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Chapter 1: Introduction

What is the Internet?

Network of networks Heterogeneous Distributed Owned by many different entities Allows easy additions and removal from the network

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The Internet: “nuts and bolts” view

n millions of connectedcomputing devices: hosts= end systems

n running network appsn communication links

n fiber, copper, radio, satelliten transmission rate =bandwidth

n routers: forward packets(chunks of data)

local ISP

companynetwork

regional ISP

router workstationserver

mobile

1/8/2017Introduction 1-8Introduction

The Internet: “nuts and bolts” view

vmillions of connectedcomputing devices:§ hosts = end systems§ running network apps

vcommunication links§ fiber, copper,

radio, satellite§ transmission rate:

bandwidth

vPacket switches:forward packets (chunksof data)§ routers and switches

wiredlinks

wirelesslinks

router

mobile network

global ISP

regional ISPhomenetwork

institutional network

smartphone

server

wirelesslaptop

1/8/2017 CSE3214 - S.Datta 9

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

receiving of msgsn e.g., TCP, IP, HTTP, FTP, PPP

n Internet: “network ofnetworks”n loosely hierarchicaln public Internet versus private

intranetn Internet standards

n RFC: Request for commentsn IETF: Internet Engineering

Task Force

protocols define format, order of msgssent and received among network entities,and actions taken on msg transmission,receipt

mobile network

global ISP

regional ISP

homenetwork

institutional network

1/8/2017 CSE3214 - S.Datta 10

The Internet: a service view

n communicationinfrastructure enablesdistributed applications:n Web, email, games, e-

commerce, file sharingn communication services

provided to apps:n Connectionless unreliablen Connection-oriented reliable

What’s a protocol?

human protocols:v “what’s the time?”v “I have a question”v introductions

… specific msgs sent… specific actions taken

when msgs received,or other events

network protocols:v machines rather than

humansv all communication

activity in Internetgoverned by protocols

protocols define format, orderof msgs sent and receivedamong network entities,

and actions taken on msgtransmission, receipt

a human protocol and a computer networkprotocol:

Got thetime?2:00

TCP connectionresponse

Get http://www.awl.com/kurose-ross

<file>time

TCP connectionrequest

What’s a protocol?

Access networks and physical media

Q: How to connect endsystems to edgerouter?

v residential access netsv institutional access

networks (school,company)

v mobile access networks

keep in mind:v bandwidth (bits per

second) of accessnetwork?

v shared or dedicated?1-13

Access net: digital subscriber line (DSL)

central office

telephonenetwork

voice, data transmittedat different frequencies over

dedicated line to central office

use existing telephone line to central office DSLAM§ over DSL phone line goes to Internet§ voice over DSL phone line goes to telephone net

v < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)v < 24 Mbps downstream transmission rate (typically < 10

DSLmodem

splitter

DSL accessmultiplexer

Access net: cable network

cablemodem

splitter

…cable headend

Channels

CONTROL

1 2 3 4 5 6 7 8 9

frequency division multiplexing: different channels transmittedin different frequency bands

data, TV transmitted at differentfrequencies over shared cable

distribution network

cablemodem

splitter

…cable headend

cable modemtermination system

v HFC: hybrid fiber coax§ asymmetric: up to 30Mbps downstream transmission

rate, 2 Mbps upstream transmission ratev network of cable, fiber attaches homes to ISP router

§ homes share access network to cable headend§ unlike DSL: DSL has dedicated access to central office

Access net: cable network

Access net: home network

to/from headend or centraloffice

cable or DSL modem

router, firewall, NAT

wired Ethernet (100 Mbps)

wireless accesspoint (54 Mbps)

wirelessdevices

often combinedin single box

Enterprise access networks (Ethernet)

v typically used in companies, universities, etcv 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission ratesv today, end systems typically connect into Ethernet

switch

Ethernetswitch

institutional mail,web servers

institutional router

institutional link toISP (Internet)

1/8/2017 CSE3214 - S.Datta 19

A closer look at network structure

n network edge: applicationsand hosts

n network core:n interconnected routersn network of networks

n access networks, physicalmedia: wired, wirelesscommunication links

Wireless access networks

v shared wireless access network connects end system torouter§ via base station aka “access point”

wireless LANs:§ within building (100 ft)§ 802.11b/g (WiFi): 11, 54

Mbps transmission rate

wide-area wireless access§ provided by telco (cellular)

operator, 10’s km§ between 1 and 10 Mbps§ 3G, 4G: LTE

to Internet

1/8/2017Introduction 1-21

Host: sends packets of data

host sending function:vtakes applicationmessagevbreaks into smallerchunks, known aspackets, of length L bitsvtransmits packet intoaccess network attransmission rate R

§ link transmissionrate, aka linkcapacity, aka linkbandwidth

R: link transmission ratehost

two packets,L bits each

packettransmission

time needed totransmit L-bit

packet into link

L (bits)R (bits/sec)= =

Physical media

v bit: propagates betweentransmitter/receiver pairs

v physical link: what liesbetween transmitter &receiver

v guided media:§ signals propagate in

solid media: copper,fiber, coax

v unguided media:§ signals propagate freely,

e.g., radio

twisted pair (TP)v two insulated copper

wires§ Category 5: 100 Mbps, 1

Gpbs Ethernet§ Category 6: 10Gbps

Physical media: coax, fiber

coaxial cable:v two concentric copper

conductorsv bidirectionalv broadband:

§ multiple channels oncable

§ HFC

fiber optic cable:v glass fiber carrying light

pulses, each pulse a bitv high-speed operation:

§ high-speed point-to-pointtransmission (e.g., 10’s-100’sGpbs transmission rate)

v low error rate:§ repeaters spaced far apart§ immune to electromagnetic

Physical media: radio

v signal carried inelectromagneticspectrum

v no physical “wire”v bidirectionalv propagation environment

effects:§ reflection§ obstruction by objects§ interference

radio link types:v terrestrial microwave

§ e.g. up to 45 Mbps channelsv LAN (e.g., WiFi)

§ 11Mbps, 54 Mbpsv wide-area (e.g., cellular)

§ 3G cellular: ~ few Mbpsv satellite

§ Kbps to 45Mbps channel (ormultiple smaller channels)

§ 270 msec end-end delay§ geosynchronous versus low

altitude

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The network edge

n end systems (hosts):n run application programsn e.g. Web, emailn at “edge of network”

n client/server modeln client host requests, receives

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

client/server

n peer-peer model:n minimal (or no) use of dedicated

serversn e.g. Gnutella, KaZaA

1/8/2017 CSE3214 - S.Datta 26

Network edge: connection-oriented service

Goal: data transfer betweenend systems

n handshaking: setup(prepare for) data transferahead of timen Hello, hello back human

protocoln set up “state” in two

communicating hostsn TCP - Transmission

Control Protocoln Internet’s connection-

oriented service

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

stream data transfern loss: acknowledgements and

retransmissionsn flow control:

n sender won’t overwhelmreceiver

n congestion control:n senders “slow down sending

rate” when network congested

Connection-oriented service not the

same as that in traditional telephony.

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Network edge: connectionless service

Goal: data transfer betweenend systemsn same as before!

n UDP - User Datagram Protocol[RFC 768]:

n connectionlessn unreliable data transfern no flow controln no congestion control

App’s using TCP:n HTTP (Web), FTP (file

transfer), Telnet (remotelogin), SMTP (email)

App’s using UDP:n streaming media,

teleconferencing, DNS,Internet telephony

v mesh of interconnectedrouters

v packet-switching: hostsbreak application-layermessages into packets§ forward packets from

one router to the next,across links on pathfrom source todestination

§ each packet transmittedat full link capacity

The network core

Packet-switching: store-and-forward

v takes L/R seconds totransmit (push out) L-bitpacket into link at R bps

v store and forward: entirepacket must arrive atrouter before it can betransmitted on next link

one-hop numericalexample:

§ L = 7.5 Mbits§ R = 1.5 Mbps§ one-hop transmission

delay = 5 secmore on delay shortly …

sourceR bps destination

L bitsper packet

v end-end delay = 2L/R (assumingzero propagation delay)

Packet Switching: queueing delay, loss

CR = 100 Mb/s

R = 1.5 Mb/s D

Equeue of packetswaiting for output link

queuing and loss:v If arrival rate (in bits) to link exceeds transmission rate

of link for a period of time:§ packets will queue, wait to be transmitted on link§ packets can be dropped (lost) if memory (buffer) fills

Network Layer 4-31Network Layer 4-31

Two key network-core functions

forwarding: move packetsfrom router’s input toappropriate router output

routing: determines source-destination route taken bypackets

§ routing algorithms

routing algorithm

local forwarding tableheader value output link

0100010101111001

dest address in arrivingpacket’s header

Alternative core: circuit switching

end-end resourcesallocated to, reserved for“call” between source &dest:

v In diagram, each link hasfour circuits.§ call gets 2nd circuit in top

link and 1st circuit in rightlink.

v dedicated resources: nosharing§ circuit-like (guaranteed)

performancev circuit segment idle if not

used by call (no sharing)v Commonly used in traditional

telephone networks

Circuit switching: FDM versus TDM

frequency

timeTDM

frequency

4 usersExample:

Packet switching versus circuit switching

example:§ 1 Mb/s link§ each user:

100 kb/s when “active” active 10% of time

vcircuit-switching:§ 10 users

vpacket switching:§ with 35 users, probability >

10 active at same time isless than .0004 *

packet switching allows more users to use network!

Nusers

1 Mbps link

Q: how did we get value0.0004?Q: what happens if > 35users ?

1-34* Check out the online interactive exercises for more examples

v great for bursty data§ resource sharing§ simpler, no call setup

v excessive congestion possible: packet delay and loss§ protocols needed for reliable data transfer, congestion

controlv Q: How to provide circuit-like behavior?

§ bandwidth guarantees needed for audio/video apps§ still an unsolved problem (chapter 7)

is packet switching a “slam dunk winner?”

Q: human analogies of reserved resources (circuitswitching) versus on-demand allocation (packet-switching)?

Packet switching vs circuit switching

Internet structure: network of networks

v End systems connect to Internet via access ISPs(Internet Service Providers)§ Residential, company and university ISPs

v Access ISPs in turn must be interconnected.v So that any two hosts can send packets to each other

v Resulting network of networks is very complexv Evolution was driven by economics and national

policiesv Let’s take a stepwise approach to describe current

Internet structure

Question: given millions of access ISPs, how to connectthem together?

accessnet

accessnetaccess

accessnet

………

Option: connect each access ISP to every other accessISP?

accessnet

accessnetaccess

accessnet

………

connecting each access ISP toeach other directly doesn’t scale:

O(N2) connections.

accessnet

accessnetaccess

accessnet

………

Option: connect each access ISP to a global transit ISP?Customer and provider ISPs have economic agreement.

globalISP

accessnet

accessnetaccess

accessnet

………

But if one global ISP is viable business, there will becompetitors ….

accessnet

accessnetaccess

accessnet

………

But if one global ISP is viable business, there will becompetitors …. which must be interconnected

peering link

Internet exchange point

accessnet

accessnetaccess

accessnet

………

… and regional networks may arise to connect access netsto ISPS

regional net

accessnet

accessnetaccess

accessnet

………

… and content provider networks (e.g., Google, Microsoft,Akamai ) may run their own network, to bring services,content close to end users

regional net

Content provider network

v at center: small # of well-connected large networks§ “tier-1” commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national

& international coverage§ content provider network (e.g, Google): private network that

connects it data centers to Internet, often bypassing tier-1, regionalISPs

ac-cessISP

RegionalISP

Tier 1ISP

Tier 1ISP Google

Tier-1 ISP: e.g., Sprint

to/from customers

peering

to/from backbone

………

POP: point-of-presence

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Internet Design Philosophy

n Simple core, complex edgen Best effort servicen Great support for heterogeneityn Dynamic by designn One network for many, many purposesn Designed primarily for non-real-time text traffic with no QoS requirements other than reliable delivery.

Q: Does this explain why the internet does not work well formany applications?

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Protocol “Layers”

Networks are complex!n many “pieces”:

n hostsn routersn links of various

median applicationsn protocolsn hardware, software

Pros and cons of layering:n explicit structure allows

identification,relationship of complexsystem’s pieces

n modularization easesmaintenance, updatingof systemn change of

implementation oflayer’s servicetransparent to rest ofsystem

1/8/2017 CSE3214 - S.Datta 48

Internet protocol “stack”

n application: supporting network applicationsn FTP, SMTP, STTP

n transport: host-host data transfern TCP, UDP

n network: routing of datagrams from source todestinationn IP, routing protocols

n link: data transfer between neighboringnetwork elementsn PPP, Ethernet

n physical: bits “on the wire”

application

transport

network

physical

1/8/2017 CSE3214 - S.Datta 49

messagesegment

datagramframe

sourceapplicationtransportnetwork

linkphysical

destinationapplicationtransportnetwork

linkphysical

networklink

physical

linkphysical

router

switch

Encapsulation

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Internet History

n 1961: Kleinrock -queueing theory showseffectiveness of packet-switching

n 1964: Baran - packet-switching in military nets

n 1967: ARPAnetconceived by AdvancedResearch ProjectsAgency

n 1969: first ARPAnet nodeoperational

n 1972:n ARPAnet

demonstrated publiclyn NCP (Network Control

Protocol) first host-hostprotocol

n first e-mail programn ARPAnet has 15 nodes

1961-1972: Early packet-switching principles

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Internet History

n 1970: ALOHAnet satellitenetwork in Hawaii

n 1973: Metcalfe’s PhD thesisproposes Ethernet

n 1974: Cerf and Kahn -architecture for interconnectingnetworks

n late70’s: proprietaryarchitectures: DECnet, SNA,XNA

n late 70’s: switching fixed lengthpackets (ATM precursor)

n 1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworkingprinciples:n minimalism, autonomy - no

internal changes required tointerconnect networks

n best effort service modeln stateless routersn decentralized control

define today’s Internet architecture

1972-1980: Internetworking, new and proprietary nets

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Internet History

n Early 1990’s: ARPAnetdecommissioned

n 1991: NSF lifts restrictions oncommercial use of NSFnet(decommissioned, 1995)

n early 1990s: Webn hypertext [Bush 1945, Nelson

1960’s]n HTML, HTTP: Berners-Leen 1994: Mosaic, later Netscapen late 1990’s: commercialization

of the Web

Late 1990’s – 2000’s:n more killer apps: instant

messaging, P2P file sharingn network security to forefrontn est. 50 million host, 100

million+ usersn backbone links running at

1990, 2000’s: commercialization, the Web, new apps

1/8/2017 CSE3214 - S.Datta 53

Next: Delay and loss in networks

n Reading: Ch 1, 2.

cse 3214: computer network protocols and applications · 2017-01-08 · 1/8/2017 cse3214 - s.datta...

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