11

NetworkingNetworking

22

Internet HistoryInternet History

1961:1961: Kleinrock - Kleinrock - queueing theory shows queueing theory shows effectiveness of packet-effectiveness of packet-switchingswitching

1964:1964: Baran - packet- Baran - packet-switching in military netsswitching in military nets

1967:1967: ARPAnet conceived ARPAnet conceived by Advanced Research by Advanced Research Projects AgencyProjects Agency

1969:1969: first ARPAnet node first ARPAnet node operationaloperational

1972:1972: ARPAnet ARPAnet

demonstrated demonstrated publiclypublicly

NCP (Network NCP (Network Control Protocol) first Control Protocol) first host-host protocol host-host protocol

first e-mail programfirst e-mail program ARPAnet has 15 ARPAnet has 15

nodesnodes

1961-1972: Early packet-switching 1961-1972: Early packet-switching principlesprinciples

33

Internet HistoryInternet History

1970:1970: ALOHAnet satellite ALOHAnet satellite network in Hawaiinetwork in Hawaii

1973:1973: Metcalfe’s PhD thesis Metcalfe’s PhD thesis proposes Ethernetproposes Ethernet

1974:1974: Cerf and Kahn - Cerf and Kahn - architecture for architecture for interconnecting networksinterconnecting networks

late70’s:late70’s: proprietary proprietary architectures: DECnet, SNA, architectures: DECnet, SNA, XNAXNA

late 70’s:late 70’s: switching fixed switching fixed length packets (ATM length packets (ATM precursor)precursor)

1979:1979: ARPAnet has 200 nodes ARPAnet has 200 nodes

Cerf and Kahn’s Cerf and Kahn’s internetworking principles:internetworking principles: minimalism, autonomy - minimalism, autonomy -

no internal changes no internal changes required to interconnect required to interconnect networksnetworks

best effort service best effort service modelmodel

stateless routersstateless routers decentralized controldecentralized control

define today’s Internet define today’s Internet architecturearchitecture

1972-1980: Internetworking, new and 1972-1980: Internetworking, new and proprietary netsproprietary nets

44

Internet HistoryInternet History

1983:1983: deployment of deployment of TCP/IPTCP/IP

1982:1982: SMTP e-mail SMTP e-mail protocol defined protocol defined

1983:1983: DNS defined for DNS defined for name-to-IP-address name-to-IP-address translationtranslation

1985:1985: FTP protocol FTP protocol defineddefined

1988:1988: TCP congestion TCP congestion controlcontrol

new national new national networks: Csnet, networks: Csnet, BITnet, NSFnet, MinitelBITnet, NSFnet, Minitel

100,000 hosts 100,000 hosts connected to connected to confederation of confederation of networksnetworks

1980-1990: new protocols, a proliferation 1980-1990: new protocols, a proliferation of networksof networks

55

Internet HistoryInternet History

Early 1990’s: Early 1990’s: ARPAnet ARPAnet decommissioneddecommissioned

1991: 1991: NSF lifts restrictions on NSF lifts restrictions on commercial use of NSFnet commercial use of NSFnet (decommissioned, 1995)(decommissioned, 1995)

early 1990s:early 1990s: Web Web hypertext [Bush 1945, hypertext [Bush 1945,

Nelson 1960’s]Nelson 1960’s] HTML, HTTP: Berners-LeeHTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape1994: Mosaic, later Netscape late 1990’s: late 1990’s:

commercialization of the commercialization of the WebWeb

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

instant messaging, instant messaging, peer2peer file sharing peer2peer file sharing (e.g., Naptser)(e.g., Naptser)

network security to network security to forefrontforefront

est. 50 million host, est. 50 million host, 100 million+ users100 million+ users

backbone links backbone links running at Gbpsrunning at Gbps

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

Structure of the InternetStructure of the Internet

Europe

Japan

Backbone 1

Backbone 2

Backbone 3

Backbone 4, 5, N

Australia

Regional A

Regional B

NAP

NAP

NAP

NAP

SOURCE: CISCO SYSTEMS

MAPS UUNET MAPKOREA

Internet Host Count 1991-Internet Host Count 1991-20032003

172,000,000ESTIMATE:300,000,000 hosts by 2005

“Host” computer than can be reached by a URL

Internet Leverage by CountryInternet Leverage by CountryRankRank CountryCountry UsersUsers % of % of

UsersUsers% of World% of World LeveragLeverag

ee

11 U.S.U.S. 166M166M 25.025.0 4.524.52 5.555.55

22 JapanJapan 56M56M 8.48.4 2.052.05 4.204.20

33 ChinaChina 46M46M 7.07.0 20.9720.97 0.330.33

44 U.K.U.K. 35M35M 5.35.3 0.970.97 5.465.46

55 GermanyGermany 32M32M 4.84.8 1.341.34 3.583.58

66 S. KoreaS. Korea 26M26M 3.93.9 0.780.78 5.005.00

77 ItalyItaly 20M20M 3.03.0 0.930.93 3.233.23

88 RussiaRussia 18M18M 2.72.7 2.342.34 1.151.15

99 FranceFrance 17M17M 2.62.6 0.970.97 2.682.68

1010 CanadaCanada 17M17M 2.62.6 0.510.51 5.105.10

1111 BrazilBrazil 14M14M 2.12.1 2.842.84 0.740.74

1212 AustraliaAustralia 11M11M 1.71.7 0.320.32 5.315.31

1313 NetherlandNetherlandss

10M10M 1.51.5 0.260.26 5.775.77

LEVERAGE = % OF INTERNET USERS ÷ % OF WORLD POPULATION

WORLD TOTAL USERS (AUG. 2003): 700,000,000

99

What’s the Internet: “nuts and What’s the Internet: “nuts and bolts” viewbolts” view

millions of connected millions of connected computing devices: computing devices: hosts, hosts, end-systemsend-systems PCs workstations, PCs workstations,

serversservers PDAs phones, toastersPDAs phones, toasters

running running network appsnetwork apps communication linkscommunication links

fiber, copper, radio, fiber, copper, radio, satellitesatellite

transmission rate = transmission rate = bandwidthbandwidth

routers:routers: forward packets forward packets (chunks of data)(chunks of data)

local ISP

companynetwork

regional ISP

router workstation

servermobile

1010

““Cool” internet appliancesCool” internet appliances

World’s smallest web serverhttp://www-ccs.cs.umass.edu/~shri/iPic.html

IP picture framehttp://www.ceiva.com/

Web-enabled toaster+weather forecaster

1111

What’s the Internet: “nuts and What’s the Internet: “nuts and bolts” viewbolts” view

protocolsprotocols control sending, control sending, receiving of msgsreceiving of msgs e.g., TCP, IP, HTTP, FTP, e.g., TCP, IP, HTTP, FTP,

PPPPPP Internet: Internet: “network of “network of

networks”networks” loosely hierarchicalloosely hierarchical public Internet versus public Internet versus

private intranetprivate intranet Internet standardsInternet standards

RFC: Request for commentsRFC: Request for comments IETF: Internet Engineering IETF: Internet Engineering

Task ForceTask Force

local ISP

companynetwork

regional ISP

router workstation

servermobile

1212

What’s the Internet: a service viewWhat’s the Internet: a service view communication communication

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

commerce, database., commerce, database., voting, file (MP3) sharingvoting, file (MP3) sharing

communication services communication services provided to apps:provided to apps: connectionlessconnectionless connection-orientedconnection-oriented

cyberspacecyberspace [Gibson]: [Gibson]:

““a consensual hallucination experienced daily by a consensual hallucination experienced daily by billions of operators, in every nation, ...." billions of operators, in every nation, ...."

1313

What’s a protocol?What’s a protocol?human protocols:human protocols: ““what’s the time?”what’s the time?” ““I have a question”I have a question” introductionsintroductions

… … specific msgs sentspecific msgs sent

… … specific actions specific actions taken when msgs taken when msgs received, or other received, or other eventsevents

network protocols:network protocols: machines rather than machines rather than

humanshumans all communication all communication

activity in Internet activity in Internet governed by protocolsgoverned by protocols

protocols define format, protocols define format, order of msgs sent and order of msgs sent and

received among received among network entities, and network entities, and actions taken on msg actions taken on msg transmission, receipttransmission, receipt

1414

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

Q:Q: Other human protocols? Other human protocols?

Hi

Hi

Got thetime?

2:00

TCP connection req

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

<file>time

1515

1616

A closer look at network A closer look at network structure:structure: network edge:network edge: applications applications

and hostsand hosts network core:network core:

routersrouters network of networksnetwork of networks

access networks, physical access networks, physical media:media: communication links communication links

1717

The network edge:The network edge: end systems (hosts):end systems (hosts):

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

client/server modelclient/server model client host requests, receives client host requests, receives

service from always-on service from always-on serverserver

e.g. Web browser/server; e.g. Web browser/server; email client/serveremail client/server

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

dedicated serversdedicated servers e.g. Gnutella, KaZaAe.g. Gnutella, KaZaA

1818

Network edge: connection-oriented Network edge: connection-oriented serviceservice

Goal:Goal: data transfer between data transfer between end systemsend systems

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

protocolprotocol set up “state”set up “state” in two in two

communicating hostscommunicating hosts TCP - Transmission Control TCP - Transmission Control

Protocol Protocol Internet’s connection-Internet’s connection-

oriented serviceoriented service

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

stream data transferstream data transfer loss: loss:

acknowledgements and acknowledgements and retransmissionsretransmissions

flow control:flow control: sender won’t sender won’t

overwhelm receiveroverwhelm receiver congestion control:congestion control:

senders “slow down senders “slow down sending rate” when sending rate” when network congestednetwork congested

1919

Network edge: connectionless Network edge: connectionless serviceservice

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

UDPUDP - User Datagram - User Datagram Protocol [RFC 768]: Protocol [RFC 768]: Internet’s connectionless Internet’s connectionless serviceservice unreliable data transferunreliable data transfer no flow controlno flow control no congestion controlno congestion control

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

transfer), Telnet transfer), Telnet (remote login), SMTP (remote login), SMTP (email)(email)

App’s using UDP:App’s using UDP: streaming media, streaming media,

teleconferencing, teleconferencing, DNS, Internet DNS, Internet telephonytelephony

2020

The Network CoreThe Network Core mesh of interconnected mesh of interconnected

routersrouters thethe fundamental question: fundamental question:

how is data transferred how is data transferred through net?through net? circuit switching:circuit switching:

dedicated circuit per dedicated circuit per call: telephone netcall: telephone net

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

2121

Network Core: Circuit Network Core: Circuit SwitchingSwitching

End-end resources End-end resources reserved for “call”reserved for “call”

link bandwidth, switch link bandwidth, switch capacitycapacity

dedicated resources: dedicated resources: no sharingno sharing

circuit-like circuit-like (guaranteed) (guaranteed) performanceperformance

call setup requiredcall setup required

2222

Network Core: Circuit Network Core: Circuit SwitchingSwitching

network resources network resources (e.g., bandwidth) (e.g., bandwidth) divided into divided into “pieces”“pieces”

pieces allocated to pieces allocated to callscalls

resource piece resource piece idleidle if not used by if not used by owning call owning call (no (no sharing)sharing)

dividing link dividing link bandwidth into bandwidth into “pieces”“pieces” frequency frequency

divisiondivision time divisiontime division

2323

Packet switching versus circuit Packet switching versus circuit switchingswitching

1 Mbit link1 Mbit link each user: each user:

100 kbps when 100 kbps when “active”“active”

active 10% of timeactive 10% of time circuit-switching: circuit-switching:

10 users10 users packet switching: packet switching:

with 35 users, with 35 users, probability > 10 probability > 10 active less active less than .0004than .0004

Packet switching allows more users to use network!Packet switching allows more users to use network!

N users

1 Mbps link

2424

Network TaxonomyNetwork TaxonomyTelecommunication

networks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

• Datagram network is not either connection-oriented or connectionless.• Internet provides both connection-oriented (TCP) and connectionless services (UDP) to apps.

2525

Access networks and physical Access networks and physical mediamedia

Q: Q: How do connection end How do connection end systems connect to edge systems connect to edge router?router?

residential access netsresidential access nets institutional access institutional access

networks (school, networks (school, company)company)

mobile access networksmobile access networks

Keep in mind: Keep in mind: bandwidth (bits per bandwidth (bits per

second) of access second) of access network?network?

shared or dedicated?shared or dedicated?

2626

Residential access: point to point Residential access: point to point accessaccess

Dialup via modemDialup via modem up to 56Kbps direct access up to 56Kbps direct access

to router (often less)to router (often less) Can’t surf and phone at Can’t surf and phone at

same time: can’t be same time: can’t be “always on”“always on”

ADSL:ADSL: asymmetric digital subscriber line asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps)up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps)up to 8 Mbps downstream (today typically < 1 Mbps) FDM: 50 kHz - 1 MHz for downstreamFDM: 50 kHz - 1 MHz for downstream

4 kHz - 50 kHz for upstream4 kHz - 50 kHz for upstream

0 kHz - 4 kHz for ordinary telephone0 kHz - 4 kHz for ordinary telephone

2727

Residential access: cable modemsResidential access: cable modems

HFC: hybrid fiber coaxHFC: hybrid fiber coax asymmetric: up to 10Mbps upstream, 1 Mbps asymmetric: up to 10Mbps upstream, 1 Mbps

downstreamdownstream networknetwork of cable and fiber attaches homes to ISP of cable and fiber attaches homes to ISP

routerrouter shared access to router among homeshared access to router among home issues: congestion, dimensioningissues: congestion, dimensioning

deployment: available via cable companies, e.g., deployment: available via cable companies, e.g., MediaOneMediaOne

2828

Residential access: cable modemsResidential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

2929

Cable Network Architecture: OverviewCable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

3030

Cable Network Architecture: OverviewCable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

3131

Cable Network Architecture: OverviewCable Network Architecture: Overview

home

cable headend

cable distributionnetwork

server(s)

3232

Company access: local area Company access: local area networksnetworks

company/univ company/univ local area local area networknetwork (LAN) connects (LAN) connects end system to edge end system to edge routerrouter

Ethernet:Ethernet: shared or dedicated shared or dedicated

link connects end link connects end system and routersystem and router

10 Mbs, 100Mbps, 10 Mbs, 100Mbps, Gigabit EthernetGigabit Ethernet

deployment:deployment: institutions, institutions, home LANs happening home LANs happening nownow

3333

Wireless access networksWireless access networks shared shared wirelesswireless access access

network connects end network connects end system to routersystem to router via base station aka “access via base station aka “access

point”point” wireless LANs:wireless LANs:

802.11b (WiFi): 11 Mbps802.11b (WiFi): 11 Mbps wider-area wireless accesswider-area wireless access

provided by telco operatorprovided by telco operator 3G ~ 384 kbps3G ~ 384 kbps

Will it happen??Will it happen?? WAP/GPRS in EuropeWAP/GPRS in Europe

basestation

mobilehosts

router

3434

Home networksHome networks

Typical home network components: Typical home network components: ADSL or cable modemADSL or cable modem router/firewall/NATrouter/firewall/NAT EthernetEthernet wireless accesswireless access

pointpoint

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet(switched)

3535

Physical MediaPhysical Media Bit: Bit: propagates betweenpropagates between

transmitter/rcvr pairstransmitter/rcvr pairs physical link:physical link: what lies what lies

between transmitter & between transmitter & receiverreceiver

guided media:guided media: signals propagate in solid signals propagate in solid

media: copper, fiber, coaxmedia: copper, fiber, coax unguided media:unguided media:

signals propagate freely, signals propagate freely, e.g., radioe.g., radio

Twisted Pair (TP)Twisted Pair (TP) two insulated two insulated

copper wirescopper wires Category 3: Category 3:

traditional phone traditional phone wires, 10 Mbps wires, 10 Mbps EthernetEthernet

Category 5 TP: Category 5 TP: 100Mbps Ethernet100Mbps Ethernet

3636

Physical Media: coax, fiberPhysical Media: coax, fiber

Coaxial cable:Coaxial cable: two concentric copper two concentric copper

conductorsconductors bidirectionalbidirectional baseband:baseband:

single channel on cablesingle channel on cable legacy Ethernetlegacy Ethernet

broadband:broadband: multiple channel on multiple channel on

cablecable HFCHFC

Fiber optic cable:Fiber optic cable: glass fiber carrying light glass fiber carrying light

pulses, each pulse a bitpulses, each pulse a bit high-speed operation:high-speed operation:

high-speed point-to-point high-speed point-to-point transmission (e.g., 5 Gps)transmission (e.g., 5 Gps)

low error rate: repeaters low error rate: repeaters spaced far apart ; immune spaced far apart ; immune to electromagnetic noiseto electromagnetic noise

3737

Physical media: radioPhysical media: radio

signal carried in signal carried in electromagnetic electromagnetic spectrumspectrum

no physical “wire”no physical “wire” bidirectionalbidirectional propagation propagation

environment effects:environment effects: reflection reflection obstruction by obstruction by

objectsobjects interferenceinterference

Radio link types:Radio link types: terrestrial microwaveterrestrial microwave

e.g. up to 45 Mbps channelse.g. up to 45 Mbps channels LANLAN (e.g., WaveLAN) (e.g., WaveLAN)

2Mbps, 11Mbps2Mbps, 11Mbps wide-areawide-area (e.g., cellular) (e.g., cellular)

e.g. 3G: hundreds of kbpse.g. 3G: hundreds of kbps satellitesatellite

up to 50Mbps channel (or multiple up to 50Mbps channel (or multiple smaller channels)smaller channels)

270 msec end-end delay270 msec end-end delay geosynchronous versus LEOSgeosynchronous versus LEOS

3838

Tier-1 ISP: e.g., SprintTier-1 ISP: e.g., SprintSprint US backbone network

3939

Protocol “Layers”Protocol “Layers”Networks are Networks are

complex! complex! many “pieces”:many “pieces”:

hostshosts routersrouters links of various links of various

mediamedia applicationsapplications protocolsprotocols hardware, hardware,

softwaresoftware

Question:Question: Is there any hope of Is there any hope of organizingorganizing structure of structure of

network?network?

Or at least our discussion Or at least our discussion of networks?of networks?

4040

Why layering?Why layering?Dealing with complex systems:Dealing with complex systems: explicit structure allows identification, explicit structure allows identification,

relationship of complex system’s piecesrelationship of complex system’s pieces layered layered reference modelreference model for discussion for discussion

modularization eases maintenance, updating modularization eases maintenance, updating of systemof system change of implementation of layer’s change of implementation of layer’s

service transparent to rest of systemservice transparent to rest of system e.g., change in gate procedure doesn’t e.g., change in gate procedure doesn’t

affect rest of systemaffect rest of system layering considered harmful?layering considered harmful?

4141

Network abstractionsNetwork abstractions

International Standards Organization International Standards Organization (ISO) developed the (ISO) developed the Open Systems Open Systems InterconnectionInterconnection ( (OSIOSI) model to ) model to describe networks:describe networks: 7-layer model.7-layer model.

Provides a standard way to classify Provides a standard way to classify network components and operations.network components and operations.

4242

OSI modelOSI model

physical mechanical, electrical

data link reliable data transport

network end-to-end service

transport connections

presentation data format

session application dialog control

application end-use interface

4343

OSI layersOSI layers

PhysicalPhysical: connectors, bit formats, etc.: connectors, bit formats, etc. Data linkData link: error detection and control : error detection and control

across a single link (single hop).across a single link (single hop). NetworkNetwork: end-to-end multi-hop data : end-to-end multi-hop data

communication.communication. TransportTransport: provides connections; : provides connections;

may optimize network resources.may optimize network resources.

4444

OSI layers, cont’d.OSI layers, cont’d.

SessionSession: services for end-user : services for end-user applications: data grouping, applications: data grouping, checkpointing, etc.checkpointing, etc.

PresentationPresentation: data formats, : data formats, transformation services.transformation services.

ApplicationApplication: interface between : interface between network and end-user programs.network and end-user programs.

4545

Internet protocol stackInternet protocol stack application:application: supporting network supporting network

applicationsapplications FTP, SMTP, STTPFTP, SMTP, STTP

transport:transport: host-host data transfer host-host data transfer TCP, UDPTCP, UDP

network:network: routing of datagrams from routing of datagrams from source to destinationsource to destination IP, routing protocolsIP, routing protocols

link:link: data transfer between data transfer between neighboring network elementsneighboring network elements PPP, EthernetPPP, Ethernet

physical:physical: bits “on the wire” bits “on the wire”

application

transport

network

link

physical

4646

Layering: logical communication Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

Each layer:Each layer: distributeddistributed ““entities” entities”

implement implement layer functions layer functions at each nodeat each node

entities entities perform perform actions, actions, exchange exchange messages with messages with peers peers

4747

Layering: Layering: logical logical communication communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

E.g.: transportE.g.: transport take data from take data from

appapp add addressing, add addressing,

reliability check reliability check info to form info to form “datagram”“datagram”

send datagram send datagram to peerto peer

wait for peer to wait for peer to ack receiptack receipt

analogy: post analogy: post officeoffice

data

transport

transport

ack

4848

Layering: physical communication Layering: physical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

4949

Protocol layering and dataProtocol layering and data

Each layer takes data from aboveEach layer takes data from above adds header information to create new data unitadds header information to create new data unit passes new data unit to layer belowpasses new data unit to layer below

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

datagram

frame

5050

TCP/UDPTCP/UDP

5151

Transport protocolsTransport protocols Transform Transform host-to-host host-to-host communication, offered communication, offered

by network layer, to by network layer, to process-to-process process-to-process communicationcommunication

Deliver important services to application layer:Deliver important services to application layer:1.1. Guaranteed message deliveryGuaranteed message delivery2.2. In-order deliveryIn-order delivery3.3. Detect/eliminate message replicationDetect/eliminate message replication4.4. Support arbitrarily large messagesSupport arbitrarily large messages5.5. Support synchronization between sender & receiverSupport synchronization between sender & receiver6.6. Allow receiver to apply flow control to senderAllow receiver to apply flow control to sender7.7. Support multiple application processes on each hostSupport multiple application processes on each host8.8. Other services? (congestion control, quality-of-service, Other services? (congestion control, quality-of-service,

…)…) Overview:Overview:

UDP: unreliable message delivery protocolUDP: unreliable message delivery protocol TCP: reliable stream transfer protocolTCP: reliable stream transfer protocol

5252

User Datagram Protocol User Datagram Protocol (UDP)(UDP)

SrcPort DstPort

Checksum Length

Data

0 16 31

Connectionless, unreliable, message delivery Connectionless, unreliable, message delivery But, optional checksum provides limited error detection But, optional checksum provides limited error detection

Computed over UDP header, message, and IP pseudoheaderComputed over UDP header, message, and IP pseudoheader Pseudoheader: IP src & dst addresses, protocol #, and UDP lengthPseudoheader: IP src & dst addresses, protocol #, and UDP length If source does not want to compute checksum, it sets it to zeroIf source does not want to compute checksum, it sets it to zero

Allows process demultiplexing using Allows process demultiplexing using portsports 16 bits per port: 65536 possible channels per host16 bits per port: 65536 possible channels per host

No flow control: sender can overrun receiver’s buffersNo flow control: sender can overrun receiver’s buffers

5353

Transmission Control Protocol Transmission Control Protocol (TCP)(TCP) Reliable, connection-oriented, byte-stream delivery serviceReliable, connection-oriented, byte-stream delivery service

Full duplex connectionFull duplex connection Supports flow control (and congestion control; to be covered later)Supports flow control (and congestion control; to be covered later) Supports application layer demultiplexing using portsSupports application layer demultiplexing using ports Segments vs application-layer “writes”: when does TCP transmit a Segments vs application-layer “writes”: when does TCP transmit a

segment?segment? Maximum Segment Size (MSS), Push operation, Send-TimerMaximum Segment Size (MSS), Push operation, Send-Timer

Application process

Writebytes

TCP

Send buffer

Segment Segment Segment

Transmit segments

Application process

Readbytes

TCP

Receive buffer

…

… …

5454

TCP segment formatTCP segment format Ports: as in UDPPorts: as in UDP SeqNum, AckNum, AdvWindowSeqNum, AckNum, AdvWindow: used in sliding-window algorithm : used in sliding-window algorithm

for reliable, in-order, unique delivery, and for flow-controlfor reliable, in-order, unique delivery, and for flow-control Flags: SYN, FIN, RESET, PUSH, URG, ACKFlags: SYN, FIN, RESET, PUSH, URG, ACK Checksum: computed as in UDP (but required)Checksum: computed as in UDP (but required) HdrLen: in 32-bit words; TCP header may include optionsHdrLen: in 32-bit words; TCP header may include options TCP options: Maximum Segment Size (MSS), timestamp, window TCP options: Maximum Segment Size (MSS), timestamp, window

scalescale

Options (variable)

Data

Checksum

SrcPort DstPort

HdrLen 0 Flags

UrgPtr

AdvertisedWindow

SequenceNum

Acknowledgment

0 4 10 16 31

5555

Connection establishmentConnection establishment CallerCaller (active open) and (active open) and calleecallee (passive open) (passive open) 3-way handshake algorithm3-way handshake algorithm Why don’t we set the initial sequence numbers to zero?Why don’t we set the initial sequence numbers to zero? What if any of the 3WHS messages get lost/delayed? What if any of the 3WHS messages get lost/delayed? What if the server wants to deny the connection?What if the server wants to deny the connection? Map the Unix system calls Map the Unix system calls socketsocket(), (), bindbind(), (), connectconnect(), (), listenlisten(), (),

acceptaccept() to the following diagram () to the following diagram

Active participant(client)

Passive participant(server)

SYN, SequenceNum = x

SYN + ACK, SequenceNum = y,

ACK, Acknowledgment = y + 1

Acknowledgment = x + 1

5656

Connection terminationConnection termination

Graceful closeGraceful close: independent termination of each : independent termination of each direction of the connectiondirection of the connection

Initiated by Initiated by closeclose() system call() system call After all pending data have been sent and ACKed, send After all pending data have been sent and ACKed, send

last segment with FIN bit setlast segment with FIN bit set That direction of the connection is closed 2*MSL seconds That direction of the connection is closed 2*MSL seconds

(2*120secs) after the remote end ACKs the FIN message(2*120secs) after the remote end ACKs the FIN message Why do we need to wait before closing the connection?Why do we need to wait before closing the connection? Why to wait for 2* MSL instead of 1*MSL?Why to wait for 2* MSL instead of 1*MSL?

Abrupt connection termination Abrupt connection termination Initiated by Initiated by abortabort(), or by error conditions(), or by error conditions Send segment with RST bit set, discarding any pending Send segment with RST bit set, discarding any pending

datadata

5757

TCP connection establishment & TCP connection establishment & tear-down state-transition diagramtear-down state-transition diagram

CLOSED

LISTEN

SYN_RCVD SYN_SENT

ESTABLISHED

CLOSE_WAIT

LAST_ACKCLOSING

TIME_WAIT

FIN_WAIT_2

FIN_WAIT_1

Passive open Close

Send/SYNSYN/SYN + ACK

SYN + ACK/ACK

SYN/SYN + ACK

ACK

Close/FIN

FIN/ACKClose/FIN

FIN/ACKACK + FIN/ACKTimeout after two segment lifetimes

FIN/ACK

ACK

ACK

ACK

Close/FIN

Close

CLOSED

Active open/SYN

5858

IPIP

5959

Internet Protocol (IP)Internet Protocol (IP)

Designed by Kahn & Cerf in early 70sDesigned by Kahn & Cerf in early 70s Most scalable and successful Most scalable and successful

internetworking protocol internetworking protocol

R1

ETH FDDI

IPIP

ETH

TCP R2

FDDI PPP

IP

R3

PPP ETH

IP

H1

IP

ETH

TCP

H8

6060

IP in communicationIP in communication

physical

data link

network

transport

presentation

application

session

physical

data link

network

transport

presentation

application

session

physical

data link

network

node A router node B

IP

6161

IP service modelIP service model

Service model of an internetwork should Service model of an internetwork should be feasible by any underlying network be feasible by any underlying network technologytechnology

IP service model: IP service model: host-to-host best-effort datagram host-to-host best-effort datagram

deliverydelivery ““Best-effort” means no guarantees for Best-effort” means no guarantees for

reliable or timely deliveryreliable or timely delivery IP was designed to “run over anything”IP was designed to “run over anything”

6262

IP headerIP header Important enough to remember its Important enough to remember its

fields!fields!Version HLen TOS Length

Ident Flags Offset

TTL Protocol Checksum

SourceAddr

DestinationAddr

Options (variable) Pad(variable)

0 4 8 16 19 31

Data

6363

IP addressesIP addresses IP vs MAC addressesIP vs MAC addresses Uniqueness Uniqueness

requirementrequirement Scalability Scalability

requirement: requirement: hierarchyhierarchy NetworkNetwork Host (interface)Host (interface)

ClassfulClassful addressing: addressing: Classes A, B, C, D, EClasses A, B, C, D, E

In mid-90s, addressing In mid-90s, addressing became became classlessclassless see CIDR (later)see CIDR (later)

Example: Example: GAtech web server GAtech web server

(www.gatech.edu): (www.gatech.edu): 130.207.165.120 130.207.165.120

Network Host

7 24

0(a)

Network Host

14 16

1 0(b)

Network Host

21 8

1 1 0(c)