Chapter 7 Packet-Switching Networks

Transcription

1 Chaper 7 Packe-Swiching Nework Nework Service and Inernal Nework Operaion Packe Nework Topology Daagram and Virual Circui Rouing in Packe Nework Shore Pah Rouing Chaper 7 Packe-Swiching Nework Nework Service and Inernal Nework Operaion

2 Nework Layer Nework Layer: he mo complex Require he coordinaed acion of muliple, geographically diribued nework elemen (wiche & rouer) Mu be able o deal wih very large cale Billion of uer (people & communicaing device) Bigge Challenge Addreing: where hould informaion be direced o? Rouing: wha pah hould be ued o ge informaion here? Packe Swiching Block Nework Sream Tranfer of informaion a payload in daa packe Packe undergo random delay & poible lo Differen applicaion impoe differing requiremen on he ranfer of informaion

3 Nework Service Meage Meage Nework ervice Tranpor Segmen Tranpor Nework ervice Nework Nework Nework Nework End yem α Daa link Phyical Daa link Phyical Daa link Phyical Daa link Phyical End yem β Nework can offer a variey of ervice o ranpor Connecion-oriened ervice or connecionle ervice Be-effor or delay/lo guaranee Nework Service v. Operaion Nework Service Connecionle Daagram Tranfer Connecion-Oriened Reliable and poibly conan bi rae ranfer Inernal Nework Operaion Connecionle IP Connecion-Oriened Telephone connecion ATM Variou combinaion are poible Connecion-oriened ervice over Connecionle operaion Connecionle ervice over Connecion-Oriened operaion Conex & requiremen deermine wha make ene

4 Complexiy a he Edge or in he Core? C End yem End yem α β 4 4 Medium A B Nework Phyical eniy Daa link eniy Nework eniy Nework eniy 4 Tranpor eniy The End-o-End Argumen for Syem Deign An end-o-end funcion i be implemened a a higher level han a a lower level End-o-end ervice require all inermediae componen o work properly Higher-level beer poiioned o enure correc operaion Example: ream ranfer ervice Eablihing an explici connecion for each ream acro nework require all nework elemen (NE) o be aware of connecion; All NE have o be involved in reeablihmen of connecion in cae of nework faul In connecionle nework operaion, NE do no deal wih each explici connecion and hence are much impler in deign 4

5 Nework Layer Funcion Eenial Rouing: mechanim for deermining he e of be pah for rouing packe require he collaboraion of nework elemen Forwarding: ranfer of packe from NE inpu o oupu Prioriy & Scheduling: deermining order of packe ranmiion in each NE Opional: congeion conrol, egmenaion & reaembly, ecuriy Chaper 7 Packe-Swiching Nework Packe Nework Topology 5

6 End-o-End Packe Nework Packe nework very differen han elephone nework Individual packe ream are highly bury Saiical muliplexing i ued o concenrae ream Uer demand can undergo dramaic change Peer-o-peer applicaion imulaed huge growh in raffic volume Inerne rucure highly decenralized Pah ravered by packe can go hrough many nework conrolled by differen organizaion No ingle eniy reponible for end-o-end ervice Acce Muliplexing Acce MUX To packe nework Packe raffic from uer muliplexed a acce o nework ino aggregaed ream DSL raffic muliplexed a DSL Acce Mux Cable modem raffic muliplexed a Cable Modem Terminaion Syem 6

7 Overubcripion r r r Nr Nc nc Acce Muliplexer N ubcriber c bp o mux Each ubcriber acive r/c of ime Mux ha C=nc bp o nework Overubcripion rae: N/n Find n o ha a mo % overflow probabiliy Feaible overubcripion rae increae wih ize N r/c n N/n exremely lighly loaded uer 0 very lighly loaded uer 0 lighly loaded uer 0 lighly loaded uer 40 lighly loaded uer 00 lighly loaded uer Home LAN WiFi Eherne Home Rouer To packe nework Home Rouer LAN Acce uing Eherne or WiFi (IEEE 80.) Privae IP addree in Home ( x) uing Nework Addre Tranlaion (NAT) Single global IP addre from ISP iued uing Dynamic Ho Configuraion Proocol (DHCP) 7

8 LAN Concenraion Swich / Rouer LAN Hub and wiche in he acce nework alo aggregae packe ream ha flow ino wiche and rouer Campu Nework Deparmenal Server To Inerne or wide area nework Only High-peed ougoing packe campu leave LAN backbone hrough ne rouer connec dep rouer Backbone Organizaion Server R Gaeway R S S R Server have redundan conneciviy o backbone R S R R 8

9 Connecing o Inerne Service Provider Inerne ervice provider Border rouer Campu Nework Border rouer Auonomou yem or domain LAN Inradomain level Inerdomain level nework adminiered by ingle organizaion Inerne Backbone Naional Service Provider A Naional Service Provider B NAP NAP Naional Service Provider C Privae peering Nework Acce Poin: e up during original commercializaion of Inerne o faciliae exchange of raffic Privae Peering Poin: wo-pary iner-isp agreemen o exchange raffic 9

10 (a) Naional Service Provider A Naional Service Provider B NAP Naional Service Provider C Privae peering NAP (b) NAP R A Roue Server LAN R B R C Key Role of Rouing How o ge packe from here o here? Decenralized naure of Inerne make rouing a major challenge Inerior gaeway proocol (IGP) are ued o deermine roue wihin a domain Exerior gaeway proocol (EGP) are ued o deermine roue acro domain Roue mu be conien & produce able flow Scalabiliy required o accommodae growh Hierarchical rucure of IP addree eenial o keeping ize of rouing able manageable 0

11 Chaper 7 Packe-Swiching Nework Daagram and Virual Circui The Swiching Funcion Dynamic inerconnecion of inpu o oupu Enable dynamic haring of ranmiion reource Two fundamenal approache: Connecionle Connecion-Oriened: Call eup conrol, Connecion conrol Backbone Nework Swich Acce Nework

12 Packe Swiching Nework Uer Nework Tranmiion line Packe wich Packe wiching nework Tranfer packe beween uer Tranmiion line + packe wiche (rouer) Origin in meage wiching Two mode of operaion: Connecionle Virual Circui Meage Swiching Meage Source Meage Swiche Meage Meage Deinaion Meage wiching invened for elegraphy Enire meage muliplexed ono hared line, ored & forwarded Header for ource & deinaion addree Rouing a meage wiche Connecionle

13 Meage Swiching Delay Source T Swich Swich τ Deinaion Delay Minimum delay = τ + T Addiional queueing delay poible a each link Long Meage v. Packe Mbi meage ource Approach : end Mbi meage Probabiliy meage arrive correcly BER=p=0-6 BER=0-6 de How many bi need o be ranmied o deliver meage? Approach : end 0 00-kbi packe Probabiliy packe arrive correcly P c = ( 0 ) e = e / ( 0 ) P c = e = e 0. 9 On average i ake abou On average i ake abou. ranmiion/hop ranmiion/hop Toal # bi ranmied Toal # bi ranmied 6 Mbi. Mbi

14 Packe Swiching - Daagram Meage broken ino maller uni (packe) Source & deinaion addree in packe header Connecionle, packe roued independenly (daagram) Packe may arrive ou of order Pipelining of packe acro nework can reduce delay, increae hroughpu Lower delay ha meage wiching, uiable for ineracive raffic Packe Packe Packe Packe Packe Packe Swiching Delay Aume hree packe correponding o one meage ravere ame pah Delay Minimum Delay = τ + 5(T/) (ingle pah aumed) Addiional queueing delay poible a each link Packe pipelining enable meage o arrive ooner 4

15 Delay for k-packe Meage over L Hop τ + (T/) fir bi received hop L hop Lτ + (L-)P fir bi received τ + (T/) fir bi releaed Lτ + LP fir bi releaed τ + 5 (T/) la bi releaed Lτ + LP + (k-)p la bi releaed where T = k P Rouing Table in Daagram Nework Deinaion addre Oupu por 7 6 Roue deermined by able lookup Rouing deciion involve finding nex hop in roue o given deinaion Rouing able ha an enry for each deinaion pecifying oupu por ha lead o nex hop Size of able become impracical for very large number of deinaion 5

16 Example: Inerne Rouing Inerne proocol ue daagram packe wiching acro nework Nework are reaed a daa link Ho have wo-por IP addre: Nework addre + Ho addre Rouer do able lookup on nework addre Thi reduce ize of rouing able Packe Swiching Virual Circui Packe Packe Packe Packe Virual circui Call e-up phae e up poiner in fixed pah along nework All packe for a connecion follow he ame pah Abbreviaed header idenifie connecion on each link Packe queue for ranmiion Variable bi rae poible, negoiaed during call e-up Delay variable, canno be le han circui wiching 6

17 Connecion Seup Connec reque Connec confirm SW Connec reque Connec confirm SW SW n Connec reque Connec confirm Signaling meage propagae a roue i eleced Signaling meage idenify connecion and eup able in wiche Typically a connecion i idenified by a local ag, Virual Circui Idenifier (VCI) Each wich only need o know how o relae an incoming ag in one inpu o an ougoing ag in he correponding oupu Once able are eup, packe can flow along pah Connecion Seup Delay Connec reque CR CR CC CC Connec confirm Releae Connecion eup delay i incurred before any packe can be ranferred Delay i accepable for uained ranfer of large number of packe Thi delay may be unaccepably high if only a few packe are being ranferred 7

18 Virual Circui Forwarding Table Inpu VCI Oupu por Oupu VCI Each inpu por of packe wich ha a forwarding able Lookup enry for VCI of incoming packe Deermine oupu por (nex hop) and iner VCI for nex link Very high peed are poible Table can alo include prioriy or oher informaion abou how packe hould be reaed Cu-Through wiching Source Swich Swich Deinaion Minimum delay = τ + T Some nework perform error checking on header only, o packe can be forwarded a oon a header i received & proceed Delay reduced furher wih cu-hrough wiching 8

19 Meage v. Packe Minimum Delay Meage: L τ + L T = L τ + (L )T + T Packe L τ + L P + (k ) P = L τ + (L ) P + T Cu-Through Packe (Immediae forwarding afer header) = L τ + T Above neglec header proceing delay Chaper 7 Packe-Swiching Nework Daagram and Virual Circui Srucure of a Packe Swich 9