How To Use A Network On A Network With A Powerline (Lan) On A Pcode (Lan On Alan) (Lan For Acedo) (Moe) (Omo) On An Ipo) Or Ipo (

Transcription

1 Hubs, Bidges, and Switches Used fo extending LANs in tems of geogaphical coveage, numbe of nodes, administation capabilities, etc. Diffe in egads to: m collision domain isolation m laye at which they opeate Diffeent than outes m plug and play m don t povide optimal outing of IP packets Laye 2 and below components 5: Link Laye and Local Aea Netwoks 5c-1

2 Hubs Physical Laye devices: essentially epeates opeating at bit levels: epeat eceived bits on one inteface to all othe intefaces Hubs can be aanged in a hieachy (o multitie design), with a backbone hub at its top 5: Link Laye and Local Aea Netwoks 5c-2

3 Hubs (moe) Each connected LAN is efeed to as a LAN segment Hubs do not isolate collision domains: a node may collide with any node esiding at any segment in the LAN Hub Advantages: m Simple, inexpensive device m Multi-tie povides gaceful degadation: potions of the LAN continue to opeate if one of the hubs malfunction m Extends maximum distance between node pais (100m pe Hub) 5: Link Laye and Local Aea Netwoks 5c-3

4 Hubs (moe) Hub Limitations: m Single collision domain esults in no incease in max thoughput; the multi-tie thoughput same as the the single segment thoughput m Individual LAN estictions pose limits on the numbe of nodes in the same collision domain (thus, pe Hub); and on the total allowed geogaphical coveage m Cannot connect diffeent Ethenet types (e.g., 10BaseT and 100baseT) 5: Link Laye and Local Aea Netwoks 5c-4

5 Bidges Link Laye devices: they opeate on Ethenet fames (i.e. laye 2 devices), examining the fame heade and selectively fowading a fame base on its destination Bidge isolates collision domains since it buffes fames When a fame is to be fowaded on a segment, the bidge uses CSMA/CD to access the segment and tansmit 5: Link Laye and Local Aea Netwoks 5c-5

6 Bidges (moe) Bidge advantages: m Isolates collision domains esulting in highe total max thoughput, and does not limit the numbe of nodes no geogaphical coveage m Can connect diffeent types of Ethenet since it is a stoe and fowad device m Tanspaent: no need fo any change to hosts LAN adaptes 5: Link Laye and Local Aea Netwoks 5c-6

7 Backbone Bidge 5: Link Laye and Local Aea Netwoks 5c-7

8 Inteconnection Without Backbone Not ecommended fo two easons: - Single point of failue at Compute Science hub - All taffic between EE and SE must path ove CS segment 5: Link Laye and Local Aea Netwoks 5c-8

9 Bidge Filteing Bidges lean which hosts can be eached though which intefaces and maintain filteing tables A filteing table enty: (Node LAN Addess, Bidge Inteface, Time Stamp) Filteing pocedue: if destination is on LAN on which fame was eceived then dop the fame else { lookup filteing table } if enty found fo destination then fowad the fame on inteface indicated; else flood; /* fowad on all but the inteface on which the fame aived*/ 5: Link Laye and Local Aea Netwoks 5c-9

10 Bidge Leaning When a fame is eceived, the bidge leans fom the souce addess and updates its filteing table (Node LAN Addess, Bidge Inteface, Time Stamp) Stale enties in the Filteing Table ae dopped (TTL can be 60 minutes) 5: Link Laye and Local Aea Netwoks 5c-10

11 Bidges Spanning Tee Fo inceased eliability, it is desiable to have edundant, altenate paths fom a souce to a destination With multiple simultaneous paths howeve, cycles esult on which bidges may multiply and fowad a fame foeve Solution is oganizing the set of bidges in a spanning tee by disabling a subset of the intefaces in the bidges: Bidges talk to each othe! Disabled 5: Link Laye and Local Aea Netwoks 5c-11

12 Bidges vesus Routes Both ae stoe-and-fowad devices, but Routes ae Netwok Laye devices (examine netwok laye heades) and Bidges ae Link Laye devices Routes maintain outing tables and implement outing algoithms; bidges maintain filteing tables and implement filteing, leaning and spanning tee algoithms 5: Link Laye and Local Aea Netwoks 5c-12

13 Routes vesus Bidges Bidges + and + Bidge opeation is simple equiing less pocessing bandwidth (plug and play) - Topologies ae esticted with bidges: a spanning tee must be built to avoid cycles - Bidges do not offe potection fom boadcast stoms (endless boadcasting by a host will be fowaded by a bidge) 5: Link Laye and Local Aea Netwoks 5c-13

14 Routes vesus Bidges Routes + and - + Abitay topologies can be suppoted, cycling is limited by TTL countes (and good outing pots) + Povide fiewall potection against boadcast stoms - Requie IP addess configuation (not plug and play) - Requie highe pocessing bandwidth Bidges do well in small (few hunded hosts) while outes ae equied in lage netwoks (thousands of hosts) 5: Link Laye and Local Aea Netwoks 5c-14

15 Ethenet Switches A new device came in 1990s A switch is a device that incopoates bidge functions as well as point-to-point dedicated connections A host attached to a switch via a dedicated pointto-point connection; will always sense the medium as idle; no collisions eve! Ethenet Switches povide a combinations of shaed/dedicated, 10/100/1000 Mbps connections 5: Link Laye and Local Aea Netwoks 5c-15

16 Ethenet Switches (moe) Some Ethenet switches suppot cut-though switching: fame fowaded immediately to destination without awaiting fo assembly of the entie fame in the switch buffe; slight eduction in latency (athe than stoe-and-fowad packet switching) The cut-though switching will diffe fom stoe-andfowad switching only when the output buffe is empty When output buffe is empty, thee is no need to get the whole packet befoe sending it out in cut-though switching Ethenet switches vay in size, with the lagest ones incopoating a high bandwidth inteconnection 5: Link Laye and Local Aea Netwoks 5c-16

17 Ethenet Switches (moe) Dedicated Shaed 5: Link Laye and Local Aea Netwoks 5c-17

18 IEEE Wieless LAN Wieless LANs ae becoming popula fo mobile Intenet access Applications: nomadic Intenet access, potable computing, ad hoc netwoking (multihopping) IEEE standads defines MAC potocol; unlicensed fequency spectum bands: 900Mhz, 2.4Ghz Basic Sevice Sets + Access Points Distibution System Like a bidged LAN (flat MAC addess) 5: Link Laye and Local Aea Netwoks 5c-18

19 Ad Hoc Netwoks IEEE stations can dynamically fom a goup without AP Ad Hoc Netwok: no pe-existing infastuctue Applications: laptop meeting in confeence oom, ca, aipot; inteconnection of pesonal devices (see bluetooth.com); battelfield; pevasive computing (smat spaces) IETF MANET (Mobile Ad hoc Netwoks) woking goup 5: Link Laye and Local Aea Netwoks 5c-19

20 CSMA Potocol: IEEE MAC Potocol - sense channel idle fo DISF sec (Distibuted Inte Fame Space) - tansmit fame (no Collision Detection) - eceive etuns ACK afte SIFS (Shot Inte Fame Space) -if channel sensed busy then binay backoff NAV: Netwok Allocation Vecto (min time of defeal) 5: Link Laye and Local Aea Netwoks 5c-20

21 Hidden Teminal Effect CSMA inefficient in pesence of hidden teminals Hidden teminals: A and B cannot hea each othe because of obstacles o signal attenuation; so, thei packets collide at B Solution? CSMA/CA CA = Collision Avoidance 5: Link Laye and Local Aea Netwoks 5c-21

22 Collision Avoidance: RTS-CTS exchange CTS feezes stations within ange of eceive (but possibly hidden fom tansmitte); this pevents collisions by hidden station duing data RTS and CTS ae vey shot: collisions duing data phase ae thus vey unlikely (the end esult is simila to Collision Detection) Note: IEEE allows CSMA, CSMA/CA and polling fom AP CTS: clea to send RTS: equest to send 5: Link Laye and Local Aea Netwoks 5c-22

23 Point to Point Potocol (PPP) Point to point, wied data link easie to manage than boadcast link: no Media Access Contol Seveal Data Link Potocols: PPP, HDLC, SDLC, Altenating Bit potocol, etc PPP (Point to Point Potocol) is vey popula: used in dial up connection between esidential Host and ISP; on SONET/SDH connections, etc PPP is extemely simple (the simplest in the Data Link potocol family) and vey steamlined 5: Link Laye and Local Aea Netwoks 5c-23

24 PPP Requiements Packet faming: encapsulation of IP packets bit tanspaency: must cay any bit patten in the data field of the netwok potocol eo detection (no coection) multiple netwok laye potocols connection liveness (detection of link failue) Netwok Laye Addess negotiation: Hosts/nodes acoss the link must lean/configue each othe s netwok addess (e.g. IP addess) 5: Link Laye and Local Aea Netwoks 5c-24

25 Not Povided by PPP eo coection/ecovey flow contol sequencing multipoint links (e.g., polling) 5: Link Laye and Local Aea Netwoks 5c-25

26 PPP Data Fame Flag: delimite (faming) Addess: does nothing (only one option) Contol: does nothing; in the futue possible multiple contol fields Potocol: uppe laye to which fame must be deliveed (e.g., PPP-LCP, IP, IPCP, etc) 5: Link Laye and Local Aea Netwoks 5c-26

27 Byte Stuffing Fo data tanspaency, the data field must be allowed to include the patten < > ; ie, this must not be intepeted as a flag to alet the eceive, the tansmitte stuffs an exta < > byte afte each < > data byte the eceive discads each followed by anothe , and continues data eception 5: Link Laye and Local Aea Netwoks 5c-27

28 PPP Data Contol Potocol PPP-LCP establishes/eleases the PPP connection; negotiates options Stats in DEAD state Options: max fame length; authentication potocol Once PPP link established, IPCP (Contol Potocol) moves in (on top of PPP) to configue IP netwok addesses etc. 5: Link Laye and Local Aea Netwoks 5c-28