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Purdue CS 53600 - What is traveling on the wires

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CS 536 ParkWhat is traveling on the wires?Mixed data:bulk data, audio/voice, video/image, real-time in-teractive data, etc.−→ > 85% of Internet traffic is bulk TCP traffic−→ due to Web and http−→ barriers to streaming traffic implosion−→ technical and otherTilting toward multimedia data; i.e., traffic with QoSrequirements including real-time constraints.CS 536 ParkInternet traffic is bursty:−→ multimedia: MPEG compressed video0200004000060000800000 6.6 13.3 20.0 26.6traffic volume (bits)time (min)terminatorWhy?• pattern of scene changes in movies→ within a scene few changes• across scenes, significant “scenary” changes→ “director’s eye”• video compression→ utilize inter-frame compressionCS 536 Park−→ file sizes on file servers05000001e+061.5e+062e+062.5e+060 2e+06 4e+06 6e+06 8e+06 1e+07File CountFile Size Range (bytes)File CountWhy?• bulk data: 80/20 rule-of-thumb• majority of files are small, a few very large→ disproportionate contribution to total traffic→ “elephants and mice”Usage pattern in the real-world: uneven or “unfair”CS 536 ParkGiven mixed payload:Data networks capable of carrying diverse payload on thesame network is a recent phenomenon.Even today, much of voice traffic (telephony) is carriedon an entirely separate communication network vis-`a-vis data traffic, operating under different internetworkingprinciples from the latter.−→ time-division multiplexing (TDM) for telephony−→ packet switching for data networksCS 536 ParkHow is time—viewed as a resource—shared?Time-division multiplexing:ABCDA A ABBBCCDDCTimePacket switching:TimeAB CAA ABCS 536 ParkHow is “real estate” shared?Circuit switching: Virtual channel is established and fol-lowed during the lifetime of an end-to-end connection.aabcbcabc−→ static route−→ in-order delivery−→ small routing tableTelephone networks (and ATM networks).CS 536 ParkPacket switching: Every packet belonging to an end-to-end conversation is an independent entity; may take adifferent route from other packets in the same connection.aabbcacbc−→ dynamic route−→ out-of-order delivery−→ larger route tableTrade-off between processing overhead and route good-nessCS 536 ParkTrend: convergence to packet-switched technology−→ layer 2 switching in the backbone: VC−→ move away from IP due to overhead−→ IP critical at peering pointsYet another drawback of packet switching:−→ “bully phenomenon”−→ video: 24 frames-per-second (f/s)−→ voice: 8000 samples-per-second (s/s)−→ what to do?CS 536 ParkAsynchronous transfer mode (ATM):TimeAAA BBC ABC BBBBBA−→ 53 byte packet or cell .Synergy of all forms of data, audio, video, bulk, etc. Oneunified network with “integrated” services.Addresses bully problem but ...−→ significant overhead (48 + 5)−→ why 48 bytes?CS 536 Park−→ performs its own routing (VC based)−→ function duplication−→ very complex (overloaded with features)−→ feature 6= “how to”Much has migrated to new layer 2 switching technology−→ MPLS (multiprotocol label switching)−→ ATM community reincarnated as MPLS ...−→ after shrinkage−→ supporting role to IPCS 536 ParkIn the meantime, at routers receiving mixed payload ...Try to avoid packet loss, but no loss comes at a cost:• fast memory (buffer) is not cheap• management overhead: ASIC vs. software vs. hybrid• packets have to wait in line for their turn→ queueing delay→ who gets preference?CS 536 ParkDepends on scheduling.• FIFO (first-in-first-out)• priority queue• round robin + weighted fair queue→ use TOS field of IPv4 to encode priority• reservation→ software-based “line leasing”CS 536 ParkIs adding more and more buffer space a good solution?−→ no: related to “elephants and mice”−→ bandwidth is preferred (and, presently, cheaper)When is it outright bad?−→ real-time multimedia

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