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Bertsekas and R. Gallager. Data Networks, 2nd Ed., 1992. P-H. S. Keshav. An Engineering Approach to Computer Networking. 1997. E-W J.F. Kurose and K.W. Ross. Computer Networking. 2000, E-W. L. Kleinrock. Queueing Systems, Vol. 1. 1975. Wiley J.Y.Hui, Switching and Traffic Theory for Integrated Broadband Networks, Kluwer 1990 A.M. Law and W.D. Kelton. Simulation Modeling & Analysis, 2nd Ed., 1991,M-H 9        >  (      'y  "B5 Switching" C$$   S. Keshav, An Engineering Approach to Computer Networks, A-W, 1997 M. Karol, M. Hluchyj, and S. Morgan, "Input Versus Output Queueing on a Space-Division Packet Switch," IEEE Trans. on Communications, 35(12):1347-1356, Dec. 1987. AAA8A%ABAAAAZ    G    &    c  UWhat is it all about?   How do we move traffic from one part of the network to another? Connect end-systems to switches, and switches to each other Data arriving to an input port of a switch have to be moved to one or more of the output ports     wOutline   switching - general Packet switching General Type of switches Switch generations Buffer placement Port mappers Buffer Placement Dropping policiesB%=0f=0&g    #  VTypes of switching elements   aTelephone switches switch samples Datagram routers switch datagrams ATM switches switch ATM cellst   @"           WClassification   Packet vs. circuit switches packets have headers and samples don t Connectionless vs. connection oriented connection oriented switches need a call setup setup is handled in control plane by switch controller connectionless switches deal with self-contained datagrams('f(&fC #      X!Other switching element functions "  Participate in routing algorithms to build routing tables Resolve contention for output trunks scheduling Admission control to guarantee resources to certain streamst"% *"% *    Y Requirements   Capacity of switch is the maximum rate at which it can move information, assuming all data paths are simultaneously active Primary goal: maximize capacity subject to cost and reliability constraints Circuit switch must reject call if can t find a path for samples from input to output goal: minimize call blocking Packet switch must reject a packet if it can t find a buffer to store it awaiting access to output trunk goal: minimize packet loss Don t reorder packets ,Vif,Vfif  f     xOutline   switching - general Packet switching General Type of switches Switch generations Buffer placement Port mappers Buffer Placement Dropping policiesV%=0ff$0&g    #  k$Packet switching   ]In a circuit switch, path of a sample is determined at time of connection establishment No need for a sample header--position in frame is enough In a packet switch, packets carry a destination field Need to look up destination port on-the-fly Datagram lookup based on entire destination address Cell lookup based on VCI Other than that, very similarj++&    c  |Blocking in packet switches   Can have both internal and output blocking Internal no path to output Output trunk unavailable Unlike a circuit switch, cannot predict if packets will block (why?) If packet is blocked, must either buffer or drop it`4y4y   }Dealing with blocking    Overprovisioning internal links much faster than inputs (speedup) Buffers at input or output (or both) Backpressure if switch fabric doesn t have buffers, prevent packet from entering until path is available Parallel switch fabrics increases effective switching capacity1  \'(  \ '    l&)Repeaters, bridges, routers, and gateways *  Repeaters: at physical level Bridges: at datalink level (based on MAC addresses) (L2) discover attached stations by listening Routers: at network level (L3) participate in routing protocols Application level gateways: at application level (L7) treat entire network as a single hop e.g mail gateways and transcoders Gain functionality at the expense of forwarding speed for best performance, push functionality as low as possible V(!6G6<V(!6G6 <  @)         s  yOutline   switching - general Packet switching General Type of switches Switch generations Buffer placement Port mappers Buffer Placement Dropping policiesJ%=0%f0&g    #  o$Three generations of packet switches %  Different trade-offs between cost and performance Represent evolution in switching capacity, rather than in technology With same technology, a later generation switch achieves greater capacity, but at greater cost All three generations are represented in current products>w_:wA_A:   pFirst generation switch   Most Ethernet switches and cheap packet routers S/w router, e.g., Linux/FreeBSD boxes Bottleneck can be CPU, host-adaptor or I/O bus, depending &H    A  rSecond generation switch   QPort mapping intelligence in line cards ATM switch guarantees hit in lookup cache R  sThird generation switches   uBottleneck in second generation switch is the bus (or ring) Third generation switch provides parallel paths (fabric) u    tThird generation (contd.)   Features self-routing fabric output buffer is a point of contention unless we arbitrate access to fabric potential for unlimited scaling, as long as we can resolve contention for output bufferb ;%X ;  X   zOutline   switching - general Packet switching General Type of switches Switch generations Port mappers Buffer Placement Dropping policiesB%,0%, f#&V    $  m' Port mappers&      Look up output port based on destination address Easy for VCI: just use a table Harder for datagrams: need to find longest prefix match e.g. packet with address 128.32.1.20 entries: (128.32.*, 3), (128.32.1.*, 4), (128.32.1.20, 2) A standard solution: trie vf"_f _ 4[         Tries    Some ways to improve performance cache recently used addresses in a CAM move common entries up to a higher level (match longer strings)&'g'g    ~Outline   switching - general Packet switching General Type of switches Switch generations Port mappers Buffer Placement Dropping policiesJ%,0%, f&V    $  ? Buffering   All packet switches need buffers to match input rate to service rate or cause heavy packet loses Where should we place buffers? input output in the fabric LEE    B Input buffering (input queueing)&       No speedup in buffers or trunks (unlike output queued switch) Needs arbiter Problem: head of line blocking with randomly distributed packets, utilization at most 58.6%4qZ=Z[=&      Thead of line blocking  simple upper bound*   Assume nxn switch with uniform distribution of destination Probability for an output port not to be selected is Capacity is bounded by 1-1/e = 0.63 For 2x2 switch the max capacity is 0.75 (tight bound)Vi%6( ^head of line blocking  alternative calculation/   3The success probability of an input port selection:3 CDealing with HOL blocking   pPer-output queues at inputs (VOQ) Arbiter must choose one of the input ports for each output port How to select? Parallel Iterated Matching inputs tell arbiter which outputs they are interested in output selects one of the inputs some inputs may get more than one grant, others may get none if >1 grant, input picks one at random, and tells output losing inputs and outputs try again Used in DEC Autonet 2 switch, McKeown s iSLIP, and more.9fl|s(@            DOutput queueing&      <Don t suffer from head-of-line blocking But output buffers need to run much faster than trunk speed Can reduce some of the cost by using the knockout principle unlikely that all N inputs will have packets for the same output drop extra packets, fairly distributing losses among inputs 8~ ~    GBuffered fabric   Buffers in each switch element Pros Speed up is only as much as fan-in Hardware backpressure reduces buffer requirements Cons costly (unless using single-chip switches) scheduling is hardL$U>$U>   Buffered crossbar   }What happens if packets at two inputs both want to go to same output? Can defer one at an input buffer Or, buffer crosspointsr     HHybrid solutions   XBuffers at more than one point Becomes hard to analyze and manage But common in practice Y  I Multicasting   Useful to do this in hardware Assume portmapper knows list of outputs Incoming packet must be copied to these output ports Two subproblems generating and distributing copies VCI translation for the copies 6BBL%     Q     C    K"Generating and distributing copies #  Either implicit or explicit Implicit suitable for bus-based, ring-based, crossbar, or broadcast switches multiple outputs enabled after placing packet on shared bus used in Paris and Datapath switches Explicit need to copy a packet at switch elements use a copy network place # of copies in tag element copies to both outputs and decrements count on one of them collect copies at outputs Both schemes increase blocking probability % +% /~+  &       Outline   switching - general Packet switching General Type of switches Switch generations Buffer placement Port mappers Buffer Placement Dropping policiesB%=0%=f&g    #  ePacket dropping   Packets that cannot be served immediately are buffered Full buffers => packet drop strategy Packet losses happen almost always from best-effort connections (why?) Shouldn t drop packets unless imperative? packet drop wastes resources (why?) H$Gq$    f!Classification of drop strategies "  M1. Degree of aggregation 2. Drop priorities 3. Early or late 4. Drop positionNN  K  g1. Degree of aggregation    Degree of discrimination in selecting a packet to drop E.g. in vanilla FIFO, all packets are in the same class Instead, can classify packets and drop packets selectively The finer the classification the better the protection    h2. Drop priorities    Drop lower-priority packets first How to choose? endpoint marks packets regulator marks packets congestion loss priority (CLP) bit in packet header&1d1d   iCLP bit: pros and cons   Pros if network has spare capacity, all traffic is carried during congestion, load is automatically shed Cons separating priorities within a single connection is hard what prevents all packets being marked as high priority? `drdr    k3. Early vs. late drop    _Early drop => drop even if space is available signals endpoints to reduce rate cooperative sources get lower overall delays, uncooperative sources get severe packet loss Early random drop drop arriving packet with fixed drop probability if queue length exceeds threshold intuition: misbehaving sources more likely to send packets and see packet lossesL.|.| `  l3. Early vs. late drop: RED    Random early detection (RED) makes three improvements Metric is moving average of queue lengths small bursts pass through unharmed only affects sustained overloads Packet drop probability is a function of mean queue length prevents severe reaction to mild overload Can mark packets instead of dropping them allows sources to detect network state without losses RED improves performance of a network of cooperating TCP sources No bias against bursty sources Controls queue length regardless of endpoint cooperation`D;**6`D;**6&    A  m4. Drop position    Can drop a packet from head, tail, or random position in the queue Tail easy default approach Head harder lets source detect loss earlierLH'H'   n4. Drop position (contd.)    URandom hardest if no aggregation, hurts hogs most unlikely to make it to real routers&OO V  /ZP#  ` 33̙ff` 3f3f` ___>?" dd@3?nKfd@Eu FA@ " d`  n?" dd@   @@``PR    @ ` `C p>>    (    Zxgֳgֳ ?P  Y!Click to edit Master title style ""  >  T(gֳgֳ ? @  RClick to edit Master text styles Second Level Third Level Fourth Level Fifth Level!    S    T1 ?``  f*        T̖1 ?`   Z*      T1 ?`   Z*   H  0޽h? ? ___ General   `& I( \>$om   " Z<7gֳgֳ ?p  X Click to edit Master title style!!   # T9gֳgֳ ? @   [#Click to edit Master subtitle style$$    $  `8>gֳgֳ ?`  b*     &  `igֳgֳ ?`@  V*  H  0޽h? ? ___  0 p\( D<0    TLJMJMJ ?    p*   ???__~~  TXMJMJ ? d  *     ???__~~p  01 ?9Vx >  T4Y!g!g ?$4a  RClick to edit Master text styles Second level Third level Fourth level Fifth level!    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Keshav 0C:\MSOffice\Templates\Presentations\General.potYuval Shavittmp163Microsoft PowerPoint 7.0sen@ @s@Ǵ61@nnG;   L&@ &&#TNPP2OMi & TNPP &&TNPP   @ --- !@---&9 4&rw@ UwUw0- @Times New Roman UwUw0- .2 BApril 10, 2000 .& 4&  .(2 3Communication Networks    .&% 4&  . 2 1.--3`-- @"HelveticaN n UwUw0- 3.(2 ngCommunication networks .--`-- 3@Monotype Sorts~ UwUw0- f. 2 gn .@"HelveticaN p UwUw0- .2 Instractor   . .'2 : Dr. Yuval Shavitt,   .@Monotype Sorts UwUw0- . 2 u.@"HelveticaN r UwUw0- .92 !Office hours: room 030, Mon 17:00u        . . 2 -. .2 18:00  .@Monotype Sorts UwUw0- f. 2 gn .@"HelveticaN t UwUw0- .2 Requiresments     . . 2 (.@Times New Roman (Hebrew)0- .. "System 0-- 2  .-..@"HelveticaN v UwUw0- . 2 {):.@Monotype Sorts UwUw0- . 2 u:.@"HelveticaN x UwUw0- .L2 .Introduction to computer communications (TAU,             . .2 BTechnion  . .2 , BGU) .@Monotype Sorts UwUw0- f. 2 $gn: .@"HelveticaN z UwUw0- .02 $Expectations from students:       .@Monotype Sorts UwUw0- . 2 Eu:.@"HelveticaN | UwUw0- .2 E Queueing r  . .2 E theory basics    .@Monotype Sorts UwUw0- . 2 au:.@"HelveticaN ~ UwUw0- .2 a Graph theory   .@Monotype Sorts UwUw0- . 2 |u:.@"HelveticaN UwUw0- .42 |Good C/C++ programming skills         .---&TNPP &՜.+,D՜.+,     ULetter Paper (8.5x11 in)l*. 8Times New RomanTimes New Roman (Hebrew) HelveticaMonotype SortsArial PalatinoSymbolGeneralMicrosoft Word DocumentMicrosoft Equation 3.0Communication networksCourse Syllabus (tentative) Source books SwitchingWhat is it all about?OutlineTypes of switching elementsClassification"Other switching element functions RequirementsOutlinePacket switchingBlocking in packet switchesDealing with blocking*Repeaters, bridges, routers, and gatewaysOutline%Three generations of packet switchesFirst generation switchSecond generation switchThird generation switchesThird generation (contd.)Outline Port mappersTriesOutline Buffering!Input buffering (input queueing)+head of line blocking simple upper bound0head of line blocking alternative calculationDealing with HOL blockingOutput queueingBuffered fabricBuffered crossbarHybrid solutions Multicasting#Generating and distributing copiesOutlinePacket dropping"Classification of drop strategies1. Degree of aggregation2. Drop prioritiesCLP bit: pros and cons3. Early vs. late drop3. Early vs. late drop: RED4. Drop position4. Drop position (contd.)  Fonts UsedDesign TemplateEmbedded OLE Servers Slide Titles.dKS[cks{     '/ TemplateType GraphicType Compression ScreenSize ScreenUsage MailAddress HomePage Other DownloadOriginal DownloadIEButton UseBrowserColor BackColor TextColor LinkColor VisitedColorTransparentButton ButtonType ShowNotes NavBtnPos OutputDirdskeshav@cs.cornell.edu'http://www.cs.cornell.edu/home/skeshavtttp  f3 )F:\wwwlink\book\slides\protocol_layeringon%_㼧 Yuval ShavittYuval Shavitt  !"#$%&'()*+,-./0123456789:;<=>?@ACDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~      !#$%&'()+,-./016Root EntrydO)PicturesCurrent User*SummaryInformation(<PowerPoint Document(BDocumentSummaryInformation8"