1、1,How might optics be used in IP routers and the Internet?Optics and Routing Seminar October 24th, 2000,Nick McKeown nickmstanford.edu http:/www.stanford.edu/nickm,2,Outline from last time,Where IP routers sit in the network What IP routers look like What do IP routers do? Some details: The internal
2、s of a “best-effort” router Lookup, buffering and switching The internals of a “QoS” router Can optics help?,3,Outline this time,Not circuit switchingEvolution of the internal workings of IP routers. What limits their performance. Discussion: The scope for optics,4,“The Internet is a mesh of routers
3、”,The Internet Core,IP Core router,IP Edge Router,5,The Internet is, in fact, a bowl of spaghetti and meatballs,and ravioli, and fettucine, and linguini, and alfredo sauce,6,The Internet is a mesh of IP routers, ATM switches, frame relay, TDM, ,Access Network,Access Network,Access Network,Access Net
4、work,Access Network,Access Network,Access Network,7,Core,Distribution,Access,Metropolitan/ Regional,Inter-City Long Haul,Transport Network Birds Eye View,Source: Tad Hofmeister, Ciena,8,The Internet is a mesh of routers mostly interconnected by (ATM and) SONET,TDM,TDM,TDM,TDM,Circuit switched crossc
5、onnects, DWDM etc.,9,Outline this time,Not circuit switchingEvolution of the internal workings of IP routers. What limits their performance. Discussion: The scope for optics,10,Basic Architectural Components,Control Plane,Datapath” per-packet processing,Switching,Forwarding Table,RoutingTable,Routin
6、g Protocols,11,Basic Architectural Components Datapath: per-packet processing,2. Interconnect,3. Egress,Forwarding Table,Forwarding Decision,1. Ingress,Forwarding Table,Forwarding Decision,Forwarding Table,Forwarding Decision,12,Can optics help?,Physical Layer,Framing & Maintenance,Packet Processing
7、,Buffer Mgmt & Scheduling,Buffer Mgmt & Scheduling,Buffer& State Memory,Buffer& State Memory,Typical IP Router Linecard,OC192c linecard: 10-30M gates 2Gbits of memory 2 square feet $10k cost,Lookup Tables,Backplane,Buffered or Bufferless Fabric,Arbitration,Optics,13,Can optics help?,Cynical view: A
8、packet switch (e.g. an IP router) must have buffering. Optical buffering is not feasible. Therefore, optical routers are not feasible. Hence, “optical switches” are circuit switches (e.g. TDM, space or Lambda switches).,14,Can optics help?,Open-minded view: Optics seem ill-suited to processing inten
9、sive functions, or where random access memory is required. Optics seems well-suited to bufferless, reconfigurable datapaths.,15,First Generation Routers,Shared Backplane,Line Interface,Fixed length “DMA” blocks or cells. Reassembled on egress linecard,Fixed length cells or variable length packets,Ty
10、pically 0.5Gb/s aggregate capacity,16,Output 2,Output N,First Generation Routers Queueing Structure: Shared Memory,Large, single dynamically allocated memory buffer: N writes per “cell” time N reads per “cell” time. Limited by memory bandwidth.,Input 1,Output 1,Input N,Input 2,Numerous work has prov
11、en and made possible: Fairness Delay Guarantees Delay Variation Control Loss Guarantees Statistical Guarantees,17,Second Generation Routers,Route Table,CPU,Line Card,Buffer Memory,Line Card,MAC,Buffer Memory,Line Card,MAC,Buffer Memory,Fwding Cache,Fwding Cache,MAC,Drop Policy,Drop Policy Or Backpre
12、ssure,Output Link Scheduling,Buffer Memory,Typically 5Gb/s aggregate capacity,18,Route Table,CPU,Second Generation Routers As caching became ineffective,Line Card,Buffer Memory,Line Card,MAC,Buffer Memory,Line Card,MAC,Buffer Memory,Fwding Table,Fwding Table,MAC,Exception Processor,19,Second Generat
13、ion Routers Queueing Structure: Combined Input and Output Queueing,Bus,20,Third Generation Routers,Line Card,MAC,Local Buffer Memory,CPU Card,Line Card,MAC,Local Buffer Memory,Switched Backplane,Line Interface,CPU,Memory,Routing Table,Fwding Table,Typically 50Gb/s aggregate capacity,21,Arbiter,Third
14、 Generation Routers Queueing Structure,Switch,22,Arbiter,Third Generation Routers Queueing Structure,Switch,Per-flow/class or per-output queues (VOQs),Per-flow/class or per-input queues,23,Third Generation Routers,19” or 23”,7,Size-constrained: 19” or 23” wide. Power-constrained: 8kW.,Supply: 100A/2
15、00A maximum at 48V,24,Fourth Generation Routers/Switches,Switch Core,Linecards,Optical links,100s of feet,25,Physically Separating Switch Core and Linecards,Distributes power over multiple racks. Allows all buffering to be placed on the linecard: Reduces power. Places complex scheduling, buffer mgmt
16、, drop policy etc. on linecard.,26,Fourth Generation Routers/Switches,Switch Core,Linecards,Optical links,27,Linecard,LCS,LCS,Physical Separation,Switch Scheduler,Switch Fabric,Switch Port,1 RTT,Per Queue Counters,28,Physical Separation Aligning Cells,Switch Scheduler,Switch Fabric,Switch Core,Linec
17、ard,Linecard,Linecard,29,Fourth Generation Routers/Switches Queueing Structure,1 write per “cell” time,1 read per “cell” time,Lookup & Drop Policy,Output Scheduling,Virtual Output Queues,Output Scheduling,Output Scheduling,Switch Fabric,Switch Arbitration,Linecard,Linecard,Switch Core (Bufferless),L
18、ookup & Drop Policy,Lookup & Drop Policy,Typically 5Tb/s aggregate capacity,30,Myths about CIOQ-based crossbar switches,“Input-queued crossbars have low throughput” An input-queued crossbar can have as high throughput as any switch. “Crossbars dont support multicast traffic well” A crossbar inherent
19、ly supports multicast efficiently. “Crossbars dont scale well” Today, it is the number of chip I/Os, not the number of crosspoints, that limits the size of a switch fabric. Expect 5-10Tb/s crossbar switches.,31,Physical Separation Separating Control & Data,Linecard,LCS,LCS,Switch Scheduler,Switch Po
20、rt,Control Channel,Data Channel,Switch Fabric,Buffer or Guard-Band,Linecard measures RTT to 1 cell time,32,Can optics help?,Physical Layer,Framing & Maintenance,Packet Processing,Buffer Mgmt & Scheduling,Buffer Mgmt & Scheduling,Buffer& State Memory,Buffer& State Memory,Typical IP Router Linecard,Lo
21、okup Tables,Optics,Physical Layer,Framing & Maintenance,Packet Processing,Buffer Mgmt & Scheduling,Buffer Mgmt & Scheduling,Buffer& State Memory,Buffer& State Memory,Typical IP Router Linecard,Lookup Tables,Optics,optical,electrical,Req/Grant,Req/Grant,33,Can the switch be optical?,Reconfiguration t
22、ime: OC192 = 40ns OC768 = 10ns MEMs? Tunable lasers? Other? Use longer “cells”? Multicast?,34,Increase Payload Size Inefficiency & “65B Problem”,64B,128B,256B,7%,25%,40%,Internet Traffic Archive,Payload size,Avg % Wasted Capacity,Variable length packet,35,Increase Payload Size Packing Packets in “Ce
23、lls”,1,2,3,4,80B,178B,40B,128B cell payload,100B,Packets all in same VOQ:,36,Can optics help?,Physical Layer,Framing & Maintenance,Packet Processing,Buffer Mgmt & Scheduling,Buffer Mgmt & Scheduling,Buffer& State Memory,Buffer& State Memory,Typical IP Router Linecard,Lookup Tables,Optics,Physical Layer,Framing & Maintenance,Packet Processing,Buffer Mgmt & Scheduling,Buffer Mgmt & Scheduling,Buffer& State Memory,Buffer& State Memory,Typical IP Router Linecard,Lookup Tables,Optics,optical,electrical,Req/Grant,Req/Grant,
