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Switching Architectures for Optical Networks COMP680E by M. Hamdi 1 Internet Reality Data Center SONET SONET DWD M DWD M SONET SONET Access Metro Long Haul COMP680E by M. Hamdi Metro Access 2 Hierarchies of Networks: IP / ATM / SONET / WDM COMP680E by M. Hamdi 3 Why Optical? • Enormous bandwidth made available – DWDM makes ~160 channels/ possible in a fiber – Each wavelength “potentially” carries about 40 Gbps – Hence Tbps speeds become a reality • Low bit error rates – 10-9 as compared to 10-5 for copper wires • Very large distance transmissions with very little amplification. COMP680E by M. Hamdi 4 Dense Wave Division Multiplexing (DWDM) 1 2 3 4 Long-haul fiber Output fibers Multiple wavelength bands on each fiber – Transmit by combining multiple lasers @ different frequencies COMP680E by M. Hamdi 5 Anatomy of a DWDM System Terminal B Terminal A Transponder Interfaces M U X PostAmp Line Amplifiers Direct Connections PreAmp D E M U X Transponder Interfaces Direct Connections Basic building blocks • Optical amplifiers • Optical multiplexers • Stable optical sources COMP680E by M. Hamdi User Services & Core Transport EDGE Frame Relay IP IP Router CORE Frame Relay ATM ATM Switch Lease Lines Sonet ADM Users Services TDM Switch OC-3 OC-3 OC-12 STS-1 STS-1 STS-1 Service Provider Networks Transport Provider Networks COMP680E by M. Hamdi 7 • Provisioned SONET circuits. • Aggregated into Lamdbas. Core Transport Services Circuit Origin • Carried over Fiber optic cables. Circuit Destination OC-3 OC-3 OC-12 STS-1 STS-1 STS-1 COMP680E by M. Hamdi 8 WDM Network: Wavelength View WDM link Edge Router Legacy Interfaces Legacy ( e.g., PoS, Gigabit Interfaces Ethernet, IP/ATM) Interfaces Legacy Interfaces Optical Switch COMP680E by M. Hamdi 9 Relationship of IP and Optical • Optical brings –Bandwidth multiplication –Network simplicity (removal of redundant layers) • IP brings –Scalable, mature control plane –Universal OS and application support –Global Internet • Collectively IP and Optical (IP+Optical) introduces a set of service-enabling technologies COMP680E by M. Hamdi 10 Typical Super POP Interconnectio n Network Core IP router DWDM DWDM + Metro Ring ADM Large Multi-service Aggregation Switch Voice Switch Core ATM Switch OXC COMP680E by M. Hamdi SONET Coupler & Opt.amp 11 Typical POP Voice Switch D W D M OXC D W D M SONET-XC COMP680E by M. Hamdi 12 What are the Challenges with Optical Networks? • Processing: Needs to be done with electronics – Network configuration and management – Packet processing and scheduling – Resource allocation, etc. • Traffic Buffering – Optics still not mature for this (use Delay Fiber Lines) – 1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360 m of fiber) • Switch configuration – Relatively slow COMP680E by M. Hamdi 13 Optical Hardware • Optical Add-Drop Multiplexer (OADM) – Allows transit traffic to bypass node optically 1 2 3 1 OADM 2 ’3 3 ’3 Add and Drop DCS COMP680E by M. Hamdi 14 Wavelength Converters • Improve utilization of available wavelengths on links • All-optical WCs being developed • Greatly reduce blocking probabilities 3 2 3 2 WC No converters 1 New request 1 3 With converters 1 New request 1 3 COMP680E by M. Hamdi 15 Late 90s: Backbone Nodes ADM ADM ADM ADM Digital Crossconnect DWDM Multiplexer & Demultiplexer IP Router ATM Switch COMP680E by M. Hamdi 16 Problems • About 80% traffic through each node is “pass- through” – No need to electronically process such traffic • 80-channel DWDM requires 80 ADMs • Speed upgrade requires replacing all the ADMs in the node COMP680E by M. Hamdi 17 Today: Optical Cross Connect (OXC) Optical Crossconnect DWDM ATM Backbone Switch Digital Cross Connect Terabit IP Router Multiplexer & Demultiplexer IP Router ATM Switch COMP680E by M. Hamdi Source: JPMS 18 Wavelength Cross-Connects (WXCs) • A WDM network consists of wavelength cross-connects (WXCs) (OXC) interconnected by fiber links. • 2 Types of WXCs – Wavelength selective cross-connect (WSXC) • Route a message arriving at an incoming fiber on some wavelength to an outgoing fiber on the same wavelength. • Wavelength continuity constraint – Wavelength interchanging cross-connect (WIXC) • Wavelength conversion employed • Yield better performance • Expensive COMP680E by M. Hamdi 19 Wavelength Router Wavelength Router Control Plane: Wavelength Routing Intelligence Data Plane: Optical Cross Connect Matrix Unidirectional DWDM Links to other Wavelength Routers Single Channel Links to IP Routers, SDH Muxes, ... COMP680E by M. Hamdi Unidirectional DWDM Links to other Wavelength Routers 20 Optical Network Architecture UNI Mesh Optical Network UNI IP Network IP Network IP Router OXC Control unit Optical Cross Connect (OXC) Control Path Data Path COMP680E by M. Hamdi 21 OXC Control Unit • Each OXC has a control unit • Responsible for switch configuration • Communicates with adjacent OXCs or the client network through single-hop light paths – These are Control light paths – Use standard signaling protocol like GMPLS for control functions • Data light paths carry the data flow – Originate and terminate at client networks/edge routers and transparently traverse the core COMP680E by M. Hamdi 22 Optical Cross-connects (No wavelength conversion) 2 4 All Optical Cross-connect (OXC) Also known as Photonic Cross-connect (PXC) 1 3 Optical Switch Fabric 3 4 1 2 COMP680E by M. Hamdi 23 Optical Cross-Connect with Full Wavelength Conversion Wavelength Converters 2 1 2 n 1,2, ... ,n 1 1 2 n 1,2, ... ,n 2 . . . 1,2, ... ,n M Wavelength Demux 1,2, ... ,n 1 n 1 1 2 n 1 2 n n 1 2 Optical CrossBar Switch 1,2, ... ,n 2 . . . 1,2, ... ,n M Wavelength Mux • M demultiplexers at incoming side • M multiplexers at outgoing side • Mn x Mn optical switch has wavelength converters at switch outputs COMP680E by M. Hamdi 24 Wavelength Router with O/E and E/O Cross-Connect Incoming Interface Incoming Wavelength Outgoing Interface Outgoing Wavelength 1 3 COMP680E by M. Hamdi 25 O-E-O Crossconnect Switch (OXC) Incoming fibers Demux 1 2 N WDM (many λs) Individual wavelengths O O O/E E/O E O/E E/O O/E O/E O/E O/E E/O E/O E/O E/O O/E O/E O/E E/O E/O E/O Outgoing fibers Mux 1 2 N Switches information signal on a particular wavelength on an incoming fiber to (another) wavelength on an outgoing fiber. COMP680E by M. Hamdi 26 Optical core network Opaque (O-E-O) and transparent (O-O) sections E/O Client signals Transparent optical island O/E O O from other nodes O O O E O O E E O O to other nodes E Opaque opticalCOMP680E network by M. Hamdi O O 27 OEO vs. All-Optical Switches OEO All-Optical • Capable of status monitoring • Optical signal regenerated – improve signal-to-noise ratio • Traffic grooming at various levels • Less aggregated throughput • More expensive • More power consumption • Unable to monitor the contents of the data stream • Only optical amplification – signalto-noise ratio degraded with distance • No traffic grooming in subwavelength level • Higher aggregated throughput • ~10X cost saving • ~10X power saving COMP680E by M. Hamdi 28 Large customers buy “lightpaths” A lightpath is a series of wavelength links from end to end. optical fibers One fiber Repeater cross-connect COMP680E by M. Hamdi 29 Hierarchical switching: Node with switches of different granularities A. Entire fibers O O Fibers O Fibers B. Wavelength subsets O O O C. Individual wavelengths O E O COMP680E by M. Hamdi “Express trains” “Local trains” 30 Wide Area Network (WAN) WAN : Up to 200-500 wavelengths 40-160 Gbit/s/ wavebands (> 10 ) OXC: Optical Wavelength/Waveband Cross Connect COMP680E by M. Hamdi 31 Packet (a) vs. Burst (b) Switching Header recognition, processing, and generation Payload C Header A Setup Synchronizer 1 2 A New headers (a) Control wavelengths Control packets D C 2 2 O/E/O 1 Control packet processing (setup/bandwidth reservation) Offset time 2 B 2 FDL’s 1 Data wavelengths 1 2 Fixed-length (but unaligned) B Switch 1 Incoming fibers 2 Switch 1 1 Data bursts (b) COMP680E by M. Hamdi D 32 MAN (Country / Region) IP packets optical burst formation COMP680E by M. Hamdi 33 Optical Switching Technologies • • • • • • • • MEMs – MicroElectroMechanical Liquid Crystal Opto-Mechanical Bubble Technology Thermo-optic (Silica, Polymer) Electro-optic (LiNb03, SOA, InP) Acousto-optic Others… Maturity of technology, Switching speed, Scalability, Cost, Reliability (moving components or not), etc. COMP680E by M. Hamdi 34 MEMS Switches for Optical Cross-Connect Moveable Micromirror Proven technology, switching time (10 to 25 msec), moving mirrors is a reliability problem. COMP680E by M. Hamdi 35 WDM “transparent” transmission system (O-O nodes) Wavelengths disaggregator O Fibers Wavelengths aggregator O O O multiple λs O O Optical switching fabric (MEMS devices, etc.) Incoming fiber Tiny mirrors COMP680E by M. Hamdi Outgoing fibers 36 Upcoming Optical Technologies • WDM routing is circuit switched – Resources are wasted if enough data is not sent – Wastage more prominent in optical networks • Techniques for eliminating resource wastage – Burst Switching – Packet Switching • Optical burst switching (OBS) is a new method to transmit data • A burst has an intermediate characteristics compared to the basic switching units in circuit and packet switching, which are a session and a packet, respectively COMP680E by M. Hamdi 37 Optical Burst Switching (OBS) • Group of packets a grouped in to ‘bursts’, which is the transmission unit • Before the transmission, a control packet is sent out – The control packet contains the information of burst arrival time, burst duration, and destination address • Resources are reserved for this burst along the switches along the way • The burst is then transmitted • Reservations are torn down after the burst COMP680E by M. Hamdi 38 Optical Burst Switching (OBS) • Has intermediate characteristics compared circuit switching and packet switching • If two bursts collide, the later burst will be dropped because of zero buffering • Bandwidth is reserved in a one-way process, without a ACK, whereas in circuit switching is a two-way process • A burst will cut through intermediate nodes without being buffered – In packet switching, a packet is stored and forwarded at each intermediate node COMP680E by M. Hamdi 39 Optical Burst Switching (OBS) COMP680E by M. Hamdi 40 Optical Packet Switching • Fully utilizes the advantages of statistical multiplexing • Optical switching and buffering • Packet has Header + Payload – Separated at an optical switch • Header sent to the electronic control unit, which configures the switch for packet forwarding • Payload remains in optical domain, and is recombined with the header at output interface COMP680E by M. Hamdi 41 Optical Packet Switch • Has – Input interface, Switching fabric, Output interface and control unit • Input interface separates payload and header • Control unit operates in electronic domain and configures the switch fabric • Output interface regenerates optical signals and inserts packet headers • Issues in optical packet switches – Synchronization – Contention resolution COMP680E by M. Hamdi 42 • Main operation in a switch: – – – – The header and the payload are separated. Header is processed electronically. Payload remains as an optical signal throughout the switch. Payload and header are re-combined at the output interface. hdr payload CPU hdr payload hdr payload Wavelength i input port j Re-combined Wavelength i output port j Optical packet Optical switch COMP680E by M. Hamdi 43 Output port contention • Assuming a non-blocking switching matrix, more than one packet may arrive at the same output port at the same time. Input ports Optical Switch payloadhdr . . . payloadhdr . . . payloadhdr COMP680E by M. Hamdi Output ports . . . . . . 44 OPS Architecture: Synchronization Occurs in electronic switches – solved by input buffering Slotted networks •Fixed packet size •Synchronization stages required Sync. COMP680E by M. Hamdi 45 OPS Architecture: Synchronization Slotted networks •Fixed packet size •Synchronization stages required Sync. COMP680E by M. Hamdi 46 OPS Architecture: Synchronization Slotted networks •Fixed packet size •Synchronization stages required Sync. COMP680E by M. Hamdi 47 OPS Architecture: Synchronization Slotted networks •Fixed packet size •Synchronization stages required Sync. COMP680E by M. Hamdi 48 OPS Architecture: Synchronization Slotted networks •Fixed packet size •Synchronization stages required Sync. COMP680E by M. Hamdi 49 OPS Architecture: Synchronization Sync. COMP680E by M. Hamdi 50 OPS: Contention Resolution • More than one packet trying to go out of the same output port at the same time – Occurs in electronic switches too and is resolved by buffering the packets at the output – Optical buffering ? • Solutions for contention – Optical Buffering – Wavelength multiplexing – Deflection routing COMP680E by M. Hamdi 51 OPS Architecture Contention Resolutions 1 2 3 1 1 2 1 4 3 4 COMP680E by M. Hamdi 52 OPS: Contention Resolution • Optical Buffering – Should hold an optical signal • How? By delaying it using Optical Delay Lines (ODL) – ODLs are acceptable in prototypes, but not commercially viable – Can convert the signal to electronic domain, store, and reconvert the signal back to optical domain • Electronic memories too slow for optical networks COMP680E by M. Hamdi 53 OPS Architecture Contention Resolutions •Optical buffering 1 1 2 3 1 2 1 3 4 4 COMP680E by M. Hamdi 54 OPS Architecture Contention Resolutions •Optical buffering 1 1 2 2 3 3 4 4 COMP680E by M. Hamdi 55 OPS Architecture Contention Resolutions •Optical buffering 1 1 1 2 2 3 3 4 4 1 COMP680E by M. Hamdi 56 OPS: Contention Resolution • Wavelength multiplexing – Resolve contention by transmitting on different wavelengths – Requires wavelength converters - $$$ COMP680E by M. Hamdi 57 OPS Architecture Contention Resolutions •Wavelength conversion 1 1 1 1 2 2 COMP680E by M. Hamdi 58 OPS Architecture Contention Resolutions •Wavelength conversion 1 1 2 2 COMP680E by M. Hamdi 59 OPS Architecture Contention Resolutions •Wavelength conversion 1 1 1 1 2 2 COMP680E by M. Hamdi 60 OPS Architecture Contention Resolutions •Wavelength conversion 1 1 2 2 COMP680E by M. Hamdi 61 OPS Architecture Contention Resolutions •Wavelength conversion 1 1 1 1 2 2 COMP680E by M. Hamdi 62 Deflection routing • When there is a conflict between two optical packets, one will be routed to the correct output port, and the other will be routed to any other available output port. • A deflected optical packet may follow a longer path to its destination. In view of this: – The end-to-end delay for an optical packet may be unacceptably high. – Optical packets may have to be re-ordered at the destination COMP680E by M. Hamdi 63 Electronic Switches Using Optical Crossbars COMP680E by M. Hamdi 64 Scalable Multi-Rack Switch Architecture Optical links Line card rack Switch Core • Number of linecards is limited in a single rack – Limited power supplement, i.e. 10KW – Physical consideration, i.e. temperature, humidity • Scaling to multiple racks – Fiber links and central fabrics COMP680E by M. Hamdi 65 Logical Architecture of Multi-rack Switches Scheduler Line Card Local Fiber I/O Framer Buffers Laser Laser Line Card Laser Laser Local Buffers Framer Fiber I/O Crossbar Line Card Local Fiber I/O Framer Buffers Line Card Laser Laser Laser Laser Local Buffers Framer Fiber I/O Switch Fabric System • Optical I/O interfaces connected to WDM fibers • Electronic packet processing and buffering – Optical buffering, i.e. fiber delay lines, is costly and not mature • Optical interconnect – Higher bandwidth, lower latency and extended link length than copper twisted lines • Switch fabric: electronic? Optical? COMP680E by M. Hamdi 66 Optical Switch Fabric Scheduler Line Card Local Fiber I/O Framer Buffers Laser Laser Line Card Laser Local Laser Buffers Framer Fiber I/O Crossbar Line Card Local Fiber I/O Framer Buffers Line Card Laser Laser Laser Laser Local Buffers Framer Fiber I/O Switch Fabric System • Less optical-to-electrical conversion inside switch – Cheaper, physically smaller • Compare to electronic fabric, optical fabric brings advantages in – – – – • Low power requirement Scalability Port density High capacity Technologies that can be used – 2D/3D MEMS, liquid crystal, bubbles, thermo-optic, etc. • COMP680E by M. Hamdi 67 Hybrid architecture takes advantage of the strengths of both electronics and optics Electronic Vs. Optical Fabric Electronic Trans. Buffer InterLine connection Inter- Buffer Trans. connection Line Switching Fabric Optical Electronic E/O or O/E Conversion Optical Trans. Buffer InterLine connection Inter- Buffer Trans. connection Line Switching Fabric COMP680E by M. Hamdi 68 Multi-rack Hybrid Packet Switch Rack Buf f er E/O O/E Buf f er Buf f er E/O O/E Buf f er Optical Optical Fiber Crossbar Buf f er E/O Optical Fiber O/E Buf f er O/E Buf f er Linecard Buf f er E/O Switch Core COMP680E by M. Hamdi 69 Features of Optical Fabric • Less E/O or O/E conversion • High capacity • Low power consumption • Less cost However, • Reconfiguration overhead (50-100ns) – Tuning of lasers (20-30ns) – System clock synchronization (10-20ns or higher) COMP680E by M. Hamdi 70 Scheduling Under Reconfiguration Overhead • Traditional slot-by-slot approach Scheduler Schedule Reconfigure Transfer Time Line • Low bandwidth usage COMP680E by M. Hamdi 71 Reduced Rate Scheduling Fabric setup (reconfigure) Traffic transfer Time slot Slot-by-slot Scheduling, zero fabric setup time Slot-by-slot Scheduling with reconfigure delay Reduced rate Scheduling, each schedule is held for some time • Challenge: fabric reconfiguration delay – • Traditional slot-by-slot scheduling brings lots of overhead Solution: slow down the scheduling frequency to compensate – • Each schedule will be held for some time Scheduling task 1. 2. Find out the matching Determine the holding time COMP680E by M. Hamdi 72 Scheduling Under Reconfiguration Overhead • Reduce the scheduling rate – Bandwidth Usage = Transfer/(Reconfigure+Transfer) Constant • Approaches – Batch scheduling: TSA-based – Single scheduling: Schedule + Hold COMP680E by M. Hamdi 73 Single Scheduling • Schedule + Hold – One schedule is generated each time – Each schedule is held for some time (holding time) – Holding time can be fixed or variable – Example: LQF+Hold COMP680E by M. Hamdi 74 Routing and Wavelength Assignment COMP680E by M. Hamdi 75 Optical Circuit Switching • An optical path established between two nodes • Created by allocation of a wavelength throughout the path. • Provides a ‘circuit switched’ interconnection between two nodes. – Path setup takes at least one RTT – No optical buffers since path is pre-set Desirable to establish light paths between every pair of nodes. • Limitations in WDM routing networks, – Number of wavelengths is limited. – Physical constraints: • limited number of optical transceivers limit the number of channels. COMP680E by M. Hamdi 76 Routing and Wavelength Assignment (RWA) • Light path establishment involves – Selecting a physical path between source and destination edge nodes – Assigning a wavelength for the light path • RWA is more complex than normal routing because – Wavelength continuity constraint • A light path must have same wavelength along all the links in the path – Distinct Wavelength Constraint • Light paths using the same link must have different wavelengths COMP680E by M. Hamdi 77 No Wavelength Converters WSXC Access Fiber Wavelength 1 POP POP Wavelength 2 Wavelength 3 COMP680E by M. Hamdi 78 Wavelength Conversion • Process of converting the wavelength of an incoming channel to another wavelength at the outgoing channel. • Assume that two packets are destined to go out of the same output port at the same time. Both packets can be still be transmitted, but on two different wavelengths. • Different categories of wavelength conversion are: – Full conversion: • Convert an incoming wavelength to any outgoing wavelength. – Limited conversion: • Convert an incoming wavelength to a subset of the outgoing wavelengths. – Fixed conversion: • Convert an incoming wavelength to a fixed outgoing wavelength (e.g., from λ1 to λ3 and λ7). – Sparse wavelength conversion: • Networks are comprised of a mix of wavelength converters. COMP680E by M. Hamdi 79 Wavelength Converters Input Output Full Wavelength conversion Limited Wavelength conversion Fixed Wavelength conversion COMP680E by M. Hamdi 80 With Wavelength Converters WIXC Wavelength 1 Access Fiber POP POP Wavelength 2 Wavelength 3 COMP680E by M. Hamdi 81 Routing and Wavelength Assignment (RWA) • RWA algorithms based on traffic assumptions: • Static Traffic – Set of connections for source and destination pairs are given • Dynamic Traffic – Connection requests arrive to and depart from network one by one in a random manner. – Performance metrics used fall under one of the following three categories: • Number of wavelengths required • Connection blocking probability: Ratio between number of blocked connections and total number of connections arrived COMP680E by M. Hamdi 82 Static and Dynamic RWA • Static RWA – Light path assignment when traffic is known well in advance – Arises in capacity planning and design of optical networks • Dynamic RWA – Light path assignment to be done when requests arrive in random fashion – Encountered during real-time network operation COMP680E by M. Hamdi 83 Static RWA – Virtual Topology Design • Problem – Given physical topology, and traffic demands, set up long-lived light paths among the edge nodes such that the RWA constraints are satisfied – Light paths create a logical or virtual topology and hence the name • A simple solution – Given N edge nodes, create a completely connected N(N-1) virtual topology – Will work great, provided • So many wavelengths can be supported in a fiber • Each node (OXC) can be built with so many Rcv and Xmt COMP680E by M. Hamdi 84 Static RWA – Virtual Topology Design • RWA is usually solved as an optimization problem with Integer Programming (IP) formulations • Objective functions – Minimize average weighted number of hops – Minimize average packet delay – Minimize the maximum congestion level – Minimize number of Wavelenghts COMP680E by M. Hamdi 85 Static RWA – Virtual Topology Design • Methodologies for solving Static RWA – Heuristics for solving the overall ILP sub-optimally – Algorithms that decompose the static RWA problem into a set of individual sub-problems, and solve a sub-set – http://www.tct.hut.fi/~esa/java/wdm/ COMP680E by M. Hamdi 86 Virtual Topology • An example B A Lightpath C B A D C D Physical Topology COMP680E by M. Hamdi Virtual Topology 87 Solving Dynamic RWA • During network operation, requests for new lightpaths come randomly • These requests will have to be serviced based on the network state at that instant • As the problem is in real-time, dynamic RWA algorithms should be simple • The problem is broken down into two sub-problems – Routing problem – Wavelength assignment problem COMP680E by M. Hamdi 88 Optical Circuit Switching all the Way: End-to-End !!! Why might this be possible: • Huge CS bandwidth (large # of wavelength) – BW efficiency is not very crucial • Circuit switches have a much higher capacity than Packet switches, and QoS is trivial • Optical Technology is suited for CS COMP680E by M. Hamdi 89 How the Internet Looks Like Today The core of the Internet is already “predominantly” CS. Even a “large” portion of the access networks use CS (Modem, DSLs) COMP680E by M. Hamdi 90 How the Internet Really Looks Like Today SONET/SDH DWDM COMP680E by M. Hamdi 91 How the Internet Really Looks Like Today Modems, DSL COMP680E by M. Hamdi 92 Why Is the Internet Packet Switched in the First Place? • PS is bandwidth efficient “Statistical Multiplexing” • PS networks are robust Gallager: “Circuit switching is rarely used for data networks, ... because of very inefficient use of the links” Tanenbaum: ”For high reliability, ... [the Internet] was to be a datagram subnet, so if some lines and [routers] were destroyed, messages could be ... rerouted” COMP680E by M. Hamdi 93 Are These Assumptions Valid Today? • • PS is bandwidth efficient • PS networks are robust • 10-15% average link utilization in the backbone today. Similar story for access networks Routers/Switches are designed for <5s down-time per year. They take >1min to recover when they do (circuit switches must recover in <50ms). COMP680E by M. Hamdi 94 How Can Circuit Switching Help the Internet? • Simple switches/routers: • • • • No buffering No per-packet processing (just per connection processing) Possible all-optical data path Peak allocation of BW • No delay jitter COMP680E by M. Hamdi Higher capacity switches Simple but strict QoS 95 Myth: Packet switching is simpler • A typical Internet router contains over 500M gates, 32 CPUs and 10Gbytes of memory. • A circuit switch of the same generation could run ten times faster with 1/10th the gates and no memory. COMP680E by M. Hamdi 96 Instructions per arriving byte Packet Switch Capacity What we’d like: (more features) QoS, Multicast, Security, … What will happen: (fewer features) Or perhaps we’re doing something wrong? COMP680E by M. Hamdi time 97 What Is the Performance of Circuit Switching? End-to-End File = 10Mbit 100 clients 1 Gb/s 1 server x 100 Circuit sw Packet sw Flow BW 1 Gb/s 10 Mb/s Avg latency 0.505 s 1s Worst latency 1 s 1s COMP680E by M. Hamdi 99% of Circuits Finish Earlier 98 What Is the Performance of Circuit Switching? File = 10Gbit/10Mbit 100 clients 1 Gb/s 1 server x 99 Circuit sw Packet sw Flow BW 1 Gb/s 10Mb/s+1Gb/s Avg latency 10.495 s 1.099 sec Worst latency 10.990 s 10.990 sec COMP680E by M. Hamdi A big file can kill CS if it blocks the link 99 What Is the Performance of Circuit Switching? File = 10Gbit/10Mbit 100 clients 1 Gb/s 1 server x 99 1 Mb/s Circuit sw Packet sw Flow BW 1 Mb/s 1 Mb/s Avg latency 109.9s 109.9sec Worst latency 10,000 s 10,000 sec COMP680E by M. Hamdi No difference between CS and PS in core 100 Possible Implementation TCP Switching • Create a separate circuit for each flow • IP controls circuits • Optimize for the most common case – TCP (85-95% of traffic) – Data (8-9 out of 10 pkts) COMP680E by M. Hamdi 101 TCP Switching Exposes Circuits to IP IP routers TCP Switches COMP680E by M. Hamdi 102 TCP “Creates” a Connection Source Router Router Router SYN Destination SYN+ACK DATA Packets Packets Packets COMP680E by M. Hamdi Packets 103 State Management Feasibility • Amount of state – Minimum circuit = 64 kb/s. – 156,000 circuits for OC-192. • Update rate – About 50,000 new entries per sec for OC-192. • Readily implemented in hardware or software. COMP680E by M. Hamdi 104 Software Implementation Results TCP Switching boundary router: • Kernel module in Linux 2.4 1GHz PC • Forwarding latency – Forward one packet: 21s. – Compare to: 17s for IP. – Compare to: 95s for IP + QoS. • Time to create new circuit: 57s. COMP680E by M. Hamdi 105