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IP over WDM network Fang Yu 294 Class Presentation Outline    History of WDM networks Current Internet: Multi-layer protocol stack between IP and WDM layers Future: IP directly over WDM     Challenge Virtual Topology Reconfiguration Multi-layer routing One proposal: Optical Burst Switching technologies History  In the late 70s   Before 1995     First fiber based optical transmission system Mostly a single high-speed optical channel All multiplexing done in electrical domain(TDM) 50Mb/s to 10Gb/s data services After 1995    WDM allows simultaneously transmitting multiple high-speed channels on different frequencies (Up to 160 wavelengths today) 40G per (OC768) Total link capacity = 160 *40G =6.4 Tbps Current Typical Protocol Stacks IP N e tw o rk D a ta lin k ATM N e tw o rk D a ta lin k WDM P h y s ic a l WDM ATM N e tw o rk SONET SONET IP D a ta lin k Transport Layer Model “Packet” “Packet” “Packet” 1/0 DCS Core ATM/IP Layers DACS III LA DS3 (45 Mb/s) PHNX ADM ADM OC48+ (2.5+ Gb/s) HardWired LA OTS OTS OTS ADM 3/1 DCS CHCG OTS 3/1 DCS Layer 3/3 DCS Layer (DACS III) ADM PHNX SONET ADM Layer CHCG OTS Wavelength Path Crossconnect (OTS: Optical Transport CHCG System) CHCG PHNX 3/1 DCS ADM OTS Service Layers CHCG DACS III Proprietary (20-400 Gb/s) LA 4E CHCG DS1 (1.5 Mb/s) 3/1 DCS ADM ADM 4E LA 3/1 DCS DACS III DACS III 4E LA 1/0 DCS DS3 (45 Mb/s) ATM/IP LA 4E 1/0 DCS ATM/IP ATM/IP ATM/IP 1/0 DCS “Packet” Fiber Conduit/ Sheath Wavelength Mux Section Crossconnect Media Layer Disadvantage of Current Multi-layer Protocol Stack  Inefficient   In IP over ATM over SONET over WDM network, 22% bandwidth used for protocol overhead Layers often do not work in concert   Every layer now runs at its own speed. So, low speed devices cannot fill the wavelength bandwidth. When detecting of failure, different layers compete for protection   Optical layer detects failure almost immediately, restores error in 2us to 60ms SONET layer detects failure in 2.3–100 us, restores error in 60 ms Disadvantage of Current Multi-layer Protocol Stack (Cont)  Functional overlap: So many layers are doing the same thing    Slow speed   Routing Protections Electronic devices can not catch the transmission speed available at optical layer Latencies of connection Historical Reason for Multilayer SONET over WDM   Conventional WDM deployment is using SONET as standard interface to higher layers IP over ATM   IP packets need to be mapped into ATM cells before transporting over WDM using SONET frame OEO conversions at every node is easier to build than all optical switch  Electronic E/O Network O/E/O O/E/O E/O Electronic Network O/E/O O/E/O O/E/O O/E/O E/O Electronic Network E/O Optical Core Electronic Network Simplified Protocol Stacks? IP IP Frame Relay ATM SONET WDM-aware Electronic layer WDM WDM Current Typical Protocol Stack Simplified Protocol Stack IP Directly Over WDM?   Establish high-speed optical layer connections (lightpaths) IP routers connected through lightpaths rather than fiber IP ro u te r B C L ig h tp a th s E W a v e le n g th c ro ssco n n e c t A D Challenge for IP over WDM network  WDM-aware Electronic layer        Reconfiguration and load balancing Protection and restoration Optical flow switching Network management/control Cross-layer optimization Reconfigurable (within milli-seconds) OXC Wavelength Converters 3 2 3 2 WC No  converters 1 New request 1 3 With  converters 1 New request 1 3 Virtual Topology Reconfiguration  Physical topology   Virtual topology: a set of nodes interconnected by lightpaths (wavelength)   Seen by optical layer Seen by electronic layer Reconfigure of light-paths in WDM network by   Changing the light path connectivity between electronic switches Tuning of the transmitter wavelength and the frequencyselective-switches A B A B C D C D Virtual Topology Reconfiguration(Cont.)  Enable network to dynamically response to changing of traffic pattern  Load balancing  Efficiency Issues:    Time scale of changes Triggered by what mechanisms IP routing properties (e. g. stability) Blocking Probability  Fixed Routing 0.1 0.01 Reconfigurable Routing X6 WDM ring, 20 nodes one transceiver/node call BW = 1 wavelength 0.001 0.01 0.02 0.03 0.04 Call arrival rate 0.05 Multi-layer Routing   IP layer routing is the bottleneck of present Internet Solution: Routing long duration flows at lower layers User 1 ... Router 1 Network control Router 2 User 2 ... Router 3 WDM layer • • • Conventional packet routing Optical bypass of intermediate routers for high volume traffic End-to end (user-to-user) flow of entire file bypassing routers LIDS Switching all the packets in optical layer?    Requires intelligence in the optical layer Need to store packet during header processing Optical buffers are extremely hard to implement   1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360 m of fiber) Optical Packet Switch still has a long way to go……………………… Various Optical Switching Technologies Optical Burst Packet Switching  Retrospect the goal of IP over WDM:    Avoid electronic bottlenecks Decrease the cost by simplifying the multiple layer architecture OBS is one proposal of how to realize such a network Optical Burst Switching  Resources are allocated using one way reservation      Sender sends a request Sender sends burst without waiting for an acknowledgement of its reservation request Switch does preparation for the burst when getting the request Bursts can have variable lengths Burst switching does not necessarily require buffering Various OBSs    The schemes differ in the way bandwidth release is triggered. In-band-terminator (IBT) – header carries the routing information, then the payload followed by silence (needs to be done optically). Tell-and-go (TAG) – a control packet is sent out to reserve resources and then the burst is sent without waiting for acknowledgement. Refresh packets are sent to keep the path alive. Main Characteristics of Optical Burst Switching   There is a time separation(offset time) between header and data Header and data are usually carried on different channels   Header goes through sophisticated electronic processing Data is kept in optical domain Conclusion   Current IP over ATM over SONET over WDM network is inefficient and redundant Future IP directly over WDM network    Advantages  Less latency  Automatic provisioning  Higher bandwidth utilization Challenge of packet directly over WDM network  Optical buffer Optical burst switch is one of the proposed techniques to IP over WDM network Reference          John Strand, “Optical Networking and IP over Optical”, Feb 4, 2002 Kumar N. Sivarajan, “IP over Intelligent Optical Networks”, Jan 5, 2001 Gaurav Agarwal, “A Brief Introduction to Optical Networks”, 2001 Yang Lihong, “Optical Burst Switching”, CMU networking seminar presentation Vincent W. S. Chan, “Optical Networks: Technology and Architecture” Eytan Modian, “WDM-Based Packet Networks”, IEEE Communication Magazine, March 1999 Ornan (Ori) Gerstel, Rajiv Ramaswami,, “Optical Layer Survivability—An Implementation Perspective”, IEEE Journal on selected areas in communications, October 2000 Eytan Modiano, Aradhana Narula-Tam, “Survivable lightpath routing:a new approach to the design of WDM-based networks”, IEEE JSAC,April 2002 R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical Perspective, San Francisco: Morgan Kaufmann, 1998.