1. 10/3/991 Interworking IP and WDM Networks Malathi VeeraraghavanMark Karol Polytechnic UniversityLucent Technologies mv@poly.edumk@lucent.com Outline: Provisioned mode Switched mode

2. 10/3/992 WDM as a transmission technology Use WDM multiplexers/demultiplexers Increased bandwidth - immediate value IP Router DWDM Multiplexer IP Router DWDM Demultiplexer

3. 10/3/993 WDM as a networking technology Circuit switches –Optical add/drop multiplexers (OADM) –Optical crossconnects (OXC) –Commercially available –We assume that WDM switches are of this variety for this talk. Packet switches –In research laboratories; optical buffering issues

4. 10/3/994 Types of networks A network is defined by its “switching mode” and its “networking mode” Circuit switching vs. packet switching –Circuit-switching: switching based on position (space, time, ) of arriving bits –Packet-switching: switching based on information in packet headers Connectionless vs. Connection-oriented networking: –CL: Packets routed based on address information in headers –CO: Connection set up (resources reserved) prior to data transfer Packet-switching Circuit-switching Switching modes Connectionless Connection-oriented Networking modes ATM IP MPLS IP switch Telephone network, SONET/SDH, WDM Shades of gray: provisioned vs. switched modes

5. 10/3/995 Use of WDM networking technology to carry IP traffic For WANs, usage expected to be in provisioned mode - need “CO” service for guaranteed bandwidth –Interconnect IP routers with provisioned (connections set up a priori) lightpaths Core network of OXCs/OADMs R2R2 Enterprise 2 LAN R3R3 Lightpath R5R5 Enterprise 1 LAN R4R4 Enterprise 1 LAN R1R1

6. 10/3/996 Alternatives Alternatives for the core network nodes: –Packet switches with packets of format anything other than the IP datagram format, e.g. ATM, MPLS (MultiProtocol Label Switching) –SONET/SDH circuit switches (TDM) –“IP switches” - resource reservation at the IP layer using RSVP or some network management system hardware-based IP forwarding variable-length packet switching –WDM Optical crossconnects and WDM Optical add/drop multiplexers

7. 10/3/997 Which alternative is “best?” Issues/assumptions: –IP traffic even in core measured to be bursty –Protocol layer overhead resulting from protocol encapsulation –Bandwidth granularity

8. 10/3/998 Issue 1 IP traffic even in core measured to be bursty –Implication: need traffic shaping at edge routers or gateways if circuit-switched alternatives are used –Is it possible to shape IP (self-similar) traffic to a constant rate? –Is there a problem if the IP traffic delivered at the far-end router does not replicate burstiness?

9. 10/3/999 Issue 2 Protocol layer overhead resulting from protocol encapsulation –20% in case of ATM (TCP ACKs don’t fit in one ATM cell with LLC/SNAP encapsulation and ACKs are 45% of packets) –4.4% for SONET relative to IP over PPP over fiber/WDM

10. 10/3/9910 Issue 3 Bandwidth granularity: –In SONET networks, minimum rate is OC1 (~51Mbps) –In WDM networks, issue not at the OXCs but rather at the transmitter; actual rate used could be less than maximum rate possible

11. 10/3/9911 Which alternative is “best?” Alternatives for the core network nodes: –ATM, MPLS: protocol layer overhead issue –SONET/SDH: all three issues –IP switches: None –WDM OXCs/OADMs: bursty traffic issue? + granularity issue? Answer: –IP switch based solution seems best –If traffic can be shaped to constant rate and delivery of constant-rate traffic at far-end is acceptable, then WDM OXC/OADM based solution is comparable Switch costs could offset transmission cost savings

12. 10/3/9912 Test configuration R1R3 R2 Network node Core network R4 OXC, IP switch, ATM switch or SONET XC

13. 10/3/9913 Different cases

14. 10/3/9914 Comparison of OXC and IP switch based networks Graphs generated by D. Dharmaraju and R. Badri, Polytechnic Univ.

15. 10/3/9915 Comparison of SONET and OXC based networks and IP switch and ATM switch based networks Graphs generated by D. Dharmaraju and R. Badri, Polytechnic Univ.

16. 10/3/9916 Classification of optical networks One classification (B. Mukherjee’s book) –Broadcast-and-select local optical WDM networks –Wavelength-routed (wide area) optical networks Second classification (chap. by J. Bannister, M. Gerla, M. Kovacevic, in book on routing) –Optical link networks –Single-hop networks –Multi-hop networks –Hybrid networks –Photonic networks

17. 10/3/9917 Difference between optical-link and multihop networks (per ref.) Optical-link networks don’t use multiple wavelengths while multihop networks do Routing problem in optical-link networks is the simple routing problem in packet- switched networks, while in multihop networks, this problem is tightly coupled with the virtual-topology design problem

18. 10/3/9918 Two-layer routing problem R1R1 R2R2 R3R3 R5R5 R6R6 R7R7 R4R4 Virtual Topology Physical Topology R1R1 R2R2 R3R3 R6R6 R7R7 R5R5 R4R4 If WDM networks are not efficient when used in provisioned mode, do not create a virtual topology by connecting IP routers with lightpaths that traverse multiple OXCs Above problem not worth solving if packet switches are IP routers - just build a single-layer IP switch based network OXC

19. 10/3/9919 How should WDM wavelength-routed networks be used for IP traffic? Hybrid network: Single-hop and optical-link –Single-hop: Use WDM circuit switches for large bulk-data transfers Operate WDM network in switched mode Need a routing protocol and signaling protocol Dynamic allocation and removal of lightpaths –Optical-link network: A packet-switched network (allow WDM mux/demux on links) Packet-switched network supports CL and CO services In contrast to other hybrid networks, which combine single-hop and multi-hop networks

20. 10/3/9920 Classification of applications Applications Non-real-time (stored at sender and receiver ends) Real-time (consumed or sent live) Interactive (two-way) (consumed and sent live) e.g. telephony, telnet, “ftp” Streaming (one-way) (consumed live; sent from live or stored source) e.g. radio/TV broadcasts Recording (one-way) (stored at receiver end; sent from live source) Short transfers (e.g. DNS query) Long transfers (e.g. large image, audio, video or data) Packet-switched CO networks Connectionless networks Circuit-switched networks

21. 10/3/9921 Use of circuit switching for long data transfers Scanned from “Fundamentals of Digital Switching,” by J. MacDonald (published 1983 - article written by Miyahara et al. in 1975)

22. 10/3/9922 Conclusions Regarding WDM wavelengh-routed (WAN) networks –Value questionable relative to other networking technologies when used in provisioned mode (pre-established lightpaths) to interconnect IP routers –In switched mode, ideal for high-bandwidth large file transfers Proposed WAN solution: hybrid networks –Optical-link networks interconnecting packet switches that support connectionless and connection-oriented services –Single-hop networks of OXCs supporting circuit-switched services for large file transfers