Interworking IP and WDM Networks

1. Interworking IP and WDM Networks Malathi Veeraraghavan Mark Karol Polytechnic University Lucent Technologies mv@poly.edu mk@lucent.com Outline: • Provisioned mode • Switched mode

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

3. 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. Networking modes Switching modes Connection-oriented Connectionless Shades of gray: provisioned vs. switched modes Packet-switching Circuit-switching 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 MPLS IP switch ATM IP Telephone network, SONET/SDH, WDM

5. Enterprise 1 LAN R4 Enterprise 1 LAN R1 Enterprise 2 LAN Enterprise1 LAN R5 Enterprise 2 LAN R2 R3 Lightpath 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

6. 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. 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. 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. 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. 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. 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. OXC, IP switch, ATM switch or SONET XC Test configuration R4 Network node R1 R3 Core network R2

13. Different cases

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

15. 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. 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. 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. OXC OXC OXC OXC Two-layer routing problem R3 R6 R6 R1 R1 R3 R5 R5 R4 R7 R2 R7 R2 R4 Virtual Topology Physical Topology • 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

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

21. 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. 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