1. Multipath Routing CS 522 F2003 Beaux Sharifi

2. Agenda Description of Multipath Routing Necessity of Multipath Routing 3 Major Components Necessary for Multipath Routing Example Multipath Routing Model Simulation Results

3. What is Multipath Routing? Multipath Routing is the spreading of traffic from a source node to a destination node over multiple paths through the network. Figure 1. Multipath Routing Model Diagram.

4. Importance of Multipath Routing The Internet is a significant part of the Global communication infrastructure. The use of the Internet is growing at an incredible rate: –Jan 1999: ~ 43 million hosts –Jan 2003: ~ 171 million hosts (source: Internet Domain Survey) QoS, throughput, and delay are difficult problems with current single- path routing architecture. From queuing theory, we know that through increased sharing, overall utilization of the entire network is improved. Multipath routing provides much better overall network performance by allowing better sharing of the available network resources.

5. 3 Major Components A Multipath Calculation algorithm to compute multiple paths. A Multipath Forwarding algorithm to insure that packets travel on their specified paths. An End-Host Protocol that effectively uses the determined multiple paths.

6. Path Algorithms Generate paths based on a the desired characteristics of the path. –i.e. Maximized throughput or minimized delay Generate Multi-Option paths and/or Multi-Service paths. Path requirements depend on the end-user application. –i.e. Telnet vs. FTP Two characteristics of a quality path: –Path Quantity –Path Independence

7. Path Algorithms (cont.) Some path algorithms that don’t work: –Shortest K Paths, Link Disjoint Paths, Maximum Flow Two path algorithms that do work: –Maximize Throughput: Capacity Removal –Minimize Latency: Discount Shortest Path Both algorithms based on Dijkstra’s Shortest Path algorithm. Both algorithms produce shortest paths with minimal overlap by incrementally adding “cost” to each of the previously found paths.

8. Path Forwarding Path Forwarding Problem: how to specify a packets path and then forward packets along that path. Each router has potentially multiple routes to a destination node. The destination address is no longer sufficient. A Path Identifier is now required for every packet. Design Requirements for Path Forwarding: –Minimize Packet Overhead –Minimize router CPU overhead of forwarding packets –Minimize additional router memory

9. End-Host Protocol Performance gains are only realized if end-hosts use the multiple paths effectively. Paths can be used concurrently or one at a time. The appropriate use of multiple paths is application specific. –Instant Messenger (multi-service) –Urgent Message (multi-option)

10. Example Multipath Routing Model Developed by Johnny Chen of Rice University in 1999. Consists of two different routing algorithms based on extensions of the traditional routing algorithms: –MPDV (MultiPath Distance Vector) –MPLS (MultiPath Link State) Both routing algorithms seek to optimize throughput by using a Capacity Removal based algorithm. Chen develops efficient path forwarding algorithms while minimizing packet and router overhead. Uses a fixed-length packet path ID to provide minimal packet overhead and allow efficient indexing into router forwarding tables.

11. Example Multipath Routing Model (cont.) Contains a new transport layer called MPTCP (Multipath TCP). MPTCP is based on single-path TCP and provides a reliable bit stream service. MPTCP operates by opening multiple TCP connections on different paths and then multiplexing data between them. The receiving MPTCP layer collects data from each of the connections and then restores the original message stream. MPTCP provides flow and congestion control. MPTCP provides increased network performance without any changes to user-applications.

12. Simulation Results Chen compares both MPDV and MPLS using a packet-level network simulator “xsim” from the University of Arizona. Simulated network is similar to the Internet topology with 100 nodes and 195 links across multiple clusters. Performance is measured in throughput, latency, and message drop-off probability. Throughput is measured using MPTCP. Latency and drop-off probability is measured using multipath ping.

13. Throughput Results Figure 2. Foreground MPTCP Performance using MPDV and MPLS.

14. Latency and Message-Drop Results Figure 3. Latency and Message Drop Percentages with MP-ping and SP-ping.

15. Summary MPDV and MPLS demonstrate that multipath routing provides higher performance than their single-path counterparts. Performance results are consistent across different network topologies and network utilization levels. The cost incurred by implementing a multipath routing algorithm doesn’t outweigh the added performance benefits.

16. References Chen, Johnny. New Approaches to Routing for Large-Scale Data Networks. Rice University, Houston, Texas: PhD Thesis, June 1999. Nua Internet How Many Online. Nua.com 11 Dec. 2003 Tanenbaum, Andrew S. Computer Networks, Fourth Edition. Upper Saddle River, New Jersey: Prentice Hall PTR, 2003.

17. Questions?