Dennis Ippoliti 12/6/ MULTI-PATH ROUTING A packet by packet multi-path routing approach

2 Dennis Ippoliti 12/6/2004 OVERVIEW Multi-path routing (Benefits / Problems) Multi-Path routing protocol Multi-Path routing Transport Protocol Per-hop Packet Distribution Simulation results

3 Dennis Ippoliti 12/6/2004 Multi Path Routing In a well connected network multiple paths exist Typically, one path at a time is chosen and all traffic is sent over that path With Multi-Path routing, traffic is diffused over several paths at the same time

4 Dennis Ippoliti 12/6/2004 Benefits of Multi-Path routing Enables Load balancing implementations Simplifies algorithms if single flows can take multiple paths Increases throughput Decreases delay Takes advantage of considerable redundancy 90% of all US Sprintlink POP pairs are connected by 4 or more paths Increases Robustness to Eavesdropping Attackers must sniff multiple links when traffic is diffused

5 Dennis Ippoliti 12/6/2004 Challenges in Multi-Path routing Route Identification Identifying available routes Route Selection Round Robin, Weighted Selection, Other Metrics (Throughput / Delay / Drop rate) Different subsets of routes will maximize/minimize different metrics Leads to persistent packet re-sequencing When multiple routes are used, the probability that packets are received out of sequence is high

6 Dennis Ippoliti 12/6/2004 Multi-Path Routing Algorithms In a network G = (N, L) with N nodes and L links, MP Algorithms identify S(I,j) such that S(I,j) = the set of successor nodes to rout traffic from node I to node j. Multi-path routing algorithms identify S(I,j) and rank order according to some minimum or maximum desired metric or combination of metrics

7 Dennis Ippoliti 12/6/2004 Multi-Path Routing Algorithms Multi-Path Distance Vector (MPDV) Multi-Path Link State (MPLS) Enhanced Interior Gateway Routing Protocol

8 Dennis Ippoliti 12/6/2004 Multi-Path Transport Protocol Multi-Path environment causes persistent packet reordering

9 Dennis Ippoliti 12/6/2004 Multi-Path Transport Protocols TCP is not effective in this environment TCP uses windowing for error and congestion control When packets are received out of order, DUPACKS are generated DUPACKS typically decrease window size by 50% DUPACKS cause sender to enter Fast Retransmit Persistent DUPACKS reduce throughput while increasing traffic load

10 Dennis Ippoliti 12/6/2004 Multi Path Transport Protocols Eifel Algorithm Uses time-stamp option to differentiate between transmissions and re-transmissions Restores TCP congestion window to value prior to retransmit when packet received DSACK Uses DSACK option to communicate from receiver to sender Dynamically manipulate dupthresh value TCP Persistent Reordering Ignores DUPACKS. Uses timers to identify packet loss

11 Dennis Ippoliti 12/6/2004 Route Selection Round Robin and pure load balancing not effective Do not take network conditions into consideration Minimum Delay Routing As delay increases, the proportion of traffic distributed to that rout decreases

12 Dennis Ippoliti 12/6/2004 Route Selection Minimum Delay Routing with dynamic service differentiation In multi path routing, a greedy node can starve other nodes on the network A B CD A B CD

13 Dennis Ippoliti 12/6/2004 Route Selection I experimented with Minimum Delay Routing with dynamic service differentiation Traffic that is on a primary route is given priority over traffic on a secondary route A B CD A B CD

14 Dennis Ippoliti 12/6/2004 Simulation Method Developed Network Simulator software similar to the Click Router Platform C++ objects represent Nodes and Links Static Multi-Paths RR, Load Balancing, and Minimum Delay Routing as Route Selection methods TCP-PR as transport protocol

15 Dennis Ippoliti 12/6/2004 Results TCP-PR 200% through-put over standard TCP Round Robin, Load balancing, and Minimum delay route selection performed the same when link cost equal Only Minimum Delay performed well when link cost was unequal Dynamic service differentiation prevents starvation in the presence of greedy flows

Dennis Ippoliti 12/6/ TCP-PR QUESTIONS?