Packet Caches on Routers: The Implications of Universal Redundant Traffic Elimination Ashok Anand, Archit Gupta, Aditya Akella University of Wisconsin, Madison Srinivasan Seshan Carnegie Mellon University Scott Shenker University of California, Berkeley 1 DCSLAB Smchoi

Redundant Traffic in the Internet Lots of redundant traffic in the Internet Redundancy due to… – Identical objects – Partial content match (e.g. page banners) – Application- headers –…–… 2 Same content traversing same set of links Time T Time T + 5

Redundancy Elimination Object-level caching – Application layer approaches like Web proxy caches – Store static objects in local cache – [Summary Cache: SIGCOMM 98, Co-operative Caching: SOSP 99] Packet-level caching – [Spring et. al: SIGCOMM 00] – WAN Optimization Products: Riverbed, Peribit, Packeteer,.. 3 Packet-Cache Access link Internet Enterprise Packet-level caching is better than object-level caching

Benefits of Redundancy Elimination – Reduces bandwidth usage cost – Reduces network congestion at access links – Higher throughputs – Reduces in transfer completion times 4

Towards Universal RE However, existing RE approaches apply only to point deployments – E.g. at stub network access links, or between branch offices They only benefit the system to which they are directly connected. Why not make RE a native network service that everyone can use? 5

Our Contribution Universal redundancy elimination on routers is beneficial Re-designing the routing protocol to be redundancy aware gives furthermore benefits Practical to implement redundancy elimination 6

Internet2 Universal Redundancy Elimination At All Routers Total packets with universal RE= 12 (ignoring tiny packets) Upstream router removes redundant bytes. Downstream router reconstructs full packet 7 Total packets w/o RE = 18 Wisconsin Berkeley CMU 33% Packet cache at every router

Benefits of Universal Redundancy Elimination Subsumes benefits of point deployments Also benefits Internet Service Providers – Reduces total traffic carried  better traffic engineering – Better responsiveness to sudden overload (e.g. flash crowds) Re-design network protocols with redundancy elimination in mind  Further enhance the benefits of universal RE 8

Redundancy-Aware Routing Total packets with RE + routing= 10 (Further 20% benefit ) 9 Total packets with RE = 12 Wisconsin Berkeley CMU 45% ISP needs information of traffic similarity between CMU and Berkeley ISP needs to compute redundancy- aware routes

Redundancy-Aware Routing Intra-domain Routing for ISP Every N minutes – Each border router computes a redundancy profile for the first Ts of the N-minute interval Estimates how traffic is replicated across other border routers High speed algorithm for computing profiles – Centrally compute redundancy-aware routes Route traffic for next N minutes on redundancy-aware routes. Redundancy elimination is applied hop-by-hop 10

CMU Redundancy Profile Example 11 Internet2 Data unique,pitsburgh = 30 KB Data unique,Berkeley = 30 KB Data shared = 20 KB 11 Wisconsin Berkeley Total CMU = 50 KB Total Berkeley = 50 KB

Centralized Route Computation Linear Program Objective: minimize the total traffic footprint on ISP links Traffic footprint on each link as latency of link times total unique content carried by the link Compute narrow, deep trees which aggregate redundant traffic as much as possible Impose flow conservation and capacity constraints 12 Centralized Platform Route computation

Inter-domain Routing ISP selects neighbor AS and the border router for each destination Goal: minimize impact of inter-domain traffic on intra- domain links and peering links. Challenges: – Need to consider AS relationships, peering locations, route announcements – Compute redundancy profiles across destination ASes 13

Trace-Based Evaluation Trace-based study – RE + Routing: Redundancy aware routing – RE: Shortest path routing with redundancy elimination – Baseline: Compared against shortest path routing without redundancy elimination Packet traces – Collected at University of Wisconsin access link – Separately captured the outgoing traffic from separate group of high volume Web servers in University of Wisconsin Represents moderate-sized data center Rocketfuel ISP topologies Results for intra-domain routing on Web server trace 14

Benefits in Total Network Footprint Average redundancy of this Web server trace is 50% using 2GB cache ATT topology 2GB cache per router CDF of reduction in network footprint across border routers of ATT RE gives reduction of % (RE + Routing) gives reduction of 20-45% 15

When is RE + Routing Beneficial? Topology effect – E.g., multiple multi-hop paths between pairs of border routers Redundancy profile – Lot of duplication across border routers 16

Synthetic Trace Based Study Synthetic trace for covering wide-range of situations – Duplicates striped across border routers in ISP (inter-flow redundancy) – Low striping across border routers, but high redundancy with in traffic to a border router (intra-flow-redundancy) – Understand topology effect 17

Benefits in Total Network Footprint Synthetic trace, average redundancy = 50% ATT (7018) topology Trace is assumed to enter at Seattle RE + Routing, is close to RE at high intra-flow redundancy, 50% benefit RE has benefit of 8% at zero intra-flow redundancy RE + Routing, gets benefit of 26% at zero intra-flow redundancy. 18

Benefits in Max Link Utilization Link capacities either 2.5 or 10 Gbps Comparison against traditional OSPF based traffic engineering (SP- MaxLoad) RE offers 1-25% lower maximum link load. RE + Routing offers 10-37% lower maximum link load. Max link Utilization = 80%, for SP-MaxLoad 19

Evaluation Summary RE significantly reduces network footprint RE significantly improves traffic engineering objectives RE + Routing further enhances these benefits Highly beneficial for flash crowd situations Highly beneficial in inter-domain traffic engineering 20

Implementing RE on Routers 21 Fingerprint tablePacket store Fingerprint s Main operations – Fingerprint computation Easy, can be done with CRC – Memory operations, Read and Write

High Speed Implementation Reduced the number of memory operations per packet – Fixed number of fingerprints (<10 per packet) – Used lazy invalidation of fingerprint for packet eviction – Other optimizations in paper Click-based software prototype runs at 2.3 Gbps (approx. OC 48 speed ). 22

Summary RE at every router is beneficial ( 10-50%) Further benefits (10-25%) from redesigning routing protocol to be redundancy-aware. OC48 speed attainable in software 23

Thank you 24