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Packet Caches on Routers: The Implications of Universal Redundant
Traffic Elimination
Ashok Anand, Archit Gupta, Aditya AkellaUniversity of Wisconsin, Madison
Srinivasan SeshanCarnegie Mellon University
Scott Shenker University of California, Berkeley
1
DCSLABSmchoi 2011.05.04
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 TTime 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 Packet-Cache
Access linkInternet
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
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Total packets w/o RE = 18
Wisconsin
BerkeleyCMU
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
BerkeleyCMU
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
Dataunique,pitsburgh= 30 KBDataunique,Berkeley= 30 KBDatashared= 20 KB
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Wisconsin
Berkeley
TotalCMU= 50 KBTotalBerkeley= 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
CentralizedPlatform
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 10-35%
• (RE + Routing) gives reduction of 20-45%
15
0.1 0.2 0.3 0.40
0.2
0.4
0.6
0.8
1
RE RE +Routing
Reduction in Network Footprint
Frac
tion
of B
orde
r Rou
ters
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.
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0 0.2 0.4 0.6 0.8 10
0.1
0.2
0.3
0.4
0.5
0.6
RE RE+Routing
Intra-flow redundancy
Redu
ction
in N
etw
ork
Foot
prin
t
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-MaxLoad19
(0.2,1.0) (0.5,0.5)0
0.050.1
0.150.2
0.250.3
0.350.4
RE RE + Routing
(Overall redundancy, Inter flow redundancy)
Redu
ction
inM
ax L
ink
Util
izati
on
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 table Packet 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