REDUNDANCY IN NETWORK TRAFFIC: FINDINGS AND IMPLICATIONS Ashok Anand Ramachandran Ramjee Chitra Muthukrishnan Microsoft Research Lab, India Aditya Akella University of Wisconsin, Madison

Redundancy in network traffic  Redundancy in network traffic  Popular objects, partial content matches, headers  Redundancy elimination (RE) for improving network efficiency  Application layer object caching Web proxy caches  Recent protocol independent RE approaches WAN optimizers, De-duplication, WAN Backups, etc. 2

Protocol independent RE 3  Message granularity: packet or object chunk  Different RE systems operate at different granularity WAN link

RE applications 4  Enterprise and data centers  Accelerate WAN performance  As a primitive in network architecture  Packet Caches [Sigcomm 2008]  Ditto [Mobicom 2008]

ISP ISP Protocol independent RE in enterprises Enterprises Wan Opt Data centers  Globalized enterprise dilemma  Centralized servers Simple management Hit on performance  Distributed servers Direct request to closest servers Complex management  RE gives benefits of both worlds  Deployed in network middle-boxes  Accelerate WAN traffic while keeping management simple  RE for accelerating WAN backup applications 5

ISP ISP Recent proposals for protocol independent RE Enterprises Web content University RE deployment on ISP access links to improve capacity  Reduce load on ISP access links  Improve effective capacity  Packet caches [Sigcomm 2008]  RE on all routers  Ditto [Mobicom 2008]  Use RE on nodes in wireless mesh networks to improve throughput 6

Understanding protocol independent RE systems  Currently little insight into these RE systems  How far are these RE techniques from optimal?  Are there other better schemes?  When is network RE most effective?  Do end-to-end RE approaches offer performance close to network RE?  What fundamental redundancy patterns drive the design and bound the effectiveness?  Important for effective design of current systems as well as future architectures e.g. Ditto, packet caches 7

Large scale trace-driven study  First comprehensive study  Traces from multiple vantage points  Focus on packet level redundancy elimination  Performance comparison of different RE algorithms  Average bandwidth savings  Bandwidth savings in peak and 95 th percentile utilization  Impact on burstiness  Origins of redundancy  Intra-user vs. Inter-user  Different protocols  Patterns of redundancy  Distribution of match lengths  Hit distribution  Temporal locality of matches 8

Data sets  Enterprise packet traces (3 TB) with payload  11 enterprises Small (10-50 IPs) Medium ( IPs) Large (100+ IPs)  2 weeks  Protocol composition HTTP (20-55%) Spring et al. (64%) File sharing (25-70%) Centralization of servers  UW Madison packet traces (1.6 TB) with payload  IPs; trace collected at campus border router  Outgoing /24, web server traffic  2 different periods of 2 days each  Protocol composition Incoming, HTTP 60% Outgoing, HTTP 36% 9

Evaluation methodology  Emulate memory-bound (500 MB - 4GB) WAN optimizer  Entire cache resides in DRAM (packet-level RE)  Emulate only redundancy elimination WAN optimizers do other optimizations also  Deployment across both ends of access links Enterprise to data center All traffic from University to one ISP  Replay packet trace  Compute bandwidth savings as (saved bytes/total bytes)  Includes packet headers in total bytes  Includes overhead of shim headers used for encoding 10

Large scale trace-driven study  Performance comparison of different RE algorithms  Origins of redundancy  Patterns of redundancy  Distribution of match lengths  Hit distribution 11

Redundancy elimination algorithms Redundancy suppression across different packets (Use history) Data compression only within packets (No history) MODP (Spring et al.) MAXP (new algorithm) GZIP and other variants 12

MODP Packet payload Window Rabin fingerprinting Value sampling: sample those fingerprints whose value is 0 mod p Fingerprint table Packet store Payload-1 Payload-2  Spring et al. [Sigcomm 2000]  Compute fingerprints  Lookup fingerprints in Fingerprint table 13

MAXP Choose fingerprints that are local maxima ( or minima) for p bytes region  Similar to MODP  Only selection criteria changes MODP Sample those fingerprints whose value is 0 mod p No fingerprint to represent the shaded region Gives uniform selection of fingerprints 14

Optimal  Approximate upper bound on optimal  Store every fingerprint in a bloom filter  Identify fingerprint match if bloom filter contains the fingerprint  Low false positive for bloom filter: 0.1% 15

Comparison of MODP, MAXP and optimal  MAXP outperforms MODP by 5-10% in most cases  Uniform sampling approach of MAXP  MODP loses due to non uniform clustering of fingerprints  New RE algorithm which performs better than classical MODP 16

Comparison of different RE algorithms  GZIP offers 3-15% benefit  (10ms buffering) -> GZIP increases benefit up to 5%  MAXP significantly outperforms GZIP, offers 15-60% bandwidth savings  MAXP -> (10 ms) -> GZIP further enhances benefit up to 8%  We can use combination of RE algorithms to enhance the bandwidth savings 17 -> means followed by

Large scale trace-driven study  Performance study of different RE algorithms  Origins of redundancy  Patterns of redundancy  Distribution of match lengths  Match distribution 18

Origins of redundancy Enterprise Middlebox Data Centers Middlebox Flow-1 Flow-2 Flow-3 Flow-1 Flow-2 Flow-3  Different users accessing the same content, or same content being accessed repeatedly by same user?  Middle-box deployments can eliminate bytes shared across users  How much sharing across users in practice? INTER-USER: sharing across users (a)INTER-SRC (b)INTER-DEST (c)INTER-NODE INTRA-USER: redundancy within same user (a) INTRA-FLOW (b) INTER-FLOW 19

Study of composition of redundancy  90% savings is across destinations for Uout/24  For Uin/Uout, 30-40% savings is due to intra-user  For enterprises, 75-90% savings is due to intra-user Inter User Intra User 20

Implication: End-to-end RE as a promising alternative Enterprise Middlebox Data Centers Middlebox 21  End-to-end RE as a compelling design choice  Similar savings  Deployment requires just software upgrade Middle-boxes are expensive  Middle-boxes may violate end-to-end semantics

Large scale trace-driven study  Performance study of different RE algorithms  End-to-end RE versus network RE  Patterns of redundancy  Distribution of match lengths  Hit distribution 22

Match length analysis  Do most of the savings come from full packet matches?  Simple technique of indexing full packet will be good  For partial packet matches, what should be the minimum window size? 23

Match length analysis for enterprise  70% of the matches are less than 150 bytes and contribute 20% of savings  10% of the matches come from full matches and contribute 50% of savings  Need to index small chunks of size <= 150 bytes for maximum benefit 24 Bins of different match lengths (in bytes) Percentage

Hit distribution  Contributors of redundancy  Few pieces of content repeated multiple times Small packet store would be sufficient  Many pieces of content repeated few times Large packet store 25

Zipf-like distribution for chunk matches  Chunk ranking  Unique chunk matches sorted by their hit counts  Straight line shows the zip-fian distribution  Similar to web page access frequency  How much popular chunks contribute to savings? 26

Savings due to hit distribution  80% of savings come from 20% of chunks  Need to index 80% of chunks for remaining 20% of savings  Diminishing return for cache size 27

Savings vs. cache size  Small packet caches (250 MB) provide significant percentage of savings  Diminishing returns for increasing packet cache size after 250 MB 28

Conclusion  First comprehensive study of protocol independent RE systems  Key Results  15-60% savings using protocol independent RE  A new RE algorithm, which performs 5-10% better than Spring et al. approach  Zip-fian distribution of chunk hits; small caches are sufficient to extract most of the redundancy  End-to-end RE solutions are promising alternatives to memory-bound WAN optimizers for enterprises 29

Thank you! Questions ? 30

Backup slides 31

Peak and 95 th percentile savings 32

Effect on burstiness 33  Wavelet based multi-resolution analysis  Energy plot higher energy means more burstiness  Compared with uniform compression  Results  Enterprise No reduction in burstiness Peak savings lower than average savings  University Reduction in burstiness Positive correlation of link utilization with redundancy

Redundancy across protocols 34  Large enterprise  University ProtocolPercentage VolumePercentage redundancy HTTP SMB LDAP Src code ctrl ProtocolPercentage VolumePercentage redundancy HTTP DNS RTSP3.382 FTP