CacheCast: Eliminating CacheCast: Eliminating Redundant Link Traffic for Redundant Link Traffic for Single Source Multiple Single Source Multiple Destination Transfers Destination Transfers

Piotr Srebrny, Thomas Plagemann, Vera Goebel

Department of Informatics, University of Oslo

Andreas Mauthe

Computing Department, Lancaster University

OutlineOutlineProblem statementIdeaDesignRelated workCacheCast evaluationConclusions

What is the Problem?What is the Problem?The Internet provides only a

mechanism for single source to single destination datagram transmission (unicast)

This is expressed in the IP header

IPPAYLOAD

… Destination Address Source Address …

What is the Problem? What is the Problem? (cont.)(cont.)The Internet – a network of routers and links

APB

P

CP

Redundancy!

S

AB

C

What has been done?What has been done?“Datagram Routing for Internet

Multicasting” L. Aguilar – explicit list of destinations in the IP header◦Follow-ups: XCast, Small Group Multicast

“Host Extension for IP Multicasting” S. Deering – destination address denotes a group of host

“A Case for End System Multicast” Y. hua Chu et al. – application level multicast

CacheCastCacheCastCacheCast is a network layer

caching mechanism that eliminates redundant data transmissionsS

AB

C

APB

C

BP

CP

CacheCast IdeaCacheCast Idea

1.

2.

3.

P A

0 0 0

0

A

B

P A

PP P

1 1 1

0

A

B

P AP A

P B

PP P

1 1 1

0

A

B

CacheCast Idea (cont.)CacheCast Idea (cont.)

4.

5.

PB

PP P

1 1 1

1

B

A

PP P

B B

1 1 1

0

B

A

Link CacheLink CachePoint-to-point logical linksCaching is done per link:

◦Cache Management Unit (CMU)◦Cache Store (CS)

Router

Router

Router Router

CMU

CS

CMU

CS

CMU CS

Caching

Normal processing

Link Cache RequirementsLink Cache RequirementsSimple processing

◦~72ns to process a minimum size packet on a 10Gbps link and ~18ns on a 40Gbps link Modern DDR r/w cycle ~20ns Modern SRAM r/w cycle ~5ns

Small cache size◦A link queue scaled to 250ms of the

link traffic

Source RequirementsSource RequirementsSimple cache processing

◦A source provides information on payload ID, payload size

Minimise cache size◦A source batches request for the

same data and transmits it within the minimum amount of time

Cacheable PacketsCacheable PacketsCacheCast packet carries a

metadata describing packet payload ◦Payload ID◦Payload size◦Index

Only packets with the metadata are cached

CMU & CSCMU & CS

CMU CS

Index

012

Index

012

Payload ID

000

Payload

---

AP1 x

P1

P1AP1 0

Cache miss

CMU table Cache store

CMU & CS (cont.)CMU & CS (cont.)

CMU CS

Index

012

Index

012

Payload ID

P1P2P3

Payload

---

BP2 x

P1

B1

P2P3

Cache hit

P2

CMU table Cache store

Estimating Cache SizeEstimating Cache SizeConcept of packet train

It is sufficient to hold payload in the CS for the packet train duration time

How many packet headers can send a source send within the time?

Estimating Cache Size (cont.)Estimating Cache Size (cont.)Back-of-the-envelope calculations

~10ms caches are sufficient

Source uplink speed

Packet train time

2ms 10ms 50ms

512Kbps 2 8 40

1Mbps 4 16 79

10Mbps 32 157 781

100Mbps 313 1561 7802

Implication of the Small SizeImplication of the Small Size10ms cache size on a 10Gbps

link:~12.8MB for the CS storage space~13000 entries in the CMU table

What about 100Mbps LAN?~130KB for CS~130 entries in the CMU table

We can afford that!

Related WorkRelated WorkPacket Caches on Routers: The

Implications of Universal Redundant Traffic Elimination. Ashok Anand et al.◦Per link cache◦Universal redundancy elimination◦No server support

EvaluationEvaluationBandwidth consumption

◦CacheCast vs. IP Multicast Unique packet headers Finite cache sizes

Incremental deployment◦Benefits of partial cache deployment

Congestion control◦CacheCast impact on TFRC

throughput

Bandwidth ConsumptionBandwidth ConsumptionMulticast efficiency metric:

Example:

u

mm L

L1

9,5 um LL

9

4

9

51 m

Lm – total amount of multicast linksLu – total amount of unicast links

CA B

S

Bandwidth Consumption (cont.)Bandwidth Consumption (cont.)

CacheCast unicast header part (h) and multicast payload part (p)

Thus:

E.g.: using packets which sp=1416B and sh=84B we experience reduction of 5%

uhp

mpuhCC Lss

LsLs

)(1

p

hmCC s

sr

r

,1

1

u

mm L

L1

Finite Cache SizeFinite Cache SizeThe more destination the higher

efficiency E.g.

◦512Kbps – 8 headers in 10ms, e.g. 12 destinations

Slow sources transmitting to many destinations cannot achieve the maximum efficiency

APBCDEFGHIPJKL

m

Finite Cache Size (cont.)Finite Cache Size (cont.)

Uplink PH

512Kbps 8

1Mbps 16

10Mbps 157

100Mbps 1561

Sources with different uplink speed transmitting to the growing number of destinations

S

Incremental DeploymentIncremental Deployment

1 2 3 4 5 6

The CS and CMU deployed incrementally

Incremental DeploymentIncremental Deployment

Bottleneck Link Test

ns2 implementation 100 TCP flows competing with 100

TFRC flows on a bottleneck link

Bottleneck Link Test (cont.)

Both TCP and TRFC benefit from CacheCast

CacheCast ImplementationCacheCast ImplementationRouter part

◦ Click Modular Router CMU and CS elements - in total ~400 lines of

code

Server part◦ Linux kernel – system call

msend(fd_set *write_to, fd_set *written,

char *buf, int len)◦ Paraslash tools – a streaming server

that uses the msend system call and a receiver

TestbedTestbedTestbed setup:

◦Paraslash server (S)◦Click Modular Router (R)◦Paraslash receivers (A,B)

Testbed ResultsTestbed Results

Bandwidth consumed by packet header transmission

msend overhead negligible

ConclusionsConclusionsCacheCast is:

◦A valid solution for single source multiple destinations transfers

◦Simple and reliable◦Fully distributed◦Incrementally deployable

Thank You for Your Attention!Thank You for Your Attention!