Scalable Fair Reliable Multicast Using Active

ServicesSneha Kumar Kasera, Bell

LabsSupratik Bhattacharyya,

UMassMark Keaton, TASCDiane Kiwior, TASCJim Kurose, UMass

Don Towsley, UMassSteve Zabele, TASC

Why Reliable Multicast ?

applications one-to-many file

transfer information

updates (e.g., stock quote, web cache updates)

shared whiteboard

lossy networklimited capacity links

sender

receivers

Challenges

feedback implosion

retransmission scoping

loss recovery burden

congestion control

Feedback Implosion

NAK implosion ? NAK suppression (using timers) NAK aggregation (by building hierarchy)

problem: ACK implosion solution: use NAKs

pkt

ACKNAK

pkt transmission

pkt lost

pkt retransmission

Retransmission Scoping

retransmissions go everywhere!

how to shield receivers, links from loss recovery due to other receivers ?

Loss Recovery Burden

when #receivers large, each pkt lost at some rcvr with high probability

sender retransmits almost all pkts several times

how to share burden of loss recovery ?

pkt 1lost

pkt 4lost pkt 2

lost

pkt 3lost

retransmits 1,2,3,4

Congestion Control

heterogeneity of links, receivers

feedback implosion

fairness - how to share bandwidth with unicast, other multicast sessions ?

congested link

Active Services

dynamic invocation of user defined computations within network

preserve routing, forwarding semantics at routers

for performance enhancement, not necessary for correctness

receivers

sender

server

how to place, locate, invoke, revoke services ?

what router support required ?

how to provision resources ?

Issues

Feedback Aggregation Service

for avoiding feedback (ACK, NAK, loss reports etc.) implosion

exploits the physical multicast tree, no need to construct, maintain logical hierarchy

invoked at high fan-out

NAK aggregation

lost pkt

NAK

Selective Packet Discard

for retransmission scoping

retransmissions intercepted, forwarded only when requests pending

similar services for filtering undesired, low-priority packets

noforwarding

interception

retransmission

lost pkt

retransmission

Repair Service

servers cache pkts - allowing recovery from point of loss

efficient distribution of loss recovery burden

higher performance

caching for rate conversion [MPL 97]

loss recovery

Congestion Control Using Active Services

feedback aggregation for tracking worst case receiver

rate conversion at servers

selectively discarding less important pkts

(P1,T1) (P4,T4)(P2,T2)

(P3,T3)

(P1,T1) (P4,T4)

(P4,T4)

Loss probability estimates: P1, P2, ...

Round trip time estimates: T1, T2, ...

congestion feedback aggregation

Locating, Invoking, Revoking Services in AER

[KBKKKTZ 99]

source path messages (SPMs) sent periodically

invoke service establish reverse path

router support required for

interception of SPM subcast

SPM S

SPM

SPM RS2

RS1

SPMs multicast but intercepted

NAKs take reverse path

bandwidth usage: total bytes transmitted over all links per correct transmission

active repair service-based (RSB) bandwidth reduction compared to

SRM: upto 60% DR-based (DRB): upto

35%

Network Bandwidth Reduction

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100 1000 10000 100000Tails

p = 0.05

p = 0.25

p = 0.05

p = 0.25

RSB/DRB

RSB/SRM

Tail : link(s) to receiver site

Abone Repair Latency Measurements

experiment: sender at UWash, receiver at UMass, 3 repair servers (Lincoln Labs, Aerospace Corp, UUtah)

marked reduction in repair latency when repair services on

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0 200 400 600 800 1000 1200 1400 1600Repair Latency (msec)

RS-OFF

RS-ON

Histogram over0 to 1500 msec

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0 1000 2000 3000 4000 5000 6000Repair Latency (msec)

RS-OFF

RS-ON

Histogram over0 to 6000 msec

Summary

active services comprehensively address challenges of scalable reliable multicast

future work: other services - log service, parity encoding

service, ... composable active services enhance signaling (SPM++)