Overview

DyRAM : a new approach Simulation results Conclusion and perspectives

Motivations

Router’s caching means are limited. Routers have to support many sessions

in parallel. Question :

How the memory usage can be reduced ?

Answer :Perform local recoveries from the receivers instead of the routers

Related works on local recovery

SRM any receiver in the neighborhood

RMTP, TMTP, LMS, PGM a designated receiver

LBRM a logging server

DRARM main caracteristics

Based on a tree structure constructed on a per-packet basis.

Receiver-based: use of NACKs. Receivers perform local recoveries. Routers play an active role. More efficient replier election Load balancing features Low-overhead active services

DyRAM : routers contribution

My name is ACTIVE ROUTER

and I can doNACK SUPPRESSION

SUBCASTINGDYNAMIC REPLIER

ELECTION

DyRAM: Replier election

data

datadata

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data

NACK

NACKNACKda

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data

The replier is elected on a per-packet basis.

Routers’ soft state

The NACK State (NS) structure which maintains for each received NACK,

seq : the sequence number of the requested packet.

time : the reception time of the last valid similar NACK.

subList : List of the links from which similar NACKs arrived.

Routers’ soft state (cont.)

The Track List (TL) structure which maintains for each multicast session,

lastOrdered : the sequence number of the last received packet in order

lastReceived : the sequence number of the last received data packet

lostList : list of not received data packets in between.

Reduces the replier election delay.

DyRAM main algorithms

NACK packet service Data packet service The DTD timer handler

The NACK packet service

If (processed) then check if validupdate the corresponding NS accordingly

else // not processedcreate a new NS

If (valid) then init (DTD timer)else drop this NACK

The data packet (DP) service

update the TL of the sessionIf DP is a repair then

look for the corresponding NS structuresend the DP through links in NS.subListfree NS

else simply forward the DP on all the downstream links

The DTD expiration handler

forward the NACK on link i downstream where i=(last+1)%B

with i not in NS.subList and last is the previous replier link

Last = i

Overview

DyRAM : a new approach Simulation results Conclusion and perspectives

Simulation Results

Network model and used metrics Local recovery from the receivers DyRAM vs. ARM DyRAM combined with cache at

routers

Network model

Metrics

Load at the source : the number of the retransmissions from the source.

Load at the network : the consumed bandwidth.

Completion time per packet (latency).

Local recovery from the receivers

Local recovery reduces the load at the source, the consumed BW and the recovery delay (especially for high loss rates and a large number of the receivers).

Local recovery from the receivers (cont.)

As the groups size increases, the recovery from the receivers is more and more beneficial.

DyRAM vs ARM

ARM performs better than DyRAM only for very low loss rates with considerable caching requirements

DyRAM combined with cache at the routers

When DyRAM benefits from the cache at the routers in addition to the recovery from the receivers, it always performs better than ARM.

Overview

DyRAM : a new approach Simulation results Conclusion and perspectives

Conclusion

DyRAM achieves local recovery by enabling the recovery from the receivers.

Unlike ARM, DyRAM avoids overloading the routers by caching data packets.

However, DyRAM achieves better performances than ARM in various scenarii.

DyRAM provides some load-balancing facilities.

Perspectives

DyRAM will be implemented and tested

on an active network testbed. To be considered :

NACK reverse-path requirements the DTD timer setting topology limitations optimization of the election process