Reliable multicast from end-to-end solutions to active solutions

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Reliable multicast from end-to-end solutions to active solutions C. Pham RESO/LIP-Univ. Lyon 1, France DEA DIF Nov. 13th, 2002

description

Reliable multicast from end-to-end solutions to active solutions. C. Pham RESO/LIP-Univ. Lyon 1, France DEA DIF Nov. 13th, 2002 ENS-Lyon, France. Q&A. Q1: How many people in the audience have heard about multicast? Q2: How many people in the audience know basically what multicast is? - PowerPoint PPT Presentation

Transcript of Reliable multicast from end-to-end solutions to active solutions

Page 1: Reliable multicast  from end-to-end solutions  to active solutions

Reliable multicast

from end-to-end solutions to active solutions

C. Pham

RESO/LIP-Univ. Lyon 1, France

DEA DIF Nov. 13th, 2002ENS-Lyon, France

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Q&A

Q1: How many people in the audience have heard about multicast?

Q2: How many people in the audience know basically what multicast is?

Q3: How many people in the audience have ever tried multicast technologies?

Q4: How many people think they need multicast?

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My guess on the answers

Q1: How many people in the audience have heard about multicast? 100%

Q2: How many people in the audience know basically what multicast is? about 40%

Q3: How many people in the audience have ever tried multicast technologies? 0%

Q4: How many people think they need multicast? 0%

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Purpose of this tutorial

Provide a comprehensive overview of current multicast technologies

Show the evolution in multicast technologies

Achieve 100%, 100%, 30% and 70% to the previous answers next time!

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multicast!

multicast!

How multicast can change the way people use the Internet?

multica

st!

multicast!

multi

cast

!

Everybody's talking about multicast! Really annoying ! Why would I need

multicast for by the way?

multicast!

multicast!multicast!

multicast!

multicast!

multicast!

multicast!

mu

ltic

ast!

multicast!alone

multicast!

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From unicast…

ProblemSending same data to many receivers via unicast is inefficient

ExamplePopular WWW sites become serious bottlenecks

Sender

data

datadata

data

Receiver Receiver Receiver

datadata

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…to multicast on the Internet.

Sender

Not n-unicast from the sender perspective

Efficient one to many data distribution

Towards low latence, high bandwidth

data

datadata

data

Receiver Receiver Receiver

IP multicast

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high-speed www video-conferencing video-on-demand interactive TV programs remote archival systems tele-medecine, white board high-performance computing, grids virtual reality, immersion systems distributed interactive

simulations/gaming…

New applications for the Internet

Think about…

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A whole new world for multicast…

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A very simple example

File replication 10MBytes file 1 source, n receivers (replication sites) 512KBits/s upstream access n=100

Tx= 4.55 hours

n=1000 Tx= 1 day 21 hours 30 mins!

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A real example: LHC (DataGrid)

Tier2 Center

Online System

Offline Farm~20 TIPS

CERN Computer Center > ~20 TIPS

FermilabFrance Regional Center

Italy Regional Center

UK Regional Center

InstituteInstituteInstituteInstitute ~0.25TIPS

Workstations

~100 MBytes/sec

~100 MBytes/sec

~2.4 Gbits/sec

100 - 1000 Mbits/sec

Bunch crossing per 25 nsecs.100 triggers per secondEvent is ~1 MByte in size

Physicists work on analysis “channels”.

Each institute has ~10 physicists working on one or more channels

Data for these channels should be cached by the institute server

Physics data cache

~PBytes/sec

~622 Mbits/sec or Air Freight

Tier2 CenterTier2 CenterTier2 Center

~622 Mbits/sec

Tier 0Tier 0

Tier 1Tier 1

~ 4 TIPS~ 4 TIPS

Tier 3Tier 3

1 TIPS = 25,000 SpecInt95

PC (1999) = ~15 SpecInt95

Tier2 CenterTier 2Tier 2

source DataGrid

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Multicast for computational grids

application user

from Dorian Arnold: Netsolve Happenings

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Distributed & interactive simulations:DIS, HLA,Training.

Some grid applications

Astrophysics:Black holes, neutron stars, supernovae

Mechanics:Fluid dynamic,CAD, simulation.

Chemistry&biology:Molecular simulations, Genomic simulations.

W ide- ar ea int er act ive simulat ions

IN T E R N E T

human in t he loopfl ight s imulat or

bat t le fi eld simulat ion

displaycomput er - basedsub- mar ine simulat or

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Data replications

Code & data transfers, interactive job submissions

Data communications for distributed applications (collective & gather operations, sync. barrier)

Databases, directories services

Data replications

Code & data transfers, interactive job submissions

Data communications for distributed applications (collective & gather operations, sync. barrier)

Databases, directories services

Reliable multicast: a big win for grids

Multicast address group 224.2.0.1

224.2.0.1

SDSC IBM SP1024 procs5x12x17 =1020

NCSA Origin Array256+128+1285x12x(4+2+2) =480

CPlant cluster256 nodes

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••

From reliable multicast to Nobel prize!

We see something,but too weak.

Please simulateto enhance signal!

Resource Broker:7 sites OK, but need to send data fast…

Resource Broker:LANL is best match…

but down for the moment

OK! Resource EstimatorSays need 5TB, 2TF.Where can I do this?

From [email protected]

Congratulations, you have done a great job, it's the discovery of the century!!

The phenomenon was short but we manage to react quickly. This would have not been possible without efficient multicast facilities to enable quick reaction and fast distribution of data.

Nobel Prize is on the way :-)

From [email protected]

Congratulations, you have done a great job, it's the discovery of the century!!

The phenomenon was short but we manage to react quickly. This would have not been possible without efficient multicast facilities to enable quick reaction and fast distribution of data.

Nobel Prize is on the way :-)

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Wide-area interactive simulations

human in the loopflight simulator

battle field simulation

displaycomputer-basedsub-marine simulator

INTERNET

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The challenges of multicast

SCALABILITY

SCALABILITY

SCALABILITYSCALABILITY

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Part I

The IP multicast model

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A look back in history of multicast

History Long history of usage on shared medium

networks Data distribution Resource discovery: ARP, Bootp, DHCP

Ethernet Broadcast (software filtered) Multicast (hardware filtered)

Multiple LAN multicast protocols DECnet, AppleTalk, IP

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IP Multicast - Introduction

Efficient one to many data distribution Tree style data distribution Packets traverse network links only once replication/multicast engine at the network layer

Location independent addressing IP address per multicast group

Receiver-oriented service model Receivers subscribe to any group Senders do not know who is listening Routers find receivers Similar to television model Contrasts with telephone network, ATM

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The Internet group model

multicast/group communications means... 1 n as well as n m

a group is identified by a class D IP address (224.0.0.0 to 239.255.255.255)

abstract notion that does not identify any host!

host_1

194.199.25.100194.199.25.100sourcesource

host_3

receiverreceiver133.121.11.22133.121.11.22

host_2

receiverreceiver194.199.25.101194.199.25.101

multicast group225.1.2.3 multicast router

Ethernet

multicast router

multicast router

host_1

sourcesource

host_2

Ethernet

receiverreceiver

host_3

site 1

site 2

Internet

receiverreceiver

multicast distribution tree

from logical view...

...to physical view

from V. Roca

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Example: video-conferencing

from UREC, http://www.urec.frMulticast address group 224.2.0.1

224.2.0.1

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The Internet group model... (cont’)

local-area multicast use the potential diffusion capabilities of the physical

layer (e.g. Ethernet) efficient and straightforward

wide-area multicast requires to go through multicast routers, use

IGMP/multicast routing/...(e.g. DVMRP, PIM-DM, PIM-SM, PIM-SSM, MSDP, MBGP, BGMP, etc.)

routing in the same administrative domain is simple and efficient

inter-domain routing is complex, not fully operational

from V. Roca

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IP Multicast Architecture

Hosts

Routers

Service model

Host-to-router protocolHost-to-router protocol(IGMP)(IGMP)

Multicast routing protocols(various)

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Multicast and the TCP/IP layered model

TCP UDP

IP / IP multicast

device drivers

ICMP IGMP

Application

Socket layer

multicastrouting

higher-levelservices

user spacekernel space

congestioncontrol

reliabilitymgmt

other buildingblocks

security

from V. Roca

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Internet Group Management Protocol

IGMP: “signaling” protocol to establish, maintain, remove groups on a subnet.

Objective: keep router up-to-date with group membership of entire LAN Routers need not know who all the

members are, only that members exist Each host keeps track of which mcast

groups are subscribed to Socket API informs IGMP process of all

joins

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224.0.0.1 reach all multicast host on the subnet

IGMP: subscribe to a group (1)

Host 1 Host 2 Host 3

224.2.0.1224.2.0.1 224.5.5.5 224.5.5.5

periodically sendsIGMP Query at 224.0.0.1

224.2.0.1

empty empty

from UREC

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IGMP: subscribe to a group (2)

224.2.0.1224.2.0.1 224.5.5.5 224.5.5.5

Sends Reportfor 224.2.0.1

224.2.0.1

224.2.0.1

Host 1 Host 2 Host 3

somebody has already subscribed

for the group

from UREC

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IGMP: subscribe to a group (3)

224.2.0.1224.2.0.1 224.5.5.5 224.5.5.5

Sends Reportfor 224.5.5.5224.5.5.5

224.2.0.1

224.2.0.1224.5.5.5224.5.5.5

Host 1 Host 2 Host 3

from UREC

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Data distribution example

224.2.0.1224.2.0.1 224.5.5.5 224.5.5.5224.2.0.1

224.2.0.1224.5.5.5224.5.5.5

Host 1 Host 2 Host 3

data224.2.0.1

OK

from UREC

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IGMP: leave a group (1)

Host 1 Host 2 Host 3

224.2.0.1

Sends Leavefor 224.2.0.1at 224.0.0.2

224.2.0.1224.5.5.5224.5.5.5

224.0.0.2 reach the multicast enabled router in the subnet

224.2.0.1 224.5.5.5 224.5.5.5

from UREC

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IGMP: leave a group (2)

Host 1 Host 2 Host 3

224.2.0.1

Sends IGMP Query for 224.2.0.1

224.2.0.1224.5.5.5224.5.5.5

224.2.0.1 224.5.5.5 224.5.5.5

from UREC

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IGMP: leave a group (3)

Host 1 Host 2 Host 3

224.2.0.1

Sends Reportfor 224.2.0.1

224.2.0.1224.5.5.5224.5.5.5

224.2.0.1 224.5.5.5 224.5.5.5

Hey, I'm still

here!

from UREC

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IGMP: leave a group (4)

Host 1 Host 2 Host 3

224.2.0.1 224.2.0.1

Sends Leavefor 224.5.5.5at 224.0.0.2

224.2.0.1224.5.5.5224.5.5.5

from UREC

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IGMP: leave a group (5)

Host 1 Host 2 Host 3

224.2.0.1 224.2.0.1

Sends IGMP Query for 244.5.5.5 224.2.0.1

from UREC

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Part II

Introducing reliability

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User perspective of the Internet

from UREC, http://www.urec.fr

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Links: the basic element in networks

Backbone links optical fibers 2.5 to 160 GBits/s with DWDM

techniques End-user access

9.6Kbits/s (GSM) to 2Mbits/s (UMTS) V.90 56Kbits/s modem on twisted pair

64Kbits/s to 1930Kbits/s ISDN access 512Kbits/s to 2Mbits/s with xDSL modem 1Mbits/s to 10Mbits/s Cable-modem 155Mbits/s to 2.5Gbits/s SONET/SDH

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Routers: key elements of internetworking

Routers run routing protocols and build

routing table, receive data packets and

perform relaying, may have to consider Quality

of Service constraints for scheduling packets,

are highly optimized for packet forwarding functions.

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The Wild Wild Web

important data

heterogeneity,link failures,

congested routerspacket loss, packet drop,bit errors…

?

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At the routing level management of the group address (IGMP) dynamic nature of the group membership construction of the multicast tree (DVMRP,

PIM, CBT…) multicast packet forwarding

At the transport level reliability, loss recovery strategies flow control congestion avoidance

Multicast difficulties

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Reliability Models

Reliability => requires redundancy to recover from uncertain loss or other failure modes.

Two types of redundancy: Spatial redundancy: independent backup copies

Forward error correction (FEC) codes Problem: requires huge overhead, since the FEC is

also part of the packet(s) it cannot recover from erasure of all packets

Temporal redundancy: retransmit if packets lost/error

Lazy: trades off response time for reliability Design of status reports and retransmission

optimization important

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Temporal Redundancy Model

Packets • Sequence Numbers• CRC or Checksum

Status Reports • ACKs• NAKs, • SACKs• Bitmaps

• Packets• FEC information

Retransmissions

Timeout

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Part III

End-to-end solutions

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End-to-end solutions for reliability

Sender-reliable Sender detects packet losses by gap in

ACK sequence Easy resource management

Receiver-reliable Receiver detect the packet losses and

send NACK towards the source

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Challenge: Reliable multicast scalability

many problems arise with 10,000 receivers...

Problem 1: scalable control traffic ACK each data packet (à la TCP)...oops,

10000ACKs/pkt! NAK (negative ack) only if failure... oops, if pkt is lost

close to src,10000 NAKs!

source implosion!

NACK4NACK4

NACK4

NACK4

NACK4

NACK4NACK4NACK4

source

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problem 2: exposure receivers may receive several time the same

packet

Challenge: Reliable multicast scalability

NACK4

NACK4

NACK4

NACK4

data4

data4

data4data4

data

4

data4

data4

data

4

data4

data4

data4

data4

data4

data4

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One example – SRMScalable Reliable Multicast

Receiver-reliable NACK-based Not much per-receiver state at the

sender Every member may multicast

NACK or retransmission

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SRM (con’t)

NACK/Retransmission suppression Delay before sending Based on RTT estimation Deterministic + Stochastic

Periodic session messages Sequence number: detection of loss Estimation of distance matrix among

members

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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SRM Request Suppression

Src

from Haobo Yu , Christos Papadopoulos

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Deterministic Suppression

d

d

d

d

3d

time

data

nack repair

d

session msg

4d

d

2d

3d

= sender

= repairer

= requestor

Delay = C1dS,R

from Haobo Yu , Christos Papadopoulos

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SRM Star Topology

Src

from Haobo Yu , Christos Papadopoulos

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SRM: Stochastic Suppression

datad

d

d

d

time

NACK

repair

2d

session msg

0

1

2

3

Delay = U[0,C2] dS,R

= sender

= repairer

= requestor

from Haobo Yu , Christos Papadopoulos

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What’s missing?

Losses at link (A,C) causes retransmission to the whole group

Only retransmit to those members who lost the packet

[Only request from the nearest responder] sender receiver

AA BB

EE FF

SS

CC DD

from Haobo Yu , Christos Papadopoulos

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Idea: Perform Local Recovery with scope limitation

TTL scoped multicast use the TTL field of IP packets to limit

the scope of the repair packet

Src

TTL=1 TTL=2 TTL=3

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Example: RMTP

Reliable Multicast Transport Protocol by Purdue and AT&T Research Labs

Designed for file dissemination (single-sender)

Deployed in AT&T’s billing network

from Haobo Yu , Christos Papadopoulos

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Rcvrs grouped into local regions

Rcvr unicasts periodic ACK to its ACK Processor (AP), AP unicasts its own ACK to its parent

Rcvr dynamically chooses closest statically configured Designated Receiver (DR) as its AP

RMTP: Fixed hierarchy

AA R2R2

R5R5

SS

R3R3 R4R4

R1R1

AA AA AA AA

AA

AA AA

AA

AA DR/AP AA receiver R*R* router

from Haobo Yu , Christos Papadopoulos

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RMTP: Error control

DR checks retx “request” periodically

Mcast or unicast retransmission Based on percentage of requests Scoped mcast for local recovery

from Haobo Yu , Christos Papadopoulos

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RMTP: Comments

: Heterogeneity Lossy link or slow receiver will only

affect a local region : Position of DR critical

Static hierarchy cannot adapt local recovery zone to loss points

from Haobo Yu , Christos Papadopoulos

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Summary: reliability problems

What is the problem of loss recovery? feedback (ACK or NACK) implosion replies/repairs duplications difficult adaptability to dynamic

membership changes Design goals

reduces the feedback traffic reduces recovery latencies improves recovery isolation

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Summary: end-to-end solutions

ACK/NACK aggregation based on timers are approximative!

TTL-scoped retransmissions are approximative!

Not really scalable! Can not exploit in-network

information.

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Part IV

Active solutions

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What is active networks?

Programmable nodes/routers Customized computations on packets Standardized execution environment

and programming interface However, adds extra processing cost

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Motivations behind active networking

user applications can implement, and deploy customized services and protocols

specific data filtering criteria (DIS, HLA) fast collective and gather operations…

globally better performances by reducing the amount of traffic

high throughput low end-to-end latency

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Active networks implementations

Discrete approach (operator's approach) Adds dynamic deployment features in

nodes/routers New services can be downloaded into

router's kernel Integrated approach

Adds executable code to data packets Capsule = data + code Granularity set to the packets

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DataData

The discrete approach

Separates the injection of programs from the processing of packets

active code A1

active code A2

A1A2

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The integrated approach

User packets carry code to be applied on the data part of the packet

High flexibility to define new services

data code

data datacode

data

datadata

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An active router

IP packet

IP packet

Filter Action

Forwardingtable

Routingagent

IP input processing IP output processing

IP packet

Packet scheduler

IP output processing

IP packet

Packet scheduler

some layer for executing code.Let's call it Active Layer

AL packet

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Where to put active components?

In the core network? routers already have to process millions

of packets per second gigabit rates make additional processing

difficult without a dramatic slow down At the edge?

to efficiently handle heterogeneity of user accesses

to provide QoS, implement intelligent congestion avoidance mechanisms…

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Users' accesses

offices

campus

residentials

Network Provider

metro ring

Network Provider

PSTNADSLCable…

Internet

InternetDataCenter

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Solutions

Traditional end-to-end retransmission schemes scoped retransmission with the TTL

fields receiver-based local NACK suppression

Active contributions cache of data to allow local recoveries feedback aggregation subcast early lost packet detection …

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The reliable multicast

universe

YOID

ALMI

HBMApplication-based

RMANP

ARMDyRAM

Router supported,active networking

AER

PGM

RLC

RLM

Layered/FEC

CIFL

FLID

Logging server/replier

LBRM

SRM

TRAM RMTP

LMS

XTPEnd to End

MTP

RMF

AFDP

10 human years (means much more in computer year)

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Routers have specific functionalities/services for supporting multicast flows.

Active networking goes a step further by opening routers to dynamic code provided by end-users.

Open new perspectives for efficient in-network services and rapid deployment.

RMANP

ARMDyRAM

AER

PGM

Router supported,active networking

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A step toward active services: LBRM

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Active local recovery

routers perform cache of data packets repair packets are sent by routers,

when available

data1data2data3data4data5

datadatadata5

NACK4data4

data1data2data3data4data5

data1data2data3data5

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Global NACKs suppression

NACK4NACK4

NACK4

NACK4data4

NACK4

only one NACK is forwarded to the source

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Local NACKs suppression

data

NACK

NACK

NACK

NACK

NACK

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Early lost packet detection

NACK4

NACK4

NACK4

NACK4

NACK4

A NACK is sent by the router

data3data4

data5

The repair latency can be reduced if the lost packet could be requested as soon as possible

These NACKs are ignored!

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Active subcast features

Send repair packet only to the relevant set of receivers

NACK4

NACK4

NACK4

NACK4

data

4

data4

data4

data4

data4

data4

data4data4

data

4

data4

data4

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The DyRAM framework(Dynamic Replier Active Reliable Multicast)

Motivations for DyRAM low recovery latency using local

recovery low memory usage in routers : local

recovery is performed from the receivers (no cache in routers)

low processing overheads in routers : light active services

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DyRAM's main active services

DyRAM is NACK-based with…

Global NACK suppression Early packet loss detection Subcast of repair packets Dynamic replier election

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Replier election

A receiver is elected to be a replier for each lost packet (one recovery tree per packet)

Load balancing can be taken into account for the replier election

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Replier election and repair subcast

IP multicastIP multicast

IP multicast

DyRAMDyRAM

IP multicast

IP multicast

DyRAMDyRAM

R1

R2R3R4

R5 R6 R7

0

12

1 0

NAK 2,@ NAK 2,@

NAK 2,@

NAK 2 from link 1NAK 2 from link 2

NAK 2

Repair 2

Repair 2

Repair 2

Repair 2

D0

D1

NAK 2

NAK 2

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core networkGbits rate

1000 Base FX

active routeractive router

active router

active router

active router

100 Base FX

sourcesourceThe backbone is very fast so nothing else than fast forwarding functions.

• Nacks suppresion• Subcast• Loss detection

A hierarchy of active routers can be used for processing specific functions at different layers of the hierarchy.

Any receiver can be elected as a replier for a loss packet.

•Nacks suppression•Subcast •Replier election

The DyRAM framework for grids

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Network model

10 MBytes file transfer

Source router

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Local recovery from the receivers

Local recoveries reduces the end-to-end delay (especially for high loss rates and a large number of receivers).

#grp: 6…24

4 receivers/group

p=0.25

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Local recovery from the receivers

As the group size increases, doing the recoveries from the receivers greatly reduces the bandwidth consumption

48 receivers distributed in g groups #grp: 2…24

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DyRAM vs ARM

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

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Simulation results

p=0.25

#grp: 6…244 receivers/group

EPLD is very beneficialto DyRAM

simulation resultsvery close to thoseof the analyticalstudy

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DyRAM implementation

Preliminary experimental results

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Testbed configuration

TAMANOIR active execution environment

Java 1.3.1 and a linux kernel 2.4 A set of PCs receivers and 2 PC-based

routers ( Pentium II 400 MHz 512 KB cache 128MB RAM)

Data packets are of 4KB

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Packets format : ANEP

S@IP SEQSVCD@IP isR Payload

S@IP SEQSVCD@IP S@IP

Data /Repair packets

NACK packets

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The data path

IP UDP S,@IP data

ANEP packet

IP

UDP

S,@IP dataTamanoir portFTP port

S

TAMANOIRTAMANOIR

S1

FTPFTP

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Router’s data structures

The track list TL 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. The Nack structure NS that keeps for each

lost data packet, seq : sequene number of the lost data packet subList : list of IP addresses of the downstream

receivers (active routers) that have lost it.

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The first configuration

ike

resama

resamo

resamdstan

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NACK : 135μs DP : 20μs if

no seq gap, 12ms-17ms otherwise. Only 256μs without timer setting

Repair : 123μs

Active service costs

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The second configuration

ike

resamo

NACK

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The election is performed on-the-fly.

It depends on the number of downstream links.

ranges from 0.1 to 1ms for 5 to 25 links per router.

The replier election cost

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Conclusions

Reliability on large-scale multicast is difficult.

End-to-end solutions have to face many critical problems with approximative solutions

Active services can provide more efficient solutions.

The main DyRAM design goal is reducing the end-to-end latencies using active services

Preliminary results are very encouraging