stealth multicast - a new paradigm for incremental multicast deployment

Striegel, Guest Lecture - UIUC ([email protected]) 1

Stealth Multicast - A New Paradigm Stealth Multicast - A New Paradigm for Incremental Multicast for Incremental Multicast

DeploymentDeployment

Dr. Aaron Striegel

Notre Dame Systems & Software Laboratory

Dept. of Computer Science & Engineering

University of Notre Dame

October 20, 2003


Talk OverviewTalk Overview

• Information Dissemination• Motivation• Stealth Multicast

– Basic Architecture– Example: MYDEKI– Preliminary Results

• Future Research– Inter-domain Peering– Network stack enhancement


Information DisseminationInformation Dissemination

• Distribute rich content in a timely fashion to users– Problem: Internet evolved as point-to-point

• Inefficient but currently manageable via unicasts

• Two main approaches– Active involvement - Multicast

• Close temporal proximity

• Applications, network can participate– Community participation -> network efficiency

– Passive involvement - Caching• Multiply-accessed data over time

• No required participation of apps/network– Exploit existing characteristics of network

» HTTP Caching

» Packet-level caching


Caching vs. MulticastCaching vs. Multicast

• Caching– Cannot handle rapidly changing data

• Data w/close temporal proximity

– Easy deployment• No global participation

• Multicast– Deployment problems

• Global participation– Addressed by ALM

» Delay-sensitive traffic, rich user base

• Economic incentive– Bandwidth glut, ISP benefit

– Can handle close temporal data• Group-oriented activities - synchrony is an issue


Current StateCurrent State

• Caching: Yes Multicast: ??– Several recent studies [2000, 2003]

• Lackluster adoption 150 groups (1999) -> 250 (2001)• Most groups are single source (SSM)

– Why have *, G, CBTs, etc.? » Harder form of multicast anyway

– Key lesson from caching• Incremental deployment is key

– Big-bang theory is impossible– Transition as easy as possible (FUD inertia)

• Immediate benefit– Large benefit with minimal investment

• Directable economic benefit– Avoid “If you build it, they will come…”


MotivationMotivation• Research premise

– Transparent bandwidth conservation technique– Change the paradigm of multicast

• Incremental deployment– Zero dependence on external forces

• Immediate benefit– Exploit the redundancy in the network

• Economics– Offer a significant and quantifiable benefit

• Stealth Multicast – Dynamically convert packets to/from multicast– Target

• Small to medium group-oriented apps 5-500 users• Delay-sensitive apps

– On-line gaming, video streaming

– Improve ALM-based apps


Stealth MulticastStealth Multicast

• Two governing principles– Externally transparent

• Zero modification - application (server/client)• Zero modification - external Internet• Seamless operation

– Negligible QoS impact?• Should not noticeably impact QoS• What are noticeable QoS changes?

– Depends upon application» Large buffer - streaming video» On-line game - zero buffer

– Informal definition» Additional delay should not make the application

unusable versus separate unicasts


Stealth Multicast ModelStealth Multicast Model

Unicast

Company LAN(Content Provider)

ISP Domain

Other DomainsServers

Clients

Multicast Unicast

Conversion


Multicast DetectionMulticast Detection

Edge Router

Filter

VirtualGroupMgr

Disp

ChecksumCalculation

HRules

TreeConstruction

StateManagement

Incoming Traffic (Unicast only)

Outgoing Traffic(Unicast+Multicast)

VGDM - Virtual Group Detection Manager


Further ExaminationFurther Examination

• Benefits– Dynamically convert– Zero modification– Multicast transport via

virtual groups– Exact billing

• Drawbacks– Non-zero queuing delay– Aggregation effects– Imperfect virtual groups– Not a universal solution

Virtual Group Delay

Benefit

Delay

Minimum gain

Maximum delay


Multicast Transition OptionsMulticast Transition Options

Approach

Pure

Multicast

Application

Assisted

Customer

Aware

Stealth

Mode

Separate

Unicast

Application Multicast Stealth Unicast Unicast Unicast

Internet Multicast Unicast Unicast Unicast Unicast

ISP Multicast Stealth Stealth Stealth Unicast

VGDM None ISP Company ISP Edge None

Detection

Accuracy Perfect Perfect Good OK None

Benefits Customer, ISP

Customer,

ISP

Customer, ISP

ISP None

Costs App change

Deployment

App change

Deployment

Deployment Deployment None


MYDEKI ArchitectureMYDEKI Architecture

• Implementation of stealth multicast– Multicast and You Don’t Even Know It– Three variations

• ISP• Local• Application-assisted

– Defines key issues of stealth multicast• Triggers - Virtual group release• Transport - Dynamic groups• State management - Where to place state


Virtual Group TriggersVirtual Group Triggers

• Trigger– Dilemma: Gain for waiting– When to release the virtual group

• MHT - Maximum Hold Time• TSW - Time Search Width• PSW - Packet Search Width

time

MHTTSWPSW

Target packet


Triggers - ContinuedTriggers - Continued

• Triggers/thresholds– MinGS - Minimum group size– MaxGS - Maximum group size– MVG - Maximum virtual groups

UnicastMulticastNew group

MaxGS MinGS

VG 0

VG N

.. MVG


System BalanceSystem Balance

• VGDM Limit– MVG - Maximum Virtual Groups

• Hard limit - should be avoided• No multicast benefit - overloaded

– Inputs• Filter effectiveness

– Eliminate non-candidate traffic

• Triggers - dispatch– PSW, TSW, MHT

– MaxGS

• Tradeoff– Capacity, QoS vs. efficiency


Multicast TransportMulticast Transport

• Issue– Members (clients) not known a priori– Dynamically construct tree

• Approaches– Exhaustive tree construction

• All variations, all egress points

• Problem - failure and tree reconstruction

– Broadcast/hold• Costly - queuing at edge

• Depends upon client distribution

– Encapsulation-based• Embed tree inside the packet

• Use DSMCast - DiffServ Multicast


Why Encapsulation?Why Encapsulation?

• Benefits– Dynamically construct trees

• Dynamic routing - QoS

• Heterogeneous QoS

– Stateless core• Transport only - hardware

– Simplified billing• Know tree, know cost

• Tradeoff– Deployment - upgrade core– Additional bandwidth

• Save 16x vs. 18x vs. None

• Excellent starting point for evaluation


State ManagementState Management

• Issue– Unique portions of packet

• Compress multiple packets for different destinations into a single packet

– Dest port, dest IP

– Who is responsible for exporting?• Egress A vs. Egress B vs. Egress C

• Approaches– Include in packet

• Similar to encapsulation-based approach

– Distributed knowledge• Egress points share knowledge


Why Packet-based? Why Packet-based?

• Benefits– Simple

• No timing/state issues• Good first step

– No problem with dynamics• Imprecise matching algorithms

• Weaknesses– Bandwidth cost– Limitations on clients per group

• MTU violations


Example - State ManagementExample - State Management

IP DSM State UDP Payload

Edge55

10153

Dest IP129.186.5.4129.186.6.20143.24.6.4102.67.8.2550.6.8.20

Dest Port78942004500357966901


Application-Assisted MethodApplication-Assisted Method

• Virtual group detection– Imprecise nature - best guess

• Application-assist– Application knows about VGDM– Application sends 1 packet w/state to VGDM– VGDM constructs tree

• Benefits– No change to the client - deployment– Precise group construction

• Issues– Billing– Requires change to server app


Other Issues - TCP, IPSec, IPv6Other Issues - TCP, IPSec, IPv6

• TCP– Limited benefit

• Why?– Extra state

– Retransmit of lost packets

– Potential benefit• Web serving - initial request

– Assume no cookies

• CNN on 9/11

• IPSec / VPNs• IPv6


Simulation StudiesSimulation Studies

• Simulation setup– Ns-2 simulator

• Freely available simulator

– GenMCast module for ns-2, GRIM - simulation management

• Network setup– Medium-sized multicast groups

• On-line gaming apps - 8 to 64 clients

• UDP traffic - 40 server apps

– Compare various approaches• Based on VGDM location + others

– Local, Stealth, None, App-Assist, ALM

• Evaluation metrics– Bandwidth savings– End-user QoS


Effect of Clients - Link BWEffect of Clients - Link BW

No savings, unicast

Higher up-link cost


Effect of clients - Domain BWEffect of clients - Domain BW

Trades B/W forclient B/W

Increasing savingsvs. unicast


Effect of Clients - QoS (Delay)Effect of Clients - QoS (Delay)

Limited impactof queuing


Other ResultsOther Results

• Other aspect– Out of order delivery

• VGDM Overload

• Traffic aggregation– OS/app effect

• Spacing between packets


Immediate Research AreasImmediate Research Areas

• Practical transport– Encapsulation - interesting but academic– Compare various approaches

• Fixed grouping w/hierarchy– How to find the group that maps to the egress points

– Combination of groups

• Broadcast w/hold– Impact of egress point sparsity

• ALM– Apply ALM on a domain-wise level

– Fixed vs. dynamic groups


Future Research AreasFuture Research Areas

• Inter-domain peering– Transparent bandwidth conservation

• Packet caching and stealth multicast• Edge routers of domains exchange info

– Stealth multicast• Avoid conversion to/from multicast/unicast• Construct tree for new domain

– Packet caching• Share cache in other domains

– Issues• Billing, QoS• Resource management• Protocol / security


Future Research AreasFuture Research Areas

• Network stack modification– Present: Minimize overhead

• Avoid extra IP/TCP or IP/UDP headers

– Premise• Can we increase redundancy but increase overall

system performance?

– Enhance network stack• Add End of Data marker - TCP• Modify sendmail / Apache to use

– Issues• Benefit to the network• Downstream impact -> net system impact


ConclusionsConclusions

• Stealth multicast– New paradigm for multicast– Offers several key benefits

• Solves multicast deployment issue– Zero modification outside of the domain

• Inherent resource management• Offers directable economic benefit

– Interesting research problems• Transport, state management• Inter-domain peering, stack optimization


Questions?

[email protected]

http://www.cse.nd.edu/~striegel

GenMCast Package (ns-2)

http://www.cse.nd.edu/~striegel/GenMCast

mailto:[email protected]

mailto:[email protected]


Why Multicast?Why Multicast?

• Premise– Distribute same information to

large number of users– Simple solution

• Separate unicasts– Highly inefficient

• N users -> N transmissions

– Example:• ND Football Game - Streaming audio

– 5,000 listeners - 56k modem - 4kB/s– Total BW: 20 MB/s

• Videoconference - audio + video– 50 participants - 250 kB/sec– Total BW: 12.5 MB/s


MulticastMulticast

• Operation– Reduces packet transmission

to an efficient tree– Relies on network state for

replication

• Benefits– Reduced bandwidth

• N receivers << N bandwidth

– Bottleneck relief• Relief close to source

– Simplifies sender management• Send to group vs. individuals


Obstacles/IssuesObstacles/Issues

• Why is multicast being adopted so slowly?– Chicken or the egg?

• Development/deployment/demand circle

– Global efficiency• Efficiency - adoption - global scale

– Metcalfe’s Law - Network benefit

• Additional infrastructure

– Killer app• Does not offer a fundamentally new service• No killer app - 10x, 100x improvement

– Depends upon deployment to become a killer app

– ISP Economics


Multicast - ISP EconomicsMulticast - ISP Economics

• Questionable benefit– ISPs sell bandwidth– Multicast reduces bandwidth consumption– ISP perspective

• Pay significantly, sell less

• Billing– How to charge for multicast– How to get billing info

• Distributed state of multicast

• Other concerns– Internet growth myth - investment inertia– Problem can be solved by more bandwidth


DSMCast OperationDSMCast Operation

A B

C

D

E

NodeAB

ReplicateB

D,E


Other IssuesOther Issues

• IPSec– Problem

• Can’t see UDP header - encrypted

– Match checksum - OK

• IPv6– Two issues

• Security headers• Address size

– Force egress state


Other Research ProjectsOther Research Projects

• Grid computing - GRIM– Grid Resource Interface & Manager– Managing simulations

• Script generation, stat management, grid operation

• Scalable datacenters– Scale datacenter to 10-40 Gb/s+– Manage train wreck of devices

• FW, LB, IDS, etc.

• DiffServ Multicast– Heterogeneous receivers– Resource management

stealth multicast - a new paradigm for incremental multicast deployment

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