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Stealth Multicast - A New Paradigm for Incremental Multicast Deployment. Dr. Aaron Striegel Dept. of Computer Science & Engineering University of Notre Dame. Talk Overview. Information Dissemination Motivation Stealth Multicast Basic Architecture Recent work: Dynamic groups

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stealth multicast a new paradigm for incremental multicast deployment

Stealth Multicast - A New Paradigm for Incremental Multicast Deployment

Dr. Aaron Striegel

Dept. of Computer Science & Engineering

University of Notre Dame

talk overview
Talk Overview
  • Information Dissemination
  • Motivation
  • Stealth Multicast
    • Basic Architecture
    • Recent work: Dynamic groups
    • Preliminary Results
  • Future Research
    • Inter-domain Peering
    • Network stack enhancement
information dissemination
Information 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
multicast
Multicast
  • Operation
    • Reduces packet transmissionto an efficient tree
    • Relies on network state forreplication
  • Benefits
    • Reduced bandwidth
      • N receivers << N bandwidth
    • Bottleneck relief
      • Relief close to source
    • Simplifies sender management
      • Send to group vs. individuals
caching vs multicast
Caching 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 state
Current 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…”
motivation
Motivation
  • 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 multicast
Stealth 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 applicationunusable versus separate unicasts
stealth multicast model
Stealth Multicast Model

Conversion

Other Domains

Servers

ISP Domain

Clients

Company LAN

(Content Provider)

Unicast

Multicast

Unicast

multicast detection
Multicast Detection

VGDM - Virtual Group Detection Manager

Virtual

Group

Mgr

Disp

Checksum

Calculation

Tree

Construction

H

State

Management

Rules

Filter

Edge Router

Incoming Traffic

(Unicast only)

Outgoing Traffic

(Unicast+Multicast)

further examination
Further 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

Benefit

Delay

Virtual Group Delay

Minimum gain

Maximum delay

talk overview1
Talk Overview
  • Information Dissemination
  • Motivation
  • Stealth Multicast
    • Basic Architecture
    • Recent work: Dynamic groups
    • Preliminary Results
  • Future Research
    • Inter-domain Peering
    • Network stack enhancement
dynamic trees
Dynamic Trees
  • Implementation of stealth multicast
    • Dynamically grow/shrink physical multicast groups
      • Virtual group - snapshot at current time
      • Physical group - superset of potential clients
    • Defines key issues of stealth multicast
      • Triggers- Virtual group release
      • Transport - Dynamic groups
      • State management - Where to place state
virtual group triggers
Virtual 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

Target packet

MHT

TSW

PSW

time

triggers continued
Triggers - Continued
  • Triggers/thresholds
    • MinGS - Minimum group size
    • MaxGS - Maximum group size
    • MVG - Maximum virtual groups

New group

Multicast

Unicast

VG 0

..

MVG

MaxGS

MinGS

VG N

system balance
System 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
scalability storage
Scalability & Storage
  • Examine worst case constraints
    • Worst case delay is MHT
      • 10% of an RTT of 50 ms
      • 5 ms MHT
      • Actual delay is MHT / 2
    • Worst case storage
      • PSW and TSW yield MHT, no matches
      • 1 Gb/s link, 1000 byte group overhead
        • 1 Gb/s @ 8 bit/byte * 5 ms = 625 kB
        • 625 kB/sec / 64 bytes = 9765 packets
        • 625 kB + 9765 * 1000 = ~ 11 MB
multicast transport
Multicast Transport
  • Issue
    • Members (clients) not known a priori
    • Dynamically construct tree
  • Approaches
    • Exhaustive tree construction
      • All variations, all egress points
    • Broadcast/hold
      • Costly - queuing at edge
    • Encapsulation-based
      • Embed tree inside the packet
    • Dynamic tree construction
      • Grow/shrink tree as necessary
state management
State 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
application assisted method
Application-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 ipv6
Other 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 studies
Simulation Studies
  • Simulation setup
    • Ns-2 simulator
      • Freely available simulator
    • GenMCast module for ns-2, GIPSE- 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 bw
Effect of Clients - Link BW

No savings, unicast

Higher up-link cost

effect of clients domain bw
Effect of clients - Domain BW

Increasing savings

vs. unicast

Trades B/W for

client B/W

effect of clients qos delay
Effect of Clients - QoS (Delay)

Limited impact

of queuing

other results
Other Results
  • Other aspect
    • Out of order delivery
      • VGDM Overload
  • Traffic aggregation
    • OS/app effect
      • Spacing between packets
  • Live traffic
    • Work in progress on prototype
talk overview2
Talk Overview
  • Information Dissemination
  • Motivation
  • Stealth Multicast
    • Basic Architecture
    • Dynamic Groups
    • Preliminary Results
  • Future Research
    • Inter-domain Peering
    • Network stack enhancement
immediate research areas
Immediate Research Areas
  • Practical transport
    • Encapsulation
    • Dynamic groups
    • 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 areas
Future 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 areas1
Future 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
conclusions
Conclusions
  • 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
slide37
Questions?

[email protected]

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

GenMCast Package (ns-2)

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

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