Mobile Group Communication
Mobility & Multicast Status
The Multicast Mobility Problem
Listener Mobility
ASM Source Mobility
Where are we going Mobile today?
We need Multicast Services for …
Public Content Broadcasting*
Voice and Video Conferencing*
Collaborative Environments*
Massive Multiplayer Gaming*
Self Organisation of Distributed Systems
Synchronisation of Distributed Data*
…
* under some real-time constraints
Multicast Interactive
Peer-to-Multipeer Communication
Serverless
Lightweight, Little Load on End-System
Mobile Members are
Listeners & Senders
Moviecast:
Mobile Video Multicast
Status: Where are we today?
o Internet Mobility
- Mobile IPv6 - RFC 3775 (June 2004, implemented)
o Real-Time Mobility
- FMIPv6, HMIPv6 – RFCs 4068, 4140 (August 2005, first implementations)
o Multicast Mobility
- Rough ideas in IETF … - Some proposals in IRTF
- IRTF Problem statement the only WG document
o NGNs: IPTV, DVB-H IPDC distribution services …
Multicast:
What is the Problem?
o There is Any Source Multicast:
- General Host-Group Model:
Listeners harvest streams from any source - Sparse & dense mode routing
- Complex to deploy, Interdomain problem
o There is Source Specific Multicast:
- Specialised Host-Group-Source Model:
The Key Problems
Provide Seamless Multicast Services to and from MNs
Approach native multicast forwarding in an infrastructure-compliant manner
At Listeners:
Ensure multicast reception in visited networks
Organize context transfer between mcast-enabled access networks
Expedite multicast forwarding on handovers
At Sources:
Sustain address transparency at end nodes (address duality problem)
Ensure persistence of receiver contact (decoupling problem)
Bridge tardy tree reconstruction/transformation procedures
At SSM Sources:
Manage address transparency at routers (source filtering)
Comply to source-specific security constraints
Focus on deployable solutions, minimize protocol extensions
Multicast Receiver Mobility
o Multicast Routing is ‘Mobile’ :
- On handover listeners may re-subscribe to multicast group (ASM & SSM)
- Routing will construct delivery branch
o Problem: Multicast routing not seamless, but slow
- Branch construction up to 30 s
Multicast Mobility Approaches
o Remote Subscription
- Show all movement by local multicast subscription
o Bi-directional Tunneling
- Hide all movement by tunneling via Home Agent
o Agent Based
- Compromise: Intermediate agents shield Mobile - Approaches: Extend unicast acceleration schemes
M-FMIPv6, M-HMIPv6, …
Fast Multicast Protocol for MIPv6
draft-suh-mipshop-fmcast-mip6-00
Remote subscription with agent support
Mobile multicast reception only
Built on Fast Handovers for MIPv6 (FMIPv6)
Predictive handovers based on L2 : L3 map
Handled at access routers
Extends signalling of FMIPv6 by multicast address
option
M-FMIPv6: Prediction
M-FMIPv6: Forwarding
M-FMIPv6: Handover
M-FMIPv6: Completion
Seamless Multicast Handover in a HMIPv6 Environment
draft-schmidt-waehlisch-mhmipv6-04
Agent based: MAP as Multicast agent
Mobile multicast reception and source
Built on Hierarchical MIPv6 (HMIPv6)
For mobile listeners:
Micro mobile handovers hidden by MAP
Reactive handovers between MAPs
Unicast (tunnel) forwarding MN : MAP
Change to remote subscription with MAP attendance
Extends signalling of HMIPv6 by multicast advertisement flag
M-HMIPv6: Multicast Listener
M-HMIPv6: MAP-Local Handover
M-HMIPv6: Inter-MAP Handover
M-HMIPv6: Completion
Multicast Source Mobility:
ASM Problems
o Distribution Tree (somehow) rooted at source:
- Collapses after movement
- Reconstruction very slow (up to minutes) - RPs may facilitate mobility
o Address Duality Problem:
- Logical ID: HoA at socket layer
- Topological ID: CoA at routing layer (RPF checks)
o Source Activation Problem:
Multicast Source Mobility Approaches
o Remote Subscription
- Show all movement by local multicast subscription
o Bi-directional Tunneling
- Hide all movement by tunneling via Home Agent
o Agent Based
- Use current Care-of-Address for Routing
- Use Home-Address in Destination Option at Receiver
- Use PIM RP as Mobility Anchor
Approach to Shared Tree Mobility
Use Rendezvous Point as Mobility Anchor:
Mobility-aware Rendezvous Point (MRP)
Need to Change Routing:
Extend (*,G) states to (HoA, G, MRP-ID)
Modify RPF-Check to identify CoA* sources with HoA
Operate interdomain handovers via MRP-ID
Mobility-aware Rendezvous Points
Multicast Source Mobility:
SSM ++Problems
SSM requires Source Filters:
o Receivers need to Subscribe to Source Addresses:
- HoA & current CoA needed at Receiver - Receivers need to re-subscribe to nCoA
o Routers Maintain Source Specific States:
- HoA & current CoA semantics at Routers
o Decoupling: Source cannot Control Receiver Initiated
Updates:
Multicast Source Mobility Approaches
o Remote Subscription
- Show all movement by local multicast subscription
o Bi-directional Tunneling
- Hide all movement by tunneling via Home Agent
o Agent Based
- Use current Care-of-Address for Routing
- Use Home-Addres in Destination Option at Receiver
- “Tree Walking”
Bi-Directional Tunneling
Simulation: BT in ATT Network
Internet with 154 Core Nodes
Internet with 1.540 Core Nodes
Internet with 15.400 Core Nodes
What to do with Mobile SSM ?
Need to Change Routing:
Logical (HoA) and topological (CoA) identifier needed at client and routing layer
Need to keep contact to clients after handover :
Some mobility persistent entities?
Current Ideas:
Re-introduce shared trees
Re-use trees
What effect does mobility impose on SPTs?
Analysis of ‘Moving’ Distribution Trees
Multicast Distribution Trees subsequent under Mobility are highly correlated
Previous and Next Tree overlap from receivers downward
Coinciding subtrees: self-similar URT
Results in frequent re-use of Mcast Router States
Two characteristic measures
‘Step-Size’: pDR-to-nDR Distance
Tree evolvement: Number of Receivers
Evolution of Distribution Trees
Receiver Networks
Persistent Subtrees
• Self-similar subsets
• Identical stochastic
properties
Simulation Study:
Tree Coincidence wrt. pDR-nDR Distance
≈ 80 % Coincidence for 40 Receivers and
a mobility ‘step-size’ of 5
Simulation Study:
Tree Coincidence wrt. Tree Evolvement
> 80 % Coincidence for a mobility
‘step-size’ of 5 and
100 Receivers
Source Specific Tree Modification
Need to Change Routing (Source Filters):
Extend (CoA,G) states to (CoA,HoA,G)
Need to Preserve Previous Trees:
Keep contact subsequent to handover
Idea: Morph Previous into Next Tree:
Elongate root (modify RPF Check)
Discover shortcuts
Tree Morphing
Root Elongation Phase
First Shortcut
Optimized Tree
Performance Snapshot
Security Issues
Binding Caches:
Multicast updates may hijack unicast sessions
HoA spoofing (on application layer)
SSM:
Source address (HoA ↔ CoA) correctness assumed by clients at subscription events
Reliability needed in equivalence to unicast case
Hybrid Approaches
Motivation: Bridge Interdomain Deployment Gap
Establish Multicast Gateways or Peers
Within End System Domain (Buford)
At Access Routers (Almeroth)
Transfer to Overlay Multicast
Tunnelling: AMT
Explicit: XCAST
DHT-based Overlays
Mobility: Establish a Homogeneous
Mobility-agnostic DHT Overlay (® Wählisch)
