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Multicast for Video Streaming

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Small # of video streams of varying quality sent to different multicast groups ... Used to determine next hop for a host. Inter-Domain Routing Cont. ... – PowerPoint PPT presentation

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Title: Multicast for Video Streaming


1
Multicast for Video Streaming
  • EE290T Spring 2002
  • Puneet Mehra
  • pmehra_at_eecs.berkeley.edu

2
IP Multicast Overview
  • Semantics
  • 1 -gt Many or Many -gt Many
  • Approach
  • Build tree connecting source and receivers on
  • Current Infrastructure in Net 1
  • Group Addressing provides flexibility
  • Receivers/senders unaware of each other
  • Packets delivered throughout tree.
  • Dynamic changes to tree
  • New Receiver -gt graft path onto tree
  • Receiver leaving -gt pruning path from tree
  • Uses UDP so no reliability
  • Challenges
  • Efficient routing of data to receivers

3
Video Multicast Over Net1
  • Issues in Multicast over Best Effort
  • Fixed Frame Rate regardless of delay/jitter
  • Losses degradation, possibly ungraceful
  • Heterogeneity of receivers
  • Approaches to Multicast
  • QoS resource reservation for Multicast
  • Adaptive Rate Control
  • Techniques for Rate Adaptation
  • Single Stream Video Multicast
  • Replicated Stream Video Multicast
  • Layered Video Multicast

4
Single Stream Video Multicast
  • Only send 1 stream to all receivers.
  • Pros
  • Easy To Implement
  • Cons
  • Ignores Receiver Heterogeneity
  • Feedback Implosion
  • INRIA Video Conferencing System
  • Feedback Problem handled through probabilistic
    receiver response
  • Tradeoff granularity of control vs B/W efficiency

5
Efficiency Tradeoff in Single Stream Approach
6
Replicated-Stream Video Multicast
  • Destination Set Group (DSG)
  • Small of video streams of varying quality sent
    to different multicast groups
  • Intra-stream Rate control to adjust stream rate
    by receivers
  • Inter-stream protocol used by receivers to switch
    streams
  • Pros
  • deals with heterogeneity more fair
  • Scalable since receiver-driven
  • Cons Network carries redundant info

7
Layered Video Multicast
  • Receiver-Driven Layered Multicast (RLM)
  • Send different layers to multicast groups, and
    receiver subscribes as needed -gt scalable
    solution
  • Congestion -gt layer dropping
  • Spare B/W -gt layer adding
  • Receivers conduct group join experiments and
    share info with others.

8
Layered Video Multicast Cont.
  • Layered Video Multicast with Retrans. (LVMR)
  • Improve reception w/in a layer by retransmission
  • Deal w/ congestion using Hierarchical Rate
    Control
  • Hierarchical Rate Control (HRC)
  • Congestion info distributed at both
    sender/receivers
  • Intelligent partitioning of info -gt concurrent
    experiments w/ less overhead
  • Use hierarchy to only inform those who need to
    know about an experiment affected regions
  • Collaborative layer drop better approach to
    congestion

9
Error Control in Video Multicast
  • Pure FEC
  • ARQ From LVMR
  • Local Recovery - designated receivers at each
    level in tree help w/ rtx. of pkts -gt lower
    latency
  • Dont rtx packets past deadline
  • Receivers can trade reliability/latency by
    picking parent with desired attributes

10
Multicast Routing 2,3
  • Routing construct efficient tree from source to
    receivers
  • Theoretical Results 3
  • Steiner Tree minimize total cost of a multicast
    tree. NP-Complete. So use heuristics to provide a
    good approx. to Steiner Tree.
  • Constrained Steiner Tree impose b/w delay
    constraints on links to receivers. Also
    NP-Complete. So must use heuristics
  • All practical algorithms based on shortest path
    tree minimize sum of weights on links along
    each path from source to receiver

11
Intra-Domain Routing
  • Source-based Routing
  • Tree rooted at source
  • Dense-mode routing works best when topology
    densely populated with receivers
  • Core-based Approach
  • Select a Rendezvous Point (RP) to root the tree
  • Sparse Mode Routing More efficient than dense
    mode when few, wide-spread receivers

12
Dense Mode Protocols
  • Distance Vector Multicast Routing Protocol
  • Uses broadcast prune technique to build reverse
    shortest path trees (RSP)
  • Steps
  • Src bcasts pkt on Lan. Local router fwds pkt on
    all ifaces
  • If pkt received on RPF iface, then it is
    forwarded.
  • Leaf routers send prune toward src if no attached
    receivers
  • Prune message forwarded to source, and send own
    prune if receive prune message on all ifaces.
  • A lot of state info kept in ALL routers in net.
  • Multicast extensions to OSPF
  • Uses IGMP locally, then floods info along with
    link state to net.
  • PIM-DM
  • Less complex than DVMRP since no RPF check is
    done. More inefficient as a result

13
Tree Construction in DVMRP3
  • S Source. Black Circles Receivers
  • Periodically flood net w/ datagrams
  • Leaf routers send prune toward source if there
    are no group members on leaf subnet
  • Final Tree is shown in (d).

14
Core-Based Routing
  • General Approach
  • A core, or rendezvous point (RP) is configured
    for a multicast group
  • Info about the RP mapping from group to RP is
    discovered by routers using bootstrap protocol
    (also finds alternate RP in case of failure)
  • Receivers explicitly join tree -gt contact RP
  • Src sends data to RP which sends down tree
  • More efficient since state only kept in routers
    on path from src/receivers to RP.
  • Examples
  • CBT Core-Based Trees
  • PIM-SM Protocol Independent Multicast/Sparse
    Mode

15
Tree construction in CBT
  • The Join Process for a new node
  • Receiver Contacts Local Router
  • Router sends JOIN_REQUEST to the core router
  • When msg reaches on-tree router, a JOIN_ACK is
    sent back
  • every router receiving JOIN_ACK updates state
    information
  • Periodically send echo-request to parent router.
    If echo not received in time, then router sends
    quit-notification upstream and deletes state
    information.

16
Inter-Domain Routing
  • Probs w/ multicast described
  • Large flat topology -gt complexity and instability
    since no BGP-like protocol
  • No mechanism to build hierarchical mcast routing
  • Solution Immediate Future
  • Introduce Hierarchy multi-protocol extensions
    to BGP (MBGP)
  • Each router only knows topology of its own domain
    how to reach other domains
  • Used to determine next hop for a host

17
Inter-Domain Routing Cont.
  • What if you have a src in one domain receivers
    in others?
  • Multicast Source Discovery Protocol
  • When src registers w/ RP -gt a source active (SA)
    msg is sent to MSDP peers
  • Prevent loops w/ per-RPF flooding (ie if msg
    received on correct iface -gt flood)
  • If MSDP is aware of local group members (use
    IGMP), then it will send a join to the src

18
Long-Term Inter-Domain Proposals
  • Border Gateway Multicast Protocol
  • Bidirectional shared trees between domains with
    single root. Need strict allocation of addresses
    among domains.
  • Address Allocation Protocols
  • Multi Address Set Claim Helps allocate
    addresses dynamically across domains
  • GLOP a glop of addresses statically allocated
    among domains

19
Problems Deploying IP Multicast 4
  • Complexity
  • Cant put it in core routers
  • Hardware more difficult to manage (probs w/
    firewalls)
  • Makes old routers useless
  • disrupts ISP router migration model (routers
    generally migrate from core to edge)
  • Domain Independence
  • ISPs dont want to rely on remote RPs
  • Dont want to be RP for non-customers
  • Security anyone can send/listen
  • Address Allocation anyone can pick a class D
    addr.

20
References
  • 1 Video Multicast over the Internet. Xue Li
    et al. IEEE Network. 1999.
  • 2 The Evolution of Multicast From the MBone
    to Interdomain Multicast to Internet2
    Deployment. Kevin Almeroth. IEEE Network. 2000.
  • 3 Multicast Routing and Its QoS Extension
    Problems, Algorithms, and Protocols. Bin Wang
    and Jennifer C. Hou. IEEE Network. 2000.
  • 4 Deployment Issues for the IP Multicast
    Service and Architecture. Christophe Diot et Al.
    IEEE Network. 2000.
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