Aucun titre de diapositive

1
Overview of Multicast Architectures Future
directions
Laurentiu Barza
25/11/1999
2
Definition of multicast
Multicast is the act of sending a message to
multiple receivers using a single local
transmit operation
3
The place of multicast among the data
distribution mechanisms
Unicast
Broadcast
Multicast
Send to one
Send to All
Send to some
4
Multicast routing problem
Problem Given a source and a set of
destinations, Route same packet to at least (or
exactly) this set of destinations
5
Internet multicast routing
Group membership IGMP Route etablishment DVMR
P, MOSPF, PIM, CBT Group addresing MADCAP /
AAP / MASC, GLOP Inter-domain routing BGMP,
Express, RAMA


6
Internet Group Membership Protocol
It is used by end-system to declare membership in
particular multicast group to nearest
router(s) IGMPv1 Timed-out Leave IGMPv2 Fast
(Explicit Leave) IGMPv3 Per-Source Join
7
Multicast routing protocols
Source - based Tree Protocols - DVMRP -
MOSPF - PIM-DM Shared -Tree Protocols -
CBT - PIM-SM
8
Source based tree
9
Dense mode multicast routing protocols
Dense mode protocols assume that almost all the
hosts in a domain wants to participate in the
multicast group. They are  flood and prune 
protocols - data from the sender  floods 
across the network from a sender to all possible
receivers - subnets with no receivers then send
a prune message upstream to prevent unnecessary
traffic arriving Thus all routers that are not
on the delivery tree need to hold prune state
to prevent the traffic from flowing where is not
wanted.
10
Shared tree
core

11
Sparse mode PIM

• Instead of flooding and pruning to directly build
  a shortest path
• tree, Sparse-mode PIM initially builds a shared
  tree.
• The shared tree is build by sending join messages
  towards a
• Rendezvous Point (RP).
• Once data is flowing, the shared tree can be
  converted to a
• shortest path tree if required.

12
Problems of Shared-tree based protocols (PIM-SM)
Finding the rendezvous point - by router
configuration - using a  bootstrap
mechanism  hashing into a set of candidate
RPs The number of RPs scales linearly with the
size of domain, so PIM cannot scale
globally. Traffic concentration in core
routers. Single points of failure. Deployment
problem ISP doesn t want to depend on an RP in
another ISP for multicast service between its
own customers.
13
 Glop bits  for Static Address Allocation
Addresses 233.0.0.0 to 233.255.255.255 have been
asigned for static allocation. Every domain
gets 256 addresses for their own use allocated
by embedding the Autonomous System number
as the middle 16 bits of the multicast
architecture. Static allocation of entre space
would result in poor utilization and ineffective
reuse of addresses as it has with IPv4 unicast
addresses. However, allocating a subset of
addresses this way solves the current problem.
14
Dynamic Address Allocation

• There exist an hierarchical address allocation
  scheme
• inter-domain MASC
• allocate ranges of addresses to domain
• intra-domain AAP
• allocate individual addresses from ranges
• client-server MADCAP
• simple request/response protocol

15
Multicast Source Discovery Protocol - MSDP
RP2
RP1
MSDP
R1
R2
S
R3
R4
domain2
domain1
MSDP is a glue between RPs from different domains.
16
The immediate future

• PIM-SM / MSDP become widesperad
• Some ISP restrict who can send, from security
  considerations
• ( until it will appear IGMPv3)
• GLOP for static allocation

17
Inter-domain multicast routing

• In the near term, we wont have a true
  inter-domain multicast
• routing protocol to be deployed.
• We we do get one deployed, what will it look like
  ?
• Three proposals
• BGMP GRIB
• Express
• Root-addressed Multicast (or Simple Multicast)

18
BGMP

• A protocol for inter-domain multicast routing
• Partition Class D address space
• Default Bidirectional Shared Tree for
  inter-domain routing
• Receiver domains can utilize choice of protocol
• Discussed in the IETF idmr wg

19
Express

• Express is a one-to-many multicast architecture.
• A source must join a channel (i.e. source
  addressgroup address)
• to receive data from the source.
• Address allocation is local to a source, there
  is no need of
• complicated protocols.
• Deployment is very easy (IGMPv3PIM-SM), and
  there are
• big-money customers interested in for such
  service.
• Receivers must find out who the sources are
  through some other
• mechanism (doesn t solve the binding/rendezvous
  problem).

20
Simple Multicast / RAMA

• RAMA is a multicast architecture similar to CBT,
  where to
• address a group we use a pair ( core address,
  group address ).
• Address allocation is local to a core.
• Receivers must find out the core address through
  whatever mecanism
• they use to find the group address.
• Hosts need changing to allow them to inform their
  local routers what
• the core address is.

21
Problems in deploying current architecture

• The current architecture lacks simple and
  scalable mechanisms for supporting
• Acces controls. Including group creation and
  membership.
• Security. For protection against attacks to the
  routing and data integrity of multicast
  datagrams.
• Address allocation.
• Network management. Such tools are not developed
  at this stage.

22
Requirements in deploying of multicast
ISP requirements - easy to deploy, -
control and manage, - to scale well with the
growing Internet ISP customers expect - to be
the sole owners of multicast address (even
temporary), - to have security guarantees, -
to be able to correct network problems quickly
23
(No Transcript)