CS640 Introduction to Computer Networks Multicast

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CS640Introduction to Computer NetworksMulticast

• Nov 29th, 1999Prof. Lawrence H. LandweberProf.
  Jun Murai

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One to many communication

• IP multicast

• Application level one to many communication
• multiple unicasts

R
R
S
S
R
R
R
R
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Why Multicast

• When sending same data to multiple receivers
• better bandwidth utilization
• less host/router processing
• quicker participation
• Application
• Video/Audio broadcast (TV, radio type)
• Video conferencing
• Real time news distribution

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IP multicast service model

• RFC1112 Host Extensions for IP Multicasting
• Transmission of an IP datagram to a "host group",
  
• host group identified by a class D IP address
• Members of the group could be present anywhere in
  the Internet
• Members join and leave the group and indicate
  this to the routers
• Senders and receivers are distinct i.e., a
  sender need not be a member
• Routers listen to all multicast addresses and use
  multicast routing protocols to manage groups
  (IGMP, Internet Group Management Protocol,
  RFC2236)

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IP multicast group address

• Class D address space
• high-order three 3bits are set
• 224.0.0.0 239.255.255.255
• Well-known address designated by IANA
• RFC1700
• 224.0.0.0 224.0.0.25
• 224.0.0.1 (ALL-SYSTEMS.MCAST.NET)
• all multicast hosts on the subnet
• 224.0.0.2 (ALL-ROUTERS.MCAST.NET)
• all multicast routers on the subnet

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IGMP Joining a group

• Example R joins to Group 224.2.0.1
• R sends IGMP Membership-Reportto 224.2.0.1
• DR receives it. DR will start forwarding packets
  for 224.2.0.1 to Network A
• DR periodically sends IGMP Membership-Query to
  224.0.0.1 (ALL-SYSTEMS.MCAST.NET)
• R answers IGMP Membership-Report to 224.2.0.1

IGMP Membership-Report
R
Network A
DR
Data to 224.2.0.1
Network B
R ReceiverDR Designated Router
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IGMP Leaving a group

• Example R leaves from a Group 224.2.0.1
• R sends IGMP Leave-Group to 224.0.0.2
  (ALL-ROUTERS.MCAST.NET)
• DR receives it.
• DR stops forwarding packets for 224.2.0.1 to
  Network A if no more 224.2.0.1 group members on
  Network A.

IGMP Leave-Group
R
Network A
DR
Data to 224.2.0.1
Network B
R ReceiverDR Designated Router
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Challenges in this model

• How to select receivers by a sender ?
• need authentication, authorization
• encryption of data
• key distribution
• still under research phase

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IP multicast routing

• Purpose share a Group information among routers,
  to implement a better routing for data
  distribution
• Distribution tree structure
• Source tree vs shared tree
• Data distribution policy
• ACK type vs NACK type

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Source distribution tree
S
Source
Notation (S, G) S Source G Group
E
C
R
R
Receiver 1
Receiver 2
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Shared distribution tree
S1
Source
Notation (, G) all sources G
Group
Shared Root
S2
E
C
R
R
Receiver 1
Receiver 2
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Source tree characteristics

• Source tree
• More memory O (G x S ) in routers
• optimal path from source to receiver, minimizes
  delay
• good for
• small number of senders, many receivers such as
  Radio broadcasting application

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Shared tree characteristics

• Shared tree
• less memory O (G) in routers
• Sub-optimal path from source to receiver, may
  introduce extra delay (source to root)
• May have duplicate data transfer (possible
  duplication of a path from source to root and a
  path from root to receivers)
• good for
• Many senders with low bandwidth
• environment such as most part of the shared tree
  is identical to the source tree

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Data distribution policy

• NACK type
• Start with broadcasting then prune brunches
  with no receivers, to create a distribution tree
• a lot of un-used traffic when small receivers in
  wide area
• ACK type
• forward only to the hosts which explicitly joined
  to the group
• latency by join propagation and high costs when
  many receivers

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Protocol types

• Dense mode protocols
• assumes dense group membership
• Source distribution tree and NACK type
• DVMRP (Distance Vector Multicast Routing
  Protocol)
• PIM-DM (Protocol Independent Multicast, Dense
  Mode)
• Sparse mode protocol
• assumes sparse group membership
• Shared distribution tree and ACK type
• PIM-SM (Protocol Independent Multicast, Sparse
  Mode)
• CBT

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DVMRPexchange distance vector

• Maintain multicast routing table by exchanging
  distance vector information among routers
• consistent view of a tree among all routers
• convenient to have separate paths for unicast
  versus multicast datagrams( ie tunnelings)
• Dependent routers information
• information about responsible downstream routers
  for a source
• A downstream router send poison Reverse to a
  selected upstream router to indicate the
  dependency.
• Poison Reverse metric 32 (inf)
• entry will be removed from the list by prune
  message
• Designated Forwarder
• multiple routers on the same LAN
• lower metric or lower IP address becomes the
  designated forwarder (discover when exchanging
  metric info.)

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DVMRPbroadcast prune

• Forward multicast packets based on RPF (Reverse
  path forwarding) rule
• leaf routers check and sends prune message to
  upstream router when no group member on the
  network
• upstream router prune the interface with no
  dependent downstream router.
• Graft message to create a new branch for late
  participants
• Restart forwarding after prune lifetime (standard
  720 minutes)
• draft-ietf-idmr-dvmrp-v3-09.txt (September 1999)

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RPF(reverse path forwarding)

• RPF check
• A packet received through interface I, from S
  (source) to G (multicast group) packet (S,G)
• A router looks into the routing table to find an
  interface used to send packet to S, I(parent).
• If I ! I (parent), I is a wrong interface to
  receive (S,G).
• if I I(parent), I is a correct interface to
  receive (S, G).
• If the RPF check succeeds, the datagram is
  forwarded to all interfaces except I.
• If the RPF check fails, the datagram is typically
  silently discarded
• Packet is never forwarded back out the RPF
  interface!

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DVMRP (1) form a source tree by exchanging metric
source tree
S
Source
DF
R1
Receiver 1
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DVMRP (2) broadcast
source tree
S
datagram
Source
DF
R1
Receiver 1
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DVMRP (3) prune
source tree
S
datagram
Source
IGMP DVMRP-Prune
DF
R1
Receiver 1
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DVMRP (4) X and Y pruned
source tree
S
datagram
Source
DF
X
Y
R1
Receiver 1
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DVMRP (4) New member
source tree
S
datagram
Source
IGMP DVMRP-Graft
DF
X
Y
R1
R2
Receiver 1
Receiver 2
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DVMRP (4) New branch
source tree
S
datagram
Source
IGMP DVMRP-Graft
DF
X
Y
R1
R2
Receiver 1
Receiver 2
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PIM

• PIM Protocol Independent Multicast
• independent of particular unicast routing
  protocol
• Pros simple, less overhead
• Cons may cause more broadcast-and-prunes
• All routers in a domain support PIM
• No multicast tunnel
• PIM v2 is assigned new protocol 103

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PIM DM overview(1)

• Broadcast and prune ideal for dense group
• Source tree created on demand based on RPF rule
• If the source goes inactive, the tree is torn
  down
• Easy plug-and-play
• Branches that dont want data are pruned

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PIM DM overview(2)

• Grafts used to join existing source tree
• Uses Asserts to determine the forwarder for
  multi-access LAN
• Prunes on non-RPF P2P links
• Rate-limited prunes on RPF P2P links

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PIM DM Forwarding

• PIM DM interfaces are placed on the oilist for
  a multicast group if
• PIM neighbor heard on interface
• Host on this interface has just joined the group
• Interface has been manually configured to join
  group
• Packets are flooded out all interfaces in
  oilist
• If a PIM neighbor is present, DM assumes EVERYONE
  wants to receive the group so it gets flooded to
  that link by definition

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PIM Assert Mechanism

• Routers receive packet on an interface in their
  oilist
• Only one router should continue sending to avid
  duplicate packets.
• Routers sends PIM assert messages
• Compare distance and metric values
• Router with best route to source wins
• If metric distance equal, highest IP addr wins
• Losing router stops sending (prunes interface)

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PIM DM State Maintenace

• State is maintained by the flood and prune
  behavior of Dense mode.
• Received Multicast packets reset(S,G) entry
  expiration timers.
• When (S,G) entry expiration timers count down
  to zero, the entry is deleted.
• Interface prune state timers out every 210
  seconds causing periodic reflooding and pruning

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PIM-DM(1)Initial flood of data
S
Source
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
Receiver 2
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PIM-DM(2)prune non-RPF p2p link
S
IGMP PIM-Prune
Source
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
Receiver 2
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PIM-DM(3) C and D Assert to DetermineForwarder
for the LAN, C Wins
S
IGMP PIM-Assertwith its own IP address
Source
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
Receiver 2
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PIM-DM(4)I, E, G send PruneH send Join to
override Gs Prune
S
IGMP PIM-Prune
Source
IGMP PIM-Join
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
Receiver 2
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PIM-DM(5)I Gets PrunedEs Prune is IgnoredGs
Prune is Overridden
S
Source
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
Receiver 2
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PIM-DM(6)New Receiver, I send Graft
S
IGMP PIM-Graft
Source
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
R3
Receiver 2
Receiver 3
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PIM-DM(6)new branch
S
IGMP PIM-Graft
Source
A
B
G
F
C
D
H
I
E
R1
R2
Receiver 1
R3
Receiver 2
Receiver 3
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PIM-SM overview (1)

• Shared Tree for a group with RP (Rendez-Vous
  Point) as a root
• Explicit Join Model
• Receivers send Join towards the RP
• Sender Register with RP
• Last hop routers can join source tree if the data
  rate warrants by sending joins to the source
• RPF check depends on tree type
• For shared trees, uses RP address
• For source tress, uses Source address

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PIM-SM overview(2)

• Only one RP is chosen for a particular group
• RP statically configured or dynamically learned
  (Auto-RP, PIM v2 candidate RP advertisements)
• Data forwarded based on the source state (S, G)
  if it exists, otherwise use the shared state (,
  G)
• RFC2362 PIM Sparse Mode Protocol Spec
  (experimental)
• Internet Draft draft-ietf-pim-v2-sm-00.txt
  (October 1999)

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PIM-SM Basics

• PIM Neighbor Discovery
• PIM SM Forwarding
• PIM SM Joining
• PIM SM REgistering
• PIM SM SPT-Swichover
• PIM SM Pruning
• PIM SM Bootstrap
• PIM SM State Maintenance

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PIM Neighbor Discovery

• PIM Hellos are multicast to the All-PIM-Routers
  (224.0.0.13, ff02d) multicast group address
  periodically
• Highest IP address elected as DR (Designated
  Router)
• If DR times-out, a new DR is elected

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PIM SM Bootstrap

• A set of routers are configured as candidate
  Bootstrap Router(BSR)s
• single BSR is selectd for the domain
• Candidate RPs periodically unicast
  Candidate-RP-Advertisement messages (C-RP-Advs)
  to BSR
• The BSR periodically sends Bootstrap messages
  containing the set of Candidate-RPs
• Bootstrap message are flooded in the domain
• Routers receive and store Bootstrap messages
  originated by the BSR.

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PIM SM State Maintenance

• Periodic Join/Prunes are sent to all PIM
  neighbors
• Periodic Joins refresh interfaces in a PIM
  neighbors oilists
• Periodic Prunes refresh prune state in a PIM
  neighbor
• Received Multicast packets reset(S,G) entry
  expiration timers.

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PIM-SM(1)
S
Source
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(2)
S
Receiver 1 Joins Group GC Creates (, G) State,
Sends(, G) Join to the RP
Source
A
B
RP
D
Join
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(3)
S
RP Creates (, G) State
Source
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(4)
S
Source Sends DataA Sends Registers to the RP
Source
Register
Data
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
48
PIM-SM(5)
S
RP de-encapsulates RegistersForwards Data Down
the Shared TreeSends Joins Towards the Source
Source
join
join
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
49
PIM-SM(6)
S
RP Sends Register-Stop OnceData Arrives Natively
Source
Register-Stop
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(7)SPT Switchover
S
C Sends (S, G) Joins to Join theShortest Path
(SPT) Tree
Source
A
B
RP
D
join
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(8)
S
C starts receiving Data natively
Source
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(9)
S
C Sends Prunes Up the RP tree forthe Source. RP
Deletes (S, G) OIF andSends Prune Towards the
Source
Source
Prune
Prune
A
B
RP
D
Prune
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(10)
S
B, RP pruned
Source
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
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PIM-SM(11)
S
Source
New receiver2 joinsE Creates State and Sends (,
G) Join
A
B
RP
D
C
E
join
R2
R1
Receiver 1
Receiver 2
55
PIM-SM(12)
S
Source
C Adds Link Towards E to the OIFList of Both (,
G) and (S, G)Data from Source Arrives at E
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
56
PIM-SM(13)
S
Source
C Adds Link Towards E to the OIFList of Both (,
G) and (S, G)Data from Source Arrives at E
A
B
RP
D
C
E
R2
R1
Receiver 1
Receiver 2
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Inter-Domain Multicast Routing

• BGP4 (Multicast BGP) for short-term solution
• MASC Multicast Address Set and Claim
• BGMP Border Gateway Multicast Protocol

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MASC

• Hierarchical multicast address allocation
• dynamic allocation (lease) by set and claim with
  collision

domain A
domain E
domain B
domain C
domain D
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MASC

• Assume Addr(A) is allocated to domain A, A notify
  to B C and E.
• B selects Addr(B) , subset of Addr(A) and send
  Claim (addr(B)) message to A and C
• A forward it to all children except B.
• If As children is already using Addr(B), report
  collision to A.
• A notify the collision to B to select other
  address space.
• B wait for a certain period before using it.
• Address space information is used to create
  distribution tree using BGMP.
• Stored in M-RIB (Multicast Routing Information
  Base)

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BGMP

• Use a PIM-like protocol between domains (BGP for
  multicast)
• BGMP builds shared tree of domains for a group
• So we can use a rendezvous mechanism at the
  domain level
• Shared tree is bidirectional
• Root of shared tree of domains is at root domain
• Runs in routers that border a multicast routing
  domain
• Runs over TCP like BGP
• Joins and prunes travel across domains
• Can build unidirectional source trees
• M-IGP(multicast Intra-Gateway Protocol) tells the
  borders about group membership

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BGMPA host in C joins to Group G
DomainE
DomainD
E1
D1
A1
A4
DomainA
join
A3
M-IGP
Root domain
A2
DomainB
join
B1
B2
M-IGP
join
C1
DomainC
DomainF
F2
F1
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BGMPTree constructed, data goes to C
DomainE
DomainD
E1
D1
A1
A4
DomainA
A3
Root domain
A2
DomainB
B1
B2
C1
DomainC
DomainF
F2
F1
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BGMPDomain E joins to G
DomainE
DomainD
E1
join
D1
A1
A4
DomainA
join
A3
A2
DomainB
B1
B2
C1
DomainC
DomainF
F2
F1
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BGMPtree constructed. Data goes to E
DomainE
DomainD
E1
D1
A1
A4
DomainA
A3
A2
DomainB
B1
B2
C1
DomainC
DomainF
F2
F1
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Multicast Routers

• mrouted (Xerox PARC) DVMRP
• GateD (Merit) DVMRP, PIM-DM, PIM-SM
• Cisco IOS DVMRP, PIM-DM, PIM-SM

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M-Bone

• Wide area IP multicast test bed using IP-in-IP
  tunneling technology
• Routing protocol
• DVMRP is used
• Transition to PIM (DM, SM) is ongoing
• Started in March 1992 for audio broadcasting of
  IETF meeting (San Diego)
• Latest tolopology
• ftp//ftp.parcftp.xerox.com/pub/net-research/mbone
  /maps/mbone-map-big.ps
• About 6000 (S,G) entries
• Discussion in by mbone_at_isi.edu

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M-BONE in 1994
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M-BONE in 1996
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M-BONE in 1998
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Future Mulicast Service

• Current multicast service - latency and packet
  drop
• Research for Reliable multicast is actively
  going on for
• large scale interactive game on the Internet
• Distributed database
• large scale news distribution etc.

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Reliable multicast technology

• SRM ( scalable Reliable Multicast)
• multicast with re-transmit (with random back-off)
• All nodes can re-transmit datagram
  (Multicast/Unicast)
• MTP (Multicast Transport Protocol RFC1301)
• FEC (Forward Error Correction)
• error packet recovery by redundant packets

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IPv6 Multicast Test10sites in Japan PIM-SM over
IPv6 (KAME)Digital Video streaming
Nov 27th, 1999
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