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Computer Networks (Graduate level). Lecture 11: Multicasting. University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani. Multicasting. IP Multicast IGMP Multicast routing Assigned reading [DC90] Multicast Routing in Datagram Internetworks and Extended LANs

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Computer networks graduate level

Computer Networks(Graduate level)

Lecture 11: Multicasting

University of Tehran

Dept. of EE and Computer Engineering

By:

Dr. Nasser Yazdani

Computer Network


Multicasting
Multicasting

  • IP Multicast

  • IGMP

  • Multicast routing

  • Assigned reading

    • [DC90] Multicast Routing in Datagram Internetworks and Extended LANs

    • Next Branch Multicast (NBM) routing protocol (2005)

    • Chapter 4, multicasting.

Computer Network


Outline
Outline

  • Multicasting Why?

  • Problems, initial solutions.

  • Multicast routing

  • Application level multicast.

Computer Network


Why multicast
Why Multicast?

  • Specify a set of receivers and only send the data to them.

  • Has a lot of applications:

    • Audio/video conferencing

    • Distance lectures

    • Internet TV

    • Stock quotes

    • and…

  • Can I just use broadcast?

Computer Network


Problems with broadcast
Problems with broadcast

  • Does not scale

    • Imagine trying to broadcast packets to everyone on Internet!

  • Wastes network resources

    • We are sending packets to people who will ignore them.

      We clearly need something different…

Computer Network


Unicast
Unicast

  • Use unicast?

    • One sender, N receivers

    • Sender sends N duplicated unicast packets, one to each receiver.

R1

S

T1

T3

T4

R2

T2

R4

R3

Example: Multicast to Ri

by using unicast

Computer Network


Problems
Problems?

  • Links carry multiple copies of the same packet.

  • The link closest to the source flooded with packets.

  • Server needs to know the list of receivers to send the packet to.

    • How to handle receivers joining and leaving?

      • How to define/manage groups?

    • Wastes bandwidth

    • Introduces complexity – now the source needs to handle receiver crashes, link failures, etc…

    • Source will be “flooded” with messages if a lot of receivers join at once.

      Ideas?

Computer Network


More problem

S

R1R2R3R4……..Rn

More problem

  • Imagine having an IP header of the form:

  • Any router along the way, forwards a packet if at least one of the destinations is downstream from it.

  • What if a group has 1000s of recipients?

  • Routers will spend more time doing forwarding lookup since they will need to search the forwarding table for each address.

source

destination

Computer Network


Ip multicast model
IP Multicast Model

  • Main idea  Multicast groups

  • Receivers can join or leave at any time.

  • Any host can send to any group at any time – open architecture

  • The routers duplicate the packets instead of the source.

  • Routers will need to:

    • Keep state of groups are there waiting packets from me?

    • Participate in IGMP*

    • Keep a separate routing table*

destination

S

Multicast Address

source

Computer Network


Division of responsibilities
Division of Responsibilities

  • Host’s responsibility to register interest with networks

    • IGMP

  • Network’s responsibility to deliver packets to host

    • Multicast routing protocol

  • Left unspecified:

    • Address assignment (random, MASC, etc.)

    • Application-to-group mapping (session directory, etc.)

Computer Network


Multicast efficient data distribution
Multicast = Efficient Data Distribution

Src

Src

Computer Network


Multicast address allocation
Multicast Address Allocation

  • Currently no standardized method for address allocation (even though an RFC exists about this)

  • There are a lot of proposed solutions to this

    • Try searching for Multicast Address Allocation on the net (MALLOC for short)

Computer Network


Logical naming
Logical Naming

  • Single name/address maps to logically related set of destinations

    • Destination set = multicast group

  • How to scale?

    • Single name/address independent of group growth or changes

Computer Network


Multicast groups
Multicast Groups

  • Members are the intended receivers

  • Senders may or may not be members

  • Hosts may belong to many groups

  • Hosts may send to many groups

  • Support dynamic creation of groups, dynamic membership, dynamic sources

Computer Network


Scope
Scope

  • Groups can have different scope

    • LAN (local scope)

    • Campus/admin scoping

    • TTL scoping

  • Concept of scope important to multipoint protocols and applications

Computer Network


Multicast scope control small ttls
Multicast Scope Control – Small TTLs

  • TTL expanding-ring search to reach or find a nearby subset of a group

s

1

2

3

Computer Network


Multicast scope control large ttls
Multicast Scope Control – Large TTLs

  • Administrative TTL Boundaries to keep multicast traffic within an administrative domain, e.g., for privacy or resource reasons

The rest of the Internet

TTL threshold set oninterfaces to these links,greater than the diameterof the admin. domain

An administrative domain

Computer Network


Multicast scope control
Multicast Scope Control

  • Administratively-Scoped Addresses (RFC 1112 )

    • Uses address range 239.0.0.0 — 239.255.255.255

    • Supports overlapping (not just nested) domains

The rest of the Internet

address boundary set oninterfaces to these links

An administrative domain

Computer Network


Multicast backbone mbone

R

R

R

H

R

R

H

Multicast Backbone (MBone)

  • An overlay network of IP multicast-capable routers

R

Host/router

H

MBone router

Physical link

Tunnel

Part of MBone

Computer Network


Mbone tunnels
MBone Tunnels

  • A method for sending multicast packets through multicast-ignorant routers

  • IP multicast packet is encapsulated in a unicast packet addressed to far end of tunnel:

  • Tunnel acts like a virtual point-to-point link

  • Each end of tunnel is manually configured with unicast address of the other end

IP header,

dest = unicast

IP header,

dest = multicast

Transport headerand data…

Computer Network


Link layer multicast on lans
Link Layer Multicast On LANs

  • Exploits the fact that LAN is a broadcast medium.

  • Ethernet multicast addresses:

    01:00:5e:00:00:00 – 01:00:5e:7f:ff:ff

  • How would an application join a group?

    • Just tell link layer not to discard packets targeted at the group of interest.

Computer Network


Internet multicast
Internet Multicast

  • Group D addresses are used for multicast:

    224.0.0.0 – 239.255.255.255

    • If you do an NSLOOKUP on these addresses you will see that they are registered as *.MCAST.NET

    • Set the highest 4 bits to 1110 use the remaining 28

    • Some well known addresses:

      • 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

  • Need a suite of protocols to take care of the various aspects of Multicast (membership management, routing, etc..)

Computer Network


Multicast addressing
Multicast Addressing

  • multicast address a set of Internet hosts comprising a multicast group.

  • Senders : Dest. Address = multicast address

  • IP multicast group Class D address

  • Class D address : 1110 + 28 bit multicast group ID  224.0.0.0 to 239.255.255.255

    0 1 2 3 ----------- 28 bits ----------

    1 1 1 0 Multicast Group ID

  • 224.0.0.0 is reserved.

  • 224.0.0.1 to 224.0.0.225  reserved for permanent assignments to various uses, including routing protocols and other protocols that require a well-known permanent address.

Computer Network


Multicast addressing1
Multicast Addressing

  • Some of the well-known groups include :

    “all systems on this subnet” 224.0.0.1

    “all routers on this subnet” 224.0.0.2

    “all DVMRP routers” 224.0.0.4

    “all OSPF routers” 224.0.0.5

    “all OSPF designated routers” 224.0.0.6

    “all RIP2 routers” 224.0.0.9

    “all PIM routers” 224.0.0.13

    “all CBT routers” 224.0.0.15

  • The remaining groups are either permanently assigned to various multicast applications or are available for dynamic assignment (239.0.0.0 to 239.255.255.255 for “Administratively scoped” applications)

Computer Network


Ip multicast protocol suite
IP Multicast Protocol Suite

  • A protocol that distributes membership information – IGMP

  • A protocol that performs the routing – DVMRP, PIM-SM, PIM-DM, etc…

  • Protocols that deal with address allocation, reliability, congestion

Computer Network


Ip multicast architecture
IP Multicast Architecture

Service model

Hosts

Host-to-router protocol(IGMP)

Routers

Multicast routing protocols(various)

Computer Network


Ip multicast service sending
IP Multicast Service — Sending

  • Uses normal IP-Send operation, with an IP multicast address specified as the destination

  • Must provide sending application a way to:

    • Specify outgoing network interface, if >1 available

    • Specify IP time-to-live (TTL) on outgoing packet

    • Enable/disable loop-back if the sending host is a member of the destination group on the outgoing interface

Computer Network


Ip multicast service receiving
IP Multicast Service — Receiving

  • Two new operations

    • Join-IP-Multicast-Group(group-address, interface)

    • Leave-IP-Multicast-Group(group-address, interface)

  • Receive multicast packets for joined groups via normal IP-Receive operation

Computer Network


Igmpv2
IGMPv2

  • Internet Group Management Protocol

    • RFC 2236

  • IGMP operates locally

    • between end hosts and their border router

    • The goal is allowing the border router to learn what groups are presented on the attached subnets.

IGMP

<G1, G2, G3>

Border Router

S

Ethernet/Lan

<G1>

A

C

R1

<G1, G2, G3>

<G1>

B

R2

<G1>

<G1, G3>

IGMP Example

Computer Network


Igmp protocol

MQ

MQ

router

LG:leave

MR:join

timeline

MR

MR

host

IGMP protocol

  • A soft-state protocol with 3 types of messages:

    • membership_query (MQ): sent by the router

      • Determines the set of joined multicast groups on the LAN

    • membership_report (MR): sent by the hosts

      • When a host joins a group or

      • When a host responds to a MQ

    • Leave_group (LG): sent by the hosts

      • When a host leaves a group

    • All of these messages are broadcasted over the LAN

Computer Network


Igmp protocol1
IGMP Protocol

  • Border router does not need to know which host(s) have joined a given multicast group.

    • Only one host needs to report

    • Why?

  • Potentially MR messages sent by the hosts could be problematic.

    • How?

    • Solution: Use feedback suppression

      • Each host waits randomly between 0 and max_resp_time

      • Send the report if no one else has sent in that period

  • Leave Group message (LG) optional…

    • Why?

Computer Network


Multicast routing
Multicast Routing

  • Basic objective – build distribution tree for multicast packets

  • Multicast service model makes it hard Why?

    • Anonymity

    • Dynamic join/leave

Computer Network


Routing techniques
Routing Techniques

  • Flood and prune

    • Begin by flooding traffic to entire network

    • Prune branches with no receivers

    • Examples: DVMRP, PIM-DM

    • Unwanted state where there are no receivers

  • Link-state multicast protocols

    • Routers advertise groups for which they have receivers to entire network

    • Compute trees on demand

    • Example: MOSPF

    • Unwanted state where there are no senders

Computer Network


Routing techniques1
Routing Techniques

  • Core based protocols

    • Specify “meeting place” aka core

    • Sources send initial packets to core

    • Receivers join group at core

    • Requires mapping between multicast group address and “meeting place”

    • Examples: CBT, PIM-SM

Computer Network


Shared vs source based trees
Shared vs. Source-based Trees

  • Source-based trees

    • Separate shortest path tree for each sender

    • DVMRP, MOSPF, PIM-DM, PIM-SM

  • Shared trees

    • Single tree shared by all members

    • Data flows on same tree regardless of sender

    • CBT, PIM-SM

Computer Network


Source based trees
Source-based Trees

Router

Source

S

Receiver

R

R

R

R

S

S

R

Computer Network


A shared tree
A Shared Tree

Router

Source

S

Receiver

R

R

R

RP

R

S

S

R

Computer Network


Shared vs source based trees1
Shared vs. Source-Based Trees

  • Source-based trees

    • Shortest path trees – low delay, better load distribution

    • More state at routers (per-source state)

    • Efficient for in dense-area multicast

  • Shared trees

    • Higher delay (bounded by factor of 2), traffic concentration

    • Choice of core affects efficiency

    • Per-group state at routers

    • Efficient for sparse-area multicast

Computer Network


Dvmrp
DVMRP

  • Builds a multicast routing table

    • By exchanging distance information amongst routers.

      • Gives consistent view of multicast tree among all routers

  • Stores ‘dependent routers’ info

  • If there are multiple routers on the same LAN lower IP address becomes the designated forwarder.

Computer Network


Dvmrp1
DVMRP

  • Multicast packets are forwarded based on Reverse Path Forwarding.

    • coming on the next slide!

  • Leaf routers check and send prune message when no group member on the network.

  • Upstream router prune the interface with no downstream router.

  • Graft message sent to create a new routing branch for late members.

  • Restart forwarding after a set prune lifetime (typical value 12 hours)

Computer Network


Reverse path forwarding rpf
Reverse Path Forwarding (RPF)

  • Procedure:

    • A packet is 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 procedure succeeds, the datagram is forwarded to all interfaces except I

  • Otherwise, typically it is silently discarded.

  • Packet is never forwarded back out I.

Computer Network


Reverse path flooding rpf
Reverse Path Flooding (RPF)

  • A router forwards a broadcast packet originating at source S if and only if it arrives via the shortest path from the router back to S (i.e., the “reverse path”). Otherwise the packet will be discarded

  • The router forwards the packet out all incident links except the one on which the packet arrived.

  • Disadvantage :

  • Any single broadcast packet may be transmitted more than once across any link, up to the number of routers that share the link.

Computer Network


Reverse path flooding rpf1

Multicast Packet from

Source 151.10.3.21

X

Packet Arrived on Wrong Interface!

Discard Packet!

Reverse Path Flooding (RPF)

A closer look:RPF Check Fails

S0

RPF Check Fails!

S1

S2

Unicast Route Table

Network Interface

151.10.0.0/16 S1

198.14.32.0/24 S0

204.1.16.0/24 E0

E0

S1

Computer Network


Reverse path flooding rpf2

Multicast Packet from

Source 151.10.3.21

Packet Arrived on Correct Interface!

Reverse Path Flooding (RPF)

A closer look:RPF Check Succeeds

S0

S1

S2

RPF Check Succeeds!

E0

Unicast Route Table

Network Interface

151.10.0.0/16 S1

198.14.32.0/24 S0

204.1.16.0/24 E0

S1

Forward out all outgoing interfaces.(i. e. down the distribution tree)

Computer Network


Reverse path broadcasting rpb
Reverse Path Broadcasting (RPB)

  • Eliminates the duplicate broadcast packets generated by Reverse Path Forwarding

  • It is necessary for each router to identify which of its links are “child” links in the shortest reverse path tree rooted at any given source S.

  • When a broadcast packet originating at S arrives via the shortest path back to S, the router can forward it out only the child links for S.

Computer Network


Truncated reverse path broadcasting trpb
Truncated Reverse Path Broadcasting (TRPB)

  • The previous algorithms used broadcasting and so were wasting the bandwidth on the links that had no group members.

  • In TRPB only non-member leaf networks are deleted from each broadcast tree.

  • Leaf networks are the networks which have no downstream router.

  • So the leaf networks must be found out and it must be determined if there is any member on the leaf network or not then.

Computer Network


Reverse path multicasting rpm
Reverse Path Multicasting (RPM)

  • Provides on-demand pruning of shortest-path multicast trees.

  • When a source first sends a multicast packet to a group, it uses TRPB algorithm.

  • When the packet reaches a router for whom all of the child links are leaves and none of them have members of the destination group, a non-membership report (NMR) for that (source, group) pair is generated and sent back to the router that is one hop towards the source.

  • If the one-hop-back router receives NMRs from all of its child routers, and if its child links also have no members, it in turn sends an NMR back to its predecessor.

  • Subsequent multicast packets from the same source to the same group are blocked from traveling down the unnecessary branches by the NMRs sitting in intermediate routers.

  • A non-membership report includes an age field that is used to cancel the NMR effect after some time.

Computer Network


Reverse path multicasting rpm1
Reverse Path Multicasting (RPM)

S

  • Send based on TRPB

  • Send Prune message

R

G

  • Prune the branches

R

G

R

R

R

G

R

G

Computer Network


Dvmrp in action 1
DVMRP in Action - 1

Forming a source tree

source tree

S

Source

DF

R1

Receiver 1

Computer Network


Dvmrp in action 2
DVMRP in Action - 2

Broadcast/flood

source tree

S

datagram

Source

DF

R1

Receiver 1

Computer Network


Dvmrp in action 3
DVMRP in Action - 3

prune

source tree

S

datagram

Source

IGMP DVMRP-Prune

DF

R1

Receiver 1

Computer Network


Dvmrp in action 4
DVMRP in Action - 4

X and Y are Pruned

source tree

S

datagram

Source

DF

X

Y

R1

Receiver1

Computer Network


Dvmrp in action 5
DVMRP in Action - 5

New Member

source tree

S

datagram

Source

IGMP DVMRP-Graft

DF

X

Y

R1

R2

Receiver 1

Receiver 2

Computer Network


Dvmrp in action 6
DVMRP in Action - 6

New branch

source tree

S

datagram

Source

DF

X

Y

R1

R2

Receiver 1

Receiver 2

Computer Network


Possible problems with ip multicast
Possible Problems with IP Multicast

  • Doesn’t scale well with number of multicast groups

    • Each router has to maintain state for every “active” multicast group.

    • Flooding in the beginning (bandwidth waste)

  • Open to DoS attacks by malicious senders.

  • Multicast address assignment problems – how to be globally consistent?

  • Providing TCP-like reliability is hard

  • Deployment problems as not all routers can do multicast. Also, lack of business incentive as not clear how to make money on this.

Computer Network


Another approach to multicast routing
Another Approach to Multicast Routing

  • PIM – Protocol Independent Multicast Protocol

    • Designed to provide scalable interdomain routing across internet

    • Can be independent of the underlying unicast routing protocol.

      • DVMRP dependent on the unicast routing protocol to find the multicast source.

    • Optimizes traffic depending on the density of receivers in the region.

    • Two main modes:

      • Dense Mode –

        • Similar to DVMRP, works with flooding

        • Builds source rooted distribution tree

    • Sparse Mode –

      • Introduces Rendezvous Points – receivers “meet” new sources at the RPs

      • Builds a shared tree

Computer Network


Shared tree example pim sm
Shared Tree Example (PIM-SM)

RP

G sets up state

to RP

F3

Sender registers

with RP

R3

R4

S

F1

F2

G

R5

Computer Network


Shared tree example pim sm1
Shared Tree Example (PIM-SM)

RP

RP -> G multicast

F3

S -> RP unicast

R3

R4

S

F1

F2

G

R5

Computer Network


Ip multicast concepts
IP Multicast Concepts

Host-to-router

Protocol (IGMP): keep router up-to-date with group membership of entire LAN

receivers

sender

Designated

Router

On-Tree

router

Multicast routing protocols (various):build distribution tree for multicast packets

On-Tree

Link

Branching

router

Computer Network


Spt vs steiner tree
SPT vs. Steiner Tree

Source

S

Router

Receiver

R

2

2

1

1

1

1

R1

R1

1

1

R2

R2

3

3

1

1

4

4

1

1

1

1

R5

R5

R3

R3

1

1

2

2

S

S

1

1

1

1

R4

R4

SPT (Shortest Path Tree)

Steiner

Computer Network


Shared vs source based trees2
Shared vs. Source-Based Trees

Source

Router

S

Receiver

R

R

R

R

R

R

R

RP

S

S

S

S

R

R

Source-Based Tree

Shared Tree

Computer Network


Tree types
Tree types

  • Shortest Path Tree

    • Simplicity of construction method

    • Distributed solutions

    • High cost

    • Source Based Tree

      • low delay, better load distribution,

      • Per-source state at routers

    • Shared trees

      • Higher delay, traffic concentration,

      • Per-group state at routers

  • Steiner trees

    • Lowest cost, highest delay

    • NP-complete,

    • Centralized solutions

Computer Network


Basic routing techniques
Basic Routing Techniques

  • Flood & prune: DVMRP, PIM-DM

    • RSPT, Periodic Flooding, inter-domain routing difficulties,

  • Link-state multicast protocols: MOSPF

    • SPT, High memory consumption, tree calculation in every node.

  • Core based protocols: CBT, PIM-SM

    • Comply well with the basic model, Sub-optimal tree, inter-domain routing difficulties, traffic concentration, sensitivity to core selection method, RSPT,

Computer Network


Alternative routing techniques
Alternative Routing Techniques

  • Explicit Multicast: Xcast, Bcast

    • Deployment, stateless, scalable,waste of data space, processing overhead, small groups only.

  • Application Level Multicast: ESM, NICE

    • Deployment, stateless, no control burden on network, scalable, overlay construction difficulties,stress, sub-optimal trees, stretch, high failure rate of host, cheating

  • Branching Point Based: NHBH , REUNITE, HBH

    • SPT, low memory requirement, incremental deployment, using unicast forwarding, high availability, Superfluous lookups.

Computer Network


Two main problems of ip multicast
Two Main Problems of IP multicast

  • State maintenance

    • Memory shortage when number of groups increase significantly

    • State invalidation due to routes changes

  • Need for complex inter-domain routing and management (PIM-SM/MSDP/MBGP)

Computer Network


Computer networks graduate level

NBM

Computer Network


Branching point idea
Branching Point Idea

  • Node types:

    • Member nodes

    • Relay nodes

    • Branching points

  • More than 80% of tree nodes are relay nodes.

Computer Network


Problems with current methods
Problems with current methods

  • Unnecessary lookups for unicast and multicast packets

Computer Network


Problems with current methods1
Problems with current methods

  • REUNITE

    • Asymmetries may result in creation of duplicate packets

    • The departure of one receiver may change the route for others

    • Route changes invalidate MCT

    • Route change may disconnect a subset of receivers from the tree even though all nodes and links work properly

  • HBH

    • All relay nodes between every two adjacent BPs must keep MFT

    • Duplicate packets creation duo to asymmetries

    • Route changes invalidate MCT

  • SEM

    • The whole multicast tree must be constructed again if:

      • a new member joins the multicast session

      • one of the existing members leaves the session

    • The number of receivers is inherently limited due to packet size limit

Computer Network


Nbm principals
NBM Principals

  • NBM main ideas:

    • Build message contains IP addresses of:

      • the new receiver

      • the next BP in the tree

    • Children of a failed BP detect failure of their parent and repair it locally by asking their grandpa to find a new parent for them.

Computer Network


Nbm principals1
NBM Principals

  • Seven Messages Type:

    • Join

      • to announce receiver desire to join the tree

    • Leave

      • to announce receiver desire to leave tree

    • Build

      • to find associated BP of the new receiver

    • Replace

      • To inform parent BP about creation of a new BP in the tree

    • Parent

      • to inform a receiver or a BP about its parent and grandpa

    • Repair

      • to locally repair the tree

    • Unlock

      • To unlock parent BP

Computer Network


Tree construction r1 join

MFT

r1

Tree construction: r1 join

s

rn1

B1

rn3

rn2

Join

Build

Parent

Replace

r1

rn5

rn6

B2

rn4

r2

r3

Computer Network


Tree construction r2 join

MFT

r1

r2

Tree construction: r2 join

s

MFT

r1

r2

B1

rn1

B1

rn3

rn2

Join

Build

Parent

Replace

r1

rn5

rn6

B2

rn4

r2

r3

Computer Network


Tree construction r3 join

MFT

r2

r3

Tree construction: r3 join

s

MFT

B1

rn1

MFT

B1

rn3

rn2

r2

B2

r1

r1

Join

Build

Parent

Replace

rn5

rn6

B2

rn4

r2

r3

Computer Network


Tree maintenance
Tree Maintenance

  • Each BP refresh its children periodically.

    • Refresh message contains IP address of grandpa

    • Refresh rates of higher level BPs increase linearly

  • If a BP or a receiver misses three consecutive refresh (parent) messages:

    • it sends a repair message toward the grandpa

  • Grandpa deal with repair requests in the same way as source do with receiver join messages:

    • It sends a Build message toward the orphaned node

    • or adds it to its MFT

Computer Network


Tree maintenance1

MFT

r2

r3

Tree Maintenance

s

MFT

Repiar

Build

Parent

Replace

B1

rn1

B1

rn3

rn2

r1

rn8

MFT

rn5

rn9

r1

B3

B2

rn6

rn7

B2

r4

B3

rn4

r2

r3

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Tree maintenance2

MFT

r2

r3

MFT

B2

r4

Tree Maintenance

s

MFT

Join

Build

Parent

Replace

B1

rn1

B1

rn3

rn2

r1

rn8

MFT

rn5

rn9

r1

B3

rn6

rn6

rn7

B2

r4

B3

rn4

r2

r3

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Height estimation
Height estimation

  • Dependent Receivers (DR)

    • A BP can estimate DR of a branch by counting the number of Build messages passing through it.

  • Height of the branch (in reduced tree) is approximately logXDR.

  • Each branch has a different refresh rate

    • Refresh period = MTI/logXDR

  • Higher level BPs refresh their children more frequently.

  • NMTI=NMEM*X2/(X-1)2

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Packet forwarding in nbm
Packet Forwarding in NBM

Node B received a packet with unicast destination Hi

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Simulation setup
Simulation Setup

  • myns: large-scale simulations

  • GT-ITM: graph generation

    • Transit-Stub model (10100 nodes)

      • 10 transit domains

      • Each transit domain has 10 nodes

      • Each transit domain has 5 stub domains

      • Each stub domain has 20 nodes

    • Average node degree: 3.5

  • 50 simulation runs for each point

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Simulation metrics
Simulation Metrics

  • Number of required table lookups

    • Multicast Forwarding Gain (MFG): the ratio between the number of required lookups in OBP and NBM

    • Overall Forwarding Gain (OFG): OFG takes unicast traffic into consideration as well

  • Number of required MFT entries

    • SPT: NBP+NRN+NMEM

    • RT: NBP+NMEM.

    • MFT Reduction Gain (MRG): the ratio between SPT and RT values.

  • Tree availability

    • Tree Availability Gain (TAG): the ratio of non-leaf components of SPT to non-leaf components of RT or: NBP+NRN/NBP

  • Stress

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Table lookups
Table Lookups

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Stress
Stress

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Tree characteristics
Tree Characteristics

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Branching factor
Branching Factor

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Tag mrg
TAG & MRG

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Control overhead
Control Overhead

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Application level multicast
Application Level Multicast

  • Is what Netmeeting does based on IP multicast?

  • The idea is – don’t mess with IP, let the applications handle the multicast.

  • Used very widely today:

    • Sources send packets to a central server which forwards them to all receivers for the group

  • Efficient application layer multicast

    • Apps self-organize into a multicast distribution structure

    • Data replication and management only performed by group members.

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Application level multicast1
Application Level Multicast

  • Pros:

    • Easy to develop

    • Pushes complexy towards the end systems

    • No address assignment problems

    • Can support a large number of groups

  • Cons

    • Duplicate packets on the same link

    • Higher delay due to distribution along longer than optimal paths

    • Longer reaction time to group joins

    • Can potentially be complex

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Current status
Current Status

  • IP Multicast

    • Many IETF groups work on various multicast related protocols.

    • New routers have implementations of DVMRP

    • Only a few ISPs have multicast feature turned on in the routers.

  • MBone (Multicast backBone)

    • A transient infrastructure before IP Multicast is fully deployed.

    • A virtual network of multicast-capable islands connected by tunnels (unicast encapsulated between islands)

    • Runs DVMRP

  • Some enterprise networks have deployed multicast.

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Next lecture end to end protocols
Next-lecture: End to end Protocols

  • End to End issues

    • UDP

    • TCP

  • Different Version of TCP

  • Assigned reading

    • Chapter 5 of the book

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