department of computer and it engineering university of kurdistan computer networks ii

Department of Computer and IT EngineeringDepartment of Computer and IT EngineeringUniversity of KurdistanUniversity of Kurdistan

Computer Networks IIMulticasting

By: Dr. Alireza AbdollahpouriBy: Dr. Alireza Abdollahpouri

یکی از مهمترین دالیل استفاده از چندپخشی، صرفه جویی در

پهنای باند است

یکی از مهمترین دالیل استفاده از چندپخشی، صرفه جویی در

پهنای باند است

Multicast vs. Unicast

IP multicast

DVMRP,PIM, MOSPF IGMP

Multicast routing protocols

Group management protocol

دسترسی به پایگاه داده •های توزیع شده

انتشار اطالعات و اخبار••Teleconferencingآموزش از راه دور••IPTVبازيهای چندنفره•

Some applications of multicasting

Multicast Applications

ConferenceXP: An Example of Multicast application

Video ConferenceDistance Learning

Multicast Issues

Naming and addressing (IP class D) (نحوه آدرسدهی)

Membership Management (IGMP)(نحوه مدیریت گروههای چندپخشی)

Routing (DVMRP, PIM, MOSPF, …)(نحوه هدایت بسته های چندپخشی)

Network multicast Router actively participate in

multicast, making copies of packets as needed and forwarding towards multicast receivers

Multicastrouters (red) duplicate and

forward multicast datagrams

Multicast: one sender to many receivers

Multicast: act of sending datagram to multiple receivers with single “transmit” operation analogy: one teacher to many students

Question: how to achieve multicast

چندپخشی در الیه ) )شبکه

چندپخشی در الیه ) (شبکه

In network-layer multicasting, the router may forward the received

packet through several of its interfaces.

Note:Note:

Application-layer multicast end systems involved in

multicast copy and forward unicast datagrams among themselves

Multicast: one sender to many receivers

چندپخشی در الیه ) )کاربرد

چندپخشی در الیه ) (کاربرد

Multicast groups

class D Internet addresses reserved for multicast:

host group semantics:o anyone can “join” (receive) multicast groupo anyone can send to multicast groupo no network-layer identification to hosts of members

needed: infrastructure to deliver mcast-addressed datagrams to all hosts that have joined that multicast group

تحویل بسته های چند پخشی در الیه پیوند داده

Change the multicast IP address 230.43.14.7 to an Ethernet multicast physical address.

SolutionWe can do this in two steps:1- We write the rightmost 23 bits of the IP address in hexadecimal. This can be done by changing the rightmost 3 bytes to hexadecimal and then subtracting 8 from the leftmost digit if it is greater than or equal to 8. In our example, the result is 2B:0E:07.

2- We add the result of part a to the starting Ethernet multicast address, which is 01:00:5E:00:00:00. The result is:

Example

Group management protocol (IGMP)

IGMP is a group management protocol. It helps a multicast router

create and update a list of loyal members related to each router

interface.

NoteNote::

IGMP message types

Encapsulation of IGMP packet

و IP در قالب بسته های ICMPبسته بندی پیغامهایسپس فریمهای الیه پایینتر

IGMP message format

8 bytes8 bytes

ثانیه( در 1/0حداکثر زمان پاسخ )بر حسب Query پیغامهای

IGMP type field

Type Value

General or special query 0x11 or 00010001

Membership report 0x16 or 00010110

Leave report 0x17 or 00010111

IGMP operation

Membership report

Leave report

No Response

The general query message does not define a particular group.

NoteNote::

General query message

No Response

Example

Imagine there are three hosts in a network, as shown in Figure below. A query message was received at time 0; the random delay

time (in tenths of seconds) for each group is shown next to the group address. Show the sequence of report messages.

Solution

The events occur in this sequence:

1. Time 12. The timer for 228.42.0.0 in host A expires and a membership report is sent, which is received by the router and every host including host B which cancels its timer for 228.42.0.0.

2. Time 30. The timer for 225.14.0.0 in host A expires and a membership report is sent, which is received by the router and every host including host C which cancels its timer for 225.14.0.0.

3. Time 50. The timer for 251.71.0.0 in host B expires and a membership report is sent, which is received by the router and every host.

4. Time 70. The timer for 230.43.0.0 in host C expires and a membership report is sent, which is received by the router and every host including host A which cancels its timer for 230.43.0.0.

In unicast routing, each router in the domain has a table that defines a

shortest path tree to possible destinations.

Note:Note:

Shortest path tree in unicast routing

In multicast routing, each involved router needs to construct a tree for

each group.

Note:Note:

Multicast Routing: Problem Statement Goal: find a tree (or trees) connecting routers having local

mcast group members tree: not all paths between routers used source-based: different tree from each sender to rcvrs shared-tree: same tree used by all group members

Shared tree Source-based trees

Approaches for building mcast trees

Approaches: source-based tree: one tree per source

shortest path trees reverse path forwarding

group-shared tree: group uses one tree minimal spanning (Steiner) center-based trees

Shortest Path Tree

mcast forwarding tree: tree of shortest path routes from source to all receivers Dijkstra’s algorithm

router with attachedgroup member

router with no attachedgroup member

link used for forwarding,i indicates order linkadded by algorithm

LEGEND

S: source

Reverse Path Forwarding

if (mcast datagram received on incoming link on shortest path back to center)

then flood datagram onto all outgoing links

else ignore datagram

rely on router’s knowledge of unicast shortest path from it to sender

each router has simple forwarding behavior:

Reverse Path Forwarding: example

• result is a source-specific reverse SPT– may be a bad choice with asymmetric

datagram will be forwarded

S: source

datagram will not be forwarded

Multicast Forwarding

RPF Check Fails!

Unicast Route TableUnicast Route Table

NetworkNetwork Interface Interface

151.10.0.0/16151.10.0.0/16 S1S1

198.14.32.0/24198.14.32.0/24 S0S0

204.1.16.0/24204.1.16.0/24 E0E0

A closer look: RPF Check Fails RPF Check Fails

Packet Arrived on Wrong Interface!

Multicast Packet fromSource 151.10.3.21

XDiscard Packet!

Multicast Forwarding

A closer look: RPF Check SucceedsRPF Check Succeeds

RPF Check Succeeds!

Unicast Route TableUnicast Route Table

NetworkNetwork Interface Interface

151.10.0.0/16151.10.0.0/16 S1S1

198.14.32.0/24198.14.32.0/24 S0S0

204.1.16.0/24204.1.16.0/24 E0E0

Multicast Packet fromSource 151.10.3.21

Packet Arrived on Correct Interface!S1S1

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

Reverse Path Forwarding: pruning forwarding tree contains subtrees with no mcast

group members no need to forward datagrams down subtree “prune” msgs sent upstream by router with no

downstream group members

prune message

S: source

links with multicastforwarding

Problem with RPF

RPF versus RPB

برای اینکه هر شبکه یک کپی از بسته چندپخشی را دریافت کند برای آن یک روتر به عنوان والد تعریف می کنیم.

Center-based trees

single delivery tree shared by all one router identified as “center” of tree to join:

edge router sends unicast join-msg addressed to center router

join-msg “processed” by intermediate routers and forwarded towards center

join-msg either hits existing tree branch for this center, or arrives at center

path taken by join-msg becomes new branch of tree for this router

Center-based trees: an example

Suppose R6 chosen as center:

path order in which join messages generated

Group-shared tree with rendezvous router

Sending a multicast packet to the rendezvous router

In CBT, the source sends the multicast packet (encapsulated in a unicast packet)

to the core router.

The core router decapsulates the packet and forwards it to all interested

interfaces.

Note:Note:

Taxonomy of common multicast protocols

Distance Vector Multicast Routing Protocol DV + RPF + Pruning DV vector carries distance to multicast sources Pruning carries a timeout (prune lifetime)

Afterwards, traffic delivery is resumed

Explicit graft message to reverse pruning Done upon join

Prune جهت هرس کردن درخت و Graft برای ایجاد شاخه جدید در درخت

Multicast Extensions to OSPF Link-state advertisements include multicast

group membership Only report directly connected hosts

Compute shortest-path spanning tree rooted at source On demand, when receiving packet from source

for the first time Forward multicast traffic along tree

Protocol Independent Multicast (PIM) is the Protocol Independent Multicast (PIM) is the name given to two independent multicast name given to two independent multicast routing protocols: routing protocols:

Protocol Independent Multicast, Dense Mode Protocol Independent Multicast, Dense Mode (PIM-DM) and (PIM-DM) and

Protocol Independent Multicast, Sparse Protocol Independent Multicast, Sparse Mode (PIM-SM). Mode (PIM-SM).

PIM-DM is used in a dense multicast environment, such as a LAN.

Note:Note:

PIM-DM uses RPF and pruning/grafting strategies to handle

multicasting.

However, it is independent from the underlying unicast protocol.

Note:Note:

PIM-SM is used in a sparse multicast environment such as a WAN.

Note:Note:

PIM-SM is similar to CBT but uses a simpler procedure.

A multicast router may not find another A multicast router may not find another multicast router in the neighborhood to multicast router in the neighborhood to forward the multicast packet. A solution forward the multicast packet. A solution for this problem is tunneling. We make a for this problem is tunneling. We make a multicast backbone (MBONE) out of these multicast backbone (MBONE) out of these isolated routers using the concept of isolated routers using the concept of tunneling.tunneling.

Logical tunneling

55QuestionsQuestionsQuestionsQuestions

department of computer and it engineering university of kurdistan computer networks ii

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