Multicast Solution

1
Multicast Solution

• How does it work ?

July 2005 version 3
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2
Note to Viewer

• The content of this tutorial provides an overview
  of IGMP used in Digital Multicast networks to
  familiarize customers with the technology.
• The information in this document is subject to
  change without notifice.
• While every precaution was taken in the
  preparation of this document, iMPath assumes no
  responsibility for errors or omissions. Neither
  is any liability assumed for damages resulting
  from the use of the information contained herein.
• Should you have any questions, please feel free
  to contact

Daniel Brisson Sr. System Engineer iMPath
Networks Inc Tel [phone] x 297 Email
dbrisson_at_impathnetworks.com
Gilles Lebel Sr. System Engineer iMPath Networks
Inc Tel [phone] x 224 Email
glebel_at_impathnetworks.com
3
Typical Network Requirements
Monitor any video from anywhere in the network
4
Multicast

• Multicast. Allows sending one copy of each packet
  to the group of computers that want to receive
  it. Multicast can be implemented at the Ethernet
  link-layer or at the network layer (layer 3 of
  the OSI model). Computers join and leave
  multicast groups by using the IGMP (Internet
  Group Management Protocol) Each host can register
  itself as a member of selected multicast groups
  through use of the Internet Group Management
  Protocol (IGMP).
• Multicast is commonly used in audio and video
  streaming applications.
• It allows a single source of traffic to be viewed
  by multiple destinations simultaneously.
• It is designed to provide an efficient
  transmission using the least amount of bandwidth
  on the network to save cost.
• IGMP is a standard IP protocol supported by most
  LAN/WAN vendors in traditional LAN products, ATM,
  and gigabit Ethernet solutions.

5
Typical Network Components
Typical high speed backbone network consisting of
Layer 2 or Layer 3 Ethernet Switches.
L3 Switch/Router
L3 Switch/Router
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
100 Meg
100 Meg
100 Meg
High Speed Switches are located at major hub
locations to collect or drop off data traffic
from this distribution center.
Field hub locations are distributed where the end
devices are located. They are used to collect and
distribute traffic for Cameras, Traffic
Controllers, Message Signs and many more.
Several topologies can be used such as Star and
Linear topologies being the most common.

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Control Center 2
Control Center 1
Typical field encoder collector network
6
Typical Network Components
Multiple Control Centers may be deployed with
this architecture.
L3 Switch/Router
L3 Switch/Router
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
100 Meg
100 Meg
100 Meg
The Control Centers provide video viewing and
control of the Camera PTZ, Traffic Controllers,
or Message signs to name just a few.
The Virtual Matrix is commonly used in digital
video networks providing video display and
control and to operate complementary integrated
applications.

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Control Center 2
Control Center 1
Typical field encoder collector network
7
Why use IGMP?
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
100 Meg
100 Meg
100 Meg
Without IGMP support, multicast traffic is
transmitted to all the ports in each network
switch. This unnecessary traffic floods the
interfaces and can quickly bog down the entire
network.

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Control Center 2
Control Center 1
Typical field encoder collector network
8
Why use IGMP?
For example With 25 cameras deployed, each
transmitting at 5 Mbps, you will have over 125
Mbps of combined traffic on your network
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
100Base-T
100Base-T
100Base-T
125 Mbps of traffic on each 100Base-X interface
!!!!!!
125 Mbps of traffic
125 Mbps of traffic

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Control Center 2
Control Center 1
Typical field encoder collector network
9
Why use IGMP?
For example With 25 cameras deployed, each
transmitting at 5 Mbps, you will have over 125
Mbps of traffic on your network
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
100Base-T
100Base-T
100Base-T
On a 100 Mbps interface (optics or electrical)
you cannot pass more then 100 Mbps of traffic.
In fact a typical recommendation in the industry
is not to exceed 70 of the bandwidth in any
segment.
PROBLEM Combined 125 Mbps of traffic on these
interfaces. The capacity of this network is
exceeded with only 25 cameras

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Control Center 2
Control Center 1
Typical field encoder collector network
10
Traffic flow with IGMP
Only 15 Mbps of multicast traffic flows on this
link
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
100 Meg
Video Stream 3
100Base-T
100Base-T
Video Stream 1
Video Stream 2
Only 5 Mbps of Multicast traffic Flows on this
port
Video Stream 3

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Traffic is only present on the backbone when a
decoder requests the specific encoder stream
Control Center 2
Control Center 1
Typical field encoder collector network
11
How does it work?
L3 Switch/Router
L3 Switch/Router
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
100 Meg
The Routers build and share a table of all the
IGMP servers available on the network. They
keep a table of all the available Multicast
Addresses
This Router will not forward any of the multicast
traffic until it receives a request from a
decoder (client)
Encoder
The Encoder is considered a server in the IGMP
world. It generates a video signal that will be
made available to any Decoder (client) on the
network.
The Encoder transmits a signal with a distinct
destination address. Between 224.x.x.x to
239.x.x.x. (some addresses are reserved for
specific applications)

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Control Center 1
Typical field encoder collector network
12
Here is how it works - Joining a Group
L3 Switch/Router
L3 Switch/Router
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
100 Meg
The Router responds and forwards the traffic to
this specific port on the Ethernet switch.
4
Encoder
224.168.32.55
The Decoder registers this address in its table
and forwards the request (join the multicast
group) to the network
3
The Virtual Matrix application forwards a message
to the decoder to view a specific video stream.
(request to see video from address 224.168.32.55)
2

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

The operator makes a request to see a video on a
specific monitor
1
Control Center 1
Typical field encoder collector network
13
Here is how it works - Leaving a Group
L3 Switch/Router
L3 Switch/Router
Digital Backbone ATM, SONET, LAN, Gigabit
Ethernet...
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
L3 Switch/Router
100 Meg
The Router stops video stream A, adds the new
video B to the group, and releases the traffic
for video B to this specific port on the Ethernet
switch.
4
Encoder
Encoder
224.168.32.55
224.168.32.107
Video A
Video B
The Decoder un-registers from the present viewing
address (a leave message is sent) followed by
a join message which is sent with the new
multicast stream.
3
the Virtual Matrix application ONLY forwards a
single message to the decoder to view video B
stream. (request to see video from address
224.168.32.107)
2

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

When the operator makes a request to change the
view from video A to video B
1
Control Center 1
Typical field encoder collector network
14
Choosing your network elements

• There are several types of digital network
  technologies to choose from.
• SONET and ATM are still applicable but are now
  rarely deployed on new installations.
• Ethernet is the most common technology due to the
  wide range of affordable products available from
  many manufacturers and the familiarity with
  Ethernet and IP technology.
• The components more commonly used to build
  Ethernet networks are Ethernet Switches.
• A high capacity Ethernet network is often
  referred to as the backbone network.

15
Choosing your network switches

• Choosing Ethernet Switches for your backbone
  network could depend on several factors
• Your specific port density requirements
• Network topology
• Temperature hardened requirements (outdoor)
• Support for IGMP protocol
• Your preferred manufacturer
• Specific product functionality
• This tutorial will explore a few topologies and
  the IGMP functionality of different Ethernet
  Switches.

16
Ethernet Switch selection

• There are 3 types of Ethernet Switches
• Layer 2 Switch
• Distributes traffic to each destination using MAC
  addressing table.
• Broadcasts the Multicast traffic across all its
  ports
• There are no Multicast traffic filters with these
  switches
• Layer 2 Switch with IGMP Snooping
• Distributes traffic to each destination using MAC
  addressing table
• Provides limited control of Multicast traffic to
  prevent broadcast of the traffic to all ports.
• Layer 3 IGMP master is needed in the network
• Layer 3 Switch/Router with IGMP
• Distributes traffic to each destination using MAC
  addressing table.
• Distributes traffic to each destination using IP
  subnet addressing table.
• Provides maximum control of Multicast traffic to
  prevent broadcast of the traffic to all ports and
  all subnet.

17
Layer 2 SwitchFunctionality
The combined Multicast Traffic is sent to all
ports in each Switch
L2 Switch
L2 Switch
20 Mbps
Bandwidth Restriction applies.
15 Mbps
15 Mbps
15 Mbps
15 Mbps
20 Mbps
20 Mbps
5 Mbps
5 Mbps
5 Mbps
5 Mbps
0 Mbps
0 Mbps
Decoder
Decoder
5 Mbps Multicast Video per Encoder
This is a valid network topology for small
networks Ensure no more then 70 of the bandwidth
of the lowest negotiated Ethernet port speed is
used. Not to be used with 10 Meg Half Duplex
devices.
18
Layer 3 Switch/Router with IGMPFunctionality
Multicast traffic is filtered out at each switch
Only the required traffic is transmitted on the
network
L3 Switch
L3 Switch
10 Mbps
Deploying a Layer 3 at each collector HUB could
be expensive
5 Meg
5 Meg
5 Meg
5 Meg
5 Meg
5 Mbps
5 Mbps
5 Mbps
5 Mbps
5 Mbps
5 Mbps
0 Mbps
0 Mbps
0 Mbps
0 Mbps
0 Mbps
0 Mbps
Decoder
Decoder
This is a valid network topology for any network
- No topology restrictions
19
Layer 2 3 SwitchTypical Topology
0 Mbps
35 Mbps Combined Multicast Video
L3 Switch
35 Mbps Combined Multicast Video
0 Mbps
0 Mbps
The L3 Switch controls all Multicast traffic. In
and out. It eliminates transmitting the combined
multicast traffic unnecessarily to each port.
Decoder
Decoder
The use of L2 Switch in this topology is very
common. Multicast traffic is repeated on all
ports of the switch within the segment but
traffic from other segments is not seen. Traffic
between the segments is controlled by the L3
switch. Economical and practical solution that
is very easy to deploy.
20
Layer 2 3 SwitchTypical Topology Industry
concern
35 Mbps
L3 Switch
0 Mbps
35 Mbps
0 Meg
5 Meg
0 Meg
5 Meg
This solution is very effective and greatly
simplifies Network Management. However, it is
sometimes necessary to filter IGMP traffic at the
edge. Such solutions were previously overlooked
for economical reasons.
Decoder
Decoder
An economical solution now exist L2 switch with
IGMP Snooping
21
Overview of OSI Model
Application
Layer 7.
Presentation
Layer 6
Session
Layer 5
Transport
Layer 4
Traditionally performed by Routers

Network
Layer 3- This layer defines the addressing and
routing structure of the Inter-network This
layer controls the Multicast traffic on the
network.
Performed by Switches

Data Link
Layer 2- This layer defines the framing,
addressing and error control of Ethernet packets.
Port addressing uses MAC address of each
device. This layer effectively treats Multicast
traffic as broadcast traffic.
Physical
Layer 1
22
Overview of OSI Model

Layer 3- This layer defines the addressing and
routing structure of the Inter-network This
layer controls the Multicast traffic on the
network.
Network
This product can be used instead of expensive
Routers
Layer 2 with IGMP Snooping- Layer 2 Switches
with IGMP Snooping functionality are now
available. Provide all the functionality of a
Layer 2 switch with PARTIAL IGMP support. This
layer provides some Multicast traffic control on
the network.

New product introduced
Available with different port densities. 100Base-F
x to Gigabit trunks. Temperature Hardened Wide
choice of manufacturers and products.

Layer 2- This layer defines the framing,
addressing and error control of Ethernet packets.
Port addressing uses MAC address of each
device. This layer effectively treats Multicast
traffic as broadcast traffic.
Data Link
23
Layer 2 Switch with IGMP SnoopingFunctionality
Local traffic is filtered out at each switch.
Eliminates multicasts traffic to all the ports
All the multicast traffic is sent to the central
site. The L3 switch still controls the IGMP table
of the network.
20 Mbps Combined Multicast Video
L2 with IGMP Snooping
L3 Switch
5 Mbps
0 Mbps
5 Mbps
0 Mbps
Decoder
Decoder
Valid network topology for any network No
topology restrictions
24
L2 with Snooping L3 SwitchTypical Topology
35 Mbps
L3 Switch
35 Mbps
L2 Switch
Encoder
Bandwidth Restriction applies. No more 70 of
link capacity
L2 Switch
L2 Switch
Encoder
Encoder
0 Mbps
5 Mbps
0 Mbps
5 Mbps
L2 Switch
L2 Switch
Encoder
Encoder
These links contain the combined Multicast
traffic from all the Encoders in their segment
i.e. 35 Mbps.
L2 Switch
Decoder
Decoder
L2 Switch
Encoder
Encoder
L2 Switch
L2 Switch
Encoder
Encoder
L2 Switch
L2 Switch
Encoder
Encoder
Switches with IGMP Snooping eliminate flooding
local interfaces with Multicast traffic.
L2 Switch
L2 Switch
Encoder
Encoder
L2 Switch
Encoder
Very practical implementation Management of the
Ethernet Switches is required.
25
How does it work?From the Encoder to the L3
Switch
The L2 Switch with IGMP Snooping detects the
Query message from the L3 Switch and logs
internally the ports that pass traffic to the L3
Switch
L3 Switch
0 Mbps
35 Mbps
L2 Switch
Encoder
0 Mbps
5 Mbps
L2 Switch
The L3 Switch forwards the IGMP Query on all its
ports to determine if there are any devices that
wish to subscribe to a Multicast Group.
Encoder
L2 Switch
Decoder
Encoder
L2 Switch eliminates flooding of the local
interfaces and passes the Multicast traffic to
the L3 Switch for processing.
L2 Switch
Encoder
L2 Switch
Encoder
L2 Switch
Encoder
The L2 Switch detects/identifies the Multicast
stream source and logs internally what port this
stream came from.
L2 Switch
Encoder
Each Encoder forwards a constant Multicast stream
to the Ethernet Switch (224-239.x.x.x)
26
How does it work?From the Encoder to the L3
Switch
At this point, the Multicast traffic from all
Encoders is combined on this link towards the L3
Switch.
35 Mbps Combined Multicast Traffic
L3 Switch
0 Mbps
L2 Switch
Encoder
L2 Switch
0 Mbps
5 Mbps
Encoder
L2 Switch
Encoder
Decoder
L2 Switch
Encoder
L2 Switch
Encoder
L2 Switch
Encoder
The L3 Switch detects the Multicast traffic
arriving on this interface and logs internally
all the Multicast address for distribution.
L2 Switch
Encoder
27
How does it work?From the L3 Switch to the
Decoder
L3 Switch
0 Meg
35 Mbps Combined Multicast Traffic
L2 Switch
Encoder
0 Mbps
5 Mbps
L2 Switch
The L3 Switch responds and releases the traffic
to this specific port on the Ethernet switch.
Encoder
L2 Switch
Decoder
Encoder
The Decoder registers this address in its table
and forwards the request (join the multicast
group) to the network
L2 Switch
Encoder
L2 Switch
Encoder
The Virtual Matrix application forwards a message
to the decoder to view a specific video stream on
a specific monitor. (request to see video from
address 224.168.32.55)
L2 Switch
Encoder
L2 Switch

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Encoder
The operator makes a request to see a video on a
specific monitor
Control Center 1
28
How does it work?From the L3 Switch to the
Decoder
L3 Switch
0 Meg
The L3 Switch responds by forwarding the stream
224.168.32.140
35 Mbps
The Decoder sends an IGMP request to join
(224.168.32.140)
L2 Switch
Encoder
0 Mbps
5 Mbps
The L3 Switch responds by stopping the stream
224.168.32.55
L2 Switch
Encoder
L2 Switch
Decoder
Encoder
The Decoder sends an IGMP leave message. No
longer need to receive the Multicast steam
(224.168.32.55)
L2 Switch
Encoder
L2 Switch
Encoder
The Decoder registers this address in its table
and forwards two messages to the switch
L2 Switch
Encoder
L2 Switch

• Virtual Matrix Control Console
• Displays video to monitors
• Controls camera PTZ

Encoder
The Virtual Matrix application forwards a message
to the decoder to view a specific video stream.
(224.168.32.140)
The operator makes a NEW request to see a video
on a specific monitor
Control Center 1
29
How does it work?Typical Star Topology
Multicast traffic flows from all Encoders to
the L3 Switch
L3 Switch controls the distribution of all
Multicast traffic to Decoders
Decoders
Encoder
L2 Switch with IGMP Snooping
30
Watch forLimitations of IGMP Snooping
If this is a Gig E link and you have more then
70 Meg of Video traffic, no other application
will run on this network until the link is
re-established. Maximum port traffic will be
exceeded.
L3 Switch
L2 Switch
Encoder
In the event of a communication break between
the L2 and L3 switches, the L2 IGMP Snooping
switch will behave like a L2 switch
L2 Switch
Encoder
L2 Switch
Decoder
Encoder
A few minutes after loss of signal, the switches
may flood all Multicast signals to the ports of
every switch Behavior may differ depending on
switch manufacturer.
L2 Switch
Encoder
L2 Switch
Encoder
L2 Switch
Encoder
L2 Switch
Encoder
L2 Switches with IGMP Snooping have limitations.
31
Watch forDistributed Control Centers
This switch will allow traffic from network A to
flow to the Decoder when a join request is
received.
Multicast traffic flows to the L3 Switch
Network A
Decoder
Decoder
Decoder
Decoder
Video Source A
Multicast join request sent to the L3 Switch
Control Center 2
Control Center 1
32
Watch forDistributed Control Centers
It will not be possible to view any video. Not
even local video.
This switch requires connectivity to the L3
switch to provide local join
Communication break
Network A
Decoder
Decoder
Decoder
Decoder
Video Source A
This limitation can be eliminated by installing
an L3 Switch at all Control Centers.
Control Center 2
Control Center 1
33
Watch forDistributed Control Centers
Decoder
Decoder
Decoder
Decoder
Video Source A
Video Source B
Control Center 2
Control Center 1
34
Configuration TipsL2 Switch with IGMP Snooping
This switch generates IGMP Queries. It is
considered as the Master or the Active device
Two IGMP configuration modes can be set in the
switches.
Passive
Passive
Passive
Decoder
Decoder
Decoder
Decoder
In this topology, there can only be one Master
unit.
Control Center 2
Control Center 1
35
Configuration TipsL2 Switch with IGMP Snooping
This switch generates IGMP Queries. It is
considered as the Master or the Active device
Some L2 Switches with IGMP Snooping can be
configured as Passive or Active
Passive
Passive
Passive
In this topology, there can only be one Master
unit.
Decoder
Decoder
Decoder
Decoder
This topology should only be considered for small
networks. Most L2 IGMP Snooping Switches do not
have the capacity to handle a large table of IGMP
Multicast traffic.
Control Center 2
Control Center 1
36
Multi-Vendor SupportAvoidMixing IGMP Snooping
Switches
Passive
Passive
Passive
Active
Manufacturer A
Manufacturer A
Manufacturer B
Manufacturer B
Decoder
Decoder
Decoder
Decoder
Control Center 2
Control Center 1
Although some L2 IGMP Snooping Switch
manufacturers may imply that they can integrate
into a multi-vendor solution, this is not
recommended since IGMP Snooping is not an RFC
standard. Implementation differs between
manufacturers. (Proven to fail in our labs)
37
Multi-Vendor SupportRecommendation
L3 Switch
Use L2 with IGMP Snooping Hardened products are
available
High end products should be used for L3 Switch to
control all your Multicast traffic. Products from
Foundry, Extreme, Nortel and Cisco (to name just
a few) should be used. These are typically
non-hardened products
Decoder
Keep it simple. A single manufacturer solution is
recommended
Ruggedcom, Etherwan, Garrettcom and IFS offer a
wide range of products for this application. All
were tested at iMPath with positive results.
38
Multi-Vendor SupportAvoid
L3 Switch
Manufacturer A
Manufacturer A
Decoder
Do not MIX different vendors IGMP Snooping
switches in this topology. It will most-likely
not work
Manufacturer A
Manufacturer A
Manufacturer B
Although some L2 IGMP Snooping Switch vendors may
suggest they can integrate into a multi-vendor
solution, this is not recommended since IGMP
Snooping is not a RFC standard. Implementation
differs between manufacturers. (Proven to fail in
our labs)
Manufacturer A
Manufacturer B
39
Multi-Vendor SupportRecommendation
When multi-vendor solutions are used, it is
recommended to use a single manufacturer solution
on each link. Use the L3 Switch to separate each
group (manufacturer) of L2 IGMP switches. This
is the most reliable topology to support
multi-vendor solutions.
Decoder
40
Credits

• The information shared in this document was
  obtained by performing numerous IGMP related
  tests at iMPath facilities between January and
  June 2005.
• Tests were performed using L2, L2 IGMP Snooping,
  and L3 switches.
• Over 30 MPEG-2 iMPath Encoders were used during
  these tests to validate the proper function and
  performance of the switches under stress.
• iMPath would like to thank its business partners
  for their participations and providing equipment
  and support during the research phase.
• L2 IGMP Snooping switch manufacturers
• Ruggedcom, Etherwan, Garrettcom and IFS
• L3 switch manufacturer
• Foundry Networks
• Test Coordinator
• iMPath Networks, Daniel Brisson, Sr. System
  Engineer