example shows how to configure IGMP state limiters to provide multicast CAC in
a network environment where all the multicast flows roughly utilize the same
amount of bandwidth.
This example uses
the topology illustrated in the figure.
Figure 1. IGMP State Limit Example
following illustration and example uses routers in the configuration, any
device (router or switch) can be used.
In this example, a
service provider is offering 300 Standard Definition (SD) TV channels. Each SD
channel utilizes approximately 4 Mbps.
provider must provision the Gigabit Ethernet interfaces on the PE router
connected to the Digital Subscriber Line Access Multiplexers (DSLAMs) as
follows: 50% of the link’s bandwidth (500 Mbps) must be available to
subscribers of the Internet, voice, and video on demand (VoD) service offerings
while the remaining 50% (500 Mbps) of the link’s bandwidth must be available to
subscribers of the SD channel offerings.
Because each SD
channel utilizes the same amount of bandwidth (4 Mbps), per interface IGMP
state limiters can be used to provide the necessary CAC to provision the
services being offered by the service provider. To determine the required CAC
needed per interface, the total number of channels is divided by 4 (because
each channel utilizes 4 Mbps of bandwidth). The required CAC needed per
interface, therefore, is as follows:
500Mbps / 4Mbps =
Once the required
CAC is determined, the service provider uses the results to configure the per
IGMP state limiters required to provision the Gigabit Ethernet interfaces on
the PE router. Based on the network’s CAC requirements, the service provider
must limit the SD channels that can be transmitted out a Gigabit Ethernet
interface (at any given time) to 125. Configuring a per interface IGMP state
limit of 125 for the SD channels provisions the interface for 500 Mbps of
bandwidth, the 50% of the link’s bandwidth that must always be available (but
never exceeded) for the SD channel offerings.
configuration shows how the service provider uses a per interface mroute state
limiter to provision interface Gigabit Ethernet 0/0/0 for the SD channels and
Internet, Voice, and VoD services being offered to subscribers:
description --- Interface towards the DSLAM ---
ip igmp limit 125