ePMP Multicast Configuration & Use Cases

AP Configuration.

  1. Reliable Multicast.

Reliable Multicast is supported only in TDD Mode.

Cambium Networks supports Reliable Multicast delivery mechanism on the ePMP platform. This capability opens up opportunities for IPTV delivery services with full featured QoS support, reliable transmission mechanism and support of IGMPv3.

The system automatically detects if a customer subscribes to a specific multicast stream by handling an appropriate IGMP join request. Multicast video stream is transmitted to all the subscribed users using only the most optimum MCS (Modulation and Coding Scheme) data rate. In addition individual packets are retransmitted when needed at the presence of high interference. This mechanism ensures reliable packet delivery under all conditions.

With Reliable Multicast enabled AP sends Multicast traffic using optimum MCS only to Subscriber Modules which have registered IGMP subscription requests from equipment in the LAN.

When Reliable Multicast is disabled, the AP sends IGMP multicast traffic using MCS 1 to all SMs.

Reliable Multicast provides Much Higher Multicast Throughput on optimum MCS, but can be used only in cases when Multicast users send IGMP join requests to SM.

For other cases Reliable Multicast should be disabled and AP will send Multicast on MCS1 to every SM.

 2. IGMPv2 Fast Leave Support.

This option is relevant only for cases when IGMPv2 is used in the Network.

IGMPv2 Fast Leave can be enabled only when Reliable Multicast is enabled.

When IGMPv2 Fast Leave enabled, the AP will drop IGMPv2 Leave packets coming from subscribers if there are still other SMs subscribered to this group downstream.

If IGMPv2 Fast Leave is  disabled, the AP will receive IGMPv2 Leave packets coming from subscribers and stop Multicast Transmission in the Downlink.

IGMPv2 Fast Leave is a multicast mechanism for controlling how transmission is ceased for group multicast streams. 

Typically, when an IGMP snooper switch/router receives an IGMP Leave message, the snooper waits to receive a Membership Query message from the IGMP Querier to determine if there are any additional group members connected to the interface prior to removing the entry from the bridge table.

SM Configuration.

  1. Multicast Group Limit

Configure the maximum number of simultaneous Multicast/IGMP groups allowed on the SM. Set to 0 to disable the limitation.

SM execute Multicast groups inspection in case Multicast Group Limit is enabled.

SM will not pass Multicast traffic with Multicast Group Limit enabled in case SM didn’t receive IGMP Multicast Group join requests.

When Multicast Group Limit disabled – SM will pass traffic through even without IGMP Multicast Group subscription.

Multicast Group Subscription can be verified on Monitor -> Network page in Multicast Status section on SM.


       2. Multicast VLAN

A VLAN tag will be added to Multicast untagged traffic entering the SM’s LAN port before sending it to the AP and the SM will remove tags in the opposite direction from Multicast traffic (tagged with Multicast VLAN ID) entering on the SM’s WAN port before sending to the SM’s LAN port.

       3. Multicast VLAN Priority

Multicast VLAN Priority add Priority value into 802.1Q tag field in Ethernet Frame.

End Hosts and Routers with sophisticated NICs can signal the priority associated with a frame.

Useful Links:

  1. http://community.cambiumnetworks.com/t5/ePMP-Networking/ePMP-Multicast-IPTV-Streaming/td-p/38711
  2. http://community.cambiumnetworks.com/t5/ePMP-Networking/IGMPv2-Fast-Leave-Support/td-p/52116
  3. https://en.wikipedia.org/wiki/Internet_Group_Management_Protocol


1. AP:

Reliable Multicast: - Enabled.


2. AP:

Reliable Multicast – Enabled.


3. AP:

Reliable Multicast – Disabled.


4. AP:

Reliable Multicast – Disabled;

SM1, SM2, SM3:

Multicast Group Limit – Enabled.


5. AP:

Reliable Multicast – Disabled.

SM1, SM2, SM3:

Multicast Group Limit – Enabled.


6. AP:

Reliable Multicast – Disabled.

SM1, SM3:

Multicast Group Limit – Disabled.


Multicast Group Limit – Enabled.