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By default, the 2N® Indoor Touch 2.0 is using multicast communication to be able to set up the connection towards the 2N IP intercoms. The multicast communication allows the device to reach any other device within the LAN network because L2 devices (switch) send the packet with the multicast destination IP address to all the interfaces. There are 2 multicast parameters that can be configured on the 2N® Indoor Touch 2.0:

  • Multicast video mode -  (on / off)
  • Multicast discovery parameterprotocol - (on / off)

 

Multicast Video Mode

You can switch between unicast and multicast video mode. In unicast mode the  2N® Indoor Touch 2.0 request the video stream from the intercom by using unicast packets which means  that the intercom sends the video traffic directly to a specific IP address of the answering unit. If there is multiple answering units requesting the video stream in the same time, intercom sends the video stream to each unit separately. This approach is not suitable for the large instalations installations where you have more than 4 units and there can be chance that multiple answering units will be requesting the video stream in the same time because the intercom needs to send the stream to each unit which mean that the CPU resources might be depleted.

Multicast video mode means that the intercom is sending video to a multicast address. Any answering unit which is listening this multicast address can receive the video stream. ...........Feature The benefit of this approach is that the intercom is sending just 1 video stream and each answering units which is interested in receiving the video stream can receive it so it means that the CPU  of the intercom won't be overloaded in case of huge demand for the video stream from many units.

Parameter can be found in the 2N® Intercoms application  in the section Settings->Video.


Figure 1The version 4 of the 2N® IP Mobile application for both (mobile devices & 2N® Indoor Touch 2.0) has an option to switch between the multicast and unicast communication to adjust the stream. If your network infrastructure does not support multicasting, you can use unicast in a case of a small setup (up to 3 devices in the network) or WiFi connectivity. Otherwise it is high recommended to use the multicast communication for wired connectivity.

Multicast discovery protocol

Multicast discovery enabled

By default the multicast discovery is enabled on the 2N® Indoor Touch 2.0. Info packet is sent towards the specific multicast address and reach all 2N IP intercoms within the LAN network. Info packets are used for pairing procedure between 2N® Indoor Touch 2.0 unit and intercoms. Intercoms are sending multicast messages as well. These messages are being sent periodically and contains various types of information used for the proper function of the devices.

Figure 2

To be able to fully benefit from this feature it is recommended to enable IGMP snooping on all switches within the LAN. The reason is that the switch is controlling the IGMP messages which are exchanged between the user's device and the router. IGMP messages are used for the establishment of the multicast membership between the router and the source device. The switch is controlling these messages because the multicast is sent towards all the interfaces and if there is a video stream send which will be using significant amount of the bandwidth, the switch would flooded all the interfaces with this traffic, which could cause the reduction of the overall performance of the network. With the IGMP snooping the switch is sending the multicast traffic only towards interfaces from which the IGMP group membership report message has been sent.

 

Multicast discovery disabled

In this mode, 2N® Indoor Touch 2.0 sends info packets in unicast always to the IP address of the 2N IP intercom observed and periodically to all the 2N IP intercoms in the LAN device list. In the unicast mode, info packets are only sent to the 2N IP intercoms; no other 2N® Indoor Touch 2.0 devices in the LAN are sent any info packets. This mode is beneficial in case that your switch does not support multicast or switching the multicast in wrong way. 

Examples: 

  • Switch does not support IGMP snooping is not sending multicast packets - as a result the network can be flooded by the multicast packets which contains video preview from the intercom and cause the significant reduction of the bandwidth.
  • 2N® Indoor Touch is connected to the wifi - wifi router can block the multicast traffic becuase the TTL filed is equals to 1 which means that the packet cannot be sent further into the network and also some wifi devices has troubles to handle the multicast.

 

Figure 3

 

Multicast switching

The default behavior for L2 switches is to forward all multicast traffic to all ports on the switch. However this in general might cause the reduction of the bandwidth as the traffic is send also to hosts which do not want to receive multicast traffic. Due to this fact the IGMP snooping has been introduced in switches. There are 3 types of switches: 

  • L2 switch - just sending multicast traffic to all ports
  • L3 - aware switch - IGMP snooping can be configured
  • L3 switch - this switch is also able to act as router

 


 IGMP snooping

IGMP protocol is a mechanism between hosts and routers used for the dynamic registration of hosts to a specific multicast group. Hosts joins to multicast group by sending IGMP messages to their local router. Router listen IGMP messages and periodically sends queries to discover which groups are active or inactive. IGMP snooping is a mechanism that is implemented on L3 aware and on some L2 switches. Switch "snoop" some L3 information such as IGMP join/leave messages in the IGMP packets send between the host and router. The switch is controlling IGMP messages because the multicast is sent towards all the interfaces by default and if there is a video stream send, which will be using significant amount of the bandwidth, the switch would flooded all the interfaces with this traffic, which could cause the reduction of the overall performance of the network. With the IGMP snooping enabled the switch is sending the multicast traffic only towards interfaces, from which the IGMP group membership report message has been sent.

  • If switch receive the IGMP host report from host to join a specific multicast group – it adds the switch physical port number where the host is connected to multicast table.
  • If switch receive the IGMP leave message from the host – its removes the table entry of the host.

 

However IGMP control messages are send as packets (L3 layer), so it is not possible to distinguish those messages from the rest of multicast traffic on switch. L2 switch can only identify that the frame is the multicast  based on the MAC address. In case of multicast frame, The multicast IP address is mapped to the destination MAC address. First half (24 bits) of the MAC address is always the same (01:00:5E:XX:XX:XX) and the rest is based on the last 23 bits of the multicast IP address. This means that the switch needs to check each multicast frame if it contains IGMP control message or not. This means that the low-end switches might have an issue with the speed in case of  high rates due to a slow CPU. High end switches has Application Specific Integrated Circuits (ASICs) that can perform IGMP check in hardware.

 

Multicast network setting and 2N® Indoor Touch 2.0

As described in this article, there are many types of the switches so there is no universal rule how to configure your network equipment. As already mentioned, in general L2 switches should send multicast traffic to all ports. Some L3 switches has IGMP snooping enabled by default some not. If the IGMP snooping is disabled, the switch should send a multicast traffic to all ports. 

 

Note
titleNote

Because there are no IGMP messages between 2N devices and routers - the IGMP snooping should be disabled to allow the switch send the multicast traffic to all ports. However some switches are not checking IGMP messages and just adding physical ports to its Multicast table based on the multicast traffic. Because it is possible to get a multicast address from the destination MAC address, the switch will create a multicast table with specific multicast groups. This feature is also called IGMP snooping on some switches. In such cases the IGMP snooping needs to be enabled.

 

Consequences of incorrect multicast settings:

  • Video preview does not work
  • It is not possible to open doors from the unit
  • You are not able to see other 2N devices in the device list  (Figure 4)

Image Added

Figure 4

How to resolve it:

  • Enable IGMP snooping on the switch if disabled
  • Disable IGMP snooping on the switch if enabled
  • Try to manually create IGMP snooping groups 
    • There will be two IGMP snooping groups ( 235.255.255.241:8004 and 235.255.255.240:8002)
    • Add all interfaces where 2 devices are connected to a newly created IGMP snooping groups
  • There is also option to change the IGMP version in some switches - as mentioned above we do not use IGMP protocol so the switch should forward traffic to all ports however you can try to use IGMPv1 or IGMPv2 in case that the above mentioned points wont resolve the issue