Multicast Cascading

OLT Multicast Cascading

• Ethernet cascading
  Using Ethernet cascading on the access device, the number of ports on the convergence device and the optical cable routing cost can be reduced. In addition, capacity expansion for more users in the residential community access area can be easily implemented.
  There are two common cascading network topologies, star (tree/chain) network and ring network, as shown in the following figure. Here, the star cascading network is used as an example. For details about the ring cascading network, see "Ring Network of Uplink Ports".
  
  
  
  • Multicast cascading port configuration
    The device, through the Ethernet port of its cascading boards, can be physically connected to the lower-layer device. Multicast service is configured through the multicast cascading ports, and in this way the interoperation between the devices is managed. A multicast cascading port corresponds to a physical port (the channel for carrying services can be created through the port VLAN or service stream). The following figure shows the relationship between the multicast cascading port and the multicast upstream port.
    
  • IGMP control message
    In the multicast cascading scenario, the upper-layer device and the lower-layer device run the IGMP protocol stack separately. For a device, the cascading port (its lower-layer device) can be regarded as the multicast user. Multicast users are controlled by the lower-layer device and therefore the device does not support the following service functions for multicast users: rights management, multicast preview, multicast CAC, charging, and multicast service acceptance. The device supports the fast leave and normal leave functions.
    On the cascading port, the IGMP protocol stack is based on different VLANs, as shown in the following figure.
    
    
    
    NOTE:

    If an Ethernet port is not configured as the multicast cascading port, the Ethernet port discards the IGMP report message.
    The (SIP, GIP) field of the IGMP message and the VLAN of the IGMP message are used for program matching. The policy of processing unmatched messages can be configured based on the cascading port.
    Considering the IGMP processing performance of the source node, it is recommended that all cascading devices adopt IGMP proxy instead of IGMP snooping.
  • Multicast data forwarding
    Multicast data can be forwarded only in a VLAN. According to different cascading boards, there are two forwarding architectures.
    
    • One-level forwarding architecture: The following figure uses the control board as an example.
      
      
      
    • Two-level forwarding architecture: The following figure uses the H901OXHD board as an example.
      
      
      
• xPON cascading [OLT]
  xPON cascading meets the requirements for multicast services in the FTTC/FTTB scenario.
  
  • Multicast cascading port configuration
    The device can implement the physical connection between the OLT and the MxU by using the PON line. Similar to Ethernet cascading mode, in xPON cascading mode, the interconnection between devices is also managed through the multicast cascading port object. One xPON cascading port corresponds to a logical interface (GEM port or LLID). The actual bearer channel can be created by using the service port. The following figure shows the relationship between the xPON cascading port and upstream port.
    
    
    
  • IGMP control packet
    In the xPON cascading scenario, the OLT and the MxU run the IGMP protocol stack separately. Like Ethernet cascading, xPON cascading supports normal leave and fast leave.
    On the multicast cascading port, the IGMP protocol stack is based on different VLANs, as shown in the following figure. Different from Ethernet cascading, in xPON cascading, the bearer channel is limited by the maximum number of service ports that can be created on each GEM port or LLID, because the bearer channel is based on the service port. To support an MVLAN that is beyond the supported specifications, you can configure multiple GEM ports or LLIDs.
    
    
    
  • Multicast data forwarding
    xPON cascading supports forwarding in the same VLAN and does not support cross-VLAN forwarding.
    

NOTE:

Service ports that adopt traffic classification by two-tagged VLANs do not support multicast cascading ports.

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