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Static Multicast Forwarding
Source: Lantech
In the field of industrial Ethernet, managing the multicast datagram by IGMP is a mature consensus for on-site system integrator. However, would IGMP be able to satisfy by transportation surveillance project based on its video stream management?

Implication of MRT Surveillance:
MRT (Mass Rapid Transit) is one of the significant transportation in daily life. However, a mass population relies on the surveillance system by the demanding of security either on platform or the gateway of the train. The system is to ensure the real time alert, thus providing the user with an opportunity to evaluate the incident and take preventive action if necessary. The surveillance devices enhanced the quality and maintenance of transportation environment.
Because of the multiple monitoring spots with deficiency of labor resources, majority of MRT surveillance system are digitalized to comply with SMART AI Management System in order to assist on-site system integrator, so that the video stream transmission by IP is a primary application for surveillance in MRT system. Consequently, to advance the stability of digital transmission and quality as well as supply the high resolution is the main factor of being a successful project in surveillance industry.
In most of surveillance examples, data of video stream are transmitted by muticast packet, yet it depends on the IGMP of switch to manage the Multicast datagram effectively. IGMP (Internet Group Management Protocol) is a part of IP protocol, which is one of the querior in subnet, to communicate the packet group with the server. It activates the querior to memorize that which server currently belongs to which multicast group so that the switches will be messaged to transmit the multicast packet to certain specified servers. In other words, the functionality of IGMP is to recognize and manage the multicast address in network structure.

IGMP Bottlenecks:
Among the applications, the video streams are not completely managed by IGMP. For example, each IP camera in MRT system has to transmit the data to SMART AI Management System and video server simultaneously. The system manager monitors the area via video server and being minded by AI Management System once incident occurred. Thus, the amount of digital data from independent IP camera are transmitted to AI Management System and video server in the same time to ensure both sides acquire the data synchronously. In this condition, switches manage the multicast datagram through IGMP as result of IP cameras have to apply multicasting. However, under the IGMP snoop management, each set of video resource (IP camera) has to establish one IGMP group, and there are 126 units of IP cameras in MRT station, which turns out to 126 sets of IGMP group. A large amount of IGMP groups would cause the follow issues:
1. Large quantity of IGMP groups causes time consumption for users to ensure that all IP cameras have to create their IGMP groups in the right way.
2. Lots of processing resources are needed for switches to maintain amount of IGMP groups.
3. The multicast IP address is very easy to be duplicated accidently when IGMP group is re-built due to the IP cameras being moved or replaced.

Static Multicast Forwarding:
From above concerns, the users bring up their requests to reduce the tasks. The multicast clients are stationary so that it doesn’t need to send the query message by IGMP protocol. The users request that the switches have to be capable of transmitting or the multicast datagram to indicated port to avoid flooding the other undedicated port while some IP cameras have been replaced. Meantime, the switches must support Static Multicast Forwarding function to route the multicast datagram to fixed switch port. Comparing the IGMP Snooping, the relation between IGMP Snooping and Static Multicast Forwarding equivalents to the Address Learning and Static MAC Forwarding in MAC Table. IGMP snooping activate automatically and deliver the corresponding multicast packet to an appropriate port; in contrast, Static Multicast Forwarding is manually to deliver the multicast packet to indicated port.

Advance Static Multicast Forwarding
In large-scale of MRT surveillance project, there will be more than one set of SMART AI Management and video server to perform the demands of Load balance and redundancy. Thus, switch devices must have capabilities of not only for Static Multicast Forwarding but configuring each static record for different multicast IP address. Meantime, the multicast data will be transmitted to corresponding switch port by dedicated multicast IP address so it could comply with the demands of load balance and redundancy by users.

From the MRT surveillance application, the amount of video streams are required to transmit to SMART AI Management System and video server simultaneously from each IP camera. Broadcast is not capable due to bandwidth flooding would cause the heavy loading to network throughput. Unicast cannot build the media transmission from one point to more points at the same time. In view of considerations above, the users adopt the multicast to transmit the video stream. During the multicast transmission, the switches must have function to support Static Multicast Forwarding to manage a large amount of multicast IP addresses effectively. Furthermore, in large-scale of transportation project, switch must configure corresponding switch port through unique multicast IP address for fulfilling the demands of load balanc
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