IP Multicast

PerformanceGuard can collect statistics about IP multicast UDP messages. Such multicast messages are unacknowledged (that is receivers don't confirm that they have received the messages).

Therefore, PerformanceGuard doesn't measure:

• Multicast response times
• Multicast network transmission times

but it does measure:

• The number of packets sent and received as multicast messages
• The number of bytes sent and received as multicast messages

A packet is considered a multicast packet if the destination IP address is in the range 224.0.0.0 to 239.255.255.255.

The illustration (click thumbnail to view image in full size) shows how multicast messages are routed.The illustration shows how multicast messages are routed. The two servers in the top part of the drawing send multicast messages on two different IP addresses. The multicast subscribers use ICMP messages to let routers know which multicast addresses they want to subscribe to. The routers are then able to calculate which multicast messages they need to send on their different interfaces.

PerformanceGuard measures multicast UDP packets when they are sent and when they are received. PerformanceGuard consolidates statistics on multicast addresses and ports for an entire reporting interval. Statistics about sent and received multicast packages are always kept separately. For received multicast messages, PerformanceGuard registers the address of the sender in addition to the multicast IP address and UDP port.