We described a method for calculating the capacity of PTP 600/650/700/800 links when the traffic consists of uniform small packet sizes in Does PTP 650/700 have a packets per second limit?
Some operators prefer to calculate capacity for an arbitrary mix of different packet sizes that approximately represents the traffic in the network. This is sometimes call an Internet mix or IMIX. For example, one possible recipe for an IMIX is:
- Seven IP packets of 40 bytes
- Four IP packets of 576 bytes
- One IP packet of 1500 bytes
We can calculate the capacity of a PTP link operating with this IMIX relative to the published capacity of the same link with 1518 byte Ethernet frames (from the User Guide or from LINKPlanner) using the following approach:
The size of the Ethernet frame is the size of the IP packet plus 18 bytes for Ethernet headers, but no less than 64 bytes.
The PTP headers are the overhead in the PTP wireless MAC layer at two bytes for each Ethernet frame transmitted.
The capacity of the link with the IMIX, relative to the capacity for 1518 byte frames is:
This shows that the reduction of capacity arising from testing with the IMIX is less than 0.5%.