Affect of Jitter and Packet loss in fax transmission using T.38 protocol

Recently we made an investigation that how higher jitter and packet loss affect fax transmission resulting in high number of dropped faxes. One of our customer has persistent complain about high number of dropped faxes on one of his ICTBroadcast (asterisk ) server among three that motivated us to plan a through investigation in this regard.

The customers has three ICTBroadcast ( asterisk ) servers in production with each server capable to broadcast 500 concurrent outbound fax calls over T.38 protocol and one server among these three has issue of high number of dropped faxes,

We have developed and installed a script on all three servers, to monitor QoS of underlying network. After running that script for two days, we had enough data to reach a conclusion that issue of high number of dropped faxes is related to underlying network performance rather than software related also we are pleased to share our findings with you for your feedback.

Following, we have prepared a table showing network statistic for all three servers also we named these servers as Server A, Server B and Server A . Server A is the server which has been reported as high number of dropped Faxes.

After analysis , We found that server-A has much higher jitter ratio and at least double packet loss ratio as compared to other servers.


To confirm these results , we have compared network statistics of "individual calls". in following image, we have arranged / grouped answered calls in two categories i.e calls with successful fax delivery, and calls with broken fax. Again we see that calls with broken fax are having at least 4 times higher jitter and packet loss ratio when compared with successful calls .