If both Skype clients were on machines with public IP addresses, then media traffic flowed directly between them over UDP.
The media traffic flowed to and from the UDP port configured in the options dialog box.
The voice packet size varied between 40 and 120 bytes.
For two users connected to Internet over 100 Mb/s Ethernet with almost no congestion in the network, roughly 85 voice packets were exchanged
both ways in one second. The total uplink and downlink bandwidth used for voice traffic was 5 kilobytes/s.
This bandwidth usage agrees with the Skype claim of 3-16 kilobytes/s.
If either caller or callee or both were behind port-restricted NAT, they sent voice traffic to each other.
The voice packet size varied between 40 and 110 bytes, which is the size of UDP payload.
The bandwidth used was about 5 kilobytes/s.
If both users were behind port-restricted NAT and UDP restricted firewall, then caller and callee sent and received voice traffic over TCP from another online Skype node.
The TCP packet payload size for voice traffic varied between 30 and 90 bytes.
The total uplink and downlink bandwidth used for voice traffic was about 5.5 kilobytes/s.
(form a study of An Analysis of the Skype)
so your regexp is for what (registration, communication, …) ?
and why you use packet-size=39 ?