I found answer to my own Q:
Bandwidth estimation for a connection using compressed speech can be calculated by Activity Factor (AF) as follow
BW=AF×bitrate(Speech)+(1-AF)×bitrate(Silence)
Where
BW=Bandwidth on L2 Layer
AF=Percentage of Activity Factor–>(1-AF) =Percentage of Silence
Bitrate
On Ethernet Link Layer:
Bitrate=(payload Size + IP header + Ethernet Framing) × Tx Rate
On IP Backbone (MPLS) Link Layer:
Bitrate= (payload Size+ IP Header + L2 Overhead) × Tx Rate
Where
TX Rate= Transmission Rate/ Packetization
Ex: A Speech Call on NB with AF=60% and using AMR 12,2 mode consume a following bandwidth (Ethernet + VLAN)
BW=(60*46.8kbps+(100-60)*4.6kbps)/100=29.9kbps
where
bitrate(Speech)= (35+40+42 bytes)* 50/s=46.8kbps
bitrate(Speech)= (9+40+42 bytes)* 6.25/s=4.6kbps
Now if occupied BW=46,8M then Virtual Channels = 46,8m/46.8=1000
For Calculating Erl we need number of channels and GOS- so very easy Carried Erlang is obtained–>ErlangTraffic(N,GOS) where GOS=.001