RAD Data comm Vmux-210 Specifications Page 34

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Chapter 1 Introduction Installation and Operation Manual
1-16 Functional Description Vmux-210 Ver. 1.1
1000 in the denominator – conversion from bits to kilobits
0.00853 – connectivity packets rate (64 bytes per minute) converted to kbps.
A Vmux Bandwidth Calculator tool is included on the Technical Documentation CD.
Bandwidth Utilization when using AAL2oMPLS
When using non-IP based Ethernet networks or the Serial uplink, the AAL2oMPLS
format can be used instead of the TDMoIP multiplexing format. The AAL2oMPLS
header is smaller than the TDMoIP header (23 rather than 50 bytes), saving about
5% in bandwidth when compared to TDMoIP multiplexing (depending on the
actual size of the multiplexed frames).
The actual bandwidth utilization is determined by the following factors:
Header sizes:
Ethernet – 18 bytes
AAL2oMPLS – 5 bytes
Size of the voice packet:
G.723 – 31 bytes (AAL2 header [3 bytes] + voice header [4 bytes] +
compressed voice payload [24 bytes])
G.729 – 17 bytes (AAL2 header [3 bytes] + voice header [4 bytes] +
compressed voice payload [10 bytes]).
Packet interval:
G.723.1 – 30 m
Sec
G.729 – 10 m
Sec.
Number of timeslots in a bundle
Silence percentage. Studies show that an average person speaks only 40% of
the time during a telephone conversation. 50% of the time is spent listening
to the other party, while the remaining 10% is spent quietly contemplating.
Connectivity packets – 64 bytes per minute.
Calculating Approximate Bandwidth Utilization (AAL2oMPLS):
The approximate bandwidth for 30 timeslots in one bundle with G.723.1 (6.4
kbps) compression, 60 % of silence is calculated as follows:
[(23 x 1000/40) + (30 x 31 x 1000/30 x 0.4)] x 8
1000
+ 0.00853 = 103.80853 kbps
}{
where:
23 – size of Ethernet and AAL2oMPLS headers
1000/40 – packets per second (pps) transmission rate, calculated according
to the packetizing interval chosen (40 m
Sec in this example)
30 – number of timeslots
Note
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