Lancom Systems LCOS 3.50 User Manual
Page 180
LANCOM Reference Manual LCOS 3.50
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Chapter 9: Quality of Service
180
Quality of
Service
In detail, delay is determined especially by the codec used, the resulting
packet size and the available bandwidth:
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The time for processing is determined by the used codec. For a sampling
time of 20 ms, exactly each 20 ms a new packet is generated. Times for
compression can mostly be neglected.
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The time for handing over the packet to the interface is defined by the
quotient of packet size and available bandwidth:
A 512 byte packet of an FTP connection occupies the line at 128 Kbps
upstream for at least 32 ms.
Besides, the packets of the VoIP connection are often much larger than
the pure net payload. The additional headers of the IP and Ethernet pack-
ets, as well eventual IPsec headers have to be added as well. The net load
results from the product of net data rate and sampling time of the used
codec. For all codecs, each 40 bytes UDP header and at least 20 bytes for
Packet size in bytes
1
64
128
256
512
1024
1500
56 Kbps
0,14
9
18
36
73
146
215
64 Kbps
0,13
8
16
32
64
128
187
128 Kbps
0,06
4
8
16
32
64
93
256 Kbps
0,03
2
4
8
16
32
47
512 Kbps
0,016
1
2
4
8
16
23
768 Kbps
0,010
0,6
1,3
2,6
5
11
16
1536 Kbps
0,005
0,3
0,6
1,3
3
5
8
150ms
In comparison: satellite quality
Processing
Serialization
Propagation
Jitter buffer