Skype - 2.0 Betriebsanweisung PDF herunterladen (Seite 14)

Page 14 IT Administrators Guide

2.2.5 Network impact

Skype is uniquely designed to function over corporate networks with little impact on their

performance. Providing specic details of the performance you can expect is difcult,

given the range of Skype tools that could be in use. It also depends on the size of your

Contacts list, how frequently the list is updated, and other factors. However, here are

some very broad gures to help you design your corporate network.

Skype high denition audio is based on SILK™, our own high performance wideband

codec. The codec can work on various sampling rates, from 8 to 24 kHz, yielding bit rates

of 6 to 40 Kbits/s:

Sampling Rate

(kHz)

Bit Rate

(kbps)

CPU

(MHz on x86 core)

Narrowband for PSTN gateways

and low-end devices

8 6 – 20 12 – 30

Mediumband for devices with

limited wideband capacity

12 7 – 25 16 – 40

Super-wideband, a new standard

in speech quality

24 12 – 40 30 – 80

SILK provides superior performance over other codecs, as these tests show:

Bit Rate (kbps)

04 0

MOS

SourceSilk AMR-WB Speex

Packet Loss (%)

05 2

MOS

SourceAMR-WB SpeexSilk

23.0518.2512.658.85

Ofce Noise, 15 dB SNR Source SILK AMR-WB Speex

MOS 3.30 3.22 3.14 2.74

The MOS (Mean Opinion Score) listening test was performed by DynaStat, an independent third-party laboratory.

Confidence intervals (95%) are +/- 0.1 MOS. All bitrates are measured and averaged over frames containing active speech.

SILK and Speex were run in the highest complexity mode and with variable bitrate. Packet loss and office noise tests were

done with all codecs running at 18.25 kbps.

Video quality can vary signicantly with trafc conditions. You should plan on at least 128

Kbits/s for each session, though we recommend 384 Kbits/s and above. For an HD (720p)

video call on Skype, at least 1 Mbps symmetrical bandwidth is required. Status controls

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