Lectures notes for 2010 - KTH

Cisco 3800 supports even more CODECs:
• ITU G.726 standard, 32k rate
• ITU G.726 standard, 24k rate
• ITU G.726 standard, 16k rate
• ITU G.728 standard, 16k rate (default)
• ITU G.729 standard, 8k rate
By using Voice Activity Detection (VAD) - you only need to send traffic if there
is something to send.
An interesting aspect is that user’s worry when they hear absolute silence, so to
help make them comfortable it is useful to play noise when there is nothing to
output. Cisco provide a “comfort-noise command to generate background noise
to fill silent gaps during calls if VAD is activated”.
Cisco 3600 series router can be used as the voice gateway with software such as
Microsoft NetMeeting.
Cisco 3800 also supports “fax-relay” - at various rates either current voice rate or
Maguire Cisco Voice Over IP 9: 45 of 71
maguire@kth.se 2010.03.21 Internetworking/Internetteknik