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Chapter 4
Business Features Package
Voice Mail: In-band Integration
The system uses DTMF tones (in-band signalling) to communicate with any compatible voice
mail system. Stations can call forward to a voice mail system. When answered, the system
will send DTMF tones routing the caller directly to the called station user’s mailbox. Keyset
users can press a key to retrieve messages from the voice mail system. A Voice Mail Trans-
fer (VT) key permits keyset users to easily transfer a caller directly to an individual voice
mailbox without navigating through menus.
Voice over IP (VoIP)
The ITM3 VoIP card supports up to 8 voice calls over an IP network connection using the in-
dustry standards-based H.323 protocol. The ITM3 card fits into any universal card slot in the
Basic KSU.
VoIP is transported by the ITM3 card using the ITU standards-based H.323 protocol. This
standard addresses the means of transferring voice, data and images through IP (Internet
Protocol) networks.
With VoIP, certain compression standards have also been adopted to represent each second
of voice with an amount of bandwidth. The ITM3 uses G.711, G.729A or G.723 standards
voice compression codecs. This allows for a selectable 64kbps, 8kbps or 6.3kbps bandwidth
when preparing voice compression for IP transport. Compression is used to reduce the digi-
tized voice into a smaller bandwidth that can be carried in smaller packets.
The ITM3 H.323 gateway determines the compression method for each call setup. There is
also a certain amount of frame/packet overhead in each compression channel. 64k of band-
width can nominally support 6–7 calls simultaneously. This can vary depending on efficiency
features like Silence Suppression and multiframe counts. Unlike switched networks, VoIP
connections consist of a sequence of numbered data packets. Since voice conversation is
usually considered "real time" these packets need to be delivered in a consistent manner
with minimal delay. This can be controlled via a Gatekeeper which tracks and monitors voice
packets. Gatekeepers are part of the H.323 standard but are not mandatory.
The ITM3 is Gatekeeper compliant. In any Ethernet environment, packet transfers are sub-
ject to delays and/or loss. If these delays are greater than 200ms the voice quality will dete-
riorate. The Ethernet data traffic and network topology should be a consideration when apply-
ing the VoIP feature. Network congestion affects call quality in any VoIP application.
Walking Class of Service (WCOS)
This feature allows users to make calls or use features from a station that is normally re-
stricted. The feature is similar to the Authorisation Code
feature. Both methods change the
class of service to correspond with the station passcode or authorisation code that is dialled.
After the call is completed, the station returns to its programmed class of service.