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Page 118 - Voice-Over-IP Appendix A: General Information
Voice-Over-IP
The IPNCs Voice-over-IP (VoIP) technology enables a data network to carry
voice traffic along with data. Support of compression, Quality of Service (QoS)
and echo cancellation technology ensures that speech quality is optimised. Voice
compression is supported on four variants of the IPNC (IPNC-VC, IPNC-M-VC,
IPNC-VC5 and IPNC-M-VC5). Each IPNC is capable of compressing either 5 or
20 simultaneous calls using a choice of industry standard algorithms.
The IPNC can implement QoS for digital serveices on all INDeX line types,
including point-to-point, WAN linkls, Frame, Relay, DPNss, Sig and BRI.
However, where density of calls is a prime requirement and IP (data) connectivity
is not, then it may be more appropriate to use the INDeX Voice Compression
Cassette (VCC).
Implementation Considerations
Bandwidth Requirements
There are two methods of connecting INDeXs using VoIP:
1) Using a directly connected Wide Area Network
2) Using an indirectly connected Wide Area Network.
See Bandwidth Requirements Calculations on page101 for details.
Voice Prioritisation
Each voice packet transmitted by the IPNC has the TOS field marked to indicate
its priority (Diffserv). When using an indirectly connected WAN all devices should
be capable of handling marked traffic at a priority to ensure prompt handling of
voice calls. Alternatively, over supplying the available bandwidth can ensure all
packets, voice and data, are handled quickly. The IPNC can also set the
maximum number of simultaneous voice calls. In a directly connected WAN, this
coupled with Diffserv has the effect of managing bandwidth, i.e. if there are no
voice calls in progress data will be allowed to occupy the full capacity of the link.
Each voice call initiated will then push back the data occupancy up to the
maximum allowed number of voice connections. In this manner it is possible to
guarantee the bandwidth available to voice and data.
Sending Voice over an Ethernet Connection
Whenever voice calls are sent over an Ethernet connection, as in the indirectly
connected WAN scenario and IP Extensions, consideration should be given to
Ethernet collisions. If there are too many devices sharing a segment collisions
can cause interruption to voice traffic. This can be simply addressed by allocating
the IPNC LAN port and the WAN routers a dedicated port on a LAN Switch.
Page 118 - Appendix A: General Information INDeX IPNC Cassette Administration Manual
Voice-Over-IP 38DHB0002UKDD – Issue 7 (22/11/02)