Page 118 - | Appendix A: General Information |
Voice-Over-IP
The IPNCs
The IPNC can implement QoS for digital serveices on all INDeX line types, including
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 |
38DHB0002UKDD – Issue 7 (22/11/02) |