NEC UNIVERGE SV9100 Manual page 12

12
In this case there is only one host on each end of the network which is unrealistic. In reality there
would be many hosts all sending data over the narrow bandwidth. This means that the routers must
buffer the packets and transmit them over the Kilostream as efficiently as possible. When this
occurs, certain packets will be dropped by the router and some packets will be delayed.
For most data applications this packet loss/delay is not critical. For example, it is unlikely to be
noticed if an email takes 1 second or 5 seconds to be transmitted. When VoIP is implemented, this
loss/delay has a massive impact on the voice quality. There will be gaps in speech, distortion and
delay – all of which are unacceptable for voice traffic.
To avoid this problem, it is possible to prioritise the VoIP packets. This means that the router will
examine all packets received, determine what priority level the packet has, and then forward it
accordingly. This of course means that the "data1" will be assigned lower priority and the "voice" will
be transmitted before it. This can have a negative impact on the "data" network if lots of "voice" is
transmitted.
1
Note that this description discusses "voice" and "data". These terms are commonly used when describing QoS,
although in the case of VoIP, the voice is actually converted to IP and transmitted as data. Therefore, everything
transmitted on a Data Network is data, but logically we think of this as "voice" and "data" traffic.
The diagram below shows how a "voice" and "data" network may be implemented.