NEC SL1100, Networking Manual

Page: 247 / 292

NEC SL1100 Issue 6.0
Networking Manual 13 - 5
Below is a table that shows the average bandwidth per VoIP call over Ethernet.
For example, if one site plans on making a maximum of 16 calls across the network
using G.729 with a 30ms packet size, there must be a minimum of 376kbps available
for voice traffic. The QOS policy for this network should allow for 376kbps to be set
aside for voice prioritization.
S
ECTION
4
Q
UALITY OF
S
ERVICE
S
ETTINGS
(QOS)
Quality of Service (QOS) is one of the most important factors for VoIP. QOS is used
to prioritize voice packets over data packets during times of network congestion.
There are many ways that QOS can be implemented in the network and one of the
most common ways QOS is implemented is by using IP Precedence or Diffserv. If the
networks QOS policy is based on IP Precedence or Diffserv then there are settings
required in the SL1100.
Program 84-10 is used to assign the IP Precedence or Diffserv Values per Protocol
Type. For SL Net only two protocol types will be selected. All signaling packets will
be marked with the values assigned for protocol type “H.323”. All voice packets will
be marked with the values assigned for protocol type “RTP/RTCP”.
S
ECTION
5
IP P
RECEDENCE
IP Precedence uses the first 3 bits of the TOS field to give eight possible precedence
values (0 ~ 7). Under normal circumstances the higher the number the higher the
priority. However this is left to the network administrator for setup. When assigning IP
Precedence values (for SL Net) go to program 84-10-01 and change the type from
Disabled to IP Precedence. Then in program 84-10-02 assign the value for the
Table 13-1 Bandwidth per VoIP Call
Codec Packet Size
Bandwidth
Used
Codec Packet Size
Bandwidth
Used
G.711 10ms 110.4kbps G.729 10ms 54.4kbps
G.711 20ms 87.2kbps G.729 20ms 31.2kbps
G.711 30ms 79.5kbps G.729 30ms 23.5kbps
G.711 40ms 75.6kbps G.729 40ms 19.6kbps
G.722 10ms 110.4kbps G.729 50ms 17.3kbps
G.722 20ms 87.2kbps G.729 60ms 15.7kbps
G.722 30ms 79.5kbps G.723 30ms 20.8kbps
G.722 40ms 75.6kbps G.723 60ms 13.2kbps