Nortel VoIP Gateway, Configuration Manual

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Network engineering 155
Norstar VoIP Gateway Configuration Guide
The peak bandwidth and average bandwidth requirements for a normal two-way call must take
into account the affects of full and half duplex links and the affects of silence suppression. Refer to
the tables in the next two sections
, below, and to Table 28 on page 157 for voice Gateway
bandwidth requirements.
Peak bandwidth is the amount of bandwidth that the link must provide for each call. Considering
voice traffic only, the number of calls a link can support is:
Number of Calls = Usable Link Bandwidth / peak Bandwidth per call
The average bandwidth takes into account the affects of silence suppression, which, over time,
tends to reduce bandwidth requirements to 50% of the continuous transmission rate. The affects of
silence suppression on peak bandwidth requirements differ depending on whether the link is
half-duplex or full-duplex. See
Appendix C, “Silence compression,” on page 167 for more
information.
When engineering total bandwidth requirements for LANs and WANs, additional bandwidth must
be allocated for data. Refer to standard Ethernet engineering tables for passive 10BaseT repeater
hubs. Refer to the manufacturer’s specification for intelligent 10BaseT layer switches. WAN links
must take into account parameters such as normal link utilization and committed information rates.
Bandwidth requirements on half duplex links
The following table provides bandwidth requirements for normal two-way voice calls on a
half-duplex link for a variety of link protocols, codec types and payload sizes.
G.723.1 (5.3 kb/s) 30 20 60 22.9 16.5 18.4
* Ethernet bandwidth includes the 14 byte Ethernet frame overhead plus a 12-byte inter-frame gap.
Table 26 VoIP Transmission Characteristics for unidirectional continuous media stream (Continued)
Codec Type Payload Size IP Packet Ethernet B/W* PPP B/W FR B/W
ms Bytes Bytes kbit/s kbit/s kbit/s