Impact of Articulation Samples and Packet Admeasurement on Bandwidth
Voice sample admeasurement is a capricious that can affect absolute bandwidth used. A articulation sample is
defined as the agenda achievement from a codec’s DSP encapsulated into a agreement abstracts unit
(PDU). Cisco uses DSPs that achievement samples based on digitization of 10 ms account of
audio. Cisco articulation accessories encapsulates 20 ms of audio in anniversary PDU by default,
regardless of the codec used. You can administer an alternative agreement command to vary
the cardinal of samples encapsulated. When you abbreviate added samples per PDU, the
total bandwidth is reduced. However, encapsulating added samples per PDU comes at the
risk of beyond PDUs, which can account capricious adjournment and astringent gaps if PDUs are dropped.
Table 2-5 demonstrates how the cardinal of packets appropriate to address one additional of
audio varies with articulation sample sizes.
Table 2-5 Impact of Articulation Samples
Codec Bandwidth (bps) Sample Admeasurement (Bytes) Packets
G.711 64,000 240 33
G.711 64,000 160 50
G.726r32 32,000 120 33
G.726r32 32,000 80 50
G.726r24 24,000 80 25
G.726r24 24,000 60 33
G.726r16 16,000 80 25
G.726r16 16,000 40 50
G.728 16,000 80 13
G.728 16,000 40 25
G.729 8000 40 25
G.729 8000 20 50
G.723r63 6300 48 16
G.723r63 6300 24 33
G.723r53 5300 40 17
G.723r53 5300 20 33
Using a simple formula, it is accessible for you to actuate the cardinal of bytes encapsulated
in a PDU based on the codec bandwidth and the sample admeasurement (20 ms is the default):
Bytes_per_Sample = (Sample_Size * codec_Bandwidth) / 8
If you administer G.711 numbers, the blueprint reveals the following:
Bytes_per_Sample = (.020 * 64000) / 8
Bytes_per_Sample = 160
Notice from Table 2-5 that the beyond the sample size, the beyond the packet, and the fewer
the encapsulated samples that accept to be beatific (which reduces bandwidth).