CODEC Selection

Owned by Kelly Evans (Unlicensed)
Last updated: Sept 30, 2022 by Rob Whyte (Unlicensed)
2 min read

The Peeredge SBC currently supports the following audio codecs.

G.711ulaw

G.722

G.726-32

G.729.1

L16

iLBC

G.711alaw

G.723

G.726-40

G.729D

L20

PCMA-WB

G.729

G.726-16

G.728

GSM

L24

PCMU-WB

G.719

G.726-24

G.729E

L8

LPC

Speex

 

Most PSTN carriers only offer support for G.711ulaw, G.711alaw, and the G.729 codecs.

For inbound PSTN calls to the customer, by default, the Peeredge SBC only forwards the PSTN vendor-supported codecs to the customer’s SBC/PBX. The Peeredge SBC can be configured to filter out codecs offered by the upstream carrier and/or add additional codecs in the SIP Invite w/SDP offer to the customer SBC/PBX.

For outbound PSTN calls, by default, the Peeredge SBC always selects the first codec in the list of codecs offered in the customer’s SIP Invite w/SDP message that the upstream carrier supports. If there are no upstream carrier-supported codecs in the list of codecs offered in the SIP Invite w/SDP message, then transcoding can be enabled on the Peeredge SBC.

Recommendations

Since most PSTN carriers only support G.711ulaw, G.711alaw, and the G.729 codecs, 46 Labs STRONGLY RECOMMENDS only including these codecs in the SIP Invite w/SDP. Our testing with several enterprise SBC/PBX systems shows there are often hidden design challenges in complex call flows when using codecs not supported by upstream carriers.

When voice quality is the primary design consideration, 46 Labs recommends using the G.711 codec.

When minimizing network bandwidth usage is the primary design consideration, the G.729 codec can be configured as the preferred codec.

The Peeredge SBC does not support video codecs. Video codecs should not be included in the SDP of any SIP messages sent to the Peeredge SBC.

Â