Grandstream Networks HT812 - Upgrading and Provisioning; Firmware Upgrade Procedure

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HT812/HT814 User Guide
DTMF Methods
The HT812/HT814 support the following DTMF mode:
 DTMF in-audio
 DTMF via RTP (RFC2833)
 DTMF via SIP INFO
Set priority of DTMF methods according to your preference. This setting should be based on your server
DTMF setting.
Preferred Vocoder (Codec)
The HT812/HT814 support following voice codecs. On Profile pages, choose the order of your favorite
codecs:
 PCMU/A (or G711µ/a)
 G729 A/B
 G723.1
 G726 (16/24/32/40)
 iLBC
 OPUS