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Intel
®
IXP400 Digital Signal Processing (DSP) Software Version 2.5
Packet Data Interface
36 API Reference Manual
7.0 Packet Data Interface
The packet data interface is a protocol for the Intel
®
IXP400 DSP Software to exchange the encoded
data packets with IP stack. This interface is defined as a packet format and two callback functions –
one is provided by DSP software release and another is provided by the user (IP stack).
7.1 Packet Formats
The ingress packet from the IP stack to the DSP software has an 8-byte header as shown below:
Similarly, the egress packet from the DSP software to the IP stack has an 8-byte header as shown
below:
The fields of the packet header and the payload are described as:
31 24 23 22 16 15 12 11 8 7 0
Channel ID M Payload Type Media Payload Length
Remote Time Stamp
:
Payload
:
31 24 23 22 16 15 12 11 8 7 0
Channel ID M Payload Type Media Payload Length
Local Time Stamp
:
Payload
:
Field Description
Local Time Stamp Packet arrival time as measured by a local clock.
Remote Time Stamp Packet data sampling time measured by a remote clock.
Payload Length Payload length in bytes.
Media
4-bit media type field is defined as:
• 0x01 – Audio
• 0x02 – Tone (RFC 2833 event type)
• 0x04 – Tone (RFC 2833 tone type)
• 0x08 – T.38 UDP
• 0x09 – T.38 TCP
M
Marker bit for the RTP packet. This bit set indicates the first speech packet after a
silence period or the first packet of a RFC-2833 tone event, otherwise 0.
Payload type RTP payload type as defined in RFC 1990.
Payload Encoded audio data or RFC-2838, tone-event information.