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Brew

Brew

TETRA Homebrew Protocol

Protocol is based on WebSocket version 13 (RFC 6455) without extensions. It's highly recommended to use socket options TCP_NODELAY and TCP_QUICKACK.

Endpoint, authentication

To establish a new connection client should make a HTTP GET call to get web socket's endpoint and pass authentication procedure. Authentication is based on HTTP Digest Access Authentication (RFC 2831). As a result of successful authentication server returns HTTP 200 and a URI to an endpoint to be used for WebSocket connection.

GET /brew/ HTTP/1.1


HTTP/1.1 200 OK

/brew/722e2b04-07ad-4976-ac55-75e845ae4d8a

Server supports following response codes: 101, 200, 401, 403, 404, 429, 500.

WebSocket transport layer

Client should support following frame opcodes:

  • Close, ping, pong. Ping and pong messages might contain a payload to measure delays.
  • Single-frame masked and unmasked binary messages. Server always send unmasked messages, client may send masked messages.

Binary messages

Every message contains two-byte prefix:

  1. Message class
  2. Message type

All following data has non-aligned values in Little-Endian order

Mobility and affiliation (message class 0xf0)

TBD

Call control (message class 0xf1)

#define CALL_STATE_GROUP_TX         2   // | Simplified
#define CALL_STATE_GROUP_IDLE       3   // |   Group Call

#define CALL_STATE_SETUP_REQUEST    4   // |                | Origin -> Receiver
#define CALL_STATE_SETUP_ACCEPT     5   // |                | Origin <- Receiver
#define CALL_STATE_SETUP_REJECT     6   // | General        | Origin <- Receiver
#define CALL_STATE_CALL_ALERT       7   // |   Circuit Call | Origin <- Receiver
#define CALL_STATE_CONNECT_REQUEST  8   // |                | Origin <- Receiver
#define CALL_STATE_CONNECT_CONFIRM  9   // |                | Origin -> Receiver
#define CALL_STATE_CALL_RELEASE     10  // |                |

#define CALL_STATE_SHORT_TRANSFER   11  // 

#define CALL_STATE_SIMPLEX_GRANTED  12  // | Simplex Call
#define CALL_STATE_SIMPLEX_IDLE     13  // |   (on top of Circuit Call)

#define CALL_STATE_PDP_REQUEST      14  // |
#define CALL_STATE_PDP_ACCEPT       15  // | Packed Data
#define CALL_STATE_PDP_REJECT       16  // |
#define CALL_STATE_PDP_RELEASE      17  // |

TBD

Voice and data frames (message class 0xf2)

#define FRAME_TYPE_TRAFFIC_CHANNEL  0
#define FRAME_TYPE_SDS_TRANSFER     1
#define FRAME_TYPE_SDS_REPORT       2
#define FRAME_TYPE_DTMF_DATA        3
#define FRAME_TYPE_PACKET_DATA      4

struct BrewFrameData
{
  uint8_t kind;       // 0xf2
  uint8_t type;       // FRAME_TYPE_*
  uuid_t identifier;  // Call session UUID
  uint16_t length;    // Length of following data in bits
  uint8_t data[0];
} __attribute__((packed));
FRAME_TYPE_TRAFFIC_CHANNEL

The audio frame contains 60 ms of audio in format, based on STE defined at ETSI TS 100 392-3-6 V1.1.1 (2003-12)

  • Octet 0: bit 7 = 1 (0x80), bita 6-2 = 4 STE control bits C1-C5, bits 1-0 = 0
  • Octet 1+: 137 bits of ACELP subframe 1
  • Octet 18+: 137 bits of ACELP subframe 2 (shifted by 1 bit right)
  • Octet 35: Bitsbits 7-6 = the rest of subframe 2, bits 5-0 = unused, 0x3f
FRAME_TYPE_SDS_TRANSFER

Data field contains full SDS Type 4 PDU. So the first octet of data should contain protocol identifier, defined at ETSI TS 100 392-2 V3.9.1 (2019-01), Table 29.21

FRAME_TYPE_SDS_REPORT

This frame indicates SDS delivery and NOT SDS-TL delivery report. Data contains single-byte status code:

  • 0 = Success
FRAME_TYPE_DTMF_DATA

Data field contains single DTMF code encoded in ASCII: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '*', '#', 'A', 'B', 'C', 'D' 

FRAME_TYPE_PACKET_DATA

Data field contains an IPv4 or IPv6 packet

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