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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
User-Agent: TETRAHS/012345


HTTP/1.1 200 OK

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

Server supports following response codes: 101 (Switching protocols), 200 (OK), 301 (Moved), 401 (Unauthorized), 403 (Forbidden), 404 (Not found), 426 (Upgrade required), 429 (Too many requests), 500 (Internal server error).

HTTP header 'User-Agent' is mandatory!

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

Subscriber control (mobility and affiliation, message class 0xf0)

#define BREW_SUBSCRIBER_DEREGISTER   0
#define BREW_SUBSCRIBER_REGISTER     1
#define BREW_SUBSCRIBER_REREGISTER   2
#define BREW_SUBSCRIBER_AFFILIATE    8
#define BREW_SUBSCRIBER_DEAFFILIATE  9

struct BrewSubscriberData
{
  uint8_t kind;        // 0xf0
  uint8_t type;        // BREW_SUBSCRIBER_*
  uint32_t number;     // ISSI
  uint64_t time;       // UNIX timestamp
  uint32_t fraction;   // Nanoseconds
  uint32_t groups[0];  // GSSIs (BREW_SUBSCRIBER_AFFILIATE / BREW_SUBSCRIBER_DEAFFILIATE)
} __attribute__((packed));

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  // |

#define PDP_FLAG_IPV4               (1 << 0)
#define PDP_FLAG_IPV6               (1 << 1)

struct BrewCircularCall
{
  uint32_t source;
  uint32_t destination;
  char number[32];        // External number (ASCII)
  uint8_t priority;       // Call priority
  uint8_t service;        // Table 14.79: Speech service
  uint8_t mode;           // Table 14.52: Circuit mode type
  uint8_t duplex;         // Duplex flag
  uint8_t method;         // Table 14.62: Hook method
  uint8_t communication;  // Table 14.54: Communication type
  uint8_t grant;          // Table 14.80: Transmission grant
  uint8_t permission;     // Table 14.81: Transmission request permission
  uint8_t timeout;        // Table 14.50: Call time-out
  uint8_t ownership;      // Table 14.38: Call ownership
  uint8_t queued;         // Table 14.48: Call queued
} __attribute__((packed));

struct BrewCircularGrant
{
  uint8_t grant;          // Table 14.80: Transmission grant
  uint8_t permission;     // Table 14.81: Transmission request permission
} __attribute__((packed));

struct BrewGroupTransmission
{
  uint32_t source;
  uint32_t destination;
  uint8_t priority;       // Call priority
  uint8_t access;         // Access priority
  uint16_t service;       // Table 14.79: Speech service
} __attribute__((packed));

struct BrewShortData
{
  uint32_t source;
  uint32_t destination;
  char number[32];        // External number (ASCII)
} __attribute__((packed));

struct BrewPacketRequest
{
  uint32_t number;           // ISSI
  uint8_t flags;             // PDP_FLAG_*
  uint32_t profile;          // GSM 04.08 QoS Profile
  uint8_t authenticator[0];  // CHAP Challenge + CHAP Response
} __attribute__((packed));

struct BrewPacketContext
{
  uint8_t flags;          // PDP_FLAG_*
  in_addr_t v4;           // IPv4
  struct in6_addr v6;     // IPv6
  uint32_t profile;       // GSM 04.08 QoS Profile
} __attribute__((packed));

struct BrewCallControlData
{
  uint8_t kind;       // 0xf1
  uint8_t type;       // CALL_STATE_*
  uuid_t identifier;  // Call session UUID
  union
  {
    uint8_t cause;    // Table 14.55: Disconnect cause / GTP cause (ETSI TS 29.060 v3.9.0 7.7)
    struct BrewShortData data;
    struct BrewCircularGrant grant;
    struct BrewCircularCall circular;
    struct BrewGroupTransmission group;
    struct BrewPacketRequest request;
    struct BrewPacketContext context;
  };
} __attribute__((packed));
CALL_STATE_GROUP_TX

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(struct BrewGroupTransmission)

CALL_STATE_GROUP_IDLE, CALL_STATE_SETUP_REJECT, CALL_STATE_CALL_RELEASE

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(uint8_t)

CALL_STATE_SETUP_ACCEPT, CALL_STATE_CALL_ALERT

Length and contents: offsetof(struct BrewCallControlData, data)

CALL_STATE_SETUP_REQUEST, CALL_STATE_CONNECT_REQUEST

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(struct BrewCircularCall)

CALL_STATE_CONNECT_CONFIRM, CALL_STATE_SIMPLEX_GRANTED, CALL_STATE_SIMPLEX_IDLE

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(struct BrewCircularGrant)

CALL_STATE_SHORT_TRANSFER

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(struct BrewShortData)

CALL_STATE_PDP_REQUEST

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(struct BrewPacketRequest) + len(CHAP_Challenge) + len(CHAP_Response)

BrewPacketRequest.authenticator[] contains two CHAP packets: challenge and response (RFC 1994).

CALL_STATE_PDP_ACCEPT

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(struct BrewPacketContext)

CALL_STATE_PDP_REJECT, CALL_STATE_PDP_RELEASE

Length and contents: offsetof(struct BrewCallControlData, data) + sizeof(uint8_t)

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: bits 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

Errors (message class 0xf3)

#define BREW_TYPE_MALFORMED          0
#define BREW_TYPE_RESTRICTED         1

struct BrewErrorData
{
  uint8_t kind;       // 0xf3
  uint8_t type;       // BREW_TYPE_*
  uint8_t data[0];
} __attribute__((packed));
BREW_TYPE_MALFORMED, BREW_TYPE_RESTRICTED

Data field contains malformed message content

Service messages (message class 0xf4)

struct BrewServiceData
{
  uint8_t kind;       // 0xf4
  uint8_t type;       // 
  char data[0];       // JSON + NULL
} __attribute__((packed));

NULL-terminator at the end of JSON is mandatory!

Query subscribers (message type 1, client -> server)
[
  1234567  // List of ISSIs to query
]

On success server will respond with subscriber profiles list (see message type 2)

Subscriber profiles (message type 2, server -> client)
{
  "1234567" :  // ISSI
  {
    "call" : "N0CALL",                      // Callsign (optional)
    "active" : true,                        // When blocked will be false (optional)
    "status" : 1,                           // Registration status (when registered)
    "date" : "2025-03-10T00:00:00.000000Z"  // Last update date and time (when registered)
  }
}

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