SCO(7)                    Linux System Administration                   SCO(7)

NAME
       sco - SCO transport

SYNOPSIS

          #include <sys/socket.h>
          #include <bluetooth/bluetooth.h>
          #include <bluetooth/sco.h>

          sco_socket = socket(PF_BLUETOOTH, SOCK_SEQPACKET, BTPROTO_SCO);

DESCRIPTION
       The SCO logical transport, is a symmetric, point-to-point transport
       between the Central and a specific Peripheral. The SCO logical
       transport reserves slots and can therefore be considered as a
       circuit-switched connection between the Central and the Peripheral.

       In addition to the reserved slots, when eSCO is supported, a
       retransmission window follows immediately after. Together, the reserved
       slots and the retransmission window form the complete eSCO window.

SOCKET ADDRESS

          struct sockaddr_sco {
              sa_family_t     sco_family;
              bdaddr_t        sco_bdaddr;
          };

       Example:

          struct sockaddr_sco addr;

          memset(&addr, 0, sizeof(addr));
          addr.sco_family = AF_BLUETOOTH;
          bacpy(&addr.sco_bdaddr, bdaddr);

SOCKET OPTIONS
       The socket options listed below can be set by using setsockopt(2) and
       read with getsockopt(2) with the socket level set to SOL_BLUETOOTH.

   BT_SECURITY (since Linux 2.6.30)
       Channel security level, possible values:

       +-------------------+-----------------+-----------------+--------------+
       |Value              | Security Level  | Link Key Type   | Encryption   |
       +-------------------+-----------------+-----------------+--------------+
       |BT_SECURITY_SDP    | 0 (SDP Only)    | None            | Not required |
       +-------------------+-----------------+-----------------+--------------+
       |BT_SECURITY_LOW    | 1 (Low)         | Unauthenticated | Not required |
       +-------------------+-----------------+-----------------+--------------+
       |BT_SECURITY_MEDIUM | 2 (Medium -     | Unauthenticated | Desired      |
       |                   | default)        |                 |              |
       +-------------------+-----------------+-----------------+--------------+
       |BT_SECURITY_HIGH   | 3 (High)        | Authenticated   | Required     |
       +-------------------+-----------------+-----------------+--------------+
       |BT_SECURITY_FIPS   | 4 (Secure Only) | Authenticated   | Required     |
       |(since Linux 3.15) |                 | (P-256 based    |              |
       |                   |                 | Secure Simple   |              |
       |                   |                 | Pairing and     |              |
       |                   |                 | Secure          |              |
       |                   |                 | Authentication) |              |
       +-------------------+-----------------+-----------------+--------------+
       Example:

          int level = BT_SECURITY_HIGH;
          int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_SECURITY, &level,
                               sizeof(level));
          if (err == -1) {
              perror("setsockopt");
              return 1;
          }

   BT_DEFER_SETUP (since Linux 2.6.30)
       Channel defer connection setup, this control if the connection
       procedure needs to be authorized by userspace before responding which
       allows authorization at profile level, possible values:

                     +------+-------------------+---------------+
                     |Value | Description       | Authorization |
                     +------+-------------------+---------------+
                     |0     | Disable (default) | Not required  |
                     +------+-------------------+---------------+
                     |1     | Enable            | Required      |
                     +------+-------------------+---------------+
       Example:

          int defer_setup = 1;
          int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_DEFER_SETUP,
                               &defer_setup, sizeof(defer_setup));
          if (err == -1) {
              perror("setsockopt");
              return err;
          }

          err = listen(sco_socket, 5);
          if (err) {
              perror("listen");
              return err;
          }

          struct sockaddr_sco remote_addr = {0};
          socklen_t addr_len = sizeof(remote_addr);
          int new_socket = accept(sco_socket, (struct sockaddr*)&remote_addr,
                                  &addr_len);
          if (new_socket < 0) {
              perror("accept");
              return new_socket;
          }

          /* To complete the connection setup of new_socket read 1 byte */
          char c;
          struct pollfd pfd;

          memset(&pfd, 0, sizeof(pfd));
          pfd.fd = new_socket;
          pfd.events = POLLOUT;

          err = poll(&pfd, 1, 0);
          if (err) {
              perror("poll");
              return err;
          }

          if (!(pfd.revents & POLLOUT)) {
              err = read(sk, &c, 1);
              if (err < 0) {
                  perror("read");
                  return err;
              }
          }

   BT_VOICE (since Linux 3.11)
       Transport voice settings, possible values:

          struct bt_voice {
              uint16_t setting;
          };

             +---------------------------+--------+--------------------+
             |Define                     | Value  | Description        |
             +---------------------------+--------+--------------------+
             |BT_VOICE_TRANSPARENT       | 0x0003 | Transparent output |
             +---------------------------+--------+--------------------+
             |BT_VOICE_CVSD_16BIT        | 0x0060 | C-VSD output PCM   |
             |                           |        | 16-bit input       |
             +---------------------------+--------+--------------------+
             |BT_VOICE_TRANSPARENT_16BIT | 0x0063 | Transparent output |
             |                           |        | PCM 16-bit input   |
             +---------------------------+--------+--------------------+
       Example:

          struct bt_voice voice;

          memset(&voice, 0, sizeof(voice));
          voice.setting = BT_VOICE_TRANSPARENT;
          int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_VOICE, &voice,
                               sizeof(voice));
          if (err == -1) {
              perror("setsockopt");
              return 1;
          }

   BT_PHY (since Linux 5.10)
       Transport supported PHY(s), possible values:

                   +-------------------+-------+-----------------+
                   |Define             | Value | Description     |
                   +-------------------+-------+-----------------+
                   |BT_PHY_BR_1M_1SLOT | BIT 0 | BR 1Mbps 1SLOT  |
                   +-------------------+-------+-----------------+
                   |BT_PHY_BR_1M_3SLOT | BIT 1 | BR 1Mbps 3SLOT  |
                   +-------------------+-------+-----------------+
                   |BT_PHY_BR_2M_1SLOT | BIT 3 | EDR 2Mbps 1SLOT |
                   +-------------------+-------+-----------------+
                   |BT_PHY_BR_2M_3SLOT | BIT 4 | EDR 2Mbps 3SLOT |
                   +-------------------+-------+-----------------+
                   |BT_PHY_BR_3M_1SLOT | BIT 6 | EDR 3Mbps 1SLOT |
                   +-------------------+-------+-----------------+
                   |BT_PHY_BR_3M_3SLOT | BIT 7 | EDR 3Mbps 3SLOT |
                   +-------------------+-------+-----------------+
   BT_CODEC (since Linux 5.14)
       Transport codec offload, possible values:

          struct bt_codec {
              uint8_t id;
              uint16_t cid;
              uint16_t vid;
              uint8_t data_path_id;
              uint8_t num_caps;
              struct codec_caps {
                  uint8_t len;
                  uint8_t data[];
              } caps[];
          } __attribute__((packed));

          struct bt_codecs {
              uint8_t num_codecs;
              struct bt_codec codecs[];
          } __attribute__((packed));

       Example:

          char buffer[sizeof(struct bt_codecs) + sizeof(struct bt_codec)];
          struct bt_codec *codecs = (void *)buffer;

          memset(codecs, 0, sizeof(codecs));
          codec->num_codecs = 1;
          codecs->codecs[0].id = 0x05;
          codecs->codecs[0].data_path_id = 1;

          int err = setsockopt(sco_socket, SOL_BLUETOOTH, BT_CODEC, codecs,
                               sizeof(buffer));
          if (err == -1) {
              perror("setsockopt");
              return 1;
          }

RESOURCES
        <http://www.bluez.org>

REPORTING BUGS
        <linux-bluetooth@vger.kernel.org>

SEE ALSO
       socket(7), scotest(1)

COPYRIGHT
       Free use of this software is granted under the terms of the GNU Lesser
       General Public Licenses (LGPL).

BlueZ                             March 2025                            SCO(7)