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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 - default) Unauthenticated Desired
BT_SECURITY_HIGH 3 (High) Authenticated Required
BT_SECURITY_FIPS (since Linux 3.15) 4 (Secure Only) Authenticated (P-256 based Secure Simple Pairing and Secure Authentication) Required

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).

March 2025 BlueZ