ZMQ_TCP(7)                        0MQ Manual                        ZMQ_TCP(7)



NAME
       zmq_tcp - 0MQ unicast transport using TCP

SYNOPSIS
       TCP is an ubiquitous, reliable, unicast transport. When connecting
       distributed applications over a network with 0MQ, using the TCP
       transport will likely be your first choice.

ADDRESSING
       A 0MQ address string consists of two parts as follows:
       transport://endpoint. The transport part specifies the underlying
       transport protocol to use, and for the TCP transport shall be set to
       tcp. The meaning of the endpoint part for the TCP transport is defined
       below.

   Assigning a local address to a socket
       When assigning a local address to a socket using zmq_bind() with the
       tcp transport, the endpoint shall be interpreted as an interface
       followed by a colon and the TCP port number to use.

       An interface may be specified by either of the following:

       o   The wild-card *, meaning all available interfaces.

       o   The primary IPv4 address assigned to the interface, in its numeric
           representation.

       o   The interface name as defined by the operating system.

           Note
           Interface names are not standardised in any way and should be
           assumed to be arbitrary and platform dependent. On Win32 platforms
           no short interface names exist, thus only the primary IPv4 address
           may be used to specify an interface.

   Connecting a socket
       When connecting a socket to a peer address using zmq_connect() with the
       tcp transport, the endpoint shall be interpreted as a peer address
       followed by a colon and the TCP port number to use.

       A peer address may be specified by either of the following:

       o   The DNS name of the peer.

       o   The IPv4 address of the peer, in it's numeric representation.

WIRE FORMAT
       0MQ messages are transmitted over TCP in frames consisting of an
       encoded payload length, followed by a flags field and the message body.
       The payload length is defined as the combined length in octets of the
       message body and the flags field.

       For frames with a payload length not exceeding 254 octets, the payload
       length shall be encoded as a single octet. The minimum valid payload
       length of a frame is 1 octet, thus a payload length of 0 octets is
       invalid and such frames SHOULD be ignored.

       For frames with a payload length exceeding 254 octets, the payload
       length shall be encoded as a single octet with the value 255 followed
       by the payload length represented as a 64-bit unsigned integer in
       network byte order.

       The flags field consists of a single octet containing various control
       flags:

       Bit 0 (MORE): More message parts to follow. A value of 0 indicates that
       there are no more message parts to follow; or that the message being
       sent is not a multi-part message. A value of 1 indicates that the
       message being sent is a multi-part message and more message parts are
       to follow.

       Bits 1-7: Reserved. Bits 1-7 are reserved for future expansion and MUST
       be set to zero.

       The following ABNF grammar represents a single frame:

               frame           = (length flags data)
               length          = OCTET / (escape 8OCTET)
               flags           = OCTET
               escape          = %xFF
               data            = *OCTET

       The following diagram illustrates the layout of a frame with a payload
       length not exceeding 254 octets:

           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           | Payload length|     Flags     |       Message body        ... |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           | Message body ...
           +-+-+-+-+-+-+- ...

       The following diagram illustrates the layout of a frame with a payload
       length exceeding 254 octets:

           0                   1                   2                   3
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |     0xff      |               Payload length              ... |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |                       Payload length                      ... |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           | Payload length|     Flags     |        Message body       ... |
           +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           |  Message body ...
           +-+-+-+-+-+-+-+ ...

EXAMPLES
       Assigning a local address to a socket.

           /* TCP port 5555 on all available interfaces */
           rc = zmq_bind(socket, "tcp://*:5555");
           assert (rc == 0);
           /* TCP port 5555 on the local loop-back interface on all platforms */
           rc = zmq_bind(socket, "tcp://127.0.0.1:5555");
           assert (rc == 0);
           /* TCP port 5555 on the first Ethernet network interface on Linux */
           rc = zmq_bind(socket, "tcp://eth0:5555");
           assert (rc == 0);

       Connecting a socket.

           /* Connecting using an IP address */
           rc = zmq_connect(socket, "tcp://192.168.1.1:5555");
           assert (rc == 0);
           /* Connecting using a DNS name */
           rc = zmq_connect(socket, "tcp://server1:5555");
           assert (rc == 0);


SEE ALSO
       zmq_bind(3) zmq_connect(3) zmq_pgm(7) zmq_ipc(7) zmq_inproc(7) zmq(7)

AUTHORS
       This 0MQ manual page was written by Martin Sustrik
       <sustrik@250bpm.com[1]> and Martin Lucina <mato@kotelna.sk[2]>.

NOTES
        1. sustrik@250bpm.com
           mailto:sustrik@250bpm.com

        2. mato@kotelna.sk
           mailto:mato@kotelna.sk



0MQ 2.1.6                         05/06/2011                        ZMQ_TCP(7)
