ZMQ_TCP(7) 0MQ Manual ZMQ_TCP(7)NAMEzmq_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:
· The wild-card *, meaning all available interfaces.
· The primary IPv4 address assigned to the interface, in its numeric
representation.
· 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:
· The DNS name of the peer.
· The IPv4 address of the peer, in its 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 ALSOzmq_bind(3)zmq_connect(3)zmq_pgm(7)zmq_ipc(7)zmq_inproc(7)zmq(7)AUTHORS
This manual page was written by the 0MQ community.
0MQ 2.2.0 04/04/2012 ZMQ_TCP(7)
