mirror of
https://github.com/zeromq/libzmq.git
synced 2024-12-12 18:40:27 +01:00
0e053e3478
The PGM transport supports the omission of the network interface to
select the default one like:
announce.connect("epgm://eth0;239.255.128.46:64646"); // Use eth0
announce.connect("epgm://239.255.128.46:64646"); // Use the default
Also, mention C++ in the additional community bindings of 0MQ in
zmq.txt.
163 lines
5.4 KiB
Plaintext
163 lines
5.4 KiB
Plaintext
zmq_pgm(7)
|
|
==========
|
|
|
|
|
|
NAME
|
|
----
|
|
zmq_pgm - 0MQ reliable multicast transport using PGM
|
|
|
|
|
|
SYNOPSIS
|
|
--------
|
|
PGM (Pragmatic General Multicast) is a protocol for reliable multicast
|
|
transport of data over IP networks.
|
|
|
|
|
|
DESCRIPTION
|
|
-----------
|
|
0MQ implements two variants of PGM, the standard protocol where PGM datagrams
|
|
are layered directly on top of IP datagrams as defined by RFC 3208 (the 'pgm'
|
|
transport) and "Encapsulated PGM" where PGM datagrams are encapsulated inside
|
|
UDP datagrams (the 'epgm' transport).
|
|
|
|
The 'pgm' and 'epgm' transports can only be used with the 'ZMQ_PUB' and
|
|
'ZMQ_SUB' socket types.
|
|
|
|
Further, PGM sockets are rate limited by default. For details, refer to the
|
|
'ZMQ_RATE', and 'ZMQ_RECOVERY_IVL' options documented in
|
|
linkzmq:zmq_setsockopt[3].
|
|
|
|
CAUTION: The 'pgm' transport implementation requires access to raw IP sockets.
|
|
Additional privileges may be required on some operating systems for this
|
|
operation. Applications not requiring direct interoperability with other PGM
|
|
implementations are encouraged to use the 'epgm' transport instead which does
|
|
not require any special privileges.
|
|
|
|
|
|
ADDRESSING
|
|
----------
|
|
A 0MQ address string consists of two parts as follows:
|
|
'transport'`://`'endpoint'. The 'transport' part specifies the underlying
|
|
transport protocol to use. For the standard PGM protocol, 'transport' shall be
|
|
set to `pgm`. For the "Encapsulated PGM" protocol 'transport' shall be set to
|
|
`epgm`. The meaning of the 'endpoint' part for both the 'pgm' and 'epgm'
|
|
transport is defined below.
|
|
|
|
|
|
Connecting a socket
|
|
~~~~~~~~~~~~~~~~~~~
|
|
When connecting a socket to a peer address using _zmq_connect()_ with the 'pgm'
|
|
or 'epgm' transport, the 'endpoint' shall be interpreted as an 'interface'
|
|
followed by a semicolon, followed by a 'multicast address', followed by a colon
|
|
and a port number.
|
|
|
|
An 'interface' may be specified by either of the following:
|
|
|
|
* The interface name as defined by the operating system.
|
|
* The primary IPv4 address assigned to the interface, in it's numeric
|
|
representation.
|
|
|
|
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'. The 'interface' part can be omitted, in that case the default one
|
|
will be selected.
|
|
|
|
A 'multicast address' is specified by an IPv4 multicast address in it's numeric
|
|
representation.
|
|
|
|
|
|
WIRE FORMAT
|
|
-----------
|
|
Consecutive PGM datagrams are interpreted by 0MQ as a single continuous stream
|
|
of data where 0MQ messages are not necessarily aligned with PGM datagram
|
|
boundaries and a single 0MQ message may span several PGM datagrams. This stream
|
|
of data consists of 0MQ messages encapsulated in 'frames' as described in
|
|
linkzmq:zmq_tcp[7].
|
|
|
|
|
|
PGM datagram payload
|
|
~~~~~~~~~~~~~~~~~~~~
|
|
The following ABNF grammar represents the payload of a single PGM datagram as
|
|
used by 0MQ:
|
|
|
|
....
|
|
datagram = (offset data)
|
|
offset = 2OCTET
|
|
data = *OCTET
|
|
....
|
|
|
|
In order for late joining consumers to be able to identify message boundaries,
|
|
each PGM datagram payload starts with a 16-bit unsigned integer in network byte
|
|
order specifying either the offset of the first message 'frame' in the datagram
|
|
or containing the value `0xFFFF` if the datagram contains solely an
|
|
intermediate part of a larger message.
|
|
|
|
Note that offset specifies where the first message begins rather than the first
|
|
message part. Thus, if there are trailing message parts at the beginning of
|
|
the packet the offset ignores them and points to first initial message part
|
|
in the packet.
|
|
|
|
The following diagram illustrates the layout of a single PGM datagram payload:
|
|
|
|
....
|
|
+------------------+----------------------+
|
|
| offset (16 bits) | data |
|
|
+------------------+----------------------+
|
|
....
|
|
|
|
The following diagram further illustrates how three example 0MQ frames are laid
|
|
out in consecutive PGM datagram payloads:
|
|
|
|
....
|
|
First datagram payload
|
|
+--------------+-------------+---------------------+
|
|
| Frame offset | Frame 1 | Frame 2, part 1 |
|
|
| 0x0000 | (Message 1) | (Message 2, part 1) |
|
|
+--------------+-------------+---------------------+
|
|
|
|
Second datagram payload
|
|
+--------------+---------------------+
|
|
| Frame offset | Frame 2, part 2 |
|
|
| 0xFFFF | (Message 2, part 2) |
|
|
+--------------+---------------------+
|
|
|
|
Third datagram payload
|
|
+--------------+----------------------------+-------------+
|
|
| Frame offset | Frame 2, final 8 bytes | Frame 3 |
|
|
| 0x0008 | (Message 2, final 8 bytes) | (Message 3) |
|
|
+--------------+----------------------------+-------------+
|
|
....
|
|
|
|
|
|
EXAMPLE
|
|
-------
|
|
.Connecting a socket
|
|
----
|
|
/* Connecting to the multicast address 239.192.1.1, port 5555, */
|
|
/* using the first Ethernet network interface on Linux */
|
|
/* and the Encapsulated PGM protocol */
|
|
rc = zmq_connect(socket, "epgm://eth0;239.192.1.1:5555");
|
|
assert (rc == 0);
|
|
/* Connecting to the multicast address 239.192.1.1, port 5555, */
|
|
/* using the network interface with the address 192.168.1.1 */
|
|
/* and the standard PGM protocol */
|
|
rc = zmq_connect(socket, "pgm://192.168.1.1;239.192.1.1:5555");
|
|
assert (rc == 0);
|
|
----
|
|
|
|
|
|
SEE ALSO
|
|
--------
|
|
linkzmq:zmq_connect[3]
|
|
linkzmq:zmq_setsockopt[3]
|
|
linkzmq:zmq_tcp[7]
|
|
linkzmq:zmq_ipc[7]
|
|
linkzmq:zmq_inproc[7]
|
|
linkzmq:zmq[7]
|
|
|
|
AUTHORS
|
|
-------
|
|
This 0MQ manual page was written by Martin Sustrik <sustrik@250bpm.com> and
|
|
Martin Lucina <mato@kotelna.sk>.
|