ZMQ_PGM(7) | 0MQ Manual | ZMQ_PGM(7) |
NAME¶
zmq_pgm - 0MQ reliable multicast transport using PGMSYNOPSIS¶
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 and incur a performance penalty when used over a loop-back interface. For details, refer to the ZMQ_RATE, ZMQ_RECOVERY_IVL and ZMQ_MCAST_LOOP options documented in zmq_setsockopt(3).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 its 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 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
+------------------+----------------------+ | offset (16 bits) | data | +------------------+----------------------+
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¶
zmq_connect(3) zmq_setsockopt(3) zmq_tcp(7) zmq_ipc(7) zmq_inproc(7) zmq(7)AUTHORS¶
This manual page was written by the 0MQ community.04/04/2012 | 0MQ 2.2.0 |