multicast address ownership#eg exchanges shows a few hundred big companies including exchanges. For example, one exchange multicast address falls within the range to
Intercontinental Exchange, Inc.
It’s educational to compare with a unicast IP address. If you own such an unicast address, you can put it on a host and bind an http server to it. No one else can bind a server to that uncast address. Any client connecting to that IP will hit your host.

As owner of a multicast address, you alone can send datagrams to it and (presumably) you can restrict who can send or receive on this group address. Alan Shi pointed out the model is pub-sub MOM.

UDP^TCP again#retrans is relevant.

FIFO — TCP; UDP — packet sequencing is uncontrolled
Virtual circuit — TCP; UDP — datagram network
Connectionless — UDP ; TCP — Connection-oriented

With http, ftp etc, you establish a Connection (like a session). No such connection for UDP communication.

Retransmission is part of — TCP; UDP — application layer (not network layer) must request retransmission

To provide guaranteed FIFO data delivery, over unreliable channel, TCP must be able to detect and request retransmission. UDP doesn’t bother. An application built on UDP need to create that functionality, as in the IDC (Interactive Data Corp) ticker plant.

joining/leaving a multicast group

Every multicast address is a group address. In other words, a multicast address identifies a group.

Sending a multicast datagram is much simpler than receiving…

[1] is a concise 4-page introduction. Describes joining/leaving.

[2] has sample code to send/receive. Note there’s no server/client actually.


broadcast^multicast shows(suggests?) that broadcast is also time-efficient since sender only does one send. However, multicast is smarter and more bandwidth-efficient.

IPv6 disabled broadcast — to prevent disturbing all nodes in a network when only a few are interested in a particular service. Instead it relies on multicast addressing, a conceptually similar one-to-many routing methodology. However, multicasting limits the pool of receivers to those that join a specific multicast receiver group.