[OASIS Issue Tracker] (MQTT-605) Should packets be identified as multicast or unicast exclusively?

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ https://issues.oasis-open.org/browse/MQTT-605?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=84039#comment-84039 ] 

Ian Craggs commented on MQTT-605:
---------------------------------

I was asked to define multicast and broadcast. Here is one definition from Stevens (Unix Network Programming 2nd Edition) Chapter 19 Multicasting:

"a unicast address identifies a _single_ interface, a broadcast address identifies _all_ interfaces on the subnet, and a multicast address identifies a _set_ of interfaces. Unicasting and broadcasting are the endpoints of the addressing spectrum (one or all) and the intent of multicasting is to provide the capability of addressing something in between these endpoints. A multicast datagram should be received only by the interfaces that are interested in the datagram, that is, by the interfaces on the hosts that are running applications that wish to participate in the multicast session. Also, broadcasting is normally limited to a LAN whereas multicasting can be used on a LAN or across a WAN."



> Should packets be identified as multicast or unicast exclusively?
> -----------------------------------------------------------------
>
>                 Key: MQTT-605
>                 URL: https://issues.oasis-open.org/browse/MQTT-605
>             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
>          Issue Type: Task
>          Components: MQTT-SN
>    Affects Versions: v2.0
>            Reporter: Ian Craggs
>            Assignee: Ian Craggs
>            Priority: Major
>
> In the 1.2 specification, the ADVERTISE, SEARCHGW and GWINFO are identified as being "broadcasted" to potentially multiple receivers, whereas the other packets are not. The question here is whether we should continue to identify these packets (and PUBLISH QoS -1,- or out of band) as broadcast (or multicast) only in normative text, or just call this out as implementation advice non-normatively.
> Andy Banks is concerned that if it is the latter, then interoperability could be affected.
> Ian Craggs thinks that which address to send packets on is an implementation decision, like the TCP/IP address and port of the MQTT broker in MQTT.



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