edw@ius2.cs.cmu.edu (Eddie Wyatt) (04/25/87)
Is multicasting support at the Un*x socket level (preferable STREAM sockets) or by some other "device" on SUN-3s? A novice networker, -- Eddie Wyatt
guy%gorodish@Sun.COM (Guy Harris) (04/28/87)
> Is multicasting support at the Un*x socket level (preferable STREAM > sockets) or by some other "device" on SUN-3s? No. Consider, for example, that if you want a stream socket, that would pretty much mean a TCP socket here. (Note to those confused by the word STREAM here - it refers neither to STREAMS as implemented in System V Release 3 nor to "Extensible Streams" as implemented by Apollo. "stream" is a horribly overloaded word....) Doing a multicast version of a protocol like TCP would be a bit messy (note that neither 4.2BSD nor 4.3BSD, for example, implement broadcast TCP). You would have to support what amounted to a connection to the given port on each host in the multicast group. Since the receiving host can decide whether it wants to belong to a multicast group or not, this would be rather tricky.... Even with UDP (which supports broadcast in the 4.[23]BSD implementations), you would need to make extensions to current IP implementations to support multicasting. There are such extensions proposed - see RFC 966 and RFC 988 - but they are not, as far as I know, widely implemented. It's certainly not implemented in the 4.2BSD TCP/IP code upon which our TCP/IP code is based. You'd have to get to the raw Ethernet level to do multicasting, and we don't currently happen to support multicasting. I don't know whether we ever will.