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Cell Relay Retreat>List Archive>month:1995-Apr> msg00038



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Mcast/Bcast problem

  • From: Grenville Armitage <gja@thumper.bellcore.com>
  • Date: Fri, 21 Apr 1995 18:44:04 -0400
  • CC: Joel Halpern <jhalpern@newbridge.com>, jkrawczy@wellfleet.com, tjsmith@vnet.ibm.com, ip-atm@matmos.hpl.hp.com, gja@thumper.bellcore.com



>>However, does this mean we then augment
>>the encapsulation of IP datagrams over ATM for just multicast or it and
>>unicast? 

It is not really an either/or situation. Unicast IP transmissions
can still quite happily use [0xAA-AA-03][0x00-00-00][0x800] encaps,
regardless of whether a given LIS has hosts.routers in it that have
been upgraded for IP multicast. The upgraded, multicast capable,
hosts would _additionally_ use a new encaps mechanism (perhaps
even over the same VC as the unicast traffic if we use some
subset of LLC/SNAP encaps). At the receiving ends unicast and
multicast IP packets could arrive over the same VC, be demuxed
separately by the ip/atm driver, and then dropped or passed
up to the same ip/atm interface.

In LISs where all hosts/routers have multicast capable IP/ATM
interfaces you could send unicast IP packets using the
encaps for multicast packets, or still retain the existing
unicast encaps.

cheers,
gja