At 10:14 PM 6/27/02, Howard C. Berkowitz wrote: > >IP multicast gets used for many purposes and those purposes may be at > >different layers: > > > >Sending routing updates (EIGRP, OSPF, RIPv2) - Layer 3 > >Establishing routing protocol neighbor relationships (EIGRP, OSPF) - Layer 3 > >Sending multimedia streaming audio or video - Layer 7 with some help from > >Layer 6 (MPEG or whatever), Layer 5 (RTSP), and Layer 4 (UDP) > >Finding services (Service Location Protocol) - Layer 7 > >Joining groups (IGMP) - Layer 3 > >Determining a dynamic L3 address assignment (IPv6) - Layer 3 > > >You're not saying, are you, that IP multicast exists at layers above >3, are you?
No, I said it's used by upper layers. Those layers are aware of it, though. The Service Location Protocol (SLP) RFC, for example, states which IP multicast address to use. The Realtime Streaming Protocol (RTSP) knows about IP multicast too. I don't know the details, but RTSP specifies a method for a client to find out what IP multicast address a server is sending to. There's a presentation description that includes the multicast address. If you look at the RFC for RTSP, there's lots of discussion of multicast. RTSP is nominally an application-layer protocol, at least according to the author of the RFC. Priscilla >I think it is correct to say that a higher-layer protocol >may assume that a lower-layer protocol will require use of a layer 3 >multicast service, but doesn't itself implement multicast. The upper >layer entity (in strict OSI terms) need not have direct access to the >multicast network layer service, but potentially could indirectly >request that functionality through higher-layer service interfaces. > >Without looking at the Transport Service Specification, I can't >remember if it has the semantics, with the Connectionless Transport >Service, of multicasts. My general recollection is that you use a >network service address and let the Network Service figure out the >semantics. > > > >There's probably lots of others too! > > > >Layer 2 multicasts are used for IP multicast, but for many other purposes > >too, such as BPDU, CDP, VTP, DISL, AppleTalk Name Binding Protocol (NBP) > >lookups, etc. > > > >Priscilla > > > > > >>TIA > >> > >>Robert > >________________________ > > > >Priscilla Oppenheimer > >http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=47637&t=47591 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
