Editing Multicast (section)

==Application layer==
Application layer multicast overlay services are not based on IP multicast or [[data link layer]] multicast. Instead, they use multiple unicast transmissions to simulate a multicast. These services are designed for application-level group communication. [[Internet Relay Chat]] (IRC) implements a single [[spanning tree]] across its [[overlay network]] for all conference groups.<ref>{{cite IETF |RFC=1324 |section=2.5.1 |title=A Discussion on Computer Network Conferencing |first1=D. |last1=Reed |date=May 1992 |website=IETF Datatracker |url=https://datatracker.ietf.org/doc/html/rfc1324 }}</ref> The lesser-known PSYC technology uses custom multicast strategies per conference.<ref>{{Citation | url = http://www.psyc.eu/whitepaper/ | publisher = PSYC | title = Whitepaper on PSYC |date=2007 |first1= Carlo |last1=v. Loesch | place = EU}}.</ref> Some [[peer-to-peer]] technologies employ the multicast concept known as [[peercasting]] when distributing content to multiple recipients.

[[Xcast|Explicit multi-unicast]] (Xcast) is another multicast strategy that includes addresses of all intended destinations within each packet. As such, given [[maximum transmission unit]] limitations, Xcast cannot be used for multicast groups with many destinations. The Xcast model generally assumes that stations participating in the communication are known ahead of time so that distribution trees can be generated and resources allocated by network elements in advance of actual data traffic.<ref>{{Cite journal |title= Explicit Multicast (Xcast) Concepts and Options |date= November 2007 |author1=Rick Boivie |author2=Nancy Feldman |author3=Yuji Imai |author4=Wim Livens |author5=Dirk Ooms |doi= 10.17487/RFC5058 |name-list-style=amp |url= http://tools.ietf.org/html/rfc5058 |id= RFC 5058 |website=Internet Engineering Task Force Datatracker |access-date= May 25, 2013 |url-access=subscription }}</ref>