Did you know that an entire segment of the Internet is dedicated to Multicasting? It is known as the MBone.
MBone acts as a common, shared utility for Multicasting. MBone can save customers significant costs, and can connect new sets of E-Commerce users together in an entirely unique fashion.
Many ISPs already offer their customers access to this service.
Mbone (short for "multicast backbone") was an experimental backbone for IP multicast traffic across the Internet developed in the early 1990s. It required specialized hardware and software. Since most Internet routers have IP multicast disabled due to concerns of bandwidth tracking and billing, the Mbone evolved to connect multicast-capable networks over the existing Internet infrastructure. The commercialization of multicast routers is difficult because there are no efficient access control capabilities to the multicast trees (multicast routers and their protocols), and because Internet service providers have difficulty computing charges for multicast traffic.
Multicast in hosts
- Send is easy. just use a class D address as destination
- Receive is more complicated
- Processes create sockets and bind to port
- Process calls setsockopt(s, IP_PROTO, IP_ADD_MEMBERSHIP)
Joins multicast group
- IP-stack sends IGMP report on network
- More than one process may join same group
Can use different (UDP) ports
- But only one IGMP report is sent
- When last process leaves IGMP leave is sent
- Ethernet - good example of hardware multicast
Most Ethernet NICs support multicast
- Ethernet multicast addresses:
The low order bit of the high order byte is 1:
- Many NICs on the same network may listen to the same Ethernet multicast address.
- Other Link-level layers may not support multicast, being NBMA (Non-Broadcast Multiple Access)
eg ATM, FR, X25