Multicast

Multicast Use Case

• Live TV show
• 4K resolution (25-50 Mbps recommended)
  • If the network can't keep up with the stream, it will lower the quality and the bandwidth so that it can get through it easier.
• Dolby TRUEHD sound (6-18 Mbps recommended)
  • Audio is being degraded, ...
• How much network do I need to deliver video to many people at once?
  • This is when Multicast comes in.
• 14,000 simultaneous users
  • I only need 1 copy of my life TV show at 50 Mbps and I sent it to a Multicast address,
  • Anyone interested can subscribe and will get a copy of that show, frame by frame.

Multicast Components

• Class D (224-240) in IPv4
• Leverages IGMP
  • Perform group management
  • The local router hears you, retrieves the stream for you using something called PIM.
  • Responsible within your VLAN for a client requesting a multicast stream.
• Leverages PIM
  • Protocol Independent Multicast
  • Gets to the server using your routing tables with regular IPv4 unicast routing.
  • Responsible for multicast routing.
• Multicast application (VLC)
  • You can take a TV show and tell VLC to stream it to 255.255.25.25, that is a multicast address.
  • IGMP joins and switch sees that request and it start sending us those stream bits.
  • Once you get the initial PIM running, adding an additional host is no big deal.
  • We are not using additional bandwidth from the source server.
• Typically UDP-based

Internet Group Management Protocol (IGMP)

The protocol that is used from a client to a router to join a multicast stream, and leave at the end.

The Internet Group Management Protocol (IGMP) is a network layer protocol used in IPv4 networks to manage multicast group memberships. It allows hosts and routers to communicate about which hosts are interested in receiving multicast traffic. IGMP is crucial for efficiently delivering data to groups of receivers without flooding the network with unnecessary packets.

PIM

• The router finds that stream using a protocol called PIM, it is protocol independent because it runs on top of the routing protocol (i.e. OSPF, EIGRP)
• Can always come up with the best path
• A loopfree path
• Using routing table it finds the most optimal path to that server.
• If anyone else needs it, it just feeds it from that link.