IP Multicast Service Models Having Three Multicast Any-Source Multicast (ASM) Source-Filtered Multicast (SFM) and Source-Specific Multicast (SSM) which work as below.
Any-Source Multicast (ASM)
- Destination ‘multicast’ address only defines ‘Group’ membership
- Will accept from ‘any source’ (unicast)
- First and oldest model, defined in RFC 1112
Source-Filtered Multicast (SFM)
- Destination ‘multicast’ address only defines ‘Group’ membership
- Adds capability to filter sources
- Excluded List (mode), implies include everything else
- Include List (mode), implies exclude everything else
Source-Specific Multicast (SSM)
- Adds new concept of ‘Channel’ rather than Group
- Source (unicast) and destination multicast Group address together define a single ‘Channel’ for membership
- Like SFM Include List (mode) but with single source which is now significant for membership
- (S,G) Channel is not the same as (S,G) Group
- ASM and SFM receivers joining a Group receives from ALL sources unless filtered
- (S,G) Group represents filtered source (include or exclude)
- Multicast network may include all three models
- ASM and SFM good for many-to-many interactions
- SSM good for one-to-many interactions
- Application may include two one-to-many, primary & Backup
Dense and Sparse Modes
- Protocol Independent Multicasting Dense Mode (PIM-DM) uses a fairly simple approach to handle IP multicast routing.
- The basic assumption behind PIM-DM is that the multicast packet stream has receivers at most locations.
- An example of this might be a company presentation by the CEO or President of a company.
- You opt out if you don’t want it
- PIM Sparse Mode (PIM-SM) assumes relatively fewer receivers.
- An example would be the initial orientation video for new employees.
- You opt in if you want it Multicast Forwarding
- Multicast Routing is backwards from Unicast Routing
- Unicast Routing is concerned about where the packet is going or will need to go.
- Multicast Routing is concerned about where the packet came from or will be coming from.
- Multicast Routing uses “Reverse Path Forwarding” (RPF) and RPF Check
- Which interface to expect multicast packet from source?
- The interface would send unicast packet back to source or shared root!
- Protects against multicast loops