In my previous post, I discussed about the overall architecture of mLDP. This post is more focused on mLDP Signalling. mLDP signalling provides two functions
1. FEC Discovery for a MP LSP
2. Assigning multicast flow to a MP LSP

mLDP can use two signalling methods; In-band Signalling and Out-of-Band Signalling. FEC uniquely defines the MP LSP within the network by using combination of VPN-ID and it’s opaque value. The signalling maps the streams that will run over that MP LSP.
• In-Band Signalling
Opaque Value is used to map an MP LSP
Opaque value is derived from the multicast flow

• Out-Of-Band Signalling
 Uses an overlay protocol to build the tree
 Opaque value are assigned by statically configured
 MP LSP creation is on-demand