Hi,
Talking about MPLS VPN across Multi AS networks involves many conditions, for instance, IGP routes are not exchanged by BGP... but still we can provision a PW across Multiple AS.
Consider this,as you might know that for a LDP based pseudowire end to end connectivity within a single autonomous system, you must have /32 host routes of PE routers and the corresponding labels, which you learn through IGP and LDP/RSVP.
Now, to obtain the same in a multi-AS environment you can use eBGP to exchange the /32 host routes of PE devices and the corresponding labels across the autonomous system boundaries and then redistributing the /32 host routes learned through EBGP into IGP.
From the point of view of the PE routers, this is similar to the single autonomous system scenario except that the /32 host routes appear to be of IGP external types in the routing tables.
Instead of using LDP, ASBRs utilize IPv4 label information along with the host route advertisements in BGP update messages and set up LSPs between one another for these host routes.
Let us know if this helped...
sultan
