To Osama's point, draft-martini (called l2circuits in JUNOS) tend to be simpler to configure in small environments, as there is no need for a BGP infrastructure. However, the true benefits of draft-kompella L2VPNs (as well as BGP-based VPLS) come from scaling. As your environment supports large numbers of PE routers and l2circuits or VPLS endpoints, the autodiscovery features of BGP-based signaling mean less redundant configuration and less concurrent control plane connections. Under the hood, the data-plane signaling is the same for draft-martini and draft-kompella l2vpn -- it's just the control plane infrastructure to establish and maintain the connections that's different.
If you're looking to support a handful of l2circuits, draft-martini is probably the right choice. However if you're looking to deploy VPLS, or if you have a larger number of tunnels, the BGP-based infrastructure will allow for a centralized location mechanism for remote endpoints, and will also use significantly fewer control plane resources. Remember that with draft-martini, the routing-engine must maintain a separate targeted LDP (TCP socket) for each tunnel -- whereas BGP-based VPNs can leverage only the required number of BGP neighbors. In draft-martini, one thousand concurrent martini tunnels means 1000x TCP sessions just for the LDP signaling.
Also, if you plan to deploy layer 3 VPNs (aka: RFC4364, aka: 2547bis) in the future, you should preconfigure your BGP sessions for both family l2vpn signaling and family inet-vpn unicast. You will then be able to leverage the same BGP infrastructure for your layer 3 services in addition to you L2VPNs and VPLS (L2VPN and VPLS use the same BGP address family for signaling and autodiscovery). As Osama correctly points out, address families are negotiated in the BGP session OPEN, and a change requires bouncing the bgp neighbor. As such, it's a good idea to make sure to configure any address families you may need in the future to avoid any operational impact from adding a new service type.
Message Edited by JNPRdbackman on 07-11-2008 11:56 PM