Well, time for another IOS XR post, this time on Interface Bundles, particularly Ethernet. With IOS XR a bundle can be considered a group of one or more ports that are aggregated together and treated as one link. The different links within a single bundle can have different speeds, where the fastest link can be up to four times faster than the slowest link. Each bundle has a single MAC, and a single IP address.
As with some other devices, you can have interfaces in a bundle across multiple line cards, thus protecting yourself from a single point of failure. If a line card fails,  the bundle interface will stay up as you configured it to span more then 1 card. A bundle also provides you with more bandwidth then might normally be available if using a single interface. Cisco IOS XR supports 802.3ad (LACP) as well as Cisco proprietary EtherChannel. In all honesty, if you use anything other then LACP you are asking for trouble – LACP has prevent many problems when GBICs have gone bad, but the interfaces are still UP/UP.
Ok, time for the meat and potatoes: