There are several alternatives which will result in aggregating 4 serial links:

- you can configure each serial link separately, giving each link its own subnet. You can then configure routing (might be static routes or might be a dynamic routing protocol like EIGRP or OSPF) to use each of the links. This will result in 4 entries in the routing table for each destination reached via the serials. Load sharing will send some traffic over each link resulting in aggregation of the links.

- you can configure each of the serial links with ppp and put each serial link into a multilink on the router. The multilink interface would get an IP address rather than the individual serial links. You would set up routing (could be static or could be a dynamic routing protocol) to use the multilink. The multilink process will aggregate the serial links.

HTH

Rick