Hello,
basically, you create a multilink interface and assign both T1 lines to that interface, the config would look like this:
interface Multilink1
ip address 192.168.10.10 255.255.255.0
no cdp enable
ppp multilink
multilink-group 1
!
interface Serial0/0
description T1 circuit 1
bandwidth 1536
encapsulation ppp
no fair-queue
no cdp enable
ppp multilink
multilink-group 1
!
interface Serial0/1
description T1 circuit 2
bandwidth 1536
encapsulation ppp
no cdp enable
ppp multilink
multilink-group 1
Depending on your IOS version, the ´multilink-group´ command might have been replaced by ´ppp multilink group´.
HTH,
GP