We're considering using MPLS to facilitate the use of QoS, and one of the questions that came up was in regard to our current bandwidth utilization and how to better take advantage of what bandwidth we do have. There is a site that has 3 T1s, 2 have been setup for outgoing traffic related to VPN tunnels, and 1 for download traffic from the Internet to our WAN. The downstream utilization on the 2 T1s is nothing, but high on the upload utilization, and the 1 T1 used for downloads is high on the downstream and nothing on the upstream. I've recommended they collapse all 3 into one logical channel and utilize the upload and download capability of all 3 T1s. I always assumed that full duplex feature on a t1 included the ability to upload and download 1.5Mbps each way for a theoratical 3 Mbps combined. I haven't been able to find a whole lot of info out there on the subject and realize it's a bit of stretch putting it in this forum, but was hoping I could get some feedback.
a single T1 can transmit up to 1.5 Mbps and receive up to 1.5 Mbps at the same time.
Be aware however, that to "collapse all 3 into one logical channel" is only possible, if all 3 T1 terminate at the same two routers. If the endpoints are not on the same pair of routers, then they can not be "collapsed".
So the question in your case is: are the 3 T1s terminating on a single WAN router in your location AND also terminating on the same service provider router?
If YES, then you could arrange with the ISP to use multilink PPP to create one logical interface with a combined bandwidth of 4.5 Mbps in each direction.
If NO, then you would need to change the topology in cooperation with the ISP to achieve the stated goal.