Adtran Atlas 550 AC Base Unit Chassis IAD Router 1200305L1. The Adtran Atlas 550 is a modular router designed to handle multiple sources of traffic. Its modular design allows users to customize the Atlas 550 for whatever purposes they may need. The Atlas 550 1200305L1 has built in support for up to six cards in its factory configuration, and a single T1 module is included with the chassis. The Atlas 550 is ideal for networks that combine voice and data traffic. Adtran Part Number: 1200305L1Model Number: Atlas 550