A comparison of next-generation IP-centric transport architectures

The popularity of the Internet and Internet protocol (IP)-based intranets i s promising enormous growth in data traffic originating from IP endpoints, prompting network operators to reconsider network architectures so that the y can most effectively absorb the projected growth. At the same time, new t echnologies are being introduced at a phenomenal pace, providing network op erators with numerous and complex choices involving dense wavelength divisi on multiplexing (DWDM), synchronous optical networks (SONETs), packet over SONET (POS), packet over wavelength (POW), and asynchronous transfer mode ( ATM). In this paper, we evaluate alternative transport architectures for ca rrying IP-based traffic using the projected traffic data, nodal configurati on, and optical fiber connectivity of a realistic, national-scale IP backbo ne. We compare the option of carrying IP directly versus IP over ATM for th ree types of transport architecture: SONET bidirectional line-switched ring s (BLSRs); mesh networks of optical (or electrical) cross connects; and DWD Ms without underlying optical cross connects (OXCs)-that is, with one or mo re wavelength links between each pair of IP switches. These options also in clude restoration choices. SONET BLSRs provide fast restoration based on se lf-healing ring technology. OXCs provide fast restoration for underlying me sh at the wavelength level. For point-to-point wavelength links, we conside r service-level (IP and ATM) restoration. We compare these options in terms of many network characteristics-port counts, circuit miles, wavelength mil es, fiber miles, and overall cost-and consider all the critical constraints and flexibilities for each choice.