 expenses (OPEX) incurred by a cellular operator. Metro and Core transport segments could become more and more complex as the size of the network grows. Some key challenges associated with transport networks are as follows: TDM based Backhaul: In 2G and 3G networks most of the traffic is TDM-based (Time Division Multiplexing) supported by TDM interfaces. Most of the existing 2G/3G solutions are based on n*E1/T1 connections which are not scalable for mobile broadband. The existing circuit and TDM- based backhaul solutions are not designed for packet-based next generation networks. Frequency Spectrum Shortage: Though the shortages of frequencies can easily be witnessed on the radio access networks, the backhaul networks also face scarcity of frequency spectrum. The point to point radio links are typically provided in 6-40 GHz frequency bands that require LOS (line of sight). The unavailability of LOS and interference from adjacent operator channels reduces the total spectrum for that particular location. Fiber Deployment Constraints: As fiber starts to get deeper into the network obtaining permissions for digging and laying fiber is becoming more and more cumbersome. In some cases it takes more than a year to get across all the permissions. This challenge applies to all segments of the transport network. Transport for Different Radio Generations: Using a dedicated transport network for successive mobile generations - PDH/SDH for 2G/2.5G; ATM for UMTS Release 99/CDMA2000; and Ether- net/IP/MPLS for UMTS revision 5/WiMAX and beyond is not as efficient or potentially cost-effective as integrating diverse traffic streams over a single backhaul link. Having said that, neither transmitting TDM frames nor ATM cells over IP/MPLS network; nor running Ethernet/IP packets over SDH in a cost-effective manner are trivial matters. 7.3 Backhaul Network Microwave radios and E1/T1 leased lines are the most common forms of point-to-point backhaul. T1 (1.544 Mbps) leased lines are heavily used in North America while microwave radios 