Carriers today are running a variety of transport networks - SDH/SONET, ATM and IP/MPLS infrastructure - which not only coexist but compete against each other. This is because each has become associated with specific telecoms services. Voice and leased-line services (nx64 kbit/s and E1/T1) are usually transported over SDH/SONET backbones. Transparent LAN services, optionally coupled with certain voice, real-time data and, of course, native ATM traffic, are the province of ATM backbones. And IP backbones, for their part, handle increasingly popular IP-VPN and Internet services.
To retain customers carriers must offer a range of services. But how can they do this without incurring the prohibitively high costs of deploying and maintaining three different transport networks, especially given the current market? How can carriers offer next-generation services while continuing to offer multiple services that include legacy protocols such as Frame Relay and leased lines? And how can carriers prepare access infrastructure for what is considered to be an inevitable migration to MPLS backbones?
New IP/MPLS backbones cannot be created out of thin air. Carriers must continue to provide legacy services to existing customers to finance and sustain the transition to IP backbones. At the same time, they must build up a customer base for new services such as Gigabit Ethernet TLS even before migration to IP backbones is fully completed. New carriers rolling out IP networks from scratch will need to provide legacy services as well. Legacy voice, after all, is a much bigger revenue-generator for carriers than data, and not all enterprise customers seeking to take advantage of IP networks are willing to junk existing PBXs. Legacy telephone systems work perfectly well, and provide hundreds of features currently unavailable on IP voice telephones based on VoIP technology.
For their part, cellular operators migrating from 2G to 3G networks must co-locate traffic from both generations over the same transport network to reduce capital investment and maintenance costs.
How will carriers and service providers manage?A logical solution is the deployment of Customer Located Equipment (CLE) access devices, which can support multiple services over any access network to any transport network. This type of solution can be used to create an Ethernet access network for an SDH/SONET backbone, enabling the carrier to deliver Ethernet services over its existing network.A mirror-image principle can be used to transport legacy services over an IP backbone. Swedish carrier Utfors has chosen a TDM-over-IP gateway to deliver voice transparently over its next-generation Ethernet backbone, assuring no loss of traditional services. And DSL Integrated Access Devices (IADs) transmit leased-line services and/or Frame Relay over ATM, while enhancing the service with ATM QoS guarantees. Cellular operators need to implement a broadband access network, ATM or IP, to provide transport for 3G. Multi-service access concentrators deliver TDM, IP and ATM traffic over ATM, while the IPmux provides connectivity for 2G legacy equipment over IP.
By using low-cost access equipment, carriers can offer almost any service over any backbone. For the majority that still run SDH/SONET or ATM backbones, this allows them to maximise profits from existing networks by running both legacy and next-generation services until they migrate to an IP/MPLS backbone. Carriers already running IP will benefit from revenue-generating legacy services and an increased customer base.