PDF of this tutorialMany challenges are associated with provisioning integrated services using a legacy architecture, as shown in Figure 1.
Figure 1. Integrated Services on a Legacy Network Architecture
Note: the DCS provides both voice and data segregation and DS–0/DS–1/DS–3 grooming.
Voice-data overlay networks result in duplicate equipment and facilities. In addition, running separate operations for Layers 2 and 3 (transport and network layers) yields high costs and slows down service provisioning. These networks are also more difficult to troubleshoot. Legacy networks have evolved into a complex mix of equipment because of advances in technology, regulatory changes, and evolving customer demand that have caused service providers to tack new capabilities onto them over the years. Generally, the architecture that was designed more than thirty years ago to carry constant-bandwidth voice circuits has been incrementally augmented with overlay components to carry data traffic.
The copper local loop used to access public network services can carry voice and data over separate DS–0s. TDM DCSs are deployed to separate voice and data and to groom multiple, partially filled DS–1s onto full DS–1s. TDM DCSs were created for fixed-bandwidth circuits; as such, they are part of an outdated network architecture and tend to impose a costly operational burden.
The operations and management systems of these DCSs are not compatible with newer data services–management systems, thus requiring the service-provisioning process to cross multiple departments, systems, and personnel. This situation increases the cost of service provisioning, can cause provisioning delays, and can introduce a high margin for error—factors that could result in the loss of frustrated customers. Once provisioned, the ongoing operations, troubleshooting, and fault management again require multidepartment, multisystem coordination.
Today, it is in the high-speed SONET transport backbone that voice, private line, and data are finally integrated, albeit using inflexible TDM to handle traffic. This infrastructure migrates to a more dynamic platform based on ATM, which operates using more efficient statistical multiplexing to aggregate traffic in a more scalable fashion.
As a quick fix for the equipment-complexity problem at smaller network access points, some service providers back-haul traffic across a SONET ring or a DS–3/OC–3 pipe to a larger point of presence (POP) by means of TDM technology. This system, however, constitutes an inefficient use of trunk-bandwidth resources. At this larger POP, DCSs are used again to distribute different types of traffic to different network components such as voice switches, frame-relay switches, IP switches and routers, and ATM switches. In many networks, this traffic must once again converge onto a common ATM backbone, causing an inefficient series of aggregating and splitting traffic.
The problems of these legacy network architectures can only be solved by embracing the new technologies that are designed to address the service providers' evolving opportunities and challenges described in the previous section. Topic 4 explores how emerging technology can remedy the problems and give service providers who embrace this new technology a competitive edge.
