PDF of this tutorialSeveral industry trends are fueling the evolution to new public switched–network architectures. These factors are discussed in the following paragraphs.
Data Traffic Explosion Exposes TDM Inefficiencies
The different characteristics of voice and data traffic have been well recognized in the industry. Data traffic tends to be bursty, consuming large volumes of bandwidth for occasional, short intervals. Legacy TDM circuit-based networks, on the other hand, were originally designed to carry more predictable streams of voice traffic, and they do not efficiently support bursty data traffic. With data growth now outpacing voice, service providers face important challenges and must shed the baggage of inefficient TDM infrastructures while preserving the integrity and quality of private-line and voice traffic through the use of ATM classes of service (CoS). Service providers are also optimizing their networks to handle rapidly growing volumes of bursty data traffic through the use of statistical multiplexing, which enables an entire transmission medium to be filled with packets. This is a more bandwidth-efficient mechanism than dedicating connection-oriented TDM circuits to particular applications, which wastes bandwidth while circuits sit idle during periods when nothing is transmitted.
Demand for Connectivity Experiences Explosive Growth
Service providers face the challenge of connecting an enormous number of diverse, relatively low-speed access services into their high-speed backbones. Supporting a wide range of access interfaces is a potentially complex and expensive undertaking but is necessary if all customers are to be served.
Because of their installed infrastructures and preferences, for example, some customers demand private-line connectivity, while others require frame relay, Internet protocol (IP), or dial-up point-to-point protocol (PPP) connections. Still others are ready to buy DS–1–speed ATM access links or use inverse multiplexing for ATM (IMA), which combines multiple DS–1/E1 lines into one logical interface for integrated voice and data access.
These new market dynamics represent the potential to achieve the following goals:
- engineering dense support of access services into the network and supporting typical copper rates of DS–0 (e.g., 64 kbps), fractional DS–1, DS–1, and inverse multiplexed n x DS–1
- designing the network to adapt to the changing service mix for private line, frame relay, IP, PPP, ATM, IMA, and other access technologies
- designing the network for integrated access of voice and data over a common DS–1 line; this is TDM–integrated access today, evolving to ATM integrated access tomorrow
Service Providers Require More Flexible Network Platforms
The pace at which new network services and features are being developed is faster today than ever before. As the race to acquire market-share becomes increasingly fierce, the service providers who will have the competitive edge are those who can most rapidly introduce new services and respond to customers' changing needs. This agility hinges on network infrastructures with a rich set of features and functionality, the support of multiple interfaces, and distributed, software-defined intelligence.
Service Providers Seek Ways to Minimize the Cost of Providing Service
As network technologies mature, price tends to become one of the dominant selection factors for purchasers of network services. To compete on price, service providers must contain the cost of provisioning these services by squeezing as much expense as possible out of service provisioning and support.
Service providers must tightly manage network-infrastructure costs to be able to build and expand networks rapidly. In addition, operations can represent a large portion of the life-cycle costs and can be heavily influenced by the network architecture's inherent manageability, flexibility, and simplicity. As a result, the network service provider must design a cost-efficient network, avoiding layers of legacy network elements and their associated operational complexity and high costs.
