ATM, at Your Service

Wireless CLECs maximize growth potential and save money with multiservice ATM virtual-path transport.

ATM is a cost-effective way for wireless CLECs needing a scaleable platform to offer multiservice capabilities to their customers. ATM virtual-path transport technology also can save you bandwidth, reduce the amount of broadband switching ports and is easy to install.

One of the biggest challenges service providers face today is building out their networks and deploying services. Finding compatible equipment, upgrading and integrating equipment, and rolling out new technologies such as ATM are imperative to stay ahead of the game. Business challenges also are tied to the tremendous growth service providers are experiencing now and are expecting over the next year.

The primary application area for ATM transport elements in the CLEC/ISP environment is as a multiservice broadband platform for a metropolitan area network (MAN). A typical MAN consists of customer-service termination points such as base sites; traffic-consolidation points and hub sites; service aggregation and traffic-routing points; and central office (CO) sites.

Usually, base sites house M1-3 multiplexers and/or service-access multiplexers (SAMs) for customer-service termination and WAN access. The hub sites usually house wideband digital cross-connects, multiplexers and/or edge switches for traffic aggregation, grooming and switching within the MAN. At the CO sites, broadband digital cross-connects, SONET add/drop multiplexers and core switches for voice and data services are deployed. These groups of equipment are used for bandwidth management, service consolidation and routing in the WAN.

The common denominator for all equipment in the MAN is the transport function. A large number of base sites are served by a single hub, which in turn feeds traffic to a CO. In a wireless CLEC MAN, there are between 50 and 100 base sites served by a single hub using T1 and channelized T3 links over wireless media. And there are about five to 10 hubs served by a single CO using DS3, OC-3 or OC-12 point-to-point facilities. The ATM transport element in this case forms an integrated transport platform interconnecting hub sites with the CO in the MAN. (See Figure 1.)

The ATM transport element is best positioned as a distributed digital cross-connect and bandwidth-management platform. As service providers build their networks, they are looking for a reliable, efficient, standards-based and cost-effective transport platform to consolidate all of their service offerings on a single transport network.

Major Advantages
CLECs using an ATM backbone hold a major advantage over their competitors. Wireless CLEC/ISPs avoid the problems of installing and maintaining cable in expensive real-estate areas, or of dealing with the local loop. By setting up wireless systems, typically consisting of antennas or satellite dishes atop their COs with some additional base stations and repeaters where needed, CLECs can grow their businesses faster.

Using ATM allows them to flexibly provision a network due to ATM's quality-of-service capabilities. More recently, ATM-based transport networks have emerged to provide a multiservice platform to deliver a wide variety of access applications (frame relay, cell relay, private line), reducing the requirement for widespread ATM switch deployment and offering a single manageable transport infrastructure. As the number of switches are reduced, so are capital costs, providing the most economical solution for service providers. It also offers a scaleable network, featuring point-to-point for smaller service providers, all the way up to OC-48 speeds. The ATM transport network operates over existing SONET facilities — again, translating to lower network costs — for redundancy and reliability. ATM virtual-path transport elements can combine the following functions:

• The service flexibility of an ATM SAM

• The functionality of a digital cross-connect

• The robustness and bandwidth efficiency of an ATM add/drop multiplexer

• The bandwidth-management capability of an ATM cross-connect or ATM switch.

Network Models
Creating an ATM transport network model shows how effective the positioning of ATM as a MAN distribution and transport platform can be in a typical wireless CLEC. For the purpose of this modeling example, the following is used:

• Each hub supports 100 DS-1 interfaces and 30 DS-3 interfaces from business sites

• Each hub handles 50% data and 50% voice traffic

• 35% traffic usage to the customer

• 20% network build-up over a 5-year period.

For simplicity, a single hub is modeled using time division multiplexing (TDM) technology as the present method of operation and using an ATM virtual path as the future method of operation, respectively.

In the present-method operation model, the following TDM technologies are used:

• A TDM digital cross-connect for bandwidth management and multiplexing of access interfaces

• OC-48 SONET add/drop multiplexer for interoffice fiber transport between the hub and the CO

• Each hub requires 13 DS-3s equivalent bandwidth to the CO (trunk bandwidth for the 100 DS-1 and 30 DS-3 access interfaces at a 35% link usage factor).

• Channelized DS-3 interfaces at the broadband switching system for data services.

More than two-thirds of the cost of implementing the TDM method is incurred in the first year because of the digital cross-connects and OC-48 SONET add/drop multiplexer investments. In addition to this capital cost, present-method operation also increases operational costs due to the need for a number of network-management platforms and the requirements for skilled technicians to run each platform.

In the future-method operation model, an ATM virtual path can be configured as a distributed digital cross-connect and bandwidth-management platform with an embodied SONET add/drop mulitplexer to satisfy hub-to-CO transport requirements with a significant cost advantage compared with traditional TDM solutions.

In the future-method operation modeling, a single ATM add/drop multiplexer at the hub and at the CO are needed in year 1. Two ATM add/drop multiplexers will be added to the network in subsequent years as more customer-access interfaces are deployed. The data from customers are terminated using the appropriate frame-relay service, cell-relay service or channelized DS-3 interfaces while the voice traffic is terminated using circuit emulation service (CES) cards.

There are nine DS-3 trunks required to backhaul the access traffic from each hub to the CO compared to the 13 DS-3 trunks used in the present-method operation. This additional savings on facility comesfrom the statistical multiplexing of data traffic by the ATM virtual path add/drop multiplexer.

The ATM transport option has a smaller initial investment compared to present-method operation and results in overall savings. Future-method operation results in overall savings of about 36% in capital cost compared to the present-method operation.

In addition to the capital cost savings, future-method operation also results in recurring cost savings of facilities. Assuming $2,000/month per DS-3 and the 50% data, 50% voice split, total savings of four DS-3s per hub is attained. This saving translates into a 31% cost savings over the 5-year network build-up period.

ATM virtual-path transport elements can result in the savings of 31% on recurring facility expenses over the 5-year network build-up period. The total savings is around 33%.

Sleath (chris_sleath@adc.com) is ADC Telecommunications program marketing manager.