LANs to WANs: The Complete Management Guide

For most customers, a 5-minute service interruption is within tolerable limits. But other customers, such as businesses that rely extensively on inbound or outbound calling, need a much shorter restoration period. For these customers, carriers offer optional services that can be used to meet individual reliability requirements. These can range from the carrier planning and building a complete private network, to customers using one or more optional reliability features to meet highly specific needs. Of the more than 1,200 carriers operating in the United States today, none has a more comprehensive set of restoration services than AT&T. The following offerings, however, can also be used to make comparisons with other carriers:

• Split-access flexible egress routing (SAFER). For users of dedicated access facilities, SAFER provides a backup mechanism to protect the exit ramp of an organization’s toll-free service to ensure consistent and reliable access to its customers. SAFER protects against network congestion, access facility failure, or a service disruption at the AT&T switch. SAFER can also be used to protect a business from a failed or busy T1 facility. If toll-free calls cannot complete through the normal terminating network switch, SAFER redirects these calls through an alternate switch in the AT&T network. This gives callers an alternate route to the business location. This mechanism is automatically activated in near real-time, whenever it is needed.

• Alternate destination call routing (ADCR). For customers with toll-free operations in more than one location, ADCR allows the AT&T switch that normally carries the calls to the company’s location to route incoming calls to another business location automatically when a problem arises. For example, if a company’s ACD at the main location is unavailable or too busy with calls, any additional calls would be forwarded automatically to an alternate location. Calls could be directed either through the original AT&T switch or through an alternate switch, thus protecting against disruptions in AT&T switches, local exchange switches, or customer equipment.

• Network protection capability (NPC). For digital service customers, the optional NPC provides a geographically diverse backup facility and will usually switch traffic to this backup route within 20 ms of a service interruption. When the service is fully restored, the NPC automatically routes traffic according to the original configuration. The backup and restoration processes occur so rapidly that the customer will not notice any disruption to service. If data is in transit during the configuration change, no data will be lost.

• Enhanced diversity routing option (EDRO). To protect a business from service disruptions in the event of a cable cut or natural disaster, EDRO provides customers with a documented physical and electrical circuit diversity program. As part of EDRO, AT&T designs and maintains physically separate paths through its network to eliminate common points of failure between circuits. Under this option, diverse circuits are separated by at least 100 feet and avoid common AT&T buildings to further reduce the possibility of a common point of failure.

• Access protection capability (APC). To protect the access portion of a customer’s circuit, APC provides immediate recovery of access circuits from certain network failures by automatically transferring service to a dedicated, separately routed access circuit.

• Customer controlled reconfiguration. This service is available in conjunction with AT&T’s digital access and cross-connect system (DACS). CCR offers a means to route around failed facilities. The DACS is not a switch (PBX) that can be used for setting up calls in real time or for performing alternate routing on a dynamic basis; it is simply a static routing device. Originally designed to automate the process of circuit provisioning to avoid having a carrier’s technician manually patch the customer’s derived 64-Kbps DS0 channels to designated long-haul transport facilities, the DACS allows CCR subscribers to organize and manage their own circuits from an on-premises management terminal. Any changes will take a few minutes to a half-hour to implement because changes must be uploaded to the carrier’s network before they take effect.

• Bandwidth manager services. For data services, AT&T offers network managers the capability of fine-tuning their WAN to handle dynamic applications requirements, such as LAN interconnection, videoconferencing, and traffic-load balancing. In addition, bandwidth management services can be used to automatically restore dedicated private-line circuits or redirect private line and frame relay service circuits to a backup location in the event of a circuit failure and/or a disaster at the primary site.

• T1.5 reserved service. This service supports applications requiring T1 (1.544 Mbps) speeds. AT&T brings a dedicated T1 facility on-line only after the customer verbally requests it with a phone call. This restoration solution requires that the customer pre-subscribe to the service and that local-access facilities already be in place.