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Specific applications that benefit from SDDN include RJE and NJE, CAD/CAE and medical imaging, distributed/shared computing, LAN interconnection, high-speed mainframe communications, PC-to-host and PC-to-PC transfer, peak traffic overflow and private line backup, videoconferencing, and Group IV facsimile.
VPN performance standards for data are comparable to private line services through the use of high-quality digital transport and an automatic restoration capability. With AT&Ts SDDN, for example, performance is measured in terms of network interface availability, network reliability, post dialing delay, call blocking, restoration, and service availability.
Network Interface Availability. For SDDN connections, an availability number indicates the percentage of time that all SDDN components are usable for customer applications. The target SDDN network interface-to-network interface (NI-to-NI) availability is 99.9% and includes ACCUNET T1.5 or DDS access links. Without the service restoration feature, the availability figure drops to 99.75%.
Network Reliability. Network reliability for SDDN is a measure of line transmission performance given in terms of EFS and SES. An EFS is a second with no bit errors, and an SES is a second with more than one error per 1,000 bits. Reliability objectives for EFS and SES are, respectively, 99.9% and 30 SES per day between AT&T serving offices (SO-to-SO), and 99.75% and 38 SES per day between network interfaces (NI-to-NI).
Post Dialing Delay (PDD). Post dialing delay refers to the amount of time from call initiation to call setup and is measured at the originating network interface. The SDDN objective is a four-second average post dialing delay, with 95% of all calls receiving network response within six seconds.
Call Blocking. Call blocking is the probability that an unsuccessful call attempt is due to network congestion. The target blocking is 1% during peak busy hours and 0.5% with planned improvements, with fewer than one call per 200 attempts blocked during peak traffic hours.
Restoration. The SDDN restoration objective for an NI-to-NI connection is less than 20 seconds for an estimated 99% of all restoration attempts. The stated restoration performance may not be guaranteed, however, in the event of a catastrophic or widespread network failure. The stated objective includes time spent in detection, redialing, and call setup stages in the SDDN network and CPE. A maximum of six seconds is allocated to CPE for failure detection and redialing an SDDN connection in response to a disconnect message.
Service Availability. Service availability objectives are improved with the use of diverse access arrangements. The split access flexible egress routing (SAFER) capability, available with AT&T 4ESS software, allows origination and distribution of calls between two toll switches, which minimizes the vulnerability to access link and nodal failures.
A new development in the VPN market is the emergence of local services. Bell Atlantic, for example, is offering a local VPN service in the mid-Atlantic region under the name of Bell Atlantic All@once VPNS. VPNS service allows companies to manage their local and intraLATA calls and save money on interLATA calls using Bell Atlantics public network as if it were their own private network.
With VPNS, customers can do such things as access their voice network remotely, make business calls from the road or home at business rates, originate calls from remote locations and bill them to the office, and block calls to certain telephone numbers or regions. Uniform pricing and billing plans are also arranged for all of the customers locations to reduce the administrative costs involved with reviewing billing statements, even if each location uses a different carrier.
Bell Atlantics service lets large business customers configure components of the public network like a customized private network without the expense of dedicated lines or equipment. Until now, services of this kind could not be used for local calls because they were offered through long-distance companies. Bell Atlantics service, however, is used for local calls and also works with the customers existing long distance services. The VPNS service also is compatible with Centrex services, PBX systems, or other customer premises equipment.
Once Bell Atlantic has achieved regulatory approval to deliver interLATA long-distance services, the company plans to expand the VPNS service to include in-region and out-of-region long distance service.
As an integral part of its All@once approach for large businesses, Bell Atlantic consults with companies to assess their communications needs and analyze their local calling patterns to design a solution that optimizes use of the public network. Bell Atlantic estimates that 25% to 75% of local phone traffic could be on a local VPN, where it could be subject to the lower rates that make VPNs attractive to users.
VPNs permit the creation of networks that combine the advantages of both private facilities and public services, drawing on the intelligence embedded in the carriers network. With services and features defined in software and implemented through out-of-band signaling methods, users have greater flexibility in configuring their networks from on-premises terminals and management systems than is possible with services implemented with manual patch panels and hardwired equipment. These capabilities make VPNs attractive for data as well as for voice for regional, national, and international corporate locations and portend success for VPNs long into the future.
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