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The idea of connection-oriented communications is not new. This type of switching provides a high degree of reliability and reduces operational costs. Multiple classes of service can be defined to support voice, video, and data transfer. Excellent bandwidth management through congestion control techniques are possible and security and access control are greatly improved. Connection-oriented switching, along with easy-to-implement policy-based management and accounting facilities have enabled the phone system to become universally accessible.

Frame relay technology is centered around connection-oriented communications, as is the most promising future networking technology — ATM. ATM is the most desirable networking technology because it offers dedicated, scalable bandwidth solutions for voice, video, and data.

ATM Switching. ATM switching is connection-oriented. Communications in an ATM network can be broken down into three phases: call setup (analogous to dialing a phone), data transfer (talking on the phone), and call teardown (hanging up the phone). The use of fixed-length 53-byte cells for data transfer delivers fixed latency transfer times for CBR applications such as voice and video. ATM addressing schemes are similar to a telephone number. In fact, the original designers of ATM technology had their roots in the telephony arena at BellCore, so many analogies to the operation of the phone system can be made when referring to an ATM network.

Although the benefits of ATM networking are attractive, there are currently nearly 100 million networked personal computers that do not have ATM interfaces. Few organizations can afford to replace all of their existing desktop and server interfaces, not to mention network analyzers and troubleshooting equipment.

Through the preservation of existing interface technology, by merely changing the internetworking devices from being connectionless to connection-oriented, many of the benefits of ATM may be realized without requiring the investment in all new ATM equipment. If LANs were designed to operate using the same principles as ATM, rather than making ATM compatible with LANs, users would benefit without significant capital investments in new equipment. By adding switch technology to the middle of the network, network administrators can be spared the trouble of upgrading numerous user devices, and users can be spared the inconvenience of rewiring and disruptions at their work site during an upgrade.

FEATURES OF SWITCHING SOFTWARE

The software that runs on switches is just as important as the switches themselves. A salesperson from AT&T, Fujitsu, or Northern Telecom does not focus the potential customer on the hardware aspects of the telephone switches. On the contrary, the salesperson conveys the benefits of the call management software, accounting, and ACD functions. Switched virtual networks should also be evaluated for their ability to deliver value because of the software features.

The Virtual Network Server

Network management software has traditionally been thought of as software that passively reports the status and operation of devices in the network. In the switched virtual network, the network management software takes on a new role as an active participant in operations as well as configuration and reporting. A new middleware component known as the VNS enforces the policies of operation defined by the network administrator through management software applications. The switches provide the data transport for the users of the network.

Directory Service. One of the software features in the VNS is the directory service. The directory service allows the identification of a device by logical name, MAC address, network protocol address, and ATM address, along with the switch and port that the user is connected to within the virtual network domain. The directory listing could be populated manually or dynamically as addresses are discovered. To fully realize the benefits of switched virtual networking, automatic configuration is absolutely essential. The directory service allows end nodes to be located and identified.

Security Service. The VNS security service would be used during call setup phases to determine whether users or groups of users were allowed to connect to each other. On a user-by-user and conversation-by-conversation basis, the network manager would have control. This communications policy management is analogous to call management on a telephone PBX where 900 numbers, long-distance, or international calls can be blocked. Users could be grouped together to form policy groups in which rules could be applied to individual users, groups, or even nested groups. Policies could be defined as open or secure, inclusive or exclusive.

A sample default policy can ensure that all communications are specifically defined to the VNS in order to be authorized. Policy groups can be manipulated either through drag-and-drop GUI or programmatically through SNMP commands.

Finally, and most important, the directory service can work in conjunction with the security service to ensure that policies follow the users as they move throughout the network. This feature alone could save time spent maintaining a router access list, as occurs headaches when a user changes location in the traditional network. However, it is important to realize that switched virtual networks ease administrative chores, they do not eliminate them.

Connection Management Service. The VNS connection management service is used to define the path communications would take through the switch fabric. A site may be linked by a relatively high-speed ATM link and a parallel but relatively low-speed Ethernet link. Network connections with a defined high QOS could traverse the ATM link and lower QOS connections could traverse the Ethernet. This connection management service allows for the transparent rerouting of calls in the event of a network fault. Connection management could also provide ongoing network monitoring in which individual user conversations could be tapped or traced for easy troubleshooting.


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