Integrated LAN, ATM and Sonet platforms support multimedia services

Fast, secure and affordable data and voice routing functions can be achieved by mapping LAN protocols to ATM cell structures for transport over Sonet backbone networks

MICHAEL SABELHAUS

FUJITSU NETWORK

TRANSMISSION SYSTEMS INC.

Integrating local area network and asynchronous transfer mode interconnection services on synchronous optical networks empowers service providers to deliver the voice and data communication choices their customers need in today`s information-centric economy. With the technology to link remote or local area networks, or LANs, providers can now provide companies with seamless RJ-45 connectivity to their information resources--wherever they are located, even nationwide. By leveraging their synchronous optical networks, or Sonet, through the incorporation of protocol mapping based on asynchronous transfer mode, or ATM, providers can also create the ATM infrastructure they will need to optimize existing fiber-optic networks and to support future multimedia and enhanced services.

With the growth in distributed networking, more and more companies are seeking cost-effective ways of linking remote data resources. Whether those facilities are cross-campus, cross-town, or cross-country, the need remains the same: to transmit data securely, swiftly and economically.

For communications service providers, this corporate need offers an enormous revenue-generating opportunity, and, as a result, many providers are actively looking for ways to better support LAN interconnection services. Increasingly, these providers are recognizing that transporting native LAN traffic over fiber-optic Sonet rings holds the key to improved services and profits.

Until now, most service providers who have attempted to leverage their Sonet rings to support both voice and data have relied on overlay networks, cobbled together with dedicated fiber-optic cable runs to individual customers. Customers then had to link their routing and bridging infrastructures to these fibers. Although this networking configuration can work, it presents several problems, such as the high cost of the dedicated fiber links for providers, and for customers, the overhead of an internetworking infrastructure.

In addition, bandwidth choices are limited to DS-0, DS-1, and DS-3 links, at speeds of 64 kilobits per second and 1.5 and 45 megabits per second, respectively. Moreover, upgrades from one line to another are difficult to achieve.

Furthermore, with multiple routers, multiplexers, digital service/channel service units and other devices involved, compatibility and management of the disparate network elements frequently mandate evaluation. And finally, survivability becomes a concern because of the multiple connections required, as well as the costs of duplicating DS-3 or DS-1 links.

Data routing and bridging

To eliminate these shortcomings and make LAN-to-LAN interconnections more efficient and cost-effective for service providers as well as customers, a new architecture is available that integrates data routing and bridging directly into Sonet multiplexers. This architecture enables customers to simply interconnect their LANs through an RJ-45 connection.

In this architecture, the data routing function required for LAN interconnection services is achieved by mapping conventional LAN Ethernet and Token Ring protocols to an ATM cell structure. These ATM cells are then transported over the Sonet backbone network to their destinations.

It is critically important to note that by segmenting data from voice traffic this way, current STM voice circuits are not compromised. In fact, this ATM data segmentation enables providers to achieve a smooth migration path from present STM voice circuits to future network-wide ATM support. Although ATM network services are not yet widely available, they are being steadily implemented. Therefore, installing a data transport system that relies on this technology for meeting today`s LAN interconnection requirements will also provide a growth path to future revenue-generating services.

For now, this architecture offers a degree of flexibility previously not available. For example, it supports not only long-distance LAN interconnections, but also local bridging needs. In fact, with the bridging and routing functions integrated into the Sonet multiplexer, providers can offer any-to-any connectivity between local departmental LANs or cross-country facilities--or any combination of both.

This flexibility is particularly important in acquisition environments, where connectivity must be achieved as quickly as possible to minimize transition costs. By supporting both local bridging and long-distance routing, providers can tap into this market and save their customers the capital costs of creating their own backbones, as well as the overhead associated with selecting, implementing and maintaining this infrastructure.

Depending on their current hardware, providers may be able to add LAN interconnection services to their Sonet rings just by implementing the appropriate cards to their existing Sonet multiplexers, and without re-engineering their networks. In so doing, providers will be able to offer full support for native LAN protocols and eliminate the bottlenecks that occur in overlay networks because of bandwidth restrictions.

Achieving a 10-Mbit/sec pipe to transport full-duplexed Ethernet transmissions, for example, is not possible in an overlay network with a DS-1 link, which restricts traffic to 1.5 Mbits/sec; the alternative, a DS-3 link operating at 45 Mbits/sec, is overkill. With Sonet-based LAN interconnections that rely on ATM mapping technology, however, customers can be offered the bandwidth they need. Upgrades, if required, can be quickly and incrementally accomplished by the provider through simple configuration changes and without customer involvement.

This bandwidth granularity can be accomplished by first allocating a synchronous transport signal, level 1, or STS-1 (Sonet-equivalent to a DS-3) link for ATM cell traffic. Then, multiple, variable bandwidth virtual circuits are created within that STS-1. In addition to empowering providers to tailor bandwidths to customer needs, this segmentation capability also allows providers to leverage a single fiber run across many service subscribers. For example, take the case of a provider running a dedicated fiber-optic link from its Sonet ring to the premises of a customer who needs a DS-3 link to a corporate routed network. By running the fiber through an appropriately configured Sonet multiplexer and installing ATM service network cards, both STM and ATM bandwidth can be supported to multiple customer sites.

Security issues

The shared service between customers may initially raise security concerns, but these concerns are unfounded because all data traffic travels over virtual circuits that are based on ATM cells. In addition, at the LAN level, security is enhanced because all bridged communications conform with the closed user group security standard (IEEE 802.10). This standard specifies that all data entering the network must be tagged on a per-port basis, and that once tagged, the data can be sent only to other ports in the network that have the same user group identification. Because users cannot change these identifications, any single LAN-to-LAN interconnection is secure from others riding the same circuit.

Sonet-based LAN interconnections are therefore more secure than those based on conventional, router-based internetworks. In addition, this ATM-based protocol mapping architecture also dramatically improves the survivability of LAN interconnections. Compared to asynchronous fiber-optic transport, for example, Sonet is inherently more survivable because of its adherence to Bellcore survivability standards that require alternate path switching in under 50 milliseconds. Equally important, Sonet multiplexers support a path-switched ring and come equipped with intelligent circuits that automatically select the best of the redundant incoming signals.

Although these protection levels could certainly be achieved on the customer`s premises, the implementation is, most often, impractical and costly for a company to make the required investment in necessary redundant resources (including routing facilities and communications lines).

Furthermore, with routing facilities integrated onto the Sonet ring, several points of failure common in overlay networks are eliminated. For example, with Sonet/ATM-based routing, network connectivity is achieved via an RJ-45 connection; consequently, a digital service/channel service unit and all associated fiber runs are unnecessary.

Another benefit of integrating LAN interconnection services onto a Sonet ring is the enhanced management capabilities made possible. With overlay networks, service providers have to maintain separate management facilities for both voice and data networks. But by integrating voice and data over Sonet multiplexers and implementing software management packages that support both transaction language-1, or TL-1, protocols and simple network management protocols, or SNMPs, comprehensive network management can be achieved from a single platform in a single network operations center. This efficient management capability not only streamlines provider operations, but also serves as a marketing tool. It enables service providers, for example, to differentiate their service offerings by providing increased user control and performance guarantees. u

Michael Sabelhaus is manager, data product planning, at Fujitsu Network Transmission Systems Inc. in Richardson, TX.