Dr Kumar N. Sivarajan is currently the Chief Technology Officer of Tejas Networks. Dr Sivarajan co-founded Tejas Networks in May 2000. Prior to joining Tejas Networks, Dr Sivarajan worked (1990 to 1994) at IBM's Thomas J. Watson Research Center and then (1994 to 2000) with the Electrical Communication Engineering Department of the Indian Institute of Science in Bangalore. Dr Sivarajan is co-author of the book Optical Networks: A Practical Perspective published by Morgan Kaufmann Publishers. He is an Associate of the Indian Academy of Sciences, a recipient of the Young Engineer Award from the Indian National Academy of Engineering, and the Swarnajayanti Fellowship from the Department of Science and Technology, Government of India. He is also a recipient of the IEEE Charles LeGeyt Fortescue Fellowship, the IEEE Communications Society William R. Bennett Prise Paper Award, and the IEEE W.R.G. Baker Prise Paper Award. Kumar N. Sivarajan earned his Bachelor of Technology degree in Electrical Engineering (Electronics) from the Indian Institute of Technology, Madras, and his M.S. and Ph.D. degrees in Electrical Engineering from the California Institute of Technology, Pasadena.
High-speed, cost-effective data communication is vital to the productivity and success of most enterprises. Even though advances in fibre-optic technology have brought high capacity backbones to many businesses, the technology for leased lines remains expensive and difficult to manage. A cost-effective, easy-to-manage, Ethernet leased-line service to enterprises can be provided through the use of Ethernet over SDH technology that has recently been standardised by the ITU. This will provide smaller businesses with affordable easy access to reliable on-demand bandwidth.
Introduction The competitive service provider scenario, in countries such as India, with multiple operators for local, long-distance and wireless telephony has been a bonanza for consumers. Long-distance and cellular rates have dropped dramatically, by over 90 per cent in some cases, making long-distance voice calls far more affordable, and thereby, increasing their usage. However, a similar revolution in data communication, especially leased-line connectivity for businesses, is yet to happen. For most businesses, data communication is as important as voice communication, and this is particularly true for software development companies. The Indian software industry is poised to grow from $8.26 billion in 2000—01 to $87 billion in 2008 (source: NASSCOM) and high-speed data communication is vital to this growth. Regardless of the nature of the business, sharing of data between users within an enterprise, and providing access to the vast amounts of data available on the Internet, can be vital to its productivity and profitability. Many small and medium businesses use personal computers extensively but have poor wide-area network (WAN) connectivity, that is, data connectivity among users in different campuses or branch offices, or to the Internet. In this article, we analyse some of the reasons for this situation and suggest some solutions based on emerging standards and technologies. Enterprise Data Connectivity A typical enterprise owns multiple personal computers and, depending on the nature of the business, may have offices in multiple locations across the city or country. The technology for interconnecting these computers within the same building is almost always an Ethernet local-area network (LAN). This Ethernet LAN technology has been greatly cost-effective over time and its use has also been drastically simplified to the point where it can be effectively setup and used by almost everyone who can use a personal computer, without the need for any specialised knowledge or training. “ ...the known technology for interconnecting the enterprise LAN to the service provider network remains costly and complex. This has largely inhibited the adoption of leased lines for data connectivity between offices, or from offices to the Internet.” Technology advancing in fibre optic networking has made it possible for the deployment of very high capacity backbones at very low cost. Moreover, fibre is available to most office buildings in the major metros, thus bringing the optical network of the service provider close to the enterprise customers. However, the technology for interconnecting the enterprise LAN to the service provider network remains costly and complex. This has largely inhibited the adoption of leased lines for data connectivity between offices, or from offices to the Internet, so most small and medium businesses continue to use dial-up connections. This has resulted in such enterprises being unable to reap the full benefits of the Internet and the high-bandwidth, service-provider networks enabled by optical networking. Let us analyse the typical scenario for an enterprise setting up a leased line to either another office or to an Internet Service Provider (ISP). This is illustrated in Figure 1. While an enterprise uses Ethernet LANs within a building, service providers typically employ synchronous digital hierarchy (SDH) technology in their optical network. While both serve the purpose of transferring data between locations, the techniques as well as the interface speeds are quite different. SDH typically offers connectivity at a few different speeds such as 2 Mb/s, 34 Mb/s, and 155 Mb/s. (1 Mb/s is one million bits, or 125,000 characters, per second.) “To enable SMEs to take full advantage of the benefits of dedicated, high-speed data communication, a drastic simplification of the equipment is required to establish and manage WAN connectivity. Since LAN technology is low-cost and easy to manage, the best option is to make the WAN connection look just like another LAN connection.” Therefore, one typically uses a device called a router for the purpose of interfacing the LAN in the enterprise to the service provider's SDH network. The router typically provides an Ethernet port that connects to the LAN and a WAN port that connects to the SDH network. While the speed on the router's WAN port may match the speed required for interfacing to the SDH network, say 2 Mb/s, more often that not, the interface is typically different from that on the SDH equipment. This necessitates additional equipment, called a modem, to interface between the router in the customer premises and the SDH equipment of the service-provider. An enterprise that needs dedicated leased-line bandwidth must therefore invest not only in these routers and modems but must also employ qualified personnel to manage this connection. Enterprises such as software development houses or banks for whom such connectivity is critical have already made these investments. However, small and medium enterprises (SMEs), especially those which are not in information technology related fields have, by and large, shied away from taking leased-line connectivity between offices, or to the Internet, choosing to rely on low-speed dial-up connections instead. To enable SMEs to take full advantage of the benefits of dedicated, high-speed data communication, a drastic simplification of the equipment is required to establish and manage WAN connectivity. Since LAN technology is low-cost and easy to manage, the best option is to make the WAN connection look just like another LAN connection. The enterprise must simply be able to hook up a personal computer (PC) or an Ethernet LAN (hub/switch) to a wall-outlet connected to the service-provider: a process no more complex than hooking up another PC within the enterprise, or installing a new telephone. In order to achieve this low-cost and simple method for the enterprise customers, the service provider's SDH equipment must be capable of directly providing Ethernet interfaces to which the enterprises can connect their Ethernet LANs without the need for any additional equipment. The International Telecommunications Union (ITU) has introduced several new standards for this purpose over the last few years (see Table 1) and the equipment implementing these standards are starting to become available. Benefits of Ethernet over SDH Technology For the enterprise customer, especially SMEs, the Ethernet leased line results in a dramatic reduction in capital equipment costs and simplicity of operation/management. The router and modem required to establish such a connection are eliminated, especially when the connection is between two offices of the same enterprise, as illustrated in Figure 2. An Ethernet leased line is also much more reliable since no new equipment is needed at the customer premise to use this service. For the service provider, the ability to provide Ethernet services over his established SDH network means that he can avoid the significant expense involved in building another network infrastructure, based on Ethernet, to serve the needs of data customers. Almost all service providers have SDH networks (or the related Synchronous Optical Network – SONET – in the US and some other regions), which are used to serve their current needs, especially for voice traffic. The ability to leverage this network to provide Ethernet data services is important not only to minimise new capital expenditure but also to avoid increased operating costs and complexity involved in managing another network. “ ...an enterprise may need to have a large bandwidth for one hour a day for some backup purposes but unable to afford the lease of the required capacity on a permanent basis. With a bandwidth on demand service, he can ‘dial-up’ the bandwidth for the required period of time.” Even for large enterprises accustomed to using leased lines, Ethernet over SDH offers many advantages. The first is the increased granularity in which bandwidth is available from the service provider network. Any multiple of 2 Mb/s up to 100 Mb/s can be obtained. This enables enterprises to tailor their leased line capacity to their needs avoiding the rigidity of using either 2 Mb/s, or 34 Mb/s, or 155 Mb/s. The same property also makes this service much more bandwidth efficient for the service provider, and hence cheaper for the enterprise customer, since he need not waste 34 Mb/s of network capacity to provide a 10 Mb/s service, or 155 Mb/s to provide 100 Mb/s. (It is a common misconception that since service is provided through an Ethernet interface it should be provided at 10 Mb/s or 100 Mb/s, but this need not be the case. A bandwidth connection at any rate less than 100 Mb/s can be provided through an Ethernet connection through the use of appropriate flow-control techniques: see Table 1.) Moreover, the technology permits the service provider to use the fragmented, spare capacity in his network (say, over different paths) to provide data services much more cost-effectively. Another advantage that accrues from this technology is the potential to provide a bandwidth-on-demand service to fulfill the need for large bandwidths for short periods of time, say, an hour, for backing up data to a remote site. Since the service provider already taps into the enterprise through an Ethernet connection of, say, 100 Mb/s, while providing a bandwidth of some multiple of 2 Mb/s, say 6 Mb/s, he can easily increase this bandwidth, when requested to do so by the customer. This increase is affected entirely through software changes without any need for additional equipment either at the customer site or in the service provider's network. Thus, Ethernet over SDH lays the foundation for bandwidth-on-demand services, which can offer high-speed data communication in a cost-effective manner. For example, an enterprise may need to have a large bandwidth for one hour a day for some backup purposes but unable to afford the lease of the required capacity on a permanent basis. With a bandwidth on demand service, he can ‘dial-up’ the bandwidth for the required period of time. Conclusion The productivity of enterprises, especially SMEs, can be significantly increased if low-cost, easy-to-use, leased line data connectivity through Ethernet interfaces is available from service providers. Ethernet over SDH technology, recently standardised by the ITU, allows service providers to offer Ethernet leased lines to their customers through their existing SDH networks. Such an Ethernet over SDH service has a number of benefits. 1. It results in lower initial investments and lower operating costs. 2. It provides greater flexibility and scalability for the enterprise through the availability of a wide-range of interface speeds (any multiple of 2 Mb/s) without the need for additional equipment. 3. It results in increased reliability through the elimination of multiple equipments. 4. Ethernet over SDH also lays the foundation for service providers to offer services such as bandwidth-on-demand, which enables enterprises to utilise large bandwidth for short periods of time, further increasing their productivity at a lower cost.