One of the challenges facing today’s telco operators is whether to deliver the required bandwidth to the end customer via wireline or wireless technology. In this article Calvin Menyennett of Dimension Data explains further.
In South Africa, wireless data access via a mobile phone on the GSM network is available but speed is limited to 9,6 Kbps. Mobile data on GSM is also an expensive option, since the call rates are fairly high for the data throughput. With a 56K modem, wireline technology offers some improvement over GSM mobile data, with download speeds of up to 56 Kbps depending on the quality of the line. The 56 Kbps upper limit is due to bandwidth limitations imposed on analog signals at the exchange.
The next evolutionary step was to convert this analog access technology to digital technology, resulting in the introduction of ISDN (integrated services digital network) technology. On a normal copper pair, ISDN offers up to 144 Kbps. As it is digital, ISDN is a vast improvement over analog modem technology because it offers a guaranteed line speed. Unfortunately, the initial high pricing of ISDN in South Africa has restricted its uptake.
Digital subscriber line (DSL) technology is set to supersede ISDN. It makes use of sophisticated modulation coding techniques to dramatically improve the throughput on a normal copper pair.
One flavour of DSL is asymmetrical DSL (ADSL) which sends information at a greater bandwidth downstream (from the exchange to the customer) than upstream (from the customer to the exchange). ADSL can support downstream data rates of up to 8 Mbps and an upstream rate of up to 768 Kbps. Distance is limited to a maximum of 5,5 km, but at this distance downstream speed is more likely to be around 2 Mbps.
Numerous telco operators are rolling out ADSL technology around the world. In South Africa, Telkom is poised to release ADSL in the near future. Although ADSL is often touted as a means of providing superfast access to the Internet, this is not quite true. It is important to remember that DSL is the access transport technology at the end of the 'line' to the customer.
A normal 56K dial-up modem typically delivers transfer speeds of around 4 Kbps. This is mainly because bandwidth at the Internet service provider (ISP) is shared among a number of users, thereby lowering the throughput rate and causing bottlenecks. For example, when connecting to a website somewhere in the rest of the world, data traffic passes through numerous data links, hubs, routers and switches. If only one of these is a bottleneck, the total speed is decreased.
With ADSL technology, downstream throughput capability is 140 times greater than that of a 56K modem. In order for end users to benefit from this speed, all role players need to make huge capital investments towards upgrading the bandwidth and backbone of the Internet.
There will definitely be dramatic improvements in speed for users logging on to corporate intranets. The ADSL technology will provide access directly into the telco IP backbone. Thus, for the remote user to benefit from the increase in bandwidth the organisation will need to increase the bandwidth to its ISP and/or to the telco IP backbone.
Depending on where ADSL is positioned in terms of pricing, it could offer a cheaper alternative to leased lines for setting up WANs. Although Telkom might target the business environment for this service, the pricing position is crucial to ADSL's success.
Current marketing efforts around DSL are focusing on the speed of the technology, potentially creating unrealistic expectations for customers. Although DSL can provide very high-speed access for the customer, the bottleneck theory governs the actual throughput. If DSL is to deliver on its technological capabilities, drastic increases in the Internet and other corporate IP backbones are required.
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version