ISDN versus ADSL
ISDN
ISDN is considered a legacy technology by many, and the service has been losing ground to ADSL in many countries, including Britain where new ISDN orders are no longer processed.
While ISDN remains popular for services requiring a guaranteed constant bit rate, like broadcasting and video conferencing, it is expensive if compared to ADSL. An added drawback is that ISDN does not provide the same high downlink speeds of ADSL.
In South Africa, the number of ISDN subscribers is surprisingly still rising, which may be a result of the problems associated with ADSL installations times, restrictive usage limits and the limited availability of ADSL.
Pricing comparison
With Telkom’s Surfmore 30 Plus package, which includes rental for a customer’s ISDN2a line, CallAnswer and ISDN Internet, a subscriber gets 30 hours of surfing for R458.00.
During this 30 hour period, taking a constant maximum possible throughput rate of 8KB/s, it is possible to download 864 000 KB or 844 MB. Surfing after hours, using Telkom’s flat rated service for local calls, can significantly reduce call costs but for this particular comparison only standard call changes were considered.
A standard DSL384 ADSL service with a 3GB usage allowance is priced at R 494-00 when purchasing all components from Telkom. This is slightly more expensive than the R 458-00 for the Surfmore 30 Plus package, but allows for 3072 MB in comparison with ISDN’s 844 MB.
Apart from the higher download limit on ADSL, the download time on ADSL can be as much as 6 times faster than using a single 64 Kbits/s ISDN channel
The download time on ADSL can be as much as 64 times faster than a standard 64 Kbps ISDN line when opting for an ‘Up to 4 Mbps’ ADSL offerings from Telkom, but this comes at a higher price of R 675-00 if purchasing Telkom’s 3 GB Do Broadband offering.
Using InfinitCall
Many ISDN subscribers do not trust the Surfmore packages to offer lower fees, but rather opt for Telkom’s InfinitCall product. For an additional monthly charge of R 67.18 per month there is a price cap of R 10.65 per call for after hour and weekend calls.
The user can theoretically stay connected for around 12 hours during weekdays and for 60 hours over weekends. This allows for a maximum theoretical download limit of 3 110 400 KB or 3038 MB per week at an associated call cost of R 53.25, assuming there are no dropped calls.
Using the InfinitCall product with ISDN will in real terms allow for higher downloads that 3 GB per month with total costs rivaling that of DSL384, but the limitations in both speed and usage times may curb the joy of this system
ISDN may have a bleak future in the residential market
Many people are still opting for ISDN, despite the limitations on speed and call charges associated with the service. This is often because of low international latency, more constant bit rates, and possible savings when using ISDN only after hours and over weekends.
ADSL is however proving to be the better of the two options, and while South Africa is lagging behind the developed countries in the fixed line broadband space, ISDN in South Africa may follow its British counterpart and bow out to ADSL.
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