Why DSL upload speeds are so slow

Digital subscriber line (DSL) users in South Africa have long complained about the slow upload speeds available on services such as asymmetric DSL (ADSL).

Although the downstream capability of a DSL connection is what South Africans might use the most, the upstream bandwidth available on your Internet connection remains important.

Should you use the maximum capacity of your upload connection, for example, the performance on your downstream connection can degrade dramatically.

Making use of online services such as Dropbox, or creating video content and uploading it to YouTube, often requires that you upload a large amount of data.

Depending on how much data you wish to back up on cloud storage facilities like Dropbox, or how long and how high the quality of the video you want to upload is, this can take many hours on an ADSL connection.

However, despite the benefits greater upstream bandwidth would offer both residential and business DSL subscribers, upload speeds in South Africa have remained stagnant while download speeds have increased.

On Telkom’s relatively new high-speed VDSL services things are much the same, with upload speeds much slower than download.

To find out what the implications would be of offering DSL services with more upstream bandwidth, we asked a number of Internet service providers that have both symmetric and asymmetric broadband offerings for their insight.

Shane Chorley

Shane Chorley

XDSL’s Danie Fourie said that the asymmetric nature of Telkom’s DSL services was a factor of the technology used.

Shane Chorley, head of network and operations at Vox Telecom, added that the bandwidth profiles were initially determined from user behaviour when there was far more downloading than uploading happening.

Times are changing, though, Chorley said.

Neither Fourie nor Chorley believed that the financial implications of offering symmetric broadband services, where upstream and downstream bandwidth is equal, would have a significant financial implication for them.

The trade-off: upstream speed for more users

Laurie Fialkov

Laurie Fialkov

On the topic of cost implications, Cybersmart CEO Laurie Fialkov said it was dependent on what an Internet service provider’s network looked like.

“In our case, hosting is less than 20% of our traffic so we are always sitting with a glut of upload bandwidth,” Fialkov said.

Other providers may find it trickier to offer faster upload speeds if their web hosting services use up a larger proportion of their upstream bandwidth.

Another important consideration in terms of cost and technical trade-offs is the asymmetric nature of Gigabit Passive Optical Network (GPON) technology, Fialkov said.

GPON uses time division multiplexing to handle upstream signals, resulting in a trade-off between the number of subscribers Telkom can serve and the upstream bandwidth per subscriber.

If Telkom increased the amount of upstream bandwidth to subscribers, it would decrease the number of subscribers it could serve on the same infrastructure.

Fialkov said that this, in turn, would cause an increase in costs as fewer subscribers shared the same fibre, while additional fibre networking gear would be needed to support the same number of subscribers as before.

Telkom was asked for comment on how it decided on the DSL profiles South Africans have access to, but the company was not able to comment by the time of publication.

Thanks to Franna for sending this in, and to Simeon for his help on the finer details of GPON.

Article courtesy of MyBroadband

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