Yesterday I reported on a story that several iPhone 4 users were experiencing massive drops in their upload speeds. At first we thought perhaps AT&T were beginning to limit upload speeds, but today AT&T announced that the slowdown was in fact due to a bug in their network equipment.
Due to the increased upload demand from the iPhone 4, a software flaw has been exposed in Alcatel-Lucent’s 3G network equipment, temporarily forcing lower upstream speeds for some AT&T customers.
Alcatel are currently working on a solution and expect to know soon when it will be fixed. The flaw did not cause problems until the introduction of the iPhone 4, which comes with features such as high-definition video that can require a fast connection from the phone up to the network, she said. Downstream performance is not affected.
The problem only affects devices that use HSUPA (High-Speed Uplink Packet Access) technology, the fastest upstream system AT&T uses. Apart from the iPhone 4, AT&T’s LaptopConnect cards for PCs and netbooks also uses HSUPA. The reason the issue is only affecting certain customers is because it only exists in areas where AT&T uses Alcatel equipment, which is only affecting about 2% of customers.
While the bug is being fixed, AT&T is providing regular 3G upstream speeds instead of HSUPA, but the carrier will not shut down service in the course of solving the problem,
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