Bluetooth discussion - FAQ: Why is my GPRS, EDGE, or UMTS so slow?

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FAQ: Why is my GPRS, EDGE, or UMTS so slow?

John Navas

2005-10-20, 11:48 pm

Q: Why is my GPRS, EDGE, or UMTS so slow?

A1: SERIAL PORT BOTTLENECK: Connections between handsets and "tethered"
devices (e.g., notebook computer, PDA) are typically implemented as a
serial port, either real or virtual, and port speed usually defaults to
115 Kbps. (My own Bluetooth stack is implemented as a virtual serial
port that will go as fast as 921.6 Kbps, but which runs at only 115.2
Kbps by default.) While 115 Kbps is generally fast enough for GPRS and
CDMA 1X, it can be a bottleneck for EDGE, UMTS, and CDMA EV-DO. In
general, I recommend port speed* of 230 Kbps for GPRS and CDMA 1X, 460
Kbps for EDGE, and 920 Kbps for UMTS and CMDA EV-DO.

A2: HANDSET CAPABILITIES: Handsets (and PC Cards) do not all have the
same data performance. In general, all reasonably recent
GPRS/EDGE-capable devices from Ericsson and Sony Ericsson support Class
8 (4+1) and Class 10 (4+2, max of 5), whereas most Nokia devices are
limited to slower Class 2 (2+1), Class 4 (3+1), and Class 6 (3+2, max 4)
.. Motorola has both Class 4 and Class 8 devices. (The first number is
the max downlink slots, and the number after the "+" is the max uplink
slots.) This can translate into a substantial difference in throughput
-- if supported by the carrier:
* Class 4 or Class 6 is 50% faster on downlink than Class 2
* Class 8 or Class 10 is 100% faster on downlink than Class 2,
33% faster on downlink than Class 4 or Class 6.
* Class 10 can be 100% faster on uplink than Class 2, Class 4, or Class 8.

* To set cellular serial port speed in Windows XP:
.. Open Network Connections
.. Right-click on cellular connection, and choose Properties
.. In Properties-General, select checked cellular modem, and click Configure
.. In Modem Configuration, select desired Maximum Speed.
.. Click OK to close all windows.

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