ADAPTIVE RATE DATA TRANSMISSION OVER TELEPHONE WIRING USING ETHERNET INTERFACES
Date
1996-07
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Degree Level
Masters
Abstract
The popularity of the Internet and the World Wide Web has created a dramatic increase in demand for residential Internet access at speeds greater than the 28.8 kb/s offered by voice-band modems.
This thesis investigates one method of providing low cost, higher speed network access to the home. The existing telephone wire infrastructure is used to transmit digital data for the "last mile" from a telephone wiring center to the home over copper pair subscriber loops. At the wiring center, high speed connections to the Internet are available through fiber optic transmission facilities.
An adaptiye rate digital transmission scheme is proposed to carry the data across telephone subscriber loops. Users living near wiring centers with short loops can have higher bit rate access to the network, while users living farther away are not excluded from access, but have reduced bit rate access to the same network.
A research prototype adaptive rate transmission system was constructed for exper-imentation using Ethernet interfaces to connect the user's computer to the adaptive rate transmission line.
The digital data is transmitted over the telephone loop in the excess bandwidth above the voice-band through the use of balanced FM0 signalling. Data transmission can be performed on the same subscriber loop without disturbing regular telephone operation on that line.
For a given subscriber loop, the rate adaption algorithm selects the highest possi-ble bit rate with an acceptable error rate. An acceptable transmission rate is assumed when the bit error ratio (BER) is below approximately 10-6. Rate adaption is per-formed at system start up by sending a large number of test packets across the line at various bit rates and measuring the packet errors at each rate.
It was found through laboratory experiments that rate adaption worked well and provided data rates from a maximum of 666.7 kb/s at short (< 1.5 km) distances, down to 133.3 kb/s for a distance of 3.6 km on 24 gauge telephone wire, and down to 222.2 kb/s on 2.5 km of 26 gauge wiring.
There is a large difference in bit rates between the the Ethernet interface of the computer and the adaptive rate serial link. Proper flow control is therefore essential. The TCP layer of the TCP/IP protocol stack implements a sliding window flow control protocol which provides the necessary flow control through the system. Actual file transfers were performed using TCP/IP, and these file transfers showed satisfactory data transmission performance.
Using two, 486/66 personal computers, a data transfer rate of 300 kb/s was ob-tained with a line bit rate of 666.7 kb/s, a maximum TCP packet segment size of 1460, and a single packet TCP receive window size. At the other extreme, a data transfer rate of 65 kb/s was obtained with a line bit rate of 125.0 kb/s, a maximum segment size of 536, and again a single packet receive window size.
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Degree
Master of Science (M.Sc.)
Department
Electrical Engineering