TELESYNC TSI-1575
MODEM/NETWORK
TEST UNIT
The TSI-1575 Modem/Network
Test Unit provides an efficient set of data tests and connection
evaluation tools for the Telephone Company personnel to quickly
assess the customer’s ability to transmit higher speed dialed-up
data over telephone facilities. TSI- 1575 is installed in the telephone
company central office. The unit is capable of handling 23 separate
Modem calls simultaneously. The unit include 23 DSPs (Digital Signal
Processors) chipsets manufactured by Analog Devices a world leader
in DSP components. The DSPs acts like the ISP (Internet Service
Provider modem bank) but are also capable of generating and displaying
test results taken while the customer is connected to the 1575.
Presently most computers
are equipped with V.90 modems, which theoretically can provide up
to 56Kbit/sec receive data speed. The V.90 modem speed is asymmetrical
in their transmission. They achieve the higher data rate only downstream-receive
(ISP to the modem) up to a maximum of 53.333Kbps. Upstream-transmit
(customer modem to ISP) rates are limited to V.34 (33.6Kbps) or
a maximum speed of 28.8Kbps. When a call is launched from the Customer
Modem to the 1575 a series of audible tones are heard. During this
time the two modems negotiate the optimum data speed in order for
the modems to send and receive the optimum data speed. Once an optimum
speed is achieved the modem line test begins. The TELESYNC modem
(DSP) is sending a data file as seen scrolled on the customer computer
monitor. After a set time the customer will see a graph of transmission
level versus voice band frequency. Additional information on line
speeds as well as other telephone transmission parameters are presented.
Since line conditions
can change from call to call, it is recommend that the customer
make several calls to the 1575 to ensure an accurate diagnosis.
Test Results
Explanations
Graph – Level vs. Freq.
This graph represents
the Frequency Response of a phone line. Level on the vertical side
is represented in dBm and frequency on the horizontal side is represented
in Hz. The graph describes the potential telephone line data throughput
performance. High roll-off in the frequency vs. amplitude (level)
and a flatter top line of the graph, will permit a higher modem
baud rate.
Mr. or Ms.
Confirm the first and
the last name as entered on top of the test questionnaire.
Modem on
The Modem phone number
as entered by the customer.
Modulation:
V.90: 56000-30000
bits/sec
K56flex: 56000-32000
bits/sec
V.34: 33600-2400
bits/sec
V.32bis: 14400-7200
bits/sec
V.32: 9600-4800
bits/sec
V.22/V.22bis:
2400, 1200, 600 bits/sec
Bell212A: 1200
bits/sec
Upload Speed
Shows the modem upstream
speed (customer’s computer to the 1575). The speed is presented
in BPS (Bits Per Second).
Download Speed
Present the Modem downstream
speed (1575 to the customer’s computer). The speed is described
in BPS (Bits Per Second).
Entered Phone Num:
The modem telephone number
as identified by the Telephone Company central office switch.
SNR:
Signal-to-Noise Ratio
is a measure of customer telephone line performance arrived at by
dividing modem signal power by the noise power. The higher the ratio,
the clearer the connection and the more data can be passed across
it. Even under the best conditions, when a signal undergoes analog-to-digital
conversion, there is a 35 to 39 dB signal-to-noise ratio (the "noise
floor"), which limits practical V.34 speeds to 33.6Kbps. The Signal-to-Noise
Ratio and the Level vs. Frequency graph determine the amount of
data that can be transmitted over a telephone line.
Rx, Tx Level (dBm):
Power level is presented
in dBm which describes the power in dB (decibel) with reference
to one milliwatt of power. Results list the receive (Rx) power level
and the transmit (Tx) power level as measured at the input to the
1575. Power levels are presented with a minus (-) sign in front
of the number indicating power levels below one milliwatt. Typical
numbers are –12dBm to –20dBm. The receive power level is a direct
indication of the modem distance from the telephone central office
as well as quality of the telephone facilities. A lower receive
power level number might represent telephone line problems. The
transmit power level is limited by the FCC (Federal Communication
Commission) to a maximum of –10dBm to prevent cross talk between
the lines.
Round Trip Delay:
Measures the time it takes
for the data test file generated by the 1575 to travel to the customer
modem and back to the 1575. The delay time is directly related to
the distance the customer’s modem is from the 1575 located in the
telephone company central office. Numbers are presented in millisecond
(msecs).
Error Correction: LAPM
Link Access Procedure
for Modems (LAPM). LAPM is an error control protocol incorporated
into the V.42 standard. LAPM uses CRC (Cyclic Redundancy Checking)
and retransmission of corrupted data to ensure data integrity. Error
control protocol is specified by the ITU (International Telecommunication
Union).
Compression: V42bis
A standard issued by the
ITU, which identifies a method of compressing the modem transmit
and receive data. This algorithm can achieve up to a 4:1 compression
ratio.
Total Frames Sent:
The number of LAPM frames
which includes the data and all the protocol overhead bits as transmitted
from the 1575 to the customer modem to perform the test.
Data Frames Sent:
Number of LAPM data frames
transmitted from the 1575 to the customer modem to perform the test.
Data Frames Re-Sent:
Number of LAPM frames
re-transmitted from the 1575 to the customer modem due to errors
in the transmission path. The optimum baud rate will permit some
errors and will be higher then the baud rate for the error free
transmission.
Total Data Sent:
The actual data pattern
as seen scrolled on the customer computer scree
Compressed Data Sent:
Total data plus overhead
bits that were transmitted from the 1575 to the customer modem during
the test.
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