The first transatlantic submarine telegraph cable was laid in 1858, only 14 years after

Morse’s first official message was sent. The line was very slow (it took 16.5 h to send a

96‐word message from Queen Victoria to President Buchanan [6]). With the invention

of telephony, transatlantic telephony was considered, but clearly the required capacity

was not available. The main problem was signal dissipation through the coaxial cable,

which meant that a transmitted voice signal would be received well below the noise level.

With no fixed line telephony, transatlantic voice communications was carried out using

wireless technologies. These were unreliable as short wave radio signals were susceptible

to signal fading and noise.

To increase received signal power from coaxial cables repeater devices needed to be

installed at intervals of some 70 km. These required power which had to be supplied from

both ends. The technology for such repeaters needed for submarine cable telephony was

not developed until the 1950s. The first transatlantic cable (TAT‐1), connecting the UK,

Canada and the US was commissioned in 1954 and started operation in 1956.

TAT‐1’s useful bandwidth was 144 kHz and could provide 3 groups of 12 voice channels

(36 in total). The cost of manufacturing and laying the cable down was $36 million

in 1954, or the equivalent of some $320 million today (2014), which averaged over its

22 years of operation cost some $34 000 per channel per year. The cost of a phone call

needed to be set in the order of $3 per minute to pay back the initial investment and

operating costs [or $27 today (2014)]. This was still a major improvement over the radio

calls which had inferior voice quality, and cost some $9 per minute [7].

The transatlantic telephony link became very popular and traffic grew at an annual rate

of 20%. Soon extra capacity was needed, and therefore link capacity had to be increased

by reducing the bandwidth required for voice communication from 4 to 3 kHz. This

increased the number of circuits by 33% to 48 channels at a reduced voice quality. Even

at this quality, 48 circuits could only support 36 E of traffic. To maximise the links’ usage

transatlantic calls were handled by booking through operators.

With the popularity of the link, more submarine cable systems were commissioned and

laid around the world. Seven generations of coaxial cable‐based transatlantic cables

were laid before optical fibre technology was developed. Table 3.1 shows these seven

transatlantic cables and their respective capacities, and cost per speech channel per year.

Case Study Questions

1. How important was an understanding of teletraffic engineering to the designer of transoceanic international telephony cables such as TAT‐1?

3. Why was TAT‐1 rolled out so long after the invention of telephony?

4. What were the business issues and why did the price per call drop so dramatically?

5. Who were the initial TAT‐1 customers? Why did this change?

6. What were the roles of governments in rolling out of transoceanic telephony cables?

 

Answer rating: 100% (QA)

1 An understanding of teletraffic engineering was crucial to the designer of transoceanic international telephony cables such as TAT1 The designer needed to understand the characteristics of voice tra... View the full answer