As the packets are transmitted, each takes the optimal route available as it passes through various routing computers on the way. Each packet contains the address where it is heading and details of how it fits into the chain of packets that comprise the complete message. To make a phone call over the internet, the analogue sounds uttered are converted into digital form and chopped into packets of data, each around 1,000 to 1,500 bytes long. A more nuanced answer is that the two networks have evolved so differently that they are difficult to compare. How come people can make countless calls to places half way around the world for free with services like Skype, yet have to pay hundreds of dollars to do the same using a telephone? The short answer is that one uses the internet to transmit calls, while the other relies on the public-switched telephone network (PSTN) to do the job. Making only 20 international telephone calls a month, each lasting just ten minutes, would add $620 to his monthly telephone bill. Were he to make the same overseas calls from a conventional telephone, he would have to pay $3.10 a minute, plus a $4.95 monthly service charge. On the rare occasions he has to call an overseas house phone, Skype charges him 2.3 cents a minute. As, like himself, the recipients all have the Skype client software loaded on their mobile phones, tablets or computers, the lengthy video chats cost nothing. He makes a similar number to friends and family in Britain.
SEVERAL times a week, your correspondent makes a video call from California to relatives in Japan.
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