We live in an era when speed is absolutely everything. If from one hundred to two hundred years ago people were content with sending paper letters, which sometimes took more than one month, or even a year, now people are used to the fact that in just a couple of moments you can send an already digitized letter anywhere, even to another city, at least on another continent, and just as quickly get an answer. Now few people can imagine what it feels like to write real letters and wait for months for an answer, hoping that it reaches the recipient at all. Of course, after all this, the telegraph was invented, and then the original Internet, which accelerated the process of transferring almost any data hundreds of times. But still, it took a rather long period of time by today's standards.
What is an E1 stream ?
This is primarily a standard for the transmission of digital information, which is a multi-channel system of thirty-two separate channels. Thirty for direct transmission, and the remaining two as auxiliary (service), providing synchronization between the sending and receiving parties. Each of the thirty-two data streams has a throughput of sixty-four kilobytes per second, which, through simple calculations, in total gives us two thousand forty-eight kilobytes per second, which is equal to two megabytes. A stream of type E1 can be transmitted using a fiber optic or copper line using a modem.
Information Transfer Method
The digital stream E1 owes its bandwidth primarily to the fact that the information transmitted by it is distributed into frames, in turn, the frames are divided into thirty-two intervals (time slots), each of which has 8 bits. The number of slots can vary from one to thirty-one, depending on the type of stream. Thirty intervals are often used, leaving zero and thirty second as auxiliary.
Multi shots
In order to expand the amount of useful information without expanding the band, groups of frames called multi-frames are used. Mostly they are of two types:
- 256N - In which pairs of one even and one odd frame are used. It is used if the user has access to the sixteenth time slot. In this case, thirty-one time slots are used to transmit useful information. (One thousand nine hundred eighty-four kilobytes per second).
- 256S - In which sixteen frames and the sixteenth time slot itself serves to transmit end-to-end information. Such multi-frames are used to transmit voice information. In this mode, the maximum number of time slots used will be thirty. (One thousand nine hundred twenty kilobytes per second).
Basic flow signal
The basic signal E1 is, first of all, a digital signal, which means that it is transmitted through a binary code, that is, zeros and ones. In E1, the signal is encoded using a special modulation called HDB3, which, in turn, is an improved version of the AMI method. In AMI, code zeros were transmitted as zero voltage, and units as a positive or negative impulse. There was one significant problem with this encoding method. He could not transmit a long sequence of zero pulse, since it was impossible to transmit a synchronization signal. In HDB3, the restriction is lifted, since any sequence that is longer than four zeros will automatically be substituted with a non-zero signal, which will be filtered out on the receiving side through the so-called “Bipolar Disorder”, which interprets the sequence violation as part of the zero line and removes the unnecessary signal, restoring the original signal the code.
Where is the E1 stream used?
As it became clear from the foregoing, this is an extremely convenient way of multi-channel transmission of information with stable bandwidth. This determined the further direction in the use of this system. Connecting the E1 stream is more appropriate in large companies that urgently need an internal multi-channel telephone or Internet system. After all, with just one physical stream, you can provide thirty high-quality voice / Internet channels.
Also, do not forget that the E1 stream transfers information portionwise. This means that it is possible to assemble a “mosaic” from parts of a signal only using a special encryption algorithm. This can be played into your hands, since for each individual physical cable you can configure your personal algorithm, which will minimize the chance of information leakage when intruding into the network from the outside.
Most often, E1 flow is used in large and not very companies whose activities are closely related to telephone communications. These can be Call centers, dispatching, hot lines, as well as some simple offices. E1 is a universal thing, so you can use it almost everywhere.