In a digital transmission system, the signals from the customer are customarily grouped into 8 binary digits, called 8-bit words. As a matter of convention, each bit of the 8-bit word is numbered. The most significant bit, the first bit to arrive, is numbered Bit-0, followed by Bit-1, Bit-2, and so on. The least significant bit is Bit-7. For transmission over the telecommunications network, these 8-bit words are then combined in a serial form with 8-bit words from other customers. Thus each customer's signal occupy a period of time within a transmission line, which is shared with other customers. The time for each customer is called a "time-slot". This method of combining one customer's signal with others is called "time division multiplexing". For digital transmission systems used in North America, 24 such 8-bit words are combined into a transmission system called T1. Customers usually send a series of 8-bit words, usually 8000 times a second. These words are then serially combined with 8-bit words from other customers also at 8000 times a second. The series of 8-bit words from one customer are called a channel, or a digital communications channel.
When the T1 transmission system, also called a T1 line, reaches a juncture, called a node, the 24 channels of 8-bit words may be required to be processed for the purpose of switching. For example, a customer's signal arriving on a T1 line occupying Channel 3, may be sent on its way on a second T1 line occupying Channel 23. This process is called digital switching.
If the customer's signal is data, such as an inventory report, and is in the form of a series of 8-bit words, then the process of digital switching is relatively simple in concept. When the customer's 8-bit word arrives on a first T1 line, according to the arriving channel assignment, it is stored in a temporary memory. When it is time for the customer's 8-bit word to be sent on its way on a second T1 line, the stored word is inserted at the proper time slot according to the channel assignment. However, if the customer's signal is not data but rather a voice conversation transformed into digital signals, called digitized voice, then there are other aspects of the digital switching which must be considered. This is the signaling information.
Signaling relates to the supervision aspects of a voice conversation. For example, when a person lifts up the phone to make a telephone call, the information that the customer has lifted the phone, i.e., off-hook, must be transmitted to the far end. To the person receiving the call, the ring of the telephone is another example of signaling information. For the T1 transmission system, signaling is sent along with the digitized voice in combined 8-bit words. This process is called "robbed bit signaling". In 5 of every 6 8-bit words sent, the 8-bit words are faithfully transmitted and reproduced at the far end. However, in 1 of every 6 words sent, the least significant bit (Bit-7) of the 8-bit word is substituted with the signaling bit (i.e., A bit). The result is that the customer's voice is digitized into 8-bit words 5 out of 6 times, and digitized into 7-bit words 1 out of 6 times. In digitized voice, more bits represents greater fidelity in the overall system. In the T1 system, this method results in a fidelity commonly known as 7 5/6 bit fidelity.
When the digitized voice is to be switched, the signaling information must be extracted from the incoming T1 line and reinserted into the outgoing T1 line. This is because the location of the 1 out of 6 words, where the signaling bit is inserted, is not determined by each channel, but by the timing of the T1 transmission line. In many cases, the reinserted signaling bit on the outgoing T1 line is at a different word when compared to the incoming bit stream. Here is where procession for data and for digitized voice must be different. For data, no signaling processing should take place. Otherwise, customer's data would be mutilated due to moving what is thought to be the signaling bit into a different place. For voice, a signaling process should take place to preserve the transmission of the signaling information. Thus it is important for the system administrator to know which channel is carrying data, and which channel is carrying voice. This knowledge is obtained usually by searching the records for the original customer order whether data or voice is requested. Another way is to examine the actual 8-bit words being transmitted and make a determination, based on the characteristic difference between data and digitized voice. Such prior methods are time-consuming and unreliable.
Thus, it is desirable to provide an approach for automatically differentiating between data and voice digital signals to overcome the drawbacks of the prior art.