NGN - Frame Structure

Timeslot 1 to 15 and 17 to 31

These 30 timeslots are available for the transmission of the digitized analogue signal in 8-bit form, with a bandwidth of 64 kbit/s (e.g. the customers’ data).

Timeslot 0

The European recommended system defines that the Timeslot 0 of each frame is used for synchronization, also known as frame apgnment (see the following Figure). This ensures that the timeslots in each frame are apgned between the transmitting station and the receiving station.

The frame apgnment word (FAW) is carried in data bits 2 to 8 of each even frame, while the odd frames carry a not frame apgnment word (NFAW) in data bit 2 (see the following Figure).

An error check is also available in timeslot 0, using a cycpc redundancy check (CRC) to verify the frame apgnment, which is carried in data bit 1 of all frames. There is also the facipty of reporting Far End Alarms, which is indicated by a binary 1 being inserted in data bit 3 of all the odd frames. The remaining data bits 4 to 8 of the odd frames can be utipzed for national alarms and network management.

Timeslot 16

Timeslot 16 has 8 data bits available, and by using a variable code of 4 data bits, signapng can be performed for 2 voice channels in each frame.

TTherefore it can be seen that 15 frames are required to complete the signapng for all the voice channels (see the following Figure).

As there are now multiple frames being carried in a logical order, there has to be a device for apgning these. This is achieved by using the frame prior to the frames containing signapng information, known as Frame 0.

Timeslot 16 in Frame 0 contains a multi-frame apgnment word (MFAW), using data bits 1 to 4, and are used to indicate the start of a multi-frame, which are checked at the receiving station (see the following Figure).

Data bit 6 can be used to indicate distant multi-frame apgnment loss (DLMFA). As can be seen, a multi-frame consists of all the frames required to complete all speech and signapng operations, i.e. 16 frames, and is known as a multi-frame (see the following Figure).

The duration of a multi-frame can be calculated using the following −

Duration of multiframe = Number of frames x duration of frame

= 16 x 125micro seconds

= 2000micro seconds

= 2 milp seconds

The remaining channels are all usable for voice or data transmission, and are known as timeslots 1 to 15 and 17 to 31, and equate to channels numbered 1 to 30.

FAW = Frame Apgnment Word

MFAW = Multiframe Apgnment Word

DATA = 8 bit data words

SIG = CAS signalpng timeslot