, 30 are used to carry the speech data, and the other two are used for signaling and synchronization. Therefore, the framing format is also referred to as CEPT PCM-30. Timeslot 0 can be used for synchronization and alarm transport. In addition, in all frames the first bit of timeslot 0 is dedicated to inter- national carrier use. The Frame Alignment Signal (FAS) is transmitted in bit position 2-8 of timeslot 0 every other frame. The FAS pattern recommended by CEPT PCM-30 is 0011011, which is impossible to imitate by shifting and infringement. If a frame does not contain the FAS, it can be used to carry 5 bits of national signaling and an alarm indication bit for loss of frame alignment. Furthermore, in each CEPT PCM-30 frame, timeslot 16 is used to transmit signaling data. Because a common channel is dedicated to the signaling data of all speech circuits, this method of signaling is referred to as Common Channel Signaling (CCS). The signaling consists of 4 bits per channel, which are grouped in the two halves of timeslot 16. This means that 15 frames are required to carry the information of the 30 chan- nels. Together with the first frame (frame 0), a multiframe consisting of 16 frames is formed. The 16th timeslot of the first frame contains a Multiframe Alignment Signal (MAS), which allows unambiguous numbering of the frames within a multiframe. Figure 1.18 shows the structure of a CEPT PCM-30 multiframe. Multiframe Alternate Frames Frame Alignment Word Multiframe Alignment 0XAXX Frame 0 International Bit Multiframe Alignment Loss Alarm Alternate Frames Signaling Information I1ANNNNN 12345678 Frames 1-15 National Bits Channels 1-15 Channels 16-30 Alarm Indication Signal Fig. 1.18 CEPT PCM-30 multiframe structure. Chapter 1 Voice Transmission Table 1.2 Comparison of American and European Digital Hierarchies Europe Number of Total Bitrate Number of Total Bitrate Order Channels (Mbit/s) Order Channels (Mbit/s) 0.064 0.064 1.544 2.048 DS1-C 3.152 8.448 6.312 34.368 44.736 139.264 274.176 565.148 P (x| X0) P (x1 X1) 