CHAPTER 7

---

1. The T1 carrier supports 24 voice channels with an aggregate data rate of 1.544 Mbps out of which 8000 bps is for carrying signaling information. In T1 carrier, each frame consists of one bit for framing following by 24 slots. Each slot contains 7 bits of voice and one bit for signaling. Four T1 carriers are multiplexed to from T2 carrier. The data rate of T2 carrier is 6.312 Mbps whereas 4 × 1.544 Mbps = 6.176 Mbps. Hence the additional overhead is 0.136 Mbps.

   The complete hierarchy is given in the following Table:

   Level	Data Rate (Mbps)	No. of 64kbps Channels
   T1	1.544	24
   T1C	3.152	48
   T2	6.312	96
   T3	44.736	672
   T4	274.176	4,032

2. In satellite communication, the frequency band is divided into small bands, and a number of users share it. Hence, FDMA is used. TDMA access scheme is also used for multiple users to share the same band. In low-earth orbiting satellite systems, CDMA technique is also used.

3. The multiplexing hierarchy used in optical fiber communication systems is given in Chapter 14.

4. C band and L band are used in optical fiber for WDM and DWDM. C band corresponds to the wavelengths 1530 – 1565 nm, and L band corresponds to 1565– 1625 nm.

---