4. Question 1 (15 marks): Fill in the blank with suitable word / phrase or number. 1. In the phase of a sinusoid is altered according to the information sequence. QAM is a form of digital modulation where the digital information is contained in both the and the of the transmitted carrier. 2. SONET rings can be deployed in a self-healing manner. can provide protection at the line level, can provide protection at the path level. 3. The technique replaces the cross-points in a space switch with the reading and writing of a slot into a memory. and _dominate the design and performance of all communication systems. 5. With the basic El system, an us frame is divided into _equal time slots. 6. A T1 carrier system time-division multiplexes PCM-encoded samples from voice-band channels for transmission over a single metallic wire pair or optical fiber transmission line. 7. A refers to the span of fiber between two adjacent devices, such as two regenerators. A refers to the span between the two SONET terminals at the endpoints of the systems. 8. If 4 frequencies convey pairs of bits and the frequency (symbol) is changed every 0.5 ms, then the symbol rate is the information transfer rate is