<p dir="ltr"><img src="https://media.cheggcdn.com/media%2F685%2F685bc0d7-8bf7-4d21-b242-d9fca9643316%2Fimage.png" alt="27. Write short notes on (a) Grade of Service (b) IPV6 (c) PSTN (d) Common channel signaling (e) VolP vs VoLTE." aria-describedby="d3f"/></p><p dir="ltr"/>27. Write short notes on