GTU-MCA-SEM IV - Fundamentals of Networking

1. The Physical Layer Chapter 2

62. Packet Switching Communication broken down in to packets allows many users to share the same data path

67. Circuit switching Packet switching Circuit switching is old and expensive, and it is what PSTN uses. Packet switching is more modern. VoIP uses packet switching technology. The resources remain dedicated to the circuit during the entire transfer and the entire message follows the same path. There is no circuit dedication. The cost is shared. During the entire transfer the entire message follows the same path. In packet-switched networks, the message is broken into packets, each of which can take a different route to the destination where the packets are recompiled into the original message. Circuit-switching is more reliable than packet-switching. When you have a circuit dedicated for a session, you are sure to get all information across. When you use a circuit which is open for other services, then there is a big possibility of congestion (which is for a network what a traffic jam is for the road), and hence the delays or even packet loss.

130. 2.7.5 Cable Vs. ADSL CABLE ADSL Cable providers do not make any claims for effective capacity because the effective capacity depends on how many people are currently active on the user's cable segment. Sometimes it may be better than ADSL and sometimes it may be worse. ADSL providers give specific statements about the bandwidth (e.g., 1 Mbps downstream, 256 kbps upstream) and generally achieve about 80% of it consistently. With cable, as more subscribers sign up for Internet service, performance for existing users will drop. Because of Shared medium. As an ADSL system acquires more users, their increasing numbers have little effect on existing users , since each user has a dedicated connection. Any cable user can easily read all the packets going down the cable . For this reason, any decent cable provider will encrypt all traffic in both directions. Being a point-to-point medium, ADSL is inherently more secure than cable With cable, if the power to any amplifier along the chain fails, all downstream users are cut off instantly. The telephone system is generally more reliable than cable . For example, it has backup power and continues to work normally even during a power outage