Circuit Switching vs. Packet Switching: What’s the huge difference anyway?

Circuit Switching vs. Packet Switching
What’s the huge difference anyway?

First off, let me explain switches in general. A switched network goes through a switch instead of a router. Most networks are actually headed toward flat switches on VLANs instead of routers. A router can handle the work of a switch, but much of IT today is going toward flat switched networks. So when we’re talking about circuit switching or packet switching, we are more and more talking about doing it on a switch.

Now in my last two articles, I’ve explained the differences between circuit switching networks and packet switching networks. In principle, circuit switching and packet switching both are used in high-capacity networks. Circuit switching establishes a direct point-to-point connection is made, like in a telephone call. The dedicated line cannot be used by anyone else while it’s already in use by two other users. Packet switching doesn’t require the direct line of contact, and uses any available network connections to route data packets (data, voice, video, etc.) through different routes until it reaches its destination where the packets are reassembled to its original message.


Comparisons:

Circuit switching –
1) Ideal when data must be transmitted quickly, arrive in sequencing order, and at a constant arrival rate. Ideally, it is used for transmitting real-time data, such as audio and video.
2) Network resources are static.
3) Dominates the public switched telephone network or PSTN

Packet Switching –
1) More efficient and robust for data that is burst in its nature, and can withstand delays in transmission, such as e-mail messages, and Web pages.
2) Uses communication lines that are not dedicated to passing messages from the source to the destination. Different messages can use the same network resources within the same time period.
3) Dominates data networks like the Internet.


The difference in real-world situations:

Packet switching is acceptable when calling up a web page or downloading a file, since a tiny delay is hardly noticed. These tiny delays are very noticeable with voice, though. This point is really important. Circuit switching guarantees the best sounding call because all packets go in order without delay. Delays in packet switching for voice causes cause voice quality to fall apart, as anyone who has used VoIP can tell you.

Bottom line: 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 like a traffic jam in a network), and hence the delays or even packet loss. This explains the relatively lower quality of VoIP voice compared to PSTN.

Even so, there are protocols giving a helping hand in making packet-switching techniques to make connections more reliable. An example is the TCP protocol. Since voice is to some extent tolerant to some packet loss, packet switching is ideal for VoIP.

When you are making a PSTN call, you are actually renting the lines. This explains why international calls are expensive. Expensive enough for many people to sacrifice quality for cost efficiency. You pay for each and every minute you spend CONNECTED on a dedicated line. In a conversation, you take turn speaking. Plus, there are those moments where there is silence. Ultimately, you’re only using less than half the time of what you are paying for. With VoIP, you actually can use a network or circuit, even if there are other people using it at the same time. There is no circuit dedication. The cost is shared.


Future of circuit and packet switching for telephony:

Packet switching is getting better with improved VoIP technologies, but it may never replace the dominance of circuit switching in PSTN. Replacing circuit switched switches with packet switches across the country would be a monumental task, requiring billions of dollars over years and years. Plus, lengthy calls over the Internet place huge demands on switches that were never planned for, tying up circuits longer than ever imagined. Change is probably going to come at some point, and the Internet's traffic now motivates engineers to move toward a unified switching method in the PSTN.

While the PSTN creeps towards convergence, many telecom companies are looking at placing calls over packet switched local area networks the Internet. A company with a packet based switch will allow you to eventually store all of your e-mails, pages, faxes, and voice calls on a single computer which also acts as your phone. Convergence would enable us to access all these features. Software, not hardware, would be used to utilize features like conferencing and call forwarding; or even video conferencing if the number dialed at the office is to a computer and not to a desk telephone. The drive toward unified packet switching will enable a brand new future for the public telephone system.

Packet Switching: Circuit Switching’s Nemesis… Well alternative, but “Nemesis” is more dramatic and funnier to say

Packet Switching
Circuit Switching’s Nemesis… Well alternative, but “Nemesis” is more dramatic and funnier to say

Packet switching is a WAN (Wide Area Network) technology of protocols that divide messages/data into packets (units of information carriage), then route them individually to its destination. During the transfer of the packets, the packets can be delivered altogether or independently of each other through different routes. Once at its destination, they are recompiled into the original message.

To prevent unpredictably long delays and ensure that the network has a reliably fast transit time, a maximum length is allowed for each packet. This is why a message would be submitted to the “transport layer” first, and then divided by the “transport protocol” entity into a number of smaller packet units before transmission. The end result is a reassembled message at the destination. This method of transferring data optimizes bandwidth available in a network to minimize the transmission latency (time it takes for data to pass across a network), and to increase the strength of communication.

The costs to customers using packet switching are lower than point-to-point lines because packet switching is more efficient in using a network infrastructure. The carrier can create virtual circuits between customers’ sites through its packet routing protocols. The section of the network that is shared is often referred to as a “cloud.” Packet switching is also called connectionless networking because no physical connections, like circuit switching, are established.

Packet-switched networks using satellite or terrestrial radio as the transmission medium are known as packet satellite or packet radio networks, respectively. These networks were designed for covering large areas for mobile stations, or for applications that benefit from the availability of real-time information at several locations.

Handling messages of different lengths was always done very well by packet switching, as well as different priorities when quality of service (QoS) attributes were included. Packet switching was originally designed for data, but lately packet networks are becoming the norm for voice and video as well.

The most well known use of packet switching is the Internet, which is often referred to as a “Datagram Packet Switching Network.” The first international standard for wide area packet switching networks was X.25. Other examples of packet switching are Ethernet, frame relay, and mobile phone technologies such as GPRS and I-mode.

Already, we can see that there is more flexibility with packet switching than with circuit switching. The Internet, which is a widely used infrastructure, can be used efficiently without the need for a point-to-point connection that circuit-switching networks require.

Come back later this week as I compare circuit switching and packet switching.