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Basics of Networking - Part 2

Reviews

Basics of Networking - Part 2
Page 1 of 1
Author: kan
Date of review: 17-December-2000
Type Of Review: Networking

Packet Switching vs Circuit Switching
A good example of circuit switching is the telephone system. Circuit switching is a technique in which a system seeks out the physical “copper” path from the caller’s telephone to the receiver’s telephone. There is a need to set up an end-to-end path before any data can be sent. This is why it can take several seconds between the end of dialing and the start of ringing for international calls. During this interval, the telephone system is actually hunting for a copper path, and the call request signal must propagate all the way to the destination and be acknowledged.

On the other hand, packet switching is a type of network where small units of data are routed through a network based on their destination address in each packet. Compared to circuit switching which statically reserves the required bandwidth in advance, packet switching acquires and releases bandwidth as and when it is needed. Circuit switching is completely transparent. The sender and receiver can use any bit rate, format, or framing method they want to. As for packet switching, the carrier needs to determine these basic parameters first before transmission can occur.

The Internet is based largely on packet switching and the Net is basically a huge connectionless network joined together. By transmitting data in packets, the same data path can be shared among many users in the network.


A comparison table on Circuit Switching vs Packet Switching.


Switches, Hubs and Routers
We will now move on to familiar ground for most users – switches, hubs and routers.

Okay, so what exactly is a hub? A switch?
A hub is basically like a cable splitter which takes in signals from each port and broadcasts them to all the other ports.


The SMC 4-port 10 Mbps Hub.


The hubs for SOHO usage are usually passive in nature. However, there are also active hubs (which we sometimes call them as multiport repeaters) which will regenerate the data bits in an attempt to maintain a strong signal. Take for example an 8 port hub. If a packet is sent to a port of the hub, this packet is also broadcast to the other 7 ports. Only the computer which this packet was meant for will retain the packet. The rest will just discard the packet. This is clearly not as efficient as a switch whereby the packet goes directly to the port it was specifically meant for.

A very good explanation of the differences between a switch and a hub is available at the Farallon website:

A hub and the broadcast method.

A switch is actually a multi-port hardware device that receives incoming data at one port and then forwards the data to another port. Basically a Layer 2 switch is able to send a packet directly to the host computer. It works by broadcasting an ARP request to all the machines connected to the switch. In return, the machines will respond to the switch by sending their MAC addresses and subsequently, the switch will be aware of the machines that are hooked up to its individual ports.


A switch and the data flow.


A hub is infamous for their broadcast storms which can cripple a network. As you add in more nodes to a network, it causes an increase in unnecessary traffic through the hub and across the network. In addition, as the hub does not know how to manage the traffic passing through it, packets will have collisions fairly often, causing data to be re-sent frequently. This will lower the throughput of the network significantly, especially at high data transfer rates.

With regard to security, a switch offers better protection against “sniffers”. With a hub, it is possible for a “sniffer” to filter the traffic going through the hub by putting an Ethernet card on a computer outside the source and making destination machines enter “promiscuous” mode. With a switch, it may not be possible to perform this feat as data is going directly from one point to another without broadcasting itself.


The Intel 8-Port 10/100 Switch.


So, what’s a router?
A router is either a hardware or software device that uses headers and a forwarding table to determine where the packets should go. They use ICMP (Internet Control Message Protocol) to communicate with each other and will automatically negotiate the best route between any two hosts. A router is usually located at a gateway and it does very little filtering of data as it does not bother about the type of data passing through.

For a software router, you can check out the Linux Router Project or WinRoute.

With more people having multiple PCs in their homes, broadband routers are slowly becoming the norm. With simple installation and easy administration, these devices are easier to use and configure than software solutions.


The SMC Barricade Broadband Router.


Having covered the differences between a switch, hub and router, our next installation will cover a detailed review on the Intel 10/100 8-port switch. We will run benchmarks to demonstrate the superiority of a switch over a hub. Stay tuned, and connected!





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