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A Beginners Guide to Network Devices

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Devices Everywhere

computers, smartphones, scanners, printers, servers, IP phone routers, and switches all connected to the Internet

With modern advancements in computing, consumers are demanding more and more data. We think its really interesting how these technologies work, which devices play an integral role in allowing other devices to communicate, and hope you do too! This article provides a simple overview of the types of devices that comprise a network and how they interact to transmit information from one place to another.

Modems

Modems were one of the first devices that came into being as a means to transmit information electronically from one device to another, especially as it pertains to single or household users. They modulate and demodulate electric signals carrying digital payloads.

The modulater is a sophisticated digital-to-analog signal encoder; it takes digital information and converts it to an analog signal that can be transmitted across a physical media, most commonly copper coaxial or telephony cables. The receiving modem on the other end of the transmission demodulates the analog signal to extrapolate the digital payload. Modems are most often found in dialup, DSL, and cable media connections.

We won’t go into the details of how these electrical signals are modulated or demodulate, but suffice it to say its a pretty nifty process if you’re into that sort of thing.

computers, smartphones, scanners, printers, servers, IP phone routers, and switches all connected to the Internet

Hubs

Hubs were one of the first devices that spawned local area networks. They allowed multiple devices in a home or small office to communicate with other computers or servers attached to the same local network.

All devices attached to the hub or hub network can communicate with one another; they also have the ability to reach any device on the network with a broadcast. Every signal delivered as an input to one of the ports was sent as output to each of the others.

This led to a fatal flaw that brought about their demise; the fact they share the same collision domain.

When all devices are connected to the same collision domain, electronic data collisions occur when one device attempts to send information while another is already sending its own. As the number of devices within the collision domain grows, the more frequent these collisions occur. There were some protocols that allowed collision traffic be re-transmitted, but ultimately proved to be only a temporary fix as local networks began to expand. This brought about the need for ensuring only one device could transmit at any given time.

The token ring was a sound solution for this fundamental flaw. One device held the token; as long as they had the token, they could transmit. After transmitting their data, or after their token timer expired, the token was passed around the ring from device to device so that they could transmit, until eventually making it back to the first. This process repeated itself over and over until all devices transmitted their data, then it all began anew when a device had something more to communicate.

Hubs are all but a relic of the past nowadays, but they do still pop up from time to time in some networks today.

Switches

Switches are a significant advancement in local area networking that took the concept of the hub and expanded upon it.

They utilize the same method of physical connectivity where all devices are attached to the same central hub, but they logically separate ports such that each port is a separate collision domain — meaning that one device can send data to one device at a time without the need to broadcast to every other device. Multiple devices can also send information to other devices all at the same time without the chance for electronic collisions.

A key component of the switching model is the unique media access control (MAC) address contained within each computing and networking device. Each switch learns the MAC address of every device connected to each of its ports and builds a table to distinguish one from another. When a device on a switched network sends information, it includes its source MAC address and the destination MAC address of the device it wishes to reach. The switch, having already built its MAC address table, intelligently knows which port to send the signal out to reach its destination. If it doesn’t already where to reach the destination MAC address, it sends it out its trunk port to another switch or router that may know until it eventually reaches its destination. As you can see, this is a remarkable improvement upon the large collision domains found with the now-but-obsolete hub network design.

Routers

The primary purpose of a router is to connect smaller switched networks together.

Similarly to how switched networks utilize MAC addresses to build tables where destination addresses can be reached, routers collect information about Internet Protocol (IP) addresses to build their tables — routing tables. The router makes a decision where to send traffic based on the destination IP address identified in the data packet header and compares that with its routing table. If it knows where the destination IP address can be reached, it sends the data packet out the particular interface that device is connected to. If it doesn’t know where the destination IP address is located, it sends it out to its gateway, the next upstream router that may know how to reach the destination.

Routers also share their routing tables with other nearby routers as well, and use the learned information to more efficiently route packets to the desired destination. A residential grade router has a fairly small routing table; Internet backbone routers, on the other hand, have very large routing tables with information about how to get to lots of other networks. If a data packet is travelling over a large distance, chances are its eventually going to hit one of these high capacity service provider class routers, which have the ability to route ridiculously many data packets every second.

Firewalls

Firewalls are similar to routers but add additional security features that have become necessary in the modern computing age.

We’ve all heard the horror stories of network intrusions and hacks and the direct and indirect costs incurred by business and consumers of these security breaches; the firewall’s aim is to eliminate the in-and-outbound spread of undesired information between communication networks.

They accomplish this by having various sets of rules for different types of services and traffic that can be transmitted either in or outbound from a particular network or collection of networks. If I don’t want to receive email traffic from a network in Eastern Europe, I can create a rule for that. Similarly, if I want to permit my server to only communicate within my network and not with the outside world, there’s a rule for that too.

Firewalls significantly enhance the security of a network by allowing or rejecting many types of traffic from any source or destination address and communication protocol.

Hybrids

Many networking devices, especially those designed and marketed to residential consumers, can be classified as hybrids; they perform the function of two or more stand-alone device types. Depending on the application, these prove time after time to be attractive options based on their multi-function performance at a low purchase price. A typical DSL or cable modem nowadays isn’t just a modem; they provide wired and wireless routing, switching, and even firewall applications as well.

The Big Picture

These technologies comprise the vast majority of devices used within electronic communication networks today. Understanding what they do and how they fit into the grand scheme of inter-networking communications gives us a better understanding of how small and large communication networks inter-operate.

Regardless of their size or scale, these devices are a critical and necessary component in any network and afford us the ability to communicate with any part of the world in a matter of milliseconds by utilizing many different technologies designed for specific purposes.


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