MODEM

Modem is short for MOdulator DEModulator. It’s an electronic device used to access the Internet that modulates carrier waves to encode information to be transmitted and also demodulates incoming carrier waves to decode the information they carry.

What is a modem?

A modem is a very important piece of network hardware that allows a computer to send and receive data through a telephone line or cable connection. In simple words, it’s the device that connects a computer to the Internet using telecommunication network.

The Importance of a Modem

Back in the old days, when landline phones were the primary tool to communicate over long distances, modems came in pretty handy to gain Internet connectivity using telephone lines. In fact, without modems, it would have been impossible for most users to connect to the Internet. While computer technology is purely digital, i.e., it relies on numbers to transmit and receive information, telephone technology, even to this day, is partly analog, meaning that it uses continuously varying electrical signals to transmit information.

Since your modem sends information through a telephone line by modulating digital signals, it also needs to have another kind of translator that helps it demodulate the analog signals it receives via the telephone line.

That’s why a modem is named as such, because it both modulates and demodulates signals.

ETHERNET

Ethernet is the technology that is most commonly used in wired local area networks (LANs). A LAN is a network of computers and other electronic devices that covers a small area such as a room, office, or building. It is used in contrast to a wide area network (WAN), which spans much larger geographical areas. Ethernet is a network protocol that controls how data is transmitted over a LAN. Technically it is referred to as the IEEE 802.3 protocol. The protocol has evolved and improved over time to transfer data at the speed of a gigabit per second. 

How Ethernet works

The Institute of Electrical and Electronics Engineers Inc. (IEEE) specifies in the family of standards called IEEE 802.3 that the Ethernet protocol touches both Layer 1 -- the physical layer -- and Layer 2 -- the data link layer -- on the OSI network protocol model. Ethernet defines two units of transmission: packet and frame. The frame includes not just the payload of data being transmitted, but also:

• the physical media access control (MAC) addresses of both the sender and receiver;
• VLAN tagging and quality of service information;
• Error correction information to detect transmission problems.

Advantages of using wired Ethernet network

• It is very reliable.
• Ethernet network makes use of firewalls for the security of the data.
• Data is transmitted and received at very high speed.
• It is very easy to use the wired network.

Disadvantages of using wired Ethernet network

• The wired Ethernet network is used only for short distances.
• The mobility is limited.
• Its maintenance is difficult.
• Ethernet cables, hubs, switches, routers increase the cost of installation.

Types of Ethernet network

The maximum data rate of the original Ethernet technology is 10 megabits per second (Mbps), but a second generation fast ethernet carries 100 Mbps, and the latest version called gigabit ethernet works at 1000 Mbps. Ethernet network can be classified into 3 types:

Fast Ethernet

This type of Ethernet can transfer data at a rate of 100 Mbps.  Fast Ethernet makes use of twisted pair cable or fiber optic cable for communication.
There are three types of fast Ethernet, which are as follows:
• 100BASE-TX
• 100BASE-FX
• 100BASE-T4

Gigabit Ethernet

This type of Ethernet network can transfer data at a rate of 1000 Mbps. Gigabit Ethernet also makes use of twisted pair cable or fiber optic cable. 48 bits used for addressing in Gigabit Ethernet. Nowadays gigabit Ethernet is very popular. The latest Gigabit Ethernet is a 10 Gigabit Ethernet, which can transfer data at a rate of 10 Gbps. Gigabit Ethernet was developed so that it can meet the needs of the user like faster communication network, faster transfer of data etc.

Collision and Broadcast Domain

Collision Domain

A collision domain is a network segment connected by a shared medium or through repeaters where simultaneous data transmissions collide with one another. The collision domain applies particularly in wireless networks, but also affected early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network segment at the same time. Members of a collision domain may be involved in collisions with one another. Devices outside the collision domain do not have collisions with those inside.

The following example illustrates collision domains.

As you can see, we have 6 collision domains.

Here, each port on a hub is in the same collision domain. Each port on a bridge, a switch or router is in a separate collision domain.

 Broadcast Domain 

A broadcast domain is a domain in which a broadcast is forwarded. A broadcast domain contains all devices that can reach each other at the data link layer (OSI layer 2) by using broadcast. All ports on a hub or a switch are by default in the same broadcast domain. All ports on a router are in the different broadcast domains and routers don’t forward broadcasts from one broadcast domain to another.

The following example clarifies the concept.

In the picture above we have three broadcast domains, since all ports on a hub or a switch are in the same broadcast domain, and all ports on a router are in a different broadcast domain.         

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