Network Connections

Connections between nodes (computing devices, routers, switches) in a network can be of two types:

• Wired connections: As their name suggests, wired connections need a physical wire (also referred to as a cable) between the nodes that need to be connected. The two commonly used types of cables used to connect nodes are:

  • Twisted-pair cables: These cables consist of copper wires that are twisted into pairs. They have four pairs of copper wires that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. Twisted-pair cables support very high transmission speeds and bandwidth.

  • Optic-fiber cables: These are cables made of glass fibers. The fibers transmit data using pulses of light. Optic-fiber cables have the fastest data transmission rates and the lowest amount of data loss than any other cable. Despite their high performance, the only reason the adoption of options-fiber cables has been slower is their cost and fragility. They are more expensive and less sturdy than twisted-pair cables.

• Wireless connections: Wireless connections use radio signals transmitted through the air and do not need a physical wire to connect devices on a network. This makes it much easier to set up a network since laying cables is an expensive and time-consuming job that needs space for the cables to run through.

There are two main types of wireless data communication that we are familiar with: WiFi and Cellular. Both of them use RF signals but at different frequencies in the spectrum. And both of them have different infrastructure requirements. Generally, smartphones that are connected to the cellular network for voice communication use that same wireless connection for data transfer, but they can also connect to a WiFi network. Computers generally do not have the capability to connect to a cellular network and can only use a WiFi infrastructure.

Wireless connections provide high enough data transmission speeds for most users, but are generally slower than wired connections, have a limited range, and physical obstructions, such as walls, can interfere with their transmission. Since the convenience they provide more than makes up for their limitations, they are very widely used in homes, offices, campuses, and even cities.

Since wireless connections have a limited range, they are used only for "last-mile" access. Connections across long distances, for example, two office networks in different cities, or an office connecting to the Internet (via an Internet Service Provider), will have a wired connection between the router at each end. On the other hand, the connectivity from the router to the devices in the home or office network may be wireless.

Ethernet

Ethernet is the standard technology used to connect nodes on wired networks. All network technologies need protocols, which are sets of rules or conventions used to send and receive data between nodes. Ethernet uses the Transmission Control Protocol/Internet Protocol (TCP/IP), and together they are used by most networks, including the Internet.

The Ethernet protocol defines a standard approach that all connected devices must use when sending and receiving data. Devices divide a stream of data into shorter pieces called frames. Each frame contains the source, destination addresses, and error-checking data so that damaged frames can be detected, discarded, and lost frames can be retransmitted. The addresses uniquely identify nodes, so no two Ethernet devices on the same network can have the same address.

With multiple (in the case of the Internet, millions) devices attempting to communicate with each other over a shared wire, there needs to be a way to ensure data is not lost or garbled during transmission. The Ethernet protocol implements a protocol known as CSMA/CD (Carrier Sense Multiple Access with Collision Detection).

The term Multiple Access refers to the fact that when one network node transmits, all the nodes on the network receive the transmission. Carrier Sense refers to the fact that before a node begins to transfer, it listens to the medium to determine whether another node is in communication. If the medium is quiet (no other nodes are transmitting), the node recognizes that this is an appropriate time to transfer.

CSMA works well to regulate communication between nodes. But an additional rule is required to handle some scenarios. Multiple nodes wanting to transmit may do so simultaneously after detecting a silence on the medium. If that happens, then a collision will occur, and data could be lost or corrupted.

Ethernet nodes also listen on the medium while in transition to ensure that they are the only node transmitting at that time. If the nodes hear their transmission returning in a garbled form, as would happen when some other node had begun to communicate its message at the same time, then they know that a collision occurred. When nodes detect a collision, they stop transmitting and wait a random amount of time or attempt to continue with the detection of silence on the medium.

Full-duplex is a data communications term that refers to the ability of devices on a network to send and receive data simultaneously. The other option is half-duplex, which means that a node can either send or receive data at a point in time. Ethernet networks are full-duplex, whereas wireless networks are half-duplex.

WiFi

WiFi is a widely used wireless network connection protocol that uses radio waves. WiFi works on the same principle as other wireless devices utilizing radio frequencies to send signals between devices. RF signals are in the frequency range of approximately 20 kHz to 300 GHz (Hertz or Hz is the unit of frequency). All wireless devices use RF signals at different frequency ranges. For example, a radio receives frequencies in Kilohertz and Megahertz range, while WiFi transmits and receives data in the Gigahertz range.

The cornerstone of any WiFi network is an access point (AP). The primary job of an access point is to broadcast a WiFi signal that nodes (computing devices) wanting to join the network can detect and tune in to. An access point device also acts as the interface to connect a wireless network with the router or switch on a wired network.

To connect to an access point of a wireless network, computing devices must be equipped with wireless network adapters. The wireless network adapters are also responsible for converting digital data to radio signals on the sending side and back to data on the receiving side.

Wireless connections also use TCP/IP as the underlying protocol and have rules similar to those of Ethernet for transmission and collision detection.

Cellular Connections

A cellular network is a communication network distributed over areas referred to as cells, each served by transceiver (transmitter and receiver) stations. These stations provide the cell with radio frequency coverage, which can be used to transmit voice and data. A cell typically uses a different set of frequencies from neighboring cells to avoid interference and provide guaranteed service quality within each cell. Multiple cells working together provide radio coverage over a wide geographic area.

Such an arrangement of multiple small transceivers provides better coverage than a single large transceiver. Thus, devices using cellular networks use less power since there is always a transceiver nearby. Additional cell towers can be added indefinitely to increase coverage and capacity.

Major telecommunications providers have deployed voice and data cellular networks over most of the inhabited land in their respective countries. This channel allows mobile phones and mobile computing devices to connect to a voice and data network from almost anywhere. These networks are connected to wired data networks, including the Internet, through Internet Service Providers, thus allowing mobile devices to be connected to the Internet from anywhere there is network coverage. It has a better reach than WiFi since WiFi needs access points, which cannot be deployed as widely as cellular stations.

Cellular network technology has evolved over the years, improving voice quality and data transfer speeds. The current most widely deployed technology standard is known as 4G (or fourth generation). And the next stage of evolution, which is already in place in some countries, is 5G. The main advantage of the new 5G networks is that they will have a much higher bandwidth than 4G, giving higher data transfer speeds. Because of this, it is expected that the new networks will not just serve mobile phones but also enable new applications, most significantly in the area of the Internet of Things (IoT).

Bluetooth

Bluetooth is a short-range wireless technology standard used for exchanging data between fixed and mobile devices over short distances using ultra-high frequency (UHF) radio waves, from 2.402 GHz to 2.48 GHz. Bluetooth uses low-power transmission which gives it a very short range of up to 10 metres but with the benefit of low battery power consumption.

Bluetooth and Wi-Fi are similar in that both are used to exchange data between devices. The difference is that Wi-Fi is access point-centered, with all traffic routed through the access point, while Bluetooth is symmetrical, with data exchanged directly between two Bluetooth devices. Bluetooth serves well in simple applications where two devices need to connect without a dependency on additional devices such as those required for a WiFi access point.

While Ethernet, WiFi, and cellular connections are networking protocols and can be used for data transfer across large networks, Bluetooth is a device-to-device communication protocol, not a networking protocol.

Bluetooth is widely used to exchange files between two devices and connect smartphones to audio playback systems such as headphones, eliminating the need for wires. Bluetooth is also used to connect smartphones to Arduino circuits and IoT appliances to send control signals over a very short distance.