Connection Basics

Connection Categories

Most connections will fall primarily into one of the following categories, although certain connections may spill over into more than one category:

non-cellular communication connections. The traditional telephone service, nicknamed plain old telephone service (POTS), is common and familiar example. Another example is the Digital Enhanced Cordless Telecommunications (DECT) connection, which is used primarily as a connection between cordless phones and base stations [1] [2] [3].
power connections.
A/V connections, which transmit audio and/or video from one device to another over a relatively short distance. Two important A/V connections that are used today are the High-Definition Multimedia Interface (HDMI) and DisplayPort connections, the latter of which was created by the Video Electronics Standards Association (VESA) [4] [5]. A key piece of equipment for A/V connections is a receiver, which is a device designed to allow for the connection of external speakers.
broadcast connections, the primary examples of which are radio and television (TV). The part of a device that receives a radio or TV connection is known as the tuner.
component and peripheral connections, including:
- CPU, RAM, and storage connections.
- expansion card slots. A commonly-used expansion card slot today is PCI Express (PCIe) [6], which is partially based on the older Peripheral Component Interconnect (PCI) standard [7]. Both PCI and PCIe were created by the PCI Special Interest Group (PCI-SIG) [6] [7] [8].
- external peripheral connections, which include FireWire, Universal Serial Bus (USB), Bluetooth, and Thunderbolt. The PCI-SIG has been working on an external version of PCIe called OCuLink [9 pages 28-9] [10] [11 pages 10+17].
non-cellular Internet connections.
networking connections, which are used to connect devices to each other so that they can exchange information and/or access one or more shared resources. Ethernet, Wi-Fi, HomePlug, Multimedia over Coax Alliance (MoCA), and nVoy are some modern-day examples. A key piece of equipment for networking connections is a router, which is a stand-alone device designed to allow multiple devices to share a single Internet connection.
cellular connections, which are used to connect cell phones and other devices to a cell phone network.

One Group, Many Connections

Although there have been a variety of groups responsible for standardizing connections (the previously mentioned VESA and PCI-SIG are two such examples), one of the most prolific groups in this area has been a subdivision of the Institute of Electrical and Electronics Engineers (IEEE) known as the IEEE Standards Association (IEEE-SA). The IEEE-SA standards have included IEEE 802.3 (Ethernet), IEEE 802.11 (Wi-Fi, the latest version of which is 802.11ac), IEEE 802.15.1 (Bluetooth), IEEE 1394 (FireWire), IEEE 1901 (HomePlug), and IEEE 1905.1 (nVoy) [12] [13] [14] [15] [16] [17].

Form & Delivery

A connection, in order to operate, needs some way to transmit data. This will be referred to by this website as a connection's form. Some important forms are:

electricity [18].
electromagnetic radiation (EMR) [18] [19] [20]. Physical objects that guide or redirect EMR or sound waves are sometimes referred to as waveguides [21].
- radio waves and microwaves [18] [19]. Connections that use these forms are sometimes lumped together under the category of radio frequency (RF) connections [22].
- light [18] [19] [20]. Connections that transmit information with light may be referred to as optical connections [20].
  - infrared (IR) [18] [19] [20].
  - visible [19] [20].
  - ultraviolet (UV) [19] [20].

A connection also needs a way to go from one device to another. This will be referred to by this website as a connection's delivery. Some important delivery methods are sockets, slots, cables, and wireless delivery [23] [24] [25]. Some different types of cables are:

electrical cables [25], which are typically comprised of copper wires [26].
- coaxial (coax) cables [25], which can be used with a variety of different connectors [27]. Two particularly important coax cable connectors to be aware of are the F and Radio Corporation of America (RCA) connectors [27] [28].
- cables with a phone connector, which will be referred to by this website as auxiliary cables.
- twisted pair (TP) cables [25].
optical cables [25].

The table below gives an idea of how different forms and delivery methods can be combined for different data connections:

form	electricity	RF	light
delivery	sockets, slots, and electrical cables	coax and wireless	optical cables and wireless

Measuring EMR

The different forms of EMR, including radio and light, are usually measured by frequency, wavelength, and energy [19].

The frequency measurement is used because EMR consists of waves that oscillate (go up and down) a certain number of times per second. The frequency measurement is typically done in Hz [19].

The wavelength measures the length of each wave and is done in meters. As the frequency increases, wavelength decreases [19].

The energy measurement is done with electron volts (eV). As the frequency increases, energy also increases [19].

Forms of EMR

In order from lowest frequency to highest frequency, the different forms of EMR are radio waves, microwaves, IR, visible light, UV, X-rays, and gamma rays [19].

Interference

Interference typically refers to a connection being degraded due to another nearby device or connection. Interference may also occur between the wires of an electrical cable due to improper construction and/or trying to send too much information.

Spectrum

A collection of EMR frequencies may be referred to as spectrum [29]. Spectrum that requires a license to use is referred to as licensed spectrum, while spectrum that doesn't require a license is referred to as unlicensed spectrum [30]. Connections that use unlicensed spectrum are oftentimes prone to interference, with Wi-Fi being a key example [31].

Bands

The collection of frequencies that an RF connection uses is the connection's band [30]. Although a band has a specific starting and ending frequency, it's often referred to by a single number. For example, although the band used by 802.11ac is usually referred to simply as 5 GHz, the frequencies used by 802.11ac actually range from 5.17 to 5.835 GHz, with various gaps depending on country designed to avoid interference [31] [32] [33] [34] [35] [36] [37].

Channels

Connection data is often divided, and these divisions may be referred to as channels [38]. The three primary reasons for channels are interference avoidance, scalability, and specialization.

Using Channels for Interference Avoidance

Perhaps the most common and easily understood example of channels for interference avoidance is when someone asks to change the TV channel. Broadcast TV is divided up into channels so that multiple stations can share the same space without interfering with each other. Wi-Fi also uses channels. Some connections with band gaps, such as 802.11ac, are able to combine different frequency ranges to form a single channel [32].

The range of frequencies used by a channel is known as the channel bandwidth. One important point to keep in mind is that the wider the RF channel bandwidth is, the less instances of the connection you can have occupying the same vicinity without causing interference. For example, 802.11ac allows for channel bandwidths of up to 160 MHz. However, if this channel bandwidth is used, having more than one to three 160 MHz 802.11ac networks in the same area could lead to interference (this number depends on whether or not the Terminal Doppler Weather Radar (TDWR) or discontiguous channels are used) [31] [32] [33] [34] [35] [36] [37].

Using Channels for Scalability

In terms of scalability, combining multiple lanes or spatial streams allows a connection to run at different capacities. The different scalable channels for PCIe are referred to as lanes [39 pages 21-3], while the different scalable channels for 802.11ac are referred to as spatial streams [13] [40] [41]. That being said, this usage comes with caveats.

The major caveat for PCIe lanes is that although PCIe theoretically has up to 32 lanes, for all practical purposes it really has up to 16 lanes [39 page 21] [42].

The major caveat for 802.11ac is that unless a router and the devices connected to the router support a technology known as multi-user multiple-input and multiple-output (MU-MIMO), having a router with more streams than any of the devices connected to the router can result in wasted router streams [43].

Using Channels for Specialization

Using channels for specialization is a key part of operation for many connections that use traces and wires. For example, the channels available for use in an HDMI connection include three AV channels, an Audio Return Channel (ARC), a Consumer Electronics Channel (CEC) to facilitate communication among CE devices, a Display Data Channel (DDC) to allow a device plugged in to a display to see display characteristics, an HDMI Ethernet Channel (HEC), and a clock channel to synchronize the other channels [44] [45].

Single-ended vs. Differential Signaling

A wired electrical channel will typically consist of at least one ground wire and one signal wire. Single-ended signaling involves the use of only one signal wire, while differential signaling involves the uses of two complementary signal wires [46] [47] [44].Two wires that are used for differential signaling are called a differential pair [47]. In a differential pair, one wire is typically marked with a plus sign (+) while the other wire is marked with a minus sign (-) [47] [44].

Channel Directionality

A simplex channel typically refers to a channel that only allows for data to move in one direction, although it may sometimes be used to refer to a channel that allows data to move in two directions but not at once [48]. This website will use the first meaning.

A half-duplex channel allows data to move in two directions but not at once [49].

A full-duplex channel allows for data to move in both directions at the same time [49].

A dual simplex channel is a full-duplex channel that is restricted to moving half of its data in one direction and the other half in the other direction [39 page 21] [50 page 14]. The two different simplex sub-channels are typically marked as Tx or TX for transmit and Rx or RX for receive [50 page 14] [51 page 1].

Measuring Data Rate

Measuring data rate for connections is done in various ways, such as bits per second (b/s, bit/s, or bps) / bit rate, bytes per second (B/s or Bps), clock rate (measured in Hz), or transfers per second (T/s). In order to get a better idea of these measurements, it is helpful to take a closer look at the data rate for two connections: PCIe and HDMI.

Measuring PCIe Data Rate

PCIe is dual simplex connection [39 page 21] that, prior to version 3.0, had 20% overhead due to 8b/10b encoding [39 page 23]. Version 3.0 changed the overhead to 1.(538461)% via 128/130 encoding [39 page 23]. The latest version of PCIe, 3.1, has the same data rate as version 3.0 [11 page 11] [42]. Keeping all this in mind, the ways used to measure the per-lane data rate of PCIe are:

the data rate in each direction with overhead. Prior to version 3.0, this measurement was done in T/s, which referred to the data rate in each direction with overhead in b/s. For version 3.0, the data rate in each direction with overhead can use T/s, b/s, or B/s due to the vastly reduced overhead [11 page 11] [39 page 23].
the data rate in each direction without overhead, which can use b/s or B/s [11 page 11] [39 page 23].
the data rate going in both directions with or without overhead. This measurement uses B/s [11 page 11].

PCIe 3.0 is about 8 Gb/s per lane in each direction [11 page 11] [39 page 23].

Measuring HDMI Data Rate

HDMI transmits data in groups of 30 bits, 8 of which are overhead [45] [52 page 11] [53]. There are therefore three possible ways to measure the data rate of HDMI:

the bit rate with overhead
the bit rate without overhead
the clock rate, which measures the number of groups that are sent per second. In the case of HDMI, converting clock rate to the bit rate with overhead is accomplished by multiplying the clock rate by 30, while converting the clock rate to the bit rate without overhead is accomplished by multiplying the clock rate by 24 [45] [52 page 11] [53].

The latest version of HDMI, 2.0b, has a clock rate of 600 MHz, which translates to a bit rate of 18 Gb/s with overhead and 14.4 Gb/s without overhead [45].

Transmitting Connection Data via Modulation

Modulation is sometimes used to record and/or transmit EMR or audio-based information. For connections, three commonly used forms of modulation are amplitude modulation (AM), frequency modulation (FM), and quadrature AM (QAM) [54]. QAM can operate at different levels, with higher levels allowing for higher data rates but at the potential cost of reduced reliability [55].