Antenna Gain

Antenna gain is a measure of how efficient an antenna is at transmitting or receiving radio waves in a certain direction. It is measured in dBi (decibels relative to an isotropic source - which is an antenna that radiates equally in all directions). Generally speaking, for the purposes of most Wi-Fi networking deployments, the higher the antenna gain, the better.


Wi-Fi Attenuation refers to the loss of signal as it travels through different materials. It is measured in decibels (dB) which is a logarithmic scale in which every 3dB drop represents a 50% reduction in power.

See How much signal attenuatio n (loss) should I expect from walls and floors?


Aggregated Mac Protocol Data Unit (A-MPDU) and Aggregated Mac Service Data Unit (A-MSDU) are frame aggregation schemes used in 802.11n and 802.11ac which bundle multiple Ethernet packets together into single frames, thereby eliminating much of the overhead of multiple packet headers and thus allowing for greater overall data rates.

AP Flex

AP Flex is a feature of ZyXEL Access Points designed to simplify installation and reduce the time and cost of deployment. It does this by analyzing the network environment and automatically applying the appropriate IP configuration for each new access point.

Active Directory / Radius Authentication

In order to manage and control the authentication, authorization and accounting (AAA) of access devices across a large network, it is recommended to use a separate authentication server.

Often linked to user databases within Human Resources, the AAA server provides a central mechanism for all network authentication needs whether users are connecting via Ethernet or Wi-Fi.

The two most widely used options for AAA are Active Directory from Microsoft, and Radius, which stands for Remote Authentication Dial-In User Service, and was originally developed by Livingston Enterprises, Inc. in 1991, but later brought into the Internet Engineering Task Force (IETF) standards.

Without support for one of these authentication servers across the wireless LAN (WLAN), wireless users are forced to use separate pre-shared keys in order to access the network, effectively creating an overlay that is harder to manage and therefore more prone to security vulnerabilities.


Booster / Range Extender / Repeater

A Wi-Fi Booster (sometimes called a Wi-Fi signal booster, a Wi-Fi range extender or a Wi-Fi Repeater*) is a device used to extend the range of a wireless LAN (WLAN) by rebroadcasting the signal from an existing Wi-Fi router or access point into a new expanded area of coverage.

For a detailed explanation of the pros and cons of such devices, see Do I need a Wi-Fi Booster or Range Extender or both?

*Although the terms are often used interchangeably, device function may vary insofar as some use the SSID and security setup of the existing access point, allowing users to access the new part of the network with the same log-in credentials as before, while others work by creating brand new access points with their own unique SSIDs.


Cyclic Delay Diversity (CDD)

Cyclic Delay Diversity (CDD) is a scheme first introduced in 802.11n designed to reduce the likelihood of unintentional beamforming resulting from spurious patterns in the carried data.


Dynamic Channel Selection (DCS)

When multiple APs broadcast within a limited area, it increases the chance of radio interference, especially if some or all of the APs are broadcasting on the same channel. If this interference becomes too great, then the network administrator must check the AP’s configuration options, and manually change the channels being used in order to minimise overlap. Ideally, no two APs should use the same channel, but if this is not possible, each AP should be set to use the channel with the lowest level of interference.

Dynamic channel selection frees the network administrator from this manual task by letting the AP do it automatically. The AP scans the area and sets its channel to the one with the least interference.

Usually, the DCS feature would be set globally, but ZyXEL has further enhanced its implementation to provide more granular control, allowing settings to me made at the level of individual APs, groups of APs, or even individual radios within the AP.


Low Density Parity Check (LDPC)

Low Density Parity Check (LDPC) is an important error-correcting code used to counter interference on Wi-Fi networks.

Load balancing

Load balancing is a generic networking term referring the process of spreading the traffic load more evenly between two or more network devices.

In the case of Wireless LANs (WLANs), unless otherwise directed, connections between access devices and access points are generally established based on proximity and signal strength, but this can sometimes lead to uneven loading between two overlapping coverage areas.

With the addition of an access point controller and a sufficiently advanced management solution, traffic can be balanced based on either the number of access devices or on the volume of data.

Once the threshold is crossed (either the maximum device number or the data volume), then the AP delays requests from any new device attempting to connect. This allows the access device to automatically attempt connection to another, less burdened AP if one is available. The net result greater overall performance.

Layer-2 Isolation

Layer-2 Isolation is a security technique employed by Wireless Access Points to prevent access devices on the same wireless LAN from communicating directly with one another. Instead, access is restricted to predefined network services.


MiFi / Mobile Wi-Fi

Mobile Wi-Fi is a term applied to portable wireless routers that connect to the Internet via the cellular mobile telephone network. A mobile Wi-Fi device can thus be used to extend a single mobile data subscription to multiple access devices such as your phone, tablet or PC, using Wi-Fi.

MiFi is a registered trademark used to refer to mobile Wi-Fi devices, that is owned by UK telecom provider 3 and by Novatel Wireless in other parts of the world.


Multiple-in multiple-out (MIMO) is the wireless technology used in 802.11n and 802.11ac in which multi-path signals (including the reflections off walls and ceilings for example) are combined and resynchronized to increase signal strength and thus achieve higher data throughput rates.

Maximal Ratio Combining (MRC)

Maximal Ratio Combining (MRC) is an algorithm used by MIMO-enabled Wi-Fi access points in the resynchronization of the multi-path signals.


Powerline Adapter

Powerline adapters are devices used to extend the network reach of Wi-Fi routers using the mains power circuits. The first adapter is always plugged into a mains socket close to the router and connected to it via Ethernet. Secondary adapters can then be installed at remote parts of the building where the original Wi-Fi signal is either non-existent or too weak. These then connect to your remote devices via Ethernet. Some powerline adapters also act as brand new Wi-Fi access points providing connectivity at the remote location beyond their single Ethernet ports. Both primary and secondary powerline adapters must be on the same power circuit phase.

Power over Ethernet (PoE)

Power over Ethernet refers to the capability of an Ethernet Switch to deliver operating power to connected devices via its Ethernet ports (and of course the corresponding capability of those devices to receive power via their own Ethernet ports). This can be very useful for small low-power devices such as Wi-Fi Access Points, IP phones or IP cameras, since it removes the need for a separate power cable.

Many advanced Wi-Fi access points such as the ZyXEL WAC 6500 now use this capability as standard.


RSSI (Received Signal Strength Indication)

Usually measured in decibels (dB), RSSI is a measure of Wi-Fi signal strength. Generally speaking, anything over -50dB is considered a full strength signal, anything less than -100dB means no signal at all, and for reliable communications, it is best not to go below -70dB.



The SSID, which stands for Service Set Identification, is the unique name by which active Wi-Fi access points are identified on a wireless LAN (WLAN). This ‘name’, sometimes referred to as the ‘network name’, is always represented as a series of up to 32 characters and is usually, but not necessarily, a human-recognizable character string. Wi-Fi access devices such as PCs or smart phones then use the SSID to identify those networks to which the user wants to connect.

S/NR (Signal to Noise Ratio)

Often used in conjunction with the RSSI, the signal to noise ratio is arguably the most important measurement in determining the quality of a Wi-Fi connection. In exactly the same way that we find it easier to conduct a conversation in a quiet room than in a noisy one, when the ambient Wi-Fi noise is low, a lower strength signal will suffice. However, as the noise level increases, so too must the signal strength, and it is the ratio of the latter to the former that becomes the determining factor in connection quality.

If the S/N ratio is too low, receivers will misinterpret some of the noise as data, errors will be detected, and this will lead to retransmission of packets. The more retransmissions, the lower the effective throughput until, over a certain threshold, the connection is lost altogether.

Smart Classroom Load Balancing

Unlike most other Wi-Fi environments, classrooms present the unique challenge of having to handle maybe 30 – 50 near-simultaneous connection requests as students all attempt to log-in to the class network at the start of the lesson.

To help spread the load, it is usual in such scenarios to install more than one access point, but even with standard load balancing techniques there can be significant delays before all the students are able to establish a satisfactory connection.

ZyXEL's Smart Classroom Load Balancing feature can shrink this time to a minute or less, allowing the class to proceed with minimal disruption.


Wireless Router

A Wireless router is a device used for creating a wireless LAN (WLAN) that is linked to another network – typically the Internet. It usually features 4 or more local Ethernet ports as well as an embedded firewall.

Wireless Access Point

A Wireless Access Point is a device used for creating or extending a wireless LAN (WLAN). Typically, the Access Point is connected to a network via an integrated Ethernet port.


Wired Equivalent Privacy (WEP) was the embedded encryption algorithm for the first 802.11 standard. However, after serious vulnerabilities were highlighted, it was replaced in 2004 by Wi-Fi Protected Access WPA.


Wi-Fi Protected Access (WPA) was created as an interim standard security protocol to address the shortcomings of WEP until the more robust Wi-Fi Protected Access 2 (WPA2 – 802.11i) became available. Built upon far stronger encryption (CCMP), WPA2 currently offers the strongest security for WLANs and has been a mandatory requirement for all new Wi-Fi equipment since 2006.


WPA/WPA2-PSK (or WPA-Personal) allows for WPA/WPA2 security without the need for an authentication server and is chiefly used in home and small business networks. It works through the use of a pre-shared key (PSK) of 256 bits, entered during setup as 64 hexadecimal digits, or as a password of 8 to 63 alphanumeric (ASCII) characters.

Wireless LAN Controller

A wireless LAN controller is a device installed on the network to consolidate the management of all connected access points. Through dedicated software or via a web-based console, the network administrator can then manage the wireless LAN as a whole, with visibility into the status of any access point and the ability to view or edit its configuration.

In addition to central management, such controllers, through their awareness of the network as a whole, open up new possibilities for further enhancing the connectivity, throughput, resilience, and security of the network. Examples of such functionality enabled through ZyXEL’s controllers are Smart Classroom, load balancing, a more advanced Dynamic Channel Selection called DCS 3.0, Containment mode monitor, and Layer-2 Isolation.



802.11 is the overarching standard defined by the Institute of Electrical and Electronics Engineers (IEEE) for Wireless LANs (WLANs). See What is Wi-Fi? As Wi-Fi technology has advanced, the standard has evolved through a number of iterations including 802.11a, 802.11g, 802.11n (up to 600Mbps) and most recently 802.11ac (up to 1.75 Gbps).