Telecoms Jargon: A Guide to Telecoms & IT Terminology

At CallCloud we’re proud of our plain-English approach to business. There's no need to use complex terms to describe simple concepts. However, since we work with phone systems and Unified Communications technology every day, we can sometimes forget that the acronyms we use aren't obvious to everyone. That’s why we’ve compiled this glossary; there are a lot of terms that are often used in telecoms and technology in general that you may not be familiar with. Hopefully this list will help clear a few things up for you. If there’s anything you’re still not sure of, get in touch! We’re always happy to help.


ACD - Automatic Call Distribution routes incoming calls fairly to a group of agents. Incoming calls are usually routed to the first available agent signed in to the system, making them ideal for Contact Centres handling high volumes of calls.

ADSL – Asymmetric Digital Subscriber Lines are a type of broadband internet connection. Available at every address in the UK and offering speeds of up to 24Mbps, ADSL makes up the bulk of the UK’s internet connectivity.

Auto-Attendant – Also known as an IVR (Interactive Voice Response), Auto-Attendants are automated menus played over phones to help callers reach the right department by pressing numbers on their keypads.

Bandwidth – The amount of data that can be transferred in a given amount of time. This is usually used to refer to the capacity of your internet connection, measured in Megabits or Kilobits per second.

BLF – Busy Lamp Field lights configured on desk phones indicate the status of an extension. Depending on the make of phone, they may flash when the monitored extension is ringing, illuminate green when available or red when in a call or set to DND.

Cat 5/Cat 5e/Cat 6 – These are the different categories of copper cables that carry data around a network. They are all compatible with each other, and each have different use cases. The most common cables are Category 5 Enhanced (Cat 5e), although Cat 6 is becoming more widespread.

CLI - Calling Line Identity refers to the number you see on your phone when you're being called, or the number others see when you call them. This can be withheld to hide your number from people you're calling.

Conferencing – this is the merging of two or more separate phone calls, resulting in a single call with 3 or more participants.

Contact Centre – this is the modern extension of a Call Centre. Contact Centres merge all customer contact including calls, emails and live chats, allowing one team to handle all customer communication for a business.

CRM – Customer Relationship Management software acts as a hub for all of your customer contact. CRMs can often be integrated with your phone systems to automate tasks like entering records of contact or saving contact details.

CTI – Computer Telephony Integration is the process of integrating your computers with your telephones, to allow features like Click to Dial on your PCs. Integrating your phones with CRM software can enable more advanced features like Screen Popping, which triggers your CRM to show you information it has stored on the person calling you when you receive a call.

DDI/DID - Direct Dialling Inwards (or Direct Inwards Dialling) are your direct dials. This allows individual extensions to be reached from outside your office by dialling a phone number.

DECT – Digital Enhanced Cordless Telephony is a wireless connection between a handset and a base station. These mobile handsets allow you to walk anywhere within range of the wired base station and still make and receive calls, making them perfect for workers who spend a lot of the day on their feet.

DND – Do Not Disturb is a setting that can be enabled on your phone or extension to divert any incoming calls to voicemail if you’re busy or holding a meeting.

Fibre – this is the type of broadband internet connectivity that is replacing ADSL across the UK. Available at more than 90% of addresses, Fibre broadband gives superfast bandwdith – FTTC (fibre to the cabinet), the most common technology in use, offers bandwidth of up to 80Mbps.

Firewall – Firewalls prevent unwanted visitors from invading your network over the internet. Think of firewalls like a fence around your network; they make sure that the only entrance points to your network are through the ports you open and monitor, like the gates in a fence. Firewalls are indispensable for the security they provide.

Hunt Group – Hunt Groups ‘hunt’ among their list of member extensions for one that is available to take a call. Hunt Groups are usually used internally to allow members of staff to easily reach other teams.

IP – Internet Protocol is the internet as you know it – a series of computers connected together, sharing information. Each computer on the internet has a unique IP Address, allowing other computers to access them to retrieve information like web pages or emails.

ISDN – the Integrated Services Digital Network is a method of providing digital communication over the analogue landline network. Most often used by businesses that need capacity for multiple simultaneous calls on one phone line, ISDN is being replaced by VoIP, with the UK network set to be shut down in 2025.

ISP – your Internet Service Provider is the company that provides web access to you, most often through a phone line or fibre optic cable.

Mbps/Kbps - Megabits or Kilobits per second are standard measures of bandwidth, most often used when referring to the capacity of broadband connections. One Megabit is equal to one thousand Kilobits. Gigabit (a thousand Megabits) connectivity is already available across some of the UK, with access expanding rapidly.

LAN - Local Area Network is the suite of devices you have in your office or home that connect to each other through cables or wirelessly. Your LAN will include all your PCs and office equipment, as well as any mobiles or other devices using WiFi.

Latency – This is the amount of time it takes a piece of information to travel from its source to its destination. On a phone call, it is the amount of time it takes your voice to travel down a phone line or across the internet. Low latency is important to achieve the best VoIP call quality.

PBX – Private Branch Exchanges are business phone systems. The term originates from the days of manually operated telephone exchanges – businesses had their own private switchboards catering to employees and connecting callers to the right departments. These days PBX’s are most often hosted remotely over the internet, as with CallCloud’s own services.

PMS – Property Management Systems refers to the software front of house staff at restaurants and hotels use to manage reservations and billing. Often integrates with phone systems in the same way as CRMs to help streamline processes.

PSTN – the Public Switched Telephone Network is the old network of copper landlines running across the UK. The PSTN was first used in the 1950s and is being replaced by Fibre.

QoS - Quality of Service lets you prioritise certain types of traffic on your internet connection. For example, you might want to make sure that your phone system has the highest priority through QoS to guarantee the highest call quality.

Router – This is the piece of equipment that sits between your LAN (Local Area Network) and the Internet. Routers allow your computers and other equipment to access the internet and each other.

SIP – Session Initiation Protocol is the most common method of transmitting phone calls over the Internet. A SIP Trunk is equivalent to your old analogue phone line and gives you the ability to place phone calls using SIP.

Switch – A Network Switch connects to the Router, and includes many more ports to connect to your PCs. Switches allow you to connect all your PCs to a Router with as few as 4 network ports. Switch may also refer to PBX.

Unified Communications – This is the latest phone system technology that includes video calling, instant messaging, file sharing and screen sharing among other services. All included services integrate with each other, allowing for a more ‘joined-up' experience than systems of separate services for all business communications.

VoIP – Voice over Internet Protocol refers to placing phone calls over the internet. VoIP calls are much cheaper than analogue phone calls and offer far more features to users than PSTN.

VPN – Virtual Private Networks allow you to access your business’s private local network from home, or on the road. VPNs are also often used to connect multiple sites in the same business, allowing them to share services over the Internet.