Kesher Knowledge Center
129 terms from the world of phones, networks, PBXs and cloud servers — in plain language, with diagrams, and with what really matters: how it actually works for us.
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Telephony Basics
The terms everything else builds on: what a PBX is, how voice travels over the internet, and how providers differ.
PBXA PBX (Private Branch Exchange) is the system that manages all of an organization's phones: it receives the…Read moreVirtual PBXA virtual PBX is a PBX that runs on servers in the cloud and not in a cabinet at the office. The phones, apps and extensions connect to it through…Read morePhysical PBX vs. Cloud PBXA physical PBX is equipment that sits in your office and belongs to you; a cloud PBX is a service that runs at the provider. The main difference: who maintains it, what happens…Read moreVoIPVoIP (Voice over IP) is the transmission of phone calls over a computer network and the internet, instead of over lines…Read moreSIPSIP (Session Initiation Protocol) is the "language" phones and PBXs use to talk to each other: it is responsible…Read moreSIP TrunkA SIP trunk is a single connection between a PBX and the telephone network that carries several calls at once over the internet. It replaces the lines…Read moreChannels and Concurrent CallsA channel is one call in progress at a given moment. The number of channels determines how many outside calls can take place at the same time — and that is the figure that determines…Read moreAnalog Phone LineAn analog line is the classic phone line: a pair of copper wires running from the phone company's exchange to the wall. It carries one call at a time…Read moreTypes of Telephony ProvidersA "phone company" can be several different things: a landline infrastructure operator, a mobile operator, an internet telephony provider, or a cloud PBX provider.…Read moreCodecA codec (short for Coder-Decoder) is the method by which voice is compressed for transmission over the network and expanded again on the other side. The codec determines…Read moreThe Public Telephone NetworkThe PSTN (Public Switched Telephone Network) is the public telephone network: all the lines, exchanges and cellular networks that connect every…Read moreRTP — The Voice ChannelRTP (Real-time Transport Protocol) is the protocol that carries the voice itself in an internet call. SIP manages the call — who is calling, when…Read moreSIP RegistrationSIP registration is the message in which a phone tells the PBX, "I'm extension 104, and I'm here, at this address." Without a valid registration the PBX does not…Read moreSIP Server AddressThe SIP server address is the address the phone contacts in order to register and place calls — "the PBX's address." Along with it, you enter in the phone a username…Read moreKeypad Tones (DTMF)DTMF (Dual-Tone Multi-Frequency) are the tones a phone plays when you press a key: each key has a combination of two frequencies. Thanks to them it is possible…Read moreHD VoiceHD voice, or wideband audio, is a call that carries a wider range of sounds than a regular phone. Speech sounds more natural and clearer…Read moreMOS ScoreMOS (Mean Opinion Score) is a call quality rating on a scale of 1 to 5: 5 is excellent, 1 is poor. In the past the score was set by people…Read moreSIP Response CodesEvery time a phone asks the PBX for something — to register, to dial, to hang up — it gets a reply with a three-digit number. 200 means "succeeded," 486…Read more
Extensions and Endpoint Devices
The phones, apps and adapters you answer calls on: how they differ and what suits each workstation.
ExtensionAn extension is the "address" of a workstation or employee inside the PBX — usually a short number like 201. You transfer calls to it, dial out from it, and you can…Read moreCellular, Computer-Based or IP-Phone ExtensionAll three are a regular extension on the PBX — the difference is where you answer: an IP phone is a desk device on a network cable, a computer-based extension is software…Read moreIP PhoneAn IP phone is a desk phone that connects to the computer network instead of to a phone line. IP stands for Internet Protocol — the protocol…Read moreSoftphone (Computer-Based Extension)A softphone (software phone) is software that turns a computer or smartphone into a phone: you register in it to an extension, and receive and place calls…Read moreCellular SIM ExtensionA SIM extension is a SIM card that behaves like an extension on the PBX: you answer and dial from the mobile's regular dialer, with no app and no data…Read moreSIP AdapterA SIP adapter (ATA — Analog Telephone Adapter) is a small box that connects a regular phone or a fax machine to the network. On the side…Read moreFXS and FXOFXS and FXO are two types of analog connections in telephony equipment. A phone connects to an FXS (Foreign Exchange Station), and it "gives it…Read moreDECT Cordless PhoneDECT (Digital Enhanced Cordless Telecommunications) is the standard that cordless phones work on…Read moreConference PhoneA conference phone is a device for a meeting table, with sensitive microphones and a strong speaker, so everyone sitting in the room can hear and be heard clearly in a single call.Read moreExtension Keys (BLF)BLF (Busy Lamp Field) are keys with lights on the phone that show the status of other extensions: free, ringing, or…Read moreAutomatic Phone SetupProvisioning (automatic setup) is the way a phone receives its settings from the server as it powers on, instead of someone…Read moreHeadsets for CallsA headset is a pair of earphones with a microphone close to the mouth, designed for long conversations. In a call center and when working with a softphone, they are the difference between…Read moreFanvil PhonesFanvil is a manufacturer of desktop IP phones, intercoms and communications equipment for offices. Its well-known models belong to the X series, from a phone…Read moreGrandstream — Phones and AdaptersGrandstream is a communications equipment manufacturer known mainly for two types of products: desktop IP phones (the GRP and GXP series) and adapters…Read moreYealink PhonesYealink is a major manufacturer of IP phones. It is known for its T series of desktop phones, from a simple phone to a phone with a touch screen…Read moreFirmwareFirmware is the internal software that runs a device — an IP phone, an adapter, a router or a switch. A firmware update fixes bugs, closes security holes…Read moreExpansion ModuleAn expansion module is a keypad that attaches to the side of an IP phone and adds dozens of programmed keys to it. Each key shows a different extension in the organization, and with a light…Read moreSIP Door IntercomA SIP door intercom is a doorbell with a speaker and microphone (and sometimes a camera) that connects to the PBX like an extension. Whoever presses the button at the entrance reaches the phone…Read morePagingPaging is a voice announcement played in several places at once: on phone speakers, on ceiling speakers or on speakers in the yard. Instead of having to look for…Read moreFactory ResetA factory reset returns a device — a phone, an adapter or a router — to the state it left the factory in. All settings are erased: the account on the PBX…Read more
Network and Infrastructure
What you need in the office for the phone to work well: a network cabinet, network cables, switches, a router and internet.
IP AddressAn IP address (Internet Protocol) is a device's "phone number" on the network — a number that identifies it so that information reaches it. Every phone, computer…Read moreStatic IP and Dynamic IPA static IP is a public address that does not change; a dynamic IP changes from time to time according to the internet provider. For most businesses dynamic is enough — static is needed…Read moreNATNAT (Network Address Translation) is the translation the router performs between the private addresses of the devices in the office and…Read moreRouterA router is the device that connects the office network to the internet. It hands out addresses to devices, translates them for the outside, and protects the network…Read moreNetwork SwitchA network switch is a box with many network ports that connects all the devices in the office to one another and to the router. Every phone, computer and printer…Read morePoEPoE (Power over Ethernet) is the delivery of electric power through the network cable itself. An IP phone connected to a PoE switch receives both…, all in one cable.Read moreNetwork CableA network cable is the cable that connects a device — a computer, an IP phone, a printer — to the office network. At its end is an RJ45 connector, and it runs inside the wall from a network point…Read moreNetwork CabinetA network cabinet is a metal cabinet in which all of the office's network equipment is gathered: the router, the switches, the patch panel for the network points, and backup…Read moreFiber OpticFiber optic is a cable that carries information using flashes of light inside a thin strand of glass, instead of electric current in copper wires. It is fast, stable and not…Read moreBandwidthBandwidth is the amount of information an internet connection can carry every second. A VoIP call uses little — about 100 kilobits per second in each direction…Read moreLatency, Jitter and Packet LossLatency is the time it takes for voice to reach the other side; jitter is the inconsistency of that time; and packet loss (Packet…Read moreQoS — Priority for VoiceQoS (Quality of Service) is a set of network settings that give voice traffic priority over other traffic. When someone…Read moreVLANA VLAN (Virtual LAN) is a separate network that runs over the same cables and switches. It is used to separate the phones from the rest of the computers…Read moreFirewall and PortsA firewall is a system that decides which traffic goes into and out of the network. A port is a numbered "door" in a device's address…Read moreUPS — Power BackupA UPS (Uninterruptible Power Supply) is a smart battery that keeps equipment running when the power…Read moreBackup InternetA backup internet connection is a second internet line — usually cellular — that kicks in automatically when the main connection goes down (failover). For an office that lives…Read morePingPing is a simple test that sends a small packet to a server and measures how long it takes to come back. The result, in milliseconds, shows how fast the line is…Read morePacket LossPacket loss is a situation in which some of the pieces of information sent over the network do not reach their destination. In a phone call it sounds like a missing word, choppy audio, or…Read moreSpeed TestA speed test measures how much information the line carries per second for download and upload, and usually the ping as well. For telephony, the big download number…Read moreDNSDNS is the internet's "phone book": it translates an easy-to-remember name, such as a server's name, into an IP address the computer knows how to reach. A phone…Read moreDHCPDHCP is the service that automatically gives every device that connects to the network what it needs to work: an IP address, the router's address and DNS servers.…Read moreWi-Fi and TelephonyWi-Fi is a network without cables, and calls can travel over it — but it is sensitive to interference, distance and load, and a call is more sensitive to all of these than browsing is.…Read moreVPN and CallsA VPN is an encrypted "tunnel" that carries a computer's traffic through another server, for example the office network. It is useful for working from home and for security, but…Read moreMAC AddressA MAC address is a permanent identifier burned into every network card — in a phone, a computer, a printer. Unlike an IP address, which changes depending on the network, the MAC address…Read moreNetwork Capacity for TelephonyThe number of phones you can connect is almost unlimited as far as the network itself is concerned — what determines it is how many calls take place at the same time, and what else shares the line. In the article…Read morePatch PanelA patch panel is a strip of sockets in the network cabinet to which all the cables from the office walls arrive. From the panel you connect short cables — patch cables…Read more
Call Management
What happens to a call from the moment it comes in: menu, queue, hunt group, transfer, voicemail box and recording.
IVR MenuAn IVR menu (Interactive Voice Response) is the message the caller hears at the start of the call — "For service…Read morePattern menuA pattern menu is a menu in which the caller presses a sequence of digits — an extension number, a student number or a code — and the PBX routes according to the pattern entered…Read moreWaiting QueueA waiting queue collects calls when all the agents are busy: callers hear music and announcements, wait in order of arrival, and each call goes to an agent…Read moreHunt groupA hunt group is several extensions that ring together or in order when someone calls one destination — for example "Office" or "Accounting." Whoever answers first…Read moreTime-Based RoutingTime-based routing is a setting that changes the call path according to the day and time: during business hours the call goes to the office, and outside them — to a message…Read moreRouting by callerCaller-based routing sends the call to a different destination depending on the number it came from: an important customer goes straight to his account manager, a regular supplier straight to accounting…Read moreCall PathA call path is the full route a call takes from the moment it comes in: the number dialed, the check of the caller and the time, the menu, the queue, and up to whoever answered — or…Read moreCall TransferCall transfer is redirecting an active call to another extension. There are two ways: a blind transfer — the call goes through immediately; and a consultative transfer — you talk…Read moreCall Forwarding and Follow MeCall forwarding sends a call to another destination when the extension doesn't answer, is busy or is not connected. "Follow Me" rings in order at different places…Read moreVoicemailA voicemail box is an extension's answering machine: when there's no answer, the caller hears a greeting and leaves a voice message. The message is saved, and you can listen to it…Read moreOpening Message and GreetingThe opening message is the recording the caller hears first — a greeting, the organization's name, or a message that the office is closed. It is the organization's first impression on the phone…Read moreMusic on HoldMusic on hold (MOH) is what the caller hears while waiting in a queue or during a transfer. Silence makes people think the call was disconnected…Read moreCallbackCallback lets a caller who is waiting in a queue hang up without losing their place: the system will call them itself as soon as an agent becomes free.Read moreListen, Whisper and BargeThese are tools for call center managers: listen — hear an active call, openly or silently; whisper — speak to the agent without the customer hearing; barge — enter…Read moreSpeed DialSpeed dial is a short code that dials a long number — for example 88 for the main branch or 91 for a regular supplier. It saves typing and mistakes.Read moreRouting codeA routing code is a short number you dial from an extension to trigger an action or reach a destination: to enter a queue, to hear the voicemail box, to reach a menu…Read moreCall PickupCall pickup is the ability to answer, from your own phone, a call that is ringing at another extension — without getting up and walking to your colleague's desk. You press a short code or…Read moreCall ParkCall park is a way to "set down" a call in a reserved spot on the PBX — a kind of numbered shelf — so anyone, from any phone, can pick it up from there.…Read moreDo Not Disturb (DND)"Do Not Disturb" (DND) is a mode in which the extension stops ringing. Calls that come to it don't disappear — they…Read moreCall WaitingCall waiting is the ability to receive a second call while you are already talking. You hear a short beep, see on the display who is calling, and choose: to answer…Read moreThree-Way CallA three-way call is connecting a third party to a call that is already in progress — straight from the phone, with no advance setup. You are talking with a customer, you call…Read moreAbandoned CallsAn abandoned call is a call in which the caller hung up before anyone answered — usually after waiting in a queue or hearing rings. Every such call is…Read moreCaller BlockingCaller blocking is the way to keep certain numbers — or callers who hide their number — from reaching employees. In the PBX you do this…Read moreFollow Me (Call Forwarding)Follow Me (call forwarding) is a setting that sends an extension's calls somewhere else — to a mobile, to a colleague or to the voicemail box. There are three main types:…Read moreQueue Position AnnouncementA queue position announcement is the message "You are third in line" that the caller hears while waiting. Estimated wait time is an estimate of how much time is left.…Read moreCall HoldCall hold is a temporary "pause" of a call without hanging up: you press Hold, the caller hears music on hold, and you can check…Read more
Numbers and Dialing
Phone numbers, porting, caller ID, short and international numbers, calling cards, and the students' phone.
Business Phone NumberA business number is the number customers dial. In a cloud PBX it isn't tied to a physical line or an address — it is connected to the PBX, and leads…Read moreNumber PortingNumber porting is moving an existing phone number from one provider to another — without the number changing. Customers keep dialing the same number, and the calls arrive…Read moreCaller IDCaller ID is the number that appears on the display when someone calls. On an outgoing call from the PBX you choose which number will be shown to the other side — usually…Read moreVirtual NumberA virtual number is a phone number with no physical line behind it: it is connected to the cloud PBX and routes calls to any destination — an extension, a mobile, a menu or…Read moreLocal Number AbroadA local number abroad is a phone number in another country — for example in New York or London — that rings at your place in Israel. The customer there dials a call…Read moreShort Number (Star Number)A short number is a short number with a star — like *3957 — that is easy to remember and publicize. Behind it is a regular number connected to the PBX, so you can connect…Read moreToll-Free Number (1-800)A 1-800 number is a number that is free for the caller to dial — the organization pays for the call. It suits customer service and support lines, when you want no one to…Read moreDialing PrefixA prefix is digits you add before a number to define how the call will go out — for example which number will be displayed, or blocking certain destinations.…Read moreCalling CardA calling card is a personal code with a balance: you enter it before a call, and the call is deducted from the card's balance. In institutions, each student gets a card…Read moreStudents' PhoneA students' phone is a phone station in an institution for children that dials only numbers the administration approved in advance — with no code and no card. The child picks up…Read more072–077 PrefixesIn Israel there are two main families of landline numbers: geographic numbers, with an area code such as 02 or 03, and numbers with the prefixes 072…Read moreGeographic NumberA geographic number is a landline number whose prefix indicates a region of Israel: 02 for Jerusalem, 03 for the Tel Aviv area, 04 for Haifa and the north, 08 for the Shfela…Read moreVanity NumberA vanity number is an easy-to-remember phone number: repeating digits, a sequence, a symmetric pattern, or digits that mean something to the organization. It helps customers remember…Read moreEmergency CallsFrom a cloud PBX, too, you can dial the emergency numbers — 100 for the police, 101 for Magen David Adom, 102 for the fire department — just as from any phone. But there are a few differences that are important…Read moreDID — Direct NumberA DID (Direct Inward Dialing) is an outside phone number that leads straight to a particular extension, department or queue, without…Read moreExtension Numbering PlanAn extension numbering plan is the advance decision on which number each phone, department and branch in the organization will get — for example 100 for management, 200 for the secretariat, 300…Read more
Cloud, Services and Security
The servers behind the PBX, the services built on it — recordings, call center, fax, SMS, API — and how it is kept safe.
Cloud Servers and Data CentersA cloud PBX runs on servers in data centers — secured buildings with backup power, cooling and fast network connections. The phones connect…Read moreResilience and RedundancyResilience is a system's ability to keep working even when something fails. Redundancy is the way to achieve it: more than one component for each role — servers…Read moreCall recordingCall recording saves calls as audio files according to rules set in advance — all calls, or only certain extensions or queues — and for a period…Read moreCall Log (CDR)A call log (CDR — Call Detail Records) is the record of every call that passed through the PBX: who called, to where, when…Read moreCall CenterA call center is a team of agents that answers a large volume of calls — or dials out to them — with tools that manage the load:…Read moreConference RoomA conference room is a shared call that several people dial into: you dial a number, enter the room code, and join. It suits management meetings…Read moreVirtual FaxA virtual fax sends and receives faxes without a machine: an incoming fax arrives by email as a file, and you send a fax from the browser from a file — and to the other side it looks…Read moreBusiness SMSBusiness SMS is sending text messages from the organization's number — confirmations of arrival, reminders, updates — straight from the telephony system, with no phone…Read moreDialer and Dialing CampaignA dialer is a system that automatically dials a list of numbers — and plays a recorded message to whoever answers, or connects them to an agent. A dialing campaign is…Read moreConnecting to a CRMA CRM (Customer Relationship Management) is a system that gathers everything that is known about each customer. Connecting it…Read morePBX APIAn API (Application Programming Interface) is an interface that lets other systems talk to the PBX: to read…Read moreWebhookA webhook is a web address the PBX "calls" when something happens — a call came in, a call ended, a message was received — so that another system…Read moreTelephony Hacking and FraudTelephony hacking (toll fraud) is the exploitation of an extension or PBX to dial at the organization's expense — usually expensive calls abroad, at night…Read moreCall EncryptionA VoIP call can travel encrypted: TLS encrypts the call management (who is calling whom), and SRTP encrypts the voice itself. That way even someone who listens to the network…Read moreSub-Customers and ResellersSub-customer management (multi-tenant) is the ability to manage several separate organizations from the same system — each with its own numbers, extensions and settings…Read moreCall TranscriptionCall transcription is turning a call recording into written text. A computerized engine listens to the recording, recognizes the words and writes them, and sometimes also marks…Read moreCall Analytics and ReportsCall analytics is turning the call log into numbers you can base decisions on: how many calls came in, how many were answered, how long callers waited…Read moreCall Center Display BoardA call center display board is a large screen hung in the room that shows everyone, in real time, what is happening on the phones: how many are waiting in the queue, how long the longest-waiting caller has waited…Read moreUsers and PermissionsUsers and permissions determine who gets into the PBX control panel and what they are allowed to see and change. The guiding principle is least privilege: each…Read moreTwo-Step VerificationTwo-step verification is logging in to the system in two steps: first a password, then a one-time code sent to a phone or email, or generated in an app.…Read moreWorking From Home With the PBXIn a cloud PBX, the extension isn't tied to a building. An employee can answer the office's calls from home, through an office phone connected to the internet at home, through…Read moreCall Recording and PrivacyCall recording is an important tool for service, training and documentation, but it is also a collection of personal information. This article explains, as general background, the questions…Read moreMissed Call AlertsA missed call alert is a message, usually by email, sent when someone called and no one answered, or when they hung up while waiting in a queue.…Read more