Glossary
Wholesale voice & VoIP glossary
Plain-English definitions of the wholesale voice and VoIP terms carriers, resellers and businesses use every day.
Routing & quality
- Wholesale voice
- The business of buying and selling call-carriage capacity between telecoms networks in bulk, rather than to end users. Carriers, resellers and platforms buy wholesale voice to complete their own traffic and to build retail products on top.Related service: Wholesale Voice Termination
- A-Z termination
- A voice service where rates are published and routed for every destination prefix in the world, from country code A to Z. Providers buy the A-Z routes they need and use them to terminate outbound calls.Related service: Wholesale Voice Termination
- Termination
- Delivering a call from one network onto its destination network, so it reaches the person being called. Outbound calls are 'terminated' by a carrier that has a route to the destination.
- Least-cost routing (LCR)
- Automatically selecting the cheapest viable route for each destination while respecting quality thresholds, usually with automatic failover to the next best route if one degrades.Related service: Wholesale Voice Termination
- CLI (Calling Line Identification)
- The caller's telephone number presented to the person receiving a call. CLI routes preserve it end to end, improving answer rates and trust; broken or altered CLI hurts both.Related service: International Voice Routing
- Non-CLI / grey routes
- Cheaper routes that strip or alter the caller's number (CLI). They lower cost but reduce answer rates and can breach regulations, so they are used selectively and transparently.
- ASR (Answer-Seizure Ratio)
- The percentage of call attempts that are answered. A key quality metric for a route: higher ASR generally means a healthier, better-connecting route.
- ACD (Average Call Duration)
- The average length of answered calls on a route. Read alongside ASR, it helps distinguish genuinely good routes from those that answer but drop quickly.
- PDD (Post-Dial Delay)
- The time between a call being placed and the caller hearing ringing. Low, consistent PDD means faster connections and less abandonment, which is critical for diallers and contact centres.Related service: Contact-Centre & BPO Voice
- CPS (Calls Per Second)
- The rate at which a system or trunk can set up new calls each second. High-volume outbound operations such as predictive diallers need generous CPS as well as concurrency.
Numbering & origination
- Origination
- Bringing inbound calls into a network, typically on virtual numbers (DIDs). It is the opposite direction to termination; most carriers need both.
- DID (Direct Inward Dialling)
- A telephone number that routes inbound calls to a destination you choose (a SIP trunk, app or call flow) without a dedicated physical line. Also called a virtual number.Related service: Cloud Telephony
- DDI (Direct Dial-In)
- The UK/European term for a DID. DDI and DID mean the same thing: a number that delivers inbound calls straight to a specific line, extension or system.
- Virtual number
- A phone number not tied to a fixed physical line, used to receive calls anywhere over IP. Local, national and toll-free virtual numbers give a presence in markets without local hardware.Related service: Cloud Telephony
- Toll-free number
- A number that is free for the caller, with the cost paid by the business receiving the call (for example UK 0800). Often used for sales and support lines.
- Number porting
- Moving a telephone number from one provider to another so the customer keeps it. Timescales and outcomes depend on the gaining and losing providers and applicable porting rules.
Connectivity & protocols
- SIP (Session Initiation Protocol)
- The signalling protocol used to set up, manage and end voice-over-IP calls. Almost all modern voice services, including SIP trunks and interconnects, are built on SIP.
- SIP trunk
- A virtual voice connection that carries calls between a phone system (IP-PBX, SBC or UC platform) and the telephone network over IP, replacing physical ISDN or PRI lines.Related service: SIP Trunking
- Interconnect
- A direct connection between two telecoms networks for exchanging traffic without intermediate transit carriers. Direct interconnects shorten routes, cut latency and raise quality.Related service: Carrier Interconnects
- SIP peering
- Interconnecting two networks over SIP so they can exchange voice traffic directly. Peering can run over the public internet, private IP or a cross-connect at a carrier hotel.Related service: Carrier Interconnects
- SBC (Session Border Controller)
- A device or software that sits at the edge of a voice network to secure and control SIP traffic, handling authentication, encryption, NAT traversal and protocol normalisation.
- RTP / SRTP
- RTP (Real-time Transport Protocol) carries the audio (media) of a call once SIP has set it up. SRTP is the encrypted version, protecting the media stream in transit.
- Codec
- The algorithm that compresses and decompresses call audio. Common voice codecs include G.711, G.729 and Opus, trading off audio quality against bandwidth.
- ENUM
- A standard for mapping telephone numbers to IP addressing using DNS, letting networks route eligible calls over IP directly instead of via the traditional phone network.
Commercial & operations
- Rate deck
- A price list of per-minute termination rates by destination prefix, issued to wholesale customers. Rate decks are updated regularly as underlying route costs change.
- CDR (Call Detail Record)
- A record of a single call's metadata: numbers, timestamps, duration, route and cost. CDRs feed billing and quality reporting for metrics such as ASR, ACD and PDD.
- KYC (Know Your Customer)
- The checks a carrier runs to verify a customer's identity and legitimacy before provisioning service, helping prevent fraud and meet regulatory obligations.
- NOC (Network Operations Centre)
- The team and systems that monitor a voice network around the clock, watching quality and capacity and responding to incidents before they affect customers.
- Voice fraud
- Abuse of a voice network for financial gain, such as traffic pumping, PBX hacking or subscription fraud. Controls include traffic profiling, spend caps and destination rules.
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