Wholesale VoIP Glossary: Terms Every NOC & Routing Engineer Should Know

Wholesale voice has its own vocabulary, and new team members hear most of it in their first week. This glossary collects the terms used across this course and in day-to-day NOC, routing and rates work, each explained in a sentence or two. Where a lesson covers the term in depth, the entry links to it. Use your browser’s find function (Ctrl+F or ⌘+F) to jump to a term.

A – C

Term	Meaning
A-number / B-number	The calling number (A) and the called number (B).
A-Z	A rate deck or offer covering every destination a carrier can reach.
ACD	Average Call Duration: answered minutes divided by answered calls. Falls when audio is poor or calls drop. Lesson 6
ASR	Answer Seizure Ratio: answered calls as a percentage of attempts.
Billing increment	How call time is rounded for charging, written like `60/60` or `1/1`: minimum first period, then step size, in seconds. Lesson 5
Busy hour	The hour of the day with the most traffic; used for capacity planning.
Call-ID	The unique identifier of a SIP call; quote it in every ticket.
Carrier	A company that carries voice traffic for others, buying and selling routes.
CC route	A “call centre” route meant for high-volume, usually short-duration traffic, with its own pricing and rules.
CDR	Call Detail Record: one line per call attempt with times, numbers, gateways, duration, cost and end reason.
Channels / ports	The number of calls that can be in progress at once on a trunk, gateway or agreement.
CLI / NCLI	Calling Line Identity. A CLI route delivers the caller’s number intact; an NCLI route does not guarantee it. Blog
Codec	The method used to encode voice into data, such as G.711, G.729 or Opus. Lesson 12
CPS	Calls Per Second: how fast new calls may be sent, often limited by vendors.

D – H

Term	Meaning
Destination	A country, network or number range that calls are sent to, identified by prefixes.
Dial plan	The set of rules that cleans, checks and matches numbers to destinations. Lesson 13
Dispute	A disagreement between partners about minutes or charges, settled by comparing CDRs.
DTMF	The key-press tones used in IVR menus, sent in-band or as RFC 4733 events.
E.164	The international number format: country code plus national number, up to 15 digits.
Early media	Audio sent before a call is answered (ringback, announcements), usually after a 183 response.
Erlang	A unit of traffic: one channel busy for one hour.
Failover	Trying the next vendor when the first one returns a failure.
FAS	False Answer Supervision: a call is reported as answered (and billed) when nobody really answered. Lesson 7
Gateway	In a softswitch, the configured definition of a partner’s connection. A mapping gateway receives customer calls; a routing gateway sends calls to a vendor. Lesson 4
Grey route	A route that terminates calls in ways that bypass the destination’s official interconnect, often with CLI changes. Unstable and often against local rules.

I – N

Term	Meaning
Interconnect	The technical and commercial link between two carriers, usually IP-based SIP.
IP whitelist	The list of partner addresses allowed to send or receive traffic. Lesson 10
IVR	Interactive Voice Response: an automated menu that callers navigate with DTMF.
Jitter	Variation in packet arrival times; too much causes choppy audio.
LCR	Least Cost Routing: preferring the cheapest vendor that meets quality targets.
Longest-prefix match	Choosing the most specific matching prefix for rating and routing.
Media relay	RTP passing through the switch rather than directly between endpoints; doubles bandwidth on the switch.
MOS	Mean Opinion Score: a 1–5 estimate of perceived audio quality.
NAT	Network Address Translation; a frequent cause of one-way audio. Lesson 9
NER	Network Effectiveness Ratio: like ASR, but counts user outcomes such as busy and no answer as successes, isolating network failures.
NOC	Network Operations Centre: the team that monitors and fixes traffic. Lesson 14

O – R

Term	Meaning
Origination	Where a call starts, or a service that delivers inbound calls to phone numbers you provide.
P-Asserted-Identity	A SIP header carrying the network-trusted identity of the caller.
Packet loss	RTP packets that never arrive; even a few percent is audible.
PDD	Post-Dial Delay: time from sending the INVITE to hearing ringback or progress.
Prefix	The leading digits that identify a destination, such as a country code or mobile range.
Prepaid / postpaid	Paying before traffic (calls stop at zero balance) versus being invoiced afterwards within a credit limit.
ptime	Packetization time: milliseconds of audio in one RTP packet, typically 20.
Q.850 cause	A numeric reason for call clearing from the telephone network, often carried in the SIP Reason header. Lesson 11
Rate deck	A price list of destinations: prefix, name, rate per minute, increments and effective date.
Rate group	A set of rates applied to an account in the softswitch.
Reconciliation	Comparing your CDRs and invoices with a partner’s to agree minutes and charges.
RTP	Real-time Transport Protocol: carries the actual audio packets.

S – Z

Term	Meaning
SBC	Session Border Controller: a device at the network edge that secures, normalises and often relays SIP and RTP.
SDP	Session Description Protocol: the part of a SIP message that lists addresses, ports and codecs for media.
SIP	Session Initiation Protocol: sets up, changes and ends calls. Lesson 2
SIP ALG	A router feature that rewrites SIP packets, often incorrectly; usually best disabled.
Softswitch	The software platform that receives, routes, rates and records calls, such as VOS3000. Lesson 3
T.38	A protocol for relaying fax over IP more reliably than audio codecs.
Tech prefix	Digits (often ending in `#`) placed in front of the number to identify a customer, route type or product. Stripped on the way in, added on the way out.
Termination	Delivering calls to their final destination network; the main product in wholesale voice. Lesson 1
Test call	A deliberate call to a known number to check a route’s connection, audio and CLI. Lesson 8
Toll fraud	Using a compromised account or system to send costly calls at someone else’s expense.
Transcoding	Converting audio between codecs; costs CPU and some quality.
Vendor / supplier	The carrier you buy a route from. Its opposite is the customer, who buys from you.
Wangiri	“One ring and cut” fraud: missed calls designed to make people call back a premium number.

How to use this glossary in training

New team members: read it once at the start, then again after Lesson 6 and at the end of the course.
Pick five terms a day and explain each to a colleague in your own words, with an example from your own traffic.
When you meet a new term at work, add it to your team’s own glossary with the local meaning — partners sometimes use words differently.

Key takeaways

Most wholesale terms describe one of four things: numbers, routes, quality or money.
KPIs (ASR, ACD, PDD, NER, MOS) are about quality; rate decks, increments and reconciliation are about money.
Gateways, prefixes and tech prefixes are how a softswitch turns business agreements into routing.
When a partner uses a term, confirm their exact meaning in writing.

Quick quiz

1. What is the difference between ASR and NER?

ASR counts only answered calls as successes; NER also counts user outcomes such as busy and no answer, so it isolates network failures.

2. What is a tech prefix?

Digits placed in front of the called number to identify a customer, route or product; removed on the way in and added for vendors on the way out.

3. What is one Erlang?

One channel continuously busy for one hour.

Wholesale VoIP glossary