VoIP & wholesale carrier basics

Before you touch a softswitch or read a SIP trace, it helps to understand the business you are working in. Wholesale VoIP is a carrier-to-carrier market: companies buy and sell call minutes in bulk, and every call usually passes through several networks before it reaches the person being called. This first lesson explains the vocabulary you will hear every day in a wholesale NOC.

Retail vs wholesale voice

A retail provider sells calls to end users — a mobile subscriber, an office with a phone system, a calling-card customer. A wholesale carrier sells to other providers. Its customers are operators, resellers and other carriers who need to deliver their users’ calls to destinations they do not reach directly.

Because no single company has direct connections to every network in the world, calls are handed from carrier to carrier. Each carrier in the chain buys from the next one and sells to the previous one, adding a small margin.

Termination vs origination

Termination means delivering a call to its destination — “terminating” it on the called party’s network. When a carrier sells “termination to Country Z”, it is offering to carry your calls to numbers in Country Z.

Origination is the other direction: the network where a call starts, or a service that delivers inbound calls to you (for example, phone numbers that ring on your platform). Most wholesale voice trading is about termination, which is why most rate decks you see are termination price lists.

Destinations, prefixes and A-Z

Destinations are identified by number prefixes. A country code is the broadest prefix; operators and number ranges inside the country have longer prefixes. Mobile numbers in a country usually have different prefixes, and often different prices, than fixed-line numbers.

An A-Z offer (also written A–Z) covers every destination the carrier can reach, normally delivered as one big rate deck. It is convenient for buyers who send traffic to many countries over a single interconnect. Buyers with large volume to particular countries often buy those destinations separately from specialist vendors.

Route types: CLI, NCLI and CC

Routes to the same destination are sold with different quality promises. The most common labels are:

• CLI routes deliver the caller’s number (Calling Line Identification) to the destination unchanged. They are used where the recipient needs to recognise the caller or call back.
• NCLI routes (non-CLI) make no promise about caller ID. The number may be hidden or replaced. They are typically cheaper.
• CC routes (call-centre routes) are intended for high-volume traffic with many short calls, such as contact centres.

The exact meaning of these labels can vary between vendors, so always confirm the details in writing. Our blog post CLI vs NCLI routes explained goes deeper.

How wholesale billing works

Wholesale voice is billed per minute of answered call time. Unanswered, busy and failed calls are normally not charged. The rate is set per destination prefix and often changes over time.

Two details on every rate deck matter a lot:

• Billing increments, written like 1/1, 30/6 or 60/60. The first number is the minimum charged duration in seconds; the second is the step after that. On a 60/60 route, a 10-second call is billed as a full minute.
• Effective dates. Vendors announce rate changes with a notice period. Your NOC and billing team must load new rates before they take effect, or margin can turn negative without anyone noticing.

A simple illustration with made-up numbers: if you buy a destination from Vendor X at 0.010 per minute and sell it to Customer Y at 0.012, your margin is 0.002 per answered minute — before any losses from quality problems, fraud or disputes. Margins in wholesale are thin, which is why monitoring and correct billing are so important.

Interconnects and the softswitch

Carriers connect to each other over SIP (Session Initiation Protocol) across the internet or private links. Each connection is called an interconnect or trunk. Both sides agree on technical details such as the IP addresses allowed to send traffic, codecs and caller-ID format.

In the middle of a wholesale carrier’s network sits a softswitch. It receives calls from customers, checks who they are and whether they have credit, picks a vendor based on the dialled number, price and quality, and records every call for billing. In this course we use VOS3000, a softswitch widely used by wholesale carriers, as our example platform.

Who does what in a wholesale carrier

• Sales / account managers find customers and vendors and negotiate prices.
• Routing / rates team loads rate decks and decides which vendor carries each destination.
• NOC (Network Operations Centre) sets up interconnects, monitors traffic and quality, tests routes and handles trouble tickets.
• Billing reconciles call records with partners, invoices customers and handles disputes.

These roles work closely together: a quality problem spotted by the NOC often leads to a routing change, and a billing dispute often starts with evidence from the NOC.

Why quality monitoring matters

Because every call crosses several networks, a problem anywhere in the chain becomes your problem. Calls that fail, have bad audio, lose their caller ID or are falsely answered all cost money or customers. Later lessons cover how to measure quality (Lesson 6), how to spot fraud such as FAS (Lesson 7), and how to test routes (Lesson 8).

Examples in this course use invented names (Vendor X, Customer Y, Country Z) and documentation IP ranges. Menu names and options differ between softswitch versions; always check your own system and vendor documentation.