Network providers or carriers provide network services. British
Telecommunications PLC (BT) is the best known since for many
years it had a monopoly in the UK and virtually all equipment
and services were BT provided.
In 1984 the market was deregulated under the Telecommunications
Act 1984. this allowed other companies to apply for licences
to provide communications equipment and services and broke
the BT monopoly.
The Act also laid out how these networks were to co-operate
and restricted activities between providers that may lead
to unfair competition and gave the requirements for the services
to be provided by the carrier companies. For example each
carrier must be able to route calls to any destination over
other networks and cannot limit traffic into their own network
from other carriers.
The licences granted to the new carriers define their conditions
of operation based upon the 1984 Act.
The first of these new companies was Mercury Communications
Ltd owned by Cable and Wireless. Subsequently the number of
alternative carriers has increased until today there are a
large number of companies offering services to customers.
The large numbers of carriers mean that persons involved with
the specification of telephone equipment and systems must
keep up to date with the benefits and drawbacks of their services
when applied to their requirements. With time this is becoming
a very specialised process and mistakes can easily be made.
There are two methods of connection to the carriers available.
Subscriptions to their services can be mixed so that different
call types can be routed via the best carrier. For example
local calls via one carrier, national calls via a second and
international calls via a third. The two methods are Direct
Direct connection as the name suggest is the physical connection
to the lines from the carrier direct to the customer equipment
and used in the same manner as traditional exchange
Indirect connection is connection to an alternative carrier
by dialling an access request to the direct carrier, which
then connects the user to the required network. The recipient
network will usually require some form of identification from
the user to verify their rights to use the network. This may
be via a Personal Identification Number (PIN) or by receiving
the user's CLI, or telephone number, from the directly connected
network and verifying these against its user database. Though
dialling indirect will take longer than using the direct method
the delays are small and most modern equipment includes provision
for automating the indirect dialling process either by a button
or memory which sends the access code and PIN before dialling
or via some form of automatic route selection within the equipment.
The more sophisticated the equipment being used the more highly
automated this process will be.