A core network, or network core, is the central part of a telecommunications
network that provides various services to customers who are connected by the
access network. One of the main functions is to route telephone calls
across the PSTN. Typically the term refers to the high
capacity communication facilities that connect primary nodes. Core/backbone
network provides paths for the exchange of information between different
sub-networks. For enterprise private networks serving one organization, the
term backbone is more used, while for service providers, the term core network
is more used. In the United States, local exchange
core networks are linked by several competing interexchange networks; in the
rest of the world, the core network has been extended to national boundaries.
Core/backbone network usually has a mesh topology that provides any-to-any
connections among devices on the network. Many main service providers
would have their own core/backbone networks, that are interconnected. Some
large enterprises have their own core/backbone network, which are
typically connected to the public networks.
The devices and facilities in the core / backbone networks are switches and
routers. The trend is to push the intelligence and decision making into
access and edge devices and keep the core devices dumb and fast. As a result,
switches are more and more often used in the core/backbone network facilities.
Technologies used in the core and backbone facilities are data link layer
and network layer technologies such as SONET, DWDM, ATM, IP, etc. For
enterprise backbone network, Gigabit Ethernet or 10 Gigabit Ethernet
technologies are also often used. Primary functions
Core networks typically provide the following functionality:
Aggregation: The highest level of aggregation in a service provider
network. The next level in the hierarchy under the core nodes is the distribution
networks and then the edge networks. Customer-premises equipment do not
normally connect to the core networks of a large service provider.
Authentication: The function to decide whether the user requesting a service
from the telecom network is authorized to do so within this network or not.
Call Control/Switching: call control or switching functionality decides the
future course of call based on the call signalling processing. E.g. switching
functionality may decide based on the "called number" that the call be routed
towards a subscriber within this operator's network or with number
portability more prevalent to another operator's network.
Charging: This functionality handles the collation and processing of charging
data generated by various network nodes. Two common types of charging mechanisms
found in present-day networks are prepaid charging and postpaid charging.
See Automatic Message Accounting Service Invocation: Core network
performs the task of service invocation for its subscribers. Service invocation
may happen based on some explicit action by user or implicitly. Its important to
note however that service "execution" may or may not be a core network
functionality as third party network/nodes may take part in actual
service execution. Gateways: Gateways shall be present in
the core network to access other networks. Gateway functionality is
dependent on the type of network it interfaces with.
Physically, one or more of these logical functionalities may simultaneously exist
in a given core network node. Other functions
Besides above mentioned functionalities, the following also form part of a core
network: O&M: Operations & Maintenance centre or
Operations Support Systems to configure and provision the core network nodes.
Number of subscribers, peak hour call rate, nature of services, geographical
preferences are some of the factors which impact the configuration. Network
statistics collection, alarm monitoring and logging of various network nodes
actions also happens in the O&M centre. These stats, alarms and traces form
important tools for a network operator to monitor the network health and
performance and improvise on the same. Subscriber Database: Core network also
hosts the subscribers database. Subscriber database is accessed by core
network nodes for functions like authentication, service invocation etc.
Mobile There exist basically two core network
types for mobile telephony: The Mobile Application Part used for GSM
and UMTS The IS-41 core network used for D-AMPS,
cdmaOne and CDMA2000. Both variants have evolved over time to
integrate new services and air interfaces.