In telecommunications, a core network – also called a backbone network – is a central conduit designed to transfer network traffic at high speeds. Core networks focus on optimizing the performance and reliability of long-distance and large-scale data communications. They connect wide-area networks (WAN) and local area networks (LAN) altogether.
While core networks provide a plethora of services, one of their key functions includes routing telephone calls across the public switched telephone network (PSTN). Usually, the term denotes the high-functioning communication facilities that interlink the primary nodes. Moreover, the core network provides routes to exchange information among different sub-networks. While the term ‘backbone’ is often used in enterprise network solutions rather than core network, network services providers mostly use the term core network. Furthermore, in 4G long-term evolution (LTE), core networks are known as evolved packet core (EPC).
The devices and facilities used for the core networks are generally switches and routers, with the former being in more usage. The aim is to keep the essential devices fast, but not ‘smart’ in particular, equipping the devices with the intelligence as well as the edge areas of the network.
The technologies used for the core network facilities primarily include data link and network layer technologies, such as IP, asynchronous transfer mode (ATM), internet protocol (IP), synchronous optical networking (SONET), and dense wavelength division multiplexing (DWDM).
In addition, for enterprise backbone networks, gigabit ethernet or 10 GB ethernet technologies are also utilised in several cases.
In general, core networks offer the following functionalities:
Core nodes deliver the highest level of aggregation in a service provider network (SPN). Aggregation applies to different techniques of fusing numerous network links simultaneously to improve throughput beyond the capability of a single link and deliver redundancy if one of the connections breaks down.
Within the core nodes, next in the hierarchy, come the distribution networks, followed by the edge networks. Unfortunately, customer-provided equipment (CPE) doesn’t usually get coupled with the core networks of a large networking service provider.
Equipment within the core networks can determine whether the user demanding service from the telecom network is allowed to accomplish the task within this network.
Call control or switching functionality determines the further course of a call as per the call signalling processing. For instance, the switching functionality might determine, as per the ‘dialled number,’ whether the call should be routed toward a subscriber within the network operator’s radar or with number portability more frequent to another secure network service.
Core network equipment can manage the processing and collation of charging the data produced by different network nodes. Today’s secure network services come with two prevalent charging mechanisms - postpaid and prepaid charging.
The core network carries out the service invocation task for its subscribers. Service invocation might occur due to the user's specific action (like call transfer) or implicitly (call waiting). But, keep in mind that service implementation may or may not be a core network capability as third-party nodes/networks might engage in actual service implementation.
In core networks, gateways find usage in accessing other networks. Their functionality relies on the kind of network they interface with. Physically, at least one of these logical functionalities might exist in unison in a specific core network node.
Apart from the functionalities mentioned above, telecom core networks provide the following functionalities:
Core networks also house the subscribers’ database (such as HLR in GSM systems). In addition, the core network nodes access the subscriber database for functions, such as profiling, authentication, and service invocation.
Operations and Maintenance (O&M) centre or operations support systems to build up and provision the core network nodes. Factors that influence the configuration include the peak hour call rate, number of subscribers, geographical preferences, and nature of services.
Also, operations, including alarm tracking (fault management), network statistics aggregation (performance management), and logging of multiple network node actions (event management), happen in the O&M centre. These alarms, stats, and traces make crucial tools for network operators to oversee the network performance and health and capitalise on the same.
In a collapsed backbone network (also called backbone-in-a-box or inverted backbone), all locations feature a connection back to a central point linked to the collapsed backbone network. The collapsed backbone can be a router, single switch, or cluster. The architecture and topology of a collapsed backbone is a rooted tree or star.
A distributed backbone network contains multiple connectivity devices linked to a range of central connectivity devices, including switches, hubs, or routers, in a pyramid. This sort of topology enables reduced capital spending, and straightforward expansion for growth as more layers of the devices can be added over the existing layers.
A serial backbone is the simplest type of backbone network. It contains at least two internet-working devices interlinked by a single cable in a daisy-chain style.
Hubs are often linked in this way to extend a network. Besides hubs, routers, gateways, bridges, and switches also form part of the serial backbone network. Furthermore, serial backbone finds usage in corporate-level networks, even though it is rarely executed for that purpose.
A parallel backbone network is a version of a collapsed backbone that utilises a central node or connection point, though it enables duplicate links in case of more than one switch or router. All routers and switches are linked by twin cables. By having at least one cable connecting every device, parallel backbone networks assure connectivity to any location of the corporate-level network.
Parallel backbones are costlier than other backbone networks as they require more wiring compared to different network topologies. That said, the performance and fault tolerance it delivers offsets the expenses.
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