An access network is that part of a communications network which connects subscribers to their immediate service provider. It is contrasted with the core network, for example the Network Switching Subsystem in GSM. The access network may be further divided between feeder plant or distribution network, and drop plant or edge network.
An access network or outside plant refers to the series of wires, cables and equipment lying between a consumer/business telephone termination point (the point at which a telephone connection reaches the customer) and the local telephone exchange. The local exchange contains banks of automated switching equipment to direct a call or connection to the consumer. The access network is perhaps one of the oldest assets a telecom operator owns, and is constantly evolving, growing as new customers are connected, and as new services are offered. This makes the access network one of the most complex networks in the world to maintain and keep track of.
In 2007, many telecomunications operators experienced increasing problems maintaining the quality of the records which describe the network. In 2006, according to an independent Yankee Group report, globally operators experience profit leakage in excess of €15 Billion each year.
The access network is also perhaps the most valuable asset an operator owns, since this is what physically allows them to offer a service.
Access networks consist largely of pairs of copper wires, each travelling in a direct path between the exchange and the customer. In some instances, these wires may even be aluminium, the use of which was common in the 1960s and 1970s following a massive increase in the cost of copper. As it happened, the price increase was temporary, but the effect of this decision is still felt today because the aluminium wires oxidize and lose their ability to carry large quantities of data.
Access is essential to the future profitability of operators who are experiencing massive reductions in revenue from POTS (plain old telephone services), due in part to the opening of historically nationalised companies to competition, and in part to increased use of mobile phones and VOIP (voice over IP) services. Operators now look toward additional services such as xDSL based broadband and IPTV (Internet Protocol Television) to guarantee future profit. The access network is again the main barrier to achieving these profits since operators world wide have accurate records of only 40% to 60% of the network. Without understanding or even knowing the characteristics of these enormous copper spider webs, it is very difficult, and expensive to 'provision' (connect) new customers and assure the data rates required to receive next generation services.
Over time, we will see the access networks around the world evolve to include more and more optical fibre technology. Optical fibre already makes up the majority of core networks, and will start to creep closer and closer to the customer, until a full transition to 21st Century Networks is achieved delivering value add services over fibre to the home (FTTH).
Without an access network, a fixed line telco can not exist, yet this network has been undervalued and under invested for decades. Telcos today, need to massively improve their understanding of these networks to remain profitable in the short term, and remain in existence in the longer term.
An access attempt ends either in successful access or in access failure - an unsuccessful access that results in termination of the attempt in any manner other than initiation of user information transfer between the intended source and destination (sink) within the specified maximum access time.
Access failure can be the result of access outage, user blocking, incorrect access, or access denial. Access denial (system blocking) can include:
Although some access charges are billed directly to local end users, a very large part of all access charges is paid by interexchange carriers.