In telecommunications with the term access network This refers to the part of the network intended for connecting the premises of individual end users to the first switching center and, more generally, for connecting a user to their provider. Its fundamental components are the physical carriers and the exchange transmission equipment intended both for the distribution of specific types of service (access nodes) and for the bundling of user connections (multiplexing and concentration) and their transport from the access node to the termination point of the transport network, i.e., the network that distributes traffic to the various providers.
The portion of the access network that runs from the customer's premises to the first access node is often referred to as the last mile.
Access networks for fixed devices
Types of physical connections
As regards fixed telephony and more generally telecommunication services dedicated to fixed devices, at the physical carrier level three distinct technologies can be distinguished:
- Copper cable connection (twisted pair), typical for analog telephony services (POTS), ISDN, and xDSL broadband. Copper is also used for connections to first-level digital concentrators (voice-equivalent channel multiplexers or first-level 2 Mbps PDH bundling).
- Fiber optic connection for access to broadband or ultra-broadband services (NGN over FTTx).
- Radio connection, used mainly in areas with very low population density or which present particular logistical difficulties for wired access.
Topology and distribution modes
The typical topology of access networks is a tree (or star) topology with a hierarchical structure.
For voice access, starting from the termination of the transport network (identified as the local telephone exchange), the overall signal flow is partitioned via splitters and switches and sent to the relevant distribution centers (primary access network), where, via splitter cabinets, the individual flows are extracted and transmitted over dedicated cabling to the individual end user (secondary access network). When using a copper cable network, xDSL access services are multiplexed together with voice services via DSLAMs. The various types of ultra-broadband FTTx fiber optic connections from the end user to the access network.
For optical access, the termination of the transport network is identified with the primary POP, where the flows coming from the transport network are extracted, differentiated between data flows (typically over IP) and voice flows, and then sent over low-capacity metropolitan optical rings (typically based on STM-1 type SDH transport, i.e. 155 Mbps for mixed voice-data services, or on optical Gigabit Ethernet rings in the case of purely data services) towards the destination site that bundles the flows of all end users. In the case of mixed services over SDH, the information flows are terminated on a network device (CPE, Customer Premise Equipment) capable of separating and extracting the data flow, typically IP over Ethernet, from the voice flow. The data flow can be connected directly to the customer's local network (for example, via a router or gateway), while the voice flows can be connected directly to the user's PABX or switchboard. In the case of purely data services over Gigabit Ethernet, distribution to individual recipients occurs via local Ethernet switches and/or hubs.
For radio access, distribution occurs via area stations (master stations), which perform a role similar to an area telephone exchange and distribute flows to peripheral stations, which act as secondary distribution points to the base stations to which individual user terminals are ultimately connected. The types of services that can be distributed depend on the capacity of the radio system. Narrowband systems (with carrier frequencies below 10 GHz) are used for voice access, while broadband systems (with carrier frequencies above 10 GHz) can also carry video and IP services.
Access protocols
Network access protocols depend on the type of service. The most commonly used protocols are:
- POTS and VoIP for traditional telephony (voice services)
- PSTN and ISDN for low-bandwidth voice and data access
- xDSL and Ethernet for high-speed, high-bandwidth data access
- WI-FI for broadband radio access