Access Networks

General Features of Access

Wired access networks are fixed networks in which the user connects via his or her terminal at a particular geographical point at which the service provider delivers a connection through a wire. That access “wire” may be made of copper pairs, coaxial cable, or optical fiber.

Access nodes may be telephone switchboards, remote phones, access concentrators, DSLAMS (Digital Subscriber Line Access Multiplexers), PON nodes, multiservice nodes, switches, routers, or access gateways, and so on.

The characteristic feature of wireless access networks is precisely that the medium used for communication between the user’s terminal and the network is wireless, i.e. brought about by electromagnetic waves passing through the air. Where they have been developed most is in mobile cellular telephony networks.

Such networks have one communication advantage over fixed networks, namely that they enable the user to be mobile. The two most widely used technologies in such networks are GSM and 3G. Apart from audio communications, they also provide data transmission. 3G, in particular, provides faster data transmission than GSM. Work is currently underway on moving on to 4G, or long-term evolution technology, which allows data to be transmitted even faster.

Wireless media are used in fixed networks as well as in mobile networks: for instance, using WiFi technology in LAN networks and WiMax technology in WAN networks. WiMax, as of version E, includes mobility.

Fixed and Fiber-to-the-Home (FTTH) networks

Fixed access networks were first developed using copper pairs as the access medium, a technology found the world over and still used today. The trend today is for those types of network to evolve toward networks using optical fiber as the medium of access, particularly in what are known as New Generation Networks.

Telecommunications operators first provided telephone services and subsequently incorporated data transmission services. Thus, although initially copper networks sufficed, subsequently, as the demand for broadband data transmission expanded, it became necessary to resort increasingly to optical fiber.

At first, the access nodes were telephone switchboards. Later came data nodes, such as the DSLAM, in order to provide data transmission services using copper and digital subscriber line (DSL) technology for mass transmission services. Other types of access node were also brought in, such as switches, routers, and a whole range of technological options for corporate services.

In general, fixed access optical fiber networks may be classified under the following categories:

• FTTH: Fiber to the [customer’s] home. The path between the network operator’s switchboard or access node and the customer’s home is via optical fiber.

• FTTB/C: Fiber to the building/curb. The path between the network operator’s switchboard or access node and the customer’s building is via optical fiber and the connection inside the customer’s building is via copper. For that, a small node or network terminal is placed inside the customer’s building. In this case there could also be optical fiber to a node in a cabinet located in the same block (curb) as the customer's home and then copper between that point and the customer’s home.

• FTTCab: Fiber to the Cabinet. The path between the network operator’s switchboard or access node and another node in a cabinet close to where the customer is located is made of optical fiber and the path between that cabinet and the location of the customer is made of copper.

Let us illustrate these three possibilities in the following figure:

Terms used:
ONT: Optical Network Termination
NT: Network Termination
OLT: Optical Line Termination

Fig. 2 – Types of wired access networks

Access Networks in Next-Generation Networks

New telecommunication operators use implementation of Next-Generation Networks as a service provision strategy and established operators are in the process of transforming their networks into Next-Generation Networks.

Next-Generation networks are based on switching and bundling of packages (transporte de paquetes), which mean that they can offer telecommunication services using multiple broadband technologies, with quality service.

Those networks can carry multiple last-mile technologies, which means that within the access network different technologies can be used, as needed: for instance, DSL-type fixed technologies or FTTH fiber access technologies, which we will be looking at in the course, or wireless technologies, like 36 cellular technology or Wimax. All these technologies can coexist in an operator's network, although in some cases there are signs of some being replaced by others, as in the case of DSL, for instance, which eventually will probably be replaced by FTTH.

At the same time, Next-Generation Networks are also being required to support a wide range of services, applications, and mechanisms (in real time, streaming, not in real time, multimedia, and others). To reach customers with these kinds of services, we need an access network with sufficient bandwidth to provide all services to the majority of customers.
 

Gustavo Sandler
Universidad Católica del Uruguay