Creation of a broadband network based on gpon technology qualification work of bachelor

3. PON NETWORK ARCHITECTURE
3.1. Features of the transmission medium
One of the main challenges facing modern telecommunications access networks is the so-called "last mile" problem, providing as much bandwidth as possible to individual and corporate subscribers at minimal cost.The essence of PON technology is that a completely passive optical network with a tree topology is created between the receiving and transmitting module of the OLT central node (optical line terminal) and remote ONT subscriber nodes (optical network terminal). In the intermediate nodes of the tree, passive optical splitters (splitters) are placed - compact devices that do not require power and maintenance, as shown in Picture 3. One OLT transceiver module allows you to transmit information to multiple ONT subscriber devices. The number of ONTs connected to a single OLT can be as large as the power budget and maximum speed of the transceiver equipment allow.
For forward and reverse channel transmission, one optical fiber is used, the bandwidth of which is dynamically distributed between subscribers, or two fibers in the case of redundancy.The downstream streamfrom the central node to subscribers is at a wavelength of 1490 nm and 1550 nm for video. Upstream streamsupstreamfrom subscribers are transmitted at a wavelength of 1310 nm using the Time Division Multiple Access (TDMA) protocol.
The point - to-multipoint topology is used to build a PONмноготочка, and the network itself has a tree structure. Each fiber-optic segment is connected to a single transceiver in a central node (as opposed to a point-to-point topology), which also provides significant savings in equipment costs. A single fiber-optic segment of the PON network can cover up to 32 subscriber nodes in a radius of up to 20 km for EPON / BPON technologies and up to 128 subscriber nodes in a radius of up to 60 km for GPON technology. Each subscriber node is designed for an ordinary residential building or office building and, in turn, can cover hundreds of subscribers. All subscriber nodes are terminal nodes, and the shutdown or failure of one or more subscriber nodes does not affect the operation of the rest.
The central PON node can have ATM, SDH (STM-1), and Gigabit Ethernet network interfaces for connecting to backbone networks. The subscriber node can provide service interfaces 10/100Base-TX, FXS (2, 4, 8 and 16 ports for connecting analog devices), E1, digital video, ATM (E3, DS3, STM-1c).
Even today, optical communications are perceived as something unconventional that requires a lot of investment. At the same time, the development of fiber optics and optical transmission systems makes it possible to create complex but cost-effective infrastructures.
Among the advantages of fiber optics, the ability to simultaneously deliver signals with different wavelengths over a single fiber is particularly valuable. Such delivery can significantly increase the bandwidth of the communication channel. This phenomenon is called "spectral compaction, or multiplexing of signals over wavelengths" (Wave Division Multiplexing - WDM).
As you know, there are various technologies that ensure the exchange of information in electronic form, starting from reading it from a carrier, then redirecting it and delivering it to the addressee. Today, signal processing at network hubs takes place in three stages. The signal coming from the optical fiber is converted into an electrical signal. Then the packets are analyzed and redirected, after which the electrical signal is converted back to optical. Thus, this is a fairly complex procedure, and it does not affect the overall transfer rate just because of the speed of the equipment.
In optical systems, it is necessary to repeatedly perform the "optics-electronics" transformation and vice versa. But unlike an electrical cable, optical fiber does not allow you to connect an unauthorized tap. In addition, it is impossible to "remove" traffic from an optical cable using contactless methods, since electromagnetic interference is not generated in this environment, that is, fiber optics provide much better information protection.
This, the spread of optical networks, which have the highest potential for the speed and volume of information flows, constrains the complexity and, accordingly, the cost of active equipment.
In backbone networks, optical fiber has long been a standard transmission medium, since large volumes of traffic make it economically feasible to use expensive equipment. In access networks, the situation is different. Currently, offices and the residential sector are connected mainly via copper cables. However, there is a need to increase the capacity to provide consumers with modern services. The solution to this problem can be the widespread adoption of optical systems (an example of this is the Asia-Pacific region). And, in particular, PON is the optimal choice of access technology.
PON technology uses spectral stream separation, broadcast delivery of downlink traffic, and temporary uplink multiplexing, as shown in Picture 4.

Picture 3.1-Basic elements of the PON architecture and how they work