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Advantages and disadvantages of PON Network

Posted By: technopediasite

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To understand why FTTx architecture is based on PON network, it is necessary make a direct comparison between the point-to-point (P2P), passive point-tomultipoint (PON) and active point-to-multipoint networks (AON).

Below is a comparative table showing advantages and disadvantages of each of the three types of network clearly justify the use of FTTx PON compared to other configurations.

 Advantages and disadvanteges of PON Network
Comparative table of different types of networks

As shown in the table above, PON are the most appropriate to the design of physical network architecture for FTTx deployments. The fact of having lines specifically dedicated for user towards to central office (where the OLT is), considerably reduces the cost of initial network deployment. This is not covered by point-to-point networks, which despite providing a high bandwidth per user, it's not worth their high cost of deployment.

As for active networks, the inclusion of active elements increases not only the cost of deployment of the network itself, but also the operation and maintenance of the same, forcing to manage and centralize it by software and hardware level. PON reduces these unnecessary costs. In conclusion, the use of PON architectures means very important advantages when designing, installation and subsequent maintenance of the network.

Advantages of PON Network
Many of the PON properties are given by the use of fiber, and of course, of the passive elements that compose the network, which added to the specific configuration of a star or tree give it certain advantages over other topologies. This gives to PON two undoubtedly important advantages: cost savings in implementation and the capacity and bandwidth of passive optical networks.

However, these advantages are not the only ones, and among other, the most relevant are listed below:

· A PON allows for longer distances between central offices and customer premises. While with the Digital Subscriber Line (DSL) the maximum distance between the central office and the customer is only 18000 feet (approximately 5.5 km), a PON local loop can operate at distances of over 20 km.

· There is the possibility of providing every information source in a different wavelength, avoiding the mix of signals to each other, and facilitating diffusion from the OLT to the different ONTs. Therefore, signals voice and data are managed by so-called P-OLT, which operates in second window wavelengths, and video signals in diffusion managed by the so-called V-OLT, operating in third window wavelengths. This fact gives scalability to PON transmission system, given the variety of wavelengths to use for the same by CWDM / DWDM.

· To this, it adds the reduced cost of network deployment in the outside plant. The use of passive elements in the network supposes a lower cost of implementation. On the one hand it reduces the cost of installation of active elements, and on the other hand the cost of passive element itself, which is much lower.

· The installation of PON from these elements is much more economic, and prevents operation and maintenance costs, such as absence of falls or maintenance of the network feeds.

· Finally, it is noteworthy that the high bandwidth allowed by systems based on PON  architectures which can reach the 10 Gbps rate down to the user. The need to increase the bandwidth and the speed is nowadays just another justification for the use of PON. This is an essential support for services such as HD Video, services called "on demand"

Disadvantages of PON Network
Despite the many advantages that have the PON to own intrinsic configuration, there are some disadvantages associated with it. However, there are not significant enough to avoid choosing PON as the best possible configuration.

One of the first disadvantages to be considered is that caused by distribution of information from the OLT to the different ONTs. The fact that a divisor distributes information from the OLT to all ONTs that are connected to the same stage or distribution tree, it causes a reduction in network efficiency.

The total capacity is divided into many ONT connected to the splitter, so that the efficiency of the channel is lower than in a point-to-multipoint link. In addition, because PON has a preset speed, it is forced to work at that speed but providing different speeds to the customer service. For example, an ONT that provides 100 Mbps to the customer is required to work at higher speed rates: 1.25 Gbps or 2.5 Gbps.

Moreover, the fact that all information flow through the same physical channel increases the likelihood of sniffing on the network, losing security, and forcing to establish a high level of encryption.

Regarding security, PON architecture is sensitive to external sabotage. This problem is given by the nature of the transmission medium itself. Injection of constant light to a particular wavelength masks all communication and service tends to fall.

Another important aspect is the fact that a stage or distribution tree, depend exclusively on a single OLT. A fault in the OLT header supposes a high impact on the network, since all the ONT and splitters connected to it are affected. However, the installation of few OLT supposes a cost reduction of network deployment enough considerable.

The ONTs of PON are quite sensitive to the level drops, and in many cases, the power budget of the network is quite limited. This budget is directly related to:

· The capacity of splitters. A greater number of users, less power reach everyone from the OLT.

· Maximum distance to achieve. The greater the distance between the OLT and end users, less power will reach the corresponding ONTs.

However, despite the disadvantages mentioned above, the most advantageous configuration for the deployment of FTTx is PON. Two of the most important

conditions that justify the use of this architecture are:

· The economic savings resulting from deploying PON networks regarding other two configurations (point to point and active optical network).

· The flexibility of the network, which allows the usage of a channel by a large number of users.
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