Details of PON Technologies : Complete guide

Details of PON Technologies : Friends often ask questions about PON technology, or request me to write a detailed article. The PON technique is described in detail in this article. The reality is that to get complete information one has to read the entire article, don't mind all of you, there are some friends who want to get complete information by reading the headings but this is not possible. Well now I move on to PON technology.

PON stands for Passive Optical Networks, a family of networks (xPON) whose origins are found in an earlier network, which was defined by FSAN, a group of 7 telecom operators unifying the specifications for broadband access to households. PON standards have evolved since the beginning. Now I am going to explain the evolution of PON standards since its inception.

AON

It was the first network defined by FSAN (full service access network). APON bases its transmission downlink in ATM (asynchronous transfer mode) bursts of cells with a maximum rate of 155 Mbps shared between ONT numbers that are connected. Its initial problem was a limit of 155 Mbps which later increased to 622 Mbps.

Two more cells (PLOAM) are being introduced in each ATM cell, which are responsible for indicating and maintaining the address of each cell. These networks are known as APON (ATM Passive Optical Networks).

BPON

BPON is considered as a development of APON. We can say that BPON is a modified form of APON. given the speed limitation of the same. BPON networks are also based on ATM cell transmission, but there is a difference of respect to APON as they support other broadband standards.

In its first version, the BPON network was defined under a fixed rate of 155 Mbps transmission for both uplink and downlink. However, it was later amended to accept asymmetric channels: Downlink: 622 Mbps, Uplink: 155 Mbps.

However, despite improvements on APON, they had high implementation costs, as well as various technical limitations. Thus, it is moving slowly to solve the problems posed by this technology, which today allows asymmetric speeds of up to 1.2 Gbps in the following way:

On the other hand, different transmission speeds other than support allow all information (upstream and downstream) to be transmitted between optical splitters and ONTs and over 1 or 2 single-mode fibers with a maximum range of 20 km between optical splitter and ONT, and between ONTs of the same stage.

The wavelength that sets the standard BPON depends on whether we can use fiber nos.1 or 2 for each ONT, although both set a dedicated wavelength for video broadcasting from OLT to ONT. , It is different from those used in transmission of voice and data. Wavelengths are:

Single fiber per ONT, sharing upstream and downstream:

➤Downstream channel: λ=1480-1500 nm

➤Upstream channel: λ=1260-1360 nm

➤Video: λ=1550-1560 nm

Two fibers for each ONT, one for upstream and one for downstream:

➤Downstream channel: λ=1260-1360 nm

➤Upstream channel: λ=1260-1360 nm

➤Video: λ=1550-1560 nm

One things more important to keep in you mind that BPON networks support a maximum ratio of 32 splitters per OLT, and each splitter supports up to 64 outputs to ONT users.

EPON

EPON stands for Ethernet PON. EPON is also originated from the FSAN, there is a new specification made by the working group EFM (Ethernet in the First Mile). In this sense FSM was intended to take advantage of the features of optical fiber technology in PON and apply them over Ethernet. In this way, they created the standard EPON (Ethernet PON) which is in development nowadays.

The architecture of EPON is based on the transport of Ethernet traffic, but omits the transfer of ATM cells to maintain the characteristics, specification, and therefore, in which the APON and BPON are standards-based and encapsulates the information on the Ethernet frame.

EPON the providing the following advantages over APON and BPON standards:

➤This allows it to work directly at Gbps speeds, being supported over Ethernet. This flow is not a single user because it is to be shared between multiple users (ONT) as it is in the system.

➤Simpler interconnection between EPON stages.

➤Non-use of ATM and SDH elements reduces some costs, which are typical of the above network.

As far as transmission speed is concerned, EPON establishes a symmetric speed of 1 Gbps for line, both downstream and upstream channels. This technology is also called GEPON (Gigabit Ethernet Passive Optical Network) due to the speed of gigabit.

It is noteworthy that standardization only allows transmission between the splitter and ONT at a maximum distance of 10 km under only 1 single-mode fiber in the downstream and upstream, and between the ONTs of a single phase (extending the distance to 20 km There is a provision to do both events.

The EPON standard establishes the dedicated wavelength as the BPON standard for the transmission of video from OLT to ONTs, different in that it is used in voice and data transmission. Wavelengths are:

➤Downstream channel: λ=1480-1500 nm

➤Upstream channel: λ=1260-1360 nm

➤Video: λ=1550-1560 nm.

EPON supports a maximum of 16 splitters per OLT, and each divider supports a maximum of 64 outputs to ONT users. Finally, it is worth mentioning that despite being an EPON standard that allows greater speed than BPON, it does not reach a higher ratio since the maximum distance between OLT and ONTs: Two times more BPON reach than EPON.

GPON

Today, the more advanced standard that is still operating, is one that arose from the development of BPON. To work better with changes in communication technologies and to meet G.984.x, the rapidly growing demand for gigabit capacity PONs, which were the basis of standard GPON (gigabit PON).

GPON allows transmission of information enclosed in two technologies:

➤ATM prefers only in case of BPON standard, but has improved.

➤Ethernet or TDM is based on the GFP (generic framing process) for that GEM (GPON encapsulation method).

GPON improves by respecting all its previous standards, in general, increasing the bandwidth in transmission and providing security to its own network at the protocol level. Thus, GPON allows various transmission rates in the range of 622 Mbps (as its predecessor BPON) to 2,488 Gbps in the downstream channel.

Like BPON, this standard allows both symmetric and asymmetric data transmission where the transmission rates for each are:

Type of Symmetric transmission: flow rates between 622 Mbps and 2,488 Gbps for downstream and upstream channel.

Type of Asymmetric transmission: Various flow rates for downstream and upstream channel. Downstream channel: up to 2,488 Gbps. and Upstream channel: up to 1,244 Gbps.

The fact of allowing very high bandwidth, enables the transmission of practically any multimedia information and supports any operator service. In addition, given their full service support (via ATM or Ethernet and TDM), they provide global multi-service support:

➤Voice transmission.

➤Ethernet 10/100 Base-T.

➤ATM Service.

➤Leased lines.

➤Wireless extension

The wavelength of the GPON standard depends on whether you use 1 or 2 fibers for each ONT, although both have a dedicated wavelength set for video transmitted from OLT to ONTs, This is different from those used in voice and data transmission. The wavelengths are the following:

ONE fiber per ONT, shared for transmission and reception:

➤Downstream channel: λ=1480-1500 nm

➤Upstream channel: λ=1260-1360 nm

➤Video: λ=1550 nm

TWO fibers for each ONT, one for transmission and another one for reception:

➤Downstream channel: λ=1260-1360 nm

➤Upstream channel: λ=1260-1360 nm

➤Video: λ=1550 nm

GPON supports 128 splitting ratios per OLT, and each splitter supports a maximum of 64 outputs to ONT users. By comparison, the GPON standard allows for a substantial increase in the number of ONTs associated with a single header OLT. Ratios respecting BPON and EPON standards is EIGHT times more GPON users than EPON.

If increase in the distance between the OLT header and different ONTs  THREE times more GPON reach than BPON and SIX times more than EPON.

NG-PON : WDM-PON 

Considered to be the next thing in FTTX, the WDM-PON (Wave Division Multiplexing Passive Optical Network) provides the dedicated bandwidth of a point-top network with fiber sharing contained in the PON network. Today there is no standard, the WDM PON is still not fully defined, but carriers and vendors expect to service up to 32 customers via a WDM-PON access fiber.

The architecture of  WDM-PON  is similar to the EPON and GPON (and their 10G versions) FTTx architecture. However, instead of a splitter, the WDM PON typically consists of an Arrayed Waveguide (AWG) filter that separates wavelengths for individual deliveries, for customer delivery.

The benefits of the WDM approach lie in completely different drift wavelengths for each customer. This provides more bandwidth, more security, and better operational control to each customer as there is no interference in the direction of drift between different wavelengths.

The biggest disadvantage of WDM-PON is its cost (and its maturity as FTTx technology). Each customer needs to have their own dedicated transceiver in OLT, and this is one of the cost advantages of other PON technologies lost with WDM PON. Additionally, AWG filters are expected to be more expensive than splitters used with GPON, EPON and BPON. A typical WDM-PON network diagram shown below-

Advantages of PON

Many of the properties of PON are given by the use of fiber, and of course, by the passive elements that make up the network, which is added to the specific configuration of a star or tree, it gives certain advantages over other topologies.

This gives PON two undoubtedly significant benefits: cost savings in implementation and the capacity and bandwidth of passive optical networks. Advantages of PON are listed below:

➤A PON allows long distances between central offices and customer premises. The maximum distance between a central office and a customer with a digital subscriber line (DSL) is only 18000 feet (about 5.5 km), a PON local loop can operate more than 20 km.

➤There is the possibility of providing each information source at a different wavelength, avoiding mixing of signals to each other, and facilitating propagation from OLT to different ONTs. Therefore, the signal voice and data are managed by the so-called P-OLT, which operates in the second window wavelength, and the video signal in propagation managed by the so-called V OLT operating in the third V wavelength. This fact provides scalability to PON transmission systems given the diversity of wavelengths for similar use by CWON / DWDM.

➤To this, it adds to the low cost of deploying the network to the outside plant. The use of passive elements in the network suppresses the low cost of implementation. On the one hand it reduces the cost of installation of active elements, and on the other hand it reduces the cost of passive elements, which is very low.

➤The installation of PONs from these elements is much more economical, and prevents the costs of operation and maintenance, such as the fall or maintenance of network feeds.

➤Finally, it is notable that the high bandwidth allowed by the system is based on the PON architecture that can reach a 10 Gbps rate for the user. The need to increase bandwidth and speed is another justification for the use of PON nowadays. This is an essential support for HD video, services called "on demand".

Disadvantages of PON

Despite the many benefits PON has with its internal configuration, there are also some disadvantages associated with it. However, PONs are not important enough to avoid choosing them as the best possible configuration.

One of the first disadvantages to be considered is due to the distribution of information from OLT to various ONTs. The fact that a divisor distributes information from the OLT to all ONTs that are connected to a single phase or distribution tree causes a decrease in network efficiency.

The total capacity is divided into multiple ONTs connected to the splitter, so that the efficiency of the channel is lower than that of multiplying the links. In addition, because PON has a preset speed, it is forced to operate at that speed but provides different speeds to customer service.

Another important aspect is the fact that a platform or distribution tree relies exclusively on an OLT. A defect in the OLT header suppresses a high impact on the network, as all ONTs and splitters associated with it are affected. However, the installation of some OLTs significantly reduces the cost of network deployment.

ONT levels of PON are quite sensitive to drop, and in many cases, the network's power budget is quite limited. This budget is directly related to:

➤Splitters capability. A large number of users reach all from low power OLT.

➤To achieve maximum distance. The greater the distance between the OLT and the end users, the less power will reach the respective ONTs.

However, despite mentioned above disadvantages, the most advantageous configuration for the deployment of FTTx is PON. The two most important conditions that justify the use of this architecture are:

➤Economic savings from deploying PON networks in relation to the other two configurations (point to point and active optical networks). 

➤Network flexibility, which allows the use of a channel by a large number of users.

Last Word

I have tried to give complete information about PON technology, by commenting, tell me how successful I have been in my endeavor. Complete information is also given about the PON Technology's advantages and disadvantages. If you are satisfied with the given information, then do like and share.