Connected using pon technology. Gpon technology. Description of GPON technology. Operating principle of PON. The principle of connecting to Rostelecom

The intensive development of the telecommunications industry, driven by the need to transmit increasingly large volumes of information, has led to the need to improve communication networks, including subscriber access networks. Today we can observe the stage of convergence of communication networks. In converged networks to provide various types services use unified multiservice networks focused on packet traffic. Providing high-quality broadband services requires the provider to have a high-speed subscriber access network.

Fiber optics is increasingly being used as a transmission medium for wired subscriber access networks. Optical cables, unlike electrical ones, have a number of advantages: high throughput, low signal attenuation, high immunity from external electromagnetic interference, small size and weight. Among optical access technologies, the most popular group of technologies is FTTx. FTTx technologies are divided according to network construction into active optical networks AON and passive optical networks PON. The main difference between these technologies is that a passive optical network, unlike an active one, does not require power supply for intermediate nodes of the subscriber line. As a result, a passive optical network will be more reliable and cheaper to operate. Other important advantages are the low cost of network construction and the possibility of its gradual expansion. Such advantages will allow expanding existing network and attract new subscribers. Thus, PON technology is of particular interest in terms of expanding the scope of broadband networks.

Optical access networks have various construction options. The “star” topology with point-to-point connections (P2P, point-to-point) involves connecting each subscriber with a separate fiber to the access node. The “star” topology is used when subscribers are densely located in the area of ​​the telephone exchange. This topology is characterized by a minimum number of optical splitters and a single installation location. The obvious disadvantage of this topology is the presence large quantity fibers and optical transmitters. The advantages of this topology: ease of maintenance, operational measurements and detection of line fault locations. This topology is characterized by high reliability, since the break of one of the fibers will not affect the operation of the entire network.

The “tree” type topology is used when subscribers are located in different locations. The optimal distribution of power between different branches is decided by selecting the division coefficients of optical splitters. The tree topology is flexible in terms of potential development and expansion of the subscriber base. Depending on the need for power supply for intermediate nodes, topologies are distinguished between “tree with active nodes” and “tree with passive nodes”. Each topology has its own advantages and disadvantages.
When using a “tree with active nodes” topology, each subscriber is connected to a switch, which in turn is connected by fiber to the access node. The switch is active equipment, that is, it requires power. If there is no power supply, subscribers connected to the switch will lose access to the network. However, this solution fits well within the Ethernet standard and is relatively cheap.

A P2MP (point-to-multipoint) tree topology uses a backbone fiber that is divided between all subscribers using a passive splitter. Each user connects to the splitter using a separate fiber. An entire segment of the tree architecture, which covers dozens of subscribers, can be connected to one access node port. The intermediate nodes are equipped with completely passive splitters that do not require power supply or maintenance. The advantages of the PON architecture include the absence of the need for power supply at intermediate nodes, high network scalability, and saving on fibers and optical transmitters in the central node. Network scalability allows you to connect as many new subscribers as the optical power budget allows.

Operating principle of PON network

The basis of PON technology is the point-to-multipoint P2MP logical structure. An entire fiber-optic segment of a tree-like architecture, covering many subscribers, can be connected to one port of the central node. At the intermediate nodes of the tree, intermediate passive elements - splitters - are installed. Splitters are designed to divide the power of an optical signal in a given ratio.

Purpose of the circuit blocks:

• The central OLT node is a network device that is located in the access node, receives data from the backbone networks via SNI interfaces and forms a downstream flow to subscribers along the PON tree.
• The ONT subscriber node is a network device that is located on the subscriber side, receives and transmits data to the OLT at wavelengths of 1550 nm and 1310 nm, respectively, converts the data and transmits it to subscribers via UNI interfaces.
• Splitter is a passive optical multiport network that distributes the flow optical radiation in one direction and combines this flow in the opposite direction.

The main idea of ​​the PON architecture is to use just one transceiver module in the central OLT node to transmit data to and receive data from multiple ONT subscriber nodes.

The number of ONT subscriber nodes connected to one OLT transceiver module depends on the power budget and maximum speed transceiver equipment. For forward (outgoing) flow transmission from OLT to ONT, a wavelength of 1550 nm is used. When transmitting reverse (upstream) data streams from subscriber nodes from ONT to OLT, a wavelength of 1310 nm is used. WDM multiplexers built into OLT and ONT equipment separate upstream and downstream streams.

WDM is wavelength division multiplexing. This technology allows you to combine several information channels over one optical fiber. In this case, each channel has its own frequency. WDM technology is based on the fact that when light is transmitted at different wavelengths, their mutual interference does not occur in the fiber. Each wavelength represents one optical channel in the fiber. The outgoing stream is broadcast - it is transmitted to all subscribers connected to the OLT. Each ONT subscriber node reads the address fields in order to select the information intended for it from the general flow. Subscriber nodes transmit at the same wavelength and, in order to avoid signal intersections, they use the TDMA time division multiple access method. Each ONT has its own individual data transmission schedule, taking into account latency adjustments. The TDMA MAC protocol solves this problem.

An ONT optical terminal is installed directly at the subscriber's premises, which is also a home access gateway. When using a unified optical transport terminal ONT, the configuration of the transport component is not tied to services. Thus, subsequent service configuration will be carried out on the home access gateway.

When building an optical network, a two-stage optical signal division scheme is used. A splitter with a division ratio of 1:2 is installed on the station side. At the entrance of the house, a splitter with a division ratio of 1:32 is installed in the optical distribution cabinet, which ensures the distribution of the optical signal among the subscribers of the residential building. It is worth noting that houses with a small number of subscribers use other optical signal distribution schemes:

• 1:4 – first level, 1:16 – second level
• 1:8 – first level, 1:8 – second level

Passive optical network technologies enable the convergence of various services. When using PON, it is possible to provide Internet access, telephony, and television services. The provision of comprehensive services is implemented using subscriber equipment. To organize access to NGN services, a hybrid service model is used, shown in the figure.

A PPPoE session is initiated on the subscriber equipment (PC). ONT is configured in bridge operating mode. Broadband router remote access BRAS terminates the PPPoE session. To organize Internet access, each virtual PPPoE adapter on the subscriber's equipment is assigned its own public IP address, which is routed on the Internet.

To organize Triple Play services, three virtual private VLANs are organized. Internet access traffic is transmitted within the first VLAN. The second VLAN carries traffic for IPTV and VoD services. The third VLAN organizes the transmission of analogue and IP telephony services. The ONT subscriber terminal compares the port identifier through which the subscriber equipment is connected and the identifier corresponding to the VLAN.

An analog telephone is connected via the FXS port, which emulates an extension of the PBX interface. To prevent broadcast relaying of multicast traffic, the IGMP snooping process is enabled on OLT equipment. IPTV and VOD access gateways, as well as a flexible Softswitch, provide access to television and telephony services, respectively.

Subscribe to our

PON technology

PON (Passive optical network)— technology of passive optical networks.

One of the main challenges facing modern telecommunications access networks is the so-called “ last mile", providing as much bandwidth as possible to individual and corporate subscribers at minimal cost.

The essence of PON technology is that between the transceiver module of the central OLT node (Optical line terminal) and remote ONT subscriber nodes (Optical network terminal) A completely passive optical network is created with a tree topology. Passive optical splitters are located in the intermediate nodes of the tree - compact devices that do not require power or maintenance. One OLT transceiver module allows information to be transmitted to multiple ONT subscriber devices. The number of ONTs connected to one OLT can be as large as the power budget and maximum speed of the transceiver equipment allows.

Rice. 1. PON network architecture

To transmit the forward and reverse channels, one optical fiber is used, the bandwidth of which is dynamically distributed between subscribers, or two fibers in case of redundancy. Downstream from the central node to subscribers is at a wavelength of 1490 nm and 1550 nm for video. Upstream streams from subscribers occur at a wavelength of 1310 nm using the Time Division Multiple Access (TDMA) protocol.

To build a PON, a point-to-multipoint topology is used and the network itself has a tree structure. Each fiber optic segment is connected to one transceiver at the central node (as opposed to a point-to-point topology, which also provides significant savings in equipment costs. One fiber optic segment of the PON network can cover up to 32 subscriber nodes within a radius of up to 20 km for EPON / BPON technologies and up to 128 nodes within 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, and shutdown or failure one or more subscriber nodes does not in any way affect the operation of the others.

The central PON node can have ATM, SDH (STM-1), 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 SLTs), E1, digital video, ATM (E3, DS3, STM-1c).

Fig.2. Technology comparison

PON network testing

When testing a PON network, an operator is usually concerned with two main questions:

• Real attenuation in the optical line between the central node and the subscriber device (operating or preparing to connect).
• The location of the problem area, if the actual attenuation in the line turned out to be higher than expected (calculated or reference).

To answer the first question, it is enough to carry out simple measurements using an optical tester. The second question is more complex and requires the use of an optical reflectometer (OTDR), as well as some experience in deciphering reflectograms.

As a rule, it is desirable that all necessary measurements can be carried out on a working PON network without disconnecting subscribers (except, perhaps, the one being tested). Such testing is carried out at a non-operating wavelength using additional devices (DWDM wavelength multiplexers, filters) so that the radiation of the measuring equipment does not interfere with the useful signal. As already mentioned, in the PON network, a wavelength of 1490 or 1550 nm (for video) is used for the forward channel (from the center to subscribers), and 1310 nm for the return channel. For PON network testing, the wavelength typically used is 1625 nm.

The radiation from the measuring equipment (tester, reflectometer) is introduced into the fiber immediately after the OLT using a wavelength multiplexer (DWDM). This radiation can cause interference on the optical receiver of the subscriber device, so a filter must be installed in front of each subscriber ONT device. In order to be able to carry out testing without disconnecting the network, the wave multiplexer and filters must be permanently included in the optical path (see Fig. 3).

Rice. 3. Connection diagram of the wave multiplexer and filters to PON

An optical tester at 1625 nm is used to measure the attenuation in the optical link between OLT and ONT. The tester's transmitter is connected to the free end of the waveform multiplexer on the OLT. The tester's receiver is connected to the free end of the fiber in front of the filter (see Fig. 4).

Rice. 4. Attenuation measurement with disconnection of the subscriber device

You can measure attenuation without disconnecting the subscriber device. To do this, you need to use not a filter on the ONT, but a wave multiplexer, as on the central node (see Fig. 5).

Rice. 5. Attenuation measurement without disconnecting the subscriber device

The attenuation at a wavelength of 1625 nm is slightly higher than at 1550 and 1490 nm (10% on average). Therefore, testing the attenuation at 1625 nm provides an upper estimate for the attenuation at the operating wavelengths. If this estimate falls within the acceptable budget (23 dB), then the attenuation at operating wavelengths certainly satisfies the budget requirements. If the attenuation at a wavelength of 1625 nm exceeds the permissible value, then to accurately determine the attenuation at operating wavelengths it is necessary to recalculate based on the optical cable data sheet.

Measurement in PON using an optical tester allows you to get the real attenuation value in the area from OLT to ONT, but does not answer the question of where the problem area is located if this attenuation is higher than expected (calculated or reference). To localize the problem area, a more complex device is used - an optical reflectometer (OTDR).

An OTDR with a 1625 nm test module is connected to the free end of the waveform multiplexer on the OLT, (see Fig. 6). The reflectometer radiation propagates along the PON tree and, due to reflection on obstacles and backscattering in the optical fiber, partially comes back to the reflectometer input. Thus, a reflectogram of the PON tree is taken - a graph of attenuation in the line depending on the distance. Each attenuation peak or jump in this graph corresponds to a specific network element or event in the fiber.

Rice. 6. Taking a reflectogram of the PON tree

The technique for testing a PON network using a reflectometer is as follows. After each change in the network topology (connection of a new subscriber, replacement of a splitter, etc.), a reference (reference) reflectogram corresponding to the normal state of the network is taken. If problems are detected in the network (for example, if the attenuation measured by the optical tester turns out to be higher than the calculated one), a new reflectogram is taken and compared with the reference one. New events on the reflectogram localize the location of the problem area (see Fig. 7).

Rice. 7. Analysis of new events on the reflectogram.

Using an OTDR, you can monitor your PON network and detect fiber degradation before problems arise. To do this, it is necessary to regularly (for example, once a week) take a reflectogram of the network and compare it with the reference reflectogram. When any deviations, and especially new events, appear on the reflectogram, it is necessary to analyze their possible causes and, if necessary, carry out adequate preventive measures.

GEPON (Gigabit Ethernet PON)- an increasingly popular technology for transmitting data over a fiber-optic network. Its essence is a point-to-multipoint tree topology, when only one fiber optic channel is used to build a network for tens and hundreds of subscribers.

The network tree is built in such a way that the branch for the subscriber is separated from the main trunk as close as possible to its location. Used for separation passive distributor - splitter. This is fundamentally different from a conventional fiber optic network topology, which is predominantly a point-to-point architecture and each branch of the line requires the installation of active network equipment.

GEPON structure

To build an optical passive network, in addition to optical fiber, the following are used:

• OLT(Optical Line Terminal) - optical line terminals that provide communication between the PON network and external networks;
• Modules SFP OLT for PON connection, with increased power and signal encoding;
• ONU(Optical Network Unit) - the final network unit (modem) at the subscriber.
• Splitters- passive splitters in network nodes.

The tree structure of GEPON suggests various construction options, from the simplest - 1 OLT, 1 SFP OLT module, 64 ONUs and required amount splitters for branching to “multi-trunk”, when all OLT ports can be used, as well as several OLTs or multiport models.

GEPON network architecture diagram:

The picture also clearly shows the method of data transfer. All packets leave the central node; at the final point, each ONU “takes” only its own, designated by an identifier.

On the way back, packets from subscribers are collected into one channel. In PON networks it is used TDMA protocol, when packets from different points are transmitted at different times.

In addition, incoming and outgoing traffic, as well as TV traffic, is separated.

Scheme complex structure GEPON:

When designing complex passive fiber network designs, it is important to remember that one channel cannot be divided into more than 64 subscriber devices, and the optical budget of the system must be taken into account.

Optical budget systems - the difference between the transmit power of the OLT and the receive sensitivity of the ONU.

Maximum distance, to which a passive optical network can be extended, taking into account losses on the channel - 20 km.

Maximum number of subscriber devices, connected to one PON “tree” - 64 . However, the final number of subscribers may be greater if a switch is connected after the ONU. Here restrictions are imposed only by the OLT and ONU MAC address table, and, naturally, throughput channel.

Minimum speed per subscriber- 16 Mb/s (1024 Mb/s on 64 ONUs).

Equipment for the GEPON network

Optical Line Terminals - OLT

These devices are second-level switches equipped with Uplink ports - for connecting to external data sources (Internet, TV, telephony) and Downlink ports - for the PON network.

OLT terminals are produced with the following designations:

• AC - a standard 220 V power supply is used to power the switch;
• DC - the terminal needs a 36-72V DC source;
• 2-AC 2-DC - the presence of 2 power sources, the main one and an instant-on backup.

User terminals (modems) - ONU

Subscriber-side devices, optical terminals, equipped with one PON port and one or more, depending on the model, ports for connecting client equipment. There are models with cable TV output.

Splitters

Inexpensive, compact, simple devices that do not require power supply, heating cabinets, control or configuration. Their the main task- traffic separation on the way from the provider to the subscriber, and traffic mixing on the way back. There are welded (with the possibility of uneven distribution of traffic) and planar (equal arms). Branching - from 1*2 to 1*128.

Disadvantages of technology

• Signal attenuation at each branch node. As a result, in a network with 64 ONUs, the total attenuation can exceed 20 dB.
• The need for maximum throughput on all devices. Although each individual subscriber receives from 16 Mbit/s, each network point (ONU) is forced to support the maximum GEPON throughput of 1 Gbit/s.
• Not enough high level data security. The technology is definitely not suitable for financial and similar organizations.
• Difficulty of modernization. In order to increase network capacity, it may be necessary to replace the entire cable on the backbone.
• Interference in the operation of the entire PON with one faulty ONU device transmitting a continuous light signal in the opposite direction. It is possible to provide WathDog to control accidental breakdowns, but it is much more difficult to prevent the actions of intruders.
• Difficulty detecting faults. Splitters, due to their extreme simplicity, are unable to help in identifying the faulty section of the network.

Advantages of GEPON

• Economical consumption of optical cable. In fact, GEPON technology can reduce the length of cable infrastructure by almost three times.
• Lack of active equipment at network nodes, which significantly reduces the costs of its implementation and maintenance.
• High supported speed- up to 1 Gbit/sec.
• Efficient load distribution in the channel. Theoretically, the speed for each subscriber will be the channel capacity/number of subscribers. In fact, if some subscribers are currently not using their entire traffic bandwidth or are not connected at all, the speed of others increases.

As you can see, GEPON has both its pros and cons. However, the growing popularity shows that many still find more advantages.

In one of our next issues - answers to FAQ relative to a passive fiber optic network.

Expanding the audience of Internet service consumers and, accordingly, broadband network users requires the introduction of new technologies. Data transmission facilities must regularly increase communication lines, which forces service companies update transport information channels. But, in addition to the growth in the volume of transmitted data, problems of a different kind arise, which are expressed in the increasing cost of servicing more massive networks and expanding the range of needs of end users. One of the methods for overall optimization of characteristics is PON technology, which also allows maintaining the potential of networks for further expansion of their power and functionality.

Optical fiber and PON technology

New development makes it easier technical organization and further operation of information data networks, but this is achieved largely due to the advantages of conventional optical lines. Even today, against the background of the introduction of high-tech materials, the use of channels built on outdated telephone pairs and xDSL means continues. It is obvious that an access network based on such elements is significantly inferior in efficiency to fiber-coaxial lines, which also cannot be considered as something productive by today’s standards.

Optical fiber has long been an alternative to traditional and wireless networks. But if previously laying such cables was an impossible task for many organizations, today optical components have become much more affordable. In fact, previously, optical fiber was used to serve ordinary subscribers, including the following. The next stage of development was a telecommunications network built on the Micro-SDH architecture, which opened up fundamentally new solutions. It is in this system that the concept of PON networks has found its application.

Network standardization

The first attempts to standardize the technology were made back in the 1990s, when a group of telecommunications companies set out to put into practice the idea of ​​multiple access over a single passive optical fiber. As a result, the organization received the name FSAN, uniting both operators and network equipment manufacturers. The main goal of FSAN was to create a package with general recommendations and requirements for the development of PON technology so that OEMs and providers can work together in the same segment. Today, passive communication lines based on PON technology are organized in accordance with ITU-T, ATM and ETSI standards.

Network operating principle

The main feature of the PON idea is that the infrastructure operates on the basis of a single module, which is responsible for the functions of receiving and transmitting data. This component is located in the central node of the OLT system and allows you to serve many subscribers with information flows. The final receiver is the ONT device, which, in turn, also acts as a transmitter. The number of subscriber points connected to the central reception and transmission module depends only on the power and maximum speed of the PON equipment used. The technology, in principle, does not limit the number of network participants, however, for optimal use of resources, developers of telecommunications projects still set certain barriers in accordance with the configuration of a particular network. The information flow is transmitted from the central receiving and transmitting module to the subscriber device at a wavelength of 1550 nm. In contrast, return data streams from consumer devices to the OLT are transmitted at a wavelength of about 1310 nm. worth considering separately.

Forward and reverse flows

The main (that is, direct) stream from the central network module is classified as broadcast. This means that optical lines segment the overall data flow, highlighting address fields. Thus, each subscriber device “reads” only information intended specifically for it. This principle of data distribution can be called demultiplexer.

In turn, the reverse stream uses one line to broadcast data from all subscribers connected to the network. This uses a time-division multiple access scheme. To eliminate the possibility of signals crossing from several information receiving nodes, each subscriber's device has its own individual schedule for data exchange, adjusted for delay. This general principle, according to which PON technology is implemented in terms of interaction of the receiving-transmitting module with end consumers. However, the network layout configuration may have different topologies.

Point-to-point topology

In this case, a P2P system is used, which can be implemented both for common standards and for special projects involving, for example, the use of optical devices. In terms of data security for subscriber points, an Internet connection of this type provides the maximum security possible for such networks. However, the installation of an optical line for each user is carried out separately, so the cost of organizing such channels increases significantly. In a way, this is not a general, but an individual network, although the center with which the subscriber node works can also serve other users. In general, this approach is appropriate for use by large subscribers for whom line security is especially important.

Ring topology

This scheme is based on the SDH configuration and is best deployed in backbone networks. Conversely, ring-type optical lines turn out to be less efficient in operating access networks. Thus, when organizing a city highway, the locations of nodes are calculated at the project development stage, but access networks do not make it possible to estimate the number of subscriber nodes in advance.

Under the condition of random temporary and territorial connection of subscribers, the ring circuit can be significantly complicated. In practice, such configurations often turn into broken circuits with many branches. This happens when new subscribers are introduced through a break in existing segments. For example, loops can be formed in a communication line, which are combined in one wire. As a result, “broken” cables appear, which during operation reduces the reliability of the network.

Features of EPON architecture

The first attempts to build a PON network, similar in terms of consumer coverage to Ethernet technology, were made in 2000. The EPON architecture became the platform for developing the principles of network formation, and the IEEE specification was introduced as the main standard, on the basis of which individual solutions for organizing PON networks. EFMC technology, for example, served a point-to-point topology using twisted pair copper. But today this system is practically not used due to the transition to fiber optics. As an alternative, ADSL-based technologies continue to be more promising areas.

In its modern form, the EPON standard is implemented using several connection schemes, but the main condition for its implementation is the use of fiber. In addition to the use of different configurations, the EPON PON connection technology also allows for the use of some optical transceiver options.

Features of GPON architecture

The GPON architecture allows the implementation of access networks based on the APON standard. In the process of organizing infrastructure, it is practiced to increase the network, as well as create conditions for more efficient transfer of applications. GPON is a scalable personnel structure that allows you to serve subscribers at information flow rates of up to 2.5 Gbit/s. At the same time, the reverse and forward flows can operate at the same or with different speed modes. In addition, the access network in a GPON configuration can provide any synchronous transport protocol encapsulation regardless of service. If in SDH it is possible to implement exclusively static division of bands, then the new GFP protocol in the GPON structure, while maintaining the characteristics of the SDH frame, also makes it possible to dynamically distribute bands.

Benefits of technology

Among the main advantages in the PON scheme are the absence of intermediate links between the central receiver-transmitter and subscribers, economy, ease of connection and ease of maintenance. To a large extent, these advantages are due to the rational organization of networks. For example, the Internet connection is provided directly, so the failure of one of the adjacent subscriber devices does not in any way affect its performance. Although the array of users, of course, is united by connecting to one central module, on which the quality of service of all participants in the infrastructure depends. Separately, it is worth considering the P2MP tree topology, which optimizes optical channels as much as possible. Thanks to the economical distribution of lines for receiving and transmitting information, this configuration ensures efficient network operation regardless of the location of subscriber nodes. At the same time, it is possible to introduce new users without fundamental changes to the existing structure.

Disadvantages of PON network

The widespread use of this technology is still hampered by several significant factors. First of all, this is the complexity of the system. The operational benefits of this type of network can only be achieved if a high-quality design is initially carried out, taking into account many technical nuances. Sometimes the solution is PON access technology, which involves organizing a simple typological scheme. But in this case, you should prepare for another drawback - the lack of redundancy.

Network testing

When all stages of the initial development of a network diagram have been completed and technical measures have been completed, specialists begin testing the infrastructure. One of the main indicators of a high-quality network is the attenuation indicator on the line. Optical testers are used to analyze the channel for problem areas. All measurements are made on the active line using multiplexers and filters. A large-scale telecommunications network is usually tested using optical reflectometers. But such equipment requires special training from users, not to mention the fact that the decoding of reflectograms must be carried out by expert groups.

Conclusion

Despite all the difficulties in transitioning to new technologies, companies providing telecommunications services are quickly mastering truly effective solutions. Fiber optic systems, which also include PON technology, are also gradually spreading. Rostelecom, for example, began introducing services of a new format back in 2013. Residents of the Leningrad region were the first to gain access to the capabilities of PON optical networks. What’s most interesting is that the service provider has even provided fiber optic infrastructure to local villages. In practice, this allowed subscribers to use not only telephone communication with Internet access, but also connect to digital television broadcasting.

GEPON technology

This material will discuss technology and equipment for organizing passive optical networks - Passive Optical Network, PON. The main differences between PON and classical optical communication channels are the use of passive equipment - optical splitters - for traffic aggregation and high port density.

It is no secret that consumer demands for the speed of information delivery from the Internet are growing exponentially. Today, in large cities, 10 Mbit/s is completely commonplace. The reasons for this process have remained unchanged for a long time - voice and video transmission, multimedia, television (lately also in high-definition versions). But the bitrates are constantly increasing.

A significant part of the costs of any provider project is borne by the cable infrastructure. Moreover, this takes into account not only the cost of the cable, but also its installation, which, if working in an existing infrastructure, can be very high. And of course, I want the investments to last a long time, not require frequent updates, and have a good supply of the required parameters. From this point of view, optical communication channels today are the most productive and “long-range” way to provide network connections between devices. At the same time, the classic architecture assumes a “point-to-point” topology, when each line has its own dedicated ports on each side, and if it is necessary to create “branches,” the installation of active equipment in the node is required. So it can be most successfully used for single long-distance lines.

However, in some situations, a tree topology may be more convenient, which is interesting from the point of view of scalability and a reduced overall length of cables to be laid. PON is just suitable for such projects. In Russia, networks of this type appeared quite a long time ago, more than five years ago.

And the increase in the number of connected users and the start of the first Russian projects class fiber to every home (Fiber To The Home, FTTH), based on PON, shows that the technology has taken root in our country.

PON network structure

A PON network consists of several elements - a switch at the communication node, communication lines with passive splitters at network nodes and modems on the subscriber side. Each modem receives all packets from the switch, and time frame multiplexing is used during transmission.

Data transmission in forward channel

Data transmission in the backward channel

ZyXEL today offers equipment of the EPON (IEEE 802.3ah) standard, also called GEPON.

Currently, the equipment is involved in several projects, as well as in testing with providers throughout Russia. This is what we will talk about next. Note that other standards of this type of network differ in speed and other technical characteristics.

The switch allows you to connect up to 32 or even 64 subscribers via one fiber (one port). The total data transfer rate (which is divided between subscribers) is 1.25 Gbit/s. Further development of EPON in the coming years also offers a transition to speeds of 10/1 Gigabit/s and 10/10 Gigabit/s. IN next year The working version of the 10G EPON standard is expected to be adopted, and the first pilot projects may start in 2010.

With a delay of two to three years, the transition to 10-gigabit speeds and GPON technologies is planned.

For reception and transmission, lasers with different wavelengths are used - 1490 nm for transmission and 1310 for reception. If necessary, it is possible to add analogue cable television channels (100 or more) to the channel, which are modulated by a 1550 nm laser. Depending on the specific network design and equipment used, the total length of the channel can be up to 20 km.

Multiservice network based on GEPON technology

The cable is laid from the switch port in the form of a tree. Splitters installed in nodes are extremely unpretentious - they do not require power supply, configuration and management, heating cabinets, are inexpensive and very compact. This allows them to be placed, for example, in existing telephone distribution cabinets.

Splitter

The simplest end devices are fiber-to-cable converters with a built-in MAC address filter. When using television, another receiver is installed in the modem, and a regular high-frequency cable is output to the TV.

To protect information, it is possible to use encryption (AES128) of all transmitted packets. The technology does not allow direct communication between individual subscribers located on the same switch port - data from one subscriber can reach another only through a GEPON switch, which relays upstream data streams at a wavelength of 1310 nm to a downstream stream at a wavelength of 1490 nm. An additional advantage from a security point of view is the use of exclusively passive equipment on the line, which makes interception difficult.

From positive aspects PON need to be noted:

• minimal use of active equipment;
• minimizing cable infrastructure;
• low cost of maintenance;
• possibility of integration with cable television;
• good scalability;
• high density of subscriber ports.

At the same time, when considering the technology, it is necessary to take into account its features, especially in comparison with point-to-point lines: the bandwidth shared between subscribers, the common environment may not be suitable for the client from a security point of view, passive splitters make it difficult to diagnose an optical line, the influence of a fault may be equipment of one subscriber for the work of the rest, less benefit if sold at the construction stage.

Equipment

ZyXEL's GEPON product line consists of three switches and three modems. The low-end model of the switch has eight GEPON ports and eight corresponding Gigabit Ethernet ports (note that Gigabit devices with lower speeds cannot be connected to them). Up to 32 modems can be connected to each optical port, resulting in 256 subscribers per device. All connectors are located on the front side of the device - 8xPON, 8xGigabit, console, 10/100BaseT off-network control and power. There is also a device reset button here. All ports have a set of indicators to determine the current status. It has a built-in gigabit L2+ switch (non-blocking switching with a throughput of 24 Gbit/s, frame switching speed of 17.8 million packets/s) and four combined 1000Base-T/SFP ports. This option can be used for channel redundancy - when two connectors (SC and RJ45) are connected simultaneously, the optics work, and in the event of a failure in the optical channel, it automatically switches to copper. The power supply and console port for this modification are located on the rear panel. These models are made in a standard 1U case and are recommended for use in fast-growing networks. The most productive model is modular. Its 4.5U chassis provides space for up to sixteen OLC-2301s. Each such linear module has a GEPON port and a combined 1000Base-T/SFP port. The chassis also houses a control module and a dual redundant power supply. Linear modules are hot-swappable, which has a positive effect on the ease of network maintenance and reliability of service provision. Maximum OLT-2300 can support 512 subscribers. All optical modules of the switches are designed for an operating range of 20 km.

OLT-1308

The latest firmware updates for the OLT-1308/OLT-1308H models allow 64 rather than 32 subscribers to operate on one channel, which significantly reduces the cost of one connection. There is no such option for OLC-2301 yet.

Chassis OLT-2300

All GEPON switches support STP/RSTP protocols and mechanisms for prioritizing traffic and organizing virtual networks (including Port Based and 802.1Q). The efficiency of multicast broadcasts is ensured by support for IGMP v.2, IGMP proxy, IGMP snooping and MVR. RS-232 and 10/100Base-TX ports are provided for control. Switches can be configured via the Web interface (SSL is supported, up to five accounts can be installed, examples of screenshots are , , ), telnet, SSH, FTP or the console port. The port numbers of all services can be changed. It is possible to restrict access by IP addresses. The web interface has a built-in help system.

The device automatically finds all connected subscriber modems and allows you to assign specific profiles to them. They include settings for speed, filtering, VLAN, priorities and other parameters. The 802.1x authentication protocol can be used.

Switches also allow you to monitor the physical condition - temperatures, fan speeds, and voltages are checked. For large networks, switches will benefit from SNMP support and compatibility with the NetAtlas EMS management system. In addition, it is possible to combine devices into clusters for general management.

At the moment, ZyXEL does not have models with built-in CATV injectors. However, to mix the TV signal into an optical channel, you can use external splitters and coaxial/optical media converters.

ONU-631HA

The first model of a subscriber GEPON modem is the . It operates in bridge mode, is easy to maintain and is controlled exclusively by the provider using a special protocol. For the user, it offers a standard Gigabit Ethernet port. There are two modifications of modems - with indexes -11 and -12. The first works at distances of up to 10 km, and the second - up to 20 km. The case is made of dark plastic; there are several indicators on the front panel (power, PON, LAN, LAN speed, duplex). On the back side there are two network ports (optical and copper) and a power supply input (12 V 1.5 A). This model is positioned for connecting corporate subscribers and operator network extensions.

ONU-634HA

The second model is more interesting for connecting home users - it has a built-in centrally managed 4-port switch with VLAN 802.1Q binding to Fast Ethernet ports. Like the 631, it is fully configured by the provider, which reduces maintenance costs. There are also now ONU-634FA samples - four network ports and a cable TV output, which allows you to directly connect a regular TV to a GEPON modem.

ONU-634FA

To build a network you will also need splitters ( approximate cost- from 400 rubles for 1×2 to 4000 rubles for 1×8, there are also 1×32 models), single-mode optical cable (the cost is equal to the price of a UTP cable: prices for fiber cable start at 7-8 rubles per meter) and connectors (from 100,140 rubles per connection).

Testing of the described equipment as part of the OLT-1308 switch and ONU-631A modems was carried out on the ZyXEL test site using the Ixia Chariot test package. The results for simultaneous operation of one, two and three clients are shown in the table (packets of maximum size, Mbit/s). Modems were connected to one of the switch ports through one splitter. It can be seen that in the case of maximum load, the speeds are evenly distributed across all clients. We also note the high efficiency of data transfer, including the operation mode of several clients - the total speed practically coincides with the maximum possible.

In general, it can be noted that the technology is not difficult to set up and operate and works according to specifications. Speeds correspond to those familiar from gigabit copper networks.

conclusions

GEPON technology can be successfully used to organize optical communication channels to the subscriber and is especially effective if there are restrictions on cable laying and installation of active equipment on the line. Efficiency this decision depends on many factors and it is clear to say that it is the best option Of course you can’t, everything is determined by the specific requirements of the customer. However, the estimates made allow us to conclude that even today, in some cases, the cost of connecting home subscribers via fiber optics may not exceed $500.

As for the equipment described, ZyXEL today offers a full line of GEPON devices that allows you to create optical networks of any scale with all the necessary control systems and technologies to improve reliability.

home » Useful » Connected using pon technology. Gpon technology. Description of GPON technology. Operating principle of PON. The principle of connecting to Rostelecom