Based on xpon technology. GPON technology. About GPON Technology

29.03.2020

GEPON (Gigabit Ethernet PON)- the technology of data transmission on a fiber optic network gaining popularity. Its essence is in a tree-like point-to-multipoint 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 conventional fiber optic network topology, which is predominantly point-to-point architecture, and each branching 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 end network unit (modem) at the subscriber.
Splitters- passive splitters in network nodes.

The GEPON tree structure assumes various construction options, from the simplest - 1 OLT, 1 SFP OLT module, 64 ONUs and the required number of splitters for branching to "multi-barrel" when all OLT ports can be used, as well as several OLT or multiport models.

GEPON Network Architecture Diagram:

The picture also clearly shows how the data is transferred. All packets leave the central node, at the end point each ONU "picks up" only its own, designated by an identifier.

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

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

Diagram of the complex structure of GEPON:

When designing complex passive optical network schemes, it is important to remember that one channel cannot be divided by more than 64 subscriber units, and the optical budget of the system should be taken into account.

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

Max distance, to which you can stretch a passive optical network, taking into account the losses on the channel - 20 km.

Maximum number of subscriber devices connected to one "tree" PON - 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 table of MAC addresses of the OLT and ONU, and, of course, by the channel bandwidth.

Minimum speed per 1 subscriber- 16 Mb/s (1024 Mb/s for 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 - for the PON network.

OLT-terminals are issued with designations:

AC - the switch is powered by a standard 220 V power supply;
DC - the terminal needs a 36-72V direct current source;
2-AC 2-DC - the presence of 2 power supplies, the main one and an instant backup.

Subscriber terminals (modems) - ONU

Devices on the subscriber's side, 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 and settings. Their main task is to separate traffic on the way from the provider to the subscriber, and mix traffic on the way back. There are welded (with the possibility of uneven distribution of traffic) and planar (equilateral). Branching - from 1*2 to 1*128.

Technology Disadvantages

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 of all devices. Although each specific subscriber receives from 16 Mbps, each point of the network (ONU) is forced to support the maximum throughput of GEPON - 1 Gbps.
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 bandwidth, it may be necessary to replace the entire cable on the backbone.
Interference in the operation of the entire PON with one faulty ONU 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 in finding faults. Splitters, due to their extreme simplicity, are unable to help in determining the faulty section of the network.

Benefits of GEPON

Economical consumption of optical cable. In fact, GEPON technology can reduce the length of the cable infrastructure by almost three times.
Lack of active equipment at the network nodes, which significantly reduces the cost of its implementation and maintenance.
High sustained speed- up to 1 Gbps.
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 in this moment they do not use their entire traffic band or are not connected at all - the speed of the rest 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 frequently asked questions regarding the passive fiber optic network.

The intensive development of the telecommunications industry, due to the need to transfer more and more 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. Converged networks use single multi-service networks focused on packet traffic to provide various types of services. The provision of 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 cables, have a number of advantages: high bandwidth, low signal attenuation, high immunity to external electromagnetic interference, small size and weight. Among the optical access technologies, the FTTx technology group is most in demand. FTTx technologies are subdivided according to network construction into AON active optical networks and PON passive optical networks. The main difference between these technologies is that a passive optical network, unlike an active one, does not require power supply for the intermediate nodes of the subscriber line. As a result, the 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 increase. Such advantages will allow expanding the existing network and attracting 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 (P2P, point-to-point) connections involves connecting each subscriber with a separate fiber to the access node. The topology "star" is used for a dense location of subscribers in the PBX area. This topology is characterized by a minimum number of optical splitters and a single location for their installation. The obvious disadvantage of this topology is the presence of a large number of fibers and optical transmitters. Advantages of this topology: ease of maintenance, operational measurements and line fault location. This topology is characterized by high reliability, since a break in one of the fibers will not affect the operation of the entire network.

Tree topologies are used for distributed subscribers. The optimal distribution of power between the various branches is decided by the selection of the division ratios of the 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, the topologies "tree with active nodes" and "tree with passive nodes" are distinguished. Each topology has its own advantages and disadvantages.
When using the "tree with active nodes" topology, each subscriber is connected to the switch, which in turn is connected by fiber to the access node. The switch is active equipment, that is, it requires power. In the absence of power, subscribers connected to the switch will lose access to the network. However, this solution fits well within the Ethernet standard and is relatively cheap.

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

The principle of operation of the PON network

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

Purpose of circuit blocks:

The OLT central node is a network device that is located in the access node, receives data from backbone networks through SNI interfaces and forms a downstream flow to subscribers along the PON tree.
Subscriber node ONT – network device, which is located on the subscriber's side, receives and transmits data to the OLT at wavelengths of 1550 nm and 1310 nm, respectively, converts the data and transmits them to subscribers via UNI interfaces.
A splitter is a passive optical multipole that distributes the flow of optical radiation in one direction and combines this flow in the opposite direction.

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

The number of ONT subscriber nodes connected to one OLT transceiver module depends on the power budget and top speed transceiver equipment. To transmit the direct (outgoing) stream 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 outgoing and upstream flows.

WDM stands for 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 transmitting light at different wavelengths, there is no mutual interference 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 extract 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 delay correction. This problem is solved by the TDMA MAC protocol.

An ONT optical terminal is installed directly at the subscriber's premises, which is also a home access gateway. When using the unified transport optical terminal ONT, the configuration of the transport component is not tied to services. Thus, the subsequent configuration of services will be carried out at 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 in the optical distribution cabinet, a splitter with a division ratio of 1:32 is installed, which ensures the distribution of the optical signal among the subscribers of the residential building. It should be noted 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 complex 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's equipment (PC). The ONT is configured in bridge mode. The BRAS Broadband Remote Access Router 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 through the Internet.

Three virtual private networks VLAN are organized for the organization of Triple Play services. Internet access traffic is carried within the first VLAN. The second VLAN carries IPTV and VoD service traffic. On the third VLAN, the transmission of analog and IP telephony services is organized. The ONT subscriber terminal compares the identifier of the port through which the subscriber equipment is connected and the identifier corresponding to the VLAN.

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

xPON is a passive optical network that provides multifunctional broadband Internet access with high-quality and reliable connection at unprecedented high speeds - up to 2400 Mbps. Through one fiber-optic cable, laid directly to the apartment, the subscriber receives data transmission and telephony services with a guaranteed quality of service.

To date, xPON is the most progressive and promising Internet access technology that can meet the rapidly growing needs for information exchange speed. xPON is not only fully responsible modern requirements, but also has the resources and potential to ensure the development of communication technologies in the future.

AdvantagesxPON

The new standard for Internet access speeds - from 25 Mbps to 2400 Mbps.
- downloading data from the Internet - 25 times faster than the maximum possible on ADSL;
- uploading data to the Internet - 100 times faster, reverse channel speed up to 500 Mbps.

High quality connection without breaks and interference.
Provision of the entire resource of the optical cable to one subscriber.
Multiservice package of services connected via one cable: Internet, Home phone and Home TV (with HD support).
A single account to pay for all services.
The possibility of paying on credit using the "Pay later" system.

How does it workxPON

Providing Internet access using xPON technology involves replacing obsolete copper cables with more advanced fiber optic cables with significantly higher bandwidth. The signal on such a cable passes by means of a light, and not an electrical impulse. The light pulse travels along the glass fibre, providing a more reliable signal and high speed at low energy costs.

xPON technology provides for the laying of fiber optic cable directly to the subscriber's home, and not to the entire building, which guarantees a constant speed of Internet access and eliminates disruptions due to network congestion. To connect to the xPON technology, a modem is installed for the subscriber - ONT(Optical Network Terminal), thanks to which the connection of all services in the future occurs remotely and in one device. The modem has built-in Wi-Fi, over the network of which you can work wirelessly from any device.

Development prospects

Today, we can say with confidence that xPON technology not only keeps up with the times, but also in many ways is ahead of it, expanding the boundaries of what is possible. The new standard of speeds will allow constantly replenishing the package of services provided. Video surveillance, telemetry, burglar alarms and other services become available to subscribers using xPON technology. Technology resources allow us to talk about the prospects for the development and implementation of many other services for a better quality of life.

xPONin Russia and in the world

xPON is rapidly developing in the USA, Japan, Korea, UAE and a number of European countries as the most promising access technology.

Russia still lags behind in terms of percentage indicators of coverage, but the dynamics of development is in line with global trends. In large Russian cities such as Chelyabinsk, Miass and others, the number of subscribers is estimated at tens of thousands, and in St. Petersburg - hundreds of thousands of people.

What is GPON and how subscribers are connected

As the needs of Internet and digital technology users are growing every day, Western providers are thinking - "How can you provide subscribers with a high-speed, practical and inexpensive way to transfer digital data?" And they came up with GPON. Technology "PON"- passive optical networks, "G"- gigabit. They are passive because no active equipment is used in the section from the PBX to the subscriber - an individual optical fiber stretches directly to the client's house. Due to this, unprecedented channel capacity is achieved and, as a result, the ability to connect several services via one line - telephone, television, Internet.

If an optical distribution network has already been built in your village, then you have the opportunity to get a fully fiber-optic communication line from the telecom operator to the subscriber. Of course, if there are still free fibers in the cable. You make an application, we check the technical feasibility of connection and agree with you on the installation time. Let's just say that on average it takes 2 days to connect. On the first day, work related to optics is performed - i.e. optical fiber is introduced directly into the house, an optical socket is installed, the quality of the signal in the line is checked. All this takes about 2 hours. Secondth day a representative of the company - a telecom operator arrives, brings necessary equipment and a contract for the provision of communication services. In some villages, all operations can be completed in one day.

So, you were assigned an installation, and you became the owner of a small optical outlet mounted on the wall from the inside of the house. And not necessarily at home. At the request of the subscriber, we can also install an optical socket in the technical room.

The device that will convert the fiber-optic interface into an Ethernet interface is an optical terminal - ONT. Depending on the modification, ONT can have functionality from minimal to a full-fledged router, with the ability to connect WiFi, IPTV and telephony. The terminal is installed in the subscriber's house or technical room, and is connected to the 220v network.

As a rule, ONTs are mounted next to the hole where the optics are tightened so that the length of the fiber around the apartment is as small as possible. Why can't you extend fiber optics deep into the house? It's simple - thin "wiring" is extremely fragile, sensitive to various bends, kinks, pressure. From all of the above procedures, the optical fiber simply breaks, the signal in the line disappears. Fiber restoration and/or replacement is a very time-consuming process.

Communication between ONT and computer, as well as between ONT and STB (if the IPTV service is connected) is carried out using a copper cable - UTP (twisted pair).

The installers configure the ONT and verify network access. If no technical problems arise, the subscriber signs an agreement with the installers (they bring it with them if the application for connection was made remotely) and installation orders.

Pros and cons of GPON technology

Pros:

Optics is conducted to the subscriber's apartment, respectively, a large channel bandwidth is obtained and, as a result, the ability to connect several services from one subscriber device (television, telephone, Internet);
There is no intermediate active equipment in the section from the PBX to the subscriber. Therefore, if the electricity goes out, at least in the whole village, and you have an alternative power source for the optical terminal and computer (as an option - a charged laptop or tablet), you can use the Internet without any problems;
Since there is no electrical voltage in the optics, the effect of moisture on the fiber is not terrible (of course, within reason). And for subscribers there is no danger of getting an electric shock.

Minuses:

The fiber is very sensitive to bends, so it is not recommended to stretch it around the house and lay it in the baseboards. Even if the fiber does not break with a large bend, the signal level will deteriorate significantly, which will lead to a decrease in the quality of the services provided.

PON (Passive Optical Networks) is a family of rapidly developing, most promising technologies for broadband multiservice access over optical fiber. The essence of PON technology follows from its name and consists in the fact that its distribution network is built without the use of active components: the optical signal is branched in a single-fiber optical communication line using passive optical power splitters - splitters.

Structurally, any passive optical network consists of three main elements - an OLT station terminal, passive optical splitters and an ONT subscriber terminal. The OLT terminal ensures the interaction of the PON network with external networks, the splitters perform the branching of the optical signal in the section of the PON path, and the ONT has the necessary interaction interfaces from the subscriber side.

Based on the PON architecture, solutions using point-to-multipoint logical topology are possible. An entire fiber-optic segment of a tree-like architecture, covering dozens of subscribers, can be connected to one port of the central node. In this case, passive optical splitters (splitters) are installed in the intermediate nodes of the tree and do not require power and maintenance.

The main idea of the PON architecture is the use of only one transceiver module in the OLT to transmit information to and receive information from multiple ONT subscriber devices.

GEPON technology (Gigabit Ethernet Passive Optical Network) is one of the varieties of PON passive optical network technology and one of the most modern options for building communication networks that provides high data transfer rates (up to 1.2 Gbps). The main advantage of the technology GEPON is that it allows you to optimally use the fiber-optic resource of the cable. For example, to connect 64 subscribers within a radius of 20 km, it is enough to use only one fiber-optic segment.

The main advantages of GEPON are:

Increasing the transmission speed to 1 Gbps in both directions and providing more broadband services;
Ensuring QoS using 802.1p/TOS mechanisms. It is possible to use strict traffic prioritization mechanisms with the help of eight dedicated queues for each type of traffic. These mechanisms make it possible to provide services such as VoIP or VoD with quality assurance;
Ability to connect 64 subscriber devices per PON branch and effective use optical fiber;
Full support for DBA (Dynamic Bandwidth Allocation) - a mechanism for dynamic bandwidth redistribution in accordance with subscriber requests and the availability of free bandwidth in the PON tree. So subscribers who are provided with a guaranteed bandwidth for data transmission, for example, 1 Mb / s, can get real speeds up to 1 Gb / s if the PON tree bandwidth remains partially unused (similar to UBR traffic in ATM);
Support for streaming video (IGMP Snooping);
Easy to install and maintain.

We get more and more questions about the implementation, how the network works, and so on.

Therefore, in the near future we will publish a series of articles on PON technology that will analyze these nuances in more detail. And let's start with the main one: what is it, why are PON networks good, and why do Ukrainian suppliers mainly offer GEPON equipment, and not GPON or EPON?

What is PON technology?

Optical fiber provides the ability to transmit data of large volume and at high speed, including such demanding signal stability as voice and video. And this is good. But optical cable is expensive, and allocating a separate fiber for each subscriber is an unsustainable expense for most providers. And this is bad. Moreover, many subscribers do not use the full potential of the dedicated fiber, and most of it is "idle".

Therefore, PON technology was developed - for the most efficient and economical use of the possibilities of a fiber optic network. The main advantage of Passive optical network is organization of connection of several dozens of subscribers to the network via ONE optical fiber. This is implemented by separating the transmission of packets in time (TDM and TDMA protocols), as well as separating the reception and transmission of data in different wave bands.

PON types. What to choose: GEPON or GPON?

About the ancestors of modern PON - technologies APON and BPON There's no point in even talking anymore. The low supported speed, coupled with the rather high price of deploying a network based on them, is the reason for their disappearance into the past. The same goes for epon, with its 100 Mb/sec.

The Ukrainian provider is left to choose between GEPON And GPON. Despite similar names and high speed, these are different standards. The picture below illustrates this: if data packets are transmitted without any special changes in GEPON, then in GPON this is more difficult, with double "packing" into GEM and GTC frames. In addition, GPON uses ATM cells, which are not available in GEPON.

GPON supports 2.5Gbps, offers efficient TDMA traffic, and has several other benefits. But all of them are crossed out by the cost of equipment (much higher than in GEPON) and its more complex setup. Only a small segment of providers serving large serious customers or building huge branched networks can afford such a network.

Most Ukrainian telecommunications companies choose GEPON:

the bandwidth of such a network meets standard modern requirements (1 Gbit);
equipment for GEPON is cheaper than for GPON and is easier to set up;
in terms of the number of connected subscribers per 1 OLT port (64) and the maximum network radius (20 km), GEPON is not inferior to GPON.

There is also 10GEPON technology which promises 10Gbps but is still under development (since 2009).

Where can I stretch PON (GEPON)?

Networks based on PON technology are universal. They can be used even in those conditions when it is unprofitable or unrealistic to organize a conventional fiber optic FTTH network or forward Wi-Fi links.

Take, for example, a standard optical-based network, when a separate fiber is allocated for each subscriber. We have already discussed above that this is disadvantageous due to the cost of the cable itself. Add to this an indispensable attribute of such a network - active equipment. Necessary:

Buy switches and put in each access point, plus provide a more powerful switch for aggregation. The price of switches (even the most unpretentious ones) for several dozen subscribers starts somewhere from $400.
Equip with SFP modules(they usually do not come with switches), media converters, etc.
Somewhere place, and that "somewhere" must be a warm, dry room.
Protect from vandals and thieves(installation lockable cabinet or box).
Take care of power supply and about backup power (or UPS), in case of a power outage.
Provide configuration, monitoring and maintenance all active equipment.

And if in the conditions of urban development this is all at least somehow realizable, then in the private sector it is unlikely.

For the private sector, an excellent solution is Wi-Fi networks. But here, too, there can be stumbling blocks: densely "populated" ether, lack of direct visibility, and the like, when GEPON becomes the way out.

And cable TV to boot

Internet connection using PON technology, in addition to saving on the cost of optical fiber, has many advantages:

The purchase of active equipment is reduced to a minimum. In fact, you need to purchase only one headend - OLT and subscriber terminals-modems (ONU). Moreover, the price of the latter can be compensated by the subscriber in the cost of connection.

Configuration and administration will only be required for the OLT.

Throughout the GEPON, only passive elements are used - splitters that do not need power supply and a heated room.

PONs make efficient use of network bandwidth. Since it is common, when one or more subscribers are idle and the load on the channel is reduced speed increases for everyone. It also falls proportionally, but the bandwidth resources are quite enough even with the heaviest load. If we divide gigabit into 64 connected subscribers (maximum), then each it turns out at least 16 Mbps!

And an additional bonus - based on GEPON, you can provide cable TV to subscribers using the same network infrastructure. TV data transmission is carried out at a different wavelength.