Pon modem. Economical fiber optic Internet - GEPON. Basic facts about the technology

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 GEPON tree structure suggests various construction options, from the simplest - 1 OLT, 1 SFP OLT module, 64 ONUs and the required number of 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.

Diagram of the complex structure of 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 table of MAC addresses of the OLT and ONU, and, naturally, by the channel bandwidth.

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.
• Insufficient level of 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 transmitting a continuous light signal to reverse side. 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 in this moment They do not use their entire traffic bandwidth 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 FAQ relative to a passive fiber optic network.

Information structures have stepped very far forward in the last ten years - today you won’t surprise anyone with unlimited broadband Internet at speeds of 10Mbps or more. Modern network construction has quickly expanded beyond the boundaries of cities - backbone network construction is actively developing. And if with highways everything is more or less clear (we laid them - we sell them), then in the cities a different situation is now observed: there is a tough struggle for consumers of provider services. Cities are completely divided into sectors, which are entirely controlled by a specific provider. Under such conditions, the expansion process client base seriously hampered by the fact that, in simple terms, there are no more clients. You can compete only by improving the quality of service (including the use of FTTx technology, and specifically FTTB and FTTH), but even here competition is no longer possible - any, even the smallest provider, is able to lay fiber to the entrance. As a result, everyone was faced with the following problem: “There is no one to connect, there is nowhere to expand.”

But in fact, the situation is not as bad as it seems, because man is a very unique animal and lives everywhere, including outside the city. Villages, towns, villages - there are plenty of clients, and everyone wants (in comparison with mobile or satellite analogues) fast, high-quality and relatively cheap Internet (as well as television and telephone, and, preferably, in one box). The problem of connecting such clients is their remoteness from the main switching nodes and, as a result, the high cost of connection and serious problems with maintaining the network infrastructure of a remote area in working order.

Many providers have attempted to use the already established “urban type” FTTH (Fiber To The Home) model to provide users with their services - we throw in a multi-fiber cable, install active equipment - everything works. It’s just expensive, inconvenient and scary - the intermediate equipment stands anywhere, washed by rains, winds, eaten by insects and spotted by birds. In addition, active network equipment is subject to the influence of two factors that are not subject to any statistics or logic: thunderstorms and those who like to use wire cutters. And everything would be conveniently solved by construction office premises, but expensive, problematic (from the bureaucracy) and not always possible. And then the alternative PON technology, which had been dormant for the time being on the shelves, entered the network building scene.

PON(English: Passive Optical Network) is a fast-growing, most promising technology for broadband multiservice multiple access over optical fiber, using wave separation of reception/transmission paths and allowing the implementation of a single-fiber tree-like point-to-multipoint topology without the use of active network elements in branching nodes. In other words, few fibers, no intermediate active equipment, zero (well, almost zero) influence of weather conditions, convenient WDM data transmission system from the “Internet production factory” to the client and back over one fiber. Active equipment in this network is available only on the provider’s side (in a clean, dry and cool server rack) and on the subscriber’s side (in the attic, in the hallway, on a good old pole, etc.). Ideal for both remote sparsely populated areas and the urban private sector.

1.2 Types of PON.

Even at a time when all the forces of the best minds of our compatriots were aimed at “cutting up” the Superpower, a group of several European telecommunications companies created a consortium to implement the idea of ​​multiple access over a single fiber, called FSAN(Full Service Access Network). The goal of FSAN was to develop common guidelines and requirements for PON equipment so that equipment manufacturers and operators could coexist together in a competitive PON access system market. The result of FSAN's work was a number of PON standards:

ITU-T G.983

APON (ATM Passive Optical Network);

BPON (Broadband PON);

ITU-T G.984

GPON (Gigabit PON);

IEEE 802.3ah

EPON/GEPON (Ethernet PON);

IEEE 802.3av

10GEPON (10 Gigabit Ethernet PON);

APON and BPON were obsolete at birth, GPON is not very developed due to its high (relative to GEPON) cost, as well as the organic reluctance of many to work with 2.5G speeds, 10GEPON is still in the development/debugging/testing stage. There is also EPON, which is no longer interesting to anyone (100Mbps is now enough for only a dozen users, and the price of the equipment is not much different from its older brother GEPON). As a result, only GEPON remains, which today meets the requirements of most providers for connecting remote subscribers (the round-trip transmission speed is 1Gbps, and up to 64 network end devices can be located on one fiber).

1.3 Operating principle of GEPON.

As already written above, GEPON is a full-fledged network built on passive optical components throughout the entire distance from provider to subscriber.

Installed on the provider side OLT(English: Optical Linear Terminal - Optical Linear Terminal) - L2 switch with all the ensuing functionality, having Uplink ports (for connecting your loved one to the L3 router) and Downlink ports (for client needs). OLT from the award-winning Chinese manufacturer BDCOM, for example, has 2 optical gigabit Uplink ports, 2 “combo” gigabit Uplink ports (2 optical + 2 copper), and 4 gigabit Downlink PON ports. OLT is managed both through the terminal port and using everyone’s favorite protocols such as SNMP, SSH and TELNET.

Set on the client side ONU(English: Optical Network Unit), which is also sometimes called ONT(English: Optical Network Terminal) is a full-fledged VLAN switch of small size. ONU from the same BDCOM standardly has one optical gigabit port and 4 copper ports (100Mbps or 1Gbps). There are ONU models with a combined optical port for television and data, with ports for telephony (SIP), with a different number of copper ports, with a Wi-Fi adapter, and also combinations of all of the above. Each ONU has a built-in MAC address filter; When receiving a packet, the ONU checks the ownership of the packet and, if the packet does not belong to it, discards it. ONU management occurs directly from the OLT, while the OLT considers the ONU to be a “subport” of its port, which has its own ports, that is, the following hierarchy is observed: OLT port -> ONU No. -> ONU port.

Between the client and the provider there is a passive optical network, which has tree topology and its derivatives. The main components of a passive optical network are optical fiber and splitters(English Splitter - separator), operating in the “splitter” mode in the provider->client direction and in the “mixer” mode in the opposite direction. The undoubted advantage of passive equipment is its independence from power supply and ease of operation (no need to configure anything): “Once installed, I’ll use it all my life.”

Figure 1 – Schematic diagram of PON connection

Passive optical network is environment shared between many subscribers, therefore the OLT acts TDM(English Time Division Multiplexing - Temporary Multiplexing), and from the ONU side - TDMA(English Time Division Multiple Access - Multiple Access with Time Division). In this case, the downward flow (we will call it the flow from OLT to ONU) is transmitted at a wavelength of 1490 nm, and the upward flow (flow from ONU to OLT) is transmitted at a wavelength of 1310 nm. This was done in order to leave room for CATV (analog television), which can also be routed through the PON tree to the subscriber. CATV transmitters broadcast at a wavelength of 1550nm or 1310nm, but GEPON equipment manufacturers took the 1310nm wavelength for UpStream in order to reduce the cost of the client device as much as possible (lasers emitting at a wavelength of 1310nm are much cheaper than lasers emitting at a wavelength of 1550nm).

The cost of laser GEPON transceivers is quite high compared to their Ethernet counterparts, and for good reason: they are very powerful. The optical budget of a GEPON system (the difference between the emitter power and the maximum sensitivity of the receiver) is about 30 dB (for ONU this figure is in the range of 25-30 dB, for OLT – 32-37 dB)! This budget is enough to “break through” more than 100 km of standard optical fiber! However, PON trees usually reach a depth of 10-15 km, with a depth limit of around 20 km. This is due to the fact that dividers introduce enormous attenuation into the line (from 3 to 22 dB), providing branching and saving fiber.

It is worth noting that the GEPON standard is somewhat different from the usual Ethernet frame structure, so “non-GEPON” devices will not work in the PON network. Moreover, the IEEE 802.3ah standard was adopted relatively recently, and almost none of the manufacturers comply with it 100% (and many don’t really want to). Because of this, there is no full cross-platform compatibility of the equipment (for example, OLT from ZYXEL will not work with ONU from HUAWEI, or OLT from HUAWEI will not reveal its full potential when working with ONU from BDCOM).

The technology of data exchange between ONU and OLT should be separately considered:

• any ONU broadcasts only at the time allocated for it by the OLT;
• for any ONU in the network, the OLT determines the time period during which the ONU can broadcast;
• the newly connected ONU interacts with the OLT using the protocol MPCP(English Multi-Point Control Protocol - Multipoint Exchange Control Protocol);
• Any ONU cannot communicate with other ONUs without the OLT participating in the communication. All packets for any recipient are centrally processed by one device on the network - OLT.

Figure 2 – Distribution of time intervals between ONUs

MPCP. This protocol is based on two Ethernet messages: GATE And REPORT. The GATE message is sent from the OLT to the ONU and is used to assign a temporary domain. The REPORT message is used by the ONU to inform the OLT of its status (buffer full, etc.) to help it make the correct decision about temporary domain allocation. Both GATE and REPORT messages are frames MAC control(type 88-08).

Exists two MPCP operating modes: auto-detection (initialization) and normal mode RTT(English: Round Trip Time - time from the moment the request is sent until the response is received) and the MAC address of this ONU. Normal mode is used to assign temporary domains to all initialized ONUs.

Standard Ethernet frames in PON are slightly modified to suit the specifics of operation in a shared TDM environment, however, OLT modifies outgoing packets so that outlet a standard Ethernet stream is obtained from PON. In the opposite direction the situation is similar. The structure of the standard Ethernet frame (IEEE 802.3), PON frame (IEEE P802.3ah) and IEEE P802.3ah control frame is shown below (Figure 3):

Figure 3 – Comparison of IEEE 802.3 and IEEE P802.3ah frame fields

The preamble of a standard Ethernet frame (Figure 3a) is modified by adding several service fields (Figure 3b):

• SOP(English Start Of Packet) – 1 byte, indicates the beginning of the frame;
• Reserve field, 4 bytes;
• LLID(English Logical Link Identifier) ​​– 2 bytes, indicates the individual identifier of the EPON node. Remains open question: How many identifiers can an ONU subscriber node have - one or several? LLID is required to emulate point-to-point and point-to-multipoint connections in an EPON network. The first bit of the field indicates the frame transmission mode (unicast or multicast). The remaining 15 bits contain the individual EPON node address;
• CRC(English: Circle Redundancy Check) – 1 byte, preamble checksum (P802.3ah standard).

When a frame leaves the GEPON network, the frame preamble is converted to a standard form - the tag is eliminated. For example, in the forward stream, the OLT modifies the preamble of each 802.3 frame entering the PON, in particular, a special LLID tag is added to the preamble. This tag is retrieved by the corresponding sublayer on the ONU, where the preamble reconstruction occurs. The ONU is in normal operating mode, i.e. when already registered, processes only those frames whose preamble LLID matches its own LLID. The remaining fields of the EPON frame are the same as those of a standard Ethernet frame:

• D.A.(English Destination Address) – 6 bytes, indicates the MAC address of the destination station. This can be a single physical address (unicast), a group address (multicast) or a broadcast address (broadcast);
• S.A.(English Source Address) – 6 bytes, indicates the MAC address of the sender station;
• L/T(English Length/Type) – 2 bytes, contains information about the length or type of frame;
• Data field, variable length;
• PAD(filler) – the field is used to fill the frame to the minimum size;
• FCS(English Frame Check Sequence) – 4 bytes, frame checksum calculated using cyclic redundancy code;
• OpCode(English Optional Code) – 2 bytes, specifies the type of control frame. There are two categories of control frames, distinguished by the value of this field: the GATE message generated by the OLT and the REPORT message generated by the ONU;
• T.S.(Time Stamp) – 4 bytes, contains the sender’s timestamp;
• message– 40 bytes, this field actually contains service information necessary for the operation of the MPCP protocol.

More detailed information information about the logical operation of PON can be found at http://book.itep.ru.

OLT and ONU provide data encapsulation in modified Ethernet frames of the IEEE P802.3ah standard, using 8B/10B channel encoding (8 user bits are converted to 10 channel bits).

The final operation algorithm of the PON network after configuration is as follows:
- ONU “listens to the line”;
- OLT receives the IEEE 802.3 standard packet from the upstream device and modifies it to the IEEE P802.3ah standard;
- OLT sends the packet to a specific destination (ONU);
- All ONUs receive the packet, but only the recipient keeps it - the rest discard the packet;
- ONU modifies the IEEE P802.3ah standard package to the IEEE 802.3 standard and sends it to the client PC;
- ONU from the client PC, modifies them from the IEEE 802.3 standard to the IEEE P802.3ah standard and buffers them;
- OLT allows data transmission to a specific ONU;
- ONU broadcasts for a certain amount of time, and then goes silent and “listens” to the line again;
- The OLT receives an IEEE P802.3ah standard packet from the ONU, modifies it to the IEEE 802.3 standard, and then transmits it to the upstream device.

The algorithm for the PON network to convert packets from one standard to another can be represented as follows (Figure 4):

Figure 4 – PON algorithm for packet conversion

1.4 Comparison of PON with the classic FTTH subscriber connection scheme.

In classic FTTH, to connect, for example, 256 subscribers in the private sector, 256 optical fibers are needed. 256 fibers means a lot of very thick and expensive cables, as well as a whole bag of problems associated with their installation, switching and other unbearable routine.

In order for traffic to “travel” along these fibers, N switches are needed: N-1 access switches (subscribers will connect to them) and one for aggregating traffic from access switches. To solve the current problem, for example, the well-known D-Link DES 3200-28F needs 11 pieces (for access), the D-Link DGS 3120-24SC needs one (for aggregation). Add to all this SFP modules, media converters, as well as problems with powering all these devices (what did you think?!), placement (yes, under a roof, warm and dry!) ​​and administration - and the headache no longer goes away .

Now imagine all this not in an urban environment (where any attic is almost a server room, and any basement is a safe haven for outputting optics), but in the harsh conditions of the private sector (without ubiquitous power lines, without a developed sewage infrastructure, without free premises for placement of active equipment)! And if you count how much fiber lies as dead weight (they removed one fiber from an 8-fiber cable, sent it to the subscriber, and then this fiber is used no more often than solar eclipses occur) - you become sad and give up.

When using GEPON, for the same task you need only 4 fibers, one OLT with SFP modules (8 pieces, 4 of them on Ethernet UpLink, 4 on PON DownLink), 256 ONUs (one for each client, they are powered directly from the client socket and that’s all happy), as well as a set of splitters and PON boxes (or couplings) for working with the cable and placing these same splitters, and sometimes the ONUs themselves, in them. The administrator’s work will be reduced only to managing the OLT (ONUs are logically a “continuation” of the OLT’s GEPON ports). Power supply is available only on the subscriber side and in the server room. Everything is simpler, isn't it?

In addition, you should take into account the fact that it is easy and simple to launch analog TV on an already built PON circuit (Figure 5):

Figure 5 – Application of PON as a medium for using CATV

So, the positive aspects of PON:

• Minimal use of active equipment;
• Minimization of 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 GEPON technology, it is necessary to take into account its features, especially in comparison with point-to-point lines: the bandwidth shared between subscribers (the shared environment may not be suitable for the client from a security point of view), passive splitters make it difficult to diagnose the optical line , a malfunction of one subscriber’s equipment may impact the work of the others, with less benefit if implemented at the construction stage.

Figure 2 – Distribution of time intervals between ONU

To support the assignment of temporary domains using OLT, the IEEE 802.3ah group developed a protocol MPCP. This protocol is based on two Ethernet messages: GATE And REPORT. The GATE message is sent from the OLT to the ONU and is used to assign a temporary domain. The REPORT message is used by the ONU to inform the OLT of its status (buffer full, etc.) to help it make the correct decision about temporary domain allocation. Both GATE and REPORT messages are MAC control frames (type 88-08).

Exists two MPCP operating modes: auto detection(initialization) and normal mode. Auto-detection mode is used to detect newly connected ONUs and determine RTT(English: Round Trip Time - time from the moment the request is sent until the response is received) and the MAC address of this ONU. Normal mode is used to assign temporary domains to all initialized ONUs.

Standard Ethernet frames in PON are slightly modified to suit the specifics of work in a shared operation TDM environment, however, OLT modifies outgoing packets so that outlet from PON it turns out standard Ethernet flow. In the opposite direction the situation is similar. Structure of the standard Ethernet frame (IEEE 802.3), PON frame (IEEE P 802.3 ah ) and control frame IEEE P 802.3ah shown below (Figure 3):

The constant development of technology makes it possible to connect the Internet to apartments at ever higher speeds. One of the methods of such connection is Gpon technology, which is also offered by Rostelecom.

Gpon – general job description

Passive optical technologies (Pon) appeared not very long ago, but are confidently replacing traditional ways organization of Internet access, working on copper cables. Optical cable has huge advantages over copper cable:

The "G" prefix assumes that the connection is at gigabit speed. This technology is called passive because there is no active network equipment between the provider’s node and the end consumer, and the optics are laid directly into the client’s apartment.

No equipment is required, because the length of the optical cable without additional signal amplification is up to 20 km, and in the near future developments are underway to increase the line to 60 km.

The connection can be carried out in synchronous and asynchronous modes. Typically, providers prefer asynchronous mode. Maximum speed limited to 2.5 Gb/s for reception, and 1.25 Gb/s for information transmission.

The principle of connecting to Rostelecom

In order to connect, a future subscriber must contact the nearest Rostelecom office and leave a request. You can connect one or more services to choose from:

• Internet;
• City (landline) telephony;
• IP TV.

Any connection to a provider via wire requires additional costs.

Those clients who were previously connected to Rostelecom via ADSL technologies, know this from their own experience, new subscribers will be told about this when submitting an application.

The main difficulty is the installation of the cable, which, due to its specific qualities, is not desirable to be strongly bent, so usually all equipment is installed in the hallway. The equipment includes a special ONT router designed to operate in fiber optic networks, which you can rent directly from the provider or buy yourself. It is advisable that an electrical outlet be installed in the hallway. The end devices are connected via a conventional twisted-pair Ethernet or via WiFi.

Gpon network diagram provided by the provider Rostelecom.

After technical issues are agreed with the client, a router is purchased, a service contract is concluded. The cable is being installed, laid, and the router is configured.

Setting up connection equipment

If the router is purchased or rented from Rostelecom, then its initial configuration is carried out during installation directly by Rostelecom employees. In cases where the subscriber is buying a router himself or he already has equipment, the configuration options may vary depending on the model and manufacturer of network equipment, as well as on its capabilities. You can find plenty of information on the Internet with step by step instructions, which you can use to configure it yourself.

Rostelecom offers its customers several models of ONT devices, one of which is G PON ONT RFT620. This is a fairly successful and versatile model that allows you to connect up to 4 devices to the LAN, and an unlimited number via wireless technology, it is possible to watch streaming TV, and connect up to 2 landline phones.

All settings are made through the web configurator. To do this, you need to type in the browser the address " 192.168.1.254", And enter the username and password: user / user. You do not need to drive in any Internet settings, this is already done by the provider. You just need to configure your home network to suit your needs:

• turn on the wireless WiFi module;
• change security settings;
• set static or dynamic IP addresses, etc.

Services and packages

Rostelecom offers its customers many different options and service packages, the most popular of which are the following:

• home Internet via fiber optic line with a choice of connection speed;
• interactive TV with more than 160 channels;
• home landline phone, with a choice of tariff for calls;
• mobile telephony;
• rent an ONT router at a low price.

All these services can be selected separately or combined into packages. The monthly subscription fee will also depend on the choice. The company conducts permanent promotions and discounts, information about which can be found on their portal. Also, for each region separately, the price for services is different.

Pros and cons of connecting using Gpon technology

Connecting via GPON, like any other method, has its positive and negative sides. The positive ones include the following:

• The cable is pulled directly between the provider's PBX and into the user's apartment, i.e. There are no intermediate nodes, which significantly increases the speed of information transfer and signal stability.
• The signal in a fiber optic cable is transmitted not by electrical, but by light pulses. This means that there is no danger of injury from electric shock at all.
• The ability to connect several services at once, through one ONT device.

There are, of course, disadvantages to this connection method:

• The optical cable is very susceptible to sharp bends, which means that it will be difficult to route it around the apartment to distant rooms. It is also not recommended to place furniture and other heavy objects on the cable.
• Although there is nothing valuable for sale in the cable, main lines and wiring in entrances are constantly under threat from vandals.
• The cable does not transmit electricity, which is why animals are of increased interest in it. It is advisable to hide it in a box.

GEPON Technology

IN this material We will talk about 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 for traffic aggregation - optical splitters - and high density ports.

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 (in Lately also in high resolution version). 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 growth in the number of connected users and the launch of the first Russian fiber to the home (FTTH) projects based on PON shows that the technology has taken root here too.

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. 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 sides 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 . 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

Recommended prices for GEPON equipment
Model	Cost ($)	Cost per subscriber ($)
ONU-631HA-11/12	372/454	372/454
ONU-634HA-11/12	388/502	388/502
OLT-1308	23 939	47
OLT-1308H	23 283	46
OLT-2300M/OLC-2301HA-12	1 317/2 670	90 (for 512 subscribers)

To build a network, you will also need splitters (approximate cost - from 400 rubles for 1x2 to 4000 rubles for 1x8, there are also 1x32 models), a single-mode optical cable (the cost is equal to the price 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, the ZyXEL company today offers a full line of GEPON devices, allowing you to create optical networks of any scale with all necessary systems management and technologies for increasing reliability.

In recent years, the speed of Internet access has increased significantly, which was due to the requirements of new services and resource-intensive applications that can only work correctly with a PON connection from Rostelecom. For this reason, fiber optic technologies have been introduced which can support the current demand for bandwidth.

PON technology from Rostelecom

Thanks to high speed data transfer, the responsiveness of networks with PON technology from Rostelecom is of greatest importance in comparison with other types of connections and will be an excellent solution for connecting large companies to the Internet.

At the moment, market speed requirements are quickly approaching the 100 Mbit/s mark, and according to forecasts they will reach 1 Gbit/s for the mass consumer. Only optical cables have the ability to maintain these high performance over the long distances that are necessarily present between the provider and the user.

Already, FTTH (Fiber to the Home) bandwidth is available to service providers, delivered to the home. The new architecture will serve as the foundation for access networks that will meet consumer demands for many years to come.

Deploying FTTH access networks is not a cheap task and in most cases requires labor-intensive construction work for laying cables to consumer homes. Even though the cost of fiber optics has dropped in recent years, the cost of the connection itself still hasn't gotten significantly lower.

Interesting! FTTH networks have evolved over the years in search of the optimal cost-effective solution. In the early stages, paired optical fiber was used - transmission / reception. It was expensive and required complex installation.

The development of wavelength division (WDM) technology, which uses a single fiber for incoming and outgoing traffic, has greatly improved the situation.

Eventually, the first of the FTTH networks moved to the new standard, where a single fiber is connected to a passive optical splitter that distributes the signal to multiple subscribers.

This standard became the PON technology now used by Rostelecom. It can support 1:64 signal splitting from a single fiber. In addition, PON technologies of the telecommunications operator Rostelecom also include additional signals that provide analog and digital television services to users without the need to use them through IP set-top boxes.

Advantages of the Internet using PON technology from Rostelecom

The obvious advantage of Rostelecom's PON Internet in general is that one common optical fiber can support many users through inexpensive passive optical splitters, which will allow the network to remain responsive with up to 64 users.

It does new technology attractive not only to consumers, but also to service providers looking to replace copper networks in dense urban areas.

Advantages and features of PON networks include:

• no need for active equipment in the access network, which prevents electromagnetic interference;
• reduction of equipment and fiber in the central office.

PON equipment from Rostelecom provides greater bandwidth and supports double distribution ratio. This means that with a 64-lane distribution, each subscriber receives an impressive connection throughput of about 35 Mbit/s. If the service provider decides to implement lower allocation factors, such as 16 or 32, subscribers will be able to receive even more bandwidth.

Higher transmission speeds become available to users by increasing the efficiency of using the bandwidth of the PON standard. Moreover, this technology is designed to provide multi-service services (data, video and voice), not just high speed access in Internet.

Interesting! As PON speeds increase on the line, the split ratios also increase, allowing for maximum flexibility and cost advantages for service provider deployment.

Modems for PON connection from Rostelecom

GPON was developed by ITU-T as an industry-wide interchangeable standard. This means that devices such as ONT can work correctly with PON modems from any manufacturer that supports the services of Rostelecom or other operators.

This factor is very important in reducing equipment costs and allows service providers to provide profitable terms for its subscribers. Additionally, updated technology based on XGPON standards improves network performance to 10 Gbps while maintaining backward compatibility with already deployed networks.

Equipment setup

PON equipment from Rostelecom does not require complex configuration, since all the main parameters in most cases are already set by the provider. Once you connect the router, you only need to personalize the software. However, in some models Wi-Fi routers that support PON technology from Rostelecom, you will need to set the wireless network settings and also enter connection parameters. The latter, when using optical fiber, are the username and password of the PPPoE type user. The provider provides this information in the concluded contract.

If all settings are in software The router from Rostelecom is entered correctly, but the PON indicator on the equipment is red, the problem most likely lies in the provider’s wiring. To resolve this, you must contact your operator.

Attention! Before making a call to Rostelecom and submitting a request to call a technician to fix the problem, it is recommended to check all the basic connection parameters on the router, as well as the integrity of the cable section located in your premises.

Current and future demands for Internet access bandwidth have led to widespread deployment of FTTH technologies. PON connections provide flexibility and cost advantages. These factors allow the provider to provide quality services according to favorable rates for its subscribers.