3.1.1 The main function module SDH networks
The main function module is a multiplexer SDH networks. The term itself is used as a multiplexer for the multiplexers that are used to build (multiplexing) a high speed flow of the low-speed and disassembly (demultiplexing) the high-flow in order to separate low-speed streams.
SDH multiplexers in contrast to conventional multiplexers are used, for example, in the PDH network, as a function properly operate the multiplexer and the terminal access function devices, allowing low-speed channels PDH connect directly to their input ports. They are more versatile and flexible devices that perform tasks other than multiplexing and switching problems still, concentration and regeneration. Accepted, however, to distinguish two main types of multiplexer: terminal multiplexer and the multiplexer input - output.
Terminal Multiplexer (TM) is a multiplexer and terminal SDH network with the access channels, the appropriate tribes PDH and SDH. TM can be administered or channels, that is, switch them with tribnogo interface input to line input or output channels, that is, switch them with a linear input to output tribnogo interface. Typically, this is limited to switching tribes 1,5 and 2 Mbit / s.
Another important feature of the multiplexer is the presence of two optical line outputs (reception / transmission channels), called aggregate outputs and used to create one hundred percent redundancy mode, or the protection of 1 + 1 in order to increase reliability.
The multiplexer input / output (ADM) has the same inlet tribo set as a terminal multiplexer. It allows you to enter and display the corresponding channels. In addition to switching capabilities provided by TM, the ADM allows a through switching output streams in both directions, as well as to the closure of the channel on the receiving channel on both sides in the case of failure of one of the directions. Finally, it allows (in case of accidental failure of the multiplexer) to skip the main optical flow by themselves in the bypass mode.
Consider options for the acquisition of synchronous multiplexers: SDM-1 (ECI Telecom, Israel), SMA-1 R2 (Siemens, Germany) and FOX-1640 (Alcatel, Germany). The comparison results are summarized in Table 1 [PV].
Currently, due to the high saturation of the market of telecommunications, equipment selection problem ceases to be purely technical and economic challenge and becomes a component of policy makers in relation to suppliers.
In this thesis project we propose to use the SDM-1 equipment company ECI Telecom (Israel), because this site is part of a single zone network route Stepnogorsk-KOCshetau.
Multiplexer SDM-1 consists of the following sections (Table 3.1):
Table 3.1-SDM-1 multiplexer Sections
| Name of section | Design |
| TR #1 - TR #8 | board component interfaces |
| ATR | two transmitter / receiver aggregate fee including: optical charge - ATRO and electrical charge - ATRE; |
| SPU | two SDH processing unit |
| MCP4 | the control Multiplexer processor (with integrated non-volatile memory NVM); |
| COM | connection fee |
| AMU1 | block signaling and notification service |
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Each SDM-1 is a unit located on the same shelf, which may contain from 21 to 63 component interfaces with a transmission speed of 2 Mbit / s, three - 34 Mbit / s, three - 45 Mbit / s, one - 140 Mbit / s or one - 155 Mbit / s (STM-1), and certain combinations of these interfaces. Since STM-1 standard allows a maximum of 155 Mbit / s aggregate line, the number of supported component interfaces (with protection) in a given moment of time is more limited: either 63 to 2 Mbit / s, three 34 Mbit / s, three 45 Mbit / with one 140 Mbit / s, a completely filled 155 Mbit / s, four partially filled with 155 Mbit / s, or some combination of these interfaces, in an amount not exceeding the STM-1 rate.
Using two modular line in an unprotected mode, you can increase the total number of supported component interfaces. In addition, SDM-1 provided more bandwidth can serve the purpose of dynamic allocation in response to changing traffic requirements.
Aggregate interfaces provide access to the lines connecting the mounting location of various SDM-1. The interface works with SDH data rate STM-1 (155.52 Mbit / s). When combined with a fiber-optic cables 1 from one another SDM SDM system 1 located in a remote location using optical aggregate interfaces. At shorter distances in this connection, instead you can use the optical electric aggregation channel.
Eight slots provided for component boards. Additional fees may give the opportunity to save on administrative costs because the network provider can place these or other additional fees in the system and enter them into operation as the demands from the traffic.
SDM-1 is monitored and controlled by the CPU, which communicates with the various parts of the system and the outside world. The system software is stored on the memory card that allows you to frequently and easily update the software by downloading from a remote source. Software communication management software is based on a seven-element model of OSI, working in a UNIX environment.
In normal operation, the system synchronizes to choose the source of synchronization. With this source connected a voltage controlled crystal oscillator, which generates an internal clock signal to SDM-1, and the time for SDH transmission line. This source can be an external timer signal, a component signal or SDH line signal. If synchronization sources are unavailable, SDM-1 is able to maintain standby mode with the stability of 4,6 ppm (parts per million).
SDM-1 is powered -48 or -60 VDC from the external battery system. The system's power structure implemented the principle of distributed architecture, ie, each card has its own built-in power supply. This achieves low cost and low power consumption in a partially filled SDM-1 configurations.
An important property of sequentially implemented in the system is its modularity. As already mentioned, all the component boards are completely interchangeable, and therefore can be installed in the same slots, regardless of the exchange rate supported by them.
SDM-1 architecture is similar to the architecture of the SDM-4 company ECI Telecom, which provides a family of products that are compatible with each other, and cost-effective in terms of maintenance and spare parts. Most boards are interchangeable with boards SDM-4, which makes it easy to modify the system.
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Proposals on Timing of SDH network sources listed at the end of the explanatory note [PG].
3.1.2 Proposal for the selection of the radiation source and photodetector
There are two types of semiconductor light sources, light emitting diodes and lasers. For the fiber optic portion of Stepnogorsk KOCshetau, you need to select as a radiation source laser.
The laser has a high speed and a narrow spectrum width. From the family of semiconductor lasers is best to choose lasers with distributed feedback. These lasers operate in single-frequency mode, the emission spectrum width is less than 0.5 km. Temperature instability wavelength lasers with distributed feedback amounts to about OD km / k. The level of the output radiation, lasers powerful version highly varies within 3 to 6 dB m.
As the photodetectors in optical fiber communication systems using semiconductor p-i-n photodiodes and avalanche photodiodes. These devices are small and fairly well joined to optical fibers. The p-i-n photodiodes each absorbed photon creates a pair of "electron-hole". In avalanche photodiodes internal amplification of the signal occurs, since they are designed so that they formed a region with a strong electric field E (3 x 106 V / cm). In this field, the electrons generated by the light, are accelerated to energies sufficient to impact ionization of atoms of the crystal lattice. The resulting ionization of the free carriers is also accelerated and give birth to a new pair. This avalanche process leads to the fact that the absorption of a photon generates more than one electron-hole pair, and the tens and hundreds. Thus, by using a highly sensitive avalanche photodiodes as photodetectors version designed for fiber optic link, you can change the input level from - 39 to -17 dBm.
Using lasers with distributed feedback and avalanche photodiodes can get quite large regeneration areas that allow IUU fishing to place in the settlements. In Kazakhstan, the distance between the settlements can be up to 250 km. In this case, the power transmission system margin may be insufficient for covering this distance. In such cases it is possible to use optical amplifiers and preamplifiers.
The main equipment optical amplifying element is an optical waveguide fiber doped with erbium. Figure 1 shows a functional block diagram of an optical amplifier [PD].
Figure 2 is a functional diagram of an optical preamplifier. The input optical signal in a location with the pumping laser beam enters the optical fiber doped with erbium, wherein the light energy is redistributed between radiations [PD].
Further, through the optical isolator radiation enters the optical bandpass filter tuned to the operating wavelength, wherein the removal of parasitic modes occurs.
The input level varies from -45 dB to -15 m. In the case of using an optical preamplifier is used as a photodetector APD power standard. The output level changes from +12 to +15 dBm.
An optical preamplifier used in conjunction with an optical amplifier, while the optical amplifier can be used separately.
