Digital transmission systems: from HDSL to G.shdsl. About SHDSL Technology

Technology that provides symmetrical duplex data transmission over a pair of copper conductors. It is mainly used to connect subscribers to the provider's access node (the so-called last mile). The main ideas are taken from HDSL2 technology.

According to the standard, SHDSL technology provides data transmission at speeds from 192 Kbps to 2.3 Mbps (in 8 Kbps increments) over one pair of wires, respectively, from 384 Kbps to 4.6 Mbps.m. for two couples.
When using TC-PAM 128 encoding methods, it became possible to increase the transmission rate to 15.2 Mbps over one pair and up to 30.4 Mbps over two pairs, respectively. [ ]

Work on G.shdsl began in 1998 at the International Telecommunication Union (ITU-T), and in February 2001 it was adopted as the G.991.2 standard. ETSI is also involved in the European version of this standard, now it is formalized in the form of specification TS 101524.

Technology features

G.shdsl was based on the ideas of HDSL2, which were further developed. Using HDSL2 line coding and modulation, it was possible to reduce the impact on adjacent ADSL lines at speeds above 784 Kbps. Since the new system uses more efficient line coding (TC-PAM) compared to 2B1Q, the SHDSL signal occupies a narrower frequency band at any rate. Consequently, the interference from the new system to other xDSLs is less powerful than the interference from HDSL 2B1Q. G.shdsl also has a signal spectral density shape that provides near-perfect compatibility with ADSL signals.

Single-pair SHDSL options offer significant hardware cost and hence product reliability benefits over two-pair options. The cost is reduced by 30% for modems and 40% for regenerators, since each pair requires an HDSL transceiver, line circuits, protection elements, etc.

To support clients of various levels, it was decided to make it possible to select the signal transfer rate. Thanks to this, operators can build a marketing policy that is closest to the needs of customers. In addition, it is possible to achieve an increase in the transmission range without the use of regenerators by reducing the speed. At maximum speed (for 0.4 mm wire), the operating range is about 3.5 km, and at minimum speed, over 6 km. It is also possible to use two pairs at the same time, which allows you to double the top speed. Currently, the maximum stable data transfer rate over a single copper pair reaches 15296 Kbps.

see also

Notes

Links

• ITU-T Recommendation G.991.2: Single-pair high-speed digital subscriber line (SHDSL) transceivers

Data transmission at speeds from 192 Kbps to 2.3 Mbps (in 8 Kbps increments) over one pair of wires, and 384 - 4.6 Mbps over two pairs.

Technology features

Links

• ITU-T Recommendation G.991.2: Single-pair high-speed digital subscriber line (SHDSL) transceivers
• Seagrand: the fastest SHDSL modem - 15.2 Mbps over one pair

see also

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See what "SHDSL" is in other dictionaries:

- (Single pair High speed Digital Subscriber Line, ITU G.991.2) - one of the xDSL technologies that describes the method of signal transmission over a pair of copper conductors. It is mainly used to solve the problem of the "last mile", i.e. connecting subscribers with ... Wikipedia

SHDSL- Saltar a navegación, búsqueda EL SHDSL (Single pair High speed Digital Subscriber Line, Línea digital de abonado de un solo par de alta velocidad) ha sido desarrollada como resultado de la unión de las diferentes tecnologías DSL de conexión… … Wikipedia Español

SHDSL- (Single pair High speed Digital Subscriber Line) ou Ligne Numérique d Abonné Symétrique à très haut niveau de transmission sur des distances plus grandes que les autres technologies DSL. Elle permet de relier des utilisateurs situés à plus de… … Wikipédia en Français

SHDSL- SDSL (Symmetric Digital Subscriber Line) ist eine DSL Zugangstechnik zu einem öffentlichen digitalen Netzwerk wie beispielsweise dem Telefonnetz über eine Telefonleitung. Im Gegensatz zu ADSL lassen sich Daten mit der gleichen Geschwindigkeit in… … Deutsch Wikipedia

SHDSL- ● en sg. m. NORM Symmetric High bitrate DSL. DSL avec un debit garanti de 2.3 Mbps sur une simple ligne telephonique … Dictionnaire d "informatique francophone

G.SHDSL

G.SHDSL- (Global Standard for Single Pair Highspeed Digital Subscriber Line) ist eine symmetrische DSL Übertragungstechnik in digitalen Weitverkehrsnetzen. Bei G.SHDSL werden die gleichen Datenübertragungsraten im Up wie im Downstream über eine oder zwei… … Deutsch Wikipedia

SHDSL (Single pair High speed + DSL), G.shdsl, ITU G.991.2 is one of the xDSL technologies that provides symmetrical duplex signal data transmission over a pair of copper conductors. It is mainly used to connect subscribers to the node ... ... Wikipedia

G.991.2- SHDSL SHDSL (Single pair High speed Digital Subscriber Line) ou Ligne Numérique d Abonné Symétrique à très haut niveau de transmission sur des distances plus grandes que les autres technologies DSL. Elle permet de relier des utilisateurs situés à ... Wikipedia en Français

ITU G.991.2- SHDSL SHDSL (Single pair High speed Digital Subscriber Line) ou Ligne Numérique d Abonné Symétrique à très haut niveau de transmission sur des distances plus grandes que les autres technologies DSL. Elle permet de relier des utilisateurs situés à ... Wikipedia en Français

1. What is meant by SHDSL?

SHDSL (Symmetric High Speed ​​Digital Subscriber Line) - a symmetrical high-speed digital subscriber line, the most modern type of DSL technology, is aimed primarily at providing a guaranteed quality of service, that is, at a given speed and data transmission distance, ensure an error level of at least 10 -7 even in the most adverse noise conditions.
This standard is an evolution of HDSL as it allows the transmission of a digital stream over a single pair.
SHDSL technology has several important advantages over HDSL. First of all, these are better performance (in terms of the maximum line length and noise margin) due to the use of a more efficient code, a precoding mechanism, more advanced correction methods and improved interface parameters. This technology is also spectrally compatible with other DSL technologies. Because the new system uses a more efficient line code than HDSL, at any rate, the SHDSL signal occupies a narrower bandwidth than the corresponding HDSL signal at the same rate. Therefore, the interference from the SHDSL system to other DSL systems is less powerful than the interference from HDSL. The spectral density of the SHDSL signal is shaped so that it is spectrally compatible with ADSL signals. As a result, compared to single-pair HDSL, SHDSL allows a 35-45% increase in transmission speed at the same range, or a 15-20% increase in range at the same speed.

2. Transfer rate over SHDSL line

To organize access via SHDSL, a dedicated line (a physical two-wire line) is required. The access speed when connecting via SHDSL is determined by technical characteristics, the length of a particular communication line and a specific modem brand, on average, full speed is possible on two-wire lines 1.5 km long. with a copper wire diameter of about 0.4 mm.
SHDSL technology provides symmetrical traffic over a single twisted pair in the speed range: from 192 Kbps to 2.3 Mbps, and over a double pair - from 384 Kbps to 4.6 Mbps.
SHDSL makes it possible to combine disparate local networks into a single corporate network, which allows you to significantly save money and time when exchanging information between enterprise branches, providing a sufficient level of information security for the corporate network. SHDSL allows you to organize video conferences when you need to maintain the same data streams in both directions.
One of the main advantages of SHDSL technology is the ability to use already existing (laid and actually working) copper pairs of wires of subscriber telephone lines, which are available all over the world in a huge amount.

3. Differences between SHDSL and SDSL.

SDSL -Symmetric Digital Subscriber Line - symmetrical digital subscriber line.
Like HDSL technology, SDSL technology provides symmetrical data transmission at rates corresponding to T1/E1 line rates, but SDSL technology has two important differences. Firstly, only one twisted pair of wires is used, and secondly, the maximum transmission distance is limited to 3 km. The technology provides the benefits necessary for business representatives: high-speed Internet access, organization of multi-channel telephone communication (VoDSL technology), etc.
SHDSL - G.shdsl, Singlepair Highspeed Digital Subscriber Line - high-speed symmetrical digital subscriber line for 1 pair.
This technology makes it possible to increase the length of a DSL line up to 20 km (with regenerators) compared to the standards currently used (which limit the length of a subscriber line to approximately 5 - 6 km). It provides data transmission over 1 pair at a speed of 192 Kbps - 2.320 Mbps or over 2 pairs at a speed of 2 times greater.

4. What is meant by the SHDSL standard.

There are three main categories of SHDSL standards today: ANSI (T1E1.4/2001-174) for North America, ETSI (TS 101524) for Europe, and ITU-T (G. 991.2) worldwide. All of these standards have been published and are sustainable. All standard varieties of ADSL (ITU G.992.1, G.992.2, and ANSI T1.413-I2) are built on the same technique - discrete multi-frequency modulation (Discrete Multi Tone - DMT).

5. What is the difference between North American and European standards?

First of all, SHDSL is an international standard. Thus the standard is defined as the specific digital loop conditions that correspond to regionally defined supplementary services (eg T1). However, most equipment will support all international requirements.

6. What is meant by TC-PAM modulation?

TC-PAM technology underlies the first ITU worldwide standard for high-speed symmetric single-pair transmission, G.shdsl. It allows you to select a line rate in the range from 144 Kbps to 2.3 Mbps (8 Kbps step), has a narrower frequency spectrum than its predecessors - 2B1Q and CAP. Thus, a long range and electromagnetic compatibility with other DSL technologies such as ISDN, ADSL, G.lite and analog PCM 15x2 systems (unlike HDB3 and 2B1Q) are provided.
The TC-PAM coding type has the best range and electromagnetic compatibility characteristics to date when operating on single-pair subscriber lines. TC-PAM stands for Trellis Coded Pulse Amplitude Modulation (trellis coded pulse amplitude modulation). The essence of this encoding method is to increase the number of levels (code states) from 4 (as in 2B1Q) to 16 and apply a special error correction mechanism.

7. What is the transmission distance for SHDSL lines?

The data transfer rate using SHDSL equipment can reach 2.3 Mbps over one twisted pair (for "regular" DSL connections - 1.5 Mbps). Moreover, the range of the new standard is claimed to be 30% better than DSL, and because the standard supports repeaters, latency for broadband applications (such as voice and media streaming) must be very low.
This technology makes it possible to increase the length of a DSL line up to 20 km (with regenerators) compared to the standards currently used (which limit the length of a subscriber line to approximately 5 - 6 kilometers). SHDSL provides data transmission over one pair at a speed of 192 Kbps - 2.320 Mbps or over 2 pairs at a speed of 2 times higher. The use of echo cancellation ensures full duplex communication at all speeds.

8. Is it possible to use repeaters in SHDSL lines?

Yes. Additional repeaters can be used for both double pair and single pair. The ITU standard supports up to eight repeaters per pair, which can reduce interference and regenerate signals before they are transmitted to the next segment, which in turn increases the transmission distance.

9. What is meant by "4-wire mode"?

The SHDSL standard supports such an additional feature as the ability to increase the speed and distance of data transmission when using two pairs of wires - "4-wire mode". The load is distributed equally between the two pairs, but data is transmitted simultaneously.

10. Is the SHDSL standard compatible with other DSL standards other than ADSL?

Absolutely. "Symmetrical" variants of DSL (SDSL and HDSL) can be used both to connect companies to the Internet and to transfer traffic between segments of Fast Ethernet networks. Modern xDSL technologies make it easier to solve those tasks where high-speed connections are required: creating an Intranet network in a geographically distributed company, organizing access to transport data transmission networks, etc.

11. What type of protocol does SHDSL technology support?

SHDSL technology supports such protocols as TDM, ATM, Frame Relay, as well as other network protocols. That allows you to build geographically distributed corporate networks, as well as to use as part of solutions related to ensuring guaranteed bandwidth of the data transmission channel (VoIP, video conferencing, etc.).

12. Can SHDSL technologies be used in PBX?

Using high-frequency channel resources and packet technologies such as ATM or IP, integrated access devices with VoDSL functions allow you to organize several (say, 4, 8, 16 or 24) telephone channels simultaneously with a high-speed data stream. VoDSL systems will help traditional operators to solve the problem of installing telephones in the residential sector (as you know, installing a telephone is often impossible due to the lack of a free copper pair) and create attractive offers for business users.

13. Hardware Compatibility

SHSDL technology ensures interoperability of equipment from different manufacturers. To do this, the G.hs.bis (G.844.1) standard was included in G.shdsl, which describes the connection initialization procedure. There are two options for the procedure. In the first case, the LTU equipment (installed on the PBX) dictates the connection parameters to the NTU (client equipment), in the second case, both devices “negotiate” about the transmission rate, taking into account the line state. Given the unknown initial conditions, during initialization, to ensure connection establishment, data exchange is carried out at a low rate, and transmission is carried out using one of the classic modulation methods (DPSK).

14. Benefits of SHDSL technology

SHDSL technology allows both high-speed Internet access and fast and high-quality transmission of a large amount of information. Also, with the help of SHDSL technology it is possible not only to receive information from the Internet, but also to use IP-telephony (urban, intercity, international calls) and video conferencing.

SHDSL is a symmetrical high-speed technology that is a further development of SDSL technology. There are a number of varieties of this technology, of which G.SHDSL can be considered one of the most promising. G.SHDSL allows you to create a standard that ensures the compatibility of different types of equipment from different service providers. G.SHDSL is currently the only symmetrical DSL technology standardized by the International Telecommunication Union (ITU).

Like any symmetrical xDSL technology, G.SHDSL is primarily aimed at the corporate sector, since it is they who need symmetrical access - voice channels, dial-up access to the enterprise network, Internet connection (web servers) and other applications in in some cases, they require the transfer of the same volume of incoming and outgoing flows.

G.SHDSL is based on the basic ideas of HDSL2, which have been further developed. This technology also uses the type of linear signal TC-PAM 16. When encoding for one clock interval of the TC-PAM 16 signal, 4 bits are transmitted, 3 of which are information bits of the original binary signal, and a signal with 16 code states is formed. The formation process is called pulse amplitude-phase modulation with the so-called lattice coding (Trellis coded modulation).

Trellis coding is used as an internal code of the microprocessor that generates the TC-PAM 16 signal. Its advantages are increased noise immunity and reduced signal processing delay. Experience in implementing this technology has shown that the signal-to-noise ratio increases by 3 dB - 6 dB compared to transmission systems using HDSL.

This conversion makes it possible to reduce the transmission rate by a factor of 16, which makes it possible to increase the length of the regeneration section by a factor of 4, while maintaining the normalized requirements for its operating attenuation and the level of transient influences. In addition, when operating on a single multi-pair cable systems using the TC-PAM 16 signal and other DSPs, mutual influences are reduced. It should be borne in mind that in this case, the requirements for limiting the signal level and suppressing its higher harmonic components must be strictly observed. All this allows us to conclude that the use of TC-PAM 16 in the "last mile" technology is promising. In this case, two digital terminal devices exchange data over a conventional telephone line at a speed of up to 2.3 Mbps.

The use of the TC-PAM coding system and frequency offset for downstream and upstream traffic makes it possible to optimally use the allocated bandwidth. It is believed that this modulation method guarantees an almost limiting transmission rate. Unlike 2B1Q or CAP coding used in HDSL, the signal spectrum is localized in a narrower frequency band. This helps to avoid crosstalk (when working together on the same cable) with equipment operating both on other DSL technologies and on G.SHDSL itself.

G.SHDSL makes good use of rate adaptation, which in this case can vary in 8 kbps increments from a minimum value of 192 kbps to a maximum value of 2.32 Mbps, at which the E1 link rate becomes possible. To do this, using a special protocol in the process of establishing a connection, the modems at both ends of the line test the signal transmission conditions. After receiving the test results, the modems exchange messages and determine the maximum transmission rate allowed under given conditions (this is especially important for determining the type of service of the transmitted traffic and the format of the transmitted frames). The maximum connection length (7.5 km at 192 kbps and over 3 km at 2.32 Mbps) is longer than other symmetric xDSL technologies operating at the same transmission rates. The use of echo cancellation ensures full duplex communication at all baud rates.

G.SHDSL provides for the possibility of using two pairs to transmit information simultaneously, which allows increasing the maximum transmission rate to 4624 kbps and provides the necessary level of redundancy. But most importantly, you can double the maximum speed, and this can be achieved when transmitting over a typical symmetrical cable to which the subscriber is connected. The standard limits the maximum delay of digital information in the transmission channel - it is no more than 500 ms. Additionally, it is possible to reduce delays in the channel due to the optimal choice of protocol. For example, for IP traffic, a protocol is established that allows you to refuse the transmission of redundant information.

Unlike ADSL and VDSL, G.SHDSL is the best fit for organizing the "last mile". So, at the maximum transmission rate of a group signal, it can be compressed by 36 voice channels. Whereas ADSL, where the limiting factor is the low transmission rate from the subscriber to the network (640 kbit / s), allows organizing only 9 voice channels, leaving no room for data transmission. Another problem successfully solved in G.SHDSL is the reduction of equipment power consumption. Since one pair is used for remote power supply of intermediate and subscriber equipment, reducing its power consumption can significantly improve the operational parameters of the line.

Compared to two-pair (or four-wire) line construction options, single-pair options provide a significant gain in hardware costs and, accordingly, product reliability. The cost reduction resource is up to 30% for modems and up to 40% for regenerators - after all, each of the pairs requires the inclusion of an HDSL transceiver, line circuits, protection elements, etc. in the hardware complex. It would seem that the new technology solves most of the accumulated problems, and with its implementation, the demand for all other symmetrical DSL solutions will disappear. However, most experts note that G.SHDSL cannot be considered as a complete replacement for existing symmetrical technologies. Most likely, it is their complement. For this reason, in the near future it can be considered the best option to use hardware platforms that can realize the possibility of using all the main technologies within a single system. They will allow the service provider to choose a solution for connecting the subscriber that best suits the existing conditions and tasks to be solved. It is probably not necessary to prove that for the normal operation of the network it is necessary to ensure the compatibility of equipment from different manufacturers. This, in turn, allows the operator and user to easily change the supplier or purchase subscriber and station equipment from different manufacturers. Thus, G.SHDSL is a fairly efficient and economical way to solve the "last mile" problem, and with the help of this technology, various specific tasks can be successfully solved.

G.SHDSL technology is likely to change in its current state - it is known that the ITU (ITU) and the International Standards Institute ETSI are now working on the G.SHDSL.bis specification, which will increase the data rate over a single pair from 2.312 Mbps from up to 3.840 Mbps (Enhanced Modulation Code TC-PAM16) and further up to 5.700 Mbps (TC-PAM32). At the same time, in real operating conditions (taking into account the interference acting on the lines, joint operation with other transmission systems, etc.), the operating range at maximum speed of devices with TC-PAM16 modulation should be about 1.7 km (for a stream of 3.8 Mbps), and with TC-PAM32 modulation - about 800 m (5.7 Mbps).