Introduction
ADSL (Asymmetric Digital Subscriber Line) is a modem technology that is available channel bandwidth is shared between the outgoing and incoming traffic is asymmetric. Since most users have incoming traffic volume is much higher than the volume of outgoing, the rate of outgoing traffic is significantly lower. This restriction was uncomfortable with the spread of peer-to-peer networks and video.
History of development
History of the development of ADSL technology started in the second half of the eighties, when were searching technology for interactive television. Pioneer family of technologies xDSL is a company Bellcore; in 1987, it introduced the first specification of a family of technologies xDSL and launched her in telephone networks USA (Aoki & Oki, 2010). Soon, however, the company disbanded, and the technology lain down on the bottom.
In the mid of 1990s the family of xDSL replenished asymmetric digital subscriber line modification called ADSL. These years followed and improved chipsets for transmission of data through ADSL. The pace of development has been slowed down because DSL was originally developed for transmission systems "video on demand". Systems themselves are not widespread, and ADSL technology got a second wind thanks to the development of networks of the Internet with the advent of the first ADSL modem, providers have seen this technology and begun to use it to provide access to the network (Aoki & Oki, 2010). Because of the need to install the equipment at each PBX costs for building and maintaining the network were markedly higher than in the case of classical dial when all modems provider installed on one PBX, but compared with the cost of other ways to provide high-speed Internet access DSL technology proved to be very cheap.
Since the mid -2000s ADSL actively displaced faster access technologies Ethernet (twisted-pair) and DOCSIS [source not specified 241 days] (TV coaxial cable). The reason for this limited bandwidth networks ADSL (up to 24 Mbit / s in ADSL2 +), especially the "upstream" from the subscriber (up to 1.4 Mbit / s), while EuroDOCSIS 2.0 provides a data transfer rate of 50 ↓ / 27 ↑ Mbit / s, Fast Ethernet - up to 100 Mbit / s, Gigabit Ethernet - up to 1 Gbit /s.
Despite the emergence of faster ways to transfer data, ADSL technology remains the market leader in broadband data. In several European countries, ADSL is the de facto standard in providing the population fast enough and affordable Internet. For example, in Finland, where every citizen legislation in June 2010 with guaranteed access to the Internet, connecting most of the houses is made by ADSL technology, and British Telecom plans to the end of spring 2013 to cover services for ADSL 2 + 90% in the UK (Aoki & Oki, 2010).
Organization
Data transmission by ADSL technology is realized through a conventional analog telephone line using a subscriber unit - modem and ADSL multiplexer access (DSL Access Multiplexer, DSLAM ), located on the PBX connects to the telephone line user, the included DSLAM equipment to most PBX . The result is a channel between them without any restrictions inherent telephone network. DSLAM multiplexes multiple DSL subscriber lines into one high-speed backbone network (Bogojevic, Gospic & Lazovic, 2005).
They can also connect to the ATM via PVC (permanent virtual circuit, Engl. Permanent Virtual Circuit (English) Russian.) with Internet service providers and other networks.
It is worth noting that two ADSL-modem cannot connect with each other, in contrast to conventional dial-up -modem.
Principle of operation
ADSL modem
ADSL technology is a variant of DSL, in which the available bandwidth of the channel is distributed between outgoing and incoming traffic. It is asymmetric for most users, the incoming traffic is much more significant than the outgoing, so providing for him most of the bandwidth is fully justified (the exceptions to the rule are peer network , video calls and e-mail , where the volume and rate of outgoing traffic are important) (Bogojevic, Gospic & Lazovic, 2005).
It uses ordinary telephone line for voice frequency band 0.3 3.4 kHz. Not to interfere with the use of the telephone network for its intended purpose, in the ADSL frequency range lower limit is at 26 kHz. The upper boundary based on the requirements of data transmission speed and capacity of the telephone cable is 1.1 MHz. This bandwidth is divided into two parts - frequencies from 26 kHz to 138 kHz laid outgoing data and frequencies from 138 kHz to 1.1 MHz - incoming. The band from 26 kHz to 1.1 MHz was chosen. In this range, the attenuation coefficient is almost independent of frequency (Bogojevic, Gospic & Lazovic, 2005).
This frequency separation allows user to talk on the phone without interrupting the exchange of data on the same line. These filters do not require additional power, so the voice channel remains in service during power outage in the event of equipment malfunction ADSL.
Transfer to the subscriber being at speeds up to 8 Mbit / s, although today there are devices that transmit data at speeds up to 25 Mbit / s (VDSL), however, the standard rate is not so defined. In systems for ADSL, service information allocated 25% of the total velocity, unlike ADSL2, wherein the amount of overhead bits in a frame can vary from 5.12% to 25%. Maximum line speed depends on several factors such as the length of the line section and the resistivity of the cable. Also a significant contribution to increasing the speed makes the fact that the ADSL line is recommended twisted pair (not TRP ) and shielded, and if it is multi-pair cable, then compliance with the direction and pitch helix (Kos, Sprljan & Zovko-Cihlar, 2003).
Separation of the transmitted and received data
When using ADSL data is transmitted over a common twisted pair in duplex form. In order to separate the transmitted and received data stream, there are two methods: frequency division multiplexing ( Engl. Frequency Division Multiplexing, FDM) and echo compensation ( Engl. Echo cancelation, EC)
Frequency division multiplexing
When using this mechanism, low-speed link data is transmitted immediately after the frequency band used for transmission of analog telephony (Kos, Sprljan & Zovko-Cihlar, 2003). High channel received data is located at higher frequencies. Bandwidth depends on the number of bits transmitted by one signal.
Comparison
- Echo canceller (EC) to improve performance by 2 dB, but is more complex to implement.
- Benefits EC grow by using more high-speed technologies such as ISDN or video telephony at 384 kbit / s. In these cases, FDM requires high channel isolation for the received data to higher frequencies, which leads to an increase in the damping and reduce the maximum transmission distance.
- Combining the two channels in the same frequency band, using the EC leads to the effect of self-NEXT, which is absent when using FDM (Jackson, 1998).
- ADSL standard provides for interaction between the different equipment that uses the mechanism of FDM, and the EC, the choice of the mechanism is defined when establishing a connection.
Link parameters
Subscriber telephone line, using its technology for ADSL, should have the following parameters:
Primary parameters
- Loop resistance - no more than 900 ohms
- The insulation resistance between the conductor and earth - more than 10 MW, between cores - more than 1 MW [4]
- Capacity loop - no more than 300 nF
- Capacitance unbalance - no more than 10 nF, or no more than 5%
- Work by increasing the loop isolation and low quality possible provided station equipment at a reduced data rate
Secondary parameters
Signal attenuation (Line Attenuation):
- up to 20 dB - excellent line
- 60 dB and above - equipment will not work
Noise level (dB relative to 1 mW at a load resistance of 600 ohms)
S / N ratio (Signal-to-Noise Ratio ( SNR )):
- 7 dB to 10 dB - may fail
- 29 dB - excellent line
For ADSL line is recommended to use twisted pair (not " noodles "), otherwise the reduced bandwidth data transmission channel.
Advantages of the technology ADSL compared to dial-up :
- High-speed Internet access;
- The phone is always free. ADSL technology allows user to surf the Internet and talk on the phone at the same time;
- Permanent access to the Internet: No need to dial a phone number: user get a permanent connection to the Internet;
- Reliable connection 24 hours a day;
- Secure access to the Internet: Telephone line, which runs ADSL-modem, used by only one user and only connected to it
Main application ADSL is of course, high-speed Internet access. It is also possible to connect to corporate LANs, various multimedia programs. For example, listen to music or watch movies and other video content on-line, i.e., in real time, without prior uploads data to user’s computer (Jackson, 1998). Well, where do without them, network game with nice graphics and many players. It is called asymmetric because the data rate of the user and the user is not the same. If user regularly visits on the Internet, user can estimate the ratio of incoming and outgoing traffic. In the "Network Connections”, user need to right click on the active connection and select "Properties." It will be seen that the incoming traffic, i.e. the user, significantly exceeds the output - to the user. This happens in the majority of ordinary users; because user is online mostly get information: view the sites, downloading software and music. While outbound traffic is of little use, for the most part only to send commands to a remote server which page to open and what to ask for. Therefore, in ADSL technology is done so that the data rate to the user - from 1.5 to 8 Mbit / s, much higher than was - 64 kbit / s to 1.5 Mbit/s (Long, 2005).
Connecting to the Internet via ADSL technology is constant (always on all-inclusive).
In the absence of any network activity when no data is transmitted or received, the telephone network resources are not used, while for analog modem after connection, regardless of whether user are looking Web-sites or drink coffee for half an hour, the line remains busy, i.e. telephone network is used to complete the program (Long, 2005).
Development of ADSL
Greater coverage
ADSL advantage compared to other high-speed data transmission systems (cable modems, FTTx, etc.) is the number of existing telephone lines substantially exceeds the number of specially routed cabling (Slabbert & Buys, 2007). This means that to connect via ADSL technology is enough to have a home phone, and special subscriber access equipment (DSLAM), installed on user’s PBX.
Quick connect
High-speed Internet access is available for existing subscriber line local telephone network that allows access to the service to any user of the local telephone subscriber line when necessary according to specifications. To use the network using ADSL technology requires ADSL-modem - a special device for transmitting data via a standard telephone line. After signing the contract for the provision and installation of the modem, just a few hours user will be able to take full advantage of broadband access to the Internet. In this case, install the modem yourself under force anyone (Slabbert & Buys, 2007). User does not need any special technical knowledge. Just follow the instructions for setting up the modem and our recommendations.
High-speed data transmission
ADSL technology enables data transmission to a user at a speed of up to 8 Mbit / s, and the direction from the user to 1.5 Mbit / s, depending on the length and line quality.
Versatility
ADSL technology enables data transmission by the same "copper wire" used for telephone communications. In this case, user can use the services completely independently as traditional voice and access to resources of a global network (Slabbert & Buys, 2007). User can call and receive calls, send and receive faxes at the same time while on the Internet or receiving data from the corporate LAN network all this according to the same telephone line.
How the ADSL Connects
"Copper wire" coming in user’s apartment, connected to the telephone exchange, which is tuned to a signal of 0.3 - 3.2 kHz, ample voice. However, the technical capabilities of most "copper pair" much higher its capacity close to 1 MHz. A DSL technology uses significantly wider bandwidth regular phone line than the existing telephone network (PSTN). Frequency bands for the higher frequencies than the spectrum of the speech signal A DSL equipment must be installed at both ends of the link, and physical line itself must be capable of transmitting a signal in a necessary band. To make a digital high-speed line at the ends of "copper pair" special connect digital devices (splitters) is one on the PBX, the other in the client's apartment - which provide simultaneous operation in phone lines and the Internet (Takeuchi, 2001). One output of the station splitter connected to the telephone and the other to a multiplexer (DSLAM), associated with the Internet. Subscriber splitter is installed in the apartment; it has two - one for the ADSL-modem and the other to all phone outlets.
Conclusion
This paper explored development of ADSL technology and finally, found it latest technology containing a data transmission technique with a high speed. This technology is used for asymmetric access. Enables the transmit signal with a rate up to 1 Mbit per second, taking - at speeds up to 6 Mbps at a distance of 7 km. Using this technology enables simultaneously talk on the phone and connect to the Internet.
References
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Bogojevic, D. C., Gospic, N., & Lazovic, S. (2005). New telecommunications services and regulation: case Serbia. TELSIKS 2005 - 2005 uth International Conference on Telecommunication in ModernSatellite, Cable and Broadcasting Services, 1. doi:10.1109/TELSKS.2005.1572102
Jackson, A. (1998). ADSL for high-speed broadband data service. 1998 IEEE Aerospace Conference Proceedings (Cat. No.98TH8339), 4. doi:10.1109/AERO.1998.682212
Kos, T., Sprljan, N., & Zovko-Cihlar, B. (2003). Comparison of broadband network technologies. The IEEE Region 8 EUROCON 2003. Computer as a Tool., 1. doi:10.1109/EURCON.2003.1248005
Long, G., Kamali, M., Fazlollahi, A. H., & Rao, V. R. (2005). Competition stimulates technology advances: experiences from ADSL development in Japan. IEEE Communications Magazine, 43. doi:10.1109/MCOM.2005.1509975
Slabbert, J. A., & Buys, A. J. (2007). Technology roadmap process to compare commercial broadband technologies available to SME and SOHO owners in South Arica. AFRICON 2007. doi:10.1109/AFRCON.2007.4401636
Takeuchi, S. (2001). Recent transmission technology development for multimedia services (ADSL for Internet multimedia). Proceedings of IEEE Region 10 International Conference on Electrical and Electronic Technology. TENCON 2001 (Cat. No.01CH37239), 1. doi:10.1109/TENCON.2001.949538
