Becoming familiar with DSL technology:

Nowadays, internet is becoming an inseparable part of human. Undoubtedly, if you have even once faced this modern day global technology, you will see its vast role, importance and necessity. The more the significance of internet increases day by day, the higher the speed of access to information through this technology increases. That is why, many different solutions have been recommended for connecting to the global network of which undoubtedly the easiest and cheapest way will always be considered. Among these methods, DSL technology has managed to take the lead in such a way that at least 20,000 supporters of this technology are added around the world per day. But indeed why? Why has DSL technology acquired such popularity. Maybe the following reasons are a sufficient for reply to this question.

You can utilize your telephone line for voice conversations while you are connected with internet.

The speed of this connection is much higher than an ordinary modem ( 5.1 mbps compared to 56 kbps with available modems).

With this method, there is no need to have new cabling and you can utilize your ordinary telephone line for connection.

Permanent connection with the internet network without disconnections.

Lower monthly charging cost.

Simple management of DSL equipment.

Support for all protocols and deploying the latest utility switches such as Traffic, IP Packet Filtering, VLAN and Shaping.

DSL: How the Technology Operates

1- Becoming familiar with ordinary telephone lines and their specifications: With doubt, the first question raised regarding DSL is that how you can utilize the telephone line for both conversations and online internet connection simultaneously? As everyone knows, the standard telephone system is based on a pair of copper wires which are installed in your house by the regional communication company. The copper wires have a lot of space for conveying information other than telephone conversations. Using a very small part of the whole bandwidth of a copper wire has an historical aspect. Furthermore, limitations on the frequency, on the other hand, is dependent on switches, telephones and other equipment which are responsible for conveying voice. But in a DSL system, the operation is based on conveying digital information and sound, and because of that, it has overcome the limitations in the present day analog system.

2- Signal analysis:
Homes and small businesses users often connect to an asymmetrical DSL (ADSL). ADSL divides the available frequencies in a line based on the theory that most internet users receive more information than what they send. There are two almost incompatible standards regarding ADSL technology. The ANSI official standard which founded the DMT method for DSL technology and certainly most ADSL equipment these days utilize it. The older standard was Carrie Less Amplitude/Phase or SCAP which was used in the past. In an ADSL system, in order to make optimal use from the 1.1 megahertz bandwidth of copper lines, it is divided to 257 channels of 4 KHz. As in order to convey voice(telephone) it is sufficient to have only a 4 KHz bandwidth, therefore, the last channel is used for conveying fax & telephone(voice) and the remaining 256 channels are divided into 64 channels for sending data and 128 channels for receiving data( and the remaining 64 channels for data control). Therefore, the best situation (considering 192 channels of 4 KHz ) we reach a speed equalling 9 mbps(megabyte per second), while the maximum usable speed in ADSLs are 3.3 mbps.

DSL: Equipment

1- DSL modem or ATU-R
Most home subscribers use this modem to receive information from the internet. The company that handles DSL usually installs the the modem as part of its system essentials .

2- Splitter
As mentioned before, voice and data are sent simultaneously on copper lines in XDSL technology. In order to separate voice and data on the subscriber's side a splitter is used so that data is sent to the computer and voice(telephone and fax) is guided to related equipment.

3- DSLAM
DSLAM receives directed communication lines from a large number of subscribers and transfers them to a high capacity single communication line. DSLAM has the ability to support several types of DSL in one telephone center and different types of protocols and modulation methods. In addition, DSLAM can provide possibilities such as route finding or allocating dynamic IP address for subscribers. In fact, DSLAM can be considered as the main difference between providing service through ADSL and cable modem.

DSL: Faults

The main fault of DSL is in the measure of the usefullnes that you receive from DSL is the distance you have from the ADSL service. ADSL is a distance sensitive service. As the distance of communication increases, the signal quality decreases and speed of communication falls. The maximum distance to provide service through ADSL system can reach 5460 meters. ADSL technology can provide a maximum of 800 Mbps downstream at a distance of approximately 1820 meters and upto 640 kbps upstream for users, but in practice the maximum speed used by ADSLs is 2.3 mbps. Why is distance a limiter for DSL systems while this limitation does not exist for telephone conversations? The answer to this question are the small relays called loading coils used by telephone companies to strengthen voice signals, and these relays are not compatible with ADSL. Of course other parameters such as Bridge Taps and fiber optic cables can have a negative effect of ADSL technology.

DSL: Future

As it was mentioned in the introduction, daily 20,000 interested people are added to DSL users around the world, and this in itself shows the competition between this technology and others such as cable modems and satellite internet. According to research done by IDC company by the year 2003 the number of home subscribers using modem cables will be beyond 8,980,000 while DSL in that year has more than 93,000,000 subscribers. In recent years, Korea with a population of 55 million has had the highest number of DSL users so that Seoul has turned into DSL paradise and active companies in the networking field in Korea are leaders of this technology in the world.

Zisa DSLAM catalogues

IPDSLAM Sereies-IA2000G -- Chassis IP DSLAM Up to 576/384Ports ADSL2+	Download
ZISA IA24B- 24Ports ADSL2+ IP DSLAM	Download
ZISA IA48G- 48Ports ADSL2+ IP DSLAM --- Giga Electric&Optical Uplink Port	Download
IPDSLAM Sereies-IA3000G -- Chassis IP DSLAM Up to 768/1152 Ports ADSL2+	Download

The following cities are direct subscribers of Nikan Network DSLAM