Technology

Today all businesses and industrial setups are based upon the mean of networking and communication. Hence, the most commonly used mean of communication is either phone, which includes landline, cell phones and pagers and the other medium of communication is internet. For communication to be faster and reliable the communication sector of the world is getting transformed by the new inventions and technology. While the computer manufacturing and communication processes keep on growing, the need for advanced speed internet access and communication is also rising. Games and digital media both have the potential to be performed over the internet. To perform these tasks in an easy manner, a high speed internet connection is needed, if it is not present, that not only bothers the user but it also fails to perform tasks efficiently (summers, 1999).

Therefore different methods of communication are present and everyone has different opinions about what they use, some people use ordinary modem while some can manage wireless networking to perform a simple communication. But some methods are very common in household and businesses which include the connecting of internet via LAN, WAN, modem cable modem, ISDN and DSL. All of these methods are fulfilling their respective purposes, however, ISDN and DSL are two of the most commonly used communicational and internet accessing devices.

ISDN
ISDN stands for Integrated Service Digital Network it is a CCITTITU combination which is used for broadcasting digital data over common telephone copper wires and other connectivity media. This devices adapter  is used in place of a simple communication modem in home and some businesses to give a higher speed up to 128kpbs, unlike an ordinary telephone modem which is capable of only giving speed up to 56kpbs (kilo byte per sec). This means of communication requires an adapter at both ends of the communication therefore the provider of ISDN also has to have an adapter (Harte  Flood, 2005).

Homes and offices use analogue lines for landline numbers, so the handset picks up the speaker voice and transmits it over to the phone line as an analogue. The modems that are used in homes, convert the digital signals from the computer in analogue signals so that they can travel through the usual copper phone line. The modem converts the phone signal into the digital form providing connectivity and it is said that 56kpbss is enough for home use but as the communication skill and equipment is increasing it is insufficient. So in this case ISDN is preferred which can give up to the speed 1.4Mbps however according to researchers 128kpbs speed is more than the usual in digital technology so its not very necessary that the speed has to be more than 128kpbs while for the communication purpose ISDN uses the Unshielded Twisted Pair (UTP) cables. The international standard for contact is digital technology and all the methods of contacting, be it by sending data, video or any voice data, is done over these ISDN digital phone lines.

There are two types of ISDN networks which are quite usual in use and include BRI (Basic rate interface) and PRI (Primary rate interface). The BRI comprises of dual 64 B-channel and a D-channel for a smooth and managed transmission of information.

Primary rate interface in United States has 23 B-channels and a D-channel and 30 B-channels and one D-channel in European countries. Moreover there is another version of ISDN known as Broadband ISDN (B-ISDN) and it uses a broadband transmission, so it is used in cases where a higher speed is required rather than the usual ISDN speed and has a capability of transmission of data up to 1.5Mbps. The B-ISDN lines need fiber optic cables for better performance while the usual UTP lines are used in case of ISDN band transmission.

An access to B-channel ISDN network is required for the normal ISDN phone line users while other special devices that are required by some of the users are known as terminal adapters. These detailed devices correspond with other ISDN devices or telephones for communication purpose (Harte  Flood, 2005).

ISDN is operated on the last three layers of the Open System Interconnection (OSI) reference model, and every layer uses a diverse requirement to send out the data. In a regular telephone line or in an analogue network a single communication channel is available by the companies. Therefore only one facility can be carried at a time, i.e. voice, video or data at single time. However in ISDN lines the similar telephone lines are sensibly partitioned into numerous channels, they are generally divided into two channels (Bhatnagar, 1997).

The first type is of B- Channel and almost 64Kbps of data can be transferred using this channel. In general ISDN lines have two B channels one channel is committed for voice and the other channel is for data communication, this whole data transmission occurs on one couple of copper wire (Harte  Flood, 2005).

The D-channel or delta channel is the second type of the channel used for setup of line and calling system. While the other types have 16kpbs of bandwidth and are not used very often as more speed provided by a phone modem.

When only ISDN is being considered the speed is said to be its highest priority and its basic advantage. This is because the usual dial-up modems used by the computers have a limit of 56kpbs and after getting connected due to many reasons this speed is decreased to only 45kpbs or even less where the ISDN contains multiple digital channels which work simultaneously on the same line on which modem is not able to provide full speed. Also if the telephone enterprise provides digital connection then the speed is made better and changes occur which are the transmission of digital signals data from telephone line rather than the normal analogue signals. So naturally the digital signals boost up the speed of ISDN lines and better results are obtained (Harte  Flood, 2005).

The other advantage of ISDN is the provision of multiple services on a single line like in case of no ISDN line if the consumer wants to fax, telephone, video conference and use the credit card machine at the same time then all these functions would require a separate line for communication while in ISDN all of this would be done on a single copper line as this technology supports simultaneous working. Other advantage of ISDN is that it takes almost 2 seconds to connect while a simple modem takes up to 30seconds or more (Bhatnagar, 1997).

The research and development is being done on the B-ISDN technology as it is said to be of higher speed. However there is sill a lot of room left for the improvement of ISDN and in it the changes in voltage level, control of ring and many other properties need to be improved and this standard working is said to be the national ISDN. Also improvement would be done in application sector as some applications are going to be useful for using ISDN and like ATM the broadband category of ISDN is also being researched, B-ISDN is very much related to ATM because ATM provides a reliable data encapsulation system that is used all over the network, beginning with TE1 or TA equipment, and covering each portion of telecommunications tools in use. So much is its importance that quite a lot of people believe ATM to be B-ISDN. People replace their phone communication system with ISDN phone network as now the companies provide the whole thing in an equipment built box which is easy to install, provides Ethernet connection using IP and has an NT1 providing two phone jacks (Brewster, 1992).

The regularity issues involved in this certain mean of communication are the policy issues which describe and demand the identity of the provider and his ownership, issues regarding the location of the provider and the receiver, the factual basis of the financial provider of the company and the technology.

Allocation of rules and regulation on the billing procedure features should be implied. The other technical issues that occur are interconnection of multiple numbers of ISDN carriers, utilization of special packages and the difference between voice and invoice performance. The other is technological advances on the interface if bit rate is converted to 64kpbs rather than 32kpbs. So these issues are soon going to be dealt with and solution would be acquired (Brewster, 1992).

Therefore, the ISDN guarantees a number of high-performance, multiservice digital networks with capability for worldwide connections. Even though some of the basic elements of ISDN are being used several places still use analog switches and in-band signaling. Microwave services are still being used for broadcast over major sections of the long-haul set of connections and these utilize analog frequency modulation for voice and data. We can expect to see many changes in the telecommunications engineering and technical advances in ISDN (Harte  Flood, 2005).

DSL
Digital Subscriber Line (DSL) is a service of fast pace internet like usual cable internet. It provides high speed networking on normal phone lines due to the presence of broadband modem. The quality of DSL is that it provides internet service and telephone service at the same time on the same phone line. This allows the user to continue with their voice or internet connection without disconnecting any one of them. DSL is said to reach up the speed of 8.448Mbps however the normal rate is approximately 1.544 or lower, so here fore has now more preference over other connections. Today various homes and businesses are using this network technology however it has a limited work area or distance and is not supported at the places where there are no telephone lines (Smith, 2007).

Two kinds of high speed internet connections are used in household and businesses, cable modems and DSL. TV cable connection wired in most homes run the cable modem while DSL, as mentioned, transfers data through existing phone lines and does not interrupt the telephone line used for talking. As compared to ordinary copper phone line they both are quite fast but they differ from each other in speed, reliability, cost, service and availability of service (Bourne  Burstein, 2001).

In order to understand how the DSL works and what technology is behind it, we will take a look at the normal standard telephone. When a phone call is made the voice signals are carried along the copper wires to the receivers handset so these conversational frequencies vary in different ranges from 0 to almost 3400 hertz. So by restraining the frequencies that travel by copper lines, the telephone packs many wires in little space and does not create interference between them. In olden days analogue signals were sent through this procedure for communication while today through the advancement of technology the phone sends digital data signals without taking up a lot of capacity of the telephone wires. This is how a DSL works (Smith, 2007).

There are many types of DSL which includes the following,
ADSL Asymmetric Digital Subscriber Line (ADCL) is a DSL type that became most known to household and small production consumers. It is asymmetric as most of its dualbandwidth is dedicated to the downstream path, through which the user gets the data. In most situations, the active phone lines work with ADSL while in a few areas, they may require advancement (summers, 1999).
CDSL Consumer DSL (CDSL) is a DSLs adaptation, registered by Rockwell Corp. it is low in speed than ADSL and a benefit that no splitter needs to be mounted users place.

G. Lite or DSL Lite G. Lite is another name for low speed ADSL and doesnt require users end line splitting but does it at the telephone company. The data rate varies from 1.544 Mbps to 6 Mbps downstream and for upstream 128 Kbps from 384 Kbps. It may become most installed device (Wolf  Zee, 2000).

HDSL High bit-rate Digital Subscriber Line (HDSL) is an initial type of DSL, used for wideband digital broadcast inside a commercial location and among the telephone corporation and a consumer.
IDSL ISDN DSL (ISDL) is said to be fake as its very close to ISDN providing the rates up to 128Kbps.

RADSL RADSL (Rate-Adaptive DSL) is technology of ADSL Westell, it has software that is capable to conclude the amount of signals that are broadcasted on a certain consumers phone line and regulate the release rate consequently.

SDSL SDSL (Symmetric DSL) is like HDSL only one twisted-pair line.
UDSL Unidirectional DSL (UDSL) is a suggestion by a European corporation. It is a one directional adaptation of HDSL.

VDSL VDSL (Very high data rate DSL) is emerging equipment that assures much superior information rates over comparatively small space (almost 51 and 55 Mbps on lines up to 1,000 feet or 300 meters in measurement lengthwise). Many standard associations are operational on it (Held, 2000).

Usually when a user connects to the internet the commonly used devices for connectivity are regular PCI modem, Local Area Network (LAN), cable modem or DSL. But DSL is becoming popular due to certain advantages.  If the user receives a call from telephone line the internet does not needs to shut down and can remain open. So this feature of simultaneously using the same line for different purpose is the main and highlighting feature of DSL (Bourne  Burstein, 2001).

The other feature is that DSLs speed is much faster than an ordinary modem, so any connection is done at high speed, it also does not require any new wiring unlike other methods which need a whole new setup of devices and wires it uses the same copper phone wire used for call making (summers, 1999).

Also the company provides the broadband modem which saves the effort of finding a separate modem and with those certain specification demanded by the company so no extra cost is required in purchasing the modem (Wolf Zee, 2000).

DSL, at the present, is being used in the majority areas of the United States, in the United Kingdom and other countries too. DSL service distribution relies on how a local corporation has made the essential savings in tools and line service and how close the user is to the telephone corporation. DSL service providers in different parts of the United States comprise of Covad, Qwest, Primary Network, BellSouth, SBC Communications, and Verizon (Burns, 2006).

But the technical issues and regularity issues that arise with this are that a DSL connection would perform better if the provider of the company office is close to the users location. The more the distance from the providers office, the weaker the signal is received.

The other issue that is being taken under consideration by the researchers and developers is that DSL connection is brilliant for receiving data from a certain source but when it comes to sending data the performance is not very appreciable.

The other issue with this technology is this that it is not available everywhere. This is because every place is not supported by wiring some places do not have this facility of copper wire transmission to communicate so as this technology works on the same copper wiring therefore places which lack these wiring facility ultimately lacks  DSLs service too. DSL is an expensive manner of communication therefore is suitable for business or commercial use. On the other hand ordinary people who are not capable of affording an expensive mean of communication tend to use other network providing devices (Bourne  Burstein, 2001).

This technology is expensive but when it comes to the reliability and speed of networking household people are going to use this device for networking purpose while other business sector are already using this device. This same line usage is the best thing technology can come up with in IT and research sector (Wolf  Zee, 2000).

DSL is now getting quite popular in most regions especially Western Europe and North America. Therefore the market requires more value added and sophisticated application so that the business competition should increase. So, in future such strategies would demand fast internet connections hence DSL, in its many forms, would provide better utilization of copper wire network communications and would give speed up to 24Mbps using the ADSL and VDSL. This would make the users of DSL in future to obtain VoD, VoIP, and IPTV. This high speed internet would then quite fast and no time is going to be taken for any connectivity, however all the research that is going on is yet to be tested (Burns, 2006).

Conclusion
Therefore, from the details of both we can see that DSL is better if the person want to use the telephone and internet at the same time, which is not provided by ISDN. Also the speed of DSL is more than ISDN and therefore ISDN is regarded as the out dated nowadays. Very few people are using this mean of networking while others have shifted themselves to DSL or other means (Held, 2000).

According to a survey in 2005 the DSL subscribers for the speed of 2Mbps were almost 26 million, for speed of 2-10Mbps the customers were almost 28 million. However today, in 2010 the people who are using DSL on 2-10Mbps speed are 55 million while the customers who are using DSL above the speed of 10Mbps are approximately 60 million worldwide. So one can understand which choice is better if a good connectivity is required. ISDN is now old fashioned but before DSL its importance was quite a lot but as the time and technology changes the previous inventions get less importance. So this is truly one of a great device and mean of communication.