Koren Antun, Saifert Danijel

Abstract :

Implementation of the information and communication technologies, as well as the appearance of the new interfaces changes thoroughly the way of business operation in graphic profession. The development of the information and communication technologies in the last decades grows exponentially; computers are stronger which offers greater possibilities in different segments. In order to use these possibilities it is necessary to improve the connections among the computers.

The connection among the computers is achieved by linking the computers into the system of local network and after that into the world local network. The local networks differ in construction, used technologies, speed of data transfer, way of data approaching and similar. The further development of the local network system is wireless connection of the computers into the working unit. The development of the wireless networks has several directions. The majority of graphic companies in the country are linked by classical cable approach of the designing the network solutions. In recent times the wireless network solutions enter into graphic companies.

This work presents the advantages and disadvantages of the wireless connections of the computers into the local networks in regard to the effectiveness improvement and quicker flow of information in the graphic industry. In accordance with this it explains how big is the necessity of the changeover from the classic network equipment to the wireless network systems.

Key words: Wireless LAN, Access Point, Station Adapter, IEEE 802.11

1 Introduction

The computer network is a complex and big system which unites great number of elements and functions (operations, processes) necessary for its successful work. The computer networks are divided into local networks and the networks of the long range. Ethernet is considered to be the most successful local network (LAN). The development of Ethernet began in the mid seventies and from then it grows exponentially from year to year. At the end of the last century the local networks developed with the speed of data transfer from 100 MBPS to 1 GBPS. Such networks of the quick data transfer started to be used in graphic companies. The further development of Ethernet goes in the direction of network communication without cable connections. This leads to the development of the network standard IEEE 802.11 known as wireless network (wireless LAN). Wireless networks accelerate the installation process, avoid the changes in the infrastructure on the network object and improve the movable communication.

Wireless LAN becomes more and more popular today among business and private people. During the years, wireless LAN has experienced the standardizations, improvements in velocity and at the end it has got the acceptable price. It is important to stress that the wireless LAN is compatible with the wire connections and they can be mutually implemented into the network system. The wireless LAN has recently become interesting to the users in the world as well as in Croatia by its quick development. In the middle of 1997 IEEE 802.11 standard was introduced, which will in future secure the mutual operability of the equipment of different producers. In the future it brings lower prices of the equipment and the lower costs for installation and maintenance. In Croatia, the wireless local networks become interesting by introducing the “Decision about the kinds of radio station which do not need the license (Narodne novine Nr. 75/97)” who were given the frequency range from 2400 to 2483,5 MHz for Radio LAN(RLAN) without special licenses and concessions. In this way the Croatian regulations become compliant with the recommendation of the European Conference of Post Offices and Telecommunication (CEPT). By this decision the radio area necessary for undisturbed operability of the wireless systems has become free. Today, it is possible to buy two types of standardized equipment for wireless connections according the standards IEEE 802.11b and IEEE 802.11g which are compatible with one another.

2 The stucture of the wireless network

Wireless LAN systems enable the working stations the communication and approach to the network using the radio signals as the transmission medium of communication. Radio communications at wireless LAN is done in ISM (Industrial, Scientific & Medical) frequency range which is accepted in the world as the range, the usage of which does not need to have the license, so called FTA – free to air speaker. ISM has three frequency ranges: 902 / 928 MHz, 2400 – 2483,5 MHz and 5728 – 5750 MHz. Wireless network can be connected to the existing LAN as the expansion or it can be the basis for completely new network. Although applicable for outer installations, WLANs are especially suitable for inner installations. The basic structure of the wireless network is a cell. This is the area covered by the wireless communication. The size of this area depends on the strength of the radio signal and the system and the way of building the walls, their arrangement and other physical properties of the area. It is possible to move the computers on the PC platforms and the portable computers inside the cell. The portable equipment in the communication via wireless network can be the different types of the notebooks, PDA equipment and the tablet portable computers. Each wireless cell needs the managing for communication and traffic. This is done by the access point (AP) which communicates with each wireless cell in the area which it covers. The cells communicate with AP over the station adapter SA, which can be an extern device with the link to LAN computer card or PC-MCIA card for portable computers.

Figure 1. Station Adapter

At PDA device wireless SA can be integrated in the device itself (HP Ipaq 5550 ) or it can be added to Compact Flash slot on the device itself as a separate extension card.

Figure 2. HP Ipaq 5550

The communication of one station with another is done over AP. In this way AP functions as a relay and increases the range of the system. The range of the standard IEEE 802.11b wireless cards for PC computers is 486 m from the card up to AP in ideal conditions. AP has also the function of a bridge between the wireless stations, the wire-network and other wireless stations. The connection of AP on the basis of the network system itself or other wireless station can be done over the wire or by means of special wireless bridges. The range of the system can be increased cascading of several wireless connections. In the case that some surface is covered by more than one AP, one can speak about overlapping of the stations. Each station automatically chooses the best possible connection with one among APs. The overlapping of the covered areas is an important characteristic of the wireless networks because it enables imperceptible roaming from one station into another. Such a roaming allows the movable users with the portable computers the free moving inside the overlapping stations without the communication break. With help of AP, it is possible to cover completely the area of the whole building or any greater surface. The overlapping of the stations is possible to use for increasing the permeability and reliability of the system. The grouping of several APs on the same spot (maximal up to 17) increases manifold the permeability of the system by load sharing, load balancing. The stations choose automatically less loaded AP. In this way the reliability of the system is increased, because by the failure on one AP the others overtake its load.

There are several standards of the wireless LAN on the market: IEEE 802.11b, 802.11a and 802.11.g. IEEE 802.11b standard enables the transmission speeds up to 11MBPS. It works on the frequency of 2.4 GHz, using Direct – Sequence Spread Spectrum (DSSS) protocol. Data encryption is possible, by using WEP key up to 256 bits. The frequency of this system is in the allowed boundaries for the free transmission, if the strength of the output emitters does not exceed 100mW.

IEEE 802.11b standard is compatible with the older 2MBPS IEEE 802.11 wireless LAN standard.

IEEE 802.11g standard enables the transmission of 54 MBPS, i.e. the data transmission is five times quicker than the IEEE 802.11b standard.

IEEE 802.11a standard enables the speeds up to 58 MBPS. Using the turbo mode, the data flow reaches 108 MBPS. By using the Orthogonal Frequency Division Multiplexing (OFDM) scheme for achieving greater transmission speeds this wireless LAN work on the frequency of 5GHz with the usage of encryption with the WEP key up to 152 bits.

3 Advantages and disadvantages off the wireless network systems in graphic companies

The majority of graphic companies in Croatia is connected by classical wire-network Ethernet and the possible expansion to the wireless LAN is very simple. Wireless LAN solutions are particularly suitable for the companies where no building works are allowed because of the site of the company, or when they are too expensive, such as cultural monuments or city centers. On such places the wireless local networks are very interesting because of the simple and quick installation. They are particularly suitable in the companies which occupy several floors in one building because of the simple setting without greater building works on infrastructure. They are suitable in the situations of combining graphic studios and printing houses which are in the neighboring buildings. By appearance of the wireless network equipment at the end of the previous century, it was manifold more expensive than the wire-network equipment. At today's state of technology, the prices of the equipment are drastically decreased, so that AP IEEE 802.11g for the commercial usage in a firm costs about 150∋ while SA IEEE 802.11 costs up to 70∋ which is very profitable.

The question of security is one of the most often put questions in regard to the wireless network. Wireless networks have become more secure than the wire-networks. There are strong arguments for that. We must not forget that the wire-networks have their wireless part, i.e. they emit rays whose intensity is not small, especially at today's UPP networks. When speaking about security, the main differences between LAN and WLAN networks originate from the different physical level. The Spread Spectrum Technology guarantees the high level of security. Apart from that many wireless devices have built in options for encrypting. IEEE 802.11 foresees the security techniques known as Wired Equivalent Privacy (WEP) which is based on the usage of the key and RC4 algorithm for encrypting. The users who do not know the key have no access to WLAN. The encryption is incomparably easier implemented at WLANs which resulted in appearance of numerous independent manufacturers specialized for WLAN security software. In order that somebody has access to WLAN network, he must 126 have the information about radio range, by using the channel and sub channel, security key and ciphers for authentication and authorization of the users. There are much more data than in classical wire-networks and it makes WLAN very secure. This means that it is very difficult to have the access to the data in one graphic company connected by the wireless LAN. The disadvantages of the wireless networks in relation to the wire-networks are the speed of data transmission for the most demanding users. Graphic studios which work in huge documents such as photographs processing, text make-up, and great scans use the speeds of 1GBPS in transmission in wire-networks while the transfer of maximally 54 MBPS is not sufficient.

4 Conclusion

The development of the modern and actual computer components is presented in this work and the development of the wireless network connections is described. The advantages and the disadvantages of the wireless networks in the field of printing are shown and the implementation of the wireless network into the system of the graphic companies is presented. In spite of numerous advantages of the wireless information transmission, the printing prefers the wire-networks because of the necessity of the great speed of data transmission. The continuous development of the wireless technology of the data transmission will probably solve this problem in future and the usage of the wireless transmission of the printing information with all the mentioned advantages will become everyday reality.

5 References

1. Dave S. Steinberg: Cooling Techniques for Electronic Equipment, 2nd Edition, Wiley-Interscience ( 1991.g )