Linux Troubleshooting for System Administrators and Power Users

2 System aspects

2.1 Apparatuses laser safety

Any laser can present danger to man, at ocular level and at cutaneous level; the human eye being very sensitive to infrared radiation. The most important factors to take into account to evaluate the risks are: the signal wavelength, power and beam form. Eye safety is governed by International Electrotechnical Commission (IEC) standards. Those in force in France are: NF EN 60825-1 and NF EN 60825-2. The lasers are divided in various classes according to the known risks which they represent, allowable exposure limit (AEL), allowable maximal exposition (AME) and nominal distances of ocular risk (NDOR).

2.2 Manufacturers and products

A review manufacturers was carried out, based on various sources of information (conferences, reviews, magazines, research engines, web sites etc) in order to obtain the most complete possible panorama of products and their capabilities.

The principal parameters considered are transmitted data type, range, data rate and the type of suggested application or other parameters such as the wavelength, type and number of optical transmitters (laser and possibly LED), emitted power, control, deployment facilities, maintenance, cost etc. Table 18.1 gives an overall picture of most of the products listed starting with information obtained by manufacturers or by consulting their web site. Figures 18.1 and 18.2 (at the end of the chapter) give the data rate suggested (Mbits/s) and range in function of the wavelength for various equipment.

Figure 18.1: Data rate (in Mbps) in function of the wavelength for various equipments

Figure 18.2: Range in function of wavelength for various equipments

2.3 Uses

In this paragraph the various uses suggested by the manufacturers are mentioned. In an artificial way, they were classified in three types of approaches: geographical, application and technical.

2.3.1 Geographical approach

Initially, an approach related to geographical specificities, is presented below, including:

• Isolated sites (mountainous sites, places of interest) or risks (lightning, IEM).

• Charged electromagnetic environments (airports, factories, etc).

• Classified sites, private domains,

• Not easily passable obstacles (motorways, rivers, etc),

• Dense urban zones.

2.3.2 Applications approach

A second approach relates to the applications aspect of a free-space optical communication link.

• temporary link,

  • event action link (sport, concert, etc),

  • intervention link (work, modification or network repair, etc),

  • help link ( accident , fast commercial action, etc),

• "last mile" connection,

• inter-site connection, independent, rented or private networks,

• closing an optical loop,

• inter- cell GSM or UMTS link (micro or picocell), etc.

2.3.3 Interface approach

This approach relates to the various types of interfaces available with a laser link. Products with interfaces of any types in the various potential fields of application are proposed by the majority of manufacturers:

• LAN Networks (Ethernet, Fast Ethernet, GigaEthernet, FFFDI, Token Ring, etc),

• Telecom (E1, E3,T1 T3, ATM, SONET, SDH, PDH, etc),

• Video (SDI, SMPTE, etc),

• Mixed LAN-Telecom (Ethernet 10BaseT and 2xE1).