Q: Can you define some of the protocols involved with networks used in security and integration?
A: Here is an overview of some protocol flavors you'll encounter in system integration. Something to watch out for is having to adapt products to applications for which the native protocol of a device is not suitable for the situation. An example of this is connecting Wiegand readers over long distances (check out “An Open & Shut Case” in the October 2006 Security Dealer ).
Cat 3 : Used for data networks using frequencies up to 16 MHz, mainly for telephone cables.
Cat 5e : Up to 125MHz. Used for 100Mbit/s and gigabit Ethernet networks.
Cat 6 : The cable standard for Gigabit Ethernet that is backward compatible with the Category 5/5e and Category 3 cable standards. Suitable for 10BaseT/100BaseTX and 1000BaseT (Gigabit Ethernet) connections. It provides performance of up to 250 MHz.
RS-232: Standard for serial binary data interconnection commonly used in computer serial ports. The maximum cable length is 50 feet, or the cable length equal to a capacitance of 2500 pF . Using a cable with low capacitance allows you to span longer distances. If UTP CAT-5 cable is used with a typical capacitance of 17 pF/ft , the maximum allowed cable length is 147 feet. RS232 standard was originally developed for 20 kbps . By halving the maximum communication speed, the allowed cable length increases by a factor of ten!
EIA-422: (formerly RS-422 ), now TIA-422 , is a technical standard which provides for data transmission, using balanced or differential signaling, with unidirectional/non-reversible, terminated or non-terminated transmission lines, point to point, or multi-drop. In contrast to RS-485 (which is multi-point), EIA-422 allows one driver and multiple receivers. Maximum data rates are 10 Mbit/s at 1.2 m or 100 kbit/s at 1200 m. EIA-422 cannot implement a truly multi-point communications network (such as with EIA-485), but one driver can connect to up to ten receivers.
EIA-485: (formerly RS-485 ) is an OSI Model physical layer electrical specification of a two-wire, half-duplex, multi-point serial connection. EIA-485 enables the configuration of inexpensive local networks and multi-drop communications links. It offers high data transmission speeds (35 Mbit/s up to 10 m and 100 kbit/s at 1200 m or about 4000 feet). The recommended arrangement of the wires is as a connected series of point-to-point nodes, a line or bus, not a star, ring, or multiply-connected network. Star and ring topologies are not recommended because of signal reflections or excessively low or high termination impedance.
RS-423: Standard for a uni-directional interface between one transmitter and many receivers. RS-423 allows for distances up to 4000 feet but limits data rates to 100 kb/sec for a maximum of ten the data values. RS-423 is a serial binary data interchange used for data rates from 20kbps to 10Mbps.
Ethernet: Wire's first specification was 10Base5; the 10 refers to the speed (10Mbps), the Base refers to a base band system, and the 5 refers to the system's maximum cable length: 500m. The first official Ethernet standard was called IEEE 802.3. Version 2 is IEEE 802.3a.
Security Dealer Technical Editor Tim O'Leary is a 35-year veteran in the security industry and a 12-year contributor to the magazine. O'Leary's background encompasses having been a security consultant since 1986 and an independent security company owner/operator, in addition to his research and evaluation of new technologies and products introduced to the physical and electronic security fields. He is a member of the VBFAA (Virginia Burglar and Fire Alarm Association); certified for Electronic Security Technician and Sales by the VADCJS ( Virginia Department of Criminal Justice Services); and has served as a judge for the SIA New Product Showcase. Send your integration questions to [email protected].
