Introduction of wireless Link in Terminal Automation at HPCL Loni.
Hindustan Petroleum Corporation limited having one of its gas plant at Loni, Ghaziabad, which was automated by M/S Honeywell Automation India Ltd. In 2001-2002. Automation in Plant is working fine over LAN connectivity suddenly one Ethernet Cable between control room to planning room got damaged/break. In addition to above I would like to introduce that distance between control rooms and planning room is more than 200 meters with 50 meters hard RCC platforms in between. And hence replacement of faulty Ethernet cable was a big project and very typical against all HPCL and Honeywell team. Suddenly one great idea of wireless communication clicked, while testing the same it was found ok and lots of advantage over wired LAN/optic fibre cable link . Then it finalized to have wireless link instead of wired link.
A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on Ethernet technology, although new standards like ITU-T G.hn also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines)
Twisted pair: wire is the most widely used medium for telecommunication. Twisted-pair wires are ordinary telephone wires which consist of two insulated copper wires twisted into pairs and are used for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 100 million bits per second.
Coaxial cable: is widely used for cable television systems, office buildings, and other worksites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
Optical fiber cable: consists of one or more filaments of glass fiber wrapped in protective layers. It transmits light which can travel over extended distances without signal loss. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of
bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than for twisted-pair wire. Although wired LAN has great connectivity and reliability but situation may be the different as follows;
span a distance beyond the capabilities of typical cabling, need to provide a backup communications link in case of normal network failure without delaying of 15 20 days. To link portable or temporary workstations, To overcome situations where normal cabling is difficult or financially impractical, or To remotely connect mobile users or networks.
To overcome these situations, favor was already given to wireless technology but recently it was not so much reliable. Now after so many changes and revisions and after adding new technologies its become a reliable source of networking to think beyond the wired LAN and also having great connectivity options ( up to 1GBPS is available in market and up to 3GBPS is upcoming in market.) with great security feature compare to wired LAN.
Wireless communication is the transfer of information over a distance without the use of enhanced electrical conductors or "wires The distances involved may be short (a few meters as in television remote control) or long (thousands or millions of kilometers for radio communications). When the context is clear, the term is often shortened to "wireless". Wireless communication is generally considered to be a branch of telecommunications.
Wireless NetworkThe bridge provides connectivity to the wireless network for wired machines in remote locations.
Introduction Wireless operations permits services, such as long range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc.) which use some form of energy (e.g. radiofrequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer information without the use of wires. Information is transferred in this manner over both short and long distances.i.e. the various types of unlicensed 2.4 GHz WiFi devices) is used to meet many needs. Perhaps the most common use is to connect laptop users who travel from location to location. Another common use is for mobile networks that connect via satellite. A wireless transmission method is a logical choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless technology:
To span a distance beyond the capabilities of typical cabling, To provide a backup communications link in case of normal network failure, To link portable or temporary workstations, To overcome situations where normal cabling is difficult or financially impractical, or To remotely connect mobile users or networks.
Applications may involve, point to point communication, point-to-multipoint communication, broadcasting, cellular networks and other. Point to point communications is a term that is used in the
telecommunications fields which refer to communications which is accomplished via a specific and distinct type of single point connection.
telecommunications field which refers to communication which is accomplished via a specific and distinct type of multipoint connection, providing multiple paths from a single location to multiple locations
Wireless Distribution System : WDS is a system that enables the wireless interconnection of access points. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required. The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client frames across links between access points An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet. A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them on to relay or main stations. Connections between "clients" are made using MAC addresses rather than by specifying IP assignments. All base stations in a Wireless Distribution System must be configured to use the same radio channel, method of encryption (none, WEP, or WPA) and encryption
keys. They can be configured to different service set identifiers (Known as SSI). WDS also requires that every base station be configured to forward to others in the system. WDS may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). It should be noted; however, that throughput in this method is halved for all clients connected wirelessly. WDS can be used to provide two modes of wireless AP-to-AP connectivity:
Wireless Bridging in which WDS APs communicate only with each other and don't allow wireless clients or Stations (STA) to access them Wireless Repeating in which APs communicate with each other and with wireless STAs
Two disadvantages to using WDS are:
The maximum wireless effective throughput is halved after the first retransmission (hop) that is made. For example, in the case of two routers connected via WDS, and communication is made between a computer that is plugged into router A and a laptop that is connected wirelessly using router B's access point, the throughput is halved, because router B has to retransmit the information during the communication of the two sides. However, in the case of communications between a computer that is plugged into router A and a computer that is plugged into router B, the throughput is not halved since there is no need to retransmit the information. ( Note: This one not covered in case of terminal Automation System or in plant operation)
Dynamically assigned and rotated encryption keys are usually not supported in a WDS connection. This means that dynamic Wi-Fi Protected Access (WPA) and other dynamic key assignment technology in most cases can not be used, though WPA using pre-shared keys is possible.
This is due to the lack of standardization in this field, which may be resolved with the upcoming 802.11s standard. As a result only static WEP or WPA keys may be used in a WDS connection, including any STAs that associate to a WDS repeating AP. Recent Apple base and some other brands stations allow WDS with WPA, though in some cases firmware updates are required. Firmware for the Renasis SAP36g Super Access Point and most third party firmware for the Linksys WRT54G(S)/GL support AES encryption using WPA2-PSK Mixed Mode security, and TKIP encryption using WPA-PSK, while operating in WDS mode. However, this mode may not be compatible with other units running stock or alternate firmware. Wireless Router Application Platform:Operating System
The WRAP is capable