09-10-2012, 02:45 PM
BHARAT SANCHAR NIGAM LIMITED HALDWANI
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BROADBAND
A trend of changes in telecommunication technology is very fast. The need of hour is large bandwidth and its optimum utilization at reasonable cost. Any data access rate more than 2Mbps is considered as broadband access.
As per the recent broadband policy of govt. of India, access rate over 256kbps will come under category of broadband access.
Equipment's required in customer premises are
• Filter:-The filter separates out the signal for telephone. (Called as Splitter)
• Modem:-The modem directs the signal to PC and TV.
• Set Top Box (STB)-The STB converts the digital IP based signal to a form compatible with the TV set.
• PC and TV
What is DSL?
• A high speed digital communication line
• Has several advantages over other high speed communication solutions.
• DSL runs on existing copper
• DSL helps carriers reduce congestion on their voice-switching systems
• Very high speed.
Data Card
There are two type of data card:
1. IX data card (speed -144kbps (max))
2. E-VDO data card (speed - 2Mbps)
OCB EXCHANGE SYSTEM
SALIENT FEATURES
• OCB stands for organ control bhersion.
• Digital switching system developed by CIT ALCATEL of France.
• OMC & S/N duplicated.
• Varieties of service provided are: basic telephony, ISDN, Mobile, Videotext etc.
• Supports different types of signaling system.
• Max. no. of junctions may be 60000 and 35 types of cards can be used.
• Less space requirement.
• Automatic fault recovery and remote monitoring.
• Environmental requirement is not very stringent.
MAJOR UNITS OF OCB SYSTEM
Subscriber Connection Unit (CSN)
A CSN basically consists of 1 basic rack and 3 extension racks capacity of CSN is 5000.Subs may be analog and digital.
TRUNK & JUNCTION CONNECTION UNIT (SMT)
It is the interface between switching network and junctions from other exchanges (or remote connection unit).
SWITCHING MATRIX
The Switching matrix is a single stage ‘t’ made up of host switching matrix and branch selection & amplification function, SMX is duplicated.
AUXILLIARY EQUIPMENT CONTROL STATION (SMA)
It consists of frequency receiver/generator conference call CCTS, tone generators etc,
CONTROL UNIT (SMC)
The six control units are as under:
• Multi register (MR) for connecting and disconnecting calls.
• Translator (TR) for storing exchange database.
• Charging unit (TX) for carrying out charging jobs.
• Marker (MQ) for performing connection & disconnection of subscribers.
• Ccs-7 controller (PC) for carrying out routing & traffic management functions.
• Matrix system handler (GX) for monitoring connection in S/N.
OPERATION & MAINTENANCE UNIT (SMM)
It is OMC for supervising functions of different units and for taking suitable actions at the event of faults. Magnetic disks each of capability 1.2 GB for various stages.
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls. A central office is the physical building used to house inside plant equipment including telephone switches, which make phone calls "work" in the sense of making connections and relaying the speech information
MOBILE COMMUNICATION
Mobile phones send and receive radio signals with any number of cell site base stations fitted with microwave antennas. These sites are usually mounted on a tower, pole or building, located throughout populated areas, then connected to a cabled communication network and switching system. The phones have a low-power transceiver that transmits voice and data to the nearest cell sites, normally not more than 8 to 13 km (approximately 5 to 8 miles) away.
When the mobile phone or data device is turned on, it registers with the mobile telephone exchange, or switch, with its unique identifiers, and can then be alerted by the mobile switch when there is an incoming telephone call. The handset constantly listens for the strongest signal being received from the surrounding base stations, and is able to switch seamlessly between sites. As the user moves around the network, the "handoffs" are performed to allow the device to switch sites without interrupting the call.
Cell sites have relatively low-power (often only one or two watts) radio transmitters which broadcast their presence and relay communications between the mobile handsets and the switch. The switch in turn connects the call to another subscriber of the same wireless service provider or to the public telephone network, which includes the networks of other wireless carriers. Many of these sites are camouflaged to blend with existing environments, particularly in scenic areas.
The dialogue between the handset and the cell site is a stream of digital data that includes digitized audio (except for the first generation analog networks). The technology that achieves this depends on the system which the mobile phone operator has adopted. The technologies are grouped by generation. The first-generation systems started in 1979 with Japan, are all analog and include AMPS and NMT. Second-generation systems, started in 1991 in Finland, are all digital and include GSM, CDMA and TDMA.
The nature of cellular technology renders many phones vulnerable to 'cloning': anytime a cell phone moves out of coverage (for example, in a road tunnel), when the signal is re-established, the phone sends out a 're-connect' signal to the nearest cell-tower, identifying itself and signaling that it is again ready to transmit. With the proper equipment, it's possible to intercept the re-connect signal and encode the data it contains into a 'blank' phone -- in all respects, the 'blank' is then an exact duplicate of the real phone and any calls made on the 'clone' will be charged to the original account.
Third-generation (3G) networks, which are still being deployed, began in 2001. They are all digital, and offer high-speed data access in addition to voice services and include W-CDMA (known also as UMTS), and CDMA2000 EV-DO. China will launch a third generation technology on the TD-SCDMA standard. Operators use a mix of predesignated frequency bands determined by the network requirements and local regulations.
In an effort to limit the potential harm from having a transmitter close to the user's body, the first fixed/mobile cellular phones that had a separate transmitter, vehicle-mounted antenna, and handset (known as car phones and bag phones) were limited to a maximum 3 watts Effective Radiated Power. Modern handheld cell phones which must have the transmission antenna held inches from the user's skull are limited to a maximum transmission power of 0.6 watts ERP. Regardless of the potential biological effects, the reduced transmission range of modern handheld phones limits their usefulness in rural locations as compared to car/bag phones, and handhelds require that cell towers be spaced much closer together to compensate for their lack of transmission power.
Some handhelds include an optional auxiliary antenna port on the back of the phone, which allows it to be connected to a large external antenna and a 3 watt cellular booster. Alternately in fringe-reception areas, a cellular repeater may be used, which uses a long distance high-gain dish antenna or yagi antenna to communicate with a cell tower far outside of normal range, and a repeater to rebroadcast on a small short-range local antenna that allows any cell phone within a few meters to function properly.
GSM
Global System for Mobile communications (GSM: originally from Groupe Special Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 82% of the global mobile market uses the standard. GSM is used by over 3 billion people across more than 212 countries and territories. Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signaling and speech channels are digital, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was easy to build into the system.
The ubiquity of the GSM standard has been an advantage to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM). GSM also pioneered a low-cost, to the network carrier, alternative to voice calls, the Short message service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Another advantage is that the standard includes one worldwide Emergency telephone number, 112. This makes it easier for international travellers to connect to emergency services without knowing the local emergency number. Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM
Evolution (EDGE).
GSM is a cellular network, which means that mobile phones connect to it by searching for cells in the immediate vicinity. GSM networks operate in four different frequency ranges. Most GSM networks operate in the 900 MHz or 1800 MHz bands. Some countries in the Americas (including Canada and the United States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz frequency bands were already allocated.
The rarer 400 and 450 MHz frequency bands are assigned in some countries, notably Scandinavia, where these frequencies were previously used for first-generation systems.