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High Level Data Link Control (HDLC)

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 HDLC  was developed by ISO and has become the most widely accepted data link protocol. It offers a high level of flexibility, adaptability, reliability and efficiency of operation for today as well as tomorrow's synchronous data communication needs. ADCCP developed by ANSI is almost similar to HDLC, IBM'S SDLC is a proper subset of HDLC and level 2 of X-25 is a permissible option of HDLC. In this chapter, we shall study the basic features and operation of HDLC protocol. Certain liberties have been taken in the level of completeness of description so as not to cloud the overall picture with the details. GENERAL FEATURES of hdlc    HDLC is a bit oriented data link control protocol which satisfies wide variety of data link control requirements including: ·          Point-to-point and point-to-multipoint links. ·          Two way simultaneous communication over full duplex circuits. ·          Two way alternate operation over half duplex or full duplex circuits. ·

ERROR DETECTION & COORECTION

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ERROR DETECTION When a code word is transmitted, one or more of its bits may be reversed due to signal impairment. The receiver can detect these errors if the received code word is not one of the valid code word of the code set. If the corrupted received word becomes another valid code word, the error cannot be detected. When error occurs, the distance between the transmitted and received code words is equal to the number of erroneous bits . as showing in given below figure. TRANSMITTED CODE WORD RECEIVED CODE WORD NUMBER OF ERRORS DISTANCE 11001100 11001110 1 1 10010010 00011010 2 2 10101010 10100100 3 3 In other words the valid code words must be separated by a distance more than 1 else even a single bit error will generate another valid code word and the error will not be detected. The number of errors which can be detected

TRANSMISSION ERRORS

Errors are introduced in the data bits during their transmission across a sub network. These errors can be categorised into : ·           Content errors ·           Flow integrity errors Content errors are the errors in the content or a message, e.g. a "1" may be received as "0". This type of errors gets introduced due to impairment of the electrical signal in the transmission media. Flow integrity errors refer to missing blocks of data. For example, a data block may be lost in the sub-network due to its having been delivered to a wrong destination. In voice communication, the listener can tolerate a good deal of signal corruption during transmission. But data is very sensitive to errors. Measures are, therefore, built into a data communication system to counteract the effect of errors. These measures include: ·                      Introduction of additional check bits in the data bits to detect and correct content errors. ·                      Es

OSI REFERENCE MODEL

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The International Organization introduced the OSI layer for Standardization (ISO) in 1984 in order to provide a reference model to make sure products of different vendors would interoperate in networks. OSI is short for Open System Interconnection. The OSI layer shows WHAT needs to be done to send data from an application on one computer, trough a network, to an application on another computer, not HOW it should be done.  A layer in the OSI model communicates with three other layers: the layer above it, the layer below it, and the same layer at its communication partner. Data transmitted between software programs passes all 7 OSI layers. The Application, Presentation and Session layers are also known as the Upper Layers. The Data Link and Physical layers are often implemented together to define LAN and WAN specifications.   Application Layer (Layer 7) Application Layer provides network services directly to applications. Type of software programs vary a lot: from groupw

different between TRANSMISSION AND COMMUNICATION

Let us now understand the difference between transmission and communication. Transmission means physical movement of information from one point to another. Communication means meaningful exchange of information between the communicating devices. Example Two persons, one knowing English language only and the other knowing French language only cannot communicate with each other. Here transmission is taking place, but communication is not there. Therefore, for communication, we need much more than the transmission. For communication, we must have the same language, i.e. Data codes should be understood both by transmitter and the receiver. Moreover, receiver should be in a position to receive, i.e. Timing is also very important. We have two types of communication : (1)                Synchronous Communication. (2)                Asynchronous Communication. Synchronous Communication In Synchronous communication the exchange of information is in a well disciplined manner, e

Remote OMT and Remote OMT over IP

The features Remote OMT (Operation and Maintenance Terminal) and Remote OMT over IP are updated to support the new RBS 6000 DUG-20/RUS-01 configurations. In MCPA backwards compatible mode, having a BTS G11A or newer in a BSS 07B-G10B network, the configuration of an MCPA is made using OMT. Configuration in MCPA single mode (BTS G11B with BSS G10B or newer) is made from the BSC, refer to Section 5.7 on page 43. All TRXs in a DUG are connected to one or several RUSs. It is the connections between RUSs and antennas that will decide which MCPAs to use for which antenna sectors (cells). Each antenna sector is configured in the OMT with the default configuration of 3*20W (3*43.0 dBm) per MCPA. If desired it is possible to choose a different number of TRXs per MCPA, and it is possible to choose some configurations where the total MCPA mean power will end up on less than 60 W (47.8 dBm). Also the levels 40W (46.0 dBm) and 20W (43.0 dBm) are available. The chosen number of TRXs

Antenna Control - Standard TMA

The RBS 6000 Radio Units have built-in functionality for what would otherwise require external equipment so there is no need for installation of extra hardware for supervision and power feed for TMAs. The radio units in RBS 6000 will provide the power and also supervise standard TMAs by monitoring the current consumed by the TMA. Commands: • RXBFC, Radio X-ceiver Administration, BTS Feature Data, Change The parameter to activate Standard TMA (CSTMA) is added to this existing command. Printouts: • RADIO X-CEIVER ADMINISTRATION BTS FEATURE DATA (command RXBFP) • RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT CONFIGURATION DATA (command RXCDP)