TelecomStudy18

All data communication codes are based on the binary system (1s and 0s). A message can be encoded into a meaningful string of 1s and 0s that can be transmitted along a data line and decoded by a receiver. The string of 1s and 0s is meaningful because it is defined by a code that is known to both the source and the receiver. Code is limited by the number of bits (binary digits) it contains, e.g. one-bit code means that we can have 2 characters so that we can encode the letter A by '0' and B by '1'. Similarly, a 2 bit code will enable us to handle 4 characters. Thus, a n-bit code enables us to handle 2 n characters.  Some commonly used codes are : 1.              Baudot code 2.              ASCII code 3.              BCDIC code 4.           ...

TEMS CellPlanner Universal is Ericsson´s tool for mobile radio network planning. It is a highly graphical, easy-to-use, PC-based tool for design, realization, and optimization of mobile radio networks. TEMS CellPlanner Universal helps the user to roll out and expand mobile radio networks, and optimize radio network regarding service availability and service quality. It assists the user in a number of complex tasks, including network dimensioning, traffic planning, site configuration, and frequency planning. TEMS CellPlanner Universal is the key to successfully competing in the market place. TEMS CellPlanner Universal provides support for WCDMA, GSM 850, GSM 900, GSM 1800, GSM 1900, iDEN, CDMA, CDMA2000 1xRTT, TDMA/AMPS, NMT 450, NMT 900, TACS, and E-TACS. TEMS CellPlanner Universal also provides support for GPRS and EGPRS (EDGE), implemented in GSM system The modular platform makes it possible to customize TEMS CellPlanner Universal to meet the needs of every customer. TEMS Ce...

For understanding the data communication following terminology is discussed: - ·         Communication lines The medium that carries the message in a data communication system, example of  A 2W telephone line.    Communication Channel A channel is defined as a means of one way transmission. It can carry information in either direction but in only one direction at a time, e.g. A hose pipe. It can carry water in either direction, but the direction of flow depends on which end of pipe is connected to the water tap.  Simplex Transmission 1.     Message always flows in one direction only. 2.     An input Terminal can only receive and never transmit. 3.     An O/P Terminal can only transmit and never receive. Half Duplex Transmission -         A half duplex channel can transmit an...

There are three types of HDLC frames : ·          Information transfer frame (I-Frame) ·          Supervisory frame (S-Frame) ·          Unnumbered frame (U-Frame) Information Transfer Frame (I-FRAME) I-Frame is used for transporting user data. It also carries acknowledgement of the received frames. The control field of the I-Frame is as shown in Fig.7. The first bit is 0 which identifies the frame as an I-Frame. The next three bits are the sequence number N(S) of the frame. The fifth is Poll/Final (P/F) bit. Its use is explained later. The last three bits are the sequence number N(R) of the acknowledgement (RR) which is piggy backed on the I-Frame.  S upervisory f rame (S-FRAME) S-Frame does not have data field (Fig.3b) and is used to carry only acknowledgements, requests for retransmission, etc. It is identified by the first two bi...

 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 circui...

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...

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: ·             ...