Data structure is a collection of data elements. It is also called data type. It is a tool to solve problems. Used to represent entities and to implement entities operations. Elements in the data type is called values of the type. There are four basic/atomic/primitive data types – int, float, char, double. More data types can be generated from basic data types. Simple data types generated from primitive data types are – arrays, pointer, strings, record. From this simple type composite data type can be generated such as stacks, queues, trees etc..,
- Linear data type
- stacks,
- queues
- linked lists
- Nonlinear data type –
- trees
- graphs
Operations in data type are
- Creation of data types
- Deletion of data types
- Inserting an element in data type
- Accessing element in data type
Stack is an ordered list in which all insertions and deletions done in one end, this end is called top end. It is also called LIFO list. Queue is an ordered list in which all deletions are placed in front end and insertions are placed in rear end. Stack is a FIFO list. Simplest way to implement stack is by using one dimensional array of n elements
Dequeue – double ended queue, in which insertion and deletion is possible in both ends. Linked list uses self referential structure. Linked list requires more storage space but highly flexible. No need of explicit counter for number of nodes in the list. Overflow is not a problem until memory is exhausted. Queues can also be implemented as linked list. Linked queue have rear and frond end, deletion is done in rear end, an empty queue is denoted by front = 0. Linked list is superior when structures are large
Double linked list – where each node contains two links ( one for next node and other for previous node ). A graph G contains two sets V and E. V is a finite nonempty set of vertices. E is a set of pair of vertices, these pairs are called set of edges, this is ordered in an unidirectional manner [G(v1v2) = G(v2v1)]
Simple path is one in which all edges are distinct except first and last. Cycle is a simple path with first and last are same. 2-tree is a tree in which each vertex have 0 or 2 children. Binary tree consist of left subtree and right subtree
Modem
Modem is an electronic bridge. A data terminal equipment (DTE) is used with modem. Transmission medium between modems are dedicated circuit or switched telephone network
Working : DTE at transmitter sends RTS (ready to send) signal to the modem at transmitter, data communication equipment in modem sends DCD (data carrier detect) to the receiver modem, then a series of signal transmitted between receiver and transmitter modems for communication channel establishment which is called handshaking
Four wire modem uses a pair of wire used for incoming signals and other pair for outgoing. In two wire, both the wires are used for incoming and outgoing, this is used in telephone exchange. Binary continuous wave modulation is used in modem, example : ASK, FSK, PSK, DPSK. Most popular modems are V series which is published by ITU-T. 32 modem uses combined modulation and encoding technique called trelliscoded modulation, Trellis is essentially a QAM with a redundant bit.
Smart modem accepts command from the terminal via RS 232 interface. Extended command sets of modern modem use different commands to control many advanced features of modem. Scrambler is present in transmitter section of synchronous modem. In modem binary code is transformed in to Gray code. DAC in synchronous modem sends send signal to equalizer
Receiver equalizer in synchronous modem is called adaptive equalizer. It reduces delay distortion by using tapped delay line.26 modem has a modulation rate of 1200 bauds. T1 carrier uses bipolar transition signal coding method. In modems digital signal changes characteristics of carrier signal. If communication software is called traffic cop then modem is called bridge. For connecting a modem with computer, then computer should have a port with RS 232 standard, RS stands for recommended standard
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