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Telecommunication

Telecommunication

posted 1 month 2 weeks ago
इसलाम कहता है जब वजू करो तो कम पानी बहाव

फिर हम किसी का खूँन कैसे बहा सकते.....
                  मिनहाज
बहुत अफ़सोस की बात है के लोग अपनी तानाशाही चलाने के लिए निर्दोष लोगों की जान धर्म का  बैनर लगा कर ले रहें हैं हालाँकि सब ही जानते हैं के कोई धर्म भी किसी पर अत्याचार करने की अनुमति नहीं देता है। अफ़सोस की बात तो यह है के जो धर्म शांति स्थापित करने के लिए आया है उसी को आज पूरी दुनिया मे बदनाम , रुसवा किया जा रहा है जी हाँ मैं इस्लाम धर्म की ही बात कर रहा हूँ दरअसल लोगो ने इस्लाम की परिभाषा समझे बगैर ही अपने को मुस्लमान समझने लगे जिस का नतीजा यह हुवा के लोगों ने इस्लाम को अपने तरह से चलाना शरू कर दिए जबकि इस्लामिक शिक्षाओं के अनुसार मनुष्य इस्लाम को नहीं चला सकते हैं दरसल हो यह रहा है के आज इस्लाम और मुस्लमान दो अलग अलग चीज़े हो गए हैं।



एक बात यह भी सच है के लोगों को केवल मुस्लमान आतंकवादी नज़र आते है हालाँकि ऐसे लोग जो लोगो पर अत्याचार करते हैं वो मुस्लमान हो ही नही सकता। लोगो को  मववादी, नक्सली. म्यांमार, चीन , इस्राइल नज़र नही आते हैं मैं  लोगो से अपील करता हूँ की इस्लाम से अपने सोतेला पन का चश्मा उतार कर आतंकवाद को देखना शरू करे।
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Telecommunication

posted 1 year 1 month ago
Handoff procedures The process of transferring a call from one base station to another when a users radio signal becomes weaker at the first and strongest at the second base station. Weaker and stronger is quantified by a signal threshold level, which is above the minimum signal level for acceptable voice communication. Selecting this threshold level is critical to ensure f a. Unnecessary hand offs do not occur b. Call dropping does not occur Minimum acceptable signal level is between -90dbm and -100dbm, a slightly stringer signal is consider as handoff threshold. This margin is given by,  which is 0 to 6dbm.  cannot be too small or too large. If  is too large, unnecessary handoffs which burden the MSC may occur, and if  too small there may be insufficient time to complete the handoff before a call is lost due to weak signal conditions. Thus  has to be selected carefully. In diagram of improper handoff it is shown that handoff is not made and the signal drops below the minimum acceptable level to keep the channel active. This dropped event happens when excessive time is taken by MSC to assign handoff or when  is very small. To decide when to handoff it is important to ensure that the drop in signal level is not due the momentary fading but it is due to mobile moving away from base station. In order to ensure that base station monitors the signal level for a certain period of time before handoff is made. There are four types of hand off a. Hard hand off b. Soft hand off c. Mobile assisted hand off d. Intersystem hand off A. Hard hand off: Frequency channels are taken back by the older base station before new connection is established. This is break before make type of handoff. In this frequency channels are utilized properly but chances of drops are more. B. Soft hand off: Frequency channels are taken back by the older base station after new connection is established. This is break after make type of handoff. This is reliable but frequency channels are not utilized properly. C. Mobile Assisted hand off: In this a mobile scan signal strength of all base stations near to it and continuously reports the results of these measurements to the serving base station. Whenever signal strength of its current base station decreases and becomes less than the power received from the neighbouring cell, it initiates handoff. D. Intersystem hand off: This hand off occurs when the user moves from one MSC to another MSC i.e. from one cellular system to another cellular system while on a voice call. When mobile signal becomes weak in a given cell and the MSC cannot find another cell within its system to which it can transfer the call in progress intersystem handoff is implemented.
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Telecommunication

posted 1 year 2 months ago
Telecommunications network, electronic system of links and switches, and the controls that govern their operation, that allows for data transfer and exchange among multiple users.
 
When several users of telecommunications media wish to communicate with one another, they must be organized into some form of network. In theory, each user can be given a direct point-to-point link to all the other users in what is known as a fully connected topology (similar to the connections employed in the earliest days of telephony), but in practice this technique is impractical and expensive—especially for a large and dispersed network. Furthermore, the method is inefficient, since most of the links will be idle at any given time. Modern telecommunications networks avoid these issues by establishing a linked network of switches, or nodes, such that each user is connected to one of the nodes. Each link in such a network is called a communications channel. Wire, fibre-optic cable, and radio waves may be used for different communications channels.
 
TYPES OF NETWORKS
 
Switched communications network
A switched communications network transfers data from source to destination through a series of network nodes. Switching can be done in one of two ways. In a circuit-switched network, a dedicated physical path is established through the network and is held for as long as communication is necessary. An example of this type of network is the traditional (analog) telephone system. A packet-switched network, on the other hand, routes digital data in small pieces called packets, each of which proceeds independently through the network. In a process called store-and-forward, each packet is temporarily stored at each intermediate node, then forwarded when the next link becomes available. In a connection-oriented transmission scheme, each packet takes the same route through the network, and thus all packets usually arrive at the destination in the order in which they were sent. Conversely, each packet may take a different path through the network in a connectionless or datagram scheme. Since datagrams may not arrive at the destination in the order in which they were sent, they are numbered so that they can be properly reassembled. The latter is the method that is used for transmitting data through the Internet.
 
 
Broadcast network
A broadcast network avoids the complex routing procedures of a switched network by ensuring that each node’s transmissions are received by all other nodes in the network. Therefore, a broadcast network has only a single communications channel. A wired local area network (LAN), for example, may be set up as a broadcast network, with one user connected to each node and the nodes typically arranged in a bus, ring, or star topology, as shown in the figure. Nodes connected together in a wireless LAN may broadcast via radio or optical links. On a larger scale, many satellite radio systems are broadcast networks, since each Earth station within the system can typically hear all messages relayed by a satellite.
 
 
NETWORK ACCESS
 
Since all nodes can hear each transmission in a broadcast network, a procedure must be established for allocating a communications channel to the node or nodes that have packets to transmit and at the same time preventing destructive interference from collisions (simultaneous transmissions). This type of communication, called multiple access, can be established either by scheduling (a technique in which nodes take turns transmitting in an orderly fashion) or by random access to the channel.
 
 
Scheduled access
In a scheduling method known as time-division multiple access (TDMA), a time slot is assigned in turn to each node, which uses the slot if it has something to transmit. If some nodes are much busier than others, then TDMA can be inefficient, since no data are passed during time slots allocated to silent nodes. In this case a reservation system may be implemented, in which there are fewer time slots than nodes and a node reserves a slot only when it is needed for transmission.
 
A variation of TDMA is the process of polling, in which a central controller asks each node in turn if it requires channel access, and a node transmits a packet or message only in response to its poll. “Smart” controllers can respond dynamically to nodes that suddenly become very busy by polling them more often for transmissions. A decentralized form of polling is called token passing. In this system a special “token” packet is passed from node to node. Only the node with the token is authorized to transmit; all others are listeners.
 
 
 
Random access
Scheduled access schemes have several disadvantages, including the large overhead required for the reservation, polling, and token passing processes and the possibility of long idle periods when only a few nodes are transmitting. This can lead to extensive delays in routing information, especially when heavy traffic occurs in different parts of the network at different times—a characteristic of many practical communications networks. Random-access algorithms were designed specifically to give nodes with something to transmit quicker access to the channel. Although the channel is vulnerable to packet collisions under random access, various procedures have been developed to reduce this probability.
 
Carrier sense multiple access
One random-access method that reduces the chance of collisions is called carrier sense multiple access (CSMA). In this method a node listens to the channel first and delays transmitting when it senses that the channel is busy. Because of delays in channel propagation and node processing, it is possible that a node will erroneously sense a busy channel to be idle and will cause a collision if it transmits. In CSMA, however, the transmitting nodes will recognize that a collision has occurred: the respective destinations will not acknowledge receipt of a valid packet. Each node then waits a random time before sending again (hopefully preventing a second collision). This method is commonly employed in packet networks with radio links, such as the system used by amateur radio operators.
 
It is important to minimize the time that a communications channel spends in a collision state, since this effectively shuts down the channel. If a node can simultaneously transmit and receive (usually possible on wire and fibre-optic links but not on radio links), then it can stop sending immediately upon detecting the beginning of a collision, thus moving the channel out of the collision state as soon as possible. This process is called carrier sense multiple access with collision detection (CSMA/CD), a feature of the popular wired Ethernet. (For more information on Ethernet, see computer: Local area networks.)
 
 
Spread-spectrum multiple access
 
Since collisions are so detrimental to network performance, methods have been developed to allow multiple transmissions on a broadcast network without necessarily causing mutual packet destruction. One of the most successful is called spread-spectrum multiple access (SSMA). In SSMA simultaneous transmissions will cause only a slight increase in bit error probability for each user if the channel is not too heavily loaded. Error-free packets can be obtained by using an appropriate control code. Disadvantages of SSMA include wider signal bandwidth and greater equipment cost and complexity compared with conventional CSMA.
 
 
OPEN SYSTEMS INTERCONNECTION
Different communication requirements necessitate different network solutions, and these different network protocols can create significant problems of compatibility when networks are interconnected with one another. In order to overcome some of these interconnection problems, the open systems interconnection (OSI) was approved in 1983 as an international standard for communications architecture by the International Organization for Standardization (ISO) and the International Telegraph and Telephone Consultative Committee (CCITT). The OSI model, as shown in the figure, consists of seven layers, each of which is selected to perform a well-defined function at a different level of abstraction. The bottom three layers provide for the timely and correct transfer of data, and the top four ensure that arriving data are recognizable and useful. While all seven layers are usually necessary at each user location, only the bottom three are normally employed at a network node, since nodes are concerned only with timely and correct data transfer from point to point.
 
Data recognition and use
The application layer is difficult to generalize, since its content is specific to each user. For example, distributed databases used in the banking and airline industries require several access and security issues to be solved at this level. Network transparency (making the physical distribution of resources irrelevant to the human user) also is handled at this level. The presentation layer, on the other hand, performs functions that are requested sufficiently often that a general solution is warranted. These functions are often placed in a software library that is accessible by several users running different applications. Examples are text conversion, data compression, and data encryption.
 
 
User interface with the network is performed by the session layer, which handles the process of connecting to another computer, verifying user authenticity, and establishing a reliable communication process. This layer also ensures that files which can be altered by several network users are kept in order. Data from the session layer are accepted by the transport layer, which separates the data stream into smaller units, if necessary, and ensures that all arrive correctly at the destination. If fast throughput is needed, the transport layer may establish several simultaneous paths in the network and send different parts of the data over each path. Conversely, if low cost is a requirement, then the layer may time-multiplex several users’ data over one path through the network. Flow control is also regulated at this level, ensuring that data from a fast source will not overrun a slow destination.
 
Data transfer
The network layer breaks data into packets and determines how the packets are routed within the network, which nodes (if any) will check packets for errors along the route, and whether congestion control is needed in a heavily loaded network. The data-link layer transforms a raw communications channel into a line that appears essentially free of transmission errors to the network layer. This is done by breaking data up into data frames, transmitting them sequentially, and processing acknowledgment frames sent back to the source by the destination. This layer also establishes frame boundaries and implements recovery procedures from lost, damaged, or duplicated frames. The physical layer is the transmission medium itself, along with various electric and mechanical specifications.
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Telecommunication

posted 1 year 2 months ago
 
In an organization, information flows forward, backwards and sideways. This information flow is referred to as communication. Communication channels refer to the way this information flows within the organization and with other organizations.
 
In this web known as communication, a manager becomes a link. Decisions and directions flow upwards or downwards or sideways depending on the position of the manager in the communication web.
 
For example, reports from lower level manager will flow upwards. A good manager has to inspire, steer and organize his employees efficiently, and for all this, the tools in his possession are spoken and written words.
 
For the flow of information and for a manager to handle his employees, it is important for an effectual communication channel to be in place.
 
The Working of a Communication Channel
 
Through a modem of communication, be it face-to-face conversations or an inter-department memo, information is transmitted from a manager to a subordinate or vice versa.
 
An important element of the communication process is the feedback mechanism between the management and employees.
 
In this mechanism, employees inform managers that they have understood the task at hand while managers provide employees with comments and directions on employee's work.
 
Importance of a Communication Channel
 
A breakdown in the communication channel leads to an inefficient flow of information. Employees are unaware of what the company expects of them. They are uninformed of what is going on in the company.
 
This will cause them to become suspicious of motives and any changes in the company. Also without effective communication, employees become department minded rather than company minded, and this affects their decision making and productivity in the workplace.
 
Eventually, this harms the overall organizational objectives as well. Hence, in order for an organization to be run effectively, a good manager should be able to communicate to his/her employees what is expected of them, make sure they are fully aware of company policies and any upcoming changes.
 
Therefore, an effective communication channel should be implemented by managers to optimize worker productivity to ensure the smooth running of the organization.
 
Types of Communication Channels
 
The number of communication channels available to a manager has increased over the last 20 odd years. Video conferencing, mobile technology, electronic bulletin boards and fax machines are some of the new possibilities.
 
As organizations grow in size, managers cannot rely on face-to-face communication alone to get their message across.
 
A challenge the managers face today is to determine what type of communication channel should they opt for in order to carryout effective communication.
 
In order to make a manager's task easier, the types of communication channels are grouped into three main groups: formal, informal and unofficial.

Formal Communication Channels
  • A formal communication channel transmits information such as the goals, policies and procedures of an organization. Messages in this type of communication channel follow a chain of command. This means information flows from a manager to his subordinates and they in turn pass on the information to the next level of staff.
  • An example of a formal communication channel is a company's newsletter, which gives employees as well as the clients a clear idea of a company's goals and vision. It also includes the transfer of information with regard to memoranda, reports, directions, and scheduled meetings in the chain of command.
  • A business plan, customer satisfaction survey, annual reports, employer's manual, review meetings are all formal communication channels.
Informal Communication Channels
  • Within a formal working environment, there always exists an informal communication network. The strict hierarchical web of communication cannot function efficiently on its own and hence there exists a communication channel outside of this web. While this type of communication channel may disrupt the chain of command, a good manager needs to find the fine balance between the formal and informal communication channel.
  • An example of an informal communication channel is lunchtime at the organization's cafeteria/canteen. Here, in a relaxed atmosphere, discussions among employees are encouraged. Also managers walking around, adopting a hands-on approach to handling employee queries is an example of an informal communication channel.
  • Quality circles, team work, different training programs are outside of the chain of command and so, fall under the category of informal communication channels.
Unofficial Communication Channels
  • Good managers will recognize the fact that sometimes communication that takes place within an organization is interpersonal. While minutes of a meeting may be a topic of discussion among employees, sports, politics and TV shows also share the floor.
  • The unofficial communication channel in an organization is the organization's 'grapevine.' It is through the grapevine that rumors circulate. Also those engaging in 'grapevine' discussions often form groups, which translate into friendships outside of the organization. While the grapevine may have positive implications, more often than not information circulating in the grapevine is exaggerated and may cause unnecessary alarm to employees. A good manager should be privy to information circulating in this unofficial communication channel and should take positive measures to prevent the flow of false information.
  • An example of an unofficial communication channel is social gatherings among employees.

 

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