In a WiFi network that uses the MAC scheme CSMA/CA (method 1) four users want to
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Question
In a WiFi network that uses the MAC scheme CSMA/CA (method 1) four users want to send data at the times 0, 0.25, 0.75, 2.25 as shown in the figure. If DIFS = 0.5 and the random times generated following this order (1, 0.5, 0.5, 1, 0.5, 1 ) calculate the time to send the packet for each user (fill the table below) and draw the expected scenario. Clarify if any collision happens. Assume that the medium is free at time 0 and the time needed to send the packet = 0.5
User 1 User 2 User 3 User 4 0 0.5 .5 2 2.5 3 3.5 4 4.5 55.5 66.5 7 7.5 Time to send User # User 1 User 2 User 3 User 4Explanation / Answer
wireless technologies and applications are getting to be one of the quickest developing and most encouraging regions as of late. To oblige information transmission by various stations sharing the rare remote data transfer capacity, a medium access control (MAC) convention assumes a significant part in booking bundle transmission reasonably and productively. The developing remote systems, for example, impromptu systems, sensor systems or work systems, are generally multihop based and in conveyed way, which brings a considerable measure of issues and difficulties in planning adjusted MAC conventions custom-made for present day remote system.
In this book, the writers give finish and inside and out diagrams to the exemplary medium access control calculations and the related conventions, and in addition their applications in different remote information arranges particularly the best Wireless Local Area Networks (WLAN).
Bearer sense different access with impact evasion (CSMA/CA) in PC organizing, is a system various access strategy in which transporter detecting is utilized, however hubs endeavor to stay away from crashes by transmitting just when the channel is detected to be "sit still". When they do transmit, hubs transmit their parcel information completely.
It is especially essential for remote systems, where the impact recognition of the option CSMA/CD is questionable because of the shrouded hub issue.
CSMA/CA is a convention that works in the Data Link (Layer 2) of the OSI demonstrate.
Points of interest
Crash evasion is utilized to enhance the execution of the CSMA strategy by endeavoring to partition the channel to some degree similarly among all transmitting hubs inside the impact space.
Bearer Sense: before transmitting, a hub initially tunes in to the common medium, (for example, tuning in for remote flags in a remote system) to decide if another hub is transmitting or not. Note that the shrouded hub issue implies another hub might transmit which goes undetected at this stage.
Impact Avoidance: if another hub was heard, we sit tight for a timeframe (typically irregular) for the hub to quit transmitting before listening again for a free interchanges channel.
Demand to Send/Clear to Send (RTS/CTS) may alternatively be utilized now to intercede access to the mutual medium. This goes some approach to easing the issue of shrouded hubs in light of the fact that, for example, in a remote system, the Access Point just issues a Clear to Send to one hub at any given moment. Be that as it may, remote 802.11 usage don't ordinarily execute RTS/CTS for all transmissions; they may turn it off totally, or possibly not utilize it for little parcels (the overhead of RTS, CTS and transmission is excessively incredible for little information exchanges).
Transmission: if the medium was distinguished as being clear or the hub got a CTS to expressly show it can send, it sends the edge completely. Dissimilar to CSMA/CD, it is exceptionally trying for a remote hub to tune in the meantime as it transmits (its transmission will overshadow any endeavor to tune in). Proceeding with the remote illustration, the hub anticipates receipt of an affirmation bundle from the Access Point to demonstrate the parcel was gotten and checksummed effectively. In the event that such affirmation does not touch base in an opportune way, it accept the bundle slammed into some other transmission, making the hub enter a time of double exponential backoff before endeavoring to re-transmit.
In spite of the fact that CSMA/CA has been utilized as a part of an assortment of wired correspondence frameworks, it is especially gainful in a remote LAN because of a typical issue of various stations having the capacity to see the Access Point, yet not each other. This is because of contrasts in transmit control, and get affectability, and in addition separation, and area concerning the AP.This will make a station not have the capacity to 'hear' another station's communicated. This is the alleged 'concealed hub', or 'shrouded station' issue. Gadgets using 802.11 based measures can appreciate the advantages of crash evasion (RTS/CTS handshake, additionally Point coordination work), in spite of the fact that they don't do as such as a matter of course. As a matter of course they utilize a Carrier detecting system called 'exponential backoff', or (Distributed coordination work) that depends upon a station endeavoring to 'tune in' for another station's communicated before sending. CA, or PCF depends upon the AP (or the 'beneficiary' for Ad hoc arranges) conceding a station the selective appropriate to transmit for a given timeframe in the wake of asking for it (Request to Send/Clear to Send).