In the same way computer network channels also have protocols like multiple access protocols, random access protocols, etc.Let's say you are talking to your friend using a mobile phone. Just to get things working and avoid problems we have some rules or protocols, like "please stand in the queue", "do not push each other", "wait for your turn", etc. Which one do you think is more productive? The ordered one, right? And we all know the reason why. Of the slot and becomes backlogged.Above are the scenarios for approaching a ticket counter.
But as the network becomes more and more complex e.g. But remember, if the data frame is not received by the receiver (maybe due to collision) then the frame is sent again until it successfully reaches the receiver's end.Whenever we talk about a wireless broadcast system or a half-duplex two-way link, the ALOHA method works efficiently. If we succeed and the frame reaches its destination, then the next frame is lined-up for transmission. ALOHA Random Access ProtocolThe ALOHA protocol or also known as the ALOHA method is a simple communication scheme in which every transmitting station or source in a network will send the data whenever a frame is available for transmission. So here we have all the users (stations) at an equal priority, where any station can send data depending on medium's state whether it is idle or busy, meaning that if you friend is talking to someone else through the mobile phone, then its status is busy and you cannot establish a connection and since all the users are assigned equal priority you can not disconnect your friend's ongoing call and connect yours.The random access protocols consist of the following characteristics:There is no time restriction for sending the data (you can talk to your friend without a time restriction).There is a fixed sequence of stations which are transmitting the data.As in the above diagram you might have observed that the random-access protocol is further divided into four categories, which are:Let's cover each one of them, one by one. Whenever you call someone, a connection between you and the desired person is established, also anyone can call anyone.
Any number of stations can transmit data at any time.Here, any random station can transmit the data at the beginning of any random time slotHere, the time is continuous and is not globally synchronized with any other station.Here, the time is discrete unlike pure ALOHA and is also globally synchronizedProbability of successful transmission of a data packetWhere, G = no. Pure & Slotted ALOHA, the following is the difference between both.Stations can transmit the data randomly i.e. This system consists of the signals termed as beacons which are sent at precise time intervals and inform each source when the channel is clear to send the frame.Now, as we came to know about ALOHA's 2 types i.e. Following is the flow chart of Pure ALOHA.So, to minimize these collisions and to optimize network efficiency as well as to increase the number of subscribers that can use a given network, the slotted ALOHA was developed.
Successfully transmitted or failed. CSMA/CD Random Access ProtocolCSMA/CD means CSMA with Collision Detection.In this, whenever station transmits data-frame it then monitors the channel or the medium to acknowledge the state of the transmission i.e. Here, for the 1-persistent mode, the throughput is 50% when G=1 and for Non-persistent mode, the throughput can reach up to 90%. If the channel is idle, then the station waits for its turn to send the data-frame.It is comparatively much greater than the throughput of pure and slotted ALOHA. But how do they do it? The CSMA makes each station to first check the medium (whether it is busy or not) before sending any data packet.But, what to do if the channels are busy? Now, here the persistence methods can be applied to help the station act when the channel is busy or idle.1-persistent mode: In this, first the node checks the channel, if the channel is idle then the node or station transmits data, otherwise it keeps on waiting and whenever the channel is idle, the stations transmit the data-frame.Non-persistent mode: In this, the station checks the channel similarly as 1-persistent mode, but the only difference is that when the channel is busy it checks it again after a random amount of time, unlike the 1-persistent where the stations keep on checking continuously.P-persistent mode: In this, the station checks the channel and if found idle then it transmits the data frame with the probability of P and if the data is not transmitted (1-P) then the station waits for a random amount of time and again transmits the data with the probability P and this cycle goes on continuously until the data-frame is successfully sent.O-persistent: In this, the transmission occurs based on the superiority of stations which is decided beforehand and transmission occurs in that order. Till now we have understood that when 2 or more stations start sending data, then a collision occurs, so this CSMA method was developed to decrease the chances of collisions when 2 or more stations start sending their signals over the data link layer.
0 kommentar(er)
