What is Aloha? Types of Aloha

What is Aloha?

Aloha means “Hello”. It is a multiple access protocol in a data link layer and explain how multiple terminals/station access the medium or channel without any collision or interference. The basic idea is to use different frequencies in a hub/star configuration.

The hub broadcast data packet to every client at the outbound channel.
The Client broadcast data packet to Hub at the inbound channel.
If the hub receive data packet correctly a short acknowledgement is sent to the client from the hub.
If the client does not receive any acknowledgement in the meantime it assume that the hub did not received the packet and again retransmit the same data packet at a randomly selected time interval.
This mechanism is used to avoid any collision when two terminals communicate simultaneously.

There are two types of Aloha

Pure Aloha
Slotted Aloha

Pure Aloha

In pure ALOHA,Whenever station is ready they are allowed to send.
When two or more stations transmit frames simultaneously, collision occurs and the frames are destroyed.
In pure ALOHA, whenever the station transmits a frame, it expects the acknowledgement from the receiver end.
If acknowledgement is not received within specified interval of time, the station assumes that the frame (or acknowledgement) has been destroyed.
If the frame is destroyed because of collision the station waits for a random amount of time and retransmit the same frame again. This waiting time must be random otherwise the frames will collide again and again.
A central clock/station will inform all the other stations about the start of each slot.
Therefore, pure ALOHA explains that whenever there is collision, each station must wait for a random amount of time before retransmitting its frame. This randomness will help avoid more collisions.

Slotted Aloha

Slotted ALOHA was invented to improve the efficiency of pure ALOHA as chances of collision is still there because the random amount of time for which they wait before sending the frame may be same in pure ALOHA.
In slotted ALOHA, the time of the shared channel/medium is divided into discrete intervals called slots.
The stations can send a frame at the beginning of the slot only and one frame can be sent in each slot.
In slotted ALOHA, if the station misses the beginning of a slot it has to wait until the beginning of the next time slot for sending the frame.
In slotted ALOHA, there is still a possibility of collision if two stations try to send the frame at the beginning of the same time slot.
Slotted ALOHA is still better than the Pure ALOHA as chances of collision are reduced to one-half.

Comments

Computer Network : Layered Architecture

Layered Architecture Protocol Hierarchy To tackle with the design complexity most of the networks are organize as a set of layers or levels. The fundamental idea of layered architecture is to divide the design into small pieces. The layering provides modularity to the network design. The main duty of each layer is to provide offer services to higher layers, and provide abstraction. The main benefits of layered architecture are modularity and clear interfaces. Five Layered Network Design Issues: Layered architecture in computer network design Layered architectures have several advantages. Some of them are, Modularity and clear interface Provide flexibility to modify network services Ensure independence of layers Management of network architecture is easy Each layer can be ...

Can coronavirus spread through mosquitoes?

Can coronavirus spread through mosquitoes? Scientists have confirmed for the first time that the novel coronavirus behind the COVID-19 pandemic cannot be transmitted to people by mosquitoes , a finding that adds evidence to WHO claims that the disease is not mosquito-borne. The research, published in the journal Scientific Reports, provided the first experimental evidence on the capacity of SARS-CoV-2, the virus that causes COVID-19 disease, to infect and be transmitted by mosquitoes. "Here we provide the first experimental data to investigate the capacity of SARS-CoV-2 to infect and be transmitted by mosquitoes," the study noted. "While the World Health Organization (WHO) has definitively stated that mosquitoes cannot transmit the virus, our study is the first to provide conclusive data supporting the theory," said Stephen Higgs, a co-author of the research from Kansas State University in the US. According to the study, conducted at the university...

What is a pulse oximeter? How does it help a COVID-19 patient?

OXIMETER

BIT ORIENTED PROTOCOLS : SDLC, HDLC, BISYNC, LAP & LAPB

BIT ORIENTED PROTOCOLS A bit-oriented protocol is a communications protocol that sees the transmitted data as an opaque stream of bits with no semantics, or meaning. Control codes are defined in terms of bit sequences instead of characters. Bit oriented protocol can transfer data frames regardless of frame contents. It can also be stated as "bit stuffing" this technique allows the data frames to contain an arbitrary number of bits and allows character codes with arbitrary number of bits per character. SDLC Synchronous Data Link Control (SDLC) supports a variety of link types and topologies. It can be used with point-to-point and multipoint links, bounded and unbounded media, half-duplex and full-duplex transmission facilities, and circuit-switched and packet-switched networks. SDLC identifies two types of network nodes: primary and secondary. Primary nodes control the operation of other stations, called secondary. The primary polls the secondary in a predeter...

Do Google Assistant work on KaiOS?

Yes Google Assistant can now read, translate text on KaiOS Google on Tuesday announced that now within Google Assistant, KaiOS users in India can use Google Lens to read, translate, and define words. At Google I/O in 2019, the US-based search engine giant brought a camera-based translation to Google Lens to help understand information. With Lens, one can point the camera at text one see and translate it into more than 100 languages and can even speak the words out loud in the preferred language. "We brought these Lens capabilities to Google Go, so even those on the most affordable smartphones can access them. Today we are extending this capability to the millions of Google Assistant users on KaiOS devices in India," the company said in a statement. It is currently available in English and several Indian languages, including Hindi, Bengali, Telugu, Marathi, and Tamil, and will soon be available in Kannada and Gujarati. Users can simply press the right soft key ...

52 Chinese apps red-flagged by Indian Intel agencies

52 Chinese apps red-flagged by Indian Intel agencies; TikTok, ShareIt, UC Browser, Clean Master in list Indian intelligence agencies have asked the government to block or advise people to stop using a bunch of applications that are apparently extracting user data. These Chinese apps, 52 in number are linked to neighboring country China. The concern raised is that the applications in question end up extracting a huge amount of private data and sending this outside India. The list of applications includes popular tools that are used by lots of people in the country. These Chinese apps list include : TikTok Vault-Hide Vigo Video Bigo Live Weibo WeChat SHAREit UC News UC Browser BeautyPlus Xender ClubFactory Helo LIKE Kwai ROMWE SHEIN NewsDog Photo Wonder APUS Browser VivaVideo- QU Video Inc Perfect Corp CM Browser Virus Cleaner (Hi Security Lab) Mi Community DU recorder YouCam Makeup Mi Store 360 Security DU Battery Saver DU Browser DU Cleaner DU Privacy Clean Master – Cheetah...

Data link layer :Mac sub-layer, MAC Addressing,MAC vs IP addressing

MAC Sublayer In the seven-layer OSI model of computer networking, media access control (MAC) data communication protocol is a sublayer of the data link layer (layer 2). The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. Ethernet. The hardware that implements the MAC is referred to as a media access controller. The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service. MAC Addressing (Media Access Control address) In a local area network (LAN) or other network, the MAC (Media Access Control) address is your computer's unique hardware number. In a local are...

Sampoorntech

Search This Blog