ALOHA protocol calculator

PPT - Computer Networking Local Area Networks, Medium

ALOHA will calculate the area for you based on the release information you provided (up to a maximum diameter of 200 meters for spills on land). d. Click OK. The source strength information that you have entered—and the results of ALOHA's source strength calculations—appear in the Text Summary. ALOHA estimates that the release of vapor. Throughput of ALOHA Networks To express the throughput of the ALOHA random access scheme, it is often assumed that message transmission attempts occur according to a Poisson process with rate G attempts per slot. For channels in which a transmission is successful if and and only if in that slot only a single packet transmission is present, the throughput of successful messages is equal t In this case, transmitting station assumes that the transmission is successful. In framed slotted aloha based anti-collision protocols, the reader begins each interrogation round by informing all tags about the current frame size in terms of time slots. Protocol. We are going to ignore collisions. Slotted ALOHA improves all the problems that were in Pure ALOHA. In Slotted Aloha, any station. The 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. If we succeed and the frame reaches its destination, then the next frame is lined-up for transmission ALOHA Random Access Protocol. It is designed for wireless LAN (Local Area Network) but can also be used in a shared medium to transmit data. Using this method, any station can transmit data across a network simultaneously when a data frameset is available for transmission

Aloha. Norman Abramson and his colleagues were developed aloha at the University of Hawaii in the 1970s.ALOHA is a Multiple Access Protocol which is used for random access in the network.Aloha was designed for the wireless local area network (WLAN), which is also known as the radio broadcast. If more than one user transmits the data at the same time, then that data has a collision, and that. 36. Summary ALOHA is one of the random access protocol implemented at link layer. Chances of collisions are more in pure ALOHA as compared to Slotted ALOHA , but still it is least efficient as compared to other random access protocol such as CSMA (CD/CA). These protocols works efficiently when there are less active nodes Aloha in computer networks is an access control protocol. Versions of Aloha Protocol- Pure Aloha and Slotted Aloha. Pure Aloha in networking allows the stations to transmit the data at anytime. Slotted Aloha Protocol allows the stations to transmit data only at the beginning of the time slot. Difference between Pure Aloha and Slotted Aloha

Throughput of ALOHA Networks - Wireless Communicatio

For a large number of users the ALOHA protocol is considered. There are two versions of ALOHA that is Pure ALOHA and Slotted ALOHA. In Pure ALOHA no slotting was done but the efficiency was poor. In Slotted ALOHA, slots have been made, so that every frame transmission starts at the beginning of the slot and throughput is increased by a factor of 2 Slotted ALOHA. ALOHA is a medium access control (MAC) protocol for transmission of data via ashared network channel. Using this protocol, several data streams originating from multiple nodes are transferred through a multi-point transmission channel. There are two types of ALOHA protocols - Pure ALOHA and Slotted ALOHA Aloha is a multiple access protocol at the datalink layer and proposes how multiple terminals access the medium without interference or collision. The Slotted Aloha protocol involves dividing the time interval into discrete slots and each slot interval corresponds to the time period of one frame Pure ALOHA and Slotted ALOHA both are the Random Access Protocols, that are implemented on the Medium Access Control (MAC) layer, a sublayer of Data Link Layer. The purpose of the ALOHA protocol is to determine that which competing station must get the next chance of accessing the multi-access channel at MAC layer This concept of insertion of slots reduces probability of packet collisions obsered in pure ALOHA protocol above. Hence SLotted ALOHA doubles the maximum carrier throughput of pure Aloha to about 36%. Selective Reject Aloha protocol-SREJ Aloha. Figure-3 depicts operation of Selective Reject ALOHA Protocol. It is also known by SREJ Aloha

ALOHA protocols have been the basis of many wireless MACs since their inven-tion in the 1970s [8]. They are the first class of contention-based MAC protocols in a shared wireless medium. Later protocols, such as carrier sense multiple access (CSMA), achieve better performance than ALOHA in RF networks, due to their con Unlike in the regular ALOHA protocol, where other nodes can send messages that interfere with ours at any time, in the Slotted ALOHA protocol, the only other time a message can be sent to interfere with ours is if it's sent at the exact time ours is sent (since in Slotted ALOHA messages can only be sent at specific intervals, like every 5 seconds for example From the lesson. Random Access in Wifi Networks. In this lesson, we will investigate WiFi, another type of wireless network. Rather than having stringent power control algorithms as we saw for cellular, WiFi relies on random access methods to manage interference among users in the same location. Unlicensed Spectrum 5:01 In framed slotted aloha based anti-collision protocols, the reader begins each interrogation round by informing all tags about the current frame size in terms of time slots. c. N#35. Slotted Aloha Protocol allows the stations to transmit data only at the beginning of the time slot. The Slotted ALOHA makes the station to wait till the next time slot begins and allow each data frame to be.

This time slot corresponds to the length of frames. Q: what is max fraction slots successful? Therefore, the maximum throughput of Pure Aloha = 1/2e * 3.276 = (18.4 * 3.276) / 100 = 0.6027. Post the discussion to improve the above solution. Slotted Aloha. It achieves the throughput equivalent to SLotted Aloha without the need of synchronization. In Pure ALOHA, station can Slotted Aloha. Calculate Probability Of Aloha Protocol Our basic idea of packets ready for the paper itself, it is moving, and simple protocol aloha protocol i

slotted aloha efficiency calculato

In Pure ALOHA no slotting was done but the efficiency was poor. NOTE: Let me know if you have any doubts. time) node with new arriving pkt: transmit at beginning of next slot if collision: retransmit pkt in future slots with probability p, until successful. By a factor of 2: 1/(2e) instead of 1/e. Slotted ALOHA was developed in 1972 by Robert to improve the efficiency of pure ALOHA. So, G. In this case, transmitting station assumes that the transmission is successful. In framed slotted aloha based anti-collision protocols, the reader begins each interrogation round by informing all tags about the current frame size in terms of time slots. Protocol. We are going to ignore collisions. Slotted ALOHA improves all the problems that were in Pure ALOHA. In Slotted Aloha, any station. 0 0 <<Previous Next>> Discussions. What is the required value of N? Answer. Slotted ALOHA improves all the problems that were in Pure ALOHA. 1.what is normalized total traffic in channel? Pure aloha doesn't reduces the number of collisions to half. The maximum efficiency of Slotted Aloha is high due to less number of collisions. This time slot corresponds to the length of frames.

Assume that the slotted and unslotted versions of Aloha use the same stabilization method and parameters. The maximum efficiency of Pure Aloha is very less due to large number of collisions. Synchronization can be achieved in Slotted ALOHA with the help of a special station that emits a pip at the beginning of every time slot as a clock does. The main advantage of slotted aloha is that it. of the ALOHA is its low throughput under heavy load conditions. (i.e. the number of collisions are going to increase as the number of users increase.) In this third OPNET lab, we are going to simulate ALOHA random access protocol and answer the following simple questions about ALOHA based random access methods SLOTTED ALOHA SYSTEM. SLOTTED ALOHA SYSTEM IN MATLAB, INPUTS ARE qr and lambda. %OF THE VECTORS: a = sumk (vector,k). It will be described in the report, %but basically sums the first k elements of an array called 'vector'. %transmit (up to 10 new arrivals) (Same with the probabilities that up to 10 backlogged nodes finite-user slotted ALOHA protocol. Utilize Matlab to analyze the probability of 0,1,..M users in Backlog state. Portray each state probabilities and calculate the System average values of Throughput,S, and Delay, D. Study of Capture Effect for the system when backlog transmit probability is small (<<1) The TCP checksum calculation also includes source and destination IP addresses Select one True O False In digital multiplexing hieararchy, the multiplexed signal has to carry extra bits to indicate locations of bit slips Select one: True O False Which of the following statements is true for vulnerable periods, a In Aloha protocol, it is twice the

Figure 12.4 Procedure for pure ALOHA protocol 12.6. Example 12.1 The stations on a wireless ALOHA network are a maximum of 600 km apart. If we assume that signals propagate at 3 × 108 m/s, we find T p = (600 × 1055) / (3×1088) =2ms. Now we can find the value of T B for different values of K . a. For K = 1,therangeis {0, 1} Analytical calculation of throughput of ALOHA based protocols in optical wireless data networks September 2000 IEE Proceedings - Optoelectronics 147(4):322 - 32

However, it is not the rationale behind the Aloha protocol. As a mathematical model, you should consider your own scenario carefully and decide whether to use it or not. Share. Cite. Improve this answer. Follow answered Dec 18 '14 at 1:40. How to calculate probability of packet loss and drop rate? 3 slotted aloha efficiency calculator. October 31, 2020 Uncategorized. Save Saved Removed 0. Deal Score 0. 0. Deal Score 0. 0. Aloha is the type of Random access protocol, It have two types one is Pure Aloha and another is Slotted Aloha. In Pure Aloha, Stations transmit whenever data is available at arbitrary times and Colliding frames are destroyed. While In Slotted aloha, A station is required to wait for the beginning of the next slot to transmit. vulnerable period. the ALOHA protocol. Solution: transmit timeout 7. Suppose that each station in an ALOHA system transmits its frames using spread spectrum transmission. Assume that the spreading sequences for the different stations have been selected so that they have low cross-correlations. What happens when transmissions occur at the same time Back Off Time- In CSMA / CD protocol, After the occurrence of collision, station waits for some random back off time and then retransmits. This waiting time for which the station waits before retransmitting the data is called as back off time.; Back Off Algorithm is used for calculating the back off time

Random Access Protocols - ALOHA, CSMA, CSMA/CA and CSMA/CD

  1. The simplest protocol is known as ALOHA (this is actually an Hawaiian word, meaning hello). ALOHA allows any NIC to transmit at any time, but states that each NIC must add a checksum/CRC at the end of its transmission to allow the receiver(s) to identify whether the frame was correctly received
  2. e the competing station must get the next chance of accessing the multi-access channel
  3. Aloha 5/26/21 had the highest price, at that time trading at its all-time high of $0,1395. 82 days have passed since then, and now the price is 14.28% of the maximum. Based on the table data, the ALOHA vs ETH exchange volume is $149,5264

Multiple access protocols - ALOHA, CSMA, CSMA/CA and CSMA

ALOHAnet was the first to demonstrate that communication channels could be effectively and efficiently shared on a large scale using simple random access protocols In the Aloha stabilization protocols we studied, when a node experiences a collision, it decreases its transmission probability, but sets a lower bound, p_min. When it transmits successfully, it increases its protocols, but the calculations shown in the answer are more complex than we would ask on a quiz

NCR / Aloha POS is the all-in-one solution that will improve your guests' experience, grow your business, allow you to serve and manage with no boundaries, and enhance your operation with robust hardware and software designed specifically for restaurants. We understand your needs because we understand restaurants In CSMA/CD, for success, only 1 station should transmit while others shouldn't. Let p be the probability to transmit data successfully. P(success) = nC1 * p * (1-p) n-1 (by using Binomial distribution) For max P(success), differentiate with respect to p and equate to zero (to get maxima and minima) Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels With our toll-free number, you can speak with the HCS in-house Help Desk team members 16 hours a day 8:00 AM to 12:00 AM CST, seven days a week. HCS Help Desk offers help with related software troubleshooting, operations, management reports and more. Our team can access your technology through a dial-in mode in the device modem and give you.

the Slotted Aloha protocol under interfering environments. Further more Chapter 4 analyzes results of the proposed mathematical model and the simulator under interfering environments Eytan Modiano Slide 5 Analysis of CSMA • Let the state of the system be the number of backlogged nodes • Let the state transition times be the end of idle slots - Let T(n) = average amount of time between state transitions when the system is in state n T(n) = -β + (1 - eλβ (1-q r) n) When qr is small (1-q r)n ~ e-q r n => T(n) = β + (1 - e-λβ−nq r) • At the beginning of each. • Random access MAC protocol specifies: • How to detect collisions • How to recover from collisions (e.g., via delayed retransmissions) • Examples of random access MAC protocols: • Slotted ALOHA • ALOHA • CSMA and CSMA/CD Lecture 5: 9 -11-01 5 Aloha - Basic Technique • First random MAC develope

This network throughput monitor solution uses SNMP (Simple Network Management Protocol) monitoring to give you the most comprehensive view of your entire system. The tools can also combine NetFlow, J-Flow, sFlow, NetStream, and IPFIX data built into most routers to identify what's eating up all your bandwidth and slowing down your network The throughput of the Pure ALOHA is maximized when the frames are of uniform length. The formula to calculate the throughput of the Pure ALOHA is S-=G*e^-2G, the throughput is maximum when G=1/2 which is 18% of the total transmitted data frames. (b) Slotted ALOHA All earth stations transmit frames with a fixed (average) Thus, the average number of frames transmitted in the system in the time period T will be Np - A free PowerPoint PPT presentation (displayed as a Flash slide show) on PowerShow.com - id: 81696-Njkz Start studying Taher DCC Ch12. Learn vocabulary, terms, and more with flashcards, games, and other study tools 2.(a) Write a difference between pure ALOHA and slotted ALOHA. If the throughput of pure ALOHA is S = Ge-2G, show that the maximum throughput (S ma.) is 0-184. (b) Explain the working of 3-way handshake used in TCP, using a suitable diagram

We propose a method to compute the delay of the slotted ALOHA protocol with Binary Exponential Backoff (BEB) as a collision resolution algorithm. When a message which tries to reserve a channel collides n times, it chooses one of the next 2 n frames with equal probabilities and attempts the reservation again. We derive the expected access delay. b) First note, the transmission time of a single frame is give by 1500/(100Mbps)=15 micro sec, longer than the propagation delay of a bit. • At time t=0, both A and B transmit. • At time t=4.8µsec, both A and B detect a collision, and then abort. • At time t=9.6µsec last bit of B's aborted transmission arrives at A. • At time t=14.4µsec first bit of A's retransmission frame arrives.

Aloha - Tutorial And Exampl

Register with the State of Hawaii Safe Travels online system as is currently required of all trans-pacific passengers. Pre-travel testing is an alternative to the state's mandatory 10-day self-quarantine. Travelers may elect to take a pre-travel COVID-19 NAAT from a state of Hawaii Trusted Testing and Travel Partner within 72 hours of departing on the last leg of their trip to Hawaii Using the calculator/converter on this page, you can make the necessary calculations with a pair of Aloha to KRW. Q&A What is the current ALOHA to KRW exchange rate? Right now, the ALOHA/KRW exchange rate is 0. What has been the Aloha to KRW trading volume in the last 24 hours? Relying on the table data, the Aloha to KRW exchange volume is $0 Pure ALOHA and Slotted ALOHA are the Random Access Protocols, that have implemented on the MAC (Medium Access Control) layer, a sublayer of Data Link Layer. The objective of the ALOHA protocol is to determine what competing channel must find the next chance of accessing the multi-access station at the MAC layer Computer Network MCQ. 1) Which of these is a standard interface for serial data transmission? Explanation: The RS232C is a standard interface for serial data transmission that defines the protocol and physical interface for transmitting serial data fairly easily between associated appliances and computers

Explain how the slotted ALOHA protocol work and illustrate the algorithm operations using a finite-state machine (FSM) Start your trial now! First week only $4.99! arrow_forward There are two versions of ALOHA that is Pure ALOHA and Slotted ALOHA. Figure-3 depicts operation of Selective Reject ALOHA Protocol. In Slotted Aloha, any station can transmit data only at beginning of any time slot. 0 0 > Discussions. ISO 18000-6 protocol has three types A,B,C. It is also known by SREJ Aloha The model implements the ALOHA random access protocol on the Link layer, and simulates a host to server instant broadcast. ALOHA is rather simple yet convenient to demonstrate the potential of OMNeT in simulating wireless protocols. The final part evaluates the pure and the slotted ALOHA variations, in regard to the theoretical models The pure Aloha protocol is the basic protocol in the family of the Aloha protocols. It considers a single-hop system with an infinite population generating packets of equal length T according to a Poisson process with rate l packets/sec. The channel is error-free without capture: whenever a transmission of a packet does not interfere with any.

ALOHA Protocol (in detail) - SlideShar

family of protocols, Aloha and Slotted Aloha, helping in identifying the behavior of the protocol under a different envi-ronment and learn from it, aiding in designing new protocols. Understanding the nuances of the protocols, how they work and can be used in new paradigms is a challenge that we address in this paper Course Project Simulation of the Slotted Aloha Protocol Esa Alghonaim COE 543 , 2003 -2 • Simulation flow. • Reference results (The analytical equations & curves). • Simulation Results & Graphs. • Conclusion . Simulation flow. (programmed using Delphi) No Iteration > Max_Iter Yes G = Tot_attempts / Slot S = Tot_succ / Slot Delay = Tot. I'm new to networking in general and I read about this protocol called Aloha, and I would like to make a simple simulator for the Pure version of it. Although I understand the concepts, I find it difficult to start. Basically we have a N senders in the network. Each sender wants to send a packet voice call is running on top the Aloha network, delay performance is important. This paper is devoted to the study of delay in a slotted Aloha network operated with an exponential backoff protocol. Within this context, this paper has three main contributions: 1. We establish a framework for queuing analysis in the Aloha network. 2

A slotted ALOHA algorithm can decrease the probability of collision compared to a pure ALOHA algorithm [8]. In dynamic frame-slotted ALOHA (DFSA) [9-11], the length of the frame dynamically changes with the number of unidentified tags. In frame slotted ALOHA protocols, when the length of the frame is equal to the number of tags, the maximum. The ALOHA Protocol • Free for all: whenever station has a frame to send, it does so. - Station listens for maximum RTT for an ACK. - If no ACK after a specified amount of time (how long? ), re -sends frame after waiting a random amount of time (otherwise? ) - It continues to retry for a number of times and then gives up Abstract: An analytical framework for the calculation of the throughput performance of random-access protocols based on ALOHA is presented under blockage conditions in optical wireless data networks. A simple approximate Markovian channel model, which describes the channel variability, is proposed, Based on that, an analytical technique is developed for the calculation of the throughput of S.

Centralized wireless MAC protocols using slotted ALOHA and dynamic TDD transmission Finally, we evaluate the performance of these schemes, and compare TDD1 (calculations), TDD2 (simulations), and FDD (calculations). TDD schemes are found to always work as good as, or better than, FDD. TDD2 is observed to outperform TDD1 with respect to the. Simulation Of The Aloha Protocol Information Technology Essay. Published Date: 23 Mar 2015. Disclaimer: This essay has been written and submitted by students and is not an example of our work. Please click this link to view samples of our professional work witten by our professional essay writers. A Calculator for Packets. Latest News. 2020.11.22 - PacketCalc version 2020.11(27) is available on the App Store, bringing Keyboard Shortcuts on iPad, and the ability to define Custom Protocol and Payload. 2020.11.22 - PacketCalc is running on M1-based Apple Silicon Macs. What are the L1 and L2 sizes of an IPv6 packet with 16 bytes of extension headers, plus TCP header, sent over an 802.1Q.

Cyclic Redundancy Check (CRC)

Video: Aloha Pure Aloha Slotted Aloha Gate Vidyala

ALOHA Protocols - Metzner - - Major Reference Works

ALOHA: ALOHA is a seminal random-access protocol that became operational in 1971. In ALOHA, nodes transmit packets as soon as these are available, without sensing the wireless carrier. As a result, wireless packets may collide at a receiver if they are transmitted simultaneously Primary Menu. School Apparel. Class Of Shirts; Clubs; Field Day; Marching Band; Mascot Graphic

Pure ALOHA - Tutorialspoin

Question: Consider a network using the pure ALOHA medium access control protocol, where each frame is of length 1,000 bits. The channel transmission rate is 1 Mbps (= 10 6 bits per second). The aggregate number of transmissions across all the nodes (in-cluding new frame transmissions and retransmitted frames due to collisions) is modelled as a Poisson process with a rate of 1,000 frames per. Computer Network Controlled Access Protocols Computer. The protocol in this section, wait for each station connected to carl will not provide reliable data in a timer stops transmitting. ALOHA ALOHA uses acknowledgments to confirm successful data. Once a browser is configured, each browser request through an who is first directed to the Web cache

The first dynamic frame-slotted Aloha protocol was proposed in for general data networks. For RFID systems, different dynamic Aloha algorithms have been proposed in [10-15], where the frame size is dynamically adjusted according to the estimated number of tags. The difference in the aforementioned algorithms lies in that the tag number. a) Compare slotted Aloha and Aloha protocols for multiple access. b) The figure below shows the operation of slotted Aloha for a given time period. Calculate the efficiency of the protocol. [5] 1 node 1 node 2 node 3 + + time C: collision E: Empty S: Successful ш ш In [12], ALOHA- QIR protocol was proposed to reduce the collision and retransmission as well as to improve the throughput and energy efficiency by using Q-learning in Slotted ALOHA.There were three processes involved; Q-learning to acquire the learning experience; Informed Receiving (IR), to change the nodes state into a sleep mode in which to avoid from idle listening and overhearing; Ping. TDM vs. slotted alohaAloha achieves lower delays when arrival rates are low •TDM results in very large delays with large number of users, while Aloha is independent of the number of users 0 0.2 0.4 0.6 0.8 ARRIVAL RATE 4 8 DELAY ALOHA TDM, m=8 TDM, m=1

ALOHAnet, also known as the ALOHA System, or simply ALOHA, was a pioneering computer networking system developed at the University of Hawaii.ALOHAnet became operational in June, 1971, providing the first public demonstration of a wireless packet data network. ALOHA originally stood for Additive Links On-line Hawaii Area Calculations show that maximum tag reading rate can be achieved if frame size is set to a number of interrogating tags. Since the number of tags is generally unknown, it should be ALOHA (DFSA) protocol [7] with RFID style implementation given in Gen2 an Aloha protocol simulator source code(C++) that is well-documented and easy to understand. Thanks in advance for your help. Jul 22 '05 #1. Follow Post Reply. 1 3081 . Victor Bazarov. Gandu wrote: I apologize if this is not the appropriate newsgroup to post this message. Could someone please tell me a good place to get an. the Aloha-NOMA protocol [11], is a promising candidate MAC protocol that can be utilized for low complexity IoT devices. In [12] NOMA is applied to multichannel Slotted Aloha to enhance the throughput with respect to conventional multichannel slotted Aloha without the need for any bandwidth expansion. The SAN protocol is a promising method for no ALOHA and CSMA protocols are obtained only for systems with a finite population [5], [6]. Specifically, in [5], Tobagi derived the transform and moments of both the waiting time and interdeparture time distribution in slotted ALOHA and CSMA with collision detection (/CD) protocols using a discrete-time Markov chain. In [6], the matrix-geometri

GitHub - mahirjain25/Goodbye-Aloha: Implementing a

Another example of a more sophisticated Aloha based protocol is the Frame Slotted Aloha (FSA) [31] in which the slots themselves are grouped into frames and a user can transmit only once per frame. The main limitation in Slotted Aloha and Frame Slotted Aloha is that the packet transmission time cannot exceed the slot duration Explain CSMA Protocols. Explain how collisions are handled in CSMA/CD. CSMA Protocols stands for Carrier Sense Multiple Access Protocols. CSMA is a network access method used on shared network topologies such as Ethernet to control access to the network. Devices attached to the network cable listen (carrier sense) before transmitting State of Hawaii - Safe Travel slotted aloha throughput formula. By | octubre 31, 2020 | Uncategorized | Like | 2020-10-31 31 octubre 2020Uncategorized | Like | 2020-10-31 31 octubre 202 In this paper, we develop a novel mathematical model to estimate the probability distribution function of the number of tags discovered after a certain number of interrogation rounds. In addition, the pdfs of the number of rounds needed to discover all the tags are also calculated. The estimation of such pdfs will be helpful in estimating the number of interrogation rounds and the optimal.

In this paper, three random access control mechanisms based on the well-known Slotted ALOHA, NP-CSMA, and 1P-CSMA protocols are presented. The basic idea is to limit the number of transmissions and retransmissions at high traffic loads in order to minimize collisions while keeping system stability. A new medium-access control protocol called Adaptive Traffic Load (ATL) is proposed. With ATL. The first enhancement is a synchronized arrival S-Aloha (SA-Aloha) protocol, in which frames are transmitted at carefully calculated time to align the frame arrival time with the start of time slots. Propagation delay is taken into consideration in the calculation of transmit time ALOHA is the earliest proposed contention-based MAC protocol. Without any collision avoidance mechanism, ALOHA based on random access performs well in a network with sporadic packets [ 28 ]. However, it is unsuitable for either moderate or heavy load networks Measurement of a slotted ALOHA channel with an infinite number of users shown that 10 percent of the slots are idle. The maximum throughput is 0.5/e frames per frame-time (reached when G = 0.5), which is approximately 0.184 frames per frame-time. This means that, in Pure ALOHA, only about 18.4% of the time is used for successful transmissions. In Slotted ALOHA, station cannot send data in.