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Model

OSI Model TCP/IP Model

Physical Layer

Digital Transmission Analog Transmission Transmission Media Switching

Data Link Layer

Error detection and Error correction Data Link Control Multiple Access Aloha

Network Layer

Network Layer - Logical Address Address Mapping Unicast Routing Protocol

Transport Layer

Process to Process Delivery User Datagram Protocol Transmission Control Protocol Stream Control Transmission Protocol Session Layer and Presentation Layer

Application Layer

Domain Name System Application Protocol E-mail Cryptography

Misc

Classes of Routing Protocols Classification of Routing Algorithms Controlled Access Protocols in Computer Networks Differences between IPv4 and IPv6 Fixed and Flooding Routing Algorithms Advantages and Disadvantages of Fibre Optics Cable APIPA Difference between Active and Passive FTP Fiber Optics and its Types Method of Joining and Fusion of Fiber Optic Cable Define Framing in Computer Network Disadvantages of Computer Network Mesh Topology Diagram in Computer Network Ring Topology in Computer Network Star Topology in Computer Networks 4G Mobile Communication Technology Advantages and Disadvantages of LAN Advantages and Disadvantages of MAN Advantages and Disadvantages of WAN Application Layer in OSI Model Cyclic Redundancy Check Example Data link layer in OSI model Difference between Transport and Network Layer Hamming Code Example Network Layer in OSI Model Session Layer in OSI Model Transport Layer in OSI Model Two Port Network in Computer Networks Uses of Computer Networks What is Computer Network What is Framing in a Computer Network Advantages and Disadvantages of Bus Topology Difference between Star Topology and Bus Topology Subnetting in Computer Network Subnetting Questions and Answers What is Bus Topology What is Network Topology and Types in Computer Networks Access Control in Networking Basic Characteristics of Computer Network Benefits of SOCKS5 Proxy in Computer Networks Computer Network viva Questions Difference between BOOTP and RARP Difference Between Network Topologies and Network Protocols Difference between NFC and RFID Difference Between Point-to-Point Link and star Topology Network Differences Between MSS and MTU Differences Between Trunk Port and Access Port Different Modes of Communication in Computer Networks MIME Protocol in Computer Networks Modes of Communication in Computer Networks Network Attack in Computer Network Port Address in Networking Simplest Protocol in Computer Network Sliding Window Protocol in Computer Network Stop And Wait Protocol in Computer Networks TCP 3-Way Handshake Process in Computer Networks What is a Proxy Server What is APPN What is ICMP Protocol What is Point-to-Point Protocol What is Port Address in Networking What is the HDLC Protocol What is VRRP Protocol Difference Between Analog and Digital Signals Difference Between Hub and Repeater Difference between Repeater and Switch Difference Between Transparent Bridge and Source Routing Bridge Source Routing Bridge in Computer Networks Transparent Bridge in Computer Networks Transport Protocol in Computer Networks Types of CSMA in Computer Networks What is Wired and Wireless Networking Network Security in Computer Network Disadvantages of Extranet Difference Between TELNET and FTP Define Protocol in Computer Networks Guided Transmission Media in Computer Network What is a Gateway in a Computer Network IGMP in Computer Networks LAN Protocols in Computer Networks MAN Meaning in Computer Modulation Techniques in Computer Networks Switching in DCN TCP/IP Applications What is IGMP? What is Modem in Networking What is Non-Persistent CSMA Difference between Cell Splitting and Cell Sectoring Forouzen Computer Network

Aloha

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 data destroy.

Type of Aloha

Aloha has been divided into two types.

  1. Pure Aloha
  2. Slotted Aloha

Pure Aloha

Pure Aloha is also called the original aloha protocol. It's a simple but elegant protocol, i.e., whenever the system has a data frame to send, it transmits the data frame continuously. Due to which the risk of collision is very high in this aloha method. Shown in below pure aloha.

Aloha

Therefore, the acknowledgment method is used to know the status of the data frame sent in the network. If the receiver doesn't provide any acknowledgment, it is understood that frames have been destroyed, and frames are re-transmitted.

  • The maximum throughput occurs at G = 1/2, which is 18.4%.
  • In Pure Aloha, the probability of successful transmission of the data frame is S= G* e^-2G
  • In Pure Aloha, vulnerable time is: 2 * Tfr

NOTE: Pure Aloha is overall efficiency is very less due to a large number of collisions.

Example: An Aloha network uses an 18.2 kbps channel for sending message packets of 100 bits long size. Calculate the maximum throughput.

In Pure Aloha, Efficiency = 18.4%

Usable bandwidth for 18.2 kbps = 18.2 * 0.18 = 3.276 kbps

Therefore, the maximum throughput of Pure Aloha

= 1/2e * 3.276

= (18.4 * 3.276) / 100

= 0.6027

Slotted Aloha

Slotted aloha was developed to increase the performance of the pure aloha, as there are very high chances of collision in pure aloha. In this Aloha, the time of the systems is divided into slots so that the system can send only one frame to a slot, and this frame can only be sent at the beginning of the slot. If a system cannot send a frame at the beginning of the slot, then it has to wait for the next slot to start. If two systems try to transmit the frame at the beginning of a time slot. But it is better than pure Aloha because it has less chance of collision. Shown in below slotted aloha.

Aloha
  • In Slotted Aloha, maximum throughput occurs at G = 1, which is 37%.
  • In Slotted Aloha, the probability of successful transmission of the data frame:

S= G* e^-G

  • In Slotted Aloha, vulnerable time is: Tfr 

Difference between Pure Aloha and Slotted Aloha?

Pure AlohaSlotted Aloha
In Pure Aloha, at any time can be sent the data in any station.In Slotted Aloha, each station can send the data at the provided time slot.
The time is not globally synchronized in this aloha.The time is globally synchronized in this aloha.
Continuous timeDiscrete time
In Pure Aloha, vulnerable time is:                      = 2 * TfrIn Slotted Aloha, vulnerable time is:                          = Tfr 
The maximum throughput occurs at                 G = 1/2 which is 18.4%.The maximum throughput occurs at                G = 1 which is 37%.
Pure Aloha does not reduce to half the number of collisions.Slotted Aloha reduces collision numbers to half, therefore doubles the efficiency.