Found 496 Articles for Computer Engineering

Both Flow control and Congestion control are traffic controlling methods in computer networks. Flow control is a technique that allows two stations working at different speeds to communicate with each other. It is a set of measures taken to regulate the amount of data that a sender sends so that a fast sender does not overwhelm a slow receiver.Congestion occurs in a network when it receives too many packets than its designed capacity. Network congestion occurs in case of traffic overloading. There are mechanisms to control such congestion scenarios in a network.Go through this article to find out more about ... Read More

Go-Back-N is a data link layer protocol that uses a sliding window method for reliable and sequential delivery of data frames. It is a case of sliding window protocol having to send window size of N and receiving window size of 1.Selective Repeat Protocol is also a data link layer protocol that uses sliding window method for reliable delivery of data frames. Here, only the erroneous or lost frames are retransmitted, while the good frames are received and buffered.Read through this article to find out how these two data link layer protocols work and what are the major differences between ... Read More

The Aloha Protocol allows several stations to send data frames over the same communication channel at the same time. This protocol is a straightforward communication method in which each network station is given equal priority and works independently.Aloha is a medium access control (MAC) protocol for transmission of data via a shared 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.In Pure Aloha, the time of transmission is continuous. Whenever a station has an available frame, it sends ... Read More

IMAP and POP3 are the most widely used standard protocol for email retrieval. Both these protocols are supported by almost all current email clients and servers. Go through this article to find out more about POP3 and IMAP, how they function, and what are the major differences between these two protocols.What is POP3?POP3 (or Post Office Protocol Version 3) is an application layer protocol used by email clients to retrieve email messages from mail servers over TCP/IP network. POP was designed to move the messages from server to local disk but version 3 has the option of leaving a copy ... Read More

Short Interframe Spacing (SIFS), is the time interval required by a wireless device in between receiving a frame and responding to the frame. It is used in Distributed coordination function (DCF) scheme, which is a mandatory technique used to prevent collisions in IEEE 802.11-based WLAN standard (Wi-Fi).The duration of SIFS is equal to the sum of delays in radio frequency (RF), Physical Layer Convergence Procedure (PLCP) and processing delay of MAC (medium access control) layer.In IEEE 802.11 networks, SIFS is the interframe spacing maintained before and after the transmission of an acknowledgment frame and Clear To Send (CTS) frame.TechniqueThe role ... Read More

Distributed coordination function (DCF) is a mandatory technique used to prevent collisions in IEEE 802.11-based WLAN standard (Wi-Fi). It is a medium access control (MAC) sublayer technique used in areas where carrier-sense multiple access with collision avoidance (CSMA/CA) is used.Using DCF technique, a station needs to sense the status of the wireless channel before it can place its request to transmit a frame. The time interval that a station should wait before it sends its request frame is known as DCF Interframe Spacing (DIFS).TechniqueWhen a station has a frame to transmit, it waits for a random backoff time.At the end ... Read More

In IEEE 802.11 wireless LANs, automatic power save delivery (APSD) is a mechanism that aims to reduce power consumption by the devices connected in the network. It was originally introduced to IEEE 802.11e in 2005.TechniqueAPSD is generally deployed in infrastructure BSS (basic service set). In infrastructure BSS, there is are access points (APs) which are basically wireless routers forming the base stations for access. All the wireless devices i.e. clients communicate with each other through the APs. When a client has frames to send it sends the frames to the corresponding AP along with the destination address. The AP then ... Read More

In computer networks, beacon frames management frames used in IEEE 802.11 based wireless local area networks (WLANs). A beacon frame contains network information needed by a station before it can transmit a frame. They are used for announcing the presence of devices in a WLAN as well as synchronisation of the devices and services.Beacon frames are used as a part of BSS (basic service set). In infrastructure BSS, there is are access points (APs) that are wireless routers forming the base stations for access. All the devices communicate with each other through APs. The APs transmit beacon frames periodically so ... Read More

Virtual channel sense or virtual carrier sense is a mechanism to predict future traffic in wireless networks that uses carrier sense multiple access with collision avoidance (CSMA/CA). It is implemented in wireless network protocols, IEEE 802.11 and IEEE 802.16, which operates in the medium access control (MAC) layer.In virtual channel sensing, a timer mechanism is used that is based upon information of durations of previous frame transmission in order to predict future traffic in the channel. It uses network allocation vector (NAV), which can be considered as a counter that counts down to zero.TechniqueVirtual channel sensing mechanism initialises a NAV ... Read More

The network allocation vector (NAV) is a virtual carrier sensing mechanism that forms an important part of the carrier sense multiple access with collision avoidance (CSMA/CA). It is implemented in wireless network protocols, IEEE 802.11 and IEEE 802.16, which operates in the medium access control (MAC) layer.TechniqueThe network allocation vector can be considered as a counter that counts down to zero. The maximum NAV duration is the transmission time required by frame, which is the the time for which the channel will be busy. At the start of transmission of a frame, the NAV value is set to its maximum. ... Read More