Token Bus (IEEE 802.4) is a standard for implementing token ring over the virtual ring in LANs. The physical media has a bus or a tree topology and uses coaxial cables. A virtual ring is created with the nodes/stations and the token is passed from one node to the next in a sequence along this virtual ring. Each node knows the address of its preceding station and its succeeding station. A station can only transmit data when it has the token. The working principle of the token bus is similar to Token Ring.Token Passing Mechanism in Token BusA token is ... Read More

Bit-map protocol is a collision free protocol that operates in the Medium Access Control (MAC) layer of the OSI model. It resolves any possibility of collisions while multiple stations are contending for acquiring a shared channel for transmission. In this protocol, if a station wishes to transmit, it broadcasts itself before the actual transmission. Every station gets its turn for transmission in a predefined order. A method to accomplish this is to use the method of token passing.Token Passing MechanismA token is a small message that circulates among the stations of a computer network providing permission to the stations for ... Read More

RSVP is a transport layer protocol that is used to reserve resources in a computer network to get different quality of services (QoS) while accessing Internet applications. It operates over Internet protocol (IP) and initiates resource reservations from the receiver’s end.FeaturesRSVP is a receiver oriented signalling protocol. The receiver initiates and maintains resource reservation.It is used both for unicasting (sending data from one source to one destination) and multicasting (sending data simultaneously to a group of destination computers).RSVP supports dynamic automatic adaptation to changes in network.It provides a number of reservation styles. It also provides support for addition of future ... Read More

Reservation protocols are the class of protocols in which the stations wishing to transmit data broadcast themselves before actual transmission. These protocols operate in the medium access control (MAC) layer and transport layer of the OSI model.In these protocols, there is a contention period prior to transmission. In the contention period, each station broadcasts its desire for transmission. Once each station announces itself, one of them gets the desired network resources based upon any agreed criteria. Since each station has complete knowledge whether every other station wants to transmit or not before actual transmission, all possibilities of collisions are eliminated.Examples ... Read More

Bit-map protocol is a collision free protocol that operates in the Medium Access Control (MAC) layer of the OSI model. It resolves any possibility of collisions while multiple stations are contending for acquiring a shared channel for transmission.In this protocol, if a station wishes to transmit, it broadcasts itself before the actual transmission. This is an example of Reservation Protocol.Working PrincipleIn this protocol, the contention period is divided into N slots, where N is the total number of stations sharing the channel. If a station has a frame to send, it sets the corresponding bit in the slot.Suppose that there ... Read More

In computer networks, when more than one station tries to transmit simultaneously via a shared channel, the transmitted data is garbled. This event is called collision. The Medium Access Control (MAC) layer of the OSI model is responsible for handling collision of frames. Collision – free protocols are devised so that collisions do not occur. Protocols like CSMA/CD and CSMA/CA nullifies the possibility of collisions once the transmission channel is acquired by any station. However, collision can still occur during the contention period if more than one stations starts to transmit at the same time. Collision – free protocols resolves ... Read More

Multi-access ChannelsMulti-access channels are network channels that allow several transmitters to communicate with a common receiver via a shared channel. These channels are also called multiple access (MAC) channels. The network channel may be a single cable or optical fiber connecting multiple nodes, or a portion of the wireless spectrum.Random Access ChannelsRandom-access channels (RACH) are shared channels used in wireless communication systems to allow mobile devices for call set-up. RACH also handles bursty data transmission. RACH is popularly used by GSM mobiles for transmission over cellular networks.Multiple Access SchemesBoth multi-access channels and random access channels require a scheme to allow ... Read More

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) is a network protocol for carrier transmission that operates in the Medium Access Control (MAC) layer. In contrast to CSMA/CD (Carrier Sense Multiple Access/Collision Detection) that deals with collisions after their occurrence, CSMA/CA prevents collisions prior to their occurrence.AlgorithmThe algorithm of CSMA/CA is:When a frame is ready, the transmitting station checks whether the channel is idle or busy.If the channel is busy, the station waits until the channel becomes idle.If the channel is idle, the station waits for an Inter-frame gap (IFG) amount of time and then sends the frame.After sending the ... Read More

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) is a network protocol for carrier transmission that operates in the Medium Access Control (MAC) layer. It senses or listens whether the shared channel for transmission is busy or not, and defers transmissions until the channel is free. The collision detection technology detects collisions by sensing transmissions from other stations. On detection of a collision, the station stops transmitting, sends a jam signal, and then waits for a random time interval before retransmission.AlgorithmsThe algorithm of CSMA/CD is:When a frame is ready, the transmitting station checks whether the channel is idle or busy.If ... Read More

P-persistent CSMA is an approach of Carrier Sense Multiple Access (CMSA) protocol that combines the advantages of 1-persistent CMSA and non-persistent CMSA. Using CMSA protocols, more than one users or nodes send and receive data through a shared medium that may be a single cable or optical fiber connecting multiple nodes, or a portion of the wireless spectrum.In p-persistent CSMA, when a transmitting station has a frame to send and it senses a busy channel, it waits for the end of the transmission, and then transmits with a probability p. Since, it sends with a probability p, the name p ... Read More