Half-duplex networks

Half-duplex networks
4.1.4 This page will explain how collisions occur on a half-duplex network.
Originally Ethernet was a half-duplex technology. Half-duplex allows hosts to either transmit or receive at one time, but not both. Each host checks the network to see whether data is being transmitted before it transmits additional data. If the network is already in use, the transmission is delayed. Despite transmission deferral, two or more hosts could transmit at the same time. This results in a collision. When a collision occurs, the host that detects the collision first, sends out a jam signal to the other hosts. When a jam signal is received, each host stops data transmission, then waits for a random period of time to re-transmit the data. The back-off algorithm generates this random delay. As more hosts are added to the network, collisions are more likely to occur.
Ethernet LANs become saturated because users run network intensive software, such as client/server applications, which cause hosts to transmit more often and for longer periods of time. The network interface card (NIC), used by LAN devices, provides several circuits so that communication among devices can occur.

The next page will discuss some other factors that cause network congestion.

Comments

Windowing

Windowing 11.1.5 This page will explain how windows are used to transmit data. Data packets must be delivered to the recipient in the same order in which they were transmitted to have a reliable, connection-oriented data transfer. The protocol fails if any data packets are lost, damaged, duplicated, or received in a different order. An easy solution is to have a recipient acknowledge the receipt of each packet before the next packet is sent. If a sender had to wait for an ACK after each packet was sent, throughput would be low. Therefore, most connection-oriented, reliable protocols allow multiple packets to be sent before an ACK is received. The time interval after the sender transmits a data packet and before the sender processes any ACKs is used to transmit more data. The number of data packets the sender can transmit before it receives an ACK is known as the window size, or window. TCP uses expectational ACKs. This means that the ACK number refers to the next packet that is...

OSI layers / Peer-to-peer communications / TCP/IP model

OSI layers 2.3.4 This page discusses the seven layers of the OSI model. The OSI reference model is a framework that is used to understand how information travels throughout a network. The OSI reference model explains how packets travel through the various layers to another device on a network, even if the sender and destination have different types of network media. In the OSI reference model, there are seven numbered layers, each of which illustrates a particular network function. - Dividing the network into seven layers provides the following advantages: • It breaks network communication into smaller, more manageable parts. • It standardizes network components to allow multiple vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting other layers. • It divides network communication into smaller parts to make learning it easier to understand. In the foll...

1.2.2 RIP V2 Features

1.2.2 RIP V2 Features This page will discuss RIP v2, which is an improved version of RIP v1. Both versions of RIP share the following features: It is a distance vector protocol that uses a hop count metric. It uses hold down timers to prevent routing loops – default is 180 seconds. It uses split horizon to prevent routing loops. It uses 16 hops as a metric for infinite distance. RIP v2 provides prefix routing, which allows it to send out subnet mask information with the route update. Therefore, RIP v2 supports the use of classless routing in which different subnets within the same network can use different subnet masks, as in VLSM. RIP v2 provides for authentication in its updates. A set of keys can be used on an interface as an authentication check. RIP v2 allows for a choice of the type of authentication to be used in RIP v2 packets. The choice can be either clear text or Message-Digest 5 (MD5) encryption. Clear text is the default. MD5 can be used t...

CCNA :) Be a Good Network Administrator

Search This Blog