Computer Networks Manual

Topics: Ethernet, Network topology, Coaxial cable Pages: 27 (2030 words) Published: September 18, 2014
OSI REFERNCE MODEL

OSI LAYERS PROTOCOL

EQUIPMENT AT THE LAYERS
Some of the layers use equipment to support the identified functions. Hub related activity is “Layer One”.
The naming of some devices designates the functional layer such as “Layer Two Switch” or “Layer Three Switch”. Router functions focus on “Layer Three”.
User workstations and servers are often identified with “Layer Seven”.

HUB
Hub is a hardware device that contains multiple, independent ports that match the cable type of the network. Most common hubs interconnect Category 3 or 5 twisted-pair cable with RJ-45 ends, although Coax BNC and Fiber Optic BNC hubs also exist. Ethernet Hubs

An Ethernet hub is also called a multiport repeater. A repeater is a device that amplifies a signal as it passes through it, to counteract the effects of attenuation.

Multistation Access Unit
A Multistation Access Unit (MAU) is a special type of hub used for token ring networks.

Switches
Switches are a special type of hub that offers an additional layer of intelligence to basic, physical-layer repeater hubs. A switch must be able to read the MAC address of each frame it receives. This information allows switches to repeat incoming data frames only to the computer or computers to which a frame is addressed. This speeds up the network and reduces congestion

Bridges
A bridge is used to join two network segments together, it allows computers on either segment to access resources on the other. They can also be used to divide large networks into smaller segments.

Routers
Routers are networking devices used to extend or segment networks by forwarding packets from one logical network to another. Routers are most often used in large internetworks that use the TCP/IP protocol suite and for connecting TCP/IP hosts and local area networks (LANs) to the Internet using dedicated leased lines

Brouters
Brouters are a combination of router and bridge. This is a special type of equipment used for networks that can be either bridged or routed, based on the protocols being forwarded. Brouters are complex, fairly expensive pieces of equipment and as such are rarely used. Gateways

A gateway is a device used to connect networks using different protocols. Gateways operate at the network layer of the OSI model. NICs (Network Interface Card)
Network Interface Card, or NIC is a hardware card installed in a computer so it can communicate on a network. The network adapter provides one or more ports for the network cable to connect to, and it transmits and receives data onto the network cable. WAPs (Wireless Access Point)

A wireless network adapter card with a transceiver sometimes called an access point, broadcasts and receives signals to and from the surrounding computers and passes back and forth between the wireless computers and the cabled network.

Network Topologies

Star (Hub-and-Spoke) Topology

In a star network, each node (file server, workstations, and peripherals) is connected to a central device called a hub. The hub takes a signal that comes from any node and passes it along to all the other nodes in the network.

Data on a star network passes through the hub, switch, or concentrator before continuing to its destination. The hub, switch, or concentrator manages and controls all functions of the network.

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction.
A failure in any cable or device breaks the loop and can take down the entire network. To implement a ring network we use the Token Ring technology Bus Topology

All the nodes (file server, workstations, and peripherals) on a bus topology are connected by one single cable. A...
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