Network connection devices connect the various segments of network media that make up a network or internetwork.

A segment is one section of network transmission media that is assigned a specific network address; it provides servers and clients on the network with access to network resources.

A network interface board attaches a device, such as a computer, to a transmission medium.

Network interface cards (NICs) are circuit boards that provide the means to change a computer's electric signals to those used by the transmission medium.

The transceiver is the basic component of a NIC, this is what enables the NIC to send and receive data.

Hubs - a hub is a wiring concentrator for a LAN or WAN that provides a central attachment point for network cabling. Coaxial cable doesn't use hubs.

An active hub can regenerate or amplify a signal, it connects multiple media segments, extends cable length and thereby increases transmission length.

A passive hub connects multiple media segments together, it does not regenerate or amplify a signal.

Switches - Data Link - Switching hubs (Switches) - are intelligent hubs which contain circuitry that very quickly routes signals between ports on the hub. This method reduced bandwidth waste because only the device which needs to receive the packet does rather than the entire network segment.

Switch filters traffic through MAC addresses. A switch receives a transmission and retransmits it using only that port through which the intended receiver can be reached.

Repeater - Physical - Regenerates signals for retransmission. Moves packets from one physical media to another. Will pass broadcast storms. Cannot connect different network topologies or access methods.

Repeaters work in the Physical layer of the OSI model to provide fast signal regeneration. In digital computer networks, repeaters aren't simply amplifiers; repeaters deal with attenuation by receiving and evaluating the data then immediately re-transmitting a clean copy of the signal on to the next segment of the network cable.

Bridge - Data Link (MAC Sublayer) - Bridges are used to segment networks. They forward packets based on address of destination node. Uses RAM to build a routing table based on hardware addresses. Will connect dissimilar network topologies. Will forward all protocols. Regenerates the signal at the packet level.

A bridge , like a repeater, extends a network's transmission distance, however, a bridge is used to connect segments on different networks.

Bridges are used to segment networks. They forward packets based on address of destination node. Uses RAM to build a routing table based on hardware addresses. Some bridge types are capable of connecting dissimilar network topologies. Will forward all protocols. A hub is a single point where media segments can connect.

Remote Bridge - Data Link (MAC Sublayer)

Same as bridge, but used for telephone communications. Uses STA (Spanning Tree Algorithm).

Router - Network - Routes packets across multiple networks. Uses RAM to build a routing table based on network addresses (i.e. TCP address). Shares status and routing information to other routers to provide better traffic management and bypass slow connections. Will not pass broadcast traffic. Are slower than bridges due to complex functions. Strips off Data Link Layer source and destination addresses and then recreates them for packets. Routers can accomodate multiple active paths between LAN segments. Will not pass unroutable protocols.

Routers, operating in the Network layer, use network address information to move data through the best path to its destination. To connect different networks, routers must be aware of network addresses. Because routers can determine network addresses, they can be "intelligent" about routing data through a complex internetwork involving multiple networks.

Multiplexers (mux) enable several devices to simultaneously share a high-bandwidth line.

half-duplexing - each device in the configuration can send and receive information, but only one at a time; while sending the device cannot receive, very much like walkie-talkies.

full-duplexing - each device in the configuration can send and receive simultaneously. The best example of this is the telephone.

Brouter - Data Link and Network - Will act as a router for specified protocols and as a bridge for other specified protocols.

Brouters are a hybrid of routers and bridges. Brouters function like routers, relaying data transmissions between networks, but when they encounter a data unit that uses a protocol with which they are unfamiliar, they work like a bridge and forward the data to the next segment by using a physical address. Because of this ability, you can use brouters for networks on which there is mixed-protocol traffic and for networks that use protocols that do not support routing

Channel Service Unit/Digital Service Unit (CSU/DSU)
The units are designed to shield network users from electric voltages as well as electrical interference. They also ready data for transmission by adhering to any network rules.

Both units are parts of a data communications equipment (DCE) device and are collectively referred to as a CSU/DSU. A CSU/DSU operates like a modem; however, it is a digital-to-digital device rather than digital-to-analog. It readies digital signals and guarantees that they have sufficient strength and the proper format to be transmitted over digital WAN links.

Gateway - Transport, Session, Presentation and Application

Used for communications between different NOS's. Takes the packet, strips off the old protocol and repackages it for the receiving network.

A gateway basically grants a workstation a direct connection to the host computer and acts as a messenger between the two systems. Gateways operate between the OSI Transport layer through the Application Layer.

Transmission Media Adapter - - Adapter used to connect dissimilar NIC and cable connections (i.e. RJ-45 to RS-232 adapter).

MAUs - (Multistation Access Unit) an access device used to connect the main cabling structure to devices in use on a Token Ring network. This device adds fault tolerance to the network so that a single failure doesn't stop the whole network.

broadband and baseband

baseband transmissions use the entire medium's capacity for a single channel over digital signaling. Since only one signal at a time can occupy a channel, the use of a MUX will allow multiple devices to send multiple signals using a single transmission medium. Provide excellent throughput because the digital signal occupies the entire channel.

broadband transmissions share the medium's bandwidth over multiple analog channels unidirectionally. This is performed using different frequencies and a process known as FDM (frequency division multiplexing). Since these transmission work very well over long distances, WAN communications take advantage of this technology.

For more information on Networking Basics, the OSI Model and Server Administration:
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