How Do I Connect my Network Configuration?

How Do I Connect My Network Configuration?

Table of Contents | Glossary

To communicate a message over a network, you may need hardware to interpret and forward data to the correct destination. The following overview introduces you to hubs, connectors, repeaters, bridges, routers and gateways.

Hubs and concentrators

A hub consists of a metal chassis, an integral backplane, and a standard number of removable modules. Modules consist of I/O modules (such as 10BaseT, 10BaseF, and FDDI) and networking modules (such as bridges, routers, power supplies, and network management software). Each module plugs into the backplane where signals from individual modules are merged. A concentrator is a simple hub without multiple types of I/O and networking modules.

Without the networking modules installed, the hub is simply a multiport repeater; incoming signals are repeated across the hub by each I/O module. With the flexibility of I/O and networking modules, the hub can be configured to meet a wide variety of networking requirements.

Repeaters

Repeaters extend the distance a signal is normally able to travel on a LAN segment. Placed between two cable segments, the repeater regenerates incoming signals, provides synchronization, and forwards the data on the outgoing cable segment. There can be more than one repeater in a series.

The main disadvantage of a repeater is that it passes along everything it detects on the line. If there is noise or distortion, the repeater passes it along with the original signal.

There is a limit to the number of repeaters that can be used to extend a LAN's length and topology. In an Ethernet LAN, there can be a maximum of five segments interconnected by four repeaters.

Bridges

Bridges repeat data between two separate but similar types of LANs, such as Ethernet or FDDI. The bridge filters the data flow between the LANs, passing only those messages addressed to a destination on the opposite side of the device.

A bridge cannot make decisions about routes through the network because information on routes is encoded in the network address that is accessible only by the network layer.

Because of its filtering characteristic, the bridge is used to both extend and to segment a LAN. The bridge is a possible solution to a large, overloaded LAN. By breaking such a LAN into segments, the user load can be distributed to make more cost-efficient use of the media without compromising performance.

Switches

A switch extends the bridging concept from linking two networks together to linking four or more separate but similar types of LANs. The switch, like the bridge, filters and speeds the data flow between LANs.

A switch operates in several modes: Cut-through/ fast forward, cut-through/ fragment free, or store-and-forward. Cut-through/ fast forward or fragment free switching allows the switch to examine the first few bytes of an Ethernet data packet to determine the destination address. The switch then sends the packet to the proper destination. The third mode, store-and-forward switching, operates by examining the entire contents of a packet, checking the address, searching for data errors, and finally, forwarding the data.

Routers

Routers repeat data packets between multiple LANs. With the transmission capabilities built-in, the router is able to evaluate the network environment (traffic) on a per packet basis to make intelligent routing decisions.

Routers are frequently tied to other routers so there may be multiple "hops" between the originating source and final destination. Thus, a signal packet may have to pass through several routers (with multiple pathways) to reach its ultimate destination. In such a case, the intelligence behind the router allows each routing device (along the transmission path of a packet) to identify which path to the destination is best in terms of hop count, congestion and outages.

Multi-protocol routers handle information and communication between different networks. For example, Windows systems using NETBUEI protocol, Macintosh systems using AppleTalk protocol, IBM PCs using IPX/SPX protocol, and Internet systems using TCP/IP protocol can all communicate with each other. The multi-protocol router gets all these different types of data packets to the proper destinations.

Gateways

Gateways mediate incompatible protocol communications between networks. The device understands the data handling formats of each network it interconnects. Gateways are used primarily to interpret mainframe protocols.

Gateways link LANs at the session, presentation layers and application layers of the OSI model.

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Last Updated, Tuesday, December 01, 1998