Network Wiring Hubs

team lib

It's no surprise that network administrators responded to the passage of the IEEE's 10BaseT Ethernet standard with a sigh of relief. The 10BaseT standard spells out the exact ways in which Ethernet data signals can be sent over high grade telephone wire, and that should make those professionals' daily lives a good deal more pleasant than heretofore possible.

Ostensibly, 10BaseT gives them a low-cost cabling alternative unshielded twisted-pair wiring (UTP), better known as telephone wirefor transmitting Ethernet data signals. Millions of miles of telephone wire installed in buildings worldwide can now be safely used for Ethernet data transmission. The ability to use existing UTP and its resulting savings from not having to pull new cable may be a superficial benefit of 10BaseT. Not all UTP hidden behind walls can support Ethernet, so they often need new cables, anyway.

10BaseT's real benefits promise to overshadow the economics of not pulling new cabling. The true benefits of 10BaseT will be derived through increased control of Ethernet networks in general and network cabling plants specifically . The 10BaseT standard's most important feature might very well be that it gives Ethernet topological parity with IBM's Token Ring scheme, the industry's other popular networking technology.

The 10BaseT standard calls for connecting Ethernet workgroups in a star topology that focuses all network cabling in a single wiring concentrator, or hub. Token Ring's physical star topology, with its centralized wiring hub, has been one of the major reasons it has made substantial popularity gains against Ethernet in recent years .

At The LAN's Center

Why would Ethernet managers want to concentrate the wiring at the center of Network Wiring Hubs 60 61 their networks? Token Ring's centralized architecture makes its LAN cabling systems, which are in reality electrical rings, easy to manageand that's a distinct selling point to overworked network managers.

A description of a traditional Ethernet bus-style network explains the whys of centralized networks: in a standard Ethernet, the network cabling runs from one node (e.g., computer or printer) to another, in essence meandering from desk to desk in a continuous single strand . This is a simplified bus network, which can also contain cable branches running off the main, or backbone, cable; in such branching cable systems, however, the problems described here are virtually identical to those affecting nonbranching buses.

Imagine the headache of troubleshooting this seemingly never ending stretch of cable on a bus: When workstations on a bus-based LAN experience network- related trouble, a technician may have to inspect the entire cable segment, which can be several kilometers long, before finding the problem. This can be time-consuming , frustrating, and costly.

Troubleshooting a hub-based network entails no such runarounds: Each workstation is attached directly to the hub via its own unshared cable. This means the technician troubleshooting a particular network node has to worry about only the cable segment running from the hub to that node, not the entire network wiring system. This can represent substantial time savings in diagnosing network failures.

A Look At A Hub

Although each of the network hubs on the market are similar to each other, they're also dramatically different. All of the network hubs contain two basic components a chassis and topology-specific modulesthat allow creating easily reconfigurable networks. But each vendor has elected to work within its own design philosophy that makes for significant physical differences among those available.

A chassis is the hub's most visible component. It acts as the hub enclosure and serves as the interface between each of the individual modules. Individual vendor's hubs contain varying numbers of accessory slots, each of which accepts a single module.

The hubs usually contain an integral power supply and/or primary controller unit. Depending on a vendor's design philosophy, the controller unit may perform network management functions, serve as a repeater for all modules in the chassis, or act as the connection point to hubs located in other parts of a building or office of campus complex.

The modules serve as the link between the chassis and the network cabling and are thus cable-specific. That means they contain connectors that accept only certain types of connectors, each of which is associated with a specific type of cable. For example, a vendor may support IBM's Type 3 (IBM-certified UTP) Token Ring wiring and its associated connector with one module, thick and thin Ethernet coaxial cable with another, the UTP wire used in 10BaseT Ethernets with a third module, and ARCnet coax or fiber-optical cable with still other modules.

Each module usually contains connectors for multiple workstations. Placing two, four, or six connectors is common, depending of the intended use and type of cable to be attached to the module. For instance, thick coax connections require what is called a DIX connector, which is substantially larger that the RJ-45 used with UTP.

Some vendors offer modules that combine connector types, but only within a single type of network technology. For example, most hub manufacturers sell modules that support connections to both thick or thin Ethernet coax and 10BaseT UTP.

Their Physical Differences

As is often the case in free enterprise, various network product vendors have applied their own proprietary sets of design rules to their hubs. For instance, some hubs are six to eight inches high, while others are 12 to 18 inches, and the physical and/or electrical junctions that connect the module to the chassis generally differ in each vendors' implementations .

The reasons for these differences range from the complex, such as needing to cram sufficient functionality onto a product, to the simple, such as merely ensuring that the hub is physically compatible with the vendor's existing products. These design differences mean, of course, that a module designed for one vendor's wiring concentrators generally will neither fit in nor operate with another vendor's hub.

Fortunately, these physical incompatibilities don't carry over to the hubs' abilities to communicate with each other. Although the modules themselves may be physically and/or electrically incompatible, the cable-specific jacks on them provide industry-standard connections.

For instance, the 10BaseT connectors (known as eight-pin modular connectors and sometimes called RJ-45 connectors, which are physically similar but electrically dissimilar) on one vendor's hubs are identical to those on another's. This is also true for the thin and thick coax, fiber- optic , Token Ring, and ARCnet connectors.

A Wealth Of Other Benefits

The wiring hub's modular design allows vendors to integrate a wealth of other features and cabling options into them. As already noted, this architecture permits mixing the different cabling mediathat is, fiber-optic, thick and thin cable, and UTPinto one wiring center. Without such hubs, expensive inter-network devices such as bridges and routers are required.

Just as importantly, the modular approach also allows mixing different media-access technologies, such as Token Ring and Ethernet or Ethernet and Fiber Distributed Data Interface (FDDI), in a single hub. This permits merging and managing the several different types of network technologies at a single point.

This capability is especially valuable to the growing number of large corporations where small clusters of Token Rings and Ethernets have sprung up independently. Again, it often means an organization does not have to purchase an internetworking device to connect and manage a variety of workgroups.

Vendors have also moved hubs out of the local workgroup and into so-called enterprise networks. Hubs can be daisy chained togetherthat is, connected one after anotherto form large networks made up of multiple workgroups connected to separate-but-interlinked hubs.

On a more complex level, vendors are developing modulesusually in conjunction with nonhub vendorsthat provide internetwork bridging and routing capabilities. These modules route and filter network traffic between the modules in hubs, whether the hubs are in a local or remote site. Filtering allows a network manager to improve internetwork performance and security by restricting the flow of specified types of data packets across internetwork borders.

Boon To Management

Network hubs are ideal for centralizing network management capabilities. Numerous vendors have announced " intelligent " network hubs. Intelligence in this context refers to the hub's ability to accept management and configuration commands over the network cabling from a remote workstation.

Putting intelligence into a hub allows these devices to perform many functions that normally require an on-site technician's presence. For instance, network managers sitting at a centrally located network management station can not only turn remote hubs on or off, they can turn off individual modules and even individual ports within a module. They then can reroute traffic from the failed module or port to a working one.

This ability is vital in large, enterprise-wide networks, where a single manager may be in charge of a WAN spanning several cities or states. In such situations, it's not always economically feasible to maintain a technician on-site to troubleshoot occasional problems. The ability to reconfigure the hub from a remote site can thus mean the difference between keeping a network segment online or shutting it down until a technician can make the trip to repair the failed unit.

This tutorial, number 29, written by Jim Carr, was originally published in the December 1990 issue of LAN Magazine/Network Magazine.

 
team lib


Network Tutorial
Lan Tutorial With Glossary of Terms: A Complete Introduction to Local Area Networks (Lan Networking Library)
ISBN: 0879303794
EAN: 2147483647
Year: 2003
Pages: 193

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net