Network Connectives


Introduction.  Connective device is a phrase used to characterize both simple and more complex devices used to connect one part of a network to another.  This can involve things as simple as barrel connectors and as complicated as routers and switches.  In most cases it means connecting two or more lengths of cable.  We follow Littlejohn Shinder's lead and describe three main types of connectors.
  • Simple connectors
  • Complex connectors
  • Segmenting and subnetting devices
    • Bridges
    • Routers
    • Switches

Segmenting refers to devices refers to dividing a network into segments that are still part of the same network.  Subnetting divides the network into different entities called subnetworks based on network address information.

We will discuss simple and complex connectors in this page.  Then we will dedicate one web page each for  bridges, routers and then switches.

Simple Connectors.  Simple connectors are those that provide only a connection point but do not amplify or otherwise modify the signal.  We will survey the following types of simple connectors.

  • BNC Connectors
  • RJ Connectors
  • Fiber Optic Connectors
  • Patch Panels
  • Passive Hubs

10Base2, also called thinnet, networks use BNC connectors to connect the NIC to the cable.  A BNC connector is a small cylindrical device with a pin that connects to the conduction wire in the cable.  The connector locks into place by twisting of an outer ring.

Three of the most prevalent BNC devices are

  • BNC T-Connector
    • the stem attaches to the NIC
    • a piece of cable attaches to each side of the top bar
    • or a BNC terminator must be connected to the non-continuing side of the T connector
  • BNC Barrel Connector
    • a piece of cable attaches to each end of the cylinder
    • used to increase the total cable length
  • BNC Terminator
    • 50 ohm device which is installed at an end of a coax cable
    • used to ensure the signal won't bounce back and cause interference

One end of each overall cable length should be grounded.

RJ - Registered Jack connectors get their names due to their registration with the FCC - Federal Communications Commission.  The most commonly used RJ connectors are RJ-11 for telephones and RJ-45 for UTP based Ethernet networks.

Ordinary telephone wires in the US make use of RJ-11 connectors.  You've seen these when you connect telephone lines to a modem or when you connect telephones to a wall jack in your house.  Inside the walls the jack is connected to UTP, normally CAT-3 or CAT-5.

RJ-45 connectors are used on UTP cabling for Ethernet networks.  These are what are used on our laptops here at Quinnipiac.  They look exactly like RJ-11 connectors but they are a little larger.

Fiber Optic connectors are the most difficult to work with because each individual strand of glass or plastic must be precisely aligned.  Once they are aligned the cable is attached to the connector using hot melt glue, epoxy or anaerobic adhesive.

Five of the most common types of fiber optic connectors are listed below.

  • SC - push pull type
  • ST - a keyed bayonet type
  • FC - a keyed threaded lock type
  • SMA - a threaded type
  • FSD - a fixed shroud type used with FDDI

A patch panel is a connection and distribution point used to organize cables that come together at a central location.  It is actually somewhat similar to old time telephone switchboards in which connections were completed by plugging a wire into a specific jack.

For star topology networks, cables from computers at various locations come into a wiring closet where a patch panel is located.  Each cable is connected to a punch down block on the back of the panel.  RJ-45 jacks or something else more appropriate to the cabling are likely to be on the front.  Patch cables run from the panel to the hub.

A patch panel is essentially a passive hub acting as a local central connecting device.  It doesn't actually run on electric power and doesn't actually have any active electronic parts.  It doesn't regenerate any signals, it merely sends it out through all of the ports in the hub.

Complex Connectors.  Complex connectors do more than provide connections, they also do something active with the signal.  We will talk about three main types of complex connectors.

  • Media converters
  • Repeaters
  • Active/Intelligent hubs

Media converters are used to convert a segment of one network media type to another.  For example, they might convert 100BaseT Ethernet to fiber optics or 10Base2 to 10BaseT.  They are also commonly known as media adapters or media translators.

Repeaters connects two segments or lengths of cable and they regenerate the signal before transmitting it on.  These are most useful for signals that need a boost due to attenuation.  They are used to increase the effective distance/reach of a cable or segment.  In some designs they can also be used to connect cabling of different media types.

Repeaters do not filter data that passes through them, they regenerate everything that comes in.  Unfortunately, this means they regenerate noise, interference, signals and broadcast messages and pass them on.

Active hubs have multiple ports like hubs but they also regenerate any incoming signals before sending them out.  They have active electronic components and require electrical power.

Intelligent hubs are special types of active hubs.  They not only regenerate signals, they have processing capabilities to do things like perform diagnostics and detect problems with particular ports.