We continue our look into the world of the Network Operating System (NOS) by examining the Star Topology. Both the peer-to-peer network operating system model and client/server network operating system model have seen deployment implementations using a star topology.
The Star Topology Network
With a Star Topology network, each node (Servers, Workstations, and Peripherals) connects directly to a centrally located Hub / Concentrator (seeFigure ST 1).
Data always travels from the transmitting node through the hub or concentrator before continuing to its destination.
Network Management
It is the job of the hub or concentrator to manage and control all functions of the network. The central hub/concentrator also behaves like a repeater for the data flow in that it reshapes the signal before passing it on.
Switches do a similar job as well. Having discussed hubs, concentrators, switches and repeaters in earlier articles, I will not dwell on them here.
Star Topology Supported Transmission Media
One of the greatest assets of the star topology is that it can use practically any type of available transmission media. For copper-based wired networks, some flavor of twisted pair cable (usually UTP) is the most common type of transmission media generally found in star topology networks.
Copper-Based Transmission Media
Unshielded Twisted Pair (UTP) is the most abundant variety of copper cable available today. Therefore, it should come as no great surprise to discover that Unshielded Twisted Pair (UTP) cabling is in deed the predominant type of transmission medium (cable) found in the star topology networks of today.
This holds true for most of the other topologies to boot. Volume production has meant that UTP cable is considerably cheaper than its competitors are. Advances in UTP cable capabilities over the years have seen the continual evolution of UTP cabling to the point where it is today.
Star topology networks built around Shielded Twisted Pair (STP) and coaxial cable are still in active service today. They are disappearing quite rapidly however as existing networks upgrade to higher performing infrastructures. These “new” network infrastructures tend to be a mix of wireless and wired technologies.
The Wired Component
For the wired component Unshielded Twisted Pair (UTP) CAT5/CAT6 or above dominate. The use of fiber-optic cable in star topology networks is generally limited to those situations demanding “extreme” performance, immunity from Electro-Magnetic Interference (EMI), long cable runs and other scenarios where UTP is unsuitable.
Fiscal Considerations
One should never lose sight of the fact that above all else the greatest advantage that copper-based transmission media (wires/cables) has over its rivals is cost. Copper cable is considerably cheaper than fiber-optic cable.
Star Topology Protocols
Protocols commonly associated with a star topology include Ethernet and LocalTalk (Apple's Proprietary Protocol). Both protocols, Ethernet and LocalTalk require a different NIC
Star Topology Ad Hoc Networks
The star topology also lends itself for use in ad hoc networking scenarios and hence is very popular with small business and home networks. In fact, this sector constitutes over 60% of all networks. The driving impetus here has been the desire to save money by sharing an Internet connection between numerous machines.
Star topology is very popular with peer-to-peer network scenarios. The ease with which nodes come and go is one of the biggest reasons that the star topology is so popular with peer-to-peer networks. LAN parties and gaming sessions are a breeze. For these types of ad hoc network use, the star topology model is most definitely the easiest to install and configure.
Plug "N" Play Connectivity
Most ADSL, broadband modems on the market today include an integrated 4-port, switch capable of transparent bridging. The average consumer and small business alike find themselves ideally placed to use these types of “plug "n" play” network and Internet connectivity devices.
Star-Wired Ring Topology
A star-wired ring topology such as that implemented in IBM's Token Ring networks appears very similar to the classical star topology externally (physically). Both have nodes that connect to a central hub/concentrator or switch. The nodes themselves only differ in terms of the Network Interface Card (NIC) used.
- In order to connect machines to an Ethernet network an Ethernet NIC is required
- On the other hand, to connect to a Token Ring network a Token Ring NIC is required
Multi-Station Access Unit (MSAU)
All member devices of a network that uses a star-wired ring topology must connect to a special type of device called a Multi-Station Access Unit (MSAU). Externally the MSAU appears to be very much like a normal hub, switch or LAN Switch.
Internally at the hardware level however, the Multi-Station Access Unit (MSAU) contains wiring which allows information to pass from one device to another in a logical circle or ring.
