MIND QUIZ

NETWORK TOPOLOGY
In networking, the term topology refers to the layout of connected devices on a network. This article introduces the standard topologies of computer networking.
Topology in Network Design
One can think of a topology as a network's "shape." This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle, but it would be highly unlikely to find an actual ring topology there.

Network topologies are categorized into the following basic types:
bus • ring • star • tree • mesh

More complex networks can be built as hybrids of two or more of the above basic topologies.Topologies remain an important part of network design theory. You can probably build a home or small business network without understanding the difference between a bus design and a star design, but understanding the concepts behind these gives you a deeper understanding of important elements like hubs, broadcasts, ports, and routes.

BUS TOPOLGY
Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium, that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message.
Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options years ago. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.

RING TOPOLOGY
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (effectively either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

STAR TOPOLOGY
Many home networks use the star topology. A star network features a central connection point called a "hub" that may be an actual hub or a switch. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet.
Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

TREE TOPOLOGY
Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub ports) alone.

MESH TOPOLOGY
Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that in a ring, although two cable paths exist, messages can only travel in one direction.) Some WANs, like the Internet, employ mesh routing.

CLIENT / SERVER
Clients and servers are devices that perform specific functions on a network. Client devices normally request and receive information over the network. Mobile computers and most desktop PCs operate as clients. A server device hosts files, databases, Web sites, or other applications. Server devices often feature higher-powered processors, more memory, and larger disk drives than clients.
The term client/server refers to any network design utilizing clients and servers. Web, FTP, email, DNS and many other database applications are client/server designs. Client/server networks can be built on the Internet, on intranets, or in homes.
The main alternative to client/server networking is peer-to-peer networking, where network devices all perform equivalent functions.

PEER TO PEER
Peer-to-peer is a type of network design where all devices support roughly equivalent capabilities. Peer-to-peer networking (also known simply as peer networking) is in contrast to client/server networking, where certain devices have responsibility for providing or "serving" network information and other devices consume or otherwise act as "clients" of those servers.
Peer-to-peer networking is most common on small LANs, particularly Windows home networks. Peer networking on the Internet gained widespread popularity thanks to file sharing services like Napster. However, many of these file sharing services, including Napster, actually integrate both peer and client/server networking design. Technically, these are called hybrid networks.

So what does the size of the Internet have to do with Internet Protocol? Everything! For a computer to communicate with other computers and Web servers on the Internet, it must have an IP address. An IP address (IP stands for Internet Protocol) is a unique 32-bit number that identifies the location of your computer on a network. Basically, it works like your street address -- as a way to find out exactly where you are and deliver information to you.

When IP addressing first came out, everyone thought that there were plenty of addresses to cover any need. Theoretically, you could have 4,294,967,296 unique addresses (232). The actual number of available addresses is smaller (somewhere between 3.2 and 3.3 billion) because of the way that the addresses are separated into classes, and because some addresses are set aside for multicasting, testing or other special uses.

With the explosion of the Internet and the increase in home networks and business networks, the number of available IP addresses is simply not enough. The obvious solution is to redesign the address format to allow for more possible addresses. This is being developed (called IPv6), but will take several years to implement because it requires modification of the entire infrastructure of the Internet.

INTRANET
An intranet is a private LAN designed for use by everyone within an organization. A very simple intranet might consist of an internal email system or a message board. More sophisticated intranets include one or more Web site portals that contain company news, forms, and personnel information. The essential idea of an intranet is that it uses LAN (and WAN) technologies to facilitate communication between people and improve the knowledge base of an organization's employees.

OSI MODEL
The Open Systems Interconnection (OSI) reference model has been an essential component of computer network design since its inception in 1984. OSI is an abstract model, meaning that actual network implementations need not adhere to it strictly. OSI is also a standards effort, a product of the International Standards Organization (ISO). (And OSI is ISO spelled backwards, just to add to the fun). Although heavy on theory, the OSI model still provides a practical, structured introduction to network design. The OSI model divides the complex task of host-to-host networking, traditionally called internetworking, into layers. Layers in the OSI model are ordered from lowest level to highest in a stack.

OSI Model Upper Layers
OSI designates the application, presentation, and session layers as "upper" layers. Generally speaking, software in these layers performs application-specific functions like data formatting, encryption, and connection management. Examples of upper layer technologies in the OSI model are HTTP, SSL and NFS.

OSI Model Lower Layers
The remaining lower layers provide more primitive network-specific functions like routing, addressing, and flow control. Examples of lower layer technologies in the OSI model are TCP, IP, and Ethernet.

OSI Model Benefits
The layered approach in the OSI model offers several advantages to system implementers. By separating the design into logical smaller pieces, vendors can more easily solve network design problems through divide-and-conquer. A product from one vendor that implements OSI Layer 2 functionality, for example, will be much more likely to interoperate with another vendor's OSI Layer 3 product because both vendors are following the model. Finally, the OSI model makes network designs more extensible. New protocols and other network services are generally easier to add to a layered architecture than to a monolithic one.