In computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of communication. Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behavior of a hardware connection. Five different protocols are:
A network operating system (NOS) is a computer operating system system that is designed primarily to support workstation, personal computer, and, in some instances, older terminal that are connected on a local area network (LAN). Here are some examples of network operating systems:
- Artisoft’s LANtastic
- Banyan VINES
- Novell’s NetWare
- Microsoft’s LAN Manager
In addition, some multi-purpose operating systems, such as Windows NT and Digital’s OpenVMS come with capabilities that enable them to be described as a network operating system. A network operating system provides printer sharing, common file system and database sharing, application sharing, and the ability to manage a network name directory, security, and other housekeeping aspects of a network.
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- Controller – e.g. Intel (ie0 – Sun3, Sun4), Lance (le0 – Sun4m, Sun4c, Sun3/50, Sun3/60).
- Transceiver Cable – connects the controller to the transceiver box.
- Transceiver Box – electrically isolates the system from the rest of the network.
- Coaxial Cable – the ethernet backbone.
- Switch – examines the data packet to determine the destination, then sends the packet only over the segment hosting the recipient machine. If the packet is addressed to a machine on the same segment, the packet never leaves that segment. This minimizes traffic on the network segments that don’t need to see the packet.
- Bridge – operates at the Data Link layer. Designed for transparent connection of networks. Bridges and Switches allow you to break the network into smaller segments that increase the overall throughput of the total network.
- Router – joins 2 networks at the network layer; forwards packets of a particular protocol from one subnet to another; translates messages between different protocols, e.g. DECnet and TCP/IP.
- Gateway – joins different types of networks; translates one protocol into another, e.g. between OSUs SONNET backbone and the local subnets.
- Terminal Server – attach systems on a local area network to serial devices, e.g. terminals and printers; may support LAT and Telnet protocols.
In networking, the term “topology” refers to the layout of connected devices on a network. One can think of a topology as a network’s virtual shape or structure. 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 in a family room, 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.
Bus networks 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. Bus networks work best with a limited number of devices. If more than a few dozen computers are added to a network bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (either “clockwise” or “counterclockwise”). A failure in any cable or device breaks the loop and can take down the entire network. Ring topologies are found in some office buildings or school campuses.
Many home networks use the star topology. A star network features a central connection point called a hub that may be a hub, switch or router. 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.
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 connection points) alone.
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. Some WANs, most notably the Internet, employ mesh routing. A mesh network in which every device connects to every other is called a full mesh. As shown in the illustration below, partial mesh networks also exist in which some devices connect only indirectly to others.
One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common examples of area network types are:
- LAN – Local Area Network
- WLAN – Wireless Local Area Network
- WAN – Wide Area Network
- MAN – Metropolitan Area Network
- SAN – Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network
- CAN – Campus Area Network, Controller Area Network, or sometimes Cluster Area Network
- PAN – Personal Area Network
- DAN – Desk Area Network
LAN and WAN were the original categories of area networks, while the others have gradually emerged over many years of technology evolution. For more details, click the link below: