The basic of networking and digital communication and essential elements required to understand how computer network operates in the context of security of information system for out net-centric organisation.
Network: Two or more devices connected together in such way as to allow them to exchange information.
Protocol: Set of standards that defines all operations within a network, basically it is an agreed upon formate for transmitting data between two devices. It determines a number of things in the network:
Protocol defines everything from basic networking data structure to upper level application programs.
A network is a logical grouping of computers that share information and resources.
Common Categorisation:
A LAN is a single network of computers, which are physically located in the same area and rarely spans over more than one location. It usually comprise small number of computers and printers with up to five servers.
Example - Network in a small office or home office.
A WAN is a network of LANs. WANs span more than one geographic area and are used to connect remote offices to each other. Basically, a WAN comprises two or more LANs joined together by routers. It can be found in medium - to - large-sized businesses with more then one office location.
Routers are hardware devices that direct traffic from one LAN to another.
Example - A software company might have its headquarters in Delhi, but also have remote office locations, say in Aurangabad and Faridabad. The LAN in the Delhi office would be connected to the LAN in the remote offices forming a WAN.
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LANs and WANs comes in many different varient. The most popular network type is Ethernet. Ethernet network have speeds of 10 Mbps, 100 Mbps or 1 Gbps. The majority of networks today operates at 100 Mbps. An alternative to Ethernet network is token-ring networks. Token-ring networks operates at 4 or 16 Mbps and are usually found in legacy system/networks. Token-ring networks are rarely found in companies today because of their lack of speed.
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LAN: It is a system of network computers and other hardware, such as printers, that are in relatively close proximity to one another.
Backbone: It is a high-speed network that connects several LANs in a location, to provide services. Such as in a university campus several LANs are connected to provide electronic mail (e-mail) and Internet access service beyond the LAN environment.
MAN: MANs are larger than LANs, but smaller than WANs. MANs are usually characterised by very high speed connections using fiber optical cables or other digital media.
IEEE 802-2001 standard definition: A MAN (metropolitan area network) is optimized for a larger geographical area than is a LAN, ranging from several blocks of building to entire cities. MANs can also depend on communications channels of moderate-to-high data rates. A MAN might be owned and operated by a single organization, but it is usually used by many individuals and organizations. MANs might also be owned and operated as public utilities. They will often provide means for internetworking for local network. Metropolitan area networks can span up to 50 km, devices used ate modem and wire/cable.
WAN: It is a geographically dispersed communications network, with many owners, linking computers for the purpose of communication with each other, such as a national network for airline reservations or railway reservation.
Value-added Network (VAN): It is a communication channel leased from a telephone company to offer customers with modern access to network services through a local or toll-free number.
Wireless Network: It is most commonly used to refer to a telecommunication network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves.
Network architecture can be described in two ways: peer-to-peer and client/server.
A peer-to-peer network is a grouping of personal computers such that all share information among each other. It usually comprise less than 10 computers. This type of network is for the users that requires very little computer service and security.
Security Issues
A client/server network is a network comprising several workstation and one or more servers. Client (user) log in the server and gain access to their files.
Advantage over peer-to-peer network
Topology refers to the shape of a network or the network’s layout. How different nodes in a network are connected to each other and how they communicate. Each topology is suited to specific tasks and has its own advantages and disadvantages. The choice of topology is dependent on:
Physical topology is the physical layout of devices on a network. The way that the workstations are connected to the network through the actucal cables that transmit data, that is , the physical structure fo the network, is called the physical topology. Every LAN has a topology, that is, the way that the devices on a network are arranged and how they communicate with each other.
The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data pass through the network from one device to the next without regard to the physical interconnection to the device. Logical topology is also called signal topology.
A network’s logical topology is not necessarily the same as its physical topology.
Logical topologies are bound to the network protocols that direct how the data move across a network. The ethernet protocol is a common logical bus topology protocol.
In this topology, the devices are connected with many redundant interconnections between the network nodes. In a true mesh topology, every node has a connection to every other node in the network.
One of the problems with mesh topology is that its cabling expenses are high and it takes extra efforts to track down cable faults.
In this topology, all devices are connected to a central hub. Nodes communicate across the network by passing data through the hub.
Advantages of star topology are: it becomes easy to add new workstations (nodes), it allows centralised control over the network and it allows centralised monitoring of the hub/network.
Disadvantage: if the hub fails, it cripples all the workstations connected to that hub, bringing the network performance to zero, and hub are expensive network components. in terms of cost.
In the connection with the start topology, the following important terms are used:
In this topology, all devices are connected to a central cable, called the bus or backbone.
In connection with the bus topology, the following important terms are used:
In networking, a bus is a central cable that connects all devices on a LAN. It is also called the backbone.
In this topology, all devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it.
Advantages:
Disadvantages:
This is a hybrid topology. Groups of star-configured networks are connected to a linear bus backbone.
The OSI is an International Organisation for Standardisation (ISO) standard for worldwide communications that defines a networking framework for implementing protocols in seven layers.
The OSI reference model is a set of seven layers that defines the different stages that data must go through to travel from one device to another over a network. It is also referred as the OSI reference model or just the OSI model.
This is the layer that actually interacts with the operating system (OS) or application whenever the user transfers files, reads messages or perform other network related activities. The application layer supports application and end-user processes. Everything at this layer is application specific. This layer provides application services for file transfers, e-mail and other network software services.
It takes the data provided by the application layer and converts it into a standard formate that the other layers can understand. The presentation layer provides independence from differences in data presentation by translating from application to network formate and vice versa.
The presentation layer works to transform data into the form that the application layer can accept. This layer formates and encrypt data to be sent across a network, providing freedom from compatibility problems.
The presentation layer is sometimes called the syntax layer.