To be able to choose the right network technology, it is essential to understand some key terminology so that the features and capabilities of various networks and technologies can be categorized and compared. Some of the basic communication and networking terminology includes:
Contents
A station represents a single communication element on a network system. Each user of the network must access the communication capability of the network via a station. Each station usually has some implementation of the open systems interconnection (OSI) network reference model as the means of utilizing the network system.
Media access is the technique, by which individual stations establish when they are permitted to transmit, or ‘use’ the media. Media Access Control (MAC) is a function which is normally performed in the data link layer of the OSI reference model. Some of the common media access control techniques are the carrier sense multiple access with collision detection (CSMA/CD) and token passing. CSMA/CD systems such as Ethernet permit all stations on a network equal access. Each station must ‘listen’ to the network to establish periods of inactivity before transmitting. If multiple stations attempt to transmit simultaneously, a collision occurs. This is detected by all transmitting stations, which all must immediately stop transmitting and each wait a randomly determined period of time, before attempting to use the network again.
Token-passing systems have a logical ‘token’ which is exchanged among stations via network messaging. The station that holds the token has permission to transmit. All other stations are only permitted to receive messages. Stations wishing to transmit but not having the token must wait until the station holding the token passes it on.
Addressing is the concept that assigns normally unique identifiers to each station in a network system. This identifier (address) can then be utilized by the network for a variety of purposes, including identifying the origin and/or destination of messages, or arbitrating access to a shared communicate medium. Another addressing or identifier concept assigns unique identifiers not to stations but to unique pieces of data or signals that will be carried by the network. Stations then use an identifier according to what type of data they will be transmitting. Most networking techniques require the establishment of explicit address for each network station.
Bandwidth in communication systems describes the capacity of the system to transport digital data from one place to another. This term may be applied to the raw capability of the physical and data link layers to transport message data (raw bandwidth, closely related to the bit rate concept) or it may be applied to the effective rate at which user-meaningful information is transported i.e. effective bandwidth.
The bandwidth of a given system is generally inversely proportional to the worst-case node-to-node distance. The smaller the network span, the higher the bandwidth can be.
Recommended: The Ultimate Guide to Electrical Maintenance
Arbitration is used by some networks to define the procedure followed when multiple stations wish to use the network simultaneously.
Signaling refers to the actual physical representation of data e.g. electrical, optical, etc. as it is carried on the media. For instance, in some networks, data elements may be represented by certain voltage levels or waveforms in the media. In other networks, data elements may be represented by the presence of certain wavelengths of light in the media. The association of all representable data elements such as 0/1 or ON/OFF with the corresponding signal representations in the media is the signaling scheme for instance differential signaling represents a specific data element (1 or 0) as two different states on a pair of wires. Case in point is the RS-485 which represents a digital 1 data element as a 5 V signal level on the first wire and a 0 V on the second wire, and a digital 0 data element as 0 V signal level on the first wire and 5 V signal level on the second wire. One key benefit of differential signaling is that it is possible to determine the data being transmitted without knowing the ground reference potential of the transmitter. This permits the transmitter and receiver to operate reliably, even when they have different ground potentials (within limits), which is a common occurrence in communication systems.
Modulation in a classical sense refers to the signaling technique by which data information is used to control some combination of the frequency, phase and/or amplitude of a carrier signal. The carrier signal carries the information to a remote receiver where it will be demodulated to retrieve the information.
Encoding refers to the process of translating user-meaningful information into data elements or groups of data elements to be transported by the network system. A code book refers to the set of all relationships between the user-meaningful information and data carried by the network.
Encoding may happen at several levels within the OSI reference model, as user-meaningful information is transformed successful until it becomes an actual network message, produced by the data link layer. Decoding is the reverse process, whereby a network is successful translated back into user meaningful information.
Don’t miss out on key updates, join our newsletter List
Message is the basic, indivisible unit of information which is exchanged between stations. User- meaningful information will be regrouped into one or more messages by the OSI network reference model.
Multiplexing refers to the ability to use the media in a network to carry multiple messages or information streams ‘simultaneously’. Multiplexed systems allow several communication channels to use the same wire or media. Each message or information stream may have different sources and destinations.
Multiplexing may be achieved in different ways. Time division multiplexing (TDM) involves breaking access to the media into series of time quanta. During each time quantum, the media carries a separate message or information stream. The close structure of time quanta allows the network media to carry multiple messages ‘simultaneously’. Code division multiplexing (CDM) involves the separation of the code book into sections. Each section of the code book provides all the messages that will be used for a specific information stream. Thus, a specific information stream within the network media is distinguished by all of the messages that belong to the section of the code book for that stream. Frequency division multiplexing (FDM) divides an available bandwidth of a communication channel into several frequency ranges and assigns one information stream to each frequency range.
A protocol is defined method of information exchange. Protocols are generally defined at several levels within the OSI network reference model (refer to the figure above) e.g. an applications layer service might be provided for the reading of or writing to a data element contained in another device (or station) on the network. This service makes use of a data link layer service which may be provided for supporting the exchange of a message with another device (or station) on the network.
Topology refers to the physical or geographic layout or arrangement of a network. Certain types of canonical topologies are typically used in context of networks such as star (or hub), ring, daisy chain, and so forth.
Related article: Topological Network Structures used in Fieldbus Systems
A service represents a specific function or operation that is supported by a particular layer in the OSI network reference model. For instance, an application layer might be provided for the reading of or writing to a data element contained in another device (or station) on the network. This service might make use of a data link layer service which may be provided for supporting the exchange of a message with another device (or station) on the network.
Bit rate refers to the speed at which binary pieces of information (bits) are transmitted on a specific network. The raw bit rate of a network generally refers to the actual speed of transmission of bits on the network. The effective bit rate or throughput generally refers to the speed at which user information is transmitted. This number is usually less than or equal to the raw bit rate, depending on what percentage of the bits transmitted is used for carrying user information. The bits not carrying user information are overhead, used to carry protocol, timing or other network information.
Half duplex refers to a communication system in which a station can either transmit information or receive information, but not both simultaneously. A full duplex network allows a station to transmit information and receive information simultaneously.
There are occasions when communications between two or more points are best handled by multiple networks. This may be, for instance, when a single network has limitations that prevent it from tying the points together such as distance limits or when multiple networks are needed for other reasons such as to carry different types of data. When multiple networks are used to provide communications, there may be a need to pass messages or information directly from one network to another. Several devices are used to achieve this.
A repeater may be used when the networks to be joined are logically identical, and the purpose is simply to extend the length of the network or extend its capabilities in some way. Generally, a repeater has no effect on messages and simply carries all messages from one cable or port to another that is a change of physical media. A repeater allows for connection of networks at the physical layer level.
A bridge is similar to a repeater, but allows for connection of networks at the data link layer level. A bridge generally will pass all messages from one network to another, by passing messages at the data link layer level.
A router normally has the function of partitioning similar networks. Two networks may be based on the same technologies and protocol, but may not be logically identical. In these cases, some, but not all of the messages on one network may need to be carried or transported to the other network. The router function is to determine which messages to pass back and forth based on certain rules. Functions to enable efficient, automatic routing of messages may be included in layer 3 (the network layer) of the OSI network reference model and a router allows for the connection at the network layer level.
A gateway may have a function similar to a router, or it may have the functions of joining dissimilar networks, that is, networks based on dissimilar technologies and/or protocols. When functioning like a router, a gateway usually performs its discrimination at a higher protocol level than a router. When a gateway joins dissimilar networks, generally a more complex set of rules must be designed into the gateway so that message translation, mapping and routing can occur within the gateway as it establishes which messages to pass from one network to the other.
Related articles:
A closeup shot of a warning lamp in the street at night, image by Freepik…
Impeller flowmeters at times referred to as paddlewheel meters are one of the frequently utilized…
Introduction Yes! If you have old electronic devices that you are no longer using, you do…
The cosine of the angle between voltage and current in an AC circuit is referred…
Ball transfer units enable smooth, multidirectional movement of loads across flat surfaces. These mechanical components…
When designing a transmission or distribution system, the engineer must take into account not only…
