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Most internal PC data channels support simultaneous bi-directional flow of signals, but communication channels between the PC and the outside world are not so robust.
Let us learn about different alternatives available for the design of communication channel. These alternatives apply to both Analog and Digital channels and they are -
The simplest signal flow technique is the Simplex configuration. Simplex allows transmission in only one direction and is a unidirectional channel. It refers to one-way communications where one party is the transmitter and the other is the receiver. An example of simplex communications is a simple radio, which you can receive data from stations but can't transmit data.
Half Duplex refers to the transmission of data in just one direction at a time. For example, a walkie-talkie is a half-duplex device because only one party can talk at a time.
Most modems contain a switch that lets you select between half-duplex and full-duplex modes. The correct choice depends on which program you are using to transmit data through the modem.
Full Duplex refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once.
Enables for two-way Communications simultaneously.
The most expensive method in terms of equipment because two bandwidth channels are needed.
Data may be transmitted between two points in two different ways. They are
Serial data transfer refers to transmitting data one bit at a time. The objective of serial data transmission is to send the bytes from one point to another along a single line or channel. That is, the bits representing a given character are sent serially, one at a time. For example, to transmit the character A (01000001), first the digital level ‘1’ is sent followed by five digital level ‘0’, followed by digital level ‘1’and then a digital level ‘0’.
In character representation, the right most bit position is referred to as the least significant bit (LSB) and the left most bit position is referred to as the most significant bit (MSB). The character is transmitted with the LSB first and MSB last.
As the bits sent are digital electronic signals, consequently, the receiver should have the ability to recognize the serial stream of bits as characters. The receiver must be able to detect the start and end of a character.
There are two techniques for recognizing and separating characters from the serial bit stream. They are called Asynchronous transmission and Synchronous transmission.
In parallel transmission, as the name implies, the bits of a character are sent in parallel (simultaneously) using as many signal carrying lines as there are bits. For example, to transfer an eight-bit character from one subsystem to another, eight separate signal carrying lines are required.
As you can see, the entire character can be transferred in one bit time. There is an eight-fold increase in transmission speed as compared to the serial transmission.
But such increase is not without its share of problems and limitations. First of all the sender and receiver have to agree on the exchange of one or more characters. This necessitates a protocol or prior understanding between them. This can be implemented either through hardware or software. At high speeds of transfer using parallel transmission, protocols will be in the form of hardware signal exchanges. Therefore, systems capable of such high-speed transfer will be complex and are expensive to build. They are used typically for exchanges between sub-systems of a computer system. The high speed also limits the distance and hence parallel transfers are confined to shorter distance of the order of a few feet.
There are two main methods of sending/ transmitting data, Synchronous and Asynchronous transmission.
Refers to events that are synchronized or coordinated in time. For example, if the interval between transmitting characters A and B is the same as that between B and C, it is synchronous transmission. Also completing the current operation before the next one is started is considered synchronous operation.
Communication within a computer is usually synchronous and is governed by the microprocessor clock. Signals along the bus, for example, can occur only at specific points in the clock cycle.
Asynchronous refers to events that are not synchronized, or coordinated, in time. It is the opposite of synchronous.
Not synchronized => not occurring at predetermined or regular intervals.
The term asynchronous is usually used to describe communications in which data can be transmitted intermittently rather than in a steady stream. For example, a telephone conversation is asynchronous because both parties can talk whenever they like. If the communication were synchronous, each party would be required to wait a specified interval before speaking.
Most communication between computers and devices is asynchronous – it can occur at any time and at irregular intervals.
The following are considered asynchronous operations:-
The difficulty with asynchronous communications is that the receiver must have a way to distinguish between valid data and noise. In computer communications, this is usually accomplished through a special start bit and stop bit at the beginning and end of each piece of data. For this reason, asynchronous communication is sometimes called start-stop transmission.
Both the asynchronous and synchronous transmission methods are widely used in terminals. While terminals of micro-computers and mini-computers support asynchronous connection to terminals, the main-frame still support synchronous communication between the computer and the terminals. One reason in favour of asynchronous approach is the simplicity and significant low cost of realization. On the other hand synchronous communication terminals and interfaces are complex by an order or magnitude and are significantly more expensive to implement. But synchronous mode terminals are favoured in situations where fast query/response times are desirable. One must also take cognizance of the fact that the population of devices using the asynchronous method has increased dramatically due to the spectacular growth of personal computers. The PCs almost exclusively use asynchronous transmission for communication lines and for printer interfaces. It is really a matter of balancing between response time, communication channel costs and the cost of implementation.
Bridges pass data packets from one LAN, or segment of a LAN, to another, re-transmitting the data packets flowing across a network. Typically, bridges are used to segment portions of a large network to keep both the individual sections and the entire network operating efficiently.
Bridges may be used to segment networks using different protocols, such as Ethernet to Token Ring, or they can be used to segment networks and increase their efficiency by connecting users in groups to resources most appropriate for their use.
Bridges are programmed to recognize the addresses of workstations on the network and whether or not a specific packet of data needs to pass over a network divider in order to reach its destination. Should a packet of data be required to pass over a bridge, the bridge accepts that packet and then re-transmits it to another segment of the network where its destination is located.
In large networks, there are essentially two types of bridges: source routing and spanning tree. This distinction concerns how the bridges allow packets of data to reach their destination.
Source routing allows the sender to determine which bridge (in a multi-bridge network) the data packet should cross.
Spanning tree bridging requires the bridges to learn the addresses in the network and establish appropriate paths to various resources.
Concentrators are networking devices that combine the data transmissions from multiple hubs, multi-station access units, or network resources for transmission over a single medium. Concentrators are multiplexing devices; that is, they combine many signals into one to increase the overall efficiency of data communication.
Each hub, multi-station access unit, or network resource may be wired directly to a concentrator. While combining all signals into one transferable signal, each individual signal is still active; that is, each hub, multi-access unit or network resource can send data to its destination. Network designers deploy concentrators due to their ability to increase the efficiency of a data network.
Controllers are intelligent data switching networking devices that make decisions about where data packets are sent and how they get there based upon address information contained in data packet headers and footers. Their function is similar to concentrators, hubs, routers, bridges and switches.
Hubs are devices to which workstations, servers and other resources, such as printers, are connected by cable together to form a local area network (LAN) and permit the exchange of data. Each resource in the network is connected to each other through the hub. The term is primarily used when speaking of Ethernet networks. In a Token Ring networks, the term is replaced by multi-station access unit (MAU) or concentrator.
There are two types of hubs: passive and active, or intelligent. Passive hubs simply provide cable connections that link individual workstations and other resources to form a network; active hubs, in addition to providing cable connections, contain electrical circuits that filter and amplify the data traffic traveling through them.
Active, or intelligent, hubs may also provide management capabilities that allow network managers to perform maintenance tasks or configure various network parameters. To accomplish these tasks, active hubs use electrical power while passive hubs do not.
The electronic components used by active hubs help overcome signal degradation, one of the chief physical limitations of networking. As it flows through network cabling, data degrades. Because of this and other technical functions, hubs are also referred to as repeaters for their ability to re-transmit data packets received from various resources.
Routers direct data packets conforming to any of a variety of network protocols or network operating systems from one network to another. In addition to passing data packets between LANs or LAN segments, routers can determine the most efficient path through the network and forward data packets along that path to boost network performance.
Routers function as intelligent, high-speed bridges, and as such, bear higher costs than traditional bridges. Routers examine data packets flowing through them and determine the packet's protocol and its destination, determining if the two are compatible. Because of their rich feature set, which requires significant processing power, routers can also be the source of network bottlenecks.
Routers can be important to an enterprise networking strategy because they can intelligently deliver data to distinct geographically distributed networks devoted to particular business functions. For example, a company's accounting department may use one local area network (LAN) to share information while the sales department may use another LAN. To make the enterprise function more efficiently, sales and accounting need to know what each other are up to: they need to share networks. Routers can fit this bill.
Much like routers, switches split large networks into small segments, decreasing the number of users sharing the same network resources and bandwidth. This helps prevent data collisions and reduces network congestion, increasing network performance.
Unlike routers, switches allow dedicated bandwidth to be designated to each device on the network. Switches also support virtual local area networks (VLANs), which allow for the formation of small user groups within an existing network without expensive architecture modifications.
Finally, technological advances—such as Layer 3 and Layer 4 switching that assign switching functions to hardware rather than software, as in routers—are helping switches become the preferred method of both delivering data and segmenting networks on many campuses.
A recently developed technology, asynchronous transfer mode (ATM) is a very high-speed standard that many believe will allow for real-time video and voice network applications. ATM relies on hardware to break down data into relatively small cells of 53 bytes and secure a virtual channel to enable a direct transfer of data between sending and receiving machines.
ATM has proven a popular solution for use with local area networks (LANs) wide area networks (WANs) because it is capable of transmitting data at rates as high as 12.8 Gbps when implemented with optical fiber cable and the latest switches.
Ethernet is a LAN standard capable of transmitting data at 10 million bits per second (Mbps). A very popular protocol for small to medium enterprises, Ethernet excels at light to moderate duty networking and offers a very competitive price/performance ratio. An Ethernet network can use several types of cabling, from low-cost twisted copper wire typical of a regular telephone transmission to more expensive optical fiber.
Workstations on an Ethernet network transmit data by sending frames, or chunks of data, out to each station on the network. The frames carry an address in header information that targets the intended destination. Once the data reaches its targeted destination, it's read by the intended computer.
Every computer on the network has the capability of sending data at the same time. This results in frames of data colliding with each other, preventing them from reaching their destination. This limitation is overcome by software that detects collisions and directs the transmitting computer to re-transmit its data until it reaches is intended target.
Gigabit Ethernet, another variation of the Ethernet protocol, is capable of transmitting data at one billion bits per second. This standard may eventually challenge ATM and Frame Relay as the high-speed LAN topology of choice, but, at present, ATM and Frame Relay still offer Quality of Service (QoS) guarantees that Gigabit Ethernet cannot match. Gigabit Ethernet can use high-quality copper wire at distances of less than 25 meters and optical fiber cabling for greater distances.
FDDI is a data transmission protocol for sending data over optical fiber cabling. FDDI allows data to be transmitted at 100 Mbps. Like a Token Ring network, FDDI uses a token-based method for transmitting data. A token passes around a network, is picked up by the computer that has data to transmit, and is released back to the network once the data has been successfully transmitted.
A frame is a generic term for a chunk of data. It is also the most basic element of networking and inter-networking. Networking protocols break up data files into small chunks for transmission: these small chunks are termed frames. Frames can be of various sizes determined by other parameters in the OSI model. Here's an analogy: individual words make up sentences, which are the vehicles for ideas. Frames make up data files, which are the vehicles for information.
NICs (also known as adapters, e.g. Ethernet adapters, Token Ring adapters) provide the physical connections to the network for PCs, servers, terminals and other network resources. The NIC provides a port for connecting network cabling from the device to a hub, router, concentrator, controller, bridge or other piece of networking hardware.
NICs are specific to specific network protocols and, once installed in a device, determine the network protocols the device will abide by.
SNA is a network topology developed in the 1970s by IBM to determine data communication between main-frame computers and their users. SNA incorporates data protocols, network interface cards and just about every facet of communication.
T1 refers to a networking standard capable of transmitting data at a rate of 1.54 Mbps. This high-bandwidth protocol is commonly employed by very large enterprises such as telecommunications companies, the Internet backbone and connections from Internet service providers to the Internet backbone.
T3 is a faster implementation of T1. Using coaxial cable, T3 allows for data transmission rates of 45 Mbps and is used for WAN backbones, the Internet backbone and connections from Internet service providers to the Internet backbone.
Token Ring is a networking protocol for LANs that tends to be more efficient in transferring data than its direct competitor, Ethernet. In a Token-Ring LAN, each user gets regular turns at transmitting their data while with Ethernet LANs, users transmit data simultaneously, resulting in garbled messages that don't reach their destination on the first attempt.
Token Ring, as its name implies, uses a token that gets passed around to each computer on the LAN. Only the computer in possession of the token can transmit a message, which is passed around the ring until it reaches its destination. Once the data is delivered, the transmitting computer turns the token over to the next machine in the ring.
Fast Token Ring is a networking protocol that transmits data at rates of up to 100 Mbps. A relatively new protocol, products supporting its high data transfer rates are coming to market with increasing frequency. Fast Token Ring can use both twisted-pair wiring and multi-mode optical fiber as its transmission medium.
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Rajeev Kumar is the primary author of How2Lab. He is a B.Tech. from IIT Kanpur with several years of experience in IT education and Software development. He has taught a wide spectrum of people including fresh young talents, students of premier engineering colleges & management institutes, and IT professionals.
Rajeev has founded Computer Solutions & Web Services Worldwide. He has hands-on experience of building variety of websites and business applications, that include - SaaS based erp & e-commerce systems, and cloud deployed operations management software for health-care, manufacturing and other industries.