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LESSON 1: DATA NETWORK FUNDAMENTALS Layer 7 – Application it’s what most users see It receives information directly fro...

LESSON 1: DATA NETWORK FUNDAMENTALS Layer 7 – Application it’s what most users see It receives information directly from users and displays DATA COMMUNICATIONS incoming data it to the user transfer of information from one point to another. ‘Data’ refers to information that is represented by a Layer 6 – Presentation sequence of zeros and ones; the same sort of data that is represents the area that is independent of data handled by computers. representation at the application layer Many communications systems handle analog data; good example of this is encryption and decryption of data examples are the telephone system, radio, and television. for secure transmission Modern instrumentation is almost wholly concerned with the transfer of digital data. Layer 5 – Session Any communications system requires a transmitter to send computers or servers need to “speak” with one another, a information, a receiver to accept it and a link between the session needs to be created two. this layer involve setup, coordination (how long should a Types of links include copper wire, optical fiber, radio, and system wait for a response, for example) and termination microwave. Some short distance links use parallel between the applications at each end of the session connections; meaning that several wires are required to carry a signal. Layer 4 – Transport data transfer between end systems and hosts The digital data is sometimes transferred using a system Transport Layer is the Transmission Control Protocol that is primarily designed for analog communication. A modem, for (TCP), which is built on top of the Internet Protocol (IP), example, works by using a digital data stream to modulate an commonly known as TCP/IP analog signal that is sent over a telephone line. At the receiving end, another modem demodulates the signal to reproduce the Layer 3 - Network original digital data. The word ‘modem’ comes from modulator and responsible for packet forwarding, including routing demodulator. through different routers STANDARDS Layer 2 – Data Link Protocols are the structures used within a communications provides node-to-node data transfer (between two directly system so that, for example, a computer can talk to a connected nodes) printer. two sublayers exist here - the Media Access Control Traditionally, developers of software and hardware (MAC) layer and the Logical Link Control (LLC) layer platforms have developed protocols, which only their products can use. Layer 1 - Physical In order to develop more integrated instrumentation and represents the electrical and physical representation of the control systems, standardization of these communication system protocols is required. can include everything from the cable type, radio Standards may evolve from the wide use of one frequency link (as in an 802.11 wireless systems), as well manufacturer’s protocol (a de facto standard) or may be as the layout of pins, voltages and other physical specifically developed by bodies that represent an requirements industry. PROTOCOLS OPEN SYSTEM INTERCONNECTION (OSI) MODEL OSI model provides a framework within which a specific protocol may be defined. A frame (packet) might consist of the following. The first byte can be a string of 1s and 0s to synchronize the receiver or flags to indicate the start of the frame. PHYSICAL STANDARDS 1. RS-232 interface standard The RS-232C interface standard was issued in the USA in 1969 to define the electrical and mechanical details of the interface between data terminal equipment (DTE) and data  communications equipment (DCE) which employ serial binary data interchange. 4. Management information traditionally provided by taking readings from 2. RS-432 interface standard meters, chart recorders, counters, and The RS-423 interface standard is an unbalanced transducers and from samples taken from the system similar to RS-232 with increased range production process. This data is required to and data transfer rates and up to 10-line monitor the overall performance of a plant or receivers per line driver. process and to provide the data necessary to manage the process. 3. RS-422 interface standard The RS-422 interface system is a balanced (4) The four devices that have made the most significant impact on system with the same range as RS-423, with how plants are controlled are: increased data rates and up to 10-line receivers per line driver. 1. Distributed control system (DCS) A DCS is hardware and software based digital 4. RS-485 interface standard process control and data acquisition based The RS-485 is a balanced system with the same system. The DCS is based on a data highway range as RS-422, but with increased data rates and has a modular, distributed, but integrated and up to 32 transmitters and receivers possible architecture. per line. Each module performs a specific dedicated task The RS-485 interface standard is very useful for such as the operator interface/analog or loop instrumentation and control systems where control/digital control. There is normally an several instruments or controllers may be interface unit situated on the data highway connected together on the same multipoint allowing easy connection to other devices such network. as PLCs and supervisory computer devices. NOTE: RS232 is full-duplex, RS485 is half-duplex, and RS422 is 2. Programmable logic controllers (PLCs) full-duplex. They are controlled by a central processor using easily written ‘ladder logic’ type programs. RS485 and RS232 are only the physical protocol of Modern PLCs now include analog and digital I/O communication (ie interface standard), RS485 is the differential modules as well as sophisticated programming transmission mode, RS232 is the single-ended transmission mode, capabilities similar to a DCS e.g. PID loop but the communication program does not have much difference. programming. High speed inter-PLC links are also available, such as 10 and 100 Mbps Ethernet. MODERN INSTRUMENTATION AND CONTROL SYSTEMS In an instrumentation and control system, data is acquired 3. Smart instruments (SIs) by measuring instruments and is transmitted to a controller In the 1960s, the 4–20 mA analog interface was – typically a computer. established as the de facto standard for The controller then transmits data (or control signals) to instrumentation technology. As a result, the control devices, which act upon a given process. manufacturers of instrumentation equipment had a standard communication interface on which to The main purpose of an instrumentation and control system, in an base their products. industrial environment, is to provide the following: Users had a choice of instruments and sensors, 1. Control of the processes and alarms from a wide range of suppliers, which could be common for equipment from various sources to integrated into their control systems. be mixed in the same control system. Stand- alone controllers and instruments have largely 4. PCs been replaced by integrated systems such as distributed control systems (DCS). NETWORKING 2. Control of sequencing, interlocking and alarms (3) There are three broad classes of network, although the provided by relays, timers and other components distinction between them is blurred and they tend to overlap: hardwired into control panels and motor control centers. The sequence control, interlocking and 1. Local area networks (LANs) alarm requirements have largely been replaced LANs are usually confined to one building or by PLCs. group of buildings within a radius of a few hundred meters. 3. An operator interface for display and control All devices on a LAN are connected to a common process and manufacturing plants were operated transmission medium such as coaxial cable. from local control panels by several operators, Transmission speeds are typically up to hundreds each responsible for a portion of the overall of Mbps. process  2. Metropolitan area networks (MANs) overcome by using buffers in the computer at the hub of A MAN covers a city or metropolitan area, and the star network. may have several LANs connected to it. Transmission speeds are generally up to hundreds of Mbps and almost always use optical fiber cable. 3. Wide area networks (WANs) WANs may cover thousands of kilometers and involve several different transmission media (such as optical fiber, satellite links, microwave and coaxial cable). Transmission speeds vary greatly. An example WAN is the public telecommunications system, which now has 200 The major disadvantages of the star network are: Mbps optical fiber links between capital cities and If the central hub is disabled, the entire system is major centers. inoperable. Depending on the physical layout, the costs of cabling a star network tend to be higher than some of the CIRCUIT AND PACKET SWITCHING alternatives. (2) The two basic types of networks are ‘circuit’ switched and ‘packet’ switched RING OR LOOP TOPOLOGY Nodes in a ring network are connected node to node, 1. Circuit switched network ultimately forming a loop. a connection is established between the two The data flow is often arranged to be unidirectional, with ends and maintained for the duration of the each node passing data on to the next node and so on. message exchange (an example is the public It is essential that each node, when receiving, can remove telephone system). data from the ring so that it does not circle through the The advantage is a guarantee of continuity, while network indefinitely. the disadvantage is cost. The circuit is tied up The basic ring network is unable to function if a node is even when no one is talking or the transmission disabled or the ring broken. rate may be slow. Consequently, if modifications or additions are to be made to the network, a complete system shutdown is necessary. 2. Packet switched network does not establish a direct connection. Instead, the message is broken up into a series of packets or frames, sometimes known as protocol data units (PDUs). These are transmitted one at a time, each carrying the destination address. Depending on the network conditions, they may take different routes to the destination, and may arrive out of order. It is the job of the protocol software to reassemble the packets in the right order. BUS TOPOLOGY Packet switching is cheaper as it makes better The bus topology consists of a communication path with use of the resources; the physical nodes connected to it like leaves off a branch. communications links carry packets from multiple The nodes are not physically inserted into the bus, as is sources concurrently. the case with ring topology, but are ‘teed-off’ the bus. Packet-switched network can offer either Bus networks can be bi-directional or unidirectional. connectionless or connection-oriented communications, depending on the protocols used. NETWORK TOPOLOGIES 1. Star 2. Ring or loop 3. Bus or multidrop STAR TOPOLOGY In the event of a disabled node, either due to a failure or There is a central node or hub and all the outlying nodes an access control malfunction (i.e. the destination node communicate back to it on separate communication links. not taking its information from the bus), the network can The central hub must have the capacity to simultaneously continue to operate as before, without the malfunctioning send and receive messages. Contention problems are node.  An IEEE 802.2 interface defines services that fall into the following categories: IEEE 802.3 (ISO 8802.3) - This standard defines the carrier sense multiple accessing with collision detection (CSMA/CD) protocol, which is the protocol used by Ethernet and is described in the section on Ethernet. TRANSMISSION TECHNIQUES IEEE 802.4 (ISO 8802.4) (2) Two main methods used for the transmission of information over - This standard defines the token passing a LAN are baseband and broadband. bus access method. Physically this looks like a bus network with the 1. Baseband operation like that of a token ring This is also known as time division multiplexing network. Nodes on the network see (TDM). themselves as being arranged in a Only one device is allowed to transmit at any one logical loop, with each node assigned an time and can use the entire bandwidth of the address. system. No carrier is used, so the signal (e.g. the - Collision problems that occurred in output from a UART) is directly applied to the CSMA/CD are solved as only one token medium. can exist on the network at one time, and only one node may own the token. 2. Broadband Token holding times exist so that no Broadband is also known as frequency division node may own the period for prolonged multiplexing (FDM). periods of time. Token bus is superior to The system bandwidth is divided into channels CSMA/CD for networks with heavy that do not overlap, meaning that many pairs of loads, because each node has a regular devices can communicate simultaneously, and time to communicate. they usually retain their channel until the message transfer is complete. IEEE 802.5 (ISO 8802.5) As only a part of the system bandwidth is - This standard defines a token ring available, data transfer rates for individual access method, similar to that used by communications are less than for TDM using the IBM for their token ring standard. same physical setup. Data is transmitted by injecting a carrier (sine) wave on to the medium and modulating the ETHERNET carrier with the data – be that by frequency Ethernet was developed by Xerox in the early 1970s and modulation, amplitude modulation, or phase standardized by Xerox, Digital Equipment and Intel in modulation. 1978. It uses CSMA/CD as a medium access control method. IEEE LAN STANDARDS The relevant standards are: The most important standard for LAN interfaces and 1. Ethernet V2 (Bluebook) protocols is IEEE 802, a series administered by the IEEE 2. IEEE 802.3 (ISO 8802.3) 802 LAN Standards Technologies Committee. The standard has several sections, each with its own Below are listed some of the hardware variations of Ethernet, which co-coordinating committee. are explained more fully later in ‘Ethernet hardware requirements. Some standards have been superseded by ISO standards as shown in brackets in the descriptions below. Standard (or thick) Ethernet (10Base5) uses 10 Mbps baseband operation on coaxial cable with a maximum IEEE 802.1 (ISO 8802.1) segment length of 500 m. Details how the other 802 standards relate to one another Thin Ethernet (10Base2) uses 10 Mbps baseband and to the ISO/OSI reference model. As with the ISO/OSI operation on coaxial cable with a maximum segment model, the IEEE 802.1 specification describes interface length of 185 m. layers or communication interfaces between different 10BaseT uses unshielded twisted pair cables and hierarchical levels of devices and activities. operates at 10 Mbps with the use of a wiring hub onto which each node connects. IEEE 802.2 (ISO 8802.2) 100BaseT is similar to 10BaseT but operates at 100 Standard has divided the ISO/OSI data link layer into two Mbps. sublayers and defines the functions of the logic link control 1000BaseT (gigabit Ethernet) is similar to Fast Ethernet, (LLC) sublayer and the media access control (MAC) but operates at 1000 Mbps. sublayer. 1BaseT is similar to 10BaseT but limited to a 1 Mbps data rate. Obsolete.  Broadband Ethernet (10Broad36) uses FDM with maximum segment length of 3600 meters (11,800 feet). Source Address - This may be either 16 bits or 48 bits, Obsolete. depending on how the system is configured. In practice it 10BaseF is a 10 Mbps baseband system operating on is almost always 48 bits. This is the address of the node optic fibers. that sent the data. Length Indicator - The two-byte length indicator specifies ETHERNET TOPOLOGY how many bytes are in the data field. Standard and thin Ethernet use a bus topology, in which each node attaches to the communications cable as Data - This is the actual message data and can be from shown. 46 to 1500 bytes in length. The minimum value is determined by the need for collision detection and the maximum value limits the access time for any one node to 1, 2 milliseconds. If the actual data is less than 46 bytes it must be ‘padded’ up to 46 bytes. Frame Check sequence - This is a 32-bit cyclic redundancy check value used for error detection. FAST ETHERNET Fast Ethernet systems operate at 100 Mbps on different forms of physical media and they retain the existing Ethernet MAC layer. 10BaseT (Ethernet) uses a star configuration in which each node is connected via two twisted pairs to a wiring IEEE 802.3u standard defines: hub as shown. 100BaseTX, which uses two pairs of category 5 UTP or STP and is the most commonly used standard. 100BaseFX, which uses two pairs of multimode (or single node) fiber. 100BaseT4, which uses four pairs of category 3, 4 or 5 UTP. This is no longer used. NOTE: The IEEE also has a standard 802.3y that defines 100BaseT2, which was to use two pairs of category 3, 4 or 5 UTP. This system has not been developed commercially. ETHERNET PROTOCOL OPERATION All data transfer is in the form of a packet or frame. It INTERNETWORK CONNECTIONS consists of an envelope containing control information 1. Repeaters (such as synchronization bytes and addresses) and the A repeater is used to connect two segments of actual message data. the same LAN, and simply retransmits an Each node examines the destination address and reads incoming signal. The repeater also carries out the data if the frame is directed at that node. collision checking. Remote segments may each have a repeater, joined by a link; also a repeater may operate between different types of segment such as coaxial cable and optical fiber cable. Preamble - This field comprises seven bytes, each with the binary value 10101010. Its purpose is to allow all receiving MAC units to synchronize with the frame. Start of frame delimiter - The SFD indicates the start of a frame and has the binary value 10101011. Destination Address - This may be either 16 bits or 48 bits, depending on how the system is configured. In practice it is almost always 48 bits. It must be the same 2. Bridges length for every node. The node with this address will read A bridge connects two networks, or two the data. segments of one network. It acts as a node as  far as each side is concerned. The data link layer protocol has to be the same on each side, but the NETWORK OPERATING SYSTEMS physical media can be different. A network operating system is the software necessary to integrate the various components of a network into a 3. Hub single entity to which users have access. On a normal hub, all ports are interconnected and hence all users connected to that hub share NETWORK ARCHITECTURES AND PROTOCOLS the same available bandwidth. Any traffic on a Though there are many Novell network and Windows NT given port will be ‘seen’ by all users connected to operating systems architectures in the market, the following three the hub. are the most popular. OSI/RM TCP/IP SNA TRANSMISSION CONTROL PROTOCOL / INTERNET PROTOCOL (TCP/IP) This is the result of a US Department of Defense initiated project to implement a global network, interconnecting various local area networks or individual computers. In this sense this is a demonstrated open system model. 4. Switches A switching hub (or ‘switch’), on the other hand, The architecture is based on a four-layer model. The layers are: only forwards each packet to the relevant port, 1. Application Layer based on the hardware address information in - This comprises the session, presentation and the header. A switch therefore acts as a application layers of the OSI model. multi-port bridge. 2. Services layer (host-to-host) - This represents the transport layer of the OSI model. 3. Internetwork Layer - This represent the network layer of the OSI model. 4. Network interface Layer - It represents the physical and data link layers of the OSI model. SYSTEM NETWORK ARCHITECTURE SNA is a layered architecture similar to OSI/RM. SNA is part of an IBM corporate design philosophy, which laid the 5. Routers framework for the data communication development of its A router transfers data between networks that products. have the same network layer protocols (such as TCP/IP) but not necessarily the same physical or 1. End user Layer data link protocols. - This describes the end user requirement of Routers maintain tables of addresses in the communication, much like the application layer of networks to which they are attached, and route OSI. each packet to the appropriate network 2. Function management layer depending on its destination address. - All the requirements of translation in terms of coding or file formats, together with their management, are described in this layer and are functionally equivalent to the presentation layer of OSI. 3. Data flow control layer - This takes care of the control aspects of creating an end-to-end connection/ session. 4. Transmission control - This describes the end-to-end data transmission details such as reliability and integrity. 5. Path control layer - The actual sequencing of information packets and its routing on the network are described in this layer and is functionally equivalent to the transport and network layers put together of OSI.  6. Data link layer 5. Gateway - This is essentially similar to that of OSI. Gateway is a network device used to connect two 7. Physical layer or more dissimilar networks. In networking - The description of the physical media details as parlance, networks that use different protocols in OSI. are dissimilar networks. A gateway usually is a computer with multiple LESSON 2: NETWORKING NICs connected to different networks. A gateway can also be configured completely NETWORK DEVICES using software. As networks connect to a Hardware devices that are used to connect computers, different network through gateways, these printers, fax machines and other electronic devices to a gateways are usually hosts or end points of the network are called network devices. These devices network. transfer data in a fast, secure and correct way over same or different networks. CABLING BASICS Network devices may be inter-network or intra-network. The most common types of cables used in data communications Some devices are installed on the device, like NIC card or systems are: RJ45 connector, whereas some are part of the network, Twisted pair like router, switch, etc. Let us explore some of these Coaxial devices in greater detail. Fiber-optic 1. Modem TWISTED PAIR CABLES Modem is a device that enables a computer to Twisted pair cables are the most economical solution for send or receive data over telephone or cable data transmission and allow for rates of up to 180 Mbps on lines. The data stored on the computer is digital communication links of up to 100 meters (330 feet). whereas a telephone line or cable wire can Longer distances are possible with lower data transfer transmit only analog data. rates. Twisted pairs are either shielded twisted pair (STP) or Types of Modem unshielded twisted pair (UTP). Simplex - A simplex modem can transfer data in only one direction, from digital device to network (modulator) or network to digital device (demodulator). Half duplex - A half-duplex modem has the capacity to transfer data in both the directions but only one at a time. Full Duplex - A full duplex modem can transmit data in both the directions simultaneously. 2. Ethernet Card Ethernet card, also known as network interface For full-duplex digital systems using balanced card (NIC), is a hardware component used by transmission, two sets of screened twisted pairs are computers to connect to Ethernet LAN and required in one cable; each set with individual and overall communicate with other devices on the LAN. screens. The entire cable is then covered by a protective PVC sheath. 3. Router A router is a network layer hardware device that The EIA-568 standard divides UTP cables into five application transmits data from one LAN to another if both categories, which are listed below: networks support the same set of protocols. So a router is typically connected to at least two LANs Category 1 UTP Low-speed data and analogue voice and the internet service provider (ISP). Category 2 UTP ISDN data It receives its data in the form of packets, which Category 3 UTP High-speed data and LAN (10 Mbps) are data frames with their destination address Category 4 UTP Extended distance LAN added. Router also strengthens the signals Category 5 UTP Extended frequency LAN (100 Mbps) before transmitting them. That is why it is also called repeater. COAXIAL CABLES Coaxial cables are used, almost without exception, for all 4. Switch antennas operating between the HF band of frequencies Switch is a network device that connects other up to the SHF band around 2 GHz, where waveguides devices to Ethernet networks through twisted pair begin to take over. cables. The impedance of a cable is determined by the ratio of the It uses packet switching technique to receive, surrounding shield and the diameter of the inner store and forward data packets on the network. conductors. The switch maintains a list of network addresses Although the characteristic impedance of a television of all the devices connected to it. antenna is 75 Ω, most communications antennas have an  impedance of 50 Ω and care should always be taken to NON-ADAPTIVE ROUTING ALGORITHM use the correct cable. Also known as a static routing algorithm The size of a coaxial cable is determined by two factors – Routing process is designed in advanced and stored in the transmitter power being fed to the antenna system and router after booting the frequency being used. Doesn’t affect with the change of network topology and If a transmitter has an output power of 500 watt, the peak traffic voltage across a 50 Ω cable will be 223 volt and the current will be about 3.3 amp. If the dielectric insulation is 1. Flooding - Every incoming packet is sent to all the insufficient, the cable will breakdown and if the inner outgoing links except the one from it has been reached. conductor is too small, there will be a high resistive loss in 2. Random walks - In case of random walks, a packet sent the cable. by the node to one of its neighbors randomly. An advantage of using random walks is that it uses the alternative routes very efficiently. ADAPTIVE ROUTING ALGORITHM Also known as dynamic routing algorithm. Routing changed based on the network topology and traffic. The main parameters related to this algorithm are hop count, distance and estimated transit time. FIBER-OPTIC CABLES 1. Centralized algorithm: Fiber-optic cables are normally used for the transmission - Global Routing algorithm of digital signals. - Global information included the topology, router The capabilities of fiber-optic cables will satisfy any future information etc., stored on a central Node requirement in data communications, allowing - Computes the least cost path based on the global transmission rates in the Gigabits per second (Gbps) information. range. There are many currently installed systems operating at around 10 Gbps. 2. Isolation algorithm: - Routing will be decided based on the local The main benefits of fiber-optic cables are: information or the neighboring links - Enormous bandwidth (greater information carrying - Disadvantage is packet may be sent into a capacity) congested line which may cause delays in - Low signal attenuation (greater speed and distance transmission characteristics) - Inherent signal security 3. Distributed algorithm: - Low error rates - Computes the least cost path based on the - Noise immunity (impervious to EMI and RFI) iterative calculations. - Logistical considerations (light in weight, smaller in size) - Also calls decentralized algorithm. - Total galvanic isolation between ends (no conductive path) - Each router has its routing table which stored the - Safe for use in hazardous areas information of the path cost of the routers in the - No crosstalk network ROUTING ALGORITHM IP ADDRESSING The routing protocol is a routing algorithm that provides IP version 4 (IPv4) addresses, which uniquely identify a the best path from the source to the destination. The best device on an IP network, are 32 bits in length and are path is the path that has the "least-cost path" from source typically communicated in a format known as dotted to the destination. decimal. Routing is the process of forwarding the packets from source to the destination but the best route to send the The 32 binary bits are: packets is determined by the routing algorithm. Divided into a network portion and host portion Broken into four octets (1 octet = 8 bits). Each octet can CLASSIFICATION OF A ROUTING ALGORITHM be converted to binary. The Routing algorithm is divided into Consider this IP address, which is presented in dotted two categories: decimal: 10.10.16.1. Adaptive Routing algorithm Non-adaptive Routing The address breaks down into the following octets: 10,10,16,1 algorithm IP version 6 (IPv6) is the next generation of IP addressing. IPv6 quadruples the number of network address bits from 32 bits (in IPv4) to 128 bits, which provides enough globally unique IP addresses for every networked device  on the planet. IPv6 is an important protocol for the future of IP networking. SUBNETTING Subnetting allows you to create multiple logical networks IP addresses are split up into several different categories, that exist within a single Class A, B, or C network. If you including Class A, B, C, D (Multicast), and E (Reserved). do not subnet, you can only use one network from your Class A, B, or C network, which is simply unrealistic. Address classes are defined, in part, based on the number To subnet a network, extend the mask using some of the of bits that make up the network portion of the address, and in turn, bits from the host ID portion of the address to create a on how many are left for the definition of individual host addresses. subnetwork ID. For example: Given a network of 192.168.5.0/24, which has a mask of 255.255.255.0, you In Class A addresses, the first octet is the network can create subnets in this manner: portion. In Class B, the first two octets are the network portion. In Class C, the first 3 octets are the network portion. https://youtu.be/eHV1aOnu7oM?si=JxrEgbkCworo5GJ3 https://youtu.be/0dFNpNgiTAA?si=JWhT5_HRIC3wL9G5 https://youtu.be/s_Ntt6eTn94?si=9HsoOm0Hw4xPpvDT https://youtu.be/uyRtYUg6bnw?si=MRwzd8jQfh3NjXi9 PRIVATE IP ADDRESSING These network ranges, known as RFC 1918 addresses, are reserved for organizations that want to build an internal network infrastructure based on TCP/IP but either do not have or do not want to use public IP space. RFC 1918 space includes the following three blocks of IP address space: 10.0.0.0 – 10.255.255.255 (10.0.0.0/8), which allows the greatest flexibility with the equivalent of 255 Class B address spaces to be used as needed. 172.16.0.0 – 172.31.255.255 (172.16.0.0/12), which allows for 16 Class B address spaces. 192.168.0.0 – 192.168.255.255 (192.168.0.0/16), which allows for one Class B address space.