Data Communication Circuits PDF

DATA COMMUNICATION S CIRCUITS  2 Introduction  The underlying purpose of a data communications circuit is to provide a transmission path between locations and to transfer digital information from one station to an...

DATA COMMUNICATION S CIRCUITS  2 Introduction  The underlying purpose of a data communications circuit is to provide a transmission path between locations and to transfer digital information from one station to another using electronic circuits. A station is simply an endpoint where subscribers gain access to the circuit. A station is sometimes called a node, which is the location of computers, computer terminals, workstations, and other digital computing equipment. There are almost as many types of data communications circuits as there are types of data communications equipment.  3 Introduction  Data communications circuits utilize electronic communications equipment and facilities to interconnect digital computer equipment. Communications facilities are physical means of interconnecting stations within a data communications system and can include virtually any type of physical transmission media or wireless radio system in existence. Communications facilities are provided to data communications users through public telephone networks (PTN), public data networks (PDN), and a multitude of private data communications systems.  4 Figure 15 shows a simplified block diagram of a two-station data communications circuit. The fundamental components of the circuit are source of digital information, transmitter, transmission medium, receiver, and destination for the digital information. Although the figure shows transmission in only one direction, bidirectional transmission is possible by providing a duplicate set of circuit components in the opposite direction. SERIAL AND PARALLEL DATA TRANSMISSION DATA COMMUNICATIONS CIRCUIT ARRANGEMENTS  Circuit Configurations  Data communications networks can be generally categorized as either two point or multipoint. A two-point configuration involves only two locations or stations, whereas a multipoint configuration involves three or more stations. Regardless of the configuration, each station can have one or more computers, computer terminals, or workstations. A two- point circuit involves the transfer of digital information between a mainframe computer and a personal computer, two mainframe computers, two personal computers, or two data communications networks. A multipoint network is generally used to interconnect a single mainframe computer (host) to many personal computers or to interconnect many personal computers.  Circuit Configurations  Data communications networks can be generally categorized as either two point or multipoint. A two-point configuration involves only two locations or stations, whereas a multipoint configuration involves three or more stations. Regardless of the configuration, each station can have one or more computers, computer terminals, or workstations. A two- point circuit involves the transfer of digital information between a mainframe computer and a personal computer, two mainframe computers, two personal computers, or two data communications networks. A multipoint network is generally used to interconnect a single mainframe computer (host) to many personal computers or to interconnect many personal computers. Transmission Modes  Simplex  In the simplex (SX) mode, data transmission is unidirectional; information can be sent in only one direction. Simplex lines are also called receive-only, transmit-only, or one-way-only lines. Commercial radio broadcasting is an example of simplex transmission, as information is propagated in only one direction— from the broadcasting station to the listener. Transmission Modes  Half duplex  In the half-duplex (HDX) mode, data transmission is possible in both directions but not at the same time. Half- duplex communications lines are also called two-way-alternate or either-way lines. Citizens band (CB) radio is an example of half-duplex transmission because to send a message, the push-to- talk (PTT) switch must be depressed, which turns on the transmitter and shuts off the receiver. To receive a message, the PTT switch must be off, which shuts off the transmitter and turns on the receiver Transmission Modes  Full duplex  In the full-duplex (FDX) mode, transmissions are possible in both directions simultaneously, but they must be between the same two stations. Full-duplex lines are also called two-way simultaneous, duplex, or both-way lines. A local telephone call is an example of full-duplex transmission. Although it is unlikely that both parties would be talking at the same time, they could if they wanted to. Transmission Modes  Full/full duplex  In the full/full duplex (F/FDX) mode, transmission is possible in both directions at the same time but not between the same two stations (i.e., one station is transmitting to a second station and receiving from a third station at the same time).  Full/full duplex is possible only on multipoint circuits. The U.S. postal system is an example of full/full duplex transmission because a person can send a letter to one address and receive a letter from another address at the same time. DATA COMMUNICATIONS NETWORKS  Any group of computers connected together can be called a data communications network, and the process of sharing resources between computers over a data communications network is called networking. In its simplest form, networking is two or more computers connected together through a common transmission medium for the purpose of sharing data. The concept of networking began when someone determined that there was a need to share soft ware and data resources and that there was a better way to do it than storing data on a disk and literally running from one computer to another. By the way, this manual technique of moving data on disks is sometimes referred to as sneaker net. The most important considerations of a data communications network are performance, transmission rate, reliability, and security. There are many factors involved when designing a computer network, including the following: 1. Network goals as defined by organizational management 2. Network security 3. Network uptime requirements 4. Network response-time requirements 5. Network and resource costs Network Components, Functions, and Features Network Components  Computer networks are like snowflakes—no two are the same. The basic components of computer networks are shown in Figure 17. All computer networks include some combination of the following: end stations, applications, and a network that will support the data traffic between the end stations. A computer network designed three years ago to support the basic networking applications of the time may have a difficult time supporting recently developed high- end applications, such as medical imaging and live video teleconferencing. Network designers, administrators, and managers must understand and monitor the most recent types and frequency of networked applications. Computer networks all share common devices, functions, and features, including servers, clients, transmission media, shared data, shared printers and other peripherals, hardware and software resources, network interface card (NIC), local operating system (LOS), and the network operating system (NOS).   Servers are computers that hold shared files, programs, and the network operating system. Servers provide access to network resources to all the users of the network. There are many different kinds of servers, and Servers. one server can provide several functions. For example, there are file servers, print servers, mail servers, communications servers, database servers, directory/security servers, fax servers, and Web servers, to name a few. Clients  Clients are computers that access and use the network and shared network resources. Client computers are basically the customers (users) of the network, as they request and receive services from the servers. Transmissio n media  Transmission media are the facilities used to interconnect computers in a network, such as twisted-pair wire, coaxial cable, and optical fiber cable. Transmission media are sometimes called channels, links, or lines. Shared data  Shared data are data that file servers provide to clients, such as data files, printer access programs, and e- mail. Shared printers and other peripherals  Shared printers and peripherals are hardware resources provided to the users of the network by servers. Resources provided include data files, printers, software, or any other items used by clients on the network. Network interface card  Each computer in a network has a special expansion card called a network interface card (NIC). The NIC prepares (formats) and sends data, receives data, and controls data flow between the computer and the network. On the transmit side, the NIC passes frames of data on to the physical layer, which transmits the data to the physical link. On the receive side, the NIC processes bits received from the physical layer and processes the message based on its contents. Network Interface Card Characteristics of NICs include the following: 1. The NIC constructs, transmits, receives, and processes data to and from a PC and the connected network. 2. Each device connected to a network must have a NIC installed. 3. A NIC is generally installed in a computer as a daughterboard, although some computer manufacturers incorporate the NIC into the motherboard during manufacturing. 4. Each NIC has a unique six-byte media access control (MAC) address, which is typically permanently burned into the NIC when it is manufactured. The MAC address is sometimes called the physical, hardware, node, Ethernet, or LAN address. 5. The NIC must be compatible with the network (i.e., Ethernet—10baseT or token ring) to operate properly. 6. NICs manufactured by different vendors vary in speed, complexity, manageability, and cost. 7. The NIC requires drivers to operate on the network. Local operating system  A local operating system (LOS) allows personal computers to access files, print to a local printer, and have and use one or more disk and CD drives that are located on the computer. Examples of LOSs are MS-DOS, PC- DOS, Unix, Macintosh, OS/2, Windows 3.11, Windows 95, Windows 98, Windows 2000, and Linux. Figure 20 illustrates the relationship between a personal computer and its LOS. Network operating system  The network operating system (NOS) is a program that runs on computers and servers that allows the computers to communicate over a network. The NOS provides services to clients such as log-in features, password authentication, printer access, network administration functions, and data file sharing. Some of the more popular network operating systems are Unix, Novell NetWare, AppleShare, Macintosh System 7, IBM LAN Server, Compaq Open VMS, and Microsoft Windows NT Server. The NOS is software that makes communications over a network more manageable. Relationship between clients, servers, and the NOS Characteristics of NOSs include the following: 1. A NOS allows users of a network to interface with the network transparently. 2. A NOS commonly offers the following services: file service, print service, mail service, communications service, database service, and directory and security services. 3. The NOS determines whether data are intended for the user’s computer or whether the data needs to be redirected out onto the network. 4. The NOS implements client software for the user, which allows them to accessservers on the network Layout of a local network operating system Network Models  Computer networks can be represented with two basic network models: peer-to-peer client/server and dedicated client/server. The client/server method specifies the way in which two computers can communicate with software over a network. Although clients and servers are generally shown as separate units, they are often active in a single computer but not at the same time. With the client/server concept, a computer acting as a client initiates a software request from another computer acting as a server. The server computer responds and attempts to satisfy the request from the client. The server computer might then act as a client and request services from another computer. The client/server concept Peer-to-peer client/server network  A peer-to-peer client/server network is one in which all computers share their resources, such as hard drives, printers, and so on, with all the other computers on the network. Therefore, the peer- to-peer operating system divides its time between servicing the computer on which it is loaded and servicing requests from other computers. In a peer-to-peer network (sometimes called a workgroup), there are no dedicated servers or hierarchy among the computers.  A peer-to-peer client/server network with four clients/servers (users) connected together through a hub. All computers are equal, hence the name peer. Peer-to-peer computer networks should be small for the following reasons: 1. When operating in the server role, the operating system is not optimized to efficiently handle multiple simultaneous requests. 2. The end user’s performance as a client would be degraded. 3. Administrative issues such as security, data backups, and data ownership may be compromised in a large peer-to-peer network. Dedicated client/server network.  In a dedicated client/server network, one computer is designated the server, and the rest of the computers are clients. As the network grows, additional computers can be designated servers. Generally, the designated servers function only as servers and are not used as a client or workstation. The servers store all the network’s shared files and applications programs, such as word processor documents, compilers, database applications, spreadsheets, and the network operating system. Client computers can access the servers and have shared files transferred to them over the transmission medium. Figure 25 shows a dedicated client/server-based network with three servers and three clients (users)  Each client can access the resources on any of the servers and also the resources on other client computers. The dedicated client/server-based network is probably the most commonly used computer networking model. There can be a separate dedicated server for each function (i.e., file server, print server, mail server, etc.) or one single general-purpose server responsible for all services. Network Topologies Network topology  Network topology describes the layout or appearance of a network— that is, how the computers, cables, and other components within a data communications network are interconnected, both physically and logically. The physical topology describes how the network is actually laid out, and the logical topology describes how data actually flow through the network.  In a data communications network, two or more stations connect to a link, and one or more links form a topology. Topology is a major consideration for capacity, cost, and reliability when designing a data communications network. The most basic topologies are point to point and multipoint. Star topology  A star topology is a multipoint data communications network where remote stations are connected by cable segments directly to a centrally located computer called a hub, which acts like a multipoint connector (see Figure 26b). In essence, a star topology is simply a multipoint circuit comprised of many two-point circuits where each remote station communicates directly with a centrally located computer. With a star topology, remote stations cannot communicate directly with one another, so they must relay information through the hub. Hubs also have store-and-forward capabilities, enabling them to handle more than one message at a time Bus topology  A bus topology is a multipoint data communications circuit that makes it relatively simple to control data flow between and among the computers because this configuration allows all stations to receive every transmission over the network. With a bus topology, all the remote stations are physically or logically connected to a single transmission line called a bus. The bus topology is the simplest and most common method of interconnecting computers. The two ends of the transmission line never touch to form a complete loop. A bus topology is sometimes called multidrop or linear bus, and all stations share a common transmission medium. Data networks using the bus topology generally involve one centrally located host computer that controls data flow to and from the other stations. Ring topology  A ring topology is a multipoint data communications network where all stations are interconnected in tandem (series) to form a closed loop or circle. A ring topology is sometimes called a loop. Each station in the loop is joined by point- to-point links to two other stations (the transmitter of one and the receiver of the other) Transmissions are unidirectional and must propagate through all the stations in the loop. Each computer acts like a repeater in that it receives signals from down-line computers then retransmits them to up-line computers. The ring topology is similar to the bus and star topologies, as it generally involves one centrally located host computer that controls data flow to and from the other stations. Mesh topology  In a mesh topology, every station has a direct two-point communications link to every other station on the circuit. The mesh topology is sometimes called fully connected. A disadvantage of a mesh topology is a fully connected circuit requires n(n -1)/2 physical transmission paths to interconnect n stations and each station must have n-1 input/output ports. Advantages of a mesh topology are reduced traffic problems, increased reliability, and enhanced security Hybrid topology  A hybrid topology is simply combining two or more of the traditional topologies to form a larger, more complex topology. Hybrid topologies are sometimes called mixed topologies. An example of a hybrid topology is the bus star topology shown in Figure 26f. Other hybrid configurations include the star ring, bus ring, and virtually every other combination you can think Network Classifications  Networks are generally classified by size, which includes geographic area, distance between stations, number of computers, transmission speed (bps), transmission media, and the network’s physical architecture. The four primary classifications of networks are local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), and global area networks (GANs). In addition, there are three primary types of interconnecting networks: building backbone, campus backbone, and enterprise network ALTERNATE PROTOCOL SUITES  Network access layer. Provides a  TCP/IP Protocol Suite means of physically delivering data packets using frames or cells  The TCP/IP protocol suite  Internet layer. Contains information (transmission control that pertains to how data can be protocol/Internet protocol) was routed through the network actually developed by the  Host-to-host layer. Services the Department of Defense before process and Internet layers to handle the reliability and session aspects of the inception of the seven- data transmission. layer OSI model  Process layer. Provides applications support ALTERNATE PROTOCOL SUITES  Core layer. The core layer is literally the core of the network, as it resides at the top of the hierarchy and  Cisco Three-Layer Model is responsible for transporting large amounts of data traffic reliably and quickly. The only purpose of the  Cisco defines a three-layer core layer is to switch traffic as quickly as possible  Distribution layer. The distribution layer is logical hierarchy that specifies sometimes called the workgroup layer. The distribution layer is the communications point where things belong, how they between the access and the core layers that provides routing, filtering, WAN access, and how fit together, and what many data packets are allowed to access the core layer. functions go where. The three  Access layer. The access layer controls workgroup layers are the core, and individual user access to internetworking resources, most of which are available locally. The distribution, and access: access layer is sometimes called the desktop layer. Thank You