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Telecommunications and the Internet

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1 Telecommunications and the Internet
Chapter 4

2 The Role of Telecommunications and Networks in Organizations
Definitions Telecommunications – the transmission of all forms of information, including digital data, voice, fax, sound, and video, from one location to another over some type of network Network – a group of computers and associated peripheral devices connected by a communication channel capable of sharing information and other resources (e.g., like a printer) between users Bandwidth – the carrying capacity of telecommunications networks

3 Types of Networks Computer networks are commonly classified by size, distance covered, and structure. The most commonly used classifications are: PBX (Private Branch Exchange) LAN ( Local Area Network) WAN ( Wide Area Network) MAN ( Metropolitan Area Network) PAN ( Personal Area Network)

4 Private Branch Exchanges
A private branch exchange (PBX) supports local phone and data communications, as well as links to outside phone and data networks. PBX is a special-purpose computer designed for handling and switching office telephone calls at company site. PBX can store, transfer, hold, and redial telephone calls. Since they use ordinary telephone lines, PBX systems have limited bandwidth. The advantage of digital PBX over local networking is that PBX does not need special wiring.

5 Local Area Network Server Network Operating System Computer1 Network
Gateway Other Network Computer2 Printer Computer3

6 Local Area Network LAN is used to connect PCs or resources (e.g. printers) in one building or several buildings in close proximity. LAN has higher transmission capacity than PBX (Private Branch Exchange). LAN can transmit video and graphics. LAN is more expensive to install than PBX and less flexible. It requires new wiring each time a LAN is moved. The server acts as a librarian. It stores programs and data files for network users. The server determines who will get access to what and in what sequence. Sever can be powerful PCs with large hard-disk capacity, workstations, minicomputers, or mainframes. The network gateway connects the LAN to public networks, such as the telephone network, or to other corporate networks.

7 Local Area Network A gateway is a communications processor that can connect dissimilar networks by translating from one set of protocols to another. LAN can use twisted wire, coaxial , or fiber-optic cable. LAN also can use wireless technology. The network operating system (NOS) can reside on every computer in the network, or it can reside on a single server. The NOS routes and manages communications on the network and sharing of network resources.

8 Wide Area Network It spans a broad geographical distance, ranging from several miles to the span of entire continent. WAN may consist of a combination of switched and dedicated lines, microwave, and satellite communications. Switched lines are telephone lines that a person can access from his or her terminal to transmit data to the designated destination. Dedicated lines are continuously available for transmission. This lines can be leased or purchased from a common carriers or private communications media vendors. Most WANS are switched.

9 Metropolitan Area Networks (MAN)
Computer network of limited geographic scope, within a city. MAN is a better option for organizations that need high-speed data transmission within a limited geographic area.

10 Personal Area Networks (PAN)
It uses wireless communication to exchange data between computing devices using short-range radio communication (10 m). It uses Bluetooth technology, a new technology. Uses for networking of desktop computers, pagers, portable devices, mobile phones, and other handheld devices.

11 Network services: Value-Added Networks (VANS)
Networks can be classified by types of service they provide. Value-added networks are private, multipath, data-only, third-party-managed network that is used by multiple organizations on a subscription basis. The VAN is set up by a firm that is in charge of managing the network. The subscribers pay only for the amount of data they transmit plus a subscription fee. Customers do not have to invest in network equipment and software or perform their own error checking, editing, routing, and protocol conversion. The network can use twisted-pair lines, satellite links, and other communication channels leased by the value-added carrier.

12 Switching Techniques In large networks there might be multiple paths linking sender and receiver. Information may be switched as it travels through various communication channels. There are three typical switching techniques available for digital traffic. Circuit Switching Message Switching Packet Switching

13 Circuit Switching Circuit switching is a technique that directly connects the sender and the receiver in an unbroken path. Telephone switching equipment, for example, establishes a path that connects the caller's telephone to the receiver's telephone by making a physical connection. With this type of switching technique, once a connection is established, a dedicated path exists between both ends until the connection is terminated. Routing decisions must be made when the circuit is first established, but no decisions are made after that time.

14 Circuit Switching Circuit switching in a network operates almost the same way as the telephone system works. A complete end-to-end path must exist before communication can take place. The computer initiating the data transfer must ask for a connection to the destination. Once the connection has been initiated and completed to the destination device, the destination device must acknowledge that it is ready and willing to carry on a transfer.

15 Circuit switching Advantages:
The communication channel (once established) is dedicated. Disadvantages: Possible long wait to establish a connection, (10 seconds, more on long- distance or international calls.) during which no data can be transmitted. More expensive than any other switching techniques, because a dedicated path is required for each connection. Inefficient use of the communication channel, because the channel is not used when the connected systems are not using it.

16 Message Switching With message switching there is no need to establish a dedicated path between two stations. When a station sends a message, the destination address is appended to the message. The message is then transmitted through the network, in its entirety, from node to node. Each node receives the entire message, stores it in its entirety on disk, and then transmits the message to the next node. This type of network is called a store-and-forward network.

17 Message Switching A message-switching node is typically a general-purpose computer. The device needs sufficient secondary-storage capacity to store the incoming messages, which could be long. A time delay is introduced using this type of scheme due to store- and-forward time, plus the time required to find the next node in the transmission path.

18 Message Switching Advantages:
Channel efficiency can be greater compared to circuit- switched systems, because more devices are sharing the channel. Traffic congestion can be reduced, because messages may be temporarily stored in route. Message priorities can be established due to store-and-forward technique. Message broadcasting can be achieved with the use of broadcast address appended in the message.

19 Message Switching Disadvantages
Message switching is not compatible with interactive applications. Store-and-forward devices are expensive, because they must have large disks to hold potentially long messages.

20 Packet Switching Packet switching can be seen as a solution that tries to combine the advantages of message and circuit switching and to minimize the disadvantages of both. There are two methods of packet switching: Datagram and virtual circuit.

21 Packet Switching In both packet switching methods, a message is broken into small parts, called packets. Each packet is tagged with appropriate source and destination addresses. Since packets have a strictly defined maximum length, they can be stored in main memory instead of disk, therefore access delay and cost are minimized => store-and-forward networks. Also the transmission speeds, between nodes, are optimized. With current technology, packets are generally accepted onto the network on a first-come, first-served basis. If the network becomes overloaded, packets are delayed or discarded (``dropped'').

22 Packet Switching (16 bits) (24 bits) (16 bits) Start Framing End
Error Control (64 bits) Check Bits Header Text Message No. Link No. Destination Source Packet No. Data are grouped into small packets, framed by identifying information, which are transmitted independently via various communication channels to maximize the potential of the paths in a network.

23 Frame relay A shared network service.
It is faster and less expensive than packet switching. It can achieve transmission speed upto megabits per second. Frame relay packages data into frames that are similar to packets. But it does not perform error correction. It works well on reliable lines that do not require frequent retransmission because of error.

24 Asynchronous Transfer Mode (ATM)
ATM is a method of transmitting voice, video, and data over high-speed LAN. It is well accepted in LAN & WAN ATM technology parcels information into uniform cells, each with 53 groups of eight bytes, eliminating the need for protocol conversion. It can seamlessly and dynamically switch voice, data, images, and video between users. It can pass data between computers from different vendors. It permits data to be transmitted at any speed the network handles. ATM can transmit up to 2.2 GBPS. It can connect LAN and WAN together more easily.

25 The Internet How Fast Is Your Connection?
Plain Old Telephone Service (POTS/PSTN): 52 kbps Integrated Services Digital Network (ISDN): operates on existing copper telephone line. Replaces analog sys Digital Subscriber Line (DSL): operates on existing copper telephone line. 32 Mbps (down link), 32 kbps to 1 Mbps (uplink) Cable Modems: operates on cable TV lines. 2 Mbps Satellite Connections T1 Lines: Can carry up to Mbps, T3 lines: 45 Mbps Asynchronous Transfer Mode (ATM): 2.2 Gbps

26 Internetworking, Connectivity & Open System
Internetworking => The linking of separate networks, each of which retains its own identity, into an interconnected network. Connectivity => The ability of computers and computer-based devices to communicate with one another and share information in a meaningful way without human intervention. Open Systems => Open systems promote connectivity because they can operate on different hardware platforms. They are built on public non-proprietary operating systems, user interfaces, application standards, and networking protocols.

27 Models of Connectivity for Networks: TCP/IP
Host A Host B Application Application Identical message Transport (TCP) Transport (TCP) Identical message Internet Protocol (IP) Internet Protocol (IP) Identical datagram Network Interface Network Interface Identical frame Physical net

28 Open System Interconnect (OSI)
This model is an alternative model developed by the International Standards Organization for linking different types of computers and networks. It is designed to support global networks with large volume of transaction processing. Like TCP/IP , OSI enables a computer connected to a network, regardless of the manufacturer, by establishing communication rules that permit the exchange of information between dissimilar systems. OSI divides the telecommunications process into seven layers.

29 Electronics Commerce & its applications
Electronic mail Voice mail Facsimile Machine (fax) Digital Information Services Teleconferencing, Dataconferencing, and Videoconferencing Groupware: The leading commercial groupware product has been Lotus Notes from Lotus Development Corporation. Group writing and commenting, distribution, scheduling meeting and appointments, shared files and databases, shares timelines and plans, electronic meeting

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