ECT 250: Survey of e-commerce technology Networking

2 In a network, communications equipment is used to connect two or more computers allowing the sharing of various hardware, software, and data resources. The basic components of a data communications systems used to transmit information are: A sending device A communications link, consisting of both communications hardware and software. A receiving device Networking

3 Binary information is represented by the presence or absence of an electronic pulse. This is referred to as digital signaling. Some communications devices in place today were designed for voice data which uses analog signals. Data communications systems may use these existing lines. Data transmission

4 If the wires in place for communication use analog signals, digital data must be converted to an analog signal in order to be transmitted. The digital signal is transformed into an analog wave in a process called modulation. The analog wave is transmitted. The analog signal is converted back into a digital signal during a process called demodulation. Piggybacking technology

5 A modem is the hardware device that does these conversions. (Short for modulate/demodulate). Modem speeds are referred to by the number of bits per second (bps) at which they can transmit and receive data. The earliest modems has speeds around 300 bps. Later modems had speeds ranging from 9600 to 33,600 bps. Today modems have speeds of 56,000 bps (or 56 Kbps). Modems

6 A communications link is the physical medium used for transmission of data. There are several kinds: Wire pairs/twisted pairs Coaxial cables Fiber optics Microwave transmission Satellite transmission Communication links

7 Sometimes called twisted pair, this media uses wire pairs twisted together to form a cable. The cable is then insulated. Wire pairs are popular since this form of cabling is already installed and available in most places (telephone cabling). It is, however, susceptible to electrical interference, called noise. Wire pairs

8 A coaxial cable is a single conductor wire that is thickly shielded. It sends a very powerful signal. It is used for cable television. These cables can transmit data at a very fast rate. Bundles of these cables can be laid underground or under the sea. Coaxial cables

9 Fiber optic cables use light instead of electricity to transmit data. The cables are made of ultra thin glass wires. Light beams can be transmitted for miles with little attenuation (reduction in signal strength). This media can handle many different types of information including voice and data at the same time. Fiber optic cables

10 In microwave transmission the signals are wireless and can travel through the atmosphere. Signals can, however, be blocked by the curvature of the earth. (Line of sight transmission) To prevent this, relay stations are located in high areas and are used to retransmit data to other relay stations. Microwave transmission

11 The basic components of satellite transmission: Earth stations: Send and receive signals. Transponder: Receives a transmission from an earth station, amplifies the signal, changes the frequency, and retransmits the data to the receiving earth station. The entire process takes only a few seconds. Communications satellites are positioned in a geosynchronous orbit. Satellite transmission

12 Internet access providers or Internet service providers offer individuals and companies access to the Internet. There are typically several connection options. The primary difference between various ISPs is the connection bandwidth (the amount of data that can travel through a communication line in a given unit of time) available. Internet service providers

13 The traffic on the Internet and the ISP can affect the net bandwidth (the actual speed at which information travels taking traffic into account). Upstream, also called upload, occurs when information is sent from you to the ISP. Downstream, called download or downlink, occurs when information flows to your computer from the ISP. Example: Web page download. Upstream bandwidth differs from downstream bandwidth for satellite and cable connections. Connection terminology

14 POTS uses existing telephone lines and an analog modem to provide a bandwidth of about 56Kbps. Higher grades of service use the Digital Subscriber Loop (DSL) protocol. These include: – Integrated Services Digital Network (ISDN), available since – Asymmetric Digital Subscriber Line (ADSL) – Symmetric Digital Subscriber Line (SDSL) Upstream: 16 to 640 Kbps Downstream: 1.5 to 9 Mbps (million bps) Telephone service

15 Cable modems connect to the same coaxial cable that serves television. It is connected via twisted pair wire to a PC and provides a cost-effective and high bandwidth connection to an ISP. Upstream: 768 Kbps Downstream: 10 Mbps Cable bandwidths vary with the number of users. Cable connections

16 Large firms with high traffic connect to an ISP using higher bandwidth telephone connections. – T1: Operates at Mbps – T3: Operates at 44.7 Mbps These connections are more expensive than the previous options. Network access providers use T1 and T3 lines as well as Asynchronous Transfer Mode (ATM) connections with bandwidths up to 622 Gbps. Higher bandwidth options

17 When making decisions about Internet connections you must consider: – Bandwidth needed – Cost of startup – Monthly fees – Traffic issues There is a chart comparing features between various options on page 72 of the text. Depending on where you live, you may have other options, such as satellite connections. See the e-commerce links and sites.e-commerce links and sites Price and speed comparisons

18 Networks can be classified according to their geographical reach. Local area network Metropolitan area network Wide area network Types of networks

19 A wide area network (WAN) is a network of computers, terminals, and peripheral devices that is located over a very large area. It can span a state, country, or the world. The central hubs or servers are usually powerful minicomputers or mainframes. (The server is usually referred to as the host computer). A single WAN may use a variety of transmission methods. Wide-area network

20 A local area network is a collection of computers that share hardware, software, and data over a shorter geographical area than a WAN. (Usually limited to a single building or compound). A LAN can also be very small. Example: LAN in my apartment contains one PC, one printer, and two laptops. Local-area network

21 Networks can also be classified according to their purpose: 1. Internet 2. Intranet 3. Extranet Purposes for networks

22 Only selected individuals can use an intranet. Example: CTI IntranetCTI Intranet Intranets are a popular and inexpensive way to distribute information. Intranets typically use existing infrastructure. Benefits include timely and current information delivery, cheaper internal communication, low maintenance costs, and easy on-line training. Intranets

23 Extranets provide the private infrastructure for companies to coordinate their purchases, exchange business documents, and communicate with each other. Some start out as intranets and become available to people outside the institution in an effort to reduce the workload for employees. Example: FedEx There are three types of extranets: – A public network – A secure (private) network – A virtual private network (VPN) Extranets

24 A public network extranet is one which can be accessed by the public or one in which two or more companies agree to link their intranets using a public network. Security is an issue in this configuration. This type of extranet is uncommon because of the risk. Public network

25 Uses a private, leased-line connection to connect two companies. A leased line is a permanent, dedicated telephone connection between two points. The line is always active. This arrangement is significantly more secure. The big drawback is the cost. This type of arrangement does not scale well since each new company requires another leased line. Private network

26 A VPN uses public networks but through a system called tunneling or encapsulation. Tunnels are private passageways through the public Internet that provide secure transmission from one partner to another. Separate security shells are used with the most sensitive data under the tightest controls. VPNs establish short-term connections in real time that are broken once the session ends. This arrangement is inexpensive and scales well. Virtual private network

27 A protocol is a set of rules for the exchange of data across communication lines. Because telecommunications systems use a wide variety of hardware and software, protocols are needed to coordinate communication. What kinds of issues do protocols need to handle? Protocols

28 Protocols need to handle the following tasks: Identify the different devices in the communications path. Establish the speed and method for transmission of data. Alert the receiving device to the incoming data. Define the method for the receiving device to confirm the receipt of the data. Determine the methods of error checking and correction. Common Internet protocols include TCP/IP, SMTP, POP, IMAP, FTP, and HTTP. We will discuss each of these in more detail later. Tasks for protocols