Ch.6 - Data Communication: Delivering Information Anywhere and Anytime

bus network topology

(also called "linear bus") connects nodes along a network segment, but the ends of the cable are not connected, as they are in a ring topology. - A hardware device called a terminator is used at each end of the cable to absorb the signal. - Without a terminator, the signal would bounce back and forth along the length of the cable and prevent network communication. - A node failure has no effect on any other node.

mesh network topology

(also called "plex" or "interconnected"), every node (which can differ in size and configuration from the others) is connected to every other node. - This topology is highly reliable - Failure of one or a few nodes does not usually cause a major problem in network operation because many other nodes are available. - However, this topology is costly and difficult to maintain and expand.

Disadvantages of the bus topology:

Fault diagnosis is difficult. The bus cable can be a bottleneck when network traffic is heavy.

presentation layer (OSI) 6

Formats message packets.

Advantages of the bus topology:

It is easy to extend. It is very reliable. The wiring layout is simple and uses the least amount of cable of any topology, which keeps costs down. It handles steady (even) traffic well.

Wireless WANs (WWANs)

These networks cover a broader area than WLANs and include the following devices: cellular networks, cellular digital packet data (CDPD), paging networks, personal communication systems (PCS), packet radio networks, broadband personal communications systems (BPCS), microwave networks, and satellite networks. - rely on the RF spectrum as the communication medium - coverage: a regional, nationwide, or international range - speed: Varies from 115 Kbps to 14 Mbps, depending on the technology - data security: usually higher than WLANs

Time Division Multiple Access (TDMA)

To improve the efficiency and quality of digital communications, divides each channel into six time slots. - Each user is allocated two slots: one for transmission and one for reception. - This method increases efficiency by 300 percent, as it allows carrying three calls on one channel.

Wireless Fidelity (Wi-Fi)

a broadband wireless technology that allows computers and other devices to communicate over a wireless signal. - Information can be transmitted over short distances, typically 120 feet indoors and 300 feet outdoors in the form of radio waves. - You can connect computers, mobile devices, smartphones, and game consoles to the Internet - connections are easy to set up, they have fast data transfer rates, and they offer mobility and flexibility. - However, they are susceptible to interference from other devices and to being intercepted, which raises security concerns. In addition, there is a lack of support for high-quality media streaming.

packet

a collection of binary digits—including message data and control characters for formatting and transmitting—sent from computer to computer over a network. -are transmitted along the best route available between sender and receiver

controller (hierachical)

a hardware and software device that controls data transfer from a computer to a peripheral device (examples are a monitor, a printer, or a keyboard) and vice versa.

multiplexer (hierarchical)

a hardware device that allows several nodes to share one communication channel.

packet switching

a network communication method that divides data into small packets and transmits them to an address, where they are reassembled - Any packet-switching network can handle multimedia data, such as text, graphics, audio, and video.

N-Tier Architectures (client/server)

attempts to balance the workload between client and server by removing application processing from both the client and server and placing it on a middle-tier server. - most common architecture is the three-tier architecture. - This arrangement leaves the presentation logic on the client and the data management logic on the server - Improving network performance is a major advantage of this architecture - However, network management is more challenging because there is more network traffic, and testing software is more difficult because more devices must communicate to respond to a user request.

Data transmission channels are generally divided into two types: broadband and narrowband

broadband and narrowband

dynamic router

can build tables that identify addresses on each network. - used more often now, particularly on the Internet

data communication applications

can enhance decision makers' efficiency and effectiveness in many ways - support just-in-time delivery of goods, which reduces inventory costs and improves the competitive edge. - also make virtual organizations possible, and these can cross geographic boundaries to develop products more quickly and effectively.

Data management logic (client/server)

concerned with data management and storage operations.

broadband data transmission

data transmission, multiple pieces of data are sent simultaneously to increase the transmission rate.

disadvantages of centralized routing

if the network routing manager is at a point far from the network's center, many links and paths that make up the network are far from the central node. Status information sent by other nodes to initiate changes to the routing table have to travel a long distance to the central node, causing a delay in routing some data and reducing network performance. - In addition, if the controlling node fails, no routing information is available.

ethernet (LAN)

is a standard communication protocol embedded in software and hardware devices used for building a LAN

ethernet cable (LAN)

is used to connect computers, hubs, switches, and routers to a network.

main advantage of the client/server architecture

its scalability, meaning its ability to grow. - Client/server architectures can be scaled horizontally or vertically. - Horizontal scaling means adding more workstations (clients) - vertical scaling means migrating the network to larger, faster servers.

three major types of networks:

local area networks (LAN), wide area networks (WAN), and metropolitan area networks (MAN).

distributed processing system

maintains centralized control and decentralized operations. Processing power is distributed among several locations. - solves two main problems—the lack of responsiveness in centralized processing and the lack of coordination in decentralized processing—by maintaining centralized control and decentralizing operations.

bandwidth

the amount of data that can be transferred from one point to another in a certain time period, usually one second. - often expressed as bits per second (bps). Other measurements include kilobits per second (Kbps), megabits per second (Mbps), and gigabits per second (Gbps)

attenuation

the loss of power in a signal as it travels from the sending device to the receiving device.

(t/f) Data communication has become so woven into the fabric of corporate activity that separating an organization's core functions from the data communication systems that enable and support them is difficult.

true

(t/f) Data communication systems make virtual organizations possible, and these can cross geographic boundaries to develop products more quickly and effectively.

true

(t/f) Routers operate at the Network layer (3) of the OSI model and handle routing packets on a network

true

(t/f) The path or route that data takes on a network is determined by the type of network and the software used to transmit data.

true

(t/f) When phone lines are used for Internet connections, an analog modem is necessary to convert a computer's digital signals to analog signals that can be transferred over analog phone lines.

true

(t/f) A strategy used by some companies called BYOD (bring your own device) has further enhanced the popularity of mobile and wireless networks. This strategy allows employees of an organization to use their own computers, tablets, smartphones, or other devices for work purposes.

true - Advantages of this strategy include cost savings, increased flexibility, increased productivity, and its attractiveness for some job-seekers. - Disadvantages include privacy and security issues related to an organization's information resources.

hierarchical network topology

(also called a "tree") combines computers with different processing strengths in different organizational levels. - For example, the bottom level might consist of workstations, with minicomputers in the middle and a server at the top - Companies that are geographically dispersed and organized hierarchically are good candidates for this type of network. - Failure of nodes at the bottom might not have a big impact on network performance, but the middle nodes and especially the top node (which controls the entire network) are crucial for network operation. - Traditional mainframe networks use this - mainframe computer is at the top, front-end processors (FEPs) are at the next level, controllers and multiplexers are at the next level, and terminals and workstations are at the bottom level. - The intermediate-level devices (FEPs and controllers) reduce the host's processing load by collecting data from terminals and workstations. - offers a great deal of network control and lower cost, compared to a star topology - disadvantages are that network expansion may pose a problem and there could be traffic congestion at the root and higher-level nodes.

the ways data communication technologies affect the workplace:

- Online training for employees can be provided via virtual classrooms. In addition, employees get the latest technology and product information immediately. - Internet searches for information on products, services, and innovations keep employees up to date. - The Internet and data communication systems facilitate lifelong learning, which will be an asset for knowledge workers of the future. - Boundaries between work and personal life are less clear-cut as data communication is more available in both homes and businesses. The increase in telecommuters is an example of this trend. - Web and video conferencing are easier, which can reduce the costs of business travel

Managers need a clear understanding of the following areas of data communication:

- The basics of data communication and networking - The Internet, intranets, and extranets - Wired and wireless networks - Network security issues and measures - Organizational and social effects of data communication - Globalization issues - Applications of data communication systems

disadvantages of distributed processing

- There may be more security and privacy challenges. - There may be incompatibility between the various pieces of equipment. - Managing the network can be challenging.

Mobile networks have a three-part architecture:

1. Base stations send and receive transmissions to and from subscribers. 2. Mobile telephone switching offices (MTSOs) transfer calls between national or global phone networks and base stations. 3. Subscribers (users) connect to base stations by using mobile communication devices

In the most basic client/server configuration, the following events usually take place:

1. The user runs client software to create a query. 2. The client accepts the request and formats it so the server can understand it. 3. The client sends the request to the server over the network. 4. The server receives and processes the query. 5. The results are sent to the client. 6. The results are formatted and displayed to the user in an understandable format.

session layer (OSI) 5

Establishes a communication session between computers

data link layer (OSI) 2

Oversees the establishment and control of the communication link

To understand client/server architecture better, you can think of it in terms of these three levels of logic:

Presentation logic Application logic Data management logic - The real challenge in a client/server architecture is how to divide these three logics between the client and server.

network layer (OSI) 3

Routes messages.

A typical data communication system includes the following components:

Sender and receiver devices Modems or routers Communication medium (channel)

application layer (OSI) 7

Serves as the window through which applications access network services. It performs different tasks, depending on the application, and provides services that support users' tasks, such as file transfers, database access, and e-mail.

Worldwide Interoperability for Microwave Access (WiMAX)

a broadband wireless technology based on the IEEE 802.16 standards. - It is designed for wireless metropolitan area networks and usually has a range of about 30 miles for fixed stations and 3-10 miles for mobile stations - compared with wi-fi, theoretically has faster data transfer rates and a longer range. - In addition, it is fast and easy to install and enables devices using the same frequency to communicate. A single station can serve hundreds of users. - disadvantages include interference from other wireless devices, high costs, and interruptions from weather conditions, such as rain. This technology also requires a lot of power; when bandwidth is shared among users, transmission speed decreases.

Digital subscriber line (DSL)

a common carrier service, is a high-speed service that uses ordinary phone lines. - users can receive data at up to 7.1 Mbps and send data at around 1 Mbps, although the actual speed is determined by proximity to the provider's location. Also, different providers might offer different speeds

network interface card (NIC)

a hardware component that enables computers to communicate over a network. - also called an "adapter card," is the physical link between a network and a workstation, so it operates at the OSI model's Physical and Data Link layers. - are available from many vendors, and the most common types of local area networks, Ethernet and token ring, can use NICs from almost any vendor.

router

a network connection device containing software that connects network systems and controls traffic flow between them. - The networks being connected can be operating on different protocols, but they must use a common routing protocol. - Routers operate at the Network layer of the OSI model and handle routing packets on a network - performs the same functions as a bridge but is a more sophisticated device. A bridge connects two LANs using the same protocol, and the communication medium does not have to be the same on both LANs. - can also choose the best possible path for packets based on distance or cost. They can prevent network jams that delay packet delivery, and they can handle packets of different sizes - can also be used to isolate a portion of the LAN from the rest of the network; this process is called "segmenting." - two types: static and dynamic

wireless network

a network that uses wireless instead of wired technology. - portable computers use small antennas to communicate with radio towers in the surrounding area. Satellites in near-Earth orbit pick up low-powered signals from mobile and portable network devices

Open Systems Interconnection (OSI) model

a seven-layer architecture for defining how data is transmitted from computer to computer in a network, from the physical connection to the network to the applications that users run. - It also standardizes interactions between network computers exchanging information.

narrowband data transmission

a voice-grade transmission channel capable of transmitting a maximum of 56,000 bps, so only a limited amount of information can be transferred in a specific period of time.

centralized processing system

all processing is done at one central computer. - In the early days of computer technology, this type of processing was justified because data-processing personnel were in short supply, hardware and software were expensive, and only large organizations could afford computers. - main advantage of this configuration is being able to exercise tight control over system operations and applications. - main disadvantage is lack of responsiveness to users' needs because the system and its users could be located far apart from each other. - not used much today

wireless LAN (WLAN)

also used to describe any wireless network. - have the same characteristics as wired LANs, except they use wireless media, such as infrared (IR) light or RF. - These networks are becoming an important alternative to wired LANs in many companies. Like their wired counterparts, WLANs are characterized by having one owner and covering a limited area. - rely on the RF spectrum as the communication medium - coverage: About 100 meters - speed: With the 802.11b wireless standard, data transfer rate up to 11 Mbps; with 802.11a, up to 54 Mbps; with 802.11n, up to 100 Mbps - security: usually lower than WWANs

Transmission Control Protocol/Internet Protocol (TCP/IP)

an industry-standard suite of communication protocols that enables interoperability. - main advantage is that it enables interoperability—in other words, it allows the linking of devices running on many different platforms. - was originally intended for Internet communication, but because it addressed issues such as portability, it also became the standard protocol for UNIX network communication. - Transmission Control Protocol (TCP), which operates at the OSI model's Transport layer, and Internet Protocol (IP), which operates at the OSI model's Network layer.

Bluetooth

can be used to create a personal area network (PAN), is a wireless technology for transferring data over short distances (usually within 30 feet) for fixed and mobile devices. - Bluetooth 5 will offer a range of up to 120 meters, which is four times that of Bluetooth 4.2, and will be two times faster, with data transfer rates of 2Mbps. - PANs can be used for communication among the devices themselves or for connecting to the Internet. - has become popular as a safer method of talking on cell phones while driving. - uses a radio technology called frequency-hopping spread spectrum (FHSS), which separates data into chunks and transmits each chunk on a different frequency, if needed. - is also used to connect devices such as computers, global positioning systems (GPSs), smartphones, laptops, printers, and digital cameras. - has no line of sight limitations (unlike infrared) - Similar to other wireless devices, its susceptibility to interception is a security concern.

wide area network (WAN)

can span several cities, states, or even countries, and it is usually owned by several different parties - data transfer speed depends on the speed of its interconnections (called "links") and can vary from 28.8 Kbps to 155 Mbps. - ex. can be useful for a company headquartered in Washington, D.C., with 30 branch offices in 30 states - makes it possible for all branch offices to communicate with headquarters and send and receive information. - can use many different communication media (coaxial cables, satellite, and fiber optics) and terminals of different sizes and sophistication (PCs, workstations, and mainframes); it can also be connected to other networks. - scope: intercity or international - ownership: multiple parties

Application logic (client/server)

concerned with the software processing requests for users.

communication media/channels (data communication system components)

connect sender and receiver devices. They can be conducted or radiated.

local area network (LAN)

connects workstations and peripheral devices that are in close proximity. - covers a limited geographical area, such as a building or campus, and one company owns it. Its data transfer speed varies from 100 Mbps to 10 Gbps. - used most often to share resources, such as peripherals, files, and software. They are also used to integrate services, such as e-mail and file sharing. - Assessing information needs and careful planning are important in setting up - scope: a building or campus - ownership: 1 party

metropolitan area network (MAN)

designed to handle data communication for multiple organizations in a city and sometimes nearby cities as well. - IEEE definition: a public, independent, high-speed network that connects a variety of data communication systems, including LANs and WANs, in metropolitan areas. - data transfer speed varies from 34 Mbps to 155 Mbps - one to several parties can own this - scope: one city to several contiguous cities

decentralized processing system

each user, department, or division has its own computer (sometimes called an "organizational unit") for performing processing tasks. - certainly more responsive to users than a centralized processing system. - have some drawbacks, including lack of coordination among organizational units, the high cost of having many systems, and duplication of efforts.

TCP's primary functions

establishing a link between hosts, ensuring message integrity, sequencing and acknowledging packet delivery, and regulating data flow between source and destination nodes.

routing table

generated automatically by software, is used to determine the best possible route for a packet. - lists nodes on a network and the path to each node, along with alternate routes and the speed of existing routes.

advantages of wireless/mobile networks

mobility, flexibility, ease of installation, and low cost. - These systems are particularly effective when no infrastructure (such as communication lines or established wired networks) is in place, which is common in many developing nations and in old buildings that do not have the necessary wiring for a network. - Instead of writing notes on paper regarding the patient's condition, then transcribing the notes into an electronic form, they can enter information directly into the handheld devices. - Because the information can be sent to and saved on a centralized database, it is available to other workers instantly. - In addition, entering notes directly prevents errors that are common during the transcription process, which improves the quality of information.

ring network topology

no host computer is required because each computer manages its own connectivity - Computers and devices are arranged in a circle so each node is connected to two other nodes: its upstream neighbor and its downstream neighbor. - Transmission is in one direction, and nodes repeat a signal before passing it to the downstream neighbor. - If any link between nodes is severed, the entire network is affected, and failure of a single node disrupts the entire network - A token ring is a common implementation: is a LAN protocol specified in the IEEE 802.5 in which all stations are connected in a ring and each station can directly receive transmissions only from its immediate neighbor. - Permission to transmit is granted by a message (token) that circulates around the ring. - Modern ring topologies, such as Fiber Distributed Data Interface (FDDI), are capable of bidirectional transmission (clockwise and counterclockwise), which prevents the problems caused by a single node failure. - needs less cable than a star topology, but it is similar to a star topology in that it is better for handling heavy but short bursts of traffic. - diagnosing problems and modifying the network are more difficult than with a star topology.

centralized routing

one node is in charge of selecting the path for all packets. - This node, considered the network routing manager, stores the routing table, and any changes to a route must be made at this node. - All network nodes periodically forward status information on the number of inbound, outbound, and processed messages to the network routing manager. - The network routing manager, therefore, has an overview of the network and can determine whether any part of it is underused or overused

point to point communication medium system

only one device at a time uses the medium

IP is responsible for

packet forwarding. To perform this task, it must be aware of the available data link protocols and the optimum size of each packet. After it recognizes the size of each packet, it must be able to divide data into packets of the correct size. - An IP address consists of 4 bytes in IPv4 or 16 bytes in IPv6 (32 bits or 128 bits) and is divided into two parts: a network address and a node address. - Computers on the same network must use the same network address, but each computer must have a unique node address. - IP networks combine network and node addresses into one IP address

conducted media

provide a physical path along which signals are transmitted, including twisted-pair copper cable, coaxial cable, and fiber optics. - Twisted-pair copper cable consists of two copper lines twisted around each other and either shielded or unshielded; it is used in telephone networks and for communication within buildings. - Coaxial cables are thick cables that can be used for both data and voice transmissions. They are used mainly for long-distance telephone transmissions and local area networks. - Fiber-optic cables are glass tubes (half the diameter of a human hair) surrounded by concentric layers of glass, called "cladding," to form a light path through wire cables. have a higher capacity, smaller size, lighter weight, lower attenuation, and higher security than other cable types; they also have the highest bandwidth of any communication medium.

distributed routing

relies on each node to calculate its own best possible route. Each node contains its own routing table with current information on the status of adjacent nodes so packets can follow the best possible route. - Each node also sends status messages periodically so adjacent nodes can update their tables. - eliminates the problems caused by having the routing table at a centralized site. - If one node is not operational, routing tables at other nodes are updated, and the packet is sent along a different path.

network topology

represents a network's physical layout, including the arrangement of computers and cables.

static router

requires the network routing manager to give it information about which addresses are on which network.

protocols

rules that govern data communication, including error detection, message length, and transmission speed. - Some deal with hardware connections, and others control data transmission and file transfers. - also specify the format of message packets sent between computers. - multiple protocol support is becoming more important, as networks need to support protocols of computers running different operating systems, such as Mac OS, Linux/UNIX, and Windows.

multipoint communication medium system

several devices share the same medium, and a transmission from one device can be sent to all other devices sharing the link

throughput

similar to bandwidth. It is the amount of data transferred or processed in a specified time, usually one second.

client/server model

software runs on the local computer (the client) and communicates with the remote server to request information or services. - A server is a remote computer on the network that provides information or services in response to client requests. -

5 common network topologies

star, ring, bus, hierarchical, and mesh.

data communication

the electronic transfer of data from one location to another. - E-collaboration is another main application of this - Decision makers can be located throughout the world but can still collaborate with their colleagues no matter where they are. - enable organizations to use e-mail and electronic file transfer to improve efficiency and productivity. A communication network, a crucial part of an organization's information system, shortens product and service development life cycles and delivers information to those who need it faster and more efficiently.

routing

the process of deciding which path to take on a network. This is determined by the type of network and the software used to transmit data. - a packet's route can change each time a connection is made, based on the amount of traffic and the availability of the circuit. - The decision about which route to follow is done in one of two ways: at a central location (centralized routing) or at each node along the route (distributed routing).

Presentation logic (client/server)

the top level, is concerned with how data is returned to the client. The Windows graphical user interface (GUI) is an example of presentation software. - An interface's main function is to translate tasks and convert them to something users can understand

(t/F) In addition to a NIC, to operate a server in a network, a network operating system (NOS) must be installed, such as Windows Server 2019 or Linux.

true

(t/f) A data communication system can also improve the flexibility of data collection and transmission.

true

(t/f) An information system's effectiveness is measured in part by how efficiently it delivers information, and a data communication system is what enables an information system to carry out this function.

true

(t/f) Before a communication link can be established between two devices, they must be synchronized, meaning that both devices must start and stop communicating at the same point. Synchronization is handled with protocols

true

radiated media

use an antenna for transmitting data through air or water. - Some of these media are based on "line of sight" (an open path between sending and receiving devices or antennas), including broadcast radio, terrestrial microwave, and satellite. - Satellites link ground-based microwave transmitters/receivers, known as Earth stations, and are commonly used in long-distance telephone transmissions and TV signals. - Terrestrial microwave systems use Earth-based transmitters and receivers and are often used for point-to-point links between buildings.

star network topology

usually consists of a central computer (host computer, often a server) and a series of nodes (typically, workstations or peripheral devices). - The host computer supplies the main processing power. - If a node fails, it does not affect the network's operation, but if the host computer fails, the entire network goes down

mobile network

(also called a cellular network) is a network operating on a radio frequency (RF), consisting of radio cells, each served by a fixed transmitter, known as a cell site or base station. -These cells are used to provide radio coverage over a wider area. 1. Base stations send and receive transmissions to and from subscribers. 2. Mobile telephone switching offices (MTSOs) transfer calls between national or global phone networks and base stations. 3. Subscribers (users) connect to base stations by using mobile communication devices. - Mobile devices register by subscribing to a carrier service (provider) licensed for certain geographic areas. - When a mobile unit is outside its provider's coverage area, roaming occurs. Roaming is using a cellular phone outside of a carrier's limited service area. By doing this, users are extending the connectivity service in a location that is different from the home location where the service was first registered. - To improve the efficiency and quality of digital communications, two technologies have been developed: Time Division Multiple Access and Code Division Multiple Access. Time Division Multiple Access (TDMA) divides each channel into six time slots. Each user is allocated two slots: one for transmission and one for reception. This method increases efficiency by 300 percent, as it allows carrying three calls on one channel. Code Division Multiple Access (CDMA) transmits multiple encoded messages over a wide frequency and then decodes them at the receiving end.

modems (data communication system components)

(short for "modulator-demodulator") - is a device that connects a user to the Internet. - Not all Internet connections require this - dial-up, digital subscriber line (DSL), and cable access require these to connect to Internet - DSL or cable modems are common than analog modems (using phone lines for Internet) - Cable modems, on the other hand, use the same cable that connects to TVs for Internet connections; they can usually reach transmission speeds of about 16 Mbps.

Two-Tier Architecture (client/server)

(the most common type), a client (tier one) communicates directly with the server (tier two). - The presentation logic is always on the client, and the data management logic is on the server. - The application logic can be on the client, on the server, or split between them, although it is usually on the client side - is effective in small workgroups (i.e., groups of 50 clients or less) - Because application logic is usually on the client side, has the advantages of application development speed, simplicity, and power - On the downside, any changes in application logic, such as stored procedures and validation rules for databases, require major modifications of clients, resulting in upgrade and modification costs, depending on the application - if the application logic is modified, it can affect the processing workload.

advantages of distributed processing

- Accessing unused processing power is possible. - Modular design means computer power can be added or removed, based on need. - Distance and location are not limiting. - It is more compatible with organizational growth because workstations can be added easily. - Fault tolerance is improved because of the availability of redundant resources. - Resources, such as high-quality laser printers, can be shared to reduce costs. - Reliability is improved because system failures can be limited to only one site. - The system is more responsive to user needs.

Advantages of the star topology:

- Cable layouts are easy to modify. - Centralized control makes detecting problems easier. - Nodes can be added to the network easily. - It is more effective at handling heavy but short bursts of traffic.

Disadvantages of the star topology:

- If the central host fails, the entire network becomes inoperable. - Many cables are required, which increases cost.

sender and receiver devices (data communication system components)

- Input/output device, or "thin client"—Used only for sending or receiving information; it has no processing power. - Smart terminal—An input/output device that can perform certain processing tasks but is not a full-featured computer. This type of device is often used on factory floors and assembly lines for collecting data and transmitting it to the main computer system. - Intelligent terminal, workstation, or personal computer—These serve as input/output devices or as stand-alone systems. Using this type of device, a remote computer can perform certain processing tasks without the main computer's support. Generally, an intelligent terminal is considered a step up from a smart terminal. - Netbook computer—A low-cost, diskless computer used to connect to the Internet or a local area network (LAN). Netbook computers run software off servers and save data to servers. - Minicomputers, mainframes, and supercomputers—These process data and send it to other devices or receive data that has been processed elsewhere, process it, then transmit it to other devices. - Smartphones— these are mobile phones with advanced capabilities, such as e-mail and Web browsing, and most have a built-in keyboard or an external USB keyboard.

disadvantages of wireless/mobile networks

- Limited throughput—Throughput is similar to bandwidth. It is the amount of data transferred or processed in a specified time, usually one second. Unlike the other disadvantages of wireless, throughput is expected to become a bigger problem in the future. - Limited range—The distance a signal can travel without losing strength is more limited in mobile and wireless networks. For example, a Wi-Fi (Wireless Fidelity) network can have a range of 120 feet indoors and 300 feet outdoors - In-building penetration problems—Wireless signals might not be able to pass through certain building materials or might have difficulty passing through walls. - Vulnerability to frequency noise—Interference from other signals, usually called "noise," can cause transmission problems. Common sources of noise include thunderstorms and lightning, which create radio waves (the same waves used by wireless networks); transformers; high-voltage cables; and fluorescent lights. - Security—Wireless network traffic can be captured with sniffers. (Security is discussed in more detail later in this module.)

1G (cellular networks)

Analog transmission with limited bandwidth

transport layer (OSI) 4

Generates the receiver's address and ensures the integrity of messages by making sure packets are delivered without error, in sequence, and with no loss or duplication. This layer provides methods for controlling data flow, ordering received data, and acknowledging received data.

physical layer (OSI ) 1

Specifies the electrical connections between computers and the transmission medium; defines the physical medium used for communication. This layer is primarily concerned with transmitting binary data, or bits, over a communication network.

2G (cellular networks)

Support for voice, data, paging, and fax services added

most widely used network protocol

TCP/IP

Code Division Multiple Access (CDMA)

To improve the efficiency and quality of digital communications, transmits multiple encoded messages over a wide frequency and then decodes them at the receiving end.