Chapter 4

network

linked computer system to share information and resources among different computers

PAN (personal area network)

a computer network normally used for short-range communications (typically less than a few meters) such as between a wireless headset and a smartphone or between a wireless mouse and its PC

LAN (local area network)

a computer network normally consisting of a collection of computers in a single building or building complex (ex: computers on a university campus or those in a manufacturing plant)

MAN (metropolitan area network)

a computer network of intermediate size such as one spanning a local community

WAN (wide area network)

a computer network linking machines over a greater distance - in neighboring cities or on opposite sides of the world

open network

a network whose internal operation is based on designs that are in the public domain

closed (proprietary) network

a network whose internal operation is based on innovations owned and controlled by a particular entity such as an individual or a corporation

bus topology

a popular network topology in which the machines are all connected to a common communication line called a bus

star topology

a network topology in which one machine serves as a central focal point to which all the others are connected

access point (AP)

in wireless networks with a star configuration and communicating by means of radio broadcast, the central machine serving as a focal point around which all communication is coordinated

hub

a device serving as a very short bus that is centrally located to all the computers in the network so that it can relay any signal it receives (maybe with some amplification) back out to all the machines connected to it; creates a network that looks like a star network but operates like a bus network

protocols

established rules by which activities are conducted so as for a network to function reliably

Carrier Sense, Multiple Access with Collision Detection (CSMA/CD) protocol

the protocol that controls the right to transmit messages in a bus network based on the Ethernet standards; dictates that each message be broadcast to all machines on the bus and each machine monitors all the messages but keeps only those addressed to itself, to transmit a message, a machine waits until the bus is silent and then begins transmitting while still monitoring the bus, in the case of a collision, both machines detect and pause briefly and independently for a random period of time and then try again; not compatible with wireless star networks in which all the machines communicate through a central AP

hidden terminal problem

a potential cause of colliding signals that occurs when a machine is unable to detect that its transmissions are colliding with those of another because the machines are blocked from each other by objects or distance even though they can all communicate with the central AP

Carrier Sense, Multiple Access with Collision Avoidance (CSMA/CA) protocol

a type of policy used by wireless networks to try to avoid collisions rather than detect them, commonly referred to as WiFi

repeater

a device that passes signals back and forth between the two original buses, usually with some form of amplification and without considering the meaning of the signals, to extend a network or connect existing networks

wifi

policies classified as CSMA/CA and standardized by the IEEE within the protocols defined in IEEE 802.11

bridge

a device that connects two buses and looks at the destination address that accompanies each message and forwards a message across the connection only when that message is destined for a computer on the other side; more efficient than a repeater

switch

a bridge with multiple connections, allowing it to connect several buses rather than just two which produces a network consisting of several buses extending from it like spokes on a wheel

internet

a network of networks in which the original networks maintain their individuality and continue to function as autonomous networks

Internet

a particular, worldwide internet; a largely commercial undertaking that links a worldwide combination of PANs, LANs, MANs, and WANs involving millions of computers

router

a special purpose computer used for forwarding messages; handles the connection between networks to form an internet

forwarding table

a table containing a router’s knowledge about the direction in which messages should be sent depending on their destination address

gateway

the point at which one network is linked to an internet; serves as a passageway between the network and the outside world

interprocess communication

communication between the various activities (or processes) executing on the different computers within a network (or on the same machine via time-sharing/multitasking) to coordinate their actions and perform their designated tasks

client/server model

a popular convention used for interprocess communication; defines the basic roles played by the processes as either a client or a server

client

in interprocess communication, a basic role in which a process makes requests of other processes

server

in interprocess communication, a basic role in which a process satisfies the requests made by clients

print server

an early application of the client/server model in which a single, high-quality printer was attached to the network where it was available to all the machines in the network and played the role of a server where the other machines were programmed to play the role of clients that sent print requests to the printer

file server

an early application of the client/server model in which one machine in a network was equipped with a high-capacity mass storage system (usually a magnetic disk) that contained all of an organization’s records; other machines on the network then requested access to the records as they needed them; the machine that contained the records

peer-to-peer (P2P) model

an interprocess communication model that involves processes that provide services to and receive service from each other; usually involves processes that execute on a temporary basis

distributed systems

systems that consist of software units that execute as processes on different computers

cluster computing

a distributed system in which many independent computers work closely together to provide computation or services comparable to a much larger machine

high-availability

at least one member of a cluster will be able to answer a request, even if other cluster members break down or are unavailable

load-balancing

the workload can be shifted automatically from members of the cluster that have too much to do to those that may have too little

grid computing

distributed systems that are more loosely coupled than clusters but still work together to accomplish large tasks

cloud computing

a distributed system in which huge pools of shared computers on the network can be allocated for use by clients as needed

Internet Service Providers (ISPs)

the organizations responsible for the construction and maintenance of the Internet’s collection of connected networks

ISP

also customary to use in reference to the networks provided by an ISP

tier-1 ISPs

the top of the hierarchy of networks operated by ISPs consisting of very high-speed, high-capacity international WANs; the backbone of the Internet

tier-2 ISP

ISPs that tend to be more regional in scope and less potent in their capabilities than tier-1 ISPs

redundancy

the many possible pathways between routers that keeps most or all of the network connected even when very important tier-1 routers fail

access or tier-1 ISP

an independent Internet operated by a single authority that is in the business of supplying Internet access to individual homes and businesses

intranet

another name for an independent Internet

end systems (hosts)

the devices that individual users connect to the access ISPs

hot spot

the area within the AP or group of APs’ range, particularly when the network access is publicly available or free

end-to-end architecture

the design aspects of the Internet that allow it to provide communication services to so many kinds of devices and technologies; facilitates connecting new devices and networks on the Internet

last mile problem

collectively, issues arising from legacy analog linkages

IP address

a unique identifying address for each computer in the system

Internet Corporation for Assigned Names and Numbers (ICANN)

a non-profit corporation established to coordinate the Internet’s operation

dotted decimal notation

the traditional notation for IP addresses in which the bytes of the address are separated by periods and each byte is expressed as an integer represented in traditional base ten notation

domain

a “region” of the Internet operated by a single authority such as a university, club, company, or government agency

registrars

companies that have been assigned the role of registering domain names with ICANN

domain name

a unique mnemonic assigned to a domain as part of the registration process; often descriptive of the organization registering the domain

top-level domains (TLDs)

the suffix after the period in a domain name used to indicate the domain’s classification (ex: .edu for educational)

country-code TLDs

two-letter TLDs for each specific country

subdomains

multiple extensions to a domain name used as a means of organizing the names within a domain; often represent different networks within the domain’s jurisdiction

name servers

numerous servers that are essentially directories that provide address translation services to clients

domain name system (DNS)

an Internet-wide directory system that collectively uses the name servers to translate domain names to IP addresses

DNS lookup

the process of using DNS to perform a translation between mnemonic and IP addresses

Network News Transfer Protocol (NNTP)

a protocol for newsreader applications to contact servers

File Transfer Protocol (FTP)

a protocol for applications listing and copying files across the network

Telnet

an early protocol used by applications for accessing another computer from a great distance

Secure Shell (SSH)

a more recent protocol used by applications for accessing another computer from a great distance

Hyper Text Transfer Protocol (HTTP)

a newer and more power protocol used by webpages to handle applications

3G

third generation phone network; provides higher data rates, allows for mobile video calls and other bandwidth-intensive activities

4G

fourth generation phone network; provides even higher data rates and a fully packet-switched IP network which allows smartphones to enjoy the connectivity and flexibility previously only available to broadband-enabled computers

email

electronic mail

SMTP (Simple Mail Transfer Protocol)

defines a way that two computers on the network may interact when transmitting an email message from one host to the other

mail server (example)

mail.skaro.gov; mail.tardis.edu;

MIME (Multipurpose Internet Mail Extensions)

a protocol developed to convert non-ASCII data to SMTP compatible form

POP3 (Post Office Protocol version 3)

a simple and popular protocol used for accessing email in which the user transfers (downloads) messages to her local computer where they can be read, stored in various folders, edited, and otherwise manipulated, all done on the user’s local machine using the local machine’s mass storage

IMAP (Internet Mail Access Protocol)

a popular protocol used for accessing email in which a user stores and manipulates messages and related materials on the same machine as the mail server; a user who must access their email from different computers can maintain records at the mail server that are then accessible from any remote computer to which the user has access

VoIP (Voice over Internet Protocol)

a more recent Internet application in which the Internet infrastructure is used to provide voice communication similar to traditional telephone systems; consists of two processes on different machines transferring audio data via the P2P model

soft phone

a form of VoIP consisting of P2P software that allows two or more PCs to share a call with no more special hardware than a speaker and a microphone (ex: Skype)

analog telephone adapters

a form of VoIP consisting of devices that allow a user to connect their traditional telephone to phone service provided by an access ISP; typically bundled with traditional Internet service and/or digital television service

embedded VoIP phones

a form of VoIP that uses devices that replace a traditional telephone with an equivalent handset connected directly to a TCP/IP network

wireless VoIP

used by the current generation of smartphones, 4G phone network is an IP-based network throughout so a 4G telephone is essentially just another broadband-connected host computer on the global Internet

streaming

transporting audio and video across the Internet in real time

N-unicast

a technique for streaming in which a server is established that would send program messages to each of the clients who requested them (unicast refers one sender sending messages to one receiver, N indicates a single sender involved with multiple unicasts)

multicast

a technique for streaming in which a server transmits a message to multiple clients by means of a single address and relies on the routers in the Internet to recognize the significance of that address and to produce and forward copies of the message to the appropriate destinations

on-demand streaming

a type of streaming in which the end user expects to view or listen to media at an arbitrary time of their choosing

CDNs (content delivery networks)

groups of servers distributed strategically around the Internet that specialize in streaming copies of content to nearby end users in their network “neighborhood”; often reside in an access ISP network

anycast

a networking technology which enables an end user to automatically connect to the closest server out of a defined group of servers

hypertext

linked documents

hyperlinks

a link to other hypertext documents

browser

a software package that allows users to access hypertext on the Internet and resides on the user’s computer and is charged with the tasks of obtaining materials requested by the user and presenting these materials to the user in an organized manner (ex: Chrome, Firefox, Safari)

webserver

a software package that allows users to access hypertext on the Internet and resides on a computer containing hypertext documents to be accessed; provides access to the documents under its control as requested by clients (browsers) (ex: Apache, Microsoft IIS, Nginx)

URL (Uniform Resource Locator)

a unique address given to each document in order to locate and retrieve documents on the Web; contains the information needed by a browser to contact the proper server and request the desired document

tags

special symbols that describe how the document should appear on a display screen, what multimedia resources (such as images) should accompany the document, and which items within the document are linked to other documents

Hypertext Markup Language (HTML)

the system of tags to structure a hypertext document

source version

the HTML-encoded version of a webpage

XML (eXtensible Markup Language)

a standardized style for designing notation systems for representing data as text files; a simplified derivative of an older set of standards called the Standard Generalized Markup Language or SGML)

markup languages

following the XML standard, notation systems developed for representing mathematics, multimedia presentations, and music

search engine

a website assist users in locating material pertaining to a subject of interest

client-side activity

an activity performed by a client (such as a browser)

server-side activity

an activity performed by a server (such as a webserver)

application layer

* the first layer in Internet software for controlling communication
* the layer from which a message typically originates
* consists of software units such as clients and servers that use Internet communication to carry out their tasks
* uses the transport layer to send and receive messages over the Internet
* provides an address that is compatible with the Internet infrastructure (may use the services of the name servers within the Internet to translate mnemonic addresses used by humans into Internet-compatible IP addresses
* deals with messages from the application’s point of view

transport layer

* the second layer in Internet software for controlling communication
* accepts messages from the application layer
* ensures that the messages are properly formatted for transmission over the Internet by dividing long messages into small segments which are transmitted over the Internet one segment at a time
* adds sequence numbers to the packets so they can be reassembled at the message’s destination
* converts messages into segments that are compatible with the Internet and reassembles messages that are received before delivering them to the appropriate application

packet

data broken into blocks of bits, which contain both the data being transmitted and control information for routing the data