Executive Summary
Is it possible for an Information Technology [IT] product to be both mature and state-of-the-art at the same time? In the case of the UNIX® system, the answer is an unqualified "Yes." The UNIX system has continued to develop over the past twenty-five years. In millions of installations running on nearly every hardware platform made, the UNIX system has earned its reputation for stability and scalability. Over the years, UNIX system suppliers have steadily assimilated new technologies so that UNIX systems today provide more functionality as any other operating system.
Perhaps the key to the continuing growth of the UNIX system is the free-market demands placed upon suppliers who produce and support software built to open standards. The "open systems" approach is in bold contrast to other operating environments that lock in their customers with resultant high switching costs. UNIX system suppliers, on the other hand, must constantly provide the highest quality systems in order to retain their customers. Those who become dissatisfied with one UNIX system implementation retain the ability to easily move to another UNIX system implementation.
The continuing success of the UNIX system should come as no surprise. No other operating environment enjoys the support of every major system supplier. Mention the UNIX system and IT professionals immediately think not only of the operating system itself, but also of the large family of application software that the UNIX system supports. In the IT marketplace, the UNIX system has been the catalyst for sweeping changes that have empowered consumers to seek the best-of-breed without the arbitrary constraints imposed by proprietary environments.
In a nutshell then, the UNIX system is the users' and suppliers' operating environment of choice. The UNIX system represents the best collective efforts of competing suppliers, the most refined standards in the public domain, and the rock-solid stability that comes from years of quality assurance testing, mission-critical use, and refinement.
This white paper examines the UNIX system with a special concern for both its extraordinary past and its equally extraordinary prospects for the future.
The UNIX System
The UNIX system has been around for a long time, and many people may remember it as it existed in the previous decades. Many IT professionals who encountered UNIX systems in the past found it uncompromising. While its power was impressive, its command-line interface required technical competence, its syntax was not intuitive, and its interface was unfriendly.
Moreover, in the UNIX system's early days, security was virtually nonexistent. Subsequently, the UNIX system became the first operating system to suffer attacks mounted over the nascent Internet. As the UNIX system matured, however, the organization of security shifted from centralized to distributed authentication and authorization systems.
Today, these perceptions are only of historical interest.
Now, a single Graphical User Interface is shipped and supported by all major vendors has replaced command-line syntax, and security systems, up to and including B1, provide appropriate controls over access to the UNIX system.
The Value of Standards
The UNIX system's increasing popularity spawned the development of a number of variations of the UNIX operating system in the 1980s, and the existence of these caused a mid-life crisis. Standardization had progressed slowly and methodically in domains such as telecommunications and third-generation languages; yet no one had addressed standards at the operating system level. For suppliers, the thought of a uniform operating environment was disconcerting. Consumer lock-in was woven tightly into the fabric of the industry. Individual consumers, particularly those with UNIX system experience, envisioned standardized environments, but had no way to pull the market in their direction.
However, for one category of consumer -governments- the standardization of the UNIX system was both desirable and within reach. Governments have clout and are the largest consumers of information technology products and services in the world. Driven by the need to improve commonality, both US and European governments endorsed a shift to the UNIX system. The Institute of Electrical and Electronic Engineers POSIX family of standards, along with standards from ISO, ANSI and others, led the way. Consortia such as the X/Open Company (merged with the Open Software Foundation in 1995 to form The Open Group) hammered out draft standards to accelerate the process.
In 1994, the definitive specification of what constitutes a UNIX system was finalized through X/Open Company's consensus process. The Single UNIX Specification was born-not from a theoretical, ivory tower approach, but by analyzing the applications that were in use in businesses across the world.
With the active support of government and commercial buyers alike, vendors began to converge on products that implement the Single UNIX Specification, and now all major vendors have products labeled UNIX 95, which indicates that the vendor guarantees that the product conforms to the Single UNIX Specification.
Vendors continue to add value to the UNIX system, particularly in areas of new technology, however that value will always be built upon a single, consensus standard. Meanwhile, the functionality of the UNIX system was established and the mid-life crisis was resolved. Suppliers today provide UNIX systems that are built upon a single, consensus standard.
It is also important to remember that even when variance among UNIX systems was at its worst, IT professionals agreed that migration among UNIX system variants was far easier than migration among the proprietary alternatives.
Now with UNIX 95 branded products available from all major systems vendors, the buyer can for the first time buy systems from different manufacturers, safe in the knowledge that each one is guaranteed to implement the complete functionality of the Single UNIX Specification and will continue to do so.
UNIX system suppliers can assure customers that they own a standards-based system by registering them to use the Open Brand. Below is a list of suppliers who give users this guarantee.
computer science the complete reference
computer security at a glance
Saturday, April 17, 2010
computer host types
Host Types
The following table describes the host types for which entries can be made in the trusted network databases. The first column shows the name used in the Security Families host type menu.
Table 7-1 Host Types, Protocols, and Notes
Name in Template Manager
Protocols and Notes
Trusted Solaris
The TSOL protocol simplifies passing security attributes between computers running Trusted Solaris 2.5.1, Trusted Solaris 7, Trusted Solaris 8, or Trusted Solaris 8 4/01 releases. TSOL is a derivative of the TSIX(RE) 1.1 - SAMP protocol that passes the security attributes in a similar place in the network protocol stack and uses similar header structures. The TSOL protocol passes security attributes in binary form and thus does not require token mapping. NOTE: For communications between Trusted Solaris computers, either the Trusted Solaris or TSIX host type can be assigned in the templates, depending on whether you want the labels to be transmitted in binary form or in token form. If only the labels' names differ on two computers while the labels' binary representations are the same, the Trusted Solaris host type can be used. If the labels' names are the same but the labels' binary representations are different on both Trusted Solaris computers, the TSIX host type can be assigned.
Unlabeled
This host type is assigned to computers running Solaris or other unlabeled operating environments to specify a default label and default clearance to apply to communications with the unlabeled computer. Also, a minimum and maximum label can be set to allow the sending of packets to an unlabeled gateway for forwarding when the packets' labels do not match the default label and would therefore not be sent to the computer as a destination.
RIPSO
Revised IP Security Option (RIPSO) described in the IETF RFC 1108. It specifies a DoD IP labeling method to incorporate labels into IP packets, which are then used for network mandatory access control checks. A fixed RIPSO label specified in the template is applied to network packets interchanged with the particular host. Though this functionality does not fully meet the RFC specifications, it is expected to supply sufficient functionality where RIPSO labels are needed.
CIPSO
Common IP Security Option (CIPSO) protocol TSIX(RE) 1.1 is used to specify security labels that are passed in the IP options field. CIPSO labels are derived automatically from the data's label. Tag type 1 is used to pass the CIPSO security label. This label is then used to make security checks at the IP level and to label the data in the network packet.
TSIX
Trusted Security Information Exchange for Restricted Environments (TSIX/RE) protocol uses token mapping to pass security attributes. Can be used for computers running the Trusted Solaris or other TSIX-cognizant operating environments. See the NOTE for the Trusted Solaris host type in the first entry in this table.
computer science reference
The following table describes the host types for which entries can be made in the trusted network databases. The first column shows the name used in the Security Families host type menu.
Table 7-1 Host Types, Protocols, and Notes
Name in Template Manager
Protocols and Notes
Trusted Solaris
The TSOL protocol simplifies passing security attributes between computers running Trusted Solaris 2.5.1, Trusted Solaris 7, Trusted Solaris 8, or Trusted Solaris 8 4/01 releases. TSOL is a derivative of the TSIX(RE) 1.1 - SAMP protocol that passes the security attributes in a similar place in the network protocol stack and uses similar header structures. The TSOL protocol passes security attributes in binary form and thus does not require token mapping. NOTE: For communications between Trusted Solaris computers, either the Trusted Solaris or TSIX host type can be assigned in the templates, depending on whether you want the labels to be transmitted in binary form or in token form. If only the labels' names differ on two computers while the labels' binary representations are the same, the Trusted Solaris host type can be used. If the labels' names are the same but the labels' binary representations are different on both Trusted Solaris computers, the TSIX host type can be assigned.
Unlabeled
This host type is assigned to computers running Solaris or other unlabeled operating environments to specify a default label and default clearance to apply to communications with the unlabeled computer. Also, a minimum and maximum label can be set to allow the sending of packets to an unlabeled gateway for forwarding when the packets' labels do not match the default label and would therefore not be sent to the computer as a destination.
RIPSO
Revised IP Security Option (RIPSO) described in the IETF RFC 1108. It specifies a DoD IP labeling method to incorporate labels into IP packets, which are then used for network mandatory access control checks. A fixed RIPSO label specified in the template is applied to network packets interchanged with the particular host. Though this functionality does not fully meet the RFC specifications, it is expected to supply sufficient functionality where RIPSO labels are needed.
CIPSO
Common IP Security Option (CIPSO) protocol TSIX(RE) 1.1 is used to specify security labels that are passed in the IP options field. CIPSO labels are derived automatically from the data's label. Tag type 1 is used to pass the CIPSO security label. This label is then used to make security checks at the IP level and to label the data in the network packet.
TSIX
Trusted Security Information Exchange for Restricted Environments (TSIX/RE) protocol uses token mapping to pass security attributes. Can be used for computers running the Trusted Solaris or other TSIX-cognizant operating environments. See the NOTE for the Trusted Solaris host type in the first entry in this table.
computer science reference
linux interview question
INTERVIEW QUESTION ON LINUX
A pretty funny story - someone was offered a test of basic Linux questions for a junior network administrator position, and figured out that the best way to impress the future employer with good answers is to post the list on UbuntuForums. Good idea, right? That’s where all the Linux experts hang out. Unfortunately, that’s where the employer hung out as well:
It didn’t seem to me that I was asking too much for people to use mailing lists, forums, IRC whatever to compile the answers themselves. I actually expected to see some questions show up on forums but I didn’t expect someone to paste the entire thing and expect the forum users to do all the work that would qualify you for an interview. I think at this point you could save us all some time and not turn the answers back in, I already have the information I need on your answers.
Anyway, the list has been made public, so enjoy:
1. Give an example of set of shell commands that will give you the number of files in a directory
2. How do you tell what process has a TCP port open in Linux
3. On a Red Hat Linux Variant how do you control whether a service starts when the system boots
4. How do you tell the amount of free disk space left on a volume
5. Give an example of a set of shell commands to tell how many times “bob†has logged on to the system this month
6. Give an example of a recursively copying a directory from one location to another.
7. How do you modify the IP and Net mask of a system running a Red Hat Variant of Linux
8. Give an example of a set of shell commands that will give you the number of “httpd†processes running on a Linux box.
9. On CentOS or Fedora based system using the package management application, how do you tell what package provided the file “libnss_ldap.soâ€Â
10. What is the difference between VTP client, server, and transparent
11. What is the maximum length of CAT6
12. How does one set up a layer two link to share VLANs
13. How does one implement redundant links at Layer 2
14. What is the difference between a hub, switch, and a router? What are the security advantages of switch vs. hub?
15. Show an example of using telnet to learn the headers of an http server.
16. In what OSI layer does PPP exist
17. What’s the difference between TCP and UDP
18. Given a DNS server that has just started (with an empty cache) and host contacting this DNS server (using it’s OS setting) to learn an address for google.com, list the steps the DNS server will take to learn it with IP addresses (each step will have multiple possible IP addresses – you need choose only one per step).
19. Why are layer 2 loops bad, and what protocol was designed to prevent them
20. Given a radius server at 10.0.0.2 and a shared key of ‘abc123′ show the IOS commands necessary to authenticate switch users against the radius server, while still allowing the use of local username / password pairs
COMPUTER SCIENCE
A pretty funny story - someone was offered a test of basic Linux questions for a junior network administrator position, and figured out that the best way to impress the future employer with good answers is to post the list on UbuntuForums. Good idea, right? That’s where all the Linux experts hang out. Unfortunately, that’s where the employer hung out as well:
It didn’t seem to me that I was asking too much for people to use mailing lists, forums, IRC whatever to compile the answers themselves. I actually expected to see some questions show up on forums but I didn’t expect someone to paste the entire thing and expect the forum users to do all the work that would qualify you for an interview. I think at this point you could save us all some time and not turn the answers back in, I already have the information I need on your answers.
Anyway, the list has been made public, so enjoy:
1. Give an example of set of shell commands that will give you the number of files in a directory
2. How do you tell what process has a TCP port open in Linux
3. On a Red Hat Linux Variant how do you control whether a service starts when the system boots
4. How do you tell the amount of free disk space left on a volume
5. Give an example of a set of shell commands to tell how many times “bob†has logged on to the system this month
6. Give an example of a recursively copying a directory from one location to another.
7. How do you modify the IP and Net mask of a system running a Red Hat Variant of Linux
8. Give an example of a set of shell commands that will give you the number of “httpd†processes running on a Linux box.
9. On CentOS or Fedora based system using the package management application, how do you tell what package provided the file “libnss_ldap.soâ€Â
10. What is the difference between VTP client, server, and transparent
11. What is the maximum length of CAT6
12. How does one set up a layer two link to share VLANs
13. How does one implement redundant links at Layer 2
14. What is the difference between a hub, switch, and a router? What are the security advantages of switch vs. hub?
15. Show an example of using telnet to learn the headers of an http server.
16. In what OSI layer does PPP exist
17. What’s the difference between TCP and UDP
18. Given a DNS server that has just started (with an empty cache) and host contacting this DNS server (using it’s OS setting) to learn an address for google.com, list the steps the DNS server will take to learn it with IP addresses (each step will have multiple possible IP addresses – you need choose only one per step).
19. Why are layer 2 loops bad, and what protocol was designed to prevent them
20. Given a radius server at 10.0.0.2 and a shared key of ‘abc123′ show the IOS commands necessary to authenticate switch users against the radius server, while still allowing the use of local username / password pairs
COMPUTER SCIENCE
A.I application
Applications of AI
computer science complete reference
Artificial Intelligence in the form of expert systems and neural networks have applications in every field of human endeavor. They combine precision and computational power with pure logic, to solve problems and reduce error in operation. Already, robot expert systems are taking over many jobs in industries that are dangerous for or beyond human ability. Some of the applications divided by domains are as follows:
Heavy Industries and Space: Robotics and cybernetics have taken a leap combined with artificially intelligent expert systems. An entire manufacturing process is now totally automated, controlled and maintained by a computer system in car manufacture, machine tool production, computer chip production and almost every high-tech process. They carry out dangerous tasks like handling hazardous radioactive materials. Robotic pilots carry out complex maneuvering techniques of unmanned spacecrafts sent in space. Japan is the leading country in the world in terms of robotics research and use.
Finance: Banks use intelligent software applications to screen and analyze financial data. Softwares that can predict trends in the stock market have been created which have been known to beat humans in predictive power.
Computer Science: Researchers in quest of artificial intelligence have created spin offs like dynamic programming, object oriented programming, symbolic programming, intelligent storage management systems and many more such tools. The primary goal of creating an artificial intelligence still remains a distant dream but people are getting an idea of the ultimate path which could lead to it.
Aviation: Air lines use expert systems in planes to monitor atmospheric conditions and system status. The plane can be put on auto pilot once a course is set for the destination.
expert system
Weather Forecast: Neural networks are used for predicting weather conditions. Previous data is fed to a neural network which learns the pattern and uses that knowledge to predict weather patterns.
Swarm Intelligence: This is an approach to, as well as application of artificial intelligence similar to a neural network. Here, programmers study how intelligence emerges in natural systems like swarms of bees even though on an individual level, a bee just follows simple rules. They study relationships in nature like the prey-predator relationships that give an insight into how intelligence emerges in a swarm or collection from simple rules at an individual level. They develop intelligent systems by creating agent programs that mimic the behavior of these natural systems!
Is artificial Intelligence really possible? Can an intelligence like a human mind surpass itself and create its own image? The depth and the powers of the human mind are just being tapped. Who knows, it might be possible, only time can tell! Even if such an intelligence is created, will it share our sense of morals and justice, will it share our idiosyncrasies? This will be the next step in the evolution of intelligence. Hope I have succeeded in conveying to you the excitement and possibilities this subject holds!
Applications of AI
Q. What are the applications of AI?
A. Here are some.
game playing
You can buy machines that can play master level chess for a few hundred dollars. There is some AI in them, but they play well against people mainly through brute force computation--looking at hundreds of thousands of positions. To beat a world champion by brute force and known reliable heuristics requires being able to look at 200 million positions per second.
speech recognition
In the 1990s, computer speech recognition reached a practical level for limited purposes. Thus United Airlines has replaced its keyboard tree for flight information by a system using speech recognition of flight numbers and city names. It is quite convenient. On the the other hand, while it is possible to instruct some computers using speech, most users have gone back to the keyboard and the mouse as still more convenient.
understanding natural language
Just getting a sequence of words into a computer is not enough. Parsing sentences is not enough either. The computer has to be provided with an understanding of the domain the text is about, and this is presently possible only for very limited domains.
computer vision
The world is composed of three-dimensional objects, but the inputs to the human eye and computers' TV cameras are two dimensional. Some useful programs can work solely in two dimensions, but full computer vision requires partial three-dimensional information that is not just a set of two-dimensional views. At present there are only limited ways of representing three-dimensional information directly, and they are not as good as what humans evidently use.
expert systems
A ``knowledge engineer'' interviews experts in a certain domain and tries to embody their knowledge in a computer program for carrying out some task. How well this works depends on whether the intellectual mechanisms required for the task are within the present state of AI. When this turned out not to be so, there were many disappointing results. One of the first expert systems was MYCIN in 1974, which diagnosed bacterial infections of the blood and suggested treatments. It did better than medical students or practicing doctors, provided its limitations were observed. Namely, its ontology included bacteria, symptoms, and treatments and did not include patients, doctors, hospitals, death, recovery, and events occurring in time. Its interactions depended on a single patient being considered. Since the experts consulted by the knowledge engineers knew about patients, doctors, death, recovery, etc., it is clear that the knowledge engineers forced what the experts told them into a predetermined framework. In the present state of AI, this has to be true. The usefulness of current expert systems depends on their users having common sense.
heuristic classification
One of the most feasible kinds of expert system given the present knowledge of AI is to put some information in one of a fixed set of categories using several sources of information. An example is advising whether to accept a proposed credit card purchase. Information is available about the owner of the credit card, his record of payment and also about the item he is buying and about the establishment from which he is buying it (e.g., about whether there have been previous credit card frauds at this establishment).
computer science complete reference
Artificial Intelligence in the form of expert systems and neural networks have applications in every field of human endeavor. They combine precision and computational power with pure logic, to solve problems and reduce error in operation. Already, robot expert systems are taking over many jobs in industries that are dangerous for or beyond human ability. Some of the applications divided by domains are as follows:
Heavy Industries and Space: Robotics and cybernetics have taken a leap combined with artificially intelligent expert systems. An entire manufacturing process is now totally automated, controlled and maintained by a computer system in car manufacture, machine tool production, computer chip production and almost every high-tech process. They carry out dangerous tasks like handling hazardous radioactive materials. Robotic pilots carry out complex maneuvering techniques of unmanned spacecrafts sent in space. Japan is the leading country in the world in terms of robotics research and use.
Finance: Banks use intelligent software applications to screen and analyze financial data. Softwares that can predict trends in the stock market have been created which have been known to beat humans in predictive power.
Computer Science: Researchers in quest of artificial intelligence have created spin offs like dynamic programming, object oriented programming, symbolic programming, intelligent storage management systems and many more such tools. The primary goal of creating an artificial intelligence still remains a distant dream but people are getting an idea of the ultimate path which could lead to it.
Aviation: Air lines use expert systems in planes to monitor atmospheric conditions and system status. The plane can be put on auto pilot once a course is set for the destination.
expert system
Weather Forecast: Neural networks are used for predicting weather conditions. Previous data is fed to a neural network which learns the pattern and uses that knowledge to predict weather patterns.
Swarm Intelligence: This is an approach to, as well as application of artificial intelligence similar to a neural network. Here, programmers study how intelligence emerges in natural systems like swarms of bees even though on an individual level, a bee just follows simple rules. They study relationships in nature like the prey-predator relationships that give an insight into how intelligence emerges in a swarm or collection from simple rules at an individual level. They develop intelligent systems by creating agent programs that mimic the behavior of these natural systems!
Is artificial Intelligence really possible? Can an intelligence like a human mind surpass itself and create its own image? The depth and the powers of the human mind are just being tapped. Who knows, it might be possible, only time can tell! Even if such an intelligence is created, will it share our sense of morals and justice, will it share our idiosyncrasies? This will be the next step in the evolution of intelligence. Hope I have succeeded in conveying to you the excitement and possibilities this subject holds!
Applications of AI
Q. What are the applications of AI?
A. Here are some.
game playing
You can buy machines that can play master level chess for a few hundred dollars. There is some AI in them, but they play well against people mainly through brute force computation--looking at hundreds of thousands of positions. To beat a world champion by brute force and known reliable heuristics requires being able to look at 200 million positions per second.
speech recognition
In the 1990s, computer speech recognition reached a practical level for limited purposes. Thus United Airlines has replaced its keyboard tree for flight information by a system using speech recognition of flight numbers and city names. It is quite convenient. On the the other hand, while it is possible to instruct some computers using speech, most users have gone back to the keyboard and the mouse as still more convenient.
understanding natural language
Just getting a sequence of words into a computer is not enough. Parsing sentences is not enough either. The computer has to be provided with an understanding of the domain the text is about, and this is presently possible only for very limited domains.
computer vision
The world is composed of three-dimensional objects, but the inputs to the human eye and computers' TV cameras are two dimensional. Some useful programs can work solely in two dimensions, but full computer vision requires partial three-dimensional information that is not just a set of two-dimensional views. At present there are only limited ways of representing three-dimensional information directly, and they are not as good as what humans evidently use.
expert systems
A ``knowledge engineer'' interviews experts in a certain domain and tries to embody their knowledge in a computer program for carrying out some task. How well this works depends on whether the intellectual mechanisms required for the task are within the present state of AI. When this turned out not to be so, there were many disappointing results. One of the first expert systems was MYCIN in 1974, which diagnosed bacterial infections of the blood and suggested treatments. It did better than medical students or practicing doctors, provided its limitations were observed. Namely, its ontology included bacteria, symptoms, and treatments and did not include patients, doctors, hospitals, death, recovery, and events occurring in time. Its interactions depended on a single patient being considered. Since the experts consulted by the knowledge engineers knew about patients, doctors, death, recovery, etc., it is clear that the knowledge engineers forced what the experts told them into a predetermined framework. In the present state of AI, this has to be true. The usefulness of current expert systems depends on their users having common sense.
heuristic classification
One of the most feasible kinds of expert system given the present knowledge of AI is to put some information in one of a fixed set of categories using several sources of information. An example is advising whether to accept a proposed credit card purchase. Information is available about the owner of the credit card, his record of payment and also about the item he is buying and about the establishment from which he is buying it (e.g., about whether there have been previous credit card frauds at this establishment).
linux & unix tutorial
Brief overview of Unix / Linux commands
Below is a listing of each of the Unix / Linux commands currently listed on Computer Hope and a brief explanation of what each of the commands do. This is a full listing which means not all the below commands will work with your distribution and may also not work because of your privileges. Clicking on any of the commands will display additional help and information about that command.
Command Description
a2p Creates a Perl script from an awk script.
ac Prints statistics about users’ connect time.
alias Create a name for another command or long command string.
ar Maintain portable archive or library.
arch Display the architecture of the current host.
arp Manipulate the system ARP cache.
as An assembler.
at Command scheduler.
awk Awk script processing program.
basename Deletes any specified prefix from a string.
bash Command Bourne interpreter
bc Calculator.
bdiff Compare large files.
bfs Editor for large files.
bg Continues a program running in the background.
biff Enable / disable incoming mail notifications.
break Break out of while, for, foreach, or until loop.
bs Battleship game.
bye Alias often used for the exit command.
cal Calendar
calendar Display appointments and reminders.
cancel Cancels a print job.
cat View and/or modify a file.
cc C compiler.
cd Change directory.
chdir Change directory.
checkeq Language processors to assist in describing equations.
checknr Check nroff and troff files for any errors.
chfn Modify your own information or if super user or root modify another users information.
chgrp Change a groups access to a file or directory.
chkey Change the secure RPC key pair.
chmod Change the permission of a file.
chown Change the ownership of a file.
chsh Change login shell.
cksum Display and calculate a CRC for files.
clear Clears screen.
cls Alias often used to clear a screen.
cmp Compare files.
col Reverse line-feeds filter.
comm Compare files and select or reject lines that are common.
compress Compress files on a computer.
continue Break out of while, for, foreach, or until loop.
copy Copy files.
cp Copy files.
cpio Creates archived CPIO files.
crontab Create and list files that you wish to run on a regular schedule.
csh Execute the C shell command interpreter
csplit Split files based on context.
ctags Create a tag file for use with ex and vi.
cu Calls or connects to another Unix system, terminal or non-Unix system.
curl Transfer a URL.
cut Cut out selected fields of each line of a file.
date Tells you the date and time in Unix.
dc An arbitrary precision arithmetic package.
df Display the available disk space for each mount.
deroff Removes nroff/troff, tbl, and eqn constructs.
dhclient Dynamic Host Configuration Protocol Client.
diff Displays two files and prints the lines that are different.
dig DNS lookup utility.
dircmp Lists the different files when comparing directories.
dirname Deliver portions of path names.
dmesg Print or control the kernel ring buffer.
dos2unix Converts text files between DOS and Unix formats.
dpost Translates files created by troff into PostScript.
du Tells you how much space a file occupies.
echo Displays text after echo to the terminal.
ed Line oriented file editor.
edit Text editor.
egrep Search a file for a pattern using full regular expressions.
elm Program command used to send and receive e-mail.
emacs Text editor.
enable Enables / Disables LP printers.
env Displays environment variables.
eqn Language processors to assist in describing equations.
ex Line-editor mode of the vi text editor.
exit Exit from a program, shell or log you out of a Unix network.
expand Expand copies of file s.
expr Evaluate arguments as an expression.
fc The FC utility lists or edits and re-executes, commands previously entered to an interactive sh.
fg Continues a stopped job by running it in the foreground
fgrep Search a file for a fixed-character string.
file Tells you if the object you are looking at is a file or if it is a directory.
find Finds one or more files assuming that you know their approximate filenames.
findsmb List info about machines that respond to SMB name queries on a subnet.
finger Lists information about the user.
fmt Simple text formatters.
fold Filter for folding lines.
for Shell built-in functions to repeatedly execute action(s) for a selected number of times.
foreach Shell built-in functions to repeatedly execute action(s) for a selected number of times.
fromdos Converts text files between DOS and Unix formats.
fsck Check and repair a Linux file system.
ftp Enables ftp access to another terminal.
getfacl Display discretionary file information.
gprof The gprof utility produces an execution profile of a program.
grep Finds text within a file.
groupadd Creates a new group account.
groupdel Enables a super user or root to remove a group.
groupmod Enables a super user or root to modify a group.
gunzip Expand compressed files.
gview A programmers text editor.
gvim A programmers text editor.
gzip Compress files.
halt Stop the computer.
hash Remove internal hash table.
hashstat Display the hash stats.
head Displays the first ten lines of a file, unless otherwise stated.
help If computer has online help documentation installed this command will display it.
history Display the history of commands typed.
host DNS lookup utility.
hostid Prints the numeric identifier for the current host.
hostname Set or print name of current host system.
id Shows you the numeric user and group ID on BSD.
ifconfig Sets up network interfaces.
ifdown take a network interface down
ifup bring a network interface up
isalist Display the native instruction sets executable on this platform.
jobs List the jobs currently running in the background.
join Joins command forms together.
keylogin Decrypt the user’s secret key.
kill Cancels a job.
ksh Korn shell command interpreter.
ld Link-editor for object files.
ldd List dynamic dependencies of executable files or shared objects.
less Opposite of the more command.
lex Generate programs for lexical tasks.
link Calls the link function to create a link to a file.
ln Creates a link to a file.
lo Allows you to exit from a program, shell or log you out of a Unix network.
locate List files in databases that match a pattern.
login Signs into a new system.
logname Returns users login name.
logout Logs out of a system.
lp Prints a file on System V systems.
lpadmin Configure the LP print service.
lpc Line printer control program.
lpq Lists the status of all the available printers.
lpr Submits print requests.
lprm Removes print requests from the print queue.
lpstat Lists status of the LP print services.
ls Lists the contents of a directory.
mach Display the processor type of the current host.
mail One of the ways that allows you to read/send E-Mail.
mailcompat Provide SunOS 4.x compatibility for the Solaris mailbox format.
mailx Mail interactive message processing system.
make Executes a list of shell commands associated with each target.
man Display a manual of a command.
mesg Control if non-root users can send text messages to you.
mii-tool View, manipulate media-independent interface status.
mkdir Create a directory.
mkfs Build a Linux file system, usually a hard disk partition.
more Displays text one screen at a time.
mount Disconnects a file systems and remote resources.
mt Magnetic tape control.
mv Renames a file or moves it from one directory to another directory.
nc TCP/IP swiss army knife.
neqn Language processors to assist in describing equations.
netstat Shows network status.
newalias Install new elm aliases for user and/or system.
newform Change the format of a text file.
newgrp Log into a new group.
nice Invokes a command with an altered scheduling priority.
niscat Display NIS+ tables and objects.
nischmod Change access rights on a NIS+ object.
nischown Change the owner of a NIS+ object.
nischttl Change the time to live value of a NIS+ object.
nisdefaults Display NIS+ default values.
nisgrep Utilities for searching NIS+ tables.
nismatch Utilities for searching NIS+ tables.
nispasswd Change NIS+ password information.
nistbladm NIS+ table administration command.
nmap Network exploration tool and security / port scanner.
nohup Runs a command even if the session is disconnected or the user logs out.
nroff Formats documents for display or line-printer.
nslookup Queries a name server for a host or domain lookup.
on Execute a command on a remote system, but with the local environment.
onintr Shell built-in functions to respond to (hardware) signals.
optisa Determine which variant instruction set is optimal to use.
pack Shrinks file into a compressed file.
pagesize Display the size of a page of memory in bytes, as returned by getpagesize.
passwd Allows you to change your password.
paste Merge corresponding or subsequent lines of files.
pax Read / write and writes lists of the members of archive files and copy directory hierarchies.
pcat Compresses file.
perl Perl is a programming language optimized for scanning arbitrary text files, extracting information from those text files.
pg Files perusal filters for CRTs.
pgrep Examine the active processes on the system and reports the process IDs of the processes
pico Simple and very easy to use text editor in the style of the Pine Composer.
pine Command line program for Internet News and Email.
ping Sends ICMP ECHO_REQUEST packets to network hosts.
pkill Examine the active processes on the system and reports the process IDs of the processes
poweroff Stop the computer.
pr Formats a file to make it look better when printed.
priocntl Display’s or set scheduling parameters of specified process(es)
printf Write formatted output.
ps Reports the process status.
pvs Display the internal version information of dynamic objects within an ELF file.
pwd Print the current working directory.
quit Allows you to exit from a program, shell or log you out of a Unix network.
rcp Copies files from one computer to another computer.
reboot Stop the computer.
red Line oriented file editor.
rehash Recomputes the internal hash table of the contents of directories listed in the path.
remsh Runs a command on another computer.
repeat Shell built-in functions to repeatedly execute action(s) for a selected number of times.
rgview A programmers text editor.
rgvim A programmers text editor.
rlogin Establish a remote connection from your terminal to a remote machine.
rm Deletes a file without confirmation (by default).
rmail One of the ways that allows you to read/send E-Mail.
rmdir Deletes a directory.
rn Reads newsgroups.
route Show / manipulate the IP routing table.
rpcinfo Report RPC information.
rsh Runs a command on another computer.
rsync Faster, flexible replacement for rcp.
rview A programmers text editor.
rvim A programmers text editor.
s2p Convert a sed script into a Perl script.
sag Graphically displays the system activity data stored in a binary data file by a previous sar run.
sar Displays the activity for the CPU.
script Records everything printed on your screen.
sdiff Compares two files, side-by-side.
sed Allows you to use pre-recorded commands to make changes to text.
sendmail Sends mail over the Internet.
set Set the value of an environment variable.
setenv Set the value of an environment variable.
setfacl Modify the Access Control List (ACL) for a file or files.
settime Change file access and modification time.
sftp Secure file transfer program.
sh Runs or processes jobs through the Bourne shell.
shred Delete a file securely, first overwriting it to hide its contents.
shutdown Turn off the computer immediately or at a specified time.
sleep Waits a x amount of seconds.
slogin OpenSSH SSH client (remote login program).
smbclient An ftp-like client to access SMB/CIFS resources on servers.
sort Sorts the lines in a text file.
spell Looks through a text file and reports any words that it finds in the text file that are not in the dictionary.
split Split a file into pieces.
stat Display file or filesystem status.
stop Control process execution.
strip Discard symbols from object files.
stty Sets options for your terminal.
su Become super user or another user.
sysinfo Get and set system information strings.
sysklogd Linux system logging utilities.
tabs Set tabs on a terminal.
tail Delivers the last part of the file.
talk Talk with other logged in users.
tac Concatenate and print files in reverse.
tar Create tape archives and add or extract files.
tbl Preprocessor for formatting tables for nroff or troff.
tcopy Copy a magnetic tape.
tcpdump Dump traffic on a network.
tee Read from an input and write to a standard output or file.
telnet Uses the telnet protocol to connect to another remote computer.
time Used to time a simple command.
timex The timex command times a command; reports process data and system activity.
todos Converts text files between DOS and Unix formats.
top Display Linux tasks.
touch Change file access and modification time.
tput Initialize a terminal or query terminfo database.
tr Translate characters.
traceroute Print the route packets take to network host.
troff Typeset or format documents.
ul Reads the named filenames or terminal and does underlining.
umask Get or set the file mode creation mask.
unalias Remove an alias.
unhash Remove internal hash table.
uname Print name of current system.
uncompress Uncompressed compressed files.
uniq Report or filter out repeated lines in a file.
unmount Crates a file systems and remote resources.
unpack Expands a compressed file.
untar Create tape archives and add or extract files.
until Execute a set of actions while/until conditions are evaluated TRUE.
useradd Create a new user or updates default new user information.
userdel Remove a users account.
usermod Modify a users account.
vacation Reply to mail automatically.
vedit Screen-oriented (visual) display editor based on ex.
vgrind Grind nice program listings
vi Screen-oriented (visual) display editor based on ex.
vim A programmers text editor.
view A programmers text editor.
w Show who is logged on and what they are doing.
wait Await process completion.
wc Displays a count of lines, words, and characters in a file
whereis Locate a binary, source, and manual page files for a command.
while Repetitively execute a set of actions while/until conditions are evaluated TRUE.
which Locate a command.
who Displays who is on the system.
whois Internet user name directory service.
write Send a message to another user.
X Execute the X windows system.
xfd Display all the characters in an X font.
xlsfonts Server font list displayer for X.
xset User preference utility for X.
xterm Terminal emulator for X.
xrdb X server resource database utility.
yacc Short for yet another compiler-compiler, yacc is a compiler.
yes Repeatedly output a line with all specified STRING(s), or ‘y’.
yppasswd Changes network password in the NIS database.
zcat Compress files.
Below is a listing of each of the Unix / Linux commands currently listed on Computer Hope and a brief explanation of what each of the commands do. This is a full listing which means not all the below commands will work with your distribution and may also not work because of your privileges. Clicking on any of the commands will display additional help and information about that command.
Command Description
a2p Creates a Perl script from an awk script.
ac Prints statistics about users’ connect time.
alias Create a name for another command or long command string.
ar Maintain portable archive or library.
arch Display the architecture of the current host.
arp Manipulate the system ARP cache.
as An assembler.
at Command scheduler.
awk Awk script processing program.
basename Deletes any specified prefix from a string.
bash Command Bourne interpreter
bc Calculator.
bdiff Compare large files.
bfs Editor for large files.
bg Continues a program running in the background.
biff Enable / disable incoming mail notifications.
break Break out of while, for, foreach, or until loop.
bs Battleship game.
bye Alias often used for the exit command.
cal Calendar
calendar Display appointments and reminders.
cancel Cancels a print job.
cat View and/or modify a file.
cc C compiler.
cd Change directory.
chdir Change directory.
checkeq Language processors to assist in describing equations.
checknr Check nroff and troff files for any errors.
chfn Modify your own information or if super user or root modify another users information.
chgrp Change a groups access to a file or directory.
chkey Change the secure RPC key pair.
chmod Change the permission of a file.
chown Change the ownership of a file.
chsh Change login shell.
cksum Display and calculate a CRC for files.
clear Clears screen.
cls Alias often used to clear a screen.
cmp Compare files.
col Reverse line-feeds filter.
comm Compare files and select or reject lines that are common.
compress Compress files on a computer.
continue Break out of while, for, foreach, or until loop.
copy Copy files.
cp Copy files.
cpio Creates archived CPIO files.
crontab Create and list files that you wish to run on a regular schedule.
csh Execute the C shell command interpreter
csplit Split files based on context.
ctags Create a tag file for use with ex and vi.
cu Calls or connects to another Unix system, terminal or non-Unix system.
curl Transfer a URL.
cut Cut out selected fields of each line of a file.
date Tells you the date and time in Unix.
dc An arbitrary precision arithmetic package.
df Display the available disk space for each mount.
deroff Removes nroff/troff, tbl, and eqn constructs.
dhclient Dynamic Host Configuration Protocol Client.
diff Displays two files and prints the lines that are different.
dig DNS lookup utility.
dircmp Lists the different files when comparing directories.
dirname Deliver portions of path names.
dmesg Print or control the kernel ring buffer.
dos2unix Converts text files between DOS and Unix formats.
dpost Translates files created by troff into PostScript.
du Tells you how much space a file occupies.
echo Displays text after echo to the terminal.
ed Line oriented file editor.
edit Text editor.
egrep Search a file for a pattern using full regular expressions.
elm Program command used to send and receive e-mail.
emacs Text editor.
enable Enables / Disables LP printers.
env Displays environment variables.
eqn Language processors to assist in describing equations.
ex Line-editor mode of the vi text editor.
exit Exit from a program, shell or log you out of a Unix network.
expand Expand copies of file s.
expr Evaluate arguments as an expression.
fc The FC utility lists or edits and re-executes, commands previously entered to an interactive sh.
fg Continues a stopped job by running it in the foreground
fgrep Search a file for a fixed-character string.
file Tells you if the object you are looking at is a file or if it is a directory.
find Finds one or more files assuming that you know their approximate filenames.
findsmb List info about machines that respond to SMB name queries on a subnet.
finger Lists information about the user.
fmt Simple text formatters.
fold Filter for folding lines.
for Shell built-in functions to repeatedly execute action(s) for a selected number of times.
foreach Shell built-in functions to repeatedly execute action(s) for a selected number of times.
fromdos Converts text files between DOS and Unix formats.
fsck Check and repair a Linux file system.
ftp Enables ftp access to another terminal.
getfacl Display discretionary file information.
gprof The gprof utility produces an execution profile of a program.
grep Finds text within a file.
groupadd Creates a new group account.
groupdel Enables a super user or root to remove a group.
groupmod Enables a super user or root to modify a group.
gunzip Expand compressed files.
gview A programmers text editor.
gvim A programmers text editor.
gzip Compress files.
halt Stop the computer.
hash Remove internal hash table.
hashstat Display the hash stats.
head Displays the first ten lines of a file, unless otherwise stated.
help If computer has online help documentation installed this command will display it.
history Display the history of commands typed.
host DNS lookup utility.
hostid Prints the numeric identifier for the current host.
hostname Set or print name of current host system.
id Shows you the numeric user and group ID on BSD.
ifconfig Sets up network interfaces.
ifdown take a network interface down
ifup bring a network interface up
isalist Display the native instruction sets executable on this platform.
jobs List the jobs currently running in the background.
join Joins command forms together.
keylogin Decrypt the user’s secret key.
kill Cancels a job.
ksh Korn shell command interpreter.
ld Link-editor for object files.
ldd List dynamic dependencies of executable files or shared objects.
less Opposite of the more command.
lex Generate programs for lexical tasks.
link Calls the link function to create a link to a file.
ln Creates a link to a file.
lo Allows you to exit from a program, shell or log you out of a Unix network.
locate List files in databases that match a pattern.
login Signs into a new system.
logname Returns users login name.
logout Logs out of a system.
lp Prints a file on System V systems.
lpadmin Configure the LP print service.
lpc Line printer control program.
lpq Lists the status of all the available printers.
lpr Submits print requests.
lprm Removes print requests from the print queue.
lpstat Lists status of the LP print services.
ls Lists the contents of a directory.
mach Display the processor type of the current host.
mail One of the ways that allows you to read/send E-Mail.
mailcompat Provide SunOS 4.x compatibility for the Solaris mailbox format.
mailx Mail interactive message processing system.
make Executes a list of shell commands associated with each target.
man Display a manual of a command.
mesg Control if non-root users can send text messages to you.
mii-tool View, manipulate media-independent interface status.
mkdir Create a directory.
mkfs Build a Linux file system, usually a hard disk partition.
more Displays text one screen at a time.
mount Disconnects a file systems and remote resources.
mt Magnetic tape control.
mv Renames a file or moves it from one directory to another directory.
nc TCP/IP swiss army knife.
neqn Language processors to assist in describing equations.
netstat Shows network status.
newalias Install new elm aliases for user and/or system.
newform Change the format of a text file.
newgrp Log into a new group.
nice Invokes a command with an altered scheduling priority.
niscat Display NIS+ tables and objects.
nischmod Change access rights on a NIS+ object.
nischown Change the owner of a NIS+ object.
nischttl Change the time to live value of a NIS+ object.
nisdefaults Display NIS+ default values.
nisgrep Utilities for searching NIS+ tables.
nismatch Utilities for searching NIS+ tables.
nispasswd Change NIS+ password information.
nistbladm NIS+ table administration command.
nmap Network exploration tool and security / port scanner.
nohup Runs a command even if the session is disconnected or the user logs out.
nroff Formats documents for display or line-printer.
nslookup Queries a name server for a host or domain lookup.
on Execute a command on a remote system, but with the local environment.
onintr Shell built-in functions to respond to (hardware) signals.
optisa Determine which variant instruction set is optimal to use.
pack Shrinks file into a compressed file.
pagesize Display the size of a page of memory in bytes, as returned by getpagesize.
passwd Allows you to change your password.
paste Merge corresponding or subsequent lines of files.
pax Read / write and writes lists of the members of archive files and copy directory hierarchies.
pcat Compresses file.
perl Perl is a programming language optimized for scanning arbitrary text files, extracting information from those text files.
pg Files perusal filters for CRTs.
pgrep Examine the active processes on the system and reports the process IDs of the processes
pico Simple and very easy to use text editor in the style of the Pine Composer.
pine Command line program for Internet News and Email.
ping Sends ICMP ECHO_REQUEST packets to network hosts.
pkill Examine the active processes on the system and reports the process IDs of the processes
poweroff Stop the computer.
pr Formats a file to make it look better when printed.
priocntl Display’s or set scheduling parameters of specified process(es)
printf Write formatted output.
ps Reports the process status.
pvs Display the internal version information of dynamic objects within an ELF file.
pwd Print the current working directory.
quit Allows you to exit from a program, shell or log you out of a Unix network.
rcp Copies files from one computer to another computer.
reboot Stop the computer.
red Line oriented file editor.
rehash Recomputes the internal hash table of the contents of directories listed in the path.
remsh Runs a command on another computer.
repeat Shell built-in functions to repeatedly execute action(s) for a selected number of times.
rgview A programmers text editor.
rgvim A programmers text editor.
rlogin Establish a remote connection from your terminal to a remote machine.
rm Deletes a file without confirmation (by default).
rmail One of the ways that allows you to read/send E-Mail.
rmdir Deletes a directory.
rn Reads newsgroups.
route Show / manipulate the IP routing table.
rpcinfo Report RPC information.
rsh Runs a command on another computer.
rsync Faster, flexible replacement for rcp.
rview A programmers text editor.
rvim A programmers text editor.
s2p Convert a sed script into a Perl script.
sag Graphically displays the system activity data stored in a binary data file by a previous sar run.
sar Displays the activity for the CPU.
script Records everything printed on your screen.
sdiff Compares two files, side-by-side.
sed Allows you to use pre-recorded commands to make changes to text.
sendmail Sends mail over the Internet.
set Set the value of an environment variable.
setenv Set the value of an environment variable.
setfacl Modify the Access Control List (ACL) for a file or files.
settime Change file access and modification time.
sftp Secure file transfer program.
sh Runs or processes jobs through the Bourne shell.
shred Delete a file securely, first overwriting it to hide its contents.
shutdown Turn off the computer immediately or at a specified time.
sleep Waits a x amount of seconds.
slogin OpenSSH SSH client (remote login program).
smbclient An ftp-like client to access SMB/CIFS resources on servers.
sort Sorts the lines in a text file.
spell Looks through a text file and reports any words that it finds in the text file that are not in the dictionary.
split Split a file into pieces.
stat Display file or filesystem status.
stop Control process execution.
strip Discard symbols from object files.
stty Sets options for your terminal.
su Become super user or another user.
sysinfo Get and set system information strings.
sysklogd Linux system logging utilities.
tabs Set tabs on a terminal.
tail Delivers the last part of the file.
talk Talk with other logged in users.
tac Concatenate and print files in reverse.
tar Create tape archives and add or extract files.
tbl Preprocessor for formatting tables for nroff or troff.
tcopy Copy a magnetic tape.
tcpdump Dump traffic on a network.
tee Read from an input and write to a standard output or file.
telnet Uses the telnet protocol to connect to another remote computer.
time Used to time a simple command.
timex The timex command times a command; reports process data and system activity.
todos Converts text files between DOS and Unix formats.
top Display Linux tasks.
touch Change file access and modification time.
tput Initialize a terminal or query terminfo database.
tr Translate characters.
traceroute Print the route packets take to network host.
troff Typeset or format documents.
ul Reads the named filenames or terminal and does underlining.
umask Get or set the file mode creation mask.
unalias Remove an alias.
unhash Remove internal hash table.
uname Print name of current system.
uncompress Uncompressed compressed files.
uniq Report or filter out repeated lines in a file.
unmount Crates a file systems and remote resources.
unpack Expands a compressed file.
untar Create tape archives and add or extract files.
until Execute a set of actions while/until conditions are evaluated TRUE.
useradd Create a new user or updates default new user information.
userdel Remove a users account.
usermod Modify a users account.
vacation Reply to mail automatically.
vedit Screen-oriented (visual) display editor based on ex.
vgrind Grind nice program listings
vi Screen-oriented (visual) display editor based on ex.
vim A programmers text editor.
view A programmers text editor.
w Show who is logged on and what they are doing.
wait Await process completion.
wc Displays a count of lines, words, and characters in a file
whereis Locate a binary, source, and manual page files for a command.
while Repetitively execute a set of actions while/until conditions are evaluated TRUE.
which Locate a command.
who Displays who is on the system.
whois Internet user name directory service.
write Send a message to another user.
X Execute the X windows system.
xfd Display all the characters in an X font.
xlsfonts Server font list displayer for X.
xset User preference utility for X.
xterm Terminal emulator for X.
xrdb X server resource database utility.
yacc Short for yet another compiler-compiler, yacc is a compiler.
yes Repeatedly output a line with all specified STRING(s), or ‘y’.
yppasswd Changes network password in the NIS database.
zcat Compress files.
wide area network
Wide Area Network Technologies Overview
A Wide Area Network ( WAN) is a computer network covering multiple distance areas, which may spread across the entire world. WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs). The world's most popular WAN is the Internet. Some segments of the Internet are also WANs in themselves. The key difference between WAN and LAN technologies is scalability C WAN must be able to grow as needed to cover multiple cities, even countries and continents.
A set of switches and routers are interconnected to form a Wide Area Network. The switches can be connected in different topologies such as full mesh and half mesh. A wide area network may be privately owned or rented from a service provider, but the term usually connotes the inclusion of public (shared user) networks.
Both packet switching and circuit switching technologies are used in the WAN. Packet switching allows users to share common carrier resources so that the carrier can make more efficient use of its infrastructure. In a packet switching setup, networks have connections into the carrier's network, and many customers share the carrier's network. The carrier can then create virtual circuits between customers' sites by which packets of data are delivered from one to the other through the network.
Circuit Switching allows data connections to be established when needed and then terminated when communication is complete. This works like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network.
WAN Diagram Software
Edraw Network Diagram is ideal for network engineers and network designers who need to draw wan diagrams. It had defined some common used WAN symbols in drawing WAN diagrams. Just drag and drop pre-drawn shapes representing computers and network devices. Double click and set equipment data.
Free Download WAN Diagram Software and View All Examples
Examples of Wide Area Network Technologies
Examples of Wide Area Network Technologies Created by Edraw!
Wide Area Network WAN Network WAN Topology
Wide Area Network WAN Network WAN Topology
Virtual private network (VPN) is a tecnology widely used in a public switched network (PSTN) to provide private and secured WAN for an organization. VPN uses encryption and other techniques to make it appear that the organisation has a dedicated network, while making use of the shared infrastructure of the WAN.
WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Key technologies often found in WANs include SONET, Frame Relay, X.25, ATM and PPP.
* ATM: A dedicated-connection switching technology that organizes digital data into 53-byte cell units. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path. Speeds on ATM networks can reach 10 Gbps.
* Frame Relay: (FR). A high-speed packet-switched data communications service, similar to X.25. Frame relay is widely used for LAN-to-LAN interconnect services, and is well suited to the bursty demands of LAN environments.
* SONET/SDH: Synchronous Optical Network is an international standard for high speed communication over fiber-optic networks. The SONET establishes Optical Carrier (OC) levels from 51.8 Mbps to 10 Gbps (OC-192) or even higher. Synchronous Digital Hierarchy (SDH) is a European equivalent of SONET.
* X.25: The X.25 protocol allows computers on different public networks to communicate through an intermediary computer at the network layer level.
* PPP: A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only.
IP can also be considered as a WAN technology in the packet switching environment
computer science the complete reference
A Wide Area Network ( WAN) is a computer network covering multiple distance areas, which may spread across the entire world. WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs). The world's most popular WAN is the Internet. Some segments of the Internet are also WANs in themselves. The key difference between WAN and LAN technologies is scalability C WAN must be able to grow as needed to cover multiple cities, even countries and continents.
A set of switches and routers are interconnected to form a Wide Area Network. The switches can be connected in different topologies such as full mesh and half mesh. A wide area network may be privately owned or rented from a service provider, but the term usually connotes the inclusion of public (shared user) networks.
Both packet switching and circuit switching technologies are used in the WAN. Packet switching allows users to share common carrier resources so that the carrier can make more efficient use of its infrastructure. In a packet switching setup, networks have connections into the carrier's network, and many customers share the carrier's network. The carrier can then create virtual circuits between customers' sites by which packets of data are delivered from one to the other through the network.
Circuit Switching allows data connections to be established when needed and then terminated when communication is complete. This works like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network.
WAN Diagram Software
Edraw Network Diagram is ideal for network engineers and network designers who need to draw wan diagrams. It had defined some common used WAN symbols in drawing WAN diagrams. Just drag and drop pre-drawn shapes representing computers and network devices. Double click and set equipment data.
Free Download WAN Diagram Software and View All Examples
Examples of Wide Area Network Technologies
Examples of Wide Area Network Technologies Created by Edraw!
Wide Area Network WAN Network WAN Topology
Wide Area Network WAN Network WAN Topology
Virtual private network (VPN) is a tecnology widely used in a public switched network (PSTN) to provide private and secured WAN for an organization. VPN uses encryption and other techniques to make it appear that the organisation has a dedicated network, while making use of the shared infrastructure of the WAN.
WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Key technologies often found in WANs include SONET, Frame Relay, X.25, ATM and PPP.
* ATM: A dedicated-connection switching technology that organizes digital data into 53-byte cell units. Individually, a cell is processed asynchronously relative to other related cells and is queued before being multiplexed over the transmission path. Speeds on ATM networks can reach 10 Gbps.
* Frame Relay: (FR). A high-speed packet-switched data communications service, similar to X.25. Frame relay is widely used for LAN-to-LAN interconnect services, and is well suited to the bursty demands of LAN environments.
* SONET/SDH: Synchronous Optical Network is an international standard for high speed communication over fiber-optic networks. The SONET establishes Optical Carrier (OC) levels from 51.8 Mbps to 10 Gbps (OC-192) or even higher. Synchronous Digital Hierarchy (SDH) is a European equivalent of SONET.
* X.25: The X.25 protocol allows computers on different public networks to communicate through an intermediary computer at the network layer level.
* PPP: A point-to-point link provides a single, pre-established WAN communications path from the customer premises through a carrier network, such as a telephone company, to a remote network. Point-to-point lines are usually leased from a carrier and thus are often called leased lines. For a point-to-point line, the carrier allocates pairs of wire and facility hardware to your line only.
IP can also be considered as a WAN technology in the packet switching environment
computer science the complete reference
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