Server monitoring and network monitoring tool

ServersCheck Monitoring is a tool running on Windows based systems for monitoring, reporting and alerting on network, servers and other IT systems availability. In addition to monitoring regular network devices, the program can also can monitor environmental devices like temperature, humidity, flooding.

ServersCheck Monitoring Software release 7.15.10



ServersCheck Monitoring Software runs as a local service and is administrated via a browser based interface. Additional features include alerts and graph output for long-term statistics tracking.


Link

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BMExtreme

While simple to use, BMExtreme offers the power and flexibility to monitor how much bandwidth is consumed when using the internet. Easily do things such as graphically monitor your connection, ignore and share LAN traffic information, setup profiles and check limits placed by your ISP. Whether for a single computer, family network, or company server - BMExtreme is perfect for any setup and a must for anyone with ADSL, Cable, or Satellite.

• Check graphs and logs in real-time.
• Setup profiles for more accurate monitoring.
• Ignore local traffic from other computers on the network.
• Track bandwidth limits placed by your internet service provider.

Features : -

Bandwidth caps

If your ISP maintains bandwidth caps, BMExtreme provides multiple ways of keeping track of them including monthly, weekly, daily and hourly cap resets. There are also day/week/month logs along with warnings when close to the limit. Bandwidth can also be blocked when within range of the cap to avoid going over for overnight downloads. Caps can be setup varying from simple global caps to multiple time caps for ISPs that monitor peak time use.

Shared connections

For those sharing bandwidth with other computers, BMExtreme can track the information in real-time without resorting to checking logs. Any on-screen statistics will incorporate all shared bandwidth and the information can be administered through the internet for checking remotely. Each computer that needs to be monitored will need its own license.

Graphs

Basic graphs include day/week/month statistics. Also available are speed graphs ranging from 5 minutes to 12 hours for extra bandwidth use. Current IP connections can also be tracked, along with the ability to track shared bandwidth in real-time.

User, cap and time profiles

Have more than one user on the computer? Keep track of what everyone uses for a better understanding of bandwidth used. Easily changed from the tray icon, is a great way to allow family members to keep separate logs. Separate caps, peak hours and percentage amounts can be setup to correspond with the rates of your internet provider.

Ignore internal LAN traffic

Easily ignore your network and keep track of actual internet bandwidth.

Terminate connections

Have BMExtreme cut all internet connection when within 5% of your bandwidth cap. Can also run a batch file when that limit is reached for restarting or shutting down the computer. Great for those who download a lot of torrents but have caps to watch out for.

Logs

Stored on a daily, weekly and monthly basis, logs can be viewed directly within the application or the saved TXT and CSV files. If profiles are used, the logs are separated to show the bandwidth for the individual profiles. There is also an option to save IP logs for bandwith grouped by IP.

Windows NT service

BMExtreme can be installed as an NT Service as well (Windows NT and XP users only).

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Maintaining Router Information

Problem—Routing Loops

Each node maintains the distance from itself to each possible destination network




Slow convergence produces inconsistent routing

Router C concludes that the best path to network 10.4.0.0 is through router B


Router A updates its table to reflect the new but erroneous hop count

Symptom: Counting to Infinity





Packets for network 10.4.0.0 bounce between routers A, B, and C.
Hop count for network 10.4.0.0 counts to infinity.

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Routing Loops

Solution: Defining a Maximum


Define a limit on the number of hops to prevent infinite loops Solution: Split Horizon
It is never useful to send information about a route back in the direction from which the original packet came

Solution: Route Poisoning


Routers set the distance of routes that have gone down to infinity

Solution: Poison Reverse


Poison reverse overrides split horizon

Solution: Holddown Timers



The router keeps an entry for the network possibly down state, allowing time for other routers to recompute for this topology change.

Solution: Triggered Updates



The router sends updates when a change in its routing table occurs

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Broadcast Address

Broadcast Addresses



Addressing Summary Example

Class B Subnet Example

• Subnet Address = 172.16.2.0
• Host Addresses = 172.16.2.1–172.16.2.254
• Broadcast Address = 172.16.2.255
• Eight Bits of Subnetting
  
  

Subnet Planning

Class C Subnet Planning Example

• Subnet Address = 192.168.5.120
• Host Addresses = 192.168.5.121–192.168.5.126
• Broadcast Address = 192.168.5.127
• Five Bits of Subnetting

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What is routing ?

Routing



To route, a router needs to do the following:

• Know the destination address.
• Identify the sources it can learn from.
• Discover possible routes.
• Select the best route.
• Maintain and verify routing information

Routers must learn destinations that are not directly connected

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Symantec

Symantec/Norton AntiVirus (SAV for Windows, NAV for Mac OS and OS X) is a virus protection program distributed by the Symantec Corporation, offering effective protection features, including infected file quarantine, online virus protection updates, and an automatic scheduler. SAV/NAV is designed to start running as soon as your computer's operating system starts. It runs in the background, checking all vulnerable files for possible infection by mischievous, sometimes malevolent, programs called viruses and worms. SAV/NAV does this by looking for the identifying signatures of these worms and viruses and comparing them to known viruses for which it has files. When it detects an infected file, it notifies you and manages the infection according to your preferences.

SAV/NAV software is available to Indiana University students, faculty, and staff for free via IUware.

In order for your antivirus software to help keep your computer secure, follow these guidelines:

• Always run the latest version of SAV/NAV software for your operating system, being sure to upgrade safely.
  
  
• Update your virus pattern files daily, and scan your computer weekly for viruses. It's easiest to set these to occur automatically.
  
  

  You can set up SAV/NAV software to automatically update your virus pattern files as often as you choose. Doing this daily helps assure that your software will detect the most recently discovered viruses. You can also schedule SAV/NAV to automatically scan your computer for viruses each week, after LiveUpdate runs.

  SAV/NAV uses a feature called LiveUpdate to update your virus pattern files to the latest version, and then uses these files to scan your computer for viruses. Older versions of SAV/NAV may not be able to use LiveUpdate in Windows. UITS recommends upgrading to a recent version. For other security reasons, UITS also recommends that you upgrade your operating system.
  
  
  

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SunOS and Solaris

SunOS is a Sun Microsystems implementation of the Unix operating system. Solaris is SunOS packaged with a number of additional tools and a graphical user interface (GUI) environment. Since Sun Microsystems did not offer Solaris until SunOS 4, SunOS and Solaris have different version conventions (e.g., Solaris 1 includes SunOS 4, while Solaris 2 includes SunOS 5). To further confuse the naming scheme, Sun now refers to Solaris by just its point release (e.g., Solaris 7, 8, or 9 instead of 2.7, 2.8, or 2.9).

Up through version 4.1.x (Solaris 1.x), SunOS was a heavily BSD-influenced Unix implementation. However, in the late 1980s, Sun entered into a partnership with AT&T, which was then developing the other major Unix flavor, System V. The result was System V release 4 (SVR4), which incorporated BSD as well as SunOS extensions (e.g., NFS). Subsequently, with its version 5.x (Solaris 2.x) releases, SunOS shifted from its BSD origins to SVR4.

In common parlance, when people speak of SunOS, they usually mean the older BSD-based versions (SunOS 1 through 4.1.x and Solaris 1.x). The term "Solaris" typically refers to the SVR4 releases (SunOS version 5 and higher, and Solaris version 2 and higher) exclusively.

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Firewall

A firewall is a system designed to prevent unauthorized access to or from a private network. You can implement a firewall in either hardware or software form, or a combination of both. Firewalls prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet (i.e., the local network to which you are connected) must pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.

Several types of firewall techniques exist:

• Packet filtering: The system examines each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.
  
  
• Circuit-level gateway implementation: This process applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.
  
  
• Acting as a proxy server: A proxy server is a type of gateway that hides the true network address of the computer(s) connecting through it. A proxy server connects to the Internet, makes the requests for pages, connections to servers, etc., and receives the data on behalf of the computer(s) behind it. The firewall capabilities lie in the fact that a proxy can be configured to allow only certain types of traffic (e.g., HTTP files, or web pages) through. A proxy server has the potential drawback of slowing network performance, since it has to actively analyze and manipulate traffic passing through it.

In practice, many firewalls use two or more of these techniques in concert.

A firewall is considered a first line of defense in protecting private information. It cannot be considered the only line, however, since firewalls are mostly designed to protect network traffic and connections, and therefore do not attempt to authenticate users (i.e., determine who is and who isn't allowed to use the computer the firewall is protecting, or see the traffic coming to it).

The most common of free software firewalls for Windows is the one built into Windows XP and Vista. Windows 2000 had packet filtering abilities, but did not include a true firewall. The filtering abilities were not intended to block traffic and protect the computer, but rather to classify certain packets and treat them differently. Earlier versions of Windows did not have firewalls built in.

Macintosh computers running Mac OS X 10.2 and later are also equipped with a built-in firewall.

Third-party packages exist, such as Zone Alarm, Norton Personal Firewall, Tiny, Black Ice Protection, and McAfee Personal Firewall. Many offer free versions or free trials of their commercial versions.

Many home and small office broadband routers have rudimentary firewall capabilities built in. These tend to be simply port/protocol filters, although models with much finer control are available.

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Viruses

About viruses, worms, and Trojan horses

A computer virus, according to Webster's Collegiate Dictionary, is "a computer program usually hidden within another seemingly innocuous program that produces copies of itself and inserts them into other programs or files, and that usually performs a malicious action (such as destroying data)". Two categories of viruses, macro viruses and worms, are especially common today. Computer viruses are never naturally occurring; they are always man-made. Once created and released, however, their spread is not directly under human control.

• Macro viruses: A macro is a piece of code that can be embedded in a data file. Some word processors (e.g., Microsoft Word) and spreadsheet programs (e.g., Microsoft Excel) allow you to attach macros to the documents they create. In this way, documents can control and customize the behavior of the programs that created them, or even extend the capabilities of the program. For example, a macro attached to a Microsoft Word document might be executed every time you save the document and cause its text to be run through an external spell-checking program.

  A macro virus is a virus that exists as a macro attached to a data file. In most respects, macro viruses are like all other viruses. The main difference is that they are attached to data files (i.e., documents) rather than executable programs. If you are unable to save a document in Microsoft Word, your computer may have a macro virus.

  Many people do not think that viruses can reside on simple document files, but any application that supports document-bound macros that automatically execute is a potential haven for macro viruses. By the end of the last century, documents became more widely shared than diskettes, and document-based viruses were more prevalent than any other type of virus. It seems highly likely that this will be a continuing trend.
  
  

• Stealth viruses: A stealth virus is one that, while active, hides the modifications it has made to files or boot records. It usually achieves this by monitoring the system functions used to read files or sectors from storage media and forging the results of calls to such functions. This means that programs that try to read infected files or sectors see the original, uninfected form instead of the actual, infected form. Thus the virus's modifications may go undetected by antivirus programs. However, in order to do this, the virus must be resident in memory when the antivirus program is executed, and the antivirus program may be able to detect its presence.
  
  
• Polymorphic viruses: A polymorphic virus is one that produces varied but operational copies of itself. This strategy assumes that virus scanners will not be able to detect all instances of the virus. One method of evading scan-string driven virus detectors is self-encryption with a variable key. More sophisticated polymorphic viruses vary the sequences of instructions in their variants by interspersing the decryption instructions with "noise" instructions (e.g., a No Operation instruction, or an instruction to load a currently unused register with an arbitrary value), by interchanging mutually independent instructions, or even by using various instruction sequences with identical net effects (e.g., Subtract A from A, and Move 0 to A). A simple-minded, scan-string based virus scanner would not be able to reliably identify all variants of this sort of virus; in this case, a sophisticated scanning engine has to be constructed after thorough research into the particular virus.
  
  
• Boot sector viruses: Boot sector viruses infect or substitute their own code for either the DOS boot sector or the Master Boot Record (MBR) of a PC. The MBR is a small program that runs every time the computer starts up. It controls the boot sequence and determines which partition the computer boots from. The MBR generally resides on the first sector of the hard disk. Since the MBR executes every time a computer is started, a boot sector virus is extremely dangerous. Once the boot code on the drive is infected, the virus will be loaded into memory on every startup. From memory, the boot virus can spread to every disk that the system reads. Boot sector viruses are typically difficult to remove, as most antivirus programs cannot clean the MBR while Windows is running. In most cases, it takes bootable antivirus disks to properly remove a boot sector virus.
  
  
• Worms: Worms are very similar to viruses in that they are computer programs that replicate functional copies of themselves (usually to other computer systems via network connections) and often, but not always, contain some functionality that will interfere with the normal use of a computer or a program. The difference is that unlike viruses, worms exist as separate entities; they do not attach themselves to other files or programs. Because of their similarity to viruses, worms are often also referred to as viruses.
  
  
• Trojan horses: Named after the wooden horse the Greeks used to infiltrate Troy, a Trojan horse is a program that does something undocumented which the programmer intended, but that the user would not approve of if he or she knew about it. According to some people, a virus is a particular case of a Trojan horse, namely one which is able to spread to other programs (i.e., it turns them into Trojans too). According to others, a virus that does not do any deliberate damage (other than merely replicating) is not a Trojan. Finally, despite the definitions, many people use the term "Trojan" to refer only to a non-replicating malicious program.

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CMOS

CMOS, short for Complementary Metal Oxide Semiconductor, is a low-power, low-heat semiconductor technology used in contemporary microchips, especially useful for battery-powered devices. The specific technology is explained in detail on this CMOS definition page.

Most commonly, though, the term CMOS is used to refer to small battery-powered configuration chips on system boards of personal computers, where the BIOS stores the date, the time, and system configuration details.

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BlackBerry Enterprise Server (BES)

The BlackBerry Enterprise Server (BES) Redirector is a billed service offered by UITS to Indiana University faculty and staff. With a BES data plan you purchase from your cellular provider, the IU BES Redirector service enables full access to your IU Exchange email account (including mail, calendar, tasks, etc.) from your BlackBerry device.

How email redirection works

A BlackBerry device requires a special data plan (from your cellular provider) and a redirector to forward email from your mailbox to the wireless network provider and then to your device. Two options for redirectors are available:

• The BlackBerry Desktop Redirector runs on your personal computer, monitoring your mailbox and redirecting a copy of each new message it finds.
  
  
• A redirector can also be a server that does the same for many people's mailboxes at once. At Indiana University, UITS provides a large enterprise solution, the BES Redirector, for those with an Exchange account.
  

Advantages of using the IU BES

For the following reasons, UITS recommends that you use the IU BES Redirector rather than the Desktop Redirector:

• If you use the Desktop Redirector, your computer must be running the Desktop Redirector and be logged into the mail server at all times. Simply turning the computer on is not sufficient, as the Desktop Redirector cannot be installed as a service; it must run as a desktop application. Using the IU BES Redirector (again, only if you have an Exchange account) frees you from this constraint.
  
  
• The IU BES service allows for centralized management of BlackBerry accounts, which can help UITS quickly troubleshoot and fix problems.
  
  
• The IU BES Redirector provides features unavailable through the Desktop Redirector:
  
  
  • Global Address List (GAL) lookups: Using the Desktop Redirector, you can do lookups only in the address book kept on the device itself.
    
    
  • Wireless data synchronization: If you use the Desktop Redirector, you must cradle your BlackBerry to synchronize your data (e.g., calendar, contacts, tasks), but the IU BES allows wireless synchronization.
    
    
  • Attachment rendering: Not possible with the Desktop Redirector
    
    
  • Wireless password reset: The Desktop Redirector does not provide for remote password reset.
    

How to get an account

The information below applies to BES accounts purchased by IU departments for their employees. Individuals can purchase their own IU BES accounts if the need arises.

Your department's telecommunications coordinator must authorize the request for a departmentally purchased account on the BES Redirector service at IU. Your coordinator will need your username and the departmental account number for billing in order to make the request.

At Indiana University Bloomington, if you do not know who your telecommunications coordinator is, complete this online form. Select faculty or staff, and click Continue. Click No, and then Continue again. From the menu for the service you're interested in, select the name of your department. Your coordinator's contact information will then appear.

To request the account, coordinators should send the individual's name, email address, and account number to commreq@indiana.edu .

How to cancel your account

To cancel your IU BES account, send email to commreq@iu.edu requesting disconnection from the IU BES.

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BlackBerry

A BlackBerry is a handheld wireless device created by Research in Motion (RIM). BlackBerries read email and calendars from enterprise-class email systems, such as Indiana University's Exchange service, and most models also function as cell phones.

While a BlackBerry is a type of personal digital assistant (PDA), it is not meant to be used in the same way as a Palm Pilot or PocketPC. Those devices are literally miniature computers that in some cases happen to have email capabilities. A BlackBerry is an email/calendar reading device with some PDA abilities, and in some cases cell phone abilities. Also, BlackBerries come with complete alphanumeric keyboards; many PDAs do not.

At IU, BlackBerry service consists of the following:

• The BlackBerry device
• Email redirection, managed in one of two ways:
  
  
  • The BlackBerry Enterprise Server (BES), which works directly with the Exchange mail server. UITS recommends this option if you have an IU Exchange account.
  • The BlackBerry Desktop Redirector runs on your personal computer and redirects messages as they arrive in Outlook. You can use this option with any Outlook mail setup (i.e., POP, IMAP, HTTP).
    
    

A BlackBerry receives email through the following process:

1. The Exchange account receives the message.
2. The redirector looks in the email account, finds the message, and forwards it to the BlackBerry service provided by RIM.
3. RIM's BlackBerry service sends the message to the wireless data network (e.g., AT&T, Verizon).
4. The wireless data network provider sends the message in a wireless signal to the BlackBerry device. (You must be in a data coverage area to receive mail.)
5. The BlackBerry receives the signal and displays the message.
   
   

A BlackBerry sends mail in the reverse of this process. The BlackBerry device sends the message to the wireless data network provider. The provider forwards it to RIM's BlackBerry service, which in turn sends it over the Internet to the redirector (either the BES server or desktop software). The redirector then sends the message to your Exchange account, from which it is sent over the Internet to the recipient.

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What are bandwidth, latency, and speed?

Bandwidth and latency are attributes that characterize the speed of a network.

Bandwidth

Bandwidth, typically measured in bits, kilobits, or megabits per second, is the rate at which data flows over the network. This is a measure of throughput (amount per second) rather than speed (distance traveled per second). Just as more water flows through a wide river than a small, narrow creek, a high bandwidth network generally can deliver more information than a low bandwidth network given the same amount of a time. Because this can make the network feel faster, high bandwidth networks and connections often are called "high-speed". Residential cable and DSL Internet connections often are advertised as high-speed connections, even though the actual speed of the information traveling from one end to another is roughly the same for cable, DSL, and normal phone connections.

Latency

Latency, usually measured in milliseconds, is the time that elapses between a request for information and its arrival. A high latency can degrade the performance of even the largest capacity network to a tremendous degree. Because it takes time for a signal to pass through wire, some latency will always be present, but slow servers, inefficient data packing, and excessive network hopping can collectively increase transmission delay.

Excess latency gives a network a low-speed feel. If a connection takes three or four seconds to respond, many users will complain the connection is "slow", even though the bandwidth is high, and even though the data comes in such a large chunk that it appears to arrive all at once.

Speed

A network's speed is essentially a subjective evaluation of the combination of bandwidth and latency. As mentioned above, the term is often used in place of bandwidth, even by technicians and professionals; many times a network administrator or hardware technician will talk about a 10BaseT, 100BaseT, or gigabit "speed" in reference to products or networks with 10KB/sec, 100KB/sec, or 1,000KB/sec bandwidths.

Most vendors advertise the theoretical bandwidths of their networking products, but due to bottlenecks, hardware problems, and high processing loads, the effective throughput is usually much less. A gigabit (1000BaseT) Ethernet card will be lucky to achieve 800Mb/s in real-world use, and in many situations will achieve far less than that.

For a scorecard of bandwidths and other networking characteristics, see:

http://www.csgnetwork.com/bandwidth.html

The page above doesn't address latencies, but modems typically have values of around 100 milliseconds, vastly higher than any of the technologies reviewed on the scorecard. For a good overview of latency and its effects, read Stuart Cheshire's It's the Latency, Stupid at:

http://rescomp.stanford.edu/~cheshire/rants/Latency.html

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AirPort, AirPort Extreme, and AirPort Express?

Introduced by Apple Computer in 1999, AirPort is a wireless networking technology based on the 802.11b standard. In 2003, Apple upgraded the AirPort product line to the faster 802.11g standard, renamed it AirPort Extreme, and ceased development of the original AirPort.

There are actually three current AirPort products: a wireless router called the AirPort Extreme Base Station, a mini Base Station called AirPort Express, and a special kind of wireless card called the AirPort Extreme Card. The Base Station is a wireless hub through which as many as 50 computers may communicate at up to 11Mbps (AirPort) or 54Mbps (AirPort Extreme). The Base Station can extend the network to a LAN or the Internet through its built-in Ethernet or modem port.

AirPort Express is a sort of mini Base Station which allows you to set up an instant wireless network, and to use a feature called AirTunes, which allows you to play your iTunes playlists wirelessly from your computer to your stereo. Although it supports fewer users at at time than the Base Station, AirPort Express can also function as a bridge to extend the range of an AirPort Extreme Base Station.

With an AirPort or AirPort Extreme Card installed, a Macintosh may participate in an AirPort network or any other wireless LAN that conforms to the 802.11 DSSS standard. All Macintosh computers manufactured after 2003 support AirPort Extreme; to determine whether your computer supports AirPort or AirPort Extreme, you can visit Apple's product specifications pages below:

http://support.apple.com/specs/ http://support.apple.com/kb/TA25953?viewlocale=en_US

Both the Airport Extreme Card and Base Station have a range of about 150 feet and are not limited to line-of-sight; the range of the AirPort Express is from 50 to 150 feet and is also not limited to line-of-sight. Additional products such as antenna attachments, bridges, and extenders can extend the range even further. The network can even be sustained through closed doors and walls. However, the range and quality of the connection will be affected by the surrounding building material.

For more information about AirPort Extreme, visit: http://www.apple.com/airportextreme/

For more information about AirPort Express, visit: http://www.apple.com/airportexpress/

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Abilene

The Abilene network is a high-performance backbone network that connects regional network aggregation points, called GigaPoPs. Abilene is a partnership of Internet2, Qwest Communications, Nortel Networks, Juniper Networks, and Indiana University. The Abilene network supports the development and deployment of advanced Internet applications and network services by Internet2 universities and research labs. Abilene complements existing research networks around the world.

IU is one of a select number of universities that participated in Abilene's Launch Group. IU runs the Abilene Network Operations Center; for more information, see the Abilene NOC web site and the Chronicle of Higher Education article on IU as the nerve center for Internet2.

For more, see the Internet2 site.

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CompTIA A+ certification

A+ (A Plus) is an entry level computer certification for PC computer service technicians. The exam is designed to certify the competency of entry level PC computer service professionals in installing, maintaining, customizing, and operating personal computers.

The A+ certification is sponsored by the Computing Technology Industry Association (CompTIA). CompTIA is a large trade group, founded in 1982 and made up of resellers, distributors, and manufacturers. It sets voluntary guidelines dealing with business ethics and professionalism, and is involved with many issues including product returns, warranty claims, and price protection.

The A+ exam contains situational, traditional, and identification types of questions. All of the questions are multiple choice, and there is only one answer for each question. The A+ exam is open to anybody, although it is designed to be taken by those with at least six months of job experience as service technicians.

Currently, A+ is the only major non-vendor-specific hardware certification available for IBM-compatible computer systems. Increasingly, many help desk positions as well as service centers are requiring A+ certification or similar experience as a basis for hiring.

CompTIA also sponsors certification for document imaging (Certified Document Imaging Architech [CDIA]) and a network certification exam (Network+). The CompTIA certifications are in general more basic and less product-specific than other certifications, such as Microsoft's MCSE or a Novell CNE.

CompTIA formerly offered a Macintosh module and certificate in the repair and installation of Apple computer systems. This module has been discontinued for several years, and currently the only hardware certification for Macintosh computer systems is available through Apple. You can find more information on the Apple service certification at:

http://www.apple.com/support/products/techtrain.html

For additional information on A+ Certification, visit:

http://www.comptia.org/

You can take the A+ certification exam, as well as many other certifications, at a number of testing centers around the world. To register for an exam via one of these centers, Sylvan Prometric, see Sylvan's online registration web page at:

http://securereg3.prometric.com/

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Cisco Systems 18th anniversary of BGP

18th anniversary of BGP. In this talk we examine the evolution of BGP over these 18 years, and look at the lessons we could learn from this.

Dr. Yakov Rekhter joined Juniper Networks in Dec 2000, where he is a Distinguished Engineer. Prior to joining Juniper, Yakov worked at Cisco Systems, where he was a Cisco Fellow. Prior to joining Cisco in 1995, he worked at IBM T.J. Watson Research Center.

Yakov Rekhter was one of the leading architects and a major software developer of the NSFNET Backbone Phase II. He co-designed the Border Gateway Protocol (BGP). He was also one of the lead designers of Tag Switching, BGP/MPLS based VPNs, and MPLS Traffic...

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Optical Storage Devices

Optical Storage Devices - CD DVD Burner -Computer Hard Drive - Data Recovery - Storage Devices - CD Rom - DVD CD - DVD Storage - CD Rewritable - CD R - CD RW

Today, the most widely used and reliable storage devices are the optical storage devices. These devices use laser technology to store and read data to and from the disk. The most popular optical storage devices are: CD-ROM drive, DVD-ROM drive, CD-Recordable drive, CD- Rewritable drive etc. Today, all PCs also contain one CD-ROM drive. These devices use laser light to write/read data to and from the optical storage media such as CDs (compact disks). A large amount oil data, software, movies and songs etc. can be stored on a single CD. Some optical storage media is read-only while others are read and write.

An optical storage media consists of a flat, round, portable metal disc, which is coated with a thin metal or plastic or other material that is highly reflective. These discs usually are 0.75 inches in diameter and less than one-twentieth of an inch thick.

The information on the optical disk is stored in the form of pits and lands. The pits are the tiny reflective bumps that are created with laser beam. The lands are flat areas separating the pits. A land reflects the laser light, which is read as binary digit 1. A pit absorbs or scatters light, which is read as binary digit 0. The high-powered laser beam creates the pits. A lower-powered laser light reads data from the disc. Like tracks on a magnetic disk, the tracks of an optical disk are divided into sectors but shape of these sectors is different than sectors of magnetic disk.

The operating system assigns a letter to the optical storage devices that come after all the hard disks and other portable disks. For example, if a computer has one floppy drive, one hard disk, one Zip disk drive and one CD-ROM drive then letters assigned to drives will be as under:

'A' for floppy disk drive
'C' for Hard disk drive
'D' for zip disk drive
'E' for CD-ROM drive

CD-ROM

CD-ROM stands for Compact Disc Read-Only-Memory. CD-ROM is a type of optical disc that uses laser technology to store and to read data to and from the disc. A large amount of data can be stored on a single disk. Once the information is stored on the CD-ROM, it becomes permanent and cannot be changed (altered). The information can only be read for processing. Therefore, it is called Compact Disc Read Only Memory.

Now-a-days CDs are commonly used in personal computers. The CD-ROM is removable and can be used to transfer data from one computer to another like a floppy disk. The storage capacity of CD-ROM is 1000 times greater than floppy disk. A typical CD-ROM has storage capacity from 650 MD to 1GB. Today, most of the software are available on the CDs. The software companies distribute their products on the CDs. For example Microsoft Office is available on one or two CDs. Similarly, Windows operating system is also available on one CD.


CD-ROM drive


The CD-ROM drive is used with computer to read the information from the CD-ROM. The data transfer rate of first CD-ROM used with computer was 150 KBps (Kilobytes per second). It was known as single speed drive and is denoted by X. This rate is much slower than that of a typical hard disk drive that reads data at a rate of 5 to 15 MBps (megabytes per second). Manufacturers measure the speed of all CDROM drive relative to the first CD-ROM drive. Today, CD-ROM drives have transfer rates (or speeds) ranging from 48X to 75X or more. For example, a 48X CD-ROM drive has a data transfer rate of 7,200KBps (i.e. 48 x 150 = 7200) or 7.2 MBps. It. means that the higher the number, the faster the CD-ROM drive. However, the faster CD-ROM drives are more expensive.

DVD-ROM

DVD stands, for Digital Video Disc or Digital Versatile Disc. DVD-ROM is an extremely high capacity optical disc with storage capacity from 4.7 GB to 17 GB. DVD disc is specially used to store movie films. It is also used to store huge databases, music, complex software etc.

The latest generation of DVD-ROM disks actually uses layers of data tracks; it is because the storage capacity of DVD-ROM is very high. The DVD-ROM drive or DYD player reads data from the first layer, and then look through it to read data from second layer and so on.

Some DVD-ROMs are double sided. It means data is stored on both sides of the disc. A DVD-ROM looks like a CD-ROM. Although the size and shape is similar to CD-ROM but DVD-ROM stores information in different manner A DVD-ROM drive can read ordinary CD-ROM disks.

CD-R

CD-R stands for Compact Disc Recordable. It is a blank disk that is used to store information. The user can also write data on an optical disc. The process of writing data on the optical disc is called burning. A locally developed CD-R can be used in any CD-ROM drive. A CD-R is functionally equivalent to a pre-recorded CDROM. Mostly the users use the CD-R to store their valuable data and software. It must be noted that once data is written on the CD-R. It cannot be changed. However, you can store data on other part of the disk until it is full. Each part of a CD-R can be written only one time and can be read as many times. Many utility programs are available to write data on CD-R but the most popular and commonly used software for personal computers is "Nero Burning ROM". Windows has its own built-in software to write data on CD-R.

Today most of the important data is backed up on the CD-R and it is the most reliable medium. The CD-writer is used to write data on CD-R.

The main disadvantage of CD-R is that information can be written only once. These cannot be overwritten and erased. The CD-ROM is also slow in accessing as compare to hard disk.

CD-Writer

A CD-writer or recorder (or simply CD-R drive) is used to write data on CDR disks. Usually, a CD-writer can read information from CD as well as write information on CD. The locally produced CD-R disks are created with CD Writers. Today, most of the PCs have CD writer.

The speed of these drives is up to 48X or more. These drives are more expensive than ordinary CD-ROM.

CD-RW

CD-RW stands for compact Disc Rewritable. The CD-RW is a new generation of optical disk. It is erasable disc. The user can write and over-write data on the CD-RW disc many times. The CD-RW disc is also referred to as erasable CD (or CD-E). The CD-RW acts like a floppy and hard disk that allow users to write and re-write data. However, the reliability of the disc tends to decrease, each time you rewrite data.

Both CD-R and CD-RW are used for taking backup of important data from a hard disk. These are also used to create audio CDs. For example, you can record your own music or movies from purchased CDs.

CD-RW Drive

You must have a CD-RW drive to write data on the CD-RW. These drives have read and write speed is up to 48X or more but the re-write speed is 10x or more. The CD-RW drive is advanced and more expensive than CD-R drive. It can write data on both CD-R and CD-RW discs and also can read data from them. Today, most of the PCs have CD-RW drive.

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Mobile Storage Devices

Mobile Storage Devices - Smart Card Reader - Smart Card - Data Storage - Flash Memory - Compact Flash - Memory Cards - Card Memory - Storage - Flash Drives

There are numerous types of mobile storage devices. The most important ones are:

1. Online Storage
2. Smart Cards
3. Flash Memory Devices

1. Online Storage

Online storage is a website on the Internet that offers the storage of data for free of cost or against some payment through credit card. The capacity of storage depends upon the packages offered by the website owner. Through the website, data is stored on a computer which remains online 24 hours a day and 7 days a week.

When you connect to the website, you can browse through your allocated memory space just as you browse with the help of Windows Explorer on your personal computer. Thus you can access your data/information wherever you travel throughout the world. National or international travelers having laptops or handheld computers mostly enjoy the online storage facilities. Many companies offer online storage facilities but www.webdepositbox.com is a famous online storage service that allows users to store, access, and organize files.

2. Smart Cards

A smart card is a small card normally of the size of credit card or ATM card. Thus you can store data/information in the card and sometimes miner processing of data/information can also be made by its built-in microprocessor. In order to read and write data on a smart card, you need a special device called smart card reader.

There are two types of smart cards:

1. Intelligent Smart card
2. Memory Smart card

An Intelligent Smart card contains a built-in microprocessor and has input, processing, output, and storage facilities. Whereas a Memory Smart card gives only data storage facility. Many digital cameras, laptops and handheld computers nowadays use smart cards.

3. Flash Memory Devices

Flash memory is a type of non-volatile memory that can be erased electronically and reprogrammed, similar to EEPROM. Most of the PCs also use flash memory to hold their startup instructions.

Flash memory is also known as Flash ROM. The Flash memory is used to upgrade I/O devices by upgrading the new software purchased from market into the Flash memory. The early I/O devices were upgraded by replacing the old circuit board or chip with a new one. It was a time consuming and costly method. The Flash memory solves this problem of the user. When new hardware devices are added to the computer, the information about devices are configured and stored in the flash memory. It is available in size up to 512MB. It does not require a battery to maintain its contents. It is more expensive than the hard disk storage.

Flash memory chips are also used in mobile computers and devices to store data and programs. For example, these are used in PDAs, digital cellular telephones, set-top boxes, digital voice recorders, pagers etc. When you enter names and addresses into PDAs, a flash memory chip stores the data. The flash memory chip in a digital cellular telephone stores names and telephone numbers. The flash memory is also used in digital camera. When we take pictures with digital camera, these are stored in a flash memory rather than on photographic film.

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Cisco Catalyst 6500 Series Application-Oriented Networking Module

Cisco Catalyst 6500 Series Application-Oriented Networking Module

Available for the Cisco Catalyst 6500 Series, the Cisco Catalyst 6500 Series Application-Oriented Networking Module (AON SM) is a service module that can be installed in any Cisco Catalyst 6500 Series Switch to take full advantage of the switch's high availability, security, and traffic-management capabilities. Cisco AON SM provides application-level intelligence, improved message visibility and security, and reduces total cost of ownership by consolidating elements of the network and application infrastructures and providing centralized management capabilities. All technical documentation and support information for the Cisco AON SM can be found from http://www.cisco.com/.

For ordering information in North America and Europe, please call your Cisco account representative or contact your local Cisco sales office for further details.

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Improve Application Visibility and Traffic Control

Many companies need a way to track application use, manage network bandwidth, identify and dispose of unwanted traffic, and prioritize mission-critical applications on a per-user basis. Unlike controlled Systems Network Architecture (SNA) environments, IP-based environments lack the structure to ensure appropriate application behavior. As a result, mission-critical applications must contend for available bandwidth with noncritical and unwanted applications, and many applications are subject to network latency and jitter that impede their ability to function properly.

Your IT department needs a solution that can prioritize application traffic and control the behavior of network traffic to help ensure that individual applications are performing optimally based on their importance to business operations. Based on application classification and control technology from the Cisco Service Control product family, the Cisco Application Performance Assurance Network Module provides application identification and prioritization for today’s demanding enterprise networks.

Features and Benefits

• Identifies and classifies applications and protocols
• Identifies network users and determines their application and network usage patterns (requires integration with existing authentication system)
• Offers a variety of reports from 100 available templates to represent existing network traffic
• Provides traffic management capability required to prioritize, block, or redirect traffic as required to minimize congestion, improve application performance, and plan more effective network bandwidth upgrades

The Cisco Application Performance Assurance Network Module solution consists of a hardware module (NME-APA-E2 or NME-APA-E3) designed for insertion into a Cisco 2800 or 3800 Series Integrated Services Router, a software license that enables view and report capability or view, report, and control capability; and the Application Performance Assurance Device Console (APA DC) which provides integrated device management, reporting, and administration in a GUI-based application.

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Cisco 2600/2800/3700/3800 Series AON Module

Cisco 2600/2800/3700/3800 Series AON Module

The Cisco 2600/2800/3700/3800 Series Application-Oriented Networking Module (Cisco AON NM) can be installed in any Cisco 2600/2800/3700/3800 Series of routers. Cisco AON NM provides application-level intelligence, improved message visibility and security, and reduces total cost of ownership by consolidating elements of network and application infrastructures and providing centralized management capabilities. Cisco AON NM enables dramatically higher levels of application and service integration at the branch office, which extends enterprise- and provider-class versatility, integration, and power to branch offices. For ordering information in North America and Europe, please call your Cisco account representative or contact your local Cisco sales office for details.

The Cisco AON Network Module (NM) can be installed in any Cisco 2600 or 3700 Series of routers as well as the Cisco 2800 Integrated Services Router and the Cisco 3800 Integrated Services Router. All technical documentation and support information for the AON Network Module can be found from http://www.cisco.com

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Cisco AON Networking Appliance Routes Application Messages

The Cisco AON 8340 Series Appliance is a standalone device that provides routing capabilities for application messages traveling on the network. The network's ability to identify and intelligently route application messages, such as customer orders, can help your company improve efficiency of business processes. Benefits of the appliance include:

• Offers an additional deployment option to existing Cisco AON interface modules, which are available for Catalyst 6500 Series switches and Cisco 2600/2800/3700/3800 series routers
• Leverages AON feature breadth to support multiple applications
• Offers High performance augmented by custom hardware acceleration
• Integrates with existing infrastructure and network management applications

The Cisco AON 8340 Series Appliance has several deployment options including:

• High-performance message routing
• Application-to-application security gateway (A2A)
• Application services offload

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Application-Oriented Networking

Component Integration Allows Flexibility

The Cisco AON state-of-the-art design pre-integrates hardware and software components into a complete subsystem that can be flexibly deployed as an embedded network function in enterprise data centers, service-provider networks, branch offices, or other deployments.

Cisco AON is available in two versions that integrate into the Cisco family of switches and routers:

• Cisco Catalyst 6500 Series Application-Oriented Networking Module, which is a service module that is primarily deployed in the enterprise core and enterprise data centers
  
  
• Cisco 2600/2800/3700/3800 Series Application-Oriented Networking Module, which is a network module that is primarily deployed at the branch office

Both the AON SM and the AON NM offer a high level of performance while providing a cost-effective solution to meet enterprise, service provider, and small-and-medium business organization needs. The Cisco AON modules also include software tools for managing and provisioning AON nodes, as well as for designing application policies using a library of "bladelets" that can be configured in different sequences as required. The modules also include a software development kit and API for flexible extension to any custom environment, operation, or format.

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Firefox Trojan Steals Passwords

A new Trojan horse program identified by anti-malware company BitDefender as Trojan.PWS.ChromeInject.B works as a Firefox plug-in.

Two files, one Javascript and one Windows executable, conspire to steal user logon credentials whenever you log on to one of 103 domains, largely belonging to banks (see the BitDefender link for the complete list). The sites are largely out of the US.

BitDefender identifies ChromeInject as "...the first malware that targets Firefox." It's the first we've heard of as well. The writeup has no information on how the file is being distributed or if it's mislabeled as something else, but they give it a spreading factor of "very low".

Take this as a warning, in case you thought otherwise, that Firefox is vulnerable to all the usual forms of attack. Use common sense when surfing even in Firefox, and especially when installing plug-ins.

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Bit DefenderTota Security 2009 v12.0.10

Bit Defender Total Security 2009 | 94 MB Unlike other security solutions, which rely heavily on a list of pre-existing viruses, BitDefender security solutions use proactive B-HAVE technology that identifies and blocks new and zero-day threats. Additionally, BitDefender Total Security 2009 System?s maintenance and backup tools keep PCs running at optimal speed and protected from data loss.

DOWNLOAD

PATCH

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Online Virus Detector any of ur Computer File

Virustotal is a service that analyzes suspicious files and facilitates the quick detection of viruses, worms, trojans, and all kinds of malware detected by antivirus engines

www.virustotal.com

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Email Communication using Microsoft Outlook Express

Microsoft Outlook Express is a utility program that is used to send and receive e-mails and to manage newsgroups. It is built-in utility program of Windows.

To open Microsoft Outlook Express, follow these steps.

• Select "Programs" from Start menu.
• Select "Microsoft Outlook Express" from "Programs" menu.

OR

• Click mail Button on the toolbar of Internet Explorer.

Composing and Sending E-mail

Composing e-mail means to prepare a message that is to be sent. It is composed very easily in any e-mail utility program. The free mail service also has this facility, when any one of the e-mail programs is used to prepare the e-mail, a window is opened that has the following elements.

To - It is a text box used to enter the e-mail address of person to whom you want to send mail. More than one c-mail addresses separated with commas can be entered into this box.

Subject - In this textbox the subject or title for the c-mail is written.

CC - CC stands for carbon copy. It is used to write e-mail address of another person.

BCC - BCC stands for blind carbon copy. It is same as CC but email address given in this field is not shown to the other recipients.

Message Box - The main message is typed in this main box.

Send Button - Used to send the e-mail.

Delete Button - Used to delete the e-mail.

Attaching File - You can attach files of any type with message you compose and send via e-mail. This process is called attaching files. You can send complete software to anyone via e-mail. Usually, the files are compressed or zipped using Zip utility programs before to attach with e-mail.

To attach a file to an e-mail, click the Attach icon on the toolbar of New Message window, Insert Attachment dialog box will appear as shown below. Select the file you want to attach and click the Attach button. You can attach mere than one files by following the same procedure.

Replying E-Mail

Sending back an e-mail that one has received to the sender person with new message is called replying e-mail. When you select a message sent by you and click Reply icon, Microsoft Outlook Express opens a New Message window. All the fields of the composing window will be filled with the information sent by sender. For example, email address of the sender is filled in “To:” and so on. Type new message and click the Send button to send the message.

Forwarding E-mail

Sending an e-mail message that one has received to another person is called forwarding e-mail. When you select a message sent by you and click Forward icon, Microsoft Outlook Express opens a New Message window containing the original message. Enter the e-mail address(s) and click the Send button to send the message. You can also forward an e-mail message with attached file by choosing "Forward As Attachment" from Message menu of Microsoft Outlook Express window.

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Uses of Online Communication!

There are many uses of online communication but the most popular uses of online communication are described below.

Internet Telephony

Internet telephony enables users to talk over the Internet. The Internet telephone software is available to use the Internet telephony. When the user speaks into a microphone, the Internet telephone software and computer’s sound card convert the sound signals into digital signals and transmit them over the Internet to the called person. Software and devices used at the receiver’s end receive the signals and convert to analog signals so the receiving person can hear your voice.

Internet Printing

Today, network printers are also available having web addresses built into them. The user cast send a print job to the network printer from anywhere in the world. A printer with Internet capability can also receive print jobs from desktop computers, mobile computers or devices and smart phones. Many hotels and Airlines use the Internet printing.

Collaboration

Much software provides a means to work (or collaborate) online with other users connected to a server. The users can also conduct online meetings with Microsoft Office XP. An online meeting allows users to share documents with others in real time. It means that all the participants can see the document at the same time. You can also type and send messages to others etc.

Workgroup & Workgroup Computing

In a computer network, people can work together online as a group even when they are thousands of miles away from each other. This concept of working together is called workgroups. Therefore workgroup may be defined as a group of people (or individuals) working together on a given project and sharing information via computer networks.

A group of people can share work together by means of linked computers. The phenomenon of sharing information by various members of workgroup is called Workgroup Computing.

The members of workgroup, who are thousands of miles away from each other cannot only share information but can also talk to each other on a computer network while seeing each other as they talk. They can also send and receive messages to each other.

Global Positioning System (GPS)

Global Positioning Systems (GPSs) help to create maps, locating and monitoring people and objects. These systems are also used in new cars to provide directions and other information.

A Global Positioning System (GPS) consists of one or more earth-based receivers that accept and analyze signals sent by satellite(s) and determine the receiver’s geographic location. A GPS receiver is a handheld or embedded device that contains an antenna, a radio receiver, a processor, and a display screen that shows an individual’s location on a map.

Short Message Service (SMS)

Short Message Service (SMS) is a means for smart phone, cellular telephone, or PDA users to send and receive shod text messages. Most SMS messages have a limit of about 160 characters per message. SMS was introduced in 1995. SMS is used for business and social purposes.

When a user sends a message, a SMS center receives it and routes it to the appropriate smart phone, cellular telephone, or PDAs. If the receiver’s phone is out of range or inactive, the SMS center holds onto the message and delivers it when that one becomes active.

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The Telephone Network

The public switched telephone network (PSTN) is the world-wide telephone system and usually this network system uses the digital technology. In the past, it was used for voice communication only but now it is playing very important role for data communication in the computer network such as in the Internet. There are different types of telephone lines that are used for data communication in the network. These are discussed below.

1. Dial-Up Lines

It is a temporary connection that uses one or more analog telephone lines for communication. Modem is used at the sending end as well as at the receiving end. A telephone number is dialed from the sending end through modem and the modem at the receiving end answers the call. In this way, connection is established for data communication between computers or electronic devices. In dial up line connection, the cost of data communication is very low. The mobile users can also access the Internet through this connection.

2. Dedicated Lines

It is a permanent connection that is used to establish connection between two devices permanently. It is better than dial-up line connection because dedicated lines provide a constant connection. These types of connections may be digital or analog. The data transmission speed, of digital lines is very fast as compare to analog dedicated line. The data transmission speed is also measured in bits per second (bps). In dial-up and dedicated lines, it is up to 56 Kbps. The dedicated lines are mostly used for business purposes. The most important digital dedicated lines are described below.

1) ISDN Lines

ISDN stands for Integrated Services Digital Network. It is a set of standards used for digital transmission over telephone line. The ISDN uses the multiplexing technique to carry three or more data signals at once through the telephone line. It is because the data transmission speed of ISDN line is very fast. In ISDN line, both ends of connections require the ISDN modem and a special telephone set for voice communication. Its data transmission speed is up to 128 Kbps.

2) DSL

DSL stands for Digital Subscriber Line. It is another digital line. In DSL, both ends of connections require the network cards and DSL modems for data communication. The data transmission speed and other functions are similar as ISDN line. DSL transmits data on existing standard copper telephone wiring. Some DSLs provide a dial tone, which allows both voice an4 data communication.

3) ADSL

The ADSL (Asymmetric Digital Subscriber Line) is another digital connection. It is faster than DSL. ADSL is much easier to install and provides much faster data transfer rate. Its data transmission speed is from 128 Kbps up to 10 Mbps. This connection is ideal for Internet access.

4) Cable Television Line

The Cable Television (CATV) line is not a standard telephone line. It is a dedicated line used to access the Internet. Its data transmission speed is 128 Kbps to 3 Mbps.

A cable modem is used with the CATV. it provides a high speed Internet connections through the cable television network. A cable modem sends and receives digital data over the cable television network.

To access the Internet using the CATV network, the CATV Company installs a splitter inside your house. From the splitter, one part of the cable runs to your television and other part connects to the cable modem. A cable modem usually is an external device, in which one end of a cable connects to a CATV wall outlet while the other end plugs into a port (such as on an Ethernet card) in the system unit.

5) T-Carrier Lines

It is very fast digital line that can carry multiple signals over a single communication line whereas a standard dialup telephone line carries only one signal. T-carrier lines use multiplexing so that multiple signals share the line. T-carrier lines provide very fast data transfer rates. The T-carrier lines are very expensive and large companies can afford these lines. The most popular T-carrier lines are:

1. TI Line
2. T3 Line
   
   

i) T1 Line

The most popular T-carrier line is the Ti line (dedicated line). Its data transmission speed is 1.5 Mbps. Businesses often use Ti lines to connect to the Internet. Many ISPs use Ti, lines to connect to the Internet backbone. Another type of TI line is the fractional TI line. It is slower than TI line but it is less expensive. The home and business users use this line to connect to the Internet and share a connection to the Ti line with other users.

ii) T3 Line

Another most popular and faster T-carrier line is T3 line. Its data transmission speed is 44 Mbps. It is more expensive than Ti line. The main users of T3 line are telephone companies and ISPs. The Internet backbone itself also uses T3 lines.

6) Asynchronous Transfer Mode (ATM)

It is very, fast data transmission connection line that can carry data, voice, video, multimedia etc. Telephone networks, Internet and other network use ATM. In near future, ATM will become the Internet standard for data transmission instead of T3 lines. Its data transmission speed is from 155 Mbps to 600 Mbps.

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Network Topologies

In networking, the term topology is the way of connecting computers or nodes on a network. There are many ways in which computers are connected together in a computer network. Therefore network topology is defined as: the schemes of joining a number of computers in the form of a network are called Network Topologies.

We know that two or more devices are connected to a link for data communication. Similarly, two or more links form a topology. The topology of a network is the geometric representation of the relationship of all the links and the nodes (communication devices) to one another.

There are three commonly used network topologies. These are:

1. Star topology
2. Ring topology
3. Bus topology

1. Star Topology

In a star network, each node (computer or other device) is directly connected to the central computer or Hub that provides connection points for nodes on the network. The star topology is the most common topology in use today. In star network, information or data is communicated from one computer to another through Hub. This form of network configuration looks like a star as shown in figure below.

Advantages

The main advantages of star topology are:

• It is easy to install and to maintain.
• You can easily add and remove nodes to and from the network without affecting the network.
• If any node fails, other nodes are not affected.

Disadvantages

The main disadvantages of star topology are:

• This type of network depends upon the central Hub. If Hub fails the entire network is failed.
• Each computer is directly connected to the Hub through a cable, so it becomes more costly.

2. Ring Topology

In ring network, each node is connected to two adjacent nodes in the form a closed ring or loop. In ring topology, the last node connects to the first node to complete the ring. In ring topology, each node has a dedicated point-to-point connection only with the two devices on either side of it.

In this network, data is communicated in one direction from node to node around the entire ring. When a computer in ring network sends message to another computer on the network, the message travels to each node or computer until it reaches its destination. The ring network configuration is shown in figure below.

Advantages

The main advantages of ring topology are:

• It is less expensive than star topology.
• Nodes can be easily added or removed.

Disadvantages

The main disadvantages of ring topology are:

• It is more difficult to install and maintain.
• If a node fails, it affects the entire network.

3. Bus Topology

In bus network, all nodes are connected to a common communication medium or central cable. The central physical cable that connects the nodes is called Bus. The data is communicated between nodes in both directions through bus. A bus topology uses the multipoint connection. The central single cable (or bus) acts as backbone to link all the devices to the network.

In bus network, when a computer sends a message to another computer it also attaches the address of the destination computer. In bus topology, a special device called a terminator is attached at the cable’s start and end points. A terminator stops the network signals.

In LAN, bus topology is mostly used. In this topology, each computer is assigned a unique address. The bus network configuration is given in figure image.

Advantages

The main advantages of bus topology are:

• It is less expensive and easy to install and maintain.
• When nodes are added and removed to and from the network, the network is not affected.
• If one node fails other nodes are not affected.

Disadvantages

The main disadvantages of bus topology are:

• It supports only a small number of nodes.
• Entire network fails if there is any problem in the central cable.

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