Cisco CCNA Certfication: Introduction to ISDN, Part I
?>
Download eBooks and Software
 Fully Verified Winning System Since 1999 & Vip Club Picks!
Winning Sports Picks & Predictions By Zcodesystem.com - Nhl, Nfl, Mlb And Nba Predictions And Picks From The Best Experts In The Industry + Fully Automated System Proven Since 1999 Awesome Conversion 5.26% And Recurring 60% Commission!
The Lotto Black Book
This Radical Approach To An Online Sales Letter Converts In The 3-5%... We've Never Seen Something Like This Since The Early Days Of 2004-2005 And I'm Sure You Haven't Either... We Convert More Than Our Competition And We Pay Out More... Try It!
Paleo Recipe Book - Brand New Paleo Cookbook
Brand New Paleo Diet Cookbook With Over 370 Recipes. Pays 70% Commission On This High-quality, Easy To Sell Product. Get Banners And Promotional Material At Http://paleorecipebook.com/affiliates.html
Articles > Computers and The InternetCisco CCNA Certfication: Introduction to ISDN, Part I
by: Chris Bryant
From the CCNA to the CCIE, ISDN is one of the most important technolgies you'll work with. It's also very common in the field; ISDN is frequently used as a backup connection in case an organization's Frame Relay connections go down. Therefore, it's important to know ISDN basics not only for your particular exam, but for job success.
ISDN is used between two Cisco routers that have BRI or PRI interfaces. Basically, with ISDN one of the routers places a phone call to the other router. It is vital to understand not only what causes one router to dial another, but what makes the link go down.
Why? Since ISDN is basically a phone call from one router to another, you're getting billed for that phone call -- by the minute. If one of your routers dials another, and never hangs up, the connection can theoretically last for days or weeks. The network manager then receives an astronomical phone bill, which leads to bad things for everyone involved!
Cisco routers use the concept of interesting traffic to decide when one router should call another. By default, there is no interesting traffic, so if you don't define any, the routers will never call each other.
Interesting traffic is defined with the dialer-list command. This command offers many options, so you can tie interesting traffic down not only to what protocols can bring the link up, but what the source, destination, or even port number must be for the line to come up.
One common misconception occurs once that link is up. Interesting traffic is required to bring the link up, but by default, any traffic can then cross the ISDN link.
What makes the link come down? Again, the concept of interesting traffic is used. Cisco routers have an idle-timeout setting for their dialup interfaces. If interesting traffic does not cross the link for the amount of time specified by the idle-timeout, the link comes down.
To summarize: Interesting traffic brings the link up; by default, any traffic can cross the link once it's up; a lack of interesting traffic is what brings the link down.
In tomorrow's article, we'll take a look at some common scenarios that make the ISDN link stay up, and what can be done about it. Keep studying, and I'll see you tomorrow!
Chris Bryant
Cisco Certified Internetwork Expert #12933
About The Author
Chris Bryant, CCIE (TM) #12933, has been active in the Cisco certification community for years. He worked his way up from the CCNA to the CCIE, and knows what CCNA and CCNP candidates need to know to be effective on the job and in the exam room.
He is the owner of http://www.thebryantadvantage.com, where he teaches CCNA and CCNP courses to small groups of exam candidates, ensuring they each receive the individual attention they deserve. Classes are offered over the Internet and in select cities. Chris has custom-written the Study Guide and Lab Workbook used in each course - no third-party training materials or simulators are used. You're invited to visit our site and check out our CCNA and CCNP courses and study aids, and to sign up for our weekly newsletter written personally by Chris. Chris is always glad to hear from Cisco certification candidates at chris@thebryantadvantage.com.
chris@thebryantadvantage.com
|
?>
News on Computers and The Internet
Google: Up to 500,000 Computers Face Disconnection From The Internet
On Tuesday internet services giant Google began warning users infected with the DNSChanger malware that they face disconnection from the web if they don't disinfect their computer. HP stock jumps after job cuts announced
COMPUTERS HP stock jumps after job cuts announced Hewlett-Packard rose the most in more than a month a day after the world's largest personal-computer maker announced plans to slice its workforce by 27,000 and reported... Eastday-Software piracy declined in 2011
Less than 40 percent of software installed on computers in China was pirated in 2011, a decline of 3 percentage points from the previous year, according to Chinalabs.com, a consulting and research company. Sports world grapples with need to both fight and embrace technology
QUEBEC CITY, Que. - The sporting world has found itself stuck in a love-hate relationship with the Internet. Google Adding DNSChanger Malware Warnings to Search Results
Don't lose Internet access on July 9! Google today pledged to warn users whose computers or home routers appear to be infected with the DNSChanger malware.
|
