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[description], Story, any other text you want to use. Cisco 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
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Netscape Corporation has created the best known secure server technologies. It uses a security protocol called Secure Sockets Layer (SSL) that provides data encryption, server authentication, message integrity and optional client authentication for a TCP/IP connection. When a client seeking to purchase gilmer county cable tv connects with a secure server, they exchange a *handshake* which initiates a secure session. With this protocol, the same server system can run both secure and unsecured web servers simultaneously. This means an gilmer county cable tv organization or company can provide some information to all users using no security, and other information that is secured. For example, a business that sells gilmer county cable tv online can have its storefront (merchandise catalog) unsecured, but ordering and payment forms can be secure. Why are these developments important? As the Internet becomes a way to buy and sell gilmer county cable tv products and services, financial transactions become essential. Right now, most gilmer county cable tv transactions involve the exchange of credit card information, either directly over the network, or by phone, to complete a transaction initiated online. Eventually, you will be able to use cash as well as credit, directly over the network. There are two basic kinds of digital cash, anonymous cash and identified cash. Anonymous cash is just like paying for gilmer county cable tv with paper cash but it also carries no information about the person making the transaction, and leaves no transaction trail. You create it by using numbered bank accounts and blind signatures. Identified cash, on the other hand, contains information revealing the identity of the person who withdrew it from the bank. Like credit card transactions, identified cash can be tracked as it moves through the system and involves fully identified accounts and non-blind signatures. Whether you use digital cash when purchasing gilmer county cable tv is entirely up to you. We suggest you employ the purchasing avenues available from the gilmer county cable tv supplier we recommend.
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