Cisco Certification: Introduction To ISDN, Part IV

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What’s the difference between Video Conferencing and Telepresence?

Telepresence picks up where video conferencing left off. Telepresence IS real time, full-high-definition, immersible sound and vision. Telepresence IS most importantly: the feeling of being “there” when you’re “here”. Telepresence is lifelike, video conferencing is not. Telepresence is that hi-line Mercedes AMG, video conferencing is a Ford Escort - Period.

Why Telepresence now?

Video conferencing has been around a while now but has always lacked the feeling we spoke about above. Jumpy computer screens, broken audio and poor lighting add to the impersonal touches of video conferencing (ie slow motion camcorder on top of your computer monitor). Finally, technology, bandwidth, vision and sound have all converged on video conferencing to create the telepresence experience. It’s about time! Crystal clear surround sound and real-time full-high-definition visual effects enhance the feeling of being there – thus telepresence. That nervous twitch, roll of the eyes, sniffle, tap of the foot – things you see when you’re present and sitting across a conference room table – things you don’t see or feel from video conferencing, but do with telepresence.

Today, what “real” uses are there for Telepresence?

There is no short answer even possible here. We’ll name a few, more like we’ll put your imagination to work. Imagine a single specialist doctor in Canada treating patients in Haiti via telepresence. Robots in space doing the actual work while the telepresence operator dons his telepresence helmet and gloves at his workstation in Texas. Meeting your Russian company vice president while you’re in the executive telepresence room at the office in Denver. Just a few…

What are “real” savings of Telepresence?

Your imagination still working on the last answer? Don’t let up yet! What carbon footprint? Don’t need that airplane ticket to go check on your staff in Russia now do you? What lost life in the Iraqi war? Unmanned drones and soldiers via telepresence. Military and combat cost savings? Immeasurable. Less travel costs, airline frustration, fuel, lost time, carbon emissions, etc. Those are tangible, real savings to name just a very limited few.

You starting to see what telepresence can do that video conferencing can’t? We hope you see what we’re seeing! Telepresence – its time has arrived!

Check out the video thread in Section 8 of the Telepresence Forum where you can watch some Telepresence YouTube videos! If a picture is worth a thousand words, a video must be worth a million!

Ride on the "Next Plane of Existence" TM

In part III of this ISDN primer, we learned that PPP has two main methods of authentication that Cisco certification candidates need to know how to configure: PAP and CHAP.

PAP has very few advantages over CHAP. PAP passwords are carried over the line in clear-text, which in today's world is a very bad idea. PAP configuration also requires additional configuration with the "ppp pap sent-username" command, so anyone who can see your running configuration can also see the PAP password.

The only advantage PAP has over CHAP is a slim one. With PAP, a different password can be used by the each of the routers involved in the authentication. CHAP requires that the password be the same. Why? We'll see as we examine CHAP authentication.

The First Step to Configuring CHAP

CHAP requires you to configure a username / password combination for any remote device that will be involved in authentication. (We're assuming that the routers have already been configured with their names via the global hostname command.) Both routers will use the password CISCO.

R1:

username R2 password CISCO

int bri0

encapsulation ppp

ppp authentication chap

R2:

username R1 password CISCO

int bri0

encapsulation ppp

ppp authentication chap

Why CHAP Authentication Requires The Same Password On Both Routers

Remember how PAP sends the password over the line in clear-text? CHAP does not actually send the password over the line at all. Instead, CHAP runs a hash algorithm using the password and a random number. It is the result of this hash that is passed over the link. The remote router receives the hash result, and runs the exact same algorithm. If the result is the same, the authentication attempt will be successful. If the result is different, the authentication will fail. For this reason, the passwords must be the same.

Debug The Connection If Authentication Fails

Since two passwords are involved, the chances of one of the passwords being mistyped doubles. If you configure CHAP and the link dials but drops almost immediately, there's an authentication problem. Run debug ppp negotiation and attempt to dial the line again. The output of this particular debug will show you where the problem is.

Chris Bryant, CCIE (TM) #12933, has been active in the Cisco certification community for years. He has written several books that have helped CCNA candidates around the world achieve the coveted CCNA certification, including several concentrating on binary math conversions and subnetting questions that the average CCNA candidate will need to answer on their CCNA exams.

He is the owner of The Bryant Advantage (http://www.thebryantadvantage.com) where he teaches affordable world-class CCNA courses via the Internet, and sells his popular Cisco certification books. He’s proud to have helped CCNA candidates around the world achieve their career goals. Mr. Bryant’s books and courses are sold on his site, on eBay, and on several other major Cisco certification sites.