Serial Interface - what kind of traffic

[Frankey]

Hello guys,

Im quite new with Cisco, im doing my CCNA, so im reading the CCNA book to Todd Lammle, its really good. But i have few unanswered questions that i hoped maybe you guys could help me with

On the Cisco routers you have a serial interface, what kind of data traffic is mostly going between serial interfaces? I might be wrong, but i think i read that the serial interface is speed of a T1 line?

Is it normal networking traffic that i send out to internet that goes thru the serial interface or does that kind of traffic goes thru the ethernet interface???

I hope that someone can give me a few lines and help my confusion :-

Frank J.M. Andersen
Norway

 

[ChrisAC]

It all depends on what type of WAN connection you are connecting through! For example, I install routers at customer sites to connect them to the internet. We have three basic connection types. ISDN, ADSL and leased line.

If the customer is having ISDN installed then the presentation at the NT1 that the telephone engineers install is RJ-45 and I install a Cisco router with a BRI port.

If the customer is having an ADSL line then the presentation is an RJ-11 on a POTS splitter, so I install a router with an ADSL WIC (ATM card) which has an RJ-11 presentation.

The most common form of connection for us is the leased line, which is a dedicated point to point connection between the CPE router and the core router, with bandwidths ranging from 64MB to 2MB (usually!!). In this case the leased line will be presented on an X.21 port, so I will connect this X.21 port to the routers serial port with an x.21 cable.

Serial ports on routers are also used for T1's (E1's in Europe). You will find that the serial port is the most commonly used method to connect WAN's. If you ever to the ICND course you will most likely simulate WAN connections by connecting two routers together, back to back using X.21 cables on the routers serial ports. One router will be DCE (and therefore set the clock rate for the connection) and the other would be the DTE.

I hope that this answers your question.

Chris.
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Chris Andrew, CCNA
chrisac@gmx.co.uk
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[Frankey]

Thanks Chrisac,

Yes indeed, it was very help full
The biggest question mark i had to this was that i have been thinking about the T1 and E1 as in speed of 1.56Mbit and 2Mbit(?).

So say that a company have a 100Mbit connection out to internet thru a backbone of some kind, would this company use the Serial link or would it most likely use some kind of module installed in the router to archieve this kind of speed?

If the Serial interface can only deliver T1/E1 speed, what kind of traffic would you send thru it then? (concider that you are using high speed connection). Would it be controll information between routers, would it be actual data to and from differente hosts?

I have those RouterSim labs and that stuff. I have notice that in the simulator the uses two routers and they uses the serial interfaces to connect two cities to each other, for example NY and LA. Wouldnt it be better to use higher speed then just T1 connection?

I`m sorry i ask all this, i just try to get more knowlegde ;-)

Frankey
Norway

 

[ChrisAC]

Higher speeds are always good, but they are also very expensive! A 100Mbit connection to the internet would be fantastic, but expensive and probably not utilised (by your average medium sized company anyway). Connection speeds to the internet are usually much slower than the speed of the LAN. Most of our customers don't go over 2Mbit for their internet connection, and even that isn't utilised to the full. However, ISPs and other carriers do require higher speeds to carry information from connected networks. Because we supply 2Mbit internet connection for may companies we must ensure that our connection can handle all the traffic, so we have 100Mbit connections out to other carriers.

The golden rule is .. "have as much bandwidth as you can afford".

Chris.
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Chris Andrew, CCNA
chrisac@gmx.co.uk
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