WANs and Dedicated Lines

[Accessdabbler]

I'm almost ready to write the Network+ exam but I'm having trouble understanding WANs and Dedicated Lines since I've never worked at an ISP or large company.

1. What do the wires that carry ISDN, T1 (and T3), ATM, X.25 and Frame Relay look like? Do they run over regular old PSTN wires?

2. I find myself memorizing ATM, Frame Relay and X.25 specs without understanding what makes them different from each other. What makes them different and why?

3. What function does a Terminal Adapter (for ISDN) or ADSL modem have? Since the connection is already digital (traditional modems convert analog to digital and back) why doesn't the broadband router connect directly to the phone line and connect this way? I have ADSL but never really understood what the modem does...

Hopefully these questions are not too broad. I'm just trying to get a mental picture of what these technologies look like and try to understand why I'd use one over the other.

 

[butchrecon]

Wow!!! Those are some questions! I cannot answer them all but I can give some insite to the Network+ exam.

I took the Network+ test several months ag. I passed. I at that time did not (And I still do not) have a full grasp on the physicall differences in T1, ISDN etc...
The physical difference over the road is verry little. They all for the most part use the same physical backbone from pole to pole. Once they get to the buildind that is where the major difference comes to play. I cannot go into great detail on this for I am not 100% sure myself since I do not do a whole lot with the physical lines. It will all depend on how many lines or channels are needed for the connection.

Anyway, dont worry too much on the minor differences between the lines and just focus on the major differences. As long as you understand networking and have some experience with it you should do fine. James Collins
Hardware Engineer
A+ Certified Professional
Network+ Certified Professional
Microsoft Certified Professional
Microsoft Certified System Administrator
(What does all that jargon below my name mean? I dont know I am still trying to figure it out!)

 

[glister]

--------------------------------------------------------------------------------
I'll try...

1. Refer to EIA/TIA-570 Residential and Light Commercial Telecommunication
Wiring Standard for more details. This standard specifies the number of
conductors and cable quality. Category 3 cable meets the requirements for
new installation of telephone and ISDN services. Cat5 is pretty much the de
facto standard for new installations these days.

The "T Carrier" (T1) is the type of transmission system. The T Carrier can
be any terrestrial network capable of carrying the 1.544 Mbps signal,
including wire, which was the original medium, fiber and microwave radio.

ATM:
UTP CAT 5 uses an 8-wire link with the following pin assignments.

>Contact # ATM User Device ATM Network Equip
>________________________________________________________
>1 Transmit + Receive +
>2 Transmit - Receive -
>3 Not used Not used
>4 Not used Not used
>5 Not used Not used
>6 Not used Not used
>7 Receive + Transmit +
>8 Receive - Transmit -

>An RJ-45 Jack/receptacle is specified.

Frame Relay:
The local loop requires termination into a network interface unit (NIU) at
the customer premise, and subsequent connection to the customer DCE device,
usually a CSU/DSU.

2. The key difference between ATM and "X.25 packet switching" and the popular "Frame Relay" technologies is that the packets of the earlier technologies varied in size. ATM is 53 octets long. T1 is usually channelized
typically split into 24 voice grade channels with each running 56/64 Kbps. X.25 is a protocol which provides the user interface into the original packet switched network.

3. Special electronics at both ends of the connection are required in order to accomplish the minor miracle of ADSL. At the carrier end of the connection is placed an ATU-C (ADSL Termination Unit-Central Office), while an ATU-R (ASDL Termination Unit-Remote) is placed at the customer premises. In order to achieve such a high data rate over UTP, relatively sophisticated compression techniques must be employed.

How's that? A+,N+,S+,L+,I+,HTI+,CET,CST,CNST,CNCT,CFOT,CCNT,ACSP,ISA CCST3