Question #18 in TechNotes

Tiana

You've just connected several new workstations to a 10Base2 segment. Now none of the network nodes are able to communicate with each other. What is most likely the cause?

a. There are 34 clients on the segment.
b. The cable segment is 150 meters.
c. The segment is terminated using 50-Ohm terminators.
d. There is a break in the cable.

At first I answered (d) then as I go over to the answer sheet it states that (a) is the correct answer, which is correct too since 10Base2, supports a maximum of 30 nodes per segment.

What makes (a) the first choice instead of (d)? I know (a) is correct but what about (d.), if there is a break in the cable none of the network nodes are able to communicate with each other too. They can only function as standalone computers but cannot transmit data to each other.

One more thing, what will happen to a network if some Maus / transceivers are more than 2.5 meters apart. Will it cause for the network nodes not be able to communicate with each other at all or not really.

Thank you so much and any help is really appreciated.

Webmaster

Hi,

The keyword in this question (which is a good example of a CompTIA question, if I may say so myself ) is 'likely', and the combination with the first sentence.

What is most likely the cause?

after

You've just connected several new workstations to a 10Base2 segment.

10base2 cabling (thinnet, coax) is not 'that' easy to break. It's much more likely (because 'you just added several new workstations to the segment) that you added too much.

Answer d. would apply to all wired networks and since the question explicitly mentions 10Base2, you have to look for 10Base2 characteristics that can cause the problem.

One more thing, what will happen to a network if some Maus / transceivers are more than 2.5 meters apart. Will it cause for the network nodes not be able to communicate with each other at all or not really.

Probably depends on how much more exactly, but too far is too far. The error/drop rate would be too high to allow a successful communication at all.

Tiana

Thank you and sorry if it takes a long time for me to response.

Now it make sense..... By the way great technotes and It's really a big help for my N+ studies.

Webmaster

You're welcome and thanks

crabeater

Regarding the Q.19 (10Base5) answer d.

Two points:
1. Nearly ALL will be more than 2.5 meters apart, since this is meant to connect distant equipment. Also MAU's are not on 10Base5, since it is a buss technology, and MAU is a token ring technology. On 10Base5 you use a transciever & AUI cable to the host.
EDIT: Since first posting this, I had forgot that Johan calls a 10Base5 transciever (vampire tap) a MAU, so suppose he is refering to that. I have not found anyone else equating the two, so missed that in TechNotes.

2. The 2.5 meter rule applies to having at least that distance, and should (must) have the transciever on the 2.5m mark that is on the cable (and the terminators must be on the mark too, and only 1 is grounded). You are bound to have connections more than 2.5m apart since it is connecting equipment in different rooms, & even buildings. I was told the 2.5 meter minimum distance is to give equipment time to react with their CSMA/CD ability.

At a Lafarge Cement factory, they wanted 10Base5 between the control room and computer room, and between the computer room and several workstations in the offices in the next building. They later asked for more host connections, and a few days later called me in because of tons of collisions - a new transciever had gone bad. With no analyzing tools, I was lucky to pick the correct one the first time.

Also, since the question intimates that things worked before adding the several workstations, we would have to assume that they at least were getting a lot of collisions if the original length was 800m (Johan didn't mention adding a repeater with the new stations, so certainly the cable was always 800m - and therefore wrong!)

This question presents a good case of 'best, most probable, answer'

Webmaster

crabeater wrote:

Regarding the Q.19 (10Base5) answer d.

Two points:
1. Nearly ALL will be more than 2.5 meters apart, since this is meant to connect distant equipment. Also MAU's are not on 10Base5, since it is a buss technology, and MAU is a token ring technology. On 10Base5 you use a transciever & AUI cable to the host.
EDIT: Since first posting this, I had forgot that Johan calls a 10Base5 transciever (vampire tap) a MAU, so suppose he is refering to that. I have not found anyone else equating the two, so missed that in TechNotes.

Just wanted to post a reference for the MAU (in addition to emailing it ):
www.ethermanage.com/ethernet/10quickref/ch3qr_6.html

try a search on google for MAU and 10base5 for many other references.

Media Access Units are the cause of a MSAU often incorrectly being referred to as a MAU.

Tiana

Thank you again and I really appreciate your help:)