Question (1 Viewer)

[crammy90]

2003 trial exam
22 d
a number of staff are experiencing poor performance when using a LAN with 50 connected PC's. Jack (net admin) discovers that all these users are directly connected to a single hub and on this hub the data collision light is virtuall always on
Identify network topology used for this LAN and discuss possible reasons why light is on:
i wrote
STAR as each node is connected to a single hub
reasons why light on
a) hubs are unintelligent and cannot inspect packets and so data is sent to all PC's. As STAR uses CSMA/CD, after data is sent by the hub the lines appear free and so other PC's try to send data and collisions occur. A jamming signal is sent to halt transmission for a random interval. After this interval is up, the lines seem free and so many PC's of the 50 will try to send data and another collision.


ANSWER:
BUS topology?
then they used the aspects of a bus topology??
can any1 see how it is this am i missing somethings
thanks,.

 

[hobby345]

Hi crammy, (shouldn't this be in the 'Communication' section? Anyway...)

Just so you know i'm not that great at explaining things but here's my attempt:

Identifying the topology:
First of all, a bus topology is where all nodes are connected to a common transmission medium (sometimes referred to as 'backbone'). This means that when data is sent along this cable, only the intended recipient will pay attention to it.
Now lets look at a hub:
A hub sends data to all nodes in the system, but only the node that the data is intended for will pay any attention to the data sent.

Do you see a similarity? Technically any system that contains only hubs is a bus topology due to the fact that they work in very similar ways. For a star topology to really work, it should have a switch as opposed to a hub.

Reasons why light is on:
Think about what collision is: it is when two or more nodes send data at the same time.
Now think about how you can relate this to bus topologies and nodes.

Anyway i hope that helped you,

-Hobby-

 

[crammy90]

Hi crammy, (shouldn't this be in the 'Communication' section? Anyway...)

Just so you know i'm not that great at explaining things but here's my attempt:

Identifying the topology:
First of all, a bus topology is where all nodes are connected to a common transmission medium (sometimes referred to as 'backbone'). This means that when data is sent along this cable, only the intended recipient will pay attention to it.
Now lets look at a hub:
A hub sends data to all nodes in the system, but only the node that the data is intended for will pay any attention to the data sent.

Do you see a similarity? Technically any system that contains only hubs is a bus topology due to the fact that they work in very similar ways. For a star topology to really work, it should have a switch as opposed to a hub.

Reasons why light is on:
Think about what collision is: it is when two or more nodes send data at the same time.
Now think about how you can relate this to bus topologies and nodes.

Anyway i hope that helped you,

-Hobby-

So with a bus topology:
a hub is placed as a node connected to the trunk cable. A node wishing to send data sends it down the drunk cable to the hub, which sends it back along the trunk cable untill a PC who it is addressed for recognises it and accepts it?
that seems pretty stupid lol why doesnt the original node's signal whilst it is first being sent down to the hub just get identified by the recipient computer who it is address do?


and when the hub sends the data out, does it go to each node and only the node its address to accepts it, or does it progress down the trunk cable to each node at a time untill one accepts it?

For a star topology to really work, it should have a switch as opposed to a hub.

but a star can be a hubbed network to?


and with a bus and how it cant work if you take a node out. if you put a terminator in its place can it work, or does the terminator stop the signal so it cant continue flowing on the bus?

 

[crammy90]

also, can you have a physical ring topology which uses a bus logical topology?

 

[hobby345]

A node wishing to send data sends it down the drunk cable to the hub, which sends it back along the trunk cable untill a PC who it is addressed for recognises it and accepts it?

When a hub receives a packet of data it simply amplifies and retransmits the packet to all attached nodes.
To explain this using an analogy...
Consider the following:
You want to send a letter to a particular address. This letter goes to the post office (hub/switch). From here, hubs and switches differ.

With a hub, it will send a copy of the letter to every single house (except from where it was sent). If the address on the letter matches the recipients address, they accept the letter. If it doesn't, they simply throw the letter away

Whereas with a switch, it goes directly to the intended address

that seems pretty stupid lol

To quote the textbook: Information Processes and Technology THE HSC COURSE by Samuel Davis;
"Hubs are dumb devices" (although i wouldn't recommend saying that in the HSC exam)

and when the hub sends the data out, does it go to each node and only the node its address to accepts it, or does it progress down the trunk cable to each node at a time untill one accepts it?

Data is sent to all attached nodes and only the node it is addressed to accepts it. The others just "throw it away"

but a star can be a hubbed network to?

Physically yes, but this question is referring to data transmission which is a logical topology.
(A logical topology is how data is transmitted. From my understanding the question was not asking about physical topology as it is referring to data collision, which means data transmission, hence the logical topology not physical)

From the textbook Information Processes and Technology THE HSC COURSE by Samuel Davis; "Hubs connect nodes together into a single network segment. This means all nodes attached to a central hub are sharing the same transmission channel meaning a logical bus topology is being used."

Remember just because in textbooks a bus topology is in a straight line, this does not mean that it is physically set up in a straight line. They do this for simplicity and to show that the nodes are not directly connected to each other.

and with a bus and how it cant work if you take a node out. if you put a terminator in its place can it work, or does the terminator stop the signal so it cant continue flowing on the bus?

I don't quite understand what your asking.. in a bus topology, it still works even if you take a node out. Data is sent along the backbone (trunk) and does not travel through the nodes. Consider this analogy of a street with houses either side:

-The backbone/trunk is the actual road/footpath
-The nodes are the houses.

If you demolish 1 house, the other houses can still function as normal.
A single break in the backbone disables the entire network. Furthermore, a fault in the cable (or road going by the analogy) is difficult to locate because it stops all the nodes from transmitting or receiving

The function of a terminator is to prevent reflection of the data signal back down the cable.

Sorry if this isn't what you where asking.

-Hobby-

 

[crammy90]

ok yeh i only just read the textbook to see there were logical and physical.
ive got it pretty much down pat now studies heaps of them last night
just to clarify one last thing.
a) if you put a hub on a physical bus using a logical bus, i dont understand the point of this bus. Because a logical bus is when the nodes recieve the same signal each time simultaneously and only the reciver its addressed to, as identified in the header address, would accept it. If you put a hub on the physical and logical bus network, when a device sends info do they send it down the trunk cable to the hub which then voices it to all listening nodes connected on the network? or do they send the data via the t-connector, which amplifies/copies the signal down the trunk cable to each connected node, leaving out the hub. if you get me

did you bother learning about MAU's and what not?
or the WAP and when its used for a physical star but a logical bus?
what mark are you hoping for hobby?

oh yeh and can you have a physical ring using a logical bus and vice versa

 

[hobby345]

If you put a hub on the physical and logical bus network, when a device sends info do they send it down the trunk cable to the hub which then voices it to all listening nodes connected on the network?

Yes

or do they send the data via the t-connector, which amplifies/copies the signal down the trunk cable to each connected node, leaving out the hub. if you get me

Consider the T-connector to be like a letterbox. The node listens for data via the t-connector (checks the letterbox. Anything addressed to them is taken the rest is discarded).

did you bother learning about MAU's and what not?

Personally, I'm not learning about that in great detail, but you should still have a basic understanding to be safe. I could be very much mistaken, but i don't think they would ask a question that requires a detailed answer about them. It may pop up in multiple choice or in a question that just requires you to 'identify'. But as i stated that is just what i think and i can be wrong.

or the WAP and when its used for a physical star but a logical bus?

Same answer as the MAU's etc.
(You should still know about them, and i am not saying that you shouldn't study them in detail, it is simply what i am doing and what i believe)

what mark are you hoping for hobby?

hah, hmm.... well the main courses that i am hoping to apply for are around the 80ish - 85 mark so I'd be happy with anything from there up =).
I have backup's in case everything goes wrong =(.

oh yeh and can you have a physical ring using a logical bus and vice versa

Oh sorry, i didnt see your penultimate post, sorry.
This I'm a bit hazy with. I will have to verify with my teacher, but i believe you can. This judgement is simply based on the fact that logical topologies refer to the data transmission, whereas physical refers to the layout. I'll get back to you with this one though after i contact my teacher
:worried:

 

[crammy90]

well hopefully youll get it. just keep studying hard.

ur lucky you can still consult your teacher lol mine went on holidays so she just gave me the sam davis book so ive been using that this week. so much stuff i didnt know aha
i dont see how i got the marks i did this year without using a textbook and just using the internet aha

are u just doing past papers? or still making summaries n stuff

Question: do logical star's use CSMA/CD,CA even though collosions cannot because they use 2 channels in their dedicated link for their sending of data to/from the central node?

and also my summary has this for analog data to a digital signal
Analog data - digital signal

* Involves analog data (continous wave) to digital data via ADC and then to a digital signal (varying voltages on a analog wave).
* HOW? analog wave passes through the ADC. According to the clock component, at certain intervals the signal is captured by the capacitor and its value sampled (converted to binary). The rate at which the clock allows the sample to be captured by the capacitor depends on the sampling rate. This digital data is then converted to a digital signal using either Manchester Encoding or QAM.

So i know Manchester is for digital data(binary) to a digital signal(still an analog wave, just with varying frequencies/amplitues to represent the varying voltages of the binary data)

what is Pulse code modulation? ive read its analog signal - digital data. Is this just sampling which is described above with the ADC? do you know how it works?






and yeh ive learn the MAU and what not just in a little detail it wont be tested i dont think any1 i know would have heard of it aha. i just know it can be used for logical ring on star physical.

 

[hobby345]

Sorry, I'm a bit busy atm, so i won't have time to answer your last post, but, in response to:

can you have a physical ring using a logical bus and vice versa

The answer is yes, but as i mention im short of time right now so ill have to post the details at a later time.