What is Bandwidth

up2thetime

Hey,

Can someone please help me out with understand bandwidth.

From Odom I get:

Bandwidth: A reference to the speed of a networking link. Its origins come from earlier communication technology in which the range, or width, of the frequency band dictated how fast communications could occur.

From Wikipedia: bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it (kbit/s, Mbit/s etc).

Does that mean that bandwidth is how much frequency is being used on a Cat 5e cable (if that is what is being used)?

I am thinking of a node connected to a switch. If the computer is sending 50Mbps on wires 1 and 2, and receiving 50 Mbps on wires 3 and 6, does that mean 100Mpbs Bandwidth is occupying that link between the node and the switch?

Thank you.

schpenxel

it's basically a speed or a throughput capability.. 100Mb/s is an example.

Does that mean that bandwidth is how much frequency is being used on a Cat 5e cable (if that is what is being used)?

not really. the total bandwidth is still 100mb/s or 1gb/s (or whatever the max speed may be depending on the technology). Now, the amount of bandwidth you're actually USING at any point in time could (kind of) be thought of as the amount of "frequency being used on the cable" at that particular moment. although i'm not sure that that is technically correct.

really you should just think of it as a speed though, in my opinion

jbrad95706

up2thetime wrote: »

Hey,

Can someone please help me out with understand bandwidth.

From Odom I get:

Bandwidth: A reference to the speed of a networking link. Its origins come from earlier communication technology in which the range, or width, of the frequency band dictated how fast communications could occur.

From Wikipedia: bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it (kbit/s, Mbit/s etc).

Does that mean that bandwidth is how much frequency is being used on a Cat 5e cable (if that is what is being used)?

I am thinking of a node connected to a switch. If the computer is sending 50Mbps on wires 1 and 2, and receiving 50 Mbps on wires 3 and 6, does that mean 100Mpbs Bandwidth is occupying that link between the node and the switch?

Thank you.

Just think of bandwidth as the speed of the connection - don't worry about frequency for cat5.

Bl8ckr0uter

up2thetime wrote: »

Hey,

Can someone please help me out with understand bandwidth.

From Odom I get:

Bandwidth: A reference to the speed of a networking link. Its origins come from earlier communication technology in which the range, or width, of the frequency band dictated how fast communications could occur.

From Wikipedia: bandwidth is a measure of available or consumed data communication resources expressed in bit/s or multiples of it (kbit/s, Mbit/s etc).

Does that mean that bandwidth is how much frequency is being used on a Cat 5e cable (if that is what is being used)?

I am thinking of a node connected to a switch. If the computer is sending 50Mbps on wires 1 and 2, and receiving 50 Mbps on wires 3 and 6, does that mean 100Mpbs Bandwidth is occupying that link between the node and the switch?

Thank you.

The way I think about is this Bandwidth in its simplest term is just that the width of a band.

Half-Duplex
Imagine highway with 10 lanes. Each lane can allow one car to go only one way.

Full-Duplex
Imagine a highway with 100 lanes. Each lane can hold one car going one way and one car going another way (north bound and south bound).


In my (terrible) examples the bandwidth or allowed cars would be 10 and 200 respectively. 200? Wait a minute Kevin you just said 100 cars and 100 lanes. I did but notice I said notrh bound and south bound. Each lane would hold 1 car going north bound and 1 car going south bound for a total of 200 cars. See?


Now when you get to higher levels of xfer rates (gigabit and beyond) They basically took the 100 lane highway and allow 10 cars going north bound and 10 cars going south bound through bandwidth effiecency schemes. Feel free to look them up if you wish.

I hope this helps and if anyone wants to add to this example feel free

Bl8ckr0uter

schpenxel wrote: »

it's basically a speed or a throughput capability.. 100Mb/s is an example.

not really. the total bandwidth is still 100mb/s or 1gb/s (or whatever the max speed may be depending on the technology). Now, the amount of bandwidth you're actually USING at any point in time could (kind of) be thought of as the amount of "frequency being used on the cable" at that particular moment. although i'm not sure that that is technically correct.

really you should just think of it as a speed though, in my opinion

Frequency is important because the frequency use to determine the speed of the wire. 1 hertz = 1 bit (correct)?

schpenxel

knwminus wrote: »

Frequency is important because the frequency use to determine the speed of the wire. 1 hertz = 1 bit (correct)?

eh.. like i said, I'm not sure. but since it isn't the case anymore then in my opinion it's best not to remember it like that

Bl8ckr0uter

schpenxel wrote: »

eh.. like i said, I'm not sure. but since it isn't the case anymore then in my opinion it's best not to remember it like that

I agree. So remembering it is useless after gigabit. Such a waste....

astorrs

knwminus wrote: »

I agree. So remembering it is useless after gigabit. Such a waste....

Yup a total waste but it hasn't held true since the days of 300 baud modems not Gigabit Ethernet... but if you're looking to fall asleep reading about it here's a post of mine from a while ago http://www.techexams.net/forums/ccna-ccent/32978-cisco-online-study-test-versus-reality.html#post228137

Bl8ckr0uter

astorrs wrote: »

Yup a total waste but it hasn't held true since the days of 300 baud modems not Gigabit Ethernet... but if you're looking to fall asleep reading about it here's a post of mine from a while ago http://www.techexams.net/forums/ccna-ccent/32978-cisco-online-study-test-versus-reality.html#post228137

Wow that was pretty heated . Yea but I have never thought about cable so deeply..

Dubuku57

knwminus wrote: »

Full-Duplex
Imagine a highway with 100 lanes. Each lane can hold one car going one way and one car going another way (north bound and south bound).

In my (terrible) examples the bandwidth or allowed cars would be 10 and 200 respectively. 200? Wait a minute Kevin you just said 100 cars and 100 lanes. I did but notice I said notrh bound and south bound. Each lane would hold 1 car going north bound and 1 car going south bound for a total of 200 cars. See?

But we gotta take care not to get confuse about full dups..if it says BW is 100Mbps, it doesnt mean that with a full-dup you will get 200Mbps. It just measn that you will get 100 both ways simultaneously. Effectively it having a full-dup doubles your BW since it can comms at saem time.

up2thetime

Thanks for your replies!

I was wondering then...

If it is just the speed that the link is capable of, then why are T1 so expensive. I was looking at the prices of T1 lines and they are WAY more than what I pay for my home internet- and I just tested my home internet at about 10Mbps.

I understand T1 is a dedicated line that is always up between links. But it only runs at 1.544Mbps. And the cost appears to start at $500. Whereas I pay less than a tenth of that and get about 6x speed and my home link has always been up...

Maybe I'm missing something.

I guess the upload and download speeds of T1 are both rated at 1.544Mpbs? Whereas home service has a much much lower upload speed.

I am just not quite clear on why business pay so much for T1, when simple home connections are much cheaper and way faster.

Thanks.

JavonR

up2thetime wrote: »

Thanks for your replies!

I was wondering then...

If it is just the speed that the link is capable of, then why are T1 so expensive. I was looking at the prices of T1 lines and they are WAY more than what I pay for my home internet- and I just tested my home internet at about 10Mbps.

I understand T1 is a dedicated line that is always up between links. But it only runs at 1.544Mbps. And the cost appears to start at $500. Whereas I pay less than a tenth of that and get about 6x speed and my home link has always been up...

Maybe I'm missing something.

I guess the upload and download speeds of T1 are both rated at 1.544Mpbs? Whereas home service has a much much lower upload speed.

I am just not quite clear on why business pay so much for T1, when simple home connections are much cheaper and way faster.

Thanks.

Those are very fair questions that have several key answers:

#1) As you said, the connection is fully dedicated. This is extremely important for businesses running VOIP and mission critical applications, as the latency of the connection will typically remain consistent as it won't be shared.

#2) THIS IS THE MOST IMPORTANT REASON, SLA = Service level agreement. Businesses will prefer to pay 500/month over say 50/month for this alone. This guarantees a certain level of uptime or response time from the carrier in case of an outage or network problem. Network outage = lots of money lost.

So basically, you get an extremely consistent connection in which you can divy up accordingly when configuring the network, then a service level agreement on top of that.

Bl8ckr0uter

Dubuku57 wrote: »

But we gotta take care not to get confuse about full dups..if it says BW is 100Mbps, it doesnt mean that with a full-dup you will get 200Mbps. It just measn that you will get 100 both ways simultaneously. Effectively it having a full-dup doubles your BW since it can comms at saem time.

That is true. I just meant like 100 + 100 = 200 total. Not like 200 going one way or the other way.

Kaminsky

up2thetime wrote: »

Maybe I'm missing something..
...
I am just not quite clear on why business pay so much for T1, when simple home connections are much cheaper and way faster.

Nope... WAN circuits just aren't cheap as they know you will never go dig up the road and lay your own cable between the points you want to connect to.

The theory and actual physics of WAN links are very straightforward. In real life though, it is a monster cash cow.

A 100mb circuit can easily set you back £10k a year easily and thats not including installation. A 64k kilostream circuit (yes they are still widely used sadly) point to point connection from BT will also cost £10k a year which is even more rediculous. 12k is about £15k. No joke.

But then, They have to make their own infrastructure and hire infrastructure from other providers (in the UK, BT practically provide most of the last km of infrastructure) . They also have to purchase the high end equipment to handle the circuits and these are typically £(6-7) figures typically. Line cards for these devices alone will set the provider back £60k-£150k depending on the number of ports on teh line card.

WAN services is very big business but then, you are never going to dig up the road tens/hundreds of kilometers and stick a fibre in there yourself and you wouldn't be allowed to legally. My old university wired up all the dorms and buildings by a load of first years running around with shovels but they owned the land. Saved themselves a fortune.

dynamik

No one's made a "series of tubes" joke yet? I'm so very disappointed in all of you

YouTube - Series of Tubes Music Video

Oh fine, here's the original version: http://www.youtube.com/watch?v=f99PcP0aFNE

cerberos

Lol, wat a primitive video Dynamik. Well, this is a little tricky question, since no book can actually explains it that easy, it needs a lot of experience and knowledge which build up and create the complex image of wat Bandwidth really means... In it's simplest meaning, if u devided the word it will give u Band (which means a group or entities that make up something, Metallica is a Band which consist of 4 persons), and Width (which means the range or wide)... In it's simplset meaning we'll give an example, if u have a Pipline, u run in it water or data, watever, this Pipline Bandwidth can handle such and such from water, more than that it will burst or get damaged, same with data, just think of Bandwidth as the Capacity of ur Pipeline, where water, data, runs and not the actual result (the water or data u really receive) which it's the Throughput... The word Bandwidth differs from Throughput.

We always measure Bandwidth theoritically, or in a LAB environment, u can say that we put numbers approximately, we can't measure it accurately because of many facts, example, in IEEE 802.11a, the throughput we know is 54Mb, and the Bandwidth is 23MHz per Channel? Sorry, just lazy to open a book coz I can't really recall , but ur not going to achieve ever the expected Throughput accodring to this Bandwidth... Many factors interfere here, Indoor, Outdoor, positioning on Antennas, Scattering Factors, EMI, RFI and alot... Same with wired things, this cable can handle 100MHz of Bandwidth, does it really achieve the Throughput we expect according to the Bandwidth? Will it give us 100MB Per Seconde Throughput? Never! Quality of the cable is a factor, Shielding is another, Serial and Parallel (which It's another longer story), the Twist Ratio, and when everything is perfect, ur still not going to achieve the Throughput expected or use all the Bandwidth... Slowly on me guys , those who intend to attack .