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I have a question: DSL, cable, wireless DSL are offer shared bandwidth. For instance, if there are 10 users and a total bandwidth of 10 Mbps, each user will get 1 Mbps if all users are connected simultaneously.
However, if only a few users are on their transmission speed is much higher because they can use the unused bandwidth of other users...
Practically, each user is "promised" in the contract a certain speed, say 3-4 Mpbs, but that is only based on the statistical assumption that some of the other users will not be connected...
Is this the way the technology work?
How is it technically called this non-dedicated method of offering bandwidth that then gets shared based on number of users? In some ways it seems a little misleading since a user may think that its speed is always high (except when other users are on)..
The world is full of things that do not work as advertised, and due to most companies valuing profits over functionality and truth, this trend will probably continue for some time...
Any IP connectivity is susceptible to what the upstream device can handle, while often limited by the connectivity medium (DSL, cable, wireless) there's always other factors at play; the cable type and quality, the distance of a major trunk, the CPU and memory free in an upstream router - all impossible for you (at the end of the chain) to anticipate how slow the connection could become under heavy load.
Your idea that 10Mbps = 1Mbps for each of 10 users is not accurate. One user could get there first, take up all 10Mbps with their streaming video or file copy, and leave next to nothing for the remaining 9 users who could experience: timeouts or at best dialup-like speeds, ultimately get frustrated and leave, perhaps change providers, or convince themselves they are happy with the status quo and try again later.
To try and make things fair, or guarantee a minimum bandwidth, providers implement technologies like QoS or packet shaping. In most every case, on a residential connection, buying 3Mbps in no way guarantee's you 3Mbps sustained, every provider allocates a minimum differently, just so it keeps working (albeit slower) and hopefully you don't call to complain.
|reply to student25 |
To expand on what supergeeky posted networks (telephone and data are aways designed statistically. In telephone lingo a network is either blocking or non-blocking. A non-blocking network has enough capacity so that even if each connection is maxed out the network has enough capacity. A good example of this kind of network is a typical Ethernet switch. The internal backbone is fast enough so that it can meet worst case demand of all the ports.
In the real world every user is not going to max out the connection all the time, especially if customers cross time zones or usage types say commercial vs residential.
A properly designed network will rarely be congested for extended periods of time. When this occurs it is an indication more capacity is needed. Being statistical design is subject to changes in usage patterns. That is occurring today in the residential broadband market. The ISPs assumed highly asymmetric usage, much more consumption then outbound traffic, and bursty web browsing and email traffic.
Over time residential usage has evolved. More and more traffic is video streaming, this is more demanding then browsing, since connection persists for long time and is vulnerable to congestion caused latency. Internet users are finding they can not only be consumers of information but are able to upload audio/video/and text. This also undercuts early assumptions to typical Internet usage.
|reply to supergeeky |
thanks for your reply. One more basic question if you allow me since you are quite good on these topics: I am using WDSL (wireless DSL) which is DSL delivered to my town using bridges of radio towers. Let's refer to the example above, the 10 Mbps one.
The WDSL provider said that if the number of users in town increases from 10 to 20, it will ask the telecom provider (I guess the one that connect to the actual internet and owns the cables) to output a signal with more bandwidth than 10 Mbps, say 30 Mbps, to accommodate the new users.....
What does that mean in practice? Does it mean that a radio signal with a higher level of modulation will be sent to the antenna of my town? Is it a more complex type of modulation that determines a bigger bandwidth for the signal? How is the signal that carries 10 Mbps different from the one that carries 30 Mbps? What does the telecom company do? I know it costs the wireless provider more to offer a 30 Mbps than a 10 Mbps, but does that it actually cost more for the Telecom company too?
OK, we'll say your WDSL provider (here we commonly call that a WISP; Wireless Internet Service Provider) exceeds the 10Mbps they currently buy from an upstream provider (probably a wired or fiber connection from the telco), let's say they buy a 30Mbps connection instead... that's nice, but what you don't know is how are they "dividing up" that 30Mbps so all customers get a "piece of the pie" there are allot of factors at play here... What you also don't know is how good is their radio hardware (not the antenna or signal modulation necessarily, but the radio/electronics attached to the antenna)
Simple example following the flow of the Internet...
1) 30Mbps from the telco provider means the WISP can use roughly 30Mbps at any time, hopefully this connection is symmetric meaning they can download 30Mbps and upload 30Mpbs at the same time... Yes, they have to pay more for this, since they are wanting more speed.
2) This 30Mbps connection most likely feeds into a router at the base of the tower, and then connects to a switch, then to the radio, then the radio connects to the antenna mounted high atop the tower.
We'll assume that their router isn't some cheap device and can actually forward packets at 30Mbps, we'll also assume the radio isn't cheap and it can actually deliver 30Mbps to a wireless client on a clear day with good signal strength....
3) Your WISP can then divide the 30Mbps up to customers however they like using software/firmware running on the router, the switch, or sometimes the radio itself. The possibilities are endless but here's some examples of what they *might* be doing...
30Mbps / 20 users = 1.5Mbps is the minimum available per user
So they have a "rule" that no customer may take more than 6Mbps during peak times of the day, unless every customer is asking for 6Mbps then throttle back to 1Mbps per customer to "make it fair"
...but, as tschmidt points out they probably don't expect all 20 customers to all be using there connection all at the same time (think: businesses use more during the day, residential uses more after kids come home from school, and through the night) so perhaps they sell 10Mbps connections, but obviously you can see if they really gave everyone 10Mbps that means they could only have 3 customers with thier 30Mbps pipe.
It's unlikely that the radio hardware, either on the tower or on your house will be changed, because most equipment now-aday's is capable of at least 54Mbps (assuming good signal and minimal interference between the two antennas). If the hardware doesn't change then it's very probable that the frequency and type of radio signal won't change either, rather it will just be used to more of it's full potential of 54Mbps (or whatever the operating limit is) Radios are capable of different speed standards, commonly 11Mbps, 54Mbps, 300Mbps (there are many other's in-between) as long as you don't need more than what the radio can offer, you don't need to change the radio hardware.
Just FYI... In your other post you mentioned streaming video. Wireless connections are pretty bad for streaming video and gaming because of latency, and the fact that packets don't always arrive sequentially (meaning they don't always arrive in the same order, like they do when sent over a wire) Some packets get lost, others arrive late, and some too late to be used at all, this results in choppiness or missing segments of streaming video. Assuming your video stream only needs 1Mbps to work great over a wire, doesn't mean buying more bandwidth (more Mbps) will solve this problem over wireless, in some cases it may make it worse because now more customers are using more Mbps and thus the radio is more busy or congested and dropping more packets.
Hello again and thanks.
I am studying your answers. Could you help me by making some comments on these technical specs given by EOLO, which is an italian wireless DSL provider?
- PDH connection at 300Mbit/s to the fiber trasport network based on router Cisco 12410
-User antenna latency- BTS EOLO less than 3ms
(what is the latency due to? Is it the radio signal travel time from radio station to radio station? Doesn't radio travel at the speed of light? The physical distances in these wireless links are the same as those for wired communication. In the case of satellite communications the distance becomes a real factor, doesn't it? I am not clear on the cause of the delay....)
-Is "less than 3ms" good enough for HD videocalling? If not, why not?
-10Gbit/s connection towards the MIX and faster than 4Gbit/s to the internet?
(what are these two speeds exactly? Where is the MIX? So we start from my home. The signal goes to the village antenna. Then it is relayed to another antenna until it reaches the telco and into the internet....what is the MIX they are talking about and what is its role?)
Thanks for educating me!
.....- PDH connection at 300Mbit/s to the fiber trasport network based on router Cisco 12410
What does PDH actually mean? I read that is means T1, T2, etc... type connections...
Is 300 Mbit/s a good speed?
Is SDH better than PDh and why?
|reply to student25 |
PDH could be fiber (speed of light, optical cable, like a wire, very fast) or it could be microwave (radio frequency, wireless from one tower to another) 300Mbit/s is plenty fast.
According to »en.wikipedia.org/wiki/Synchronou···ierarchy SDH was developed to replace PDH, so you can make the conclusion that it's better. I personally don't have hands-on experience with equipment that connects via either technology so I can't really comment.
Cisco 12410: »www.cisco.com/en/US/products/hw/···dex.html
That's a big router, it can certainly handle 300Mbit/s
Latency of 3ms is pretty great for wireless, and fine for HD video, but that number may be misleading... The 3ms may be between your house and the tower, but it does not account for tower to tower, or the final tower to the Internet, and then all the routers/peers after that to the destination. It's not limited just to wireless and radios, the number is also a measurement for wired connections. Add up all the hops, and the latency between each, and you have your practical latency number.
Example: I'm on Comcast residential (a cable based ISP), and Chicago (a city) is about 35 miles away from me by car, and when I do a speed test like »www.speedtest.net it tells me my latency to Chicago is 6ms - it varies greatly by the time of day, and is effected (usually hight) during peak times when more people are on the Internet in my neighborhood.
Here is an example of the latency between every hop it takes to get from the webserver of dnsstuff.com to the webserver of comcast.net
Cable, DSL, T-1 or other wired connections should be relatively low latency.
Wireless would always be slightly higher.
Satellite would be the highest (just think going up to space, then coming back down)
-10Gbit/s connection towards the MIX and faster than 4Gbit/s to the internet?
...not sure what this means in your WISP's infrastructure, I'm guessing they have 10Gbit/s from tower to tower, but then the last tower that actually goes wired to the Internet has only 4Gbit/s. You mentioned previously 300Mbit/s so perhaps that's the max the equipment can do between your house and the tower?? The slowest equipment speed is going to be the bottleneck, so 300Mbit/s is the fastest it can ever be.
Some of your questions are now getting very specific to your WISP, you might ask them for a diagram depicting your house, each tower, and their connection to the Internet with all the speeds labeled on each route - only they would know this, no point in guessing.