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Question about Internet speeds

hardly likely they would both use the full amount at the same time or for the same duration as one another.Just because you have 50,20,10,5 or whatever you rarely actually use it.

If a 100mbps link supports 2 users with a total of 70mbs, it means that 70 mbps worth of traffic is flowing on that pipe, with short periods of times when the link is idle between packets.

If users are generating more bandwdith than is available on a link, then the router or switch will queue packets that arrive in one port faster than they can go out the 100mbps port. That queue/buffer is relatively small and once it is full, packets simply get discarded and never delivered. It is called congestion management.

The TCP protocol is designed for this and the sender of packets will resend packest that had not been delivered and in essence alo reduce throughput of data until the loss of packets is no longer detected.

If users with different speeds are on a congested link, the user with the faster link is statistically more likely to see dropped packets since he'll be adding packets to the queue at a faster rate. Thus his speed is statistically more likelyly to slow down.

In practice though, I think all users no mattrer what speed, will see reduction of throughput because they will have lose some packets.

its like the 401, you can go really fast, but the minute 1 million cars trying to use it at once you will go very slow
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reply to vishalmalik
Thank you everyone for your reply.

JF, so how do ISPs implement different speed profiles in their networks? Do they put higher speed customers on different links than they put lower speed customers? For example, what advantage does an Extreme customer have over an Express customer on Rogers Network? Is it simply that the Extreme customer has a wider last mile than an Express customer? Or is the Extreme customer given other advantages beyond the last mile?

Speeds given to customers is primarily dictated by the speed of the modem. So the modem will limit the speed at which you can receive or send data.

ISPs put somewhere between 2000 and 4000 customers per 1gbps of trunk links. At any point of time, they expect only a certain percentage of customers to be downloading at full speed. And another percetage to be downloading at a reduced speed and another percentage to be idle while reading a web page or viewing a movie they have already finished donwloading.

For instance, if you have a 25mbps link and are watching an HD Netflix video, you are only using about 5mbps.

Thanks JF. I didn't know that it is the modem that determines the speed. That helps a lot.

A question though: If the modem determines the speed, then why are we sometimes able to hit speeds higher than the maximum allowed by the speed profile? For example, I'm on High Speed 10 with Shaw, but I routinely hit over 20 Mbps on speedtest.

speedboost.it gives 10 or 15 seconds of extra speed.Screws up speedtests big time

reply to vishalmalik
Sorry, another question:

Sometimes in evenings, I get speeds that are much lower than the 10 Mbps that I'm supposed to be receiving, which screws up my streaming experience on YouTube etc. Based on the discussion in this thread, I'm thinking that ordering higher speed from Shaw will NOT fix the streaming, since the bottleneck can't be my modem but some other link in Shaw's network. Is my thinking correct?

That thinking is generaly correct.

HOWEVER, on cable, there are now 2 types of modems, the older DOCSIS-2 and the newer DOCSIS-3 modems.

DOCSIS-2 only talks on one frequency (a TV channel assigned for data transmission). So if that channel is congested because of many customers using the internet at same time, you will see lower speeds.

If you upgrade to a higher speed tier, it is likey they will want you to upgrade to a DOCSIS-3 modem. These modems can use multiple frequemcies at the same time so the odds of congestion are less.

The shared frequencies that are being referred to here are the ones used to transmit signals across the coax/copper-network (the last mile). It doesn't affect the node specifically as the node is fed by fiber in most cases these days (I believe), but it affects the lines feeding the node on the customer side. The frequency congestion is on the cables that run to your house, as these are shared among many houses in the neighbourhood; all the houses on that wire segment are electrically connected through the cable.

Thus, the connected modems need to share the frequencies on that wire and take turns sending their signals. DOCSIS 3 modems are more efficient at sharing that wire, due to channel bonding.

Congestion can happen at any level of the network depending on where the smallest bottleneck is, and which customers are trying to send data at the same time. Upgrading to a DOCSIS 3 modem helps to alleviate local congestion, but won't help if the node itself is oversubscribed or if there's a problem further away in the network.

Edit: Frequency congestion on cable networks is pretty much an electronic limitation. A modem in this situation has to fight for time-slots on the physical wire to send its data. This has little to do with IP congestion, as far as I know.

That's what I felt, that the frequency limitation is only on the local coax, and not further away on the network. According to Wikipedia, each 6 MHz DOCSIS channel supports 42.88 Mbps. I think that's where the congestion arises, if the modems are only able to use one channel.

A question though: What does a cable company do if a channel gets regularly clogged up during peak hours in a certain neighborhood? As far as I understand, a node-split will not solve this problem, since a node-split only relieves congestion at the node. I guess all they can do is encourage users in that neighborhood to move to DOCSIS 3 and free up more channels. Am I correct?

reply to vishalmalik
So, I'm thinking of ordering a DOCSIS 3 modem from Shaw to take advantage of multiple channels, but I have a couple of questions before I do that:

1. If I don't upgrade my tier from 10 Mbps, just change my modem, will it still use multiple channels? Or are multiple channels only available to customers of higher speed profiles?

2. Out of curiosity, does someone know which particular channels Shaw uses for upstream and downstream data?

I know on Rogers' network, the channel bonding happens regardless of your speed profile. I think it has to do with the hardware used to supply that cable segment, so it should be the same for you.

Cable upstream channels are generally on the low end of the spectrum (5-42MHz or thereabouts, but I've seen even lower like 2.xMHz). Then the normal TV channels appear from around 50MHz-800MHz, and somewhere in the higher end of the TV channels, the downstream cable spectrum starts ~500MHz, I believe). I think Shaw would work around these same frequencies as well, but I don't have any evidence, anecdotal, or otherwise at the moment.