T1

[Likwidfire]

Just a quick Question....If a T1 line has a total bandwidth of 1.544Mbps, 24 channels each at 64kbps. How many users can be on a T1 line and maintain an average of 512k, before the T1 starts to become overwhelmed and performance starts to drop (Performance is key here).

What about if each user was at 256k? How many then?


Does anyone have the formula to figure this out??


Any help would be GREATLY appreciated


Thanks

AJ:confused:

[PhyberOptix]

It's pretty simple division. Convert your T1 bw of 1.544Mbps to kbps and it 1544. Divide that by 512 and you can see that a T1 could support 3 users that have a continuous stream of 512k. Likewise, it could support 6 users w/ a continuous stream of 256k.

However, this is rarely the case. You won't often find a scenario where all users/sites are streaming at that rate. This means you can overprovision the line based on the assumption that when some users/sites are running at full tilt, others will be sitting there idle.

PoX
CCNP/A, CCDA, NNCSS, MCSE, CNE

[Bouncer]

Remember that unless they're running game servers constantly, some sort of FTP/Napster type service in 24hr use or a real media type streaming server ... that traffic is bursty by nature.

Consider, it'll take five minutes to write this and two seconds to upload. If all people are doing is email, web browsing and the occaisional download of a file then they aren't actually sending or receiving info that often. They're reading text or looking at pictures. Because of this bursty nature you can comfortably support 70-150 people on one T1.

If OTOH you want to run a game server, you will saturate the T1 with a singular Q3 or Half-life/CS server and 34 players (17 per side).

Your max throughput is about 160KBps on a T1. Each game client is using 4KB or so of streaming info. Game servers EAT bandwidth like nobody's business.

Regards,
-Bouncer-

[tomsykes]

Originally posted by PhyberOptix
It's pretty simple division. Convert your T1 bw of 1.544Mbps to kbps and it 1544. Divide that by 512 and you can see that a T1 could support 3 users that have a continuous stream of 512k. Likewise, it could support 6 users w/ a continuous stream of 256k.

However, this is rarely the case. You won't often find a scenario where all users/sites are streaming at that rate. This means you can overprovision the line based on the assumption that when some users/sites are running at full tilt, others will be sitting there idle.

PoX
CCNP/A, CCDA, NNCSS, MCSE, CNE

Yep. laws of statistical multiplexing tell us that not everyone is going to be using their full bandwidth at once :) (typically)

Therefore, you can set aside a minimum value to work with - perhaps 100kbps. It depends what sort of traffic usage patterns you are planning for, and as Phyberoptix said, how much you want to oversubscribe.

Almost all ISP's do this - especially DSL carriers.

Cheers
tom

Melbourne Australia
Y2 B.Eng(Communications), RMIT
Cisco Network Specialist.

[TDBerry]

I happen to run a small cable ISP and our users are 512kbps and a few 1024kbps. There is no magic fomula. It all has to do with the quality of service you want to offer. As someone earlier mentioned a T-1 can support 3 CMs @ 512kbps. Considering the cost of a T-1 and then the price of the monthly charge on a cable modem this is not going to work for the ISP. So you work it on the fudge factor of how many customers you have online and what they are doing online. A good way to monitor your consumption is to run MRTG's. Depending on how it is setup you can see when your peak times are and how close you are getting to the point of saturation. Its good to be prepared so monitoring is good but on the other hand you could just listen to your customers. Every ISP works on fudge factors. For instance most Dial up ISPs will sell anywhere from 4 - 10 customers per line (channel). This is what really seperates the good ISP from the great ISP. The great ISP has a monitoring system in place and maintains the system as the need increases. All others simply wait until the calls get to be too great to be handled and then decide "hey we should get another T-1". Its more about management than anything else. Also the more lines and the more customers you have the more the chance that they will not be online (typically) and you can increase the ratio. Like I said a good monitoring system essential.