ISP structure/server software questions

[yuckck]

hi, i am a newbie on ISP structure and i am doing some research how ISP operates and what type of cost they incurs. i have some questions and hopefully you experts can help me a bit. thanks!

1. would it be right to say that when customer dial in, they first go through the remote access server, gets their identity verified by the radius server, then have an IP assigned by the DHCP server. then they can go check their email, surf web, etc. and the request will be processed by the WWW, Email, dns, NNTP, FTP servers in the ISP, and the router sends the data to the correct destination through the backbone? or is there something i miss or is there something that's wrong?

2. are those servers mentioned above basically computers (very good ones) with different type of software installed? by that i mean there isn't really any structural difference between the servers, just different software running on those servers?

3. any ideas what software the big isps (eg like an AOL, Earthlink, etc) use for WWW Email DNS NNTP FTP, DNS, DHCP servers?

4. also any idea where or if any one knows how much it cost to buy these servers and software? and for a certain amount i spend on a certain configuration of server, the capacity i will be able to obtain to serve the users?

i know its a lot of questions, but anyone who has some ideas will be extremely helpful!! cos i have no idea on any of these. thanks in advance!

 

[FFC]

From my experience:

1. Correct - The problem with this set-up can be scaling the RADIUS implementation when large ISP's have millions of users. This is normally done by integrating RADIUS with an industrail stength RDBMS.

2. WWW servers large scale SUN box's, clusters or big PC's. Scaling of WWW sites is done with load balancing box's which pretend to be the one ip address of the WWW site but distribute requests across a range of identically configured box's. DNS needs to be reliable but not huge, DHCP is done via the RAS box's. News servers I've seen done with multiple front end's talking to appliances whiach act as huge NFS servers to handle the data. Mail systems are probably the biggest headache. Some are proprietary others come from companies such as openwave, have a look at their WWW site.

3. See 2.

4. All commercial deals are individually made. There are many variables to take into account.

 

[FUBAR]

Here's how the small local ISP I did tech support/admin stuff worked while I was there.

1. Correct on the dial in, except the DHCP part. In our office anyway, and most others I assume, DHCP doesn't work the same as you think about normally. The modem you're dialing into actually has an IP statically assigned to it. IE, if you had a phone number with one modem assigned to it, you'd get the same IP every time. A dhcp request/ack just sends that info to the PC on the other end.

Once you're on the net, you can operate pretty much at will direct to the rest of the internet. The only time you touch their servers are if you are checking your mail with them, local news, local ftp, or web sites that happen to be hosted in house. That all changes if they have a proxy server. Then you deal with that instead of direct to the internet.

2. Servers can be anything. Our servers were (and I hear still are) mostly crappy compaq boxes, basically standard PC hardware, but add dual cpu support, a RAID cage, scsi drives. Some of the newer ones were more "server" grade. Rack mount 2U dell boxes and such. We also had a couple testing and emergency boxes that actually were PC's.

You have to get a big ISP (or just one with corporate backing) to have SUN boxes (I work in a place that sells those now, they are EXPENSIVE!) It would take a LOT of users or less staff to support that server cost, then an admin to run them.

Software was linux (redhat) in our shop. Can't remember the article, but it stated that small ISP's were linux's playground. We didn't have the money (for licenses or the extra hardware needed) to run windows. Definately didn't have the cash to run Solaris boxes. After that it's the basic suite of linux server software, apache, sendmail, innd.

4. For the cost of servers, depends on what you plan to run on that hardware, and how top of the line you need to be. A good entry level server, for linux, can cost as little as 1400, and up to the sky on the high end (1.5 Mil for a Sun E15K). We were supporting 2000-2500 dial up users on a single p2 400, 256 MB ram, 9GB hd for mail and DNS. 30+ domains on another equal server, another 15 on another. Radius and some other things on another. Those tasks can be pooled or split as load demands.


Oh yeah, and for costs.... for dial up ISP's, add the cost of incoming trunk lines. Figure 10-12 users per modem (depending on your usage patterns), each modem having a line, 24 lines to a T1.

 

[yuckck]

someone told me actually that my use of the term WWW server is not accurate in that the WWW pages subscribers requested from all over the internet goes through an "ISP server" instead of a "WWW server", which i guess makes sense except that the term ISP Server is totally new to me.

if there is a computer with a certain number of CPUs and ram and disk space, how do you go about determining how many users that computer can support for a particular function, like mail, www, etc.?

 

[ScottMac]

Server sizing can be an arcane art. The one web page you see can contain content from a number of different servers, located almost anywhere on the Internet. It's all very content-dependent. An information page, like something a "Benefits" company might display so an employee can see and change insurance information is going to be tried to a database system, which may be a dozen very large computers all by itself. The information may be collected through one (logical) server, but the actual content can come from any number of boxes. "Where's the Web server?"...."It's those five racks over there......."

The other side of the coin is a page that references a lot of outside resouces (stuff on the public Internet) may only have a couple hundred bytes of HTML, and the references & links are pulled from all over the Internet...this could be a fairly small server and still handle a large number of requests, because it only serves up a small chunk of text.

Some places could run a cluster of Web servers, with another cluster to serve up graphics, another cluster for large text chunks, another friggin huge box (or boxes) for serving up database information and so on. The scope of scale is about as wide as you can imagine. There are some testing applications you can buy (not cheap) that will put a load on the server and predict the number of concurrent users...there might even be some free/cheap ones...not usually my end of the stick, so I can't offer any suggestions.

I believe Apache, running on *nix boxes is still the most prevelant web server software on the 'net, but as mentioned above, the big Sun boxes (with whatever software) seems to be the platform-of-choice...they're wunnerful, solid, reliable boxes, and the company has a good (hardware) reputation. Solaris is OK, I like it (what little I do on it), but I've read some posts that suggest it's a bit on the slow side (which could just be the compiler...Gnu has a free compiler, but to make something sing in Solaris, the Sun optimizing compiler is much better...expensive (Thousnds $), but worth it for the speed).

The load distribution boxes, a "Server Switch," is kind of a goofy animal too. The ones I've seen only have one or two ports...but thinking about it, they don't have to do anything but distribute addresses to the next available server...they don't actually do a L2/L3 switching function, they just track addresses (in and out). Most are industrial packaged PCs running special software....Extreme just came out with an ASIC (hardware) switching box, one gig port, that'll handle ...something like 50,000 sessions per second. They were showing it at the last Networld+Interop (the one that opened about the same time the planes hit the WTC). Check it out at their web site. Nortel, and of course, Cisco, also have Server Switches.

If you're intending to get into the business, design is your best friend. Think long and hard about what you need to accomplish when the doors open, and how you are going to expand the service if things work out. Properly planned, expansion is not necessarily an ugly thing.

FWIW

Scott

 

[yuckck]

if i am to take a server's specified I/O throughput in Gbps, and divide it by the typical 56kbps bandwidth a narrowband user needs to estimate the maximum number of user served concurrently, would that be way off?

similarly, if make the same calculation for a router's throughput, would that work?