General DSL Questions

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General DSL Questions

What is DSL?

From CMP's Tech Web, (Digital Subscriber Line) A technology that dramatically increases the digital capacity of ordinary telephone lines (the local loops) into the home or office. DSL speeds are very much tied to the distance between the customer and the telco central office. The technology is geared to Internet access with its asymmetric versions (faster downstream than upstream) and short haul connections with symmetric versions (same rate coming and going).

Unlike ISDN, which is also digital but travels through the switched telephone network, DSL provides "always-on" operation. At the telco central office, DSL traffic is aggregated in a unit called the DSL Access Multiplexor (DSLAM) and forwarded to the appropriate ISP or data network.


What do DSL subscribers gain?

  • High access speeds at an affordable price
  • Avoid voice vs. data conflict on a single line
  • "Always on" connection to the internet
  • Relief from local busy signal
  • Easy to use


Exactly how fast is DSL?

Hard to say as it depends on so many factors: CenturyLink's implementation of the technology in real world situations, the speed of machines on each end of a connection, bottlenecks along the way, etc. XMission won't max out our parts of the equation though since we have control over it and its cost-effective technology for us (i.e., no phone line charges and we don't need to purchase hardware each time we add new customers since it's all handled over an ATM that we already have in-house). It won't likely be a full 256kbps (or whatever speed you purchased from CenturyLink) any more than any other technology reaches its full capacity.

One thing to keep in mind though is this: most people won't use a fraction of their bandwidth since browsing web pages and using email are sporadic uses of bandwidth and not too bandwidth intensive.

Also, since basic DSL account users aren't allowed to use server services (even over a DSL Business account), their bandwidth usage will stay down. Some people will get DSL because of the larger, "burstable" capacity so that when they need to download a file or want to browse the web any slowdown won't be on their side.


Is DSL the same speed for upload as it is for download?

No. This depends upon the type of DSL used but RADSL (Rate Adaptive Digital Subscriber Line), the type available currently in our area, is asymmetric, which means that you can transfer data more quickly in one direction (down) than in the other. At 256k, this difference isn't very high, but on the top end they reach a 700% disparity. For example, the maximum transfer rates (if you qualify for them) are 7 Megabit downstream and 1 megabit upstream.

This discrepancy illustrates one of the most obvious differences between DSL and frame relay. Obviously, even if you or your company qualifies for the higher bandwidth DSL options, server services over DSL peak at lower upstream rates than frame relay.


Is DSL really on the same line as my phone?

Yes. The DSL digital signal is running at a much higher frequency on your phone line. We recommend you use filters on your telephones to help prevent any possible interference, though. These filters are available for free with your DSL line service from CenturyLink.

Is DSL OS/Platform-limited? (i.e., is it only for Windows)?

No. While the internal DSL adapter will only work with Windows, the external DSL modem will work with nearly any properly configured network card installed on nearly any operating system.


What are my hardware options?

You have three options for DSL hardware when ordering your DSL line through CenturyLink:

Some other brands/models are known to work, such as the Zoom X6, and while XMission may have the needed settings listed, we are not able to troubleshoot specific configuration issues.

Getting DSL

If DSL is available in my area, does that mean I can get it?

No. Even if your prefix is serviced, that doesn't mean your line will qualify. DSL is distance-prohibitive (maximum 15,000-18,000 feet). To find out if your line qualifies, call XMission Sales at 801-539-0852, or CenturyLink at 1-800-244-1111.


What exactly does "loop-qualify" mean?

To "Loop Qualify", your phone line needs to be tested to see if it can pass the strict requirements necessary to pass DSL signals. Currently, the limitations for DSL are:

  • The line cannot have any load coils on it
  • All bridge taps should be counted since too many of these prevent the signal
  • Maximum length of any bridge tap not to exceed 2,000 ft
  • Total bridge tap length not to exceed 6,000 ft
  • You cannot have a DLC(Digital Loop Carrier) between you and your CO (Central Office)
  • You need to be within 15,000 ft of your CO, although you can be up to 18,000 ft if higher quality wire is used in your area


What is DLC and why can't I get DSL because of it?

DSL may not be available in some areas due to digital-loop-carrier (DLC); deployed by your local phone company to make the most out of copper lines already layed out in the streets. DLC is also known by the terms: line concentrator, channel bank, PairGain, SLiC96, SLiC2000 and UDC. Ask your local telephone company repair engineer if this applies.

Your XMission DSL Account

Can I have normal (analog) dial-up with a DSL account too?

No, you would need to purchase an additional account for this. We are able to offer this service at such low prices because we don't need to add new phone lines or dial-up hardware. As well, we assign your connection a static IP address but this would prevent you connecting to your account twice. If your DSL line goes down because of technical problems, though, you would be able to connect to XMission while your DSL line is down.

Business DSL accounts cannot use a 2nd line during business hours, as they would normally be allowed, but they can have uncapped DSL line speeds at no additional charge and IP addressing, up to a size 16 subnet, is available upon request.

If you travel, or occasionally connect from more than one place, you can get a $19/month Individual account or a $10/month Email-only account, which includes dial-up. You can, however, disconnect your DSL (by turning off the computer with the "modem" in it or unplugging your router) before you leave and dial up with your DSL account.


What is meant by the term, "shared bandwidth"?

People will be sharing it in a way that doesn't guarantee a full pipe to each user all the time. For example, a T1 is comparable to 6 256k connections (6 x 256k = 1.5 MB) but we'll be selling the equivalent of more than 6 DSL lines for a T1. This isn't an entirely accurate example but it's an easy way to get the idea across. For those who have demanding bandwidth needs, frame relay or T1 is highly recommended.

With shared DSL service, you're not guaranteed bandwidth. We're not going to oversell DSL services since bandwidth to Our DSL bandwidth is spread across multiple DS3's, allowing us to readily control growth and avoid saturation. CenturyLink isn't price-prohibitive and outgoing traffic from XMission has plenty of headroom. Our router stats page indicates this fact.


How many people will share the bandwidth?

We monitor this and simply add bandwidth as needed. Expect to see statistics available online that publicly show our bandwidth usage. But remember that basic DSL is not a guaranteed bandwidth service. We can only offer guaranteed bandwidth with Dedicated Bandwidth accounts such as a Frame Relay.

What, exactly, are "client" and "server" services?

On the internet, machines generally connect to each other as clients and servers. Client services are what you use when you check email, download a web page or file from FTP, run CUSeeMe or just about any Internet software. Server services describe a situation where a server feeds information out to the Internet. An example of a server would be mail.xmission.com. This is the server XMission clients connect to when they check their email. Server services include the following, for example: web, ftp, game, mail, etc. Should you have further questions as to what qualifies as a server service please give us a call or email support@xmission.com.


Can I run server services over my DSL connection?

One of the first questions we concerned ourselves about dealt with this issue since XMission has always sought to provide value-added services to its customers and not restrict anything. While the abuses of some can spoil things for everybody, we have found a compromise that allows high bandwidth for all ports but with heavy monitoring. We will be closely monitoring dsl statistics reports and those who go over their bandwidth quota, as mentioned above, will be sent a warning, then restricted. We recommend if you're running a server for personal use, that you limit the simultaneous connections to just two or three. This allows people to access their machines for work, to do various server services for personal use but prevents saturation of the DSL bandwidth.

If we didn't closely monitor our DSL accounts then a few people would very likely use the majority of bandwidth allocated to all of our DSL customers. By restricting server traffic, we are able to provide dedicated services at previously unheard of prices.


Will "server services" be blocked or monitored?

Those concerned about abuse need not worry as we will be closely monitoring bandwidth usage on a per-customer basis. If it's noted that a certain customer is using more bandwith than they need for personal needs, they will be warned once, and restricted if the high-bandwidth usage doesn't cease. For most people, DSL offers a larger, burstable pipe that will remove the bottleneck on their end. As most Internet users mainly browse the web and use email, such intermittent use will generally allow for a lot of burstable bandwidth even if many people are sharing the same pipe. As you can well imagine, if XMission didn't maintain a close eye on server services, a few people running unrestricted web and or ftp servers could quickly hog a large percentage of our DSL bandwidth and ruin it for everyone else.


Will my DSL account be considered a dedicated connection?

No. DSL accounts are considered burstable to your purchased bandwidth from CenturyLink, but is not considered a dedicated account. Information on business-level dedicated accounts can be found at http://www.xmission.com/dedicated


Can I associate a Domain Name with my DSL account?

You can do this with a business account at no additional charge. If you have a personal DSL account, XMission charges an additional $7 a month for primary and secondary DNS for one domain. If you're just looking to have a name associated with your IP address, though, you can have your own machine name associated with XMission's domain like this: name.dsl.xmission.com. You can choose whichever name you'd like but it defaults to your account name if you don't have a preference. Contact support@xmission.com for more details.


Using DSL/Help

How can I FTP through a non-standard port through a firewall?

To ftp to a non-standard port with cute-ftp, select:ftp, settings, options, firewall tab, check PASV mode and check the 'firewall access' box.


How can I use ICQ through a socks5 proxy?

Using XMission's socks5 proxy server will make it easier for people to reach you via ICQ. To use it, simply follow these steps:

  1. Go to preferences
  2. Open the Connection tab
  3. Check I am behind a firewall or proxy
  4. Press the Firewall Settings button
  5. Check I am using a SOCKS5 proxy server
  6. Press Next>
  7. Enter SOCKS5 Host: socks.xmission.com
  8. Enter SOCKS5 Port: 1080
  9. Press Next>
  10. Press Check My FIREWALL/Proxy Setting
  11. Press Done

You can also use this with AOL Instant Mesanger. Under Options and Connection, set the proxy protocal to SOCKS5, the proxy to "socks.xmission.com", and the port to "1080".

If you are using an IRC client like mIRC that supports firewalls, you can again use the socks proxy server. In mIRC you goto File, Setup, and select Firewall. Check Use SOCKS firewall, select Socks5, put "socks.xmission.com" for the host, "1080" for the port, and check Initiate DCCs through firewall.


How can I set up my own firewall?

If you have the external Cisco 678, there are filtering options that come with it. There are instructions in the manual that came with the router for doing this.

Another resource that might be helpful is located at http://www.users.uswest.net/~rlutton/ADSL/. This is a good, concise resource for some basic info about the Cisco 675 and its NAT capabilities. It also explains basic security features that the casual home user can implement if so inclined.


Why do I see a lot of ICMP traffic hitting my DSL line?

ICMP provides error reporting, congesting reporting and first-hop gateway redirection. In addition to being used for ping, ICMP is used to as a message control and error-reporting protocol between a host server and a gateway to the Internet. It is normal to see ICMP traffic. However, if you're noticing a great deal of echo/echo-reply traffic (echo/echo-reply is what ping is), to the extent that it's begining to consume your bandwidth, you should probably contact technical support. For more in depth information about ICMP and how it's used, please refer to RFC 792.