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The major differences between T1 Internet Service and DSL Internet Service are directional bandwidth and symmetrical vs. asymmetrical bandwidth. Hence, the continual DSL-T1 debate and decision. You can choose T1, DSL, cable, or dial-up service to connect to the Internet. Dial-up is not even comparable, so we will leave it out of the discussion. This web page will focus on a DSL-T1 line comparison. Directional Bandwidth refers to the amount of bandwidth available for upload and/or download, at any given time. Further, marketing claims of "up to XXX speed" should be taken seriously. When claims like that are made, the maximum speed obtained is typically when the carrier's network is at its least-busy condition, say 4:00am local time. DSL ISP services are based upon a "pool" of bandwidth assigned to a group of customers, so if all the subscribers in your area are online, your available bandwidth will be far less than the speed claims of "up to" this speed or that. Symmetrical vs. Asymmetrical T1 service is symmetrical; meaning that with 1.536Mb of bandwidth is available for either upload or download, depending upon the user's needs. A simple formula can determine available bandwidth in either direction:
DSL service is asymmetrical, meaning that only a portion of the available "pooled" bandwidth will be made available to a subscriber, AND the carrier sets pre-set limits on upload and download speeds. Upload potential and Download potential are not the same, with typical DSL service offering (up to) 512kb upload, and 1.5Mb download. This (up to) has to be inserted into this statement because DSL ISPs have a built-in Contention Ratio . Contention Ratio refers to the amount of subscribers (total) compared to the amount of subscribers (online). This engineering is typically in the 15-30:1 ratio, so if all subscribers were online, and all decided to download a large file at the same time, at even a 15:1 contention ratio, the overall bandwidth demand would exceed the bandwidth supply and all users would slow down significantly. While this is no surprise to network engineers, the general public is under-informed of this fact. T1 customers, however, engineered by reputable Telephone Companies, have the ability to use their maximum speed in either direction (or a combination of both), provided that the overall demand is not greater than the 1.536Mb T1 capacity.  Besides the addition of a DSL modem, DSL installations require HF filters installed on all non-DSL compatible equipment. This means that either each telephone have an HF filter installed, or special installation requirements to utilized a copper pair that may be on-site but not used. (Most telcos will not activate DSL service on a copper pair unless they tie the service. IP Addressing Differences. T1 ISP service will typically issue between one and five static addresses for your use, whereas DSL providers will typically require you to use DHCP, so that you don't necessarily know what your IP address is. While for most SOHO applications, this is not a big deal, if the end-user requires remote access, remote monitoring, off-site network/file synchronization, etc, a Static (never changes) IP address scheme is preferred. |
DSL T1
