'T1 obsolete.' That's interesting, since most DSL service runs over bundled T1s or T3s prior to hitting the neighborhood loops. Anyway, T1s are becoming less attractive in areas that offer direct ethernet solutions. However, ethernet is more limited by distance than T1 and thus not as widely available. (DSL is also more limited by distance than a T1 - but my argument is that DSL/cable is not for the same application and for the med to ent level organization, should never be considered for more than maybe a failover scenario). T1 and DSL or cable don't really compete. A home user wouldn't have much use for a T1 line, even though they have gotten much cheaper they don't typically have enough value for a home user, but they do for businesses, especially medium size companies and up.
First, if a company has multiple voice lines (more than five) and hasn't made the move to VOIP, then a T1 is much more affordable than SBLs and will make a lot more sense for hooking up a PBX. Also with dynamic T1 or PRI, you can have the line be used for both voice and data, so you have 1.5 mbs/1.5 mbs of data and if someone in the organization makes a phone call, you lose a small portion of that for handling the voice traffic. (Or like in my case where our organization has an ethernet connection, we have a dynamic T1 for our PBX that is also connected to the firewall for failover if the ethernet went down.) Note: we have up to 10 lines of voice on a digital PBX system, and T1 is the cheapest way to go unless we switch to VOIP and that has a lot of hardware cost, so having the T1 as a data failover is virtually free. Is DSL free?
Also, even if looking strictly at data use, the speed down/up is not the only measurement or consideration, which is just as important for networks supporting many users is ping response speed and jitter, packet loss, up time, consistency of speed and what I refer to a 'stickiness'. The telecom companies are federally mandated to repair T1 service prior to repairing phone or dsl, and their up time, response time and guarantees are much better on a T1 service (compared to DSL, and cable service is even worse). In organizations, you often have multiple users (hundreds for some) sharing your WAN connections, the initial connection (the response speed you see on a ping test) is independent from the overall line speed, and is slower on DSL and cable lines than a T1.
Jitter is how much the initial response speed varies, which also causes slow down in the communication between locations, routers, switches, NICs, etc., all of which like consistency when 'talking'. Failure rate which can be as high as 2-3 percent on a DSL line (sometimes do to jitter) and even higher on cable is also a problem -- when a packet fails the whole packet has to be resent.
T1's have less than 1 percent failure rates on each packet. And then there is 'stickiness.' This is the term I use to describe how a DSL or cable line tends to allocate and hold on to more bandwidth than it needs - so if user X starts to download a file he may grade all 5 mbs of your DSL bandwidth for the download even though the file isn't even coming down that fast, meanwhile user Y requests something from the internet and that DSL connection seems like it is practically down or crawling for him.
Also, after user X gets his file the DSL/cable line may hold that bandwidth for a second or two before deciding to allow it to be allocated elsewhere. T1s are much better at channelizing the data stream and sharing it among multiple sessions even mid-stream. Now that might not sound like much if you (or even two or three people) are the only ones using the connection, but in an organization with 10, 20, 50, 100, etc. users, these things start to have a lot more impact than the speed of the connection, especially in the typical business use of the internet, where instead of having one user trying to download a video, you have a lot of users just following links or working on a hosted database or sending email etc., this works both ways too. If you are hosting a website or email server, or have remote users accessing your network, etc., having the consistent upload spread and channelization of a T1 will often out perform a much 'faster' DSL line. (It is similar to a copier's print speed versus its first print speed. If your copier can run 100 copies per minute once it gets going but takes 15 seconds for the first print - that might be great for the person/organization who runs nothing but large jobs, but for the organization that has lot of users just needing one or two copies all through out the day - that copier sucks). Just my $.02, but don't knock the T1 unless you actually know the application it is getting implemented for. Otherwise you might sound a bit ignorant.
