# How much bandwidth does a T1 typically give?

We're about to move into a new apartment which has a T1 for \$35 a month. How much bandwidth does a T1 usually supply?

Right now we are with Comcast cable which theoretically gives us 14mb down / 7mb up, but I haven't really seen any download or upload speeds going at more than 1mb in all the time we've been using it.

By definition, a T1 provides 1.544 Mbps, full duplex. (The equivalent European specification is the E1, which provides 2.048 Mbps.)

However, it is divided into 24 channels, and they can be aggregated in any number, so you can get a "partial" T1 in many different bandwidths.

And sometimes multiple T1s are sold aggregated together in what tends to be called "bonded" T1s.

Also, sometimes "T1" is used incorrectly to mean a full-duplex business-class (which usually means "better bandwidth guarantee") circuit, or possibly even something else. You need to make sure what you're getting from your vendor.

• +1 for "check what you're getting from the vendor". good tip. Commented Oct 11, 2009 at 17:51
• Keep in mind that if you get a real T1 trunk direct to your wall, you can't use a normal modem/router and you'll need to get a T1 device, which are quite a bit more expensive than a Cable/DSL device usually. Commented Oct 12, 2009 at 3:34
• Most ISPs will provide the requisite equipment and bill you for it. Commented Oct 12, 2009 at 16:22

According to Wikipedia T1 provides 1.544 Mbits/s of bandwidth both directions.

A T1 is a data circuit with 24 channels. Depending on the provisioning, it can provide different bandwidths and you won't get the full 1.544Mbps for your use. B8ZS/ESF "clear channel" uses 64k channels while AMI/D4 uses 56k channels (8k is used for control). Sometimes you'll use fewer channels, such as a fractional T1.

• 24*64k = 1.536 Mbps (slightly less due to signaling codes)
• 24*56k = 1.344 Mbps

A lot of T1s are now HDSL circuits and use a single pair instead of two pair.

Other things also use T1s like a PRI circuit. For a PRI, you often see 23 B channels to carry calls or data and 1 D channel for control.

A T-1 provides 1.536Mbps of bandwidth, total. It can be used fully up or down, or at any feasible combination of speeds in between but always maxing out at 1.536Mbps due to the 8kbps framing bit used to keep timing on the circuit. Here's a few references: This is AT&T's spec for the origination of a T-1 circuit:

TR62411a: ACCUNET® T1.5 Service Description And Interface Specification

4.6.2.2.1 Transmission Line Rate The electrical signals delivered to the Network and to the CI at the NI, must be T1 - type bipolar, except where intentional bipolar variations are introduced by B8ZS (see Section 4.2.2), operating at the nominal DS1 rate of 1.544 Mb/s ± 50 b/s (11). 11: Older equipment has rate variation up to +-200bps

5.6 64 kb/s Clear Channel Capability (64CCC) Clear Channel Capability is a characteristic of a DS1 transmission path in which the 192 information bits in a frame can represent any combination of zeros and ones. Clear Channel Capability, as an option for ACCUNET T1.5 Service customers, will be implemented exclusively through use of B8ZS line encoding both on the access and interoffice channel (IOC) segments, thus providing end-to-end B8ZS Clear Channel Capability. Thus, 64CCC implemented through B8ZS, provides users with 64 kb/s of channel capability, and on properly configured DS1 circuits, allows 1.536 Mb/s of data transmission. (See related discussions on B8ZS and Pulse Density restriction in Sections 4.2.2 and 5.5.)

In today's technological age there are T-1 approximate circuits, where they are providing you T-1 speed and guarantees, but might not be using the actual T-1 technology.

An example would be CenturyLink's Private Line service, defined as:

Private Line: T1/DS1 transmits of isochronous serial data at 1.544Mbps. The service has the capacity of 24 voice-equivalent channels.

The bolded part is the clarity some may be looking for. There are 24 bi-directional 64kbps channels on a T-1, and an 8kbps framing bit for timing. 24 channels * 64kbps each = 1536kbps + 8kbps = 1.544Mbps total CAPACITY.

A T1 line will normally give you 1.5Mbps in both directions. Normal cable internet gives you a high download speed (3Mbps+) but slower upload speed (500Kbps). A T1 line will give you a noticeable speed increase because you can send data at the same rate as you receive it. Sending mail, moving files, FTP, uploading pictures or videos, and torrenting are all uses you would see a very noticeable speed increase.

• Absolutely wrong about a speed increase. It is common to have 10/3 from cable internet nowadays. Having an increased upload speed and reduced download speed will absolutely not increase performance, especially with such a drop in download speed. Not to mention that a standard cable internet service from most major providers exceeds 1.544Mbps up and down anyway. Commented Oct 11, 2009 at 17:48
• I've never gotten 10 up 3 down on any cable provider, even when I had a 16Mbs plan I still capped at 1Mbit up. A T1 line is dedicated, cable broadband connections are a shared "best effort" line. You won't get what you pay for, at best 80% of the advertised bandwidth. Commented Oct 11, 2009 at 18:37
• Regardless of your individual experience, an 80% reduction in download speed is going to give a noticeably slower experience than a (possible) marginally increased upload speed. Commented Oct 11, 2009 at 19:01
• Where do you get an 80% reduction? My point is that a cable connection is a party line, you [strong]will[/strong] different speeds at different times of the day, and it depends on the number of people on that line and the connection to the ISP. A T1 line is a dedicated line you have all to yourself. You can host off of a T1 line, not a cable line. Static (or dedicated) IP address with a block of bandwidth. Commented Oct 11, 2009 at 20:17
• From your answer "A T1 line will give you a noticeable speed increase because you can send data at the same rate as you receive it." That's misleading. Even on a shared trunk like DOCSIS, any modern day connection will give you better performance for a home user than a T1. The question didn't involve anything about hosting at all. Commented Oct 12, 2009 at 0:51