| Common Term | Speed | Composition |
|---|---|---|
| DS.0 | 64Kbps | Equivalent to a single voice channel (regardless of medium: copper, fiber, RF, etc.). This is the basic building block of all other circuits. Although the nominal rate is 64Kbps, there are some standards which quote 56Kbps due to local standards or regional regulations. |
| ISDN BRI | 128Kbps | 2B+D: Two 64Kbps “Bearer” channels (each equivalent to a DS.0) and one 16Kbps “Data” channel. Contrarywise, the D channel is not typically used for user data, but for signalling & control information between the two connected nodes. “Basic Rate Interface” Typically delivered only over copper. |
| xDSL | 128Kbps–1.544Mbps | Any one of several varieties of “Digital Subscriber Line,” see table below for a look at currently available varieties. By design, most DSL flavors are an “asymmetric” signal that is rated for two different speeds, depending on the direction of the traffic. The slower client-to-server (upload) speed is most commonly found in the 128–384Kbps range (with a maximum near 1.5Mbps) while the server-to-client (download) speed can run from 1.5–4Mbps (with a maximum near 8Mbps). Typically delivered over a single copper circuit, DSL and analog phone services can share a single pair by performing a frequency split: analog phone service doesn’t use frequencies above 4KHz, and DSL uses frequencies at 25KHz and above. |
| Fractional T.1 | 64Kbps-1.544Mbps | Typically an arbitrary allocation of a portion (channelization) of the T.1 connection. Typically used for 128Kbps, 256Kbps, 512Kbps and 768Kbps connections, although any arbitrary number from 1bps through 1.544Mbps can be allocated. Normally delivered over copper and fiber, although wireless installations are beginning to become popular for campus linkages. |
| DS.1, T.1, ISDN PRI | 1.544Mbps | Nominally, 24 × DS.0. ISDN uses it for the “Primary Rate Interface,” and allocates one 64Kbps channel as a D channel (23B+D). Unlike the BRI, the D channel in PRI is frequently used for user data. “T.1” specifically refers to delivering DS.1 over 2 pairs copper wire. |
| E.1 (European ISDN PRI) | 2.048Mbps | At 32 × DS.0, this is the European and Japanese version of the T.1 circuit. |
| Common Term | Speed | Composition |
|---|---|---|
| E.3 | 34.368Mbps | 537 × DS.0, 22 × DS.1 |
| OC.1, DS.3, T.3 | 51.84Mbps | 672 × DS.0, 28 × DS.1 Individual circuits don’t exactly multiply here because of bandwidth lost to circuit overhead. As with lower speeds, the “T” designation refers to delivering the “DS.x” circuit over copper. In this exact case, it refers to coaxial copper cable. |
| OC.3, STM.1 | 155.52Mbps | 2016 × DS.0, 84 × DS.1, 3 × DS.3/OC.1 Unless specifically designated, OC.3 is really three OC.1 “pipes” on a single circuit, each with it’s own framing overhead. |
| OC.12, STM.4 | 622.08Mbps | 8064 × DS.0, 336 × DS.1, 4 × OC.3 |
| OC.48, STM.16 | 2488.32Mbps | 32,256 × DS.0, 1344 × DS.1, 4 × OC.12 |
| OC.192, STM.64 | 9953.28Mbps | 129,024 × DS.0, 5376 × DS.1, 4 × OC.48 |
| Type | Maximum Speeds | Primary Uses |
|---|---|---|
| ADSL | 8Mbps downstream 1.5Mbps upstream |
Standard for home and small business, but marketed in several different bandwith/price points. |
| G.lite, DSL-lite | 1.5Mbps downstream 384Kbps upstream |
Same as ADSL except for speed; unacceptable for voice and multimedia applications. The key selling point of this type is “splitterless” connections where the DSL user-end equipment plugs into the same wiring as analog telephones without any other termination equipment. |
| RADSL | 7Mbps downstream 1.5Mbps upstream |
Same as ADSL, but actual bandwidth used during transmission is adaptive, based on the line quality at the time data is actually flowing. |
| HDSL | 1.5Mbps both ways | Requires 2 wire pairs (other DSL uses 1 pair, just like analog voice loops); used by businesses as an alternative to T.1 connections |
| HDSL-II | 1.5Mbps both ways | Implementation of HDSL utilizing a single pair. |
| SDSL | 1.5Mbps both ways | Forerunner to HDSL-II; same performance but limited to termination within 10,000 feet (~3Km) of the central office. |
| IDSL | 144Kbps both ways | A hybrid of DSL and ISDN that has the performance of ISDN-BRI and the point-to-point (no call setup latency) performance of DSL |
| VDSL | 52Mbps downstream 2.3Mbps upstream |
The fastest standard DSL service; only available within 4,500 (~1.3Km) of the central office. |
| Comments? Email jim3@millard.org | Last updated October 20, 2001 |