hwobu
join:2009-02-08
Arlington, VA
|  Clarification
Karl,
I've got good news for you, there is a correct and valid industry term for what you're calling a 'mini-exchange' on VDSL. That term is DSLAM (DSL Access Module). Coincidentally this equipment is identical regardless of where it has been physically located (sized based upon cost effectiveness).
Now for some tech-talk.
A DSLAM simply provides a DSL down-stream connection to subscribers, that DSLAM is in turn supplied connectivity through an up-stream (or back-haul) connection.
The down stream connections can be almost any DSL technology, and in some cases even a few connections that aren't really DSL. This is almost always exclusively dependent upon the specific line card inserted into the DSLAM. As for the up-stream connection, there are 4 main link types and the preference for one over another is highly dependent upon site bandwidth needs. Those uplink choices are IMA (inverse multiplexed ATM)(low bandwidth needs/few customers), Single DS3 (moderate bandwidth needs for a single DSLAM), SONET (OC-3 specifically) (higher bandwidth needs for 1 or 2 DSLAMs max, but still not enough density to need a local router), and lastly Gigabit Ethernet (this usually connects to a local edge router that may have 1 or more upstream connections and almost always serves more than one DSLAM at that site if not other equipment).
More detail about the downstream technologies available on a DSLAM.
(US specs here as speeds/specs vary widely from country to country)
[IDSL] - not very common (DSL over ISDN BRI) 128k or 144k max up and down, good distance
[ADSL] - most common consumer/residential delivery (moderate upload, much faster download vs upload 8:1 ratio normal) moderate to long distance, though there is a speed penalty at longer distances
[G.lite] - very similar to normal ADSL except line filters aren't required at the phones in exchange for slightly slower up/down speeds and shorter available distance from DSLAM (less prone to users forgetting a filter or plugging them in backwards)
[SDSL] - primarily business use, not very widely deployed
[HDSL] - almost exclusively business service delivery (indirectly) very common deployment technology for Business T1 service (aka 2wire T1) - technically this can support higher speeds than T1, though rarely used outside of that role
[ADSL2] - improved/updated version of ADSL, slightly better upload speed, much better download speed, slightly better distance - Bonding possible
[VDSL] - very good up and download speeds, but at a very short distance - resulted in this technology making it little past the prototype and early deployment stages
[VDSL2] - very high up/down speed connectivity over short distances and just high speed at moderate distances, sharp speed drop thereafter - Bonding possible
[SHDSL] - same up/down speed - very limited deployment till its modified application to long-haul-ethernet (2baseTL)
[2baseTL] - specialized DSLAMs required - bonded pairs, and up to 45Mb possible up/down over short distances and tapering off of around 7Mb at 13k feet (maximum speeds and distances require bonding)
For all of the downstream DSL connections, this involves one or more copper pairs (depending on specific DSL technology).
I hope this helps clear up some of the mysteries behind this technology.
Thomas |
