DSL Confusion- Please Help

LegacyUser

Whilst acting as a Good Little Boy and telling all my workmates about the meeting 2moro @ the Mercer, the office smartass managed to show me up (only a little!) when he asked me to explain whats the difference between the following....

DSL
ASDL
XDSL
SDSL

He rightly pointed out that these were all mentioned in the Etain Doyle article in the Times Busin. Supplement 2 weeks ago and that different forms of broadband will be available throughout the country. He didn't know the answer either but he made me look a little un-informed !! So if someone can clarify this so I can "Preach" properly for IrelandOffline in the future I would be grateful.
I'm sure there are many others needing clarification and there seems to be a few very profficient technological minded members who could assist.

80p.

(PS Dahamsta- I loved the eircom joke re: Sultan of Brunei. Pity the thread was locked. As an after thought I put a clipart image of a cowboy w/ a lasoo on my desktop as a shortcut for my eircom.net dial up!! I've said it before and I'll say it now... Its only funny 'cos its true! )

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www.80project.com

LegacyUser

Ok, i'll just tell you what i know.

DSL - Digital Subscriber Line:

Exactly what it says.


ADSL - Asymmetric Digital Subscriber Line:

Basically means that you have a higher download speed than you do upload. Hence the 512Kbps download and 128Kbps upload speeds being trialled by Eircom.


SDSL - Symmetric Digital Subscriber Line:

You know what symmetry is, right? Well again basically the download and upload speeds are the same. So if you have 512Kbps download, then your upload is same.


xDSL:

This is just the generic term for all the variants of DSL. Substitute the 'x' for the 'A' of ADSL. Get the picture?


Feel free to correct me if i'm wrong.

LegacyUser

<font face="Verdana, Arial" size="2">Originally posted by K!LL!@N:

SDSL - Symmetric Digital Subscriber Line:

You know what symmetry is, right? Well again basically the download and upload speeds are the same. So if you have 512Kbps download, then your upload is same.
</font>

Just to pad this one out a little, SDSL has a greater upstream capacity than ADSL. It is often possible to get 1.1mb up/down on SDSL, which is not possible with standard ADSL. This is part of the reason why it is often said to be more appropriate for business use.

dahamsta

You can also randomly substitute "Digital" with "Direct" and "Line" with "Loop". Subcriber seems to remain static though...

adam /who goes back to writing the FAQ again/

LegacyUser

thanks for the "greatest hits" as such of DSL.
I now have some ammunition in store to show up a certain smarty pants. (U KNOW WHO U ARE)
As ever, most indebted for your contributions.
80p.

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www.80project.com

LegacyUser

I copy, paste and add some info from another newsgroup.

xDSL is the generic term for all DSL type technologies. Often the DSLAM located in the Eircom exchange can support many different xDSL variants. Alcatel are the suppliers to Eircom of ADSL kit. The difference in cost to Eircom between ADSL, gSHDSL, or VDSL is marginal, however from a corporate point of view anything but ADSL will canabalise their leased line revenue. ADSL is the 'pond scum' of DSL technologies.

HDSL is used by Eircom to supply E1 or sub E1 leased lines.

ADSL Asymmetric Digital Subscriber Line: Modems attached to twisted pair copper wiring that transmit from 1.5 Mbps to 9 Mbps downstream (to the subscriber) and from 16 kbps to 800 kbps upstream, depending on line distance. Normally sold with a contention ratio of up to 25:1, that means for every 25 Mbit/s sold to customers, only 1 Mbit/s of capacity is available at a minimum at any one time for the customers shared benefit.

ATM Asynchronous Transfer Mode: an ultra high speed cell based data transmission protocol which may be run over ADSL.

BDSL Same as VDSL.

DSLAM Digital Subscriber Line Access Multiplexer: specifically, a device which takes a number of ADSL subscriber lines and concentrates these to a single ATM line

E1 European basic multiplex rate which packs thirty voice channels into a 256 bit frame and transmitted at 2.048 Mbps.

FTTH Fibre To The Home: network where an optical fibre runs from telephone switch to the subscriber's premises or home.

FTTK or FTTC Fiber To the Kerb: a network where an optical fiber runs from telephone switch to a kerbside distribution point close to the subscriber where it is converted to a copper pair.

HDSL High data rate Digital Subscribe Line: Modems on either end of one or more twisted pair wires that deliver T1 or E1 speeds. At present T1 requires two lines and E1 requires three. See SDSL for one line HDSL.

ISDL Uses ISDN transmission technology to deliver data at 128kbps into an IDSL "modem bank" connected to a router.

Loop Qualification The process of determining if a line (or loop) will support a sepcific type of DSL transmission at a given rate.

POTS Plain Old Telephone Service: the only name recognized around the world for basic analog telephone service. POTS takes the lowest 4kHz of bandwidth on twisted pair wiring. Any service sharing a line with POTS must either use frequencies a bove POTS or convert POTS to digital and interleave with other data signals.

RADSL Rate Adaptive ADSL: a version of ADSL where the modems test the line at start up and adapt their operating speed to the fastest the line can handle.

Splitter A filter to separate ADSL signals from POTS signals to prevent mutual interference.

SDSL Symmetric Digital Subscriber Line: HDSL plus POTS over a single telephone line. This name has not been adopted by a standards group, but is being discussed by ETSI. It is important to distinguish, however, as SDSL operates over POTS and would be suitable for symmetric services to premises of individual customers.

UDSL Unidirectional HDSL as proposed by one company in Europe without much sign of interest from anyone else.

VADSL Very high speed ADSL: same as VDSL (or a subset of VDSL, if VDSL includes symmetric mode transmission)

VDSL Very high data rate Digital Subscriber Line: Modem for twisted-pair access operating at data rates from 12.9 to 52.8 Mbps with corresponding maximum reach ranging from 4500 feet to 1000 feet of 24 gauge twisted pair.

LegacyUser

rardagh bt have a coonection ratio of 50 to 1 not 25 - 1, you can bet eircom and esat will do the same

LegacyUser

What is that of the connection rato? Could someone explain me throroughly please? 50:1 or 25:1? I've no idea, why that appears on any Cable, DSL connection.

Cuz I've seeen it everywhere but no idea what it is.

CHeers.

JamworkS

LegacyUser

<font face="Verdana, Arial" size="2">Originally posted by JamworkS:
What is that of the connection rato? Could someone explain me throroughly please?
</font>

Contention ratio would be a more correct term for this. Essentially its the ratio of bandwidth supplied to a number of users to the amount of bandwidth sold to them.

For example if a DSLAM holds 100 users, each of whom has been sold a 1mbit DSL connection, no ISP is going to provide 100mbit of connectivity to the DSLAM, mostly because teh chances that all of them are online and downloading at 1mbit simultaneously are statistically low. Instead only a very small fraction will be provided to be shared between the users.

Typical contention ratios are 25:1 (or 4mbit between 100 1mbit customers) and 50:1 (or 2mbit between 100 1mbit customers).

Its generally held that a 25:1 contention ratio allows pretty decent performace at all times, whereas a 50:1 ratio can result in dial-up type speeds at peak times. But it all depends on who you're sharing the bandwidth with

LegacyUser

whats connection would a leased line have

Bard

<font face="Verdana, Arial" size="2">Originally posted by Gladiator:
whats connection would a leased line have</font>

What are you talking about? How is the line connected to your system? What the connections speed would be? What the connection ration would be? Could you rephrase that so that it is grammatically correct and makes sense, please?

LegacyUser

<font face="Verdana, Arial" size="2">Originally posted by Gladiator:
whats connection would a leased line have</font>

A leased line uses the Telcos core ISDN Network, with a permanently reserved path through it from the office to the ISP interconnection point. SO if you have a 256k leased line, it means that 256k is permanently reserved for you right through the Telcos network. Thats why htey're so expensive.

This leads on to the problem of FRIACO. The reason, IMHO, that FRIACO is a sham, is because dialup works the same way, with a reserved path through the network, so the cost to the telco of people staying on the net 24/7 are similar to the costs of a leased line, but instead of being paid 200IEP, they're being paid 10IEP.

People talking about FRIACO being handled on the basis of cost are being ridiculous, because the cost to the telco of providing such a service is probably waaaay higher than the user is willing to pay for 56k dialup.

However, I agree that we have a (social, business) need for always-on net access, just not this type of flat rate. Therefore, I think its only fair to allow Eircom to refuse to supply FRIACO on lines which it is willing to deliver broadband on.

Everybody wins that way - Eircom has an incentive to roll out data services aggressively, and customers won't have to put up with FRIACO nonsense for any longer than they have to.



[This message has been edited by hudson806 (edited 19-07-2001).]

LegacyUser

hudson seems to have seen what i was saying,

and hudson that make far to much sense for the goverment to do, jesus if we did that there would be broadband in nearly every city and town in the country,