What Speed is ADSL

leprykawn

Hey there. I'm a newbie, and I'm wondering what kind of connection speeds is ADSL promising? a couple of megs a second? or more?

Xterminator

Here is a horribly abbreviated synopsis of xDSL technology.
It helps to understand the basis of the technology.

DSL is a technology for pushing a (relatively) large number of bits through wiring that is typical for "last mile" telephone connections -- i.e. small gage copper wire of lengths less than 18,000 feet. There are a number of different protocols that fall under the DSL umbrella: ADSL, RADSL, HDSL -- and even different subvariations (e.g. CAP encoding ADSL versus DMT encoding ADSL), thus the acronym xDSL to represent the technology in total, without regard to the specific protocol. It's a little like the 56k modem field before the V.90 standard unified the two main contenders, X2 and KFlex.

xDSL is used to push high bit rates through copper wires that run from point A to point B. For most people, point A will be their home and point B will be the other end of the copper phone wire, that is the substation of the local phone company.

Standard telecom modems (e.g. 56k, 28.8k, etc) establish a data stream between two arbitrary points using the entire telecom system--that is, from the sender's local loop, through the telephone switching system (mostly digital switches now) and then to the receiver's local loop. Standard modem connections can span continents, with one end being thousands of kilometers from the other end.

DSL modems, on the other hand, establish a connection from one end of a copper wire to the other end of that copper wire: the signal does not pass into the telephone switching system. Consequently, DSL modems are not limited to using only the voice frequencies passed by the standard telephone system (typically 0-4kHz); DSL modems typically use more than 100kHhz.

To reiterate, one end of the DSL link will be at the consumer site, the other end must be at the other end of the copper cable -- usually this means your local telephone exchange. At your local phone company the local loop first goes into a splitter that splits the data frequencies from the voice frequencies. The voice frequencies are wired into a traditional POTS switch and enter the normal telephone switching network. The data frequencies are wired into a corresponding DSL modem at the CO end and the resulting high-speed digital data stream coming from (or going to) the consumer is than handled as normal data (not analog voice) and may be hooked into any number of networking technologies for further connection to the data's destination. Thus, the data never enters the standard telephone switching system.

Typically the data will be routed over a LAN/WAN connection (10Base-T Ethernet, T1, T3, ATM, frame relay, whatever) to a business office. The business may be an ISP (EG Eircom ESAT etc) which may then route the data onto the Internet, thus providing you with Internet connectivity.
Because the other end of your xDSL connection has to be at the local phone company, the choice of which xDSL protocol your modem should support is made for you: whatever the local phone company dictates.

To sum it up, Speed is dependant on what hardware is implemented at the exchange, how many users are sharing bandwidth etc.

Eircom plan to offer ADSL, as eircom i-stream solo, with a download speed of up to 512kbps and an upload speed of up to 128kbps.
In theory.

X

leprykawn

In other words, eircom's i-stream, in practice, will be a souped-up version of ISDN.:mad:

Dustaz

No, there are substantial differences between DSL and ISDN (which ill let others explain ).

That is only the entry level speed option and its a pretty standard one. Most Telcos worldwide offer this speed (altho the upload speed is usually 256kbps).

The range of DSL products eircom intend to launch can be found here .

leprykawn

I meant in terms of the speeds IN PRACTICE.

dahamsta

I meant in terms of the speeds IN PRACTICE.

Nope, not in practise either.

adam

Praetorian

On a modem you might get 5K a sec downloading

On isdn you should get 7k a sec

On dual isdn 14k a sec

on 512kb adsl you can get 50k a sec (but only 14k upload)

Mercury_Tilt

This post has been deleted.

ando

and for some weird reason, irish Isdn is Much better for online gaming than Irish DSL ? (ping times)

Felix Randel

Originally posted by Dustaz
No, there are substantial differences between DSL and ISDN (which ill let others explain ).

How is it possible to have more than one service provided over a single line? ISDN is a digital service. Because it is digital, it is possible to divide the bandwidth on a single twisted pair into different channels. The three types of channels are B-channels, D-channels, and
H-channels. B-channels, or bearer channels, carry information. D-channels, or data channels, are used for signaling and control. H-channels, or high-speed channels, are used to accommodate bandwidth-intensive applications. H-channels are actually formed by bonding multiple B-channels. These channels provided through one of two standard interfaces: basic rate interface (BRI) or primary rate interface (PRI).

BRI is also known as 2B+D because it consists of two B- channels and a D-channel. Each B-channel operates at 64 Kbps. Each B-channel is capable of carrying data, voice, or low-speed data. The D-channel operates at 16 Kbps and is used for signaling and control, messaging, and network management. The D-channel can also be used to transport packet data transmissions such as credit card transactions. BRI is primarily used for residential and small business applications. It can also be used for videoconferencing if the B-channels are bonded as mentioned earlier. One BRI line can support up to 16 devices, including
telephones, fax machines, and computers.

PRI is also commonly known as 23B+D because it consists of 23 B-channels and a D-channel. All the channels operate at 64 Kbps. The B-channels are used just as they are for BRI, but the D-channel is reserved specifically for signaling.

An ADSL line is also divided into channels. A high-speed downstream channel is provided in increments of 1.536 Mbps up to 6.144 Mbps. A bi-directional channel is also provided in 64 Kbps intervals up to 640 Kbps. Dividing the frequency within the signal creates individual
channels. The frequency division occurs in an ATU-R (ADSL Transmission Unit-Remote) ((eircom splitter box))located on the customer’s premise. Here the bandwidth is divided into three channels: the downstream channel, the bi-directional channel, and the voice channel.

As a matter of interest, Eircom sell BRI isdn while esat sell PRI isdn. You can also have free 16k internet on an isdn line because you dont have to make a call to use the D channel. Next time someone calls to your house to sell isdn ask them why the D channel isnt free.

Originally posted by ando
and for some weird reason, irish Isdn is Much better for online gaming than Irish DSL ? (ping times)

Ando, when installing the adsl network, eircom had a simple option, low pings or larger customer radius. Im not aware of what exactly they did but im certain it is not allowed in other countries.

m1ke

from what people have told me of dsl (people who have it in the uk). the 512k version gets ~ 60k/sec

longword

Eircom seem to be offering two speeds - 512Kbit down/128Kbit up and 1Mbit down/256Kbit up. If properly implemented you should get 50-60Kbytes/sec download and about 10-15KBytes/sec upload with the slower service, 100-120K/sec download 20-30K/sec upload on the faster service.

The key is 'if properly implemented'. The first hurdle is the wires between you and the exchange. Longer distances and poorer quality cables will introduce interferance. Eircom tests your line before they'll offer you a service, but who knows what criteria they're using to pass or fail a line.

The next possible bottleneck is the link between the exchange and the Network Operations Center of the ISP. This link is shared between all of the DSL users connected to that exchange and will typically be a fraction of the combined max bandwidth of those DSL users. For example you might have twenty 512kbit subscribers on an exchange, all sharing a 2Mbit link from the exchange to the ISP. In that case some serious praying will be required to ensure that four of those twenty aren't ardent Kazaa users :-)

Once it gets into the ISP's NOC you're at the mercy of their national and international connectivity ("peering"), shared between all of their users. Past this point you're battling the congestion of internet backbones and your target web site.

If you're looking for gaming performance, ISDN can offer lower latency for small packets because the modulation used (how it stuffs the bits down the wire) is much simpler than DSL which introduces delays as part of the modulation scheme to get better reliability. The bigger the packet, the more likely it is that DSL's faster rate will make up for the delay and beat ISDN. In a perfect world with no delays, 128k ISDN will take about 100ms to transmit a 1500 byte packet. A zero delay 512k DSL downstream would get it in 25ms. If the DSL delay is less than 75ms, and it should be a LOT less, DSL wins. The slower upstream of ADSL will nearly always lose to ISDN but game clients tend to receive more data than they transmit.

A decent DSL implementation should offer a ping of 20ms or so to your ISP compared to 160ms of a typical v.90 connection. DSL ping time can vary with tweaking of some DSL parameters. The ISP may choose to trade low ping times for a more reliable connection.

Kenshin

I had 256/128 Kbps ADSL in Spain, and I can tell you from experience that the maximum download speed I got was 27 KBps (and upload speed was around 15 I think).
Unfortunately the pings were kinda high, with around 60 ms to the first hop
I would love to have SDSL... you would have the lowest pings ever.

m1ke

from what i've heard off adsl trialists eircom i-stream is shoddy for games. So they must have traded ms for whateverrr.

[-Morpheus-]

Originally posted by Praetorian
On a modem you might get 5K a sec downloading

On isdn you should get 7k a sec

On dual isdn 14k a sec

on 512kb adsl you can get 50k a sec (but only 14k upload)

On 64k i can get 8.5k and on 128k i can get up to 17 k d/l

PiE

All you really need to know is this:

DSL > 56k

Dustaz

One eircome I-stream Solo (512/128), you get on average 50k downloads and a ping from 60 to 100 depending on where and what you are playing

dahamsta

Hey Dusty, you pissed at me yet?

adam

Dustaz

No, my love for you is as true as ever

Glad your posting a lot again tho, I cant answer the difficult questions, just lock the stupid ones:)