Splitter
The splitter is the first piece of hardware. The little box filters out all the jitter from your phone so it won't mess with the adsl frequency. The splitter box does not filter adsl frequencies!
If you have no phone on the same line, no filter is required. If you have 2 or more phones and you can't put the plitter before all the phones, put another filter before each phone.
The router is connected on your side of the phone line. On the other side of the line things are the same: a filter between your phone line and the PBX (= the telephone exchange which determines what your phone number is) and a straight connection into the DSLAM. The DSLAM is sort of a modem that provides the adsl signal to many phone lines and has a network connection on the other side for internet.
Circuit
Your router starts to pulse the line, making contact with the DSLAM. If you have set the right VPI/VCI numbers, this can take up to a minute, but usually it's only a few seconds. Once the connection has been established, the light on the router saying DSL or CD (=carrier detect) will lit up. (TOT uses VPI/VCI 1/32)
The local loop has been established.
If you call the support desk, they usually ask if the DSL light is lit. If this light remains off, it usually indicates a problem with the phone line. If you hear no dial tone from the phone, it's probably a line break.
This connection that has been established is an analogue signal. It can be good, average or bad. The quality of this signal is measured in decibel (dB) and several routers can display the signal strength - look for Noise margin or SNR / Signal to Noise Ratio.If the value displayed is more than 10dB, the quality is fine.
If the value displayed is less than 4dB, you'll experience a lot of outages.
The signal quality is affected by several factors.
Generally two types of outdoor phone cable are used: lines with 0.6mm copper diameter and lines with 0.9mm copper diameter. The 0.6mm lines is much more susceptible to interference.
If the phone line hangs very close to a transformer (close = 2m), the interference will vary with the load of that transformer.
Phone line comes on rolls of 200m. Engineers tend to connect a new role by simply twisting the copper wires and sealing it off with pvc insulation tape. This connection will degrade rapidly, as the copper corrodes and gets wet eventually. A better connection is made by soldering the cables and sealing it off with rubber splicing tape, which ensures an air-tight and water-proof connection.
Once the circuit is up, your router will start to establish a PPP connection. This connection is made between your router and the CO-router of your ISP. This CO or Central Office is located between the DSLAM and the backbone of the ISP. If the PPP connection fails, there may be a problem with the network between the DSLAM and the CO - in this case nobody in your area will have a working internet connection.
Note: newer DSLAMs are able to handle the PPP connections as well now.
There are 2 flavours of PPP: PPPoA and PPPoE.
PPPoA means ppp-over-atm. This connection is usually faster, however not supported on all routers.
PPPoE means ppp-over-ethernet. This type is more flexible. The router can be configured to use PPPeE, but one can also configure the router to just bridge the adsl signal and configure the PPPoE connection on another router or your own computer (in the last case, your computer gets a public IP address).
PPP requires a user-id and a password, which are supplied by your ISP.
Once the PPP connection has been established, the internet light or PPP light on your router will lit up.
Example of a problem-adsl-line
This page is from a 3Com OfficeConnect router, displaying the ADSL status. This router has established a connection to the internet, but the signal quality is so poor (noise margin downstream is 1dB), that the actual speed is only 224k up and 544k down (this is a 512/1024 line).
Main reason: bad phone line from the DSLAM to this router.
Solution: TOT should install a brand new line.
Example of a good line:
This output is from a Cisco router, displaying the interface. The signal quality is good; more than 20dB up- and downstream, and the router does not have to amplify the signal too much (Attenuation). The speed is 512/2048.
When you call the helpdesk, they will aks you for the lights on your router. if you call TOT, they'll ask:
dsl light on?
internet light on?
Since you're calling them, you have a problem and one of the lights is probably off. Don't accept them calling you back (because they won't) but offer to hold the line while they check out what the problem is.
If they're unable to diagnose it, post it here. This forum will not be able to fix your problem, but many members here have a lot more knowledge than the Thai ISPs.
