DSL and interleaving

[turfsniffer0]

Hello,

Was wondering if someone can help with a problem. I have a customer at a remote location that connects via DSL and they connect to corporate network over an ipsec tunnel. I don't support the line or the cisco router, (only the tunnel) - but would like to help them stablise the DSL connection.

I noticed that the attenuation and noise margins were bad, as well as seeing the dsl flapping quite a bit so I referred the customer to thier provider. THe DSL link sappears to be a good distance away from their local exchange so provider enabled interleaving. It seems to have made some difference. Noise margin is now average (although attenuation is the same) -

output from the sh dsl interface atm0 command

Alcatel 20150 chipset information

                ATU-R (DS)                      ATU-C (US)

Modem Status:    Showtime (DMTDSL_SHOWTIME)

DSL Mode:        ITU G.992.1 (G.DMT)

ITU STD NUM:     0x01                            0x1

Vendor ID:       'ALCB'                          'TSTC'

Vendor Specific: 0x0000                          0x0000

Vendor Country:  0x00                            0xB5

Capacity Used:   91%                             100%

Noise Margin:     8.5 dB                          6.0 dB

Output Power:    16.5 dBm                        12.0 dBm

Attenuation:     64.5 dB                         31.5 dB

Defect Status:   None                            None

Last Fail Code:  Handshake or init message invalid or had bad CRC

Selftest Result: 0x00

Subfunction:     0x15

Interrupts:      6432 (0 spurious)

PHY Access Err:  0

Activations:     309

Init FW:         embedded

Operation FW:    embedded

SW Version:      3.8131

FW Version:      0x1A04

                                Interleave             Fast    Interleave              Fast

Speed (kbps):                     160                0           416                 0

Reed-Solomon EC:          28752                0          4047                10

CRC Errors:                        798                0          1189                11

Header Errors:                    268                0           853                 6

Bit Errors:               0                0

BER Valid sec:            0                0

BER Invalid sec:          0                0

Question is do I need to manually configure the clock rate on the ATM0 interface with interleaving on? Also IP CEF is not enabled - will it be of any benefit having it on?

Also the highlight speeds above - are they operational speeds? Why is one 160kbps and the other 416kbps? The link is a slow DSL link - its in a remote location with poor broadband coverage.

[Giuseppe Larosa]

Hello turtsniffer0,

>> Also the highlight speeds above - are they operational speeds? Why is one 160kbps and the other 416kbps?

Yes, they are the operational speeds that are negotiated between the ATU-R (the modem) and the ATU-C in the central office.

The two devices attempt to achieve a decent noise margin, so they step down the speed by putting less bits per subcarrier (tone of DMT they are rougly 250 some are used for upstream and other for downstream). Each direction is negotiated indipendently.

The process is dynamic so they can move to better speeds over time if noise conditions change.

>> The link is a slow DSL link - its in a remote location with poor broadband coverage.

This is true.

On the router please enable IP CEF on the interface at globally on the router .

Hope to help

Giuseppe