Only_Dead_Fish_Go_With_The_Flow: Replacing an Optima-ADSL Annex-A router

updated jun 29, 2012

Context & Problem: Since 2008 we have a business phone and internet access contract with Optima Telekom croatia ( http://www.optima.hr/ ).

The internet link was served by an ADSL Huawei Smartax MT-880 device, that was supplied by Optima.
Some days ago, there was a storm, and the Huawei router broke.

Had a call with Optima tech support, but found that the supplied router is out of warranty, and that the suggested option they propose is a contract upgrade, with a higher monthly cost and a new router.

Solution: reuse an old T-COM Siemens ADSL C-010-i router, to connect to Optima ADSL line, with proper reconfiguration.

I had an old T-COM router, sitting there, a Siemens ADSL C-010-i, with Conexant chipset. This device has just a LAN RJ-45 port and a RJ-11 ADSL WAN port whose cable goes in the ADSL splitter. According to some documents I found on the internet, this device also have an internal USB port which is only accessible opening the case (which I did not do).

T-Com branded Siemens c010i

from a previous installation, and I decided to try to use that. Had a look on the internet, and another call with Optima tech support. Optima could not support me in reconfiguring the device, because is not among the one they support.

After many hours of fiddling, i managed to have it working, and now I am sharing here the settings with which I had it working.

The Siemens C-010-i default factory configuration is at ip 192.168.1.1/24, with http username and password being admin/epicrouter. There is a small button that allows to set it back to factory configuration.
My Siemens unit has probably been manufactured before 2008.

The main setting that allowed me to connect the Siemens router to the optima ADSL were:

PVC: 0
VPI: 0
VCI: 35
ADSL mode: ANNEX-A
ADSL Handshake protocol & modulation: Autosense, G.dmt first
Encapsulation: PPPoE
Multiplex: LLC
Service Category: UBR

With these settings, the line got up again (after some moments post modem reboot, ADSL line light stops flashing and becomes steady green).

After these settings, and after a router restart, this is what I got on the system log.

router system log
01/01/1970 00:00:00> DNS: Add IP address 8.8.4.4 (User defined)
01/01/1970 00:00:00> DNS: Add IP address 8.8.8.8 (User defined)
01/01/1970 00:00:00> PPP1 Session is up.
01/01/1970 00:00:00> DNS: Add IP address 85.114.32.8 (Auto discovered)
01/01/1970 00:00:00> DNS: Add IP address 85.114.32.7 (Auto discovered)
01/01/1970 00:00:00> No Static Session Information is defined.
01/01/1970 00:00:00> NAT/NAPT Session Start: interface ppp1, WAN IP is 95.178.172.206
01/01/1970 00:00:00> PPP1: DNS Secondary IP address is 85.114.32.8
01/01/1970 00:00:00> PPP1: DNS Primary IP address is 85.114.32.7
01/01/1970 00:00:00> PPP1: PPP Gateway IP address is 95.178.160.1
01/01/1970 00:00:00> PPP1: PPP IP address is 95.178.172.206
01/01/1970 00:00:00> PPP1 PAP Authentication success
01/01/1970 00:00:00> PPP1 PPPoE Session is established.
01/01/1970 00:00:00> PPP1 PPPoE PADS Received Service-Name:adsl AC-Name:br01os01
01/01/1970 00:00:00> PPP1 PPPoE PADR Sent, Service-Name:adsl AC-Name:br01os01
01/01/1970 00:00:00> PPP1 PPPoE PADI Sent
01/01/1970 00:00:00> ATM Tx Error Count: 0, Rx Error Count: 0
01/01/1970 00:00:00> u/s total bit capacity: 136bits, used: 136bits
01/01/1970 00:00:00> d/s total bit capacity: 1845bits, used: 1392bits
01/01/1970 00:00:00> d/s Latency: INTERLEAVED, u/s Latency: INTERLEAVED
01/01/1970 00:00:00> d/s Data Rate: 5024kbps, u/s Data Rate: 480kbps
01/01/1970 00:00:00> d/s Attenuation: 29.3dB, u/s Attenuation: 9.5dB
01/01/1970 00:00:00> d/s SNR: 12.4dB, u/s SNR: 15.0dB
01/01/1970 00:00:00> CO Vendor: GLOBESPAN
01/01/1970 00:00:00> Max Tx Power: -38dBm/Hz
01/01/1970 00:00:00> Annex Mode: ANNEX_A
01/01/1970 00:00:00> Modulation: G.dmt
01/01/1970 00:00:00> ADSL connected
01/01/1970 00:00:00> ATM layer is up, cell delineation achieved
01/01/1970 00:00:00> ATM Connected
01/01/1970 00:00:00> CfgMgr: 'Prism.dlz' module loaded.
01/01/1970 00:00:00> CfgMgr: 'Apimage.dlz' module loaded.
01/01/1970 00:00:00> CfgMgr: 'Washer.dlz' module loaded.
01/01/1970 00:00:00> CfgMgr: 'ShtmMib.dlz' module loading failed.
01/01/1970 00:00:00> CfgMgr: 'Shtm.dlz' module loaded.
01/01/1970 00:00:00> Initialized Dynamic NAPT.
01/01/1970 00:00:00> ATM: Setting up vcc0, VPI=0, VCI=35
01/01/1970 00:00:00> ATM: Detected
01/01/1970 00:00:00> Ethernet Device 0 Detected

update: (29 jun 2012)

Performance TUNING on MTU
With standard settings, modems sets up link with the following PPP options:
MRU=MTU=1492
MSS=1432

With these settings, I found that some downloads are aborting, and speed tests reports give inconsistent results (albeit browsing speed does not seem that bad).
In particular, speedtest.net gave consistently very poor results in speed measurement, reporting about 0.07Mbit/sec download speed and 0.15Mbit/sec upload speed.

Did some other fiddling, I set the following:
MRU=MTU=1400
MSS=1300
After these settings have been put in place, and after a router reset, I did not experience anymore failed downloads, and got much better speed measurements, and browsing speed is better too.

Here is the table of the current settings in Configuration/PPP menu of the ADSL Modem