Connection issues with Airport/Comcast

[SillyViking]

Long time no visit :(

I am in UK and trying to help a friend in US with connection issues, which began intermittently, but have seemingly increased.
The original set up was a cable modem connected to Airport Express and wireless connected Mac desktop and MacBook. Trying to isolate probable cause, I asked them to disconnect stuff, in turn, and (somewhat blindly - being only by voice) have come to the conclusion that there is an intermittent conection issue with the cable modem.

The upshot is that their cable modem (Motorola SB5100) seems to be losing connection - 'power' & 'receive' led's are on, 'send' flashes and 'online' is off. But, having got them to remove a splitter and attach the modem as the only device on the cable, the problem seemed to go away and, so, they proceeded to reset and reconnect the Airport Express. At some point during this process the connection went wrong again.

Can someone confirm to me, please (I have been known to be blonde) that there is no way the Airport Express can cause issues with 'send' & 'online' on the cable modem?
i.e. that for this problem to be showing proves that the fault is either with the modem or with the connection to the ISP and, thus, not related to the internal side of the network.

Thanks!

SV :)

[Thrax]

It sounds like the AirPort is not pulling an internet connection. To put it another way, it sounds that the router is not communicating correctly with the modem to contact the ISP.

I would look at the airport before contacting Comcast, especially as the modem works correctly when directly attached to the PC.

[SillyViking]

It sounds like the AirPort is not pulling an internet connection. To put it another way, it sounds that the router is not communicating correctly with the modem to contact the ISP.

I would look at the airport before contacting Comcast, especially as the modem works correctly when directly attached to the PC.

Hi Thrax, thanks for the quick reply.

From memory of having this same modem a few years ago, don't all of the 4 lights (power to online) light up regardless of what is happening on the "home" side of the modem (i.e. even when there is no machine connected)?

I am on Skype to the person now, who is, again, shutting it all down and trying a direct connection from desktop to modem by ethernet.

If, as you suggest, the problem is with the Airport, other than redoing the basic setup from Apple's instructions (which they did last night), is there any way of pinpointing the specific problem?? (I am a PC/Linux user and know nothing about Mac settings).

Thanks again :)

//Edit to add - they have just rebooted the modem, connected only to the incoming cable, and the boot process is stopping at the 'send' light flashing (whereas yesterday, in this same situ, it would cycle to 'online' being solid)

[Thrax]

According to the diagram of the SB5100 modem at this location (http://www.simplehelp.net/2006/07/04/cable-modem-troubleshooting-motorola-sb5100/), a solid receive light indicates:


The modem has identified and connected to an available download channel on the cable line.


This is an automatic procedure that occurs regardless of whether or not there is a PC connected to the modem. If cable connections didn't do this, no modem would ever be able to tell that there's a connection. Cable isn't like DSL where you ask for the download channel by dialing in.

A blinking send light indicates:

The modem is seeking an upload channel.


A modem is this state typically indicates that the connection manager (a PC or a router) has not performed a connection with the ISP. Establishing the upload channel is what finally gives you an internet connection to activate the online LED.

Having never seen the UI for an airport router, I could not even begin to give advice on how to configure it. I do know that most routers use the following terminology for cable connections, however:

-Always on
-DHCP connection
-No domain name
-No static IP address

Long story short: If the modem won't establish a connection while connected directly to the PC, it's a bum modem/connection. If it consistently does, it's a router problem.

[SillyViking]

I finally managed to find the connection specific Mac info on Comcast's site and it seems it stops at the DHCP stage .. ". At this point, your computer should obtain an IP Address and all the other settings from the Comcast DHCP server.", so it seems pretty likely it is modem/connection and they need to call out a tech.
Thanks, again, for your help and confirmation.