Screen Sharing.app Works — iChat Screen Sharing Does NOT

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Screen Sharing.app Works — iChat Screen Sharing Does NOT

I'm using two Google Talk accounts: one at work and another at home. I'd like to use iChat Screen Sharing to access my home computer from work and my work computer from home. When I try to use the iChat Screen Sharing, it connects for a second or two, then disconnects saying a connection could not be established. However, using the Screen Share.app, I am able to connect using an IP address and that actually works! The problem is that the Screen Share.app does not support file transfers whereas iChat Screen Sharing does, so I'd prefer to use the iChat Screen Sharing.

I'm confused as to why the app works but not through iChat! I've gone through and set my Quicktime prefs and iChat video bandwidth, as mentioned in other discussions, but that hasn't helped. I am able to iChat screen share with another buddy of mine both from home and from work, but I can't get it working from my office to my home! Any ideas?

PowerMac G5 2.5GHz Quad, Mac OS X (10.4.8)

Posted on Jul 18, 2008 12:17 PM

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Answer 1

Jul 19, 2008 10:43 AM in response to Cj Shumate

If Quicktime Streaming is at 1.5Mbps and iChat's own Bandwidth is at NONE and the ports are allowed in any routing device (which sounds likely as it works to other people) then the issue is likely to be NAT between the two routing devices involved.

If the routers at either end are doing Port Forwarding or Port Triggering they are likely to be more reliant on NAT than UPnP is.

Use UPnP where you can.

6:43 PM Saturday; July 19, 2008

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Answer 2

Cj Shumate Author

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Jul 22, 2008 9:43 AM in response to Ralph-Johns-UK

Thanks, Ralph. I see you've posted on this topic about a thousand times now 🙂 I wish I knew a bit more about NAT settings. UPnP is enabled on both routers (work and home), but that doesn't seem to do the trick. A third party is able to screen share with me both at work and at home, so it seems both routers will allow it to happen, but the two routers just don't play well together (connecting from work to home or vice versa).

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Answer 3

Jul 22, 2008 1:27 PM in response to Cj Shumate

Umm,

Any Modems involved should or are I Presume Bridged and the routers are the ones doing UPnP.

This should mean that the ports iChat is supposed to use for Screen Sharing are open.
The Documentation would suggest that these are likely to be the same ones as Apple Remote Desktop (5900 and 5988) which plain old Screen Sharing should also use.

Having said that I use Little Snitch which reports that the ports used are a lot more random than that and can be almost anywhere.

NAT is an almost bottomless pit as it in fact it is a global term for an number of ways of doing the same thing in different devices.

I take it this is using two different Screen Names from the progress you report.

Settings in routers such as Ping Blocking and DOS or SPI filters would seem not to be an Issue as it works with other people.
iChat sends a Ping in All forms of A/V Chat and as Screen Sharing has an Audio component it is included.
DOS or SPI is likely to be Threshold based and a Screen Share is less of a data Stream than Video chat is.

I take it Video chats works ?

9:27 PM Tuesday; July 22, 2008

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Answer 4

Cj Shumate Author

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Jul 22, 2008 2:02 PM in response to Ralph-Johns-UK

Both modems are from Comcast and both are bridged, as far as I know. Both routers have UPnP enabled, however this is where it's different. My home router (Netgear WGR614v5) just has a checkbox to enable UPnP. The work router's (can't recall model) UPnP settings look a lot like Port Fowarding settings where you open ports and assign internal and external ports... not as simple as clicking a checkbox!

But I am using different Screen Names and have even created additional ones to test, both using Google Talk and AIM. The connection always seems to be made, then quickly broken after a couple seconds or so.

I have no camera, so I can't say whether or not video chat works (though that'd be a good test).

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Answer 5

Jul 22, 2008 2:18 PM in response to Cj Shumate

AH Ha !

A Netgear WGR614 V5

This is unreliable with iChat.
On the whole it does not work for some reason. Version 9 seems to be the best of this series.

If the work one is a Linksys and you are using UPnP Forwarding in Applications and Gaming turn that Off and use the one in Administration

10:18 PM Tuesday; July 22, 2008

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Answer 6

Cj Shumate Author

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Jul 22, 2008 2:29 PM in response to Ralph-Johns-UK

Ah... that's too bad, I wasn't planning to purchase a new router! Thanks for all your help, I do believe the work router is a Linksys. Do you have any good router recommendations (ones that play nice with iChat, preferably)?

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Answer 7

Jul 22, 2008 2:49 PM in response to Cj Shumate

OK,

Linksys seem to do more (list/range) of compatible Routers for behind a Modem.

Netgear ones do seem to have issues although their Own Modems are fine (I had a DG834G)

On the Whole don't go for MIMO Wifi devices as this is part of the 802.11n spec and that is still in Draft so likely to change - not to mention iChat does not like MIMO (Something about the way the channel is divided up to provide this Multi-in Multi-Out)

I know several people who like Buffalo devices as Wireless Access Points/Routers.

Do go for something with UPnP
Having said that please note Note 2 in this Doc
Although this List implies Compatible without any changes the Note 2 states otherwise.

Having said that in your Netgear in the WAN Page you have got the Port Scan and SPI item Disabled and the Pings are allowed ?
Also try the MTU rate at 1492 on the same set up page.

10:49 PM Tuesday; July 22, 2008

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Answer 8

Cj Shumate Author

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Jul 22, 2008 3:08 PM in response to Ralph-Johns-UK

I'll try those new settings and see what happens tomorrow. If that doesn't work, maybe I'll do some shopping for a new router.

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Answer 9

Cj Shumate Author

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25 points

Jul 23, 2008 10:14 AM in response to Ralph-Johns-UK

I had a friend log in using one of my Google Talk accounts and he was able to Screen Share with my computer at home, so this definitely seems to be a problem in communicating between my home and work routers. The work router is a Linksys BEFSR41. I have set the UPnP on that router to 'enabled' under the Administration settings. I have set the Port Range Forwarding according to the instructions at portforward.com (well, as many as possible, the Linksys router only allows 10 and we already had a few set up). Still, however, Screen Sharing with my home computer does not work. This is really frustrating!

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Answer 10

Jul 23, 2008 11:47 AM in response to Cj Shumate

Don't use Port Forwarding and UPnP.

Disable the Port Forwarding ones.
IF the Linksys is doing DHCP your computer may not always be at the IP listed anyway.

On the Security page of the Linksys Allow it to Respond to Anonymous Pings and have the Firewall Off.

I asked before but can not see your reply as to whether Video of Audio Only chats work ?

Normally it would be all forms of A/V chat that failed.
IF it is just Screen Sharing then there must be something I am missing.

7:47 PM Wednesday; July 23, 2008

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Answer 11

Cj Shumate Author

Level 1

25 points

Jul 23, 2008 12:02 PM in response to Ralph-Johns-UK

I have disabled the Port Forwarding on the Linksys router, the other settings were already set as you suggested.

I cannot test Video chat as I have to video camera at either location, nor even a microphone to test audio chat (Mac Pro at both locations).

Something is really mucked up now because suddenly the option for Screen Sharing is grayed out for my home account!

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Answer 12

Jul 23, 2008 2:13 PM in response to Cj Shumate

How odd.

The suggestion I have for that is somewhat destructive in that it loses all the setting you have changed in iChat Preferences + Saved Status Messages.

Delec com.apple.ichat.plist

This will lose Font Choice, Colour, Bubble colour, Menu Bar icon if set, Saved Transcripts, Alerts, Video/Bandwidth settings, Anything in the General section plus as I said the Saved Status Messages.

10:13 PM Wednesday; July 23, 2008

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Answer 13

Jul 23, 2008 7:40 PM in response to Cj Shumate

In recent weeks I have endured this frustrating problem using iChat's screen sharing which seems to have introduced with 10.5.4 (since there were no problems before that upgrade). Specifically, when I would try to connect to my wife's MacBook, we could video chat, but not screen share. (I could share and control her screen using Screen Sharing.app, however.)

We discovered that the problem is somehow related to her use of an external monitor. Normally, she plugs her MacBook into a 24" display to work, and usually does not mirror the displays. In that configuration, iChat will not allow us to screen share. If she unplugs the external display, or turns on mirroring, screen sharing works instantly.

Having looked all over the internet and not seen this solution, I thought I'd post it to save others from pulling out their hair.

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Answer 14

Jul 24, 2008 11:54 AM in response to FrankinPhilly

That's useful to know.

I did wonder where all the "Double Screen, Pic too Small" threads had gone.

7:54 PM Thursday; July 24, 2008

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Answer 15

Sep 9, 2008 8:33 PM in response to FrankinPhilly

i tried to video chat with my wife for the first time on my new macbook pro (also hooked up to a 20" cinema display) today while at work. it no worky. i didn't think to try unplugging the monitor, but tomorrow i'll give it a whirl.

either way, it's kind of lame that it doesn't work with the external monitor.

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