Question : Cisco Call Manager Express remote working / branch office example

Hi Guys,

OK, I'm very new to Cisco and Voip. I have setup a 2811 router with Call Manager Express and have 2 x Cisco 7906G telephones and 1 x Cisco IP Communicator working nicely. That bit was simple. So all phones can call each other. I am trying to evaluate a Cisco solution vs, say 3cx.

So here come the questions:

1) Since the Phone images are tranferred each time via TFTP, how does this work for a remote worker? He/she will be in a hotel room with a DHCP address from the hotel, will they have to connect to the office via a VPN then somehow connect to the TFTP server and get the image? How does that work if they need DHCP Option 150 for the phone image, ie my TFTP server is 10.0.0.1 and their laptop has a 'real' ip address.

2) If I want to setup a mini branch office, does the router at the branch have to run a VOIP image or can it connect to the VOIP router in the main office and somehow pass on the TFTP image for the phone in the remote office?

I'd like to setup something really simple, just extend my two phones from being locally connected to being in another subnet to test how this might work, ie. Branch office phone connected to a switch and old 2600 router (not running VOIP image) , that router connected to my 2811 Voip/CME/DHCP router via a DB60 serial crossover-cable (to simulate a VPN/ subnet??) then connect up a Main Office phone and try to make calls.

Does anybody know how to do this or point me to a nice reference guide - I have had a good look around and can't find any config examples or explanation how I might get a TFTP image from one site to another with DHCP and option 150.

All I want to do is call the main office from a remote one.

Any help would be much appreciated.

Mike

Answer : Cisco Call Manager Express remote working / branch office example

I can absolutely confirm that you can connect both IP communicator and a remote Cisco phone to a CME router (across a WAN VPN link) without any problem.  Of course a remote hard phone requires a site-to-site VPN link, while the IP Communicator runs just fine over (MOST) VPN setups.  They key to the IP communicator is that you need to use a VPN technology which will let you assign and map a routable internal IP address subnet.  We have had the best success with Checkpoints SecureClient in "Office" mode, but the Netscreen and Cisco VPN clients work well also.

We have setup this scenario numerous times in wide variety of network environments: a phone in dubai registered to CME in Singapore, a phone in Canada registered to a CME in Dallas, etc.  It works just fine - as long as you have a stable, reasonable Internet connection.  Registration traffic takes next to no bandwidth, clear voice call requires 64k stable bandwidth and voice with video requires ~380k stable bandwidth.  However, this scenario is "best effort" which means you might very occasionally get a brief second of digitized voice quality or disconnected - depending on the reliability and clarity of the Internet connection.

 For internal office calling - itis more then adequate.

We even use this scenario to route the remote phone calls out the CME gateway to the local PSTN and route inbound calls to a local number to the remote phone 1000s of kms away.

In reference to your specific questions, you will not be able to use a hard phone from a hotel room, only the Cisco IP communicator softphone, so the option 150 is not neccessary, nor is a TFTP image download.  If you set the CallManager/TFTP server setting in IP Communicator (and have auto-reg working and available slots), the softphone will register across the VPN link.  However, remember to head the "routable IP address" requirement of your dial-up VPN technology.

If you have a site-to-site VPN setup, a hardphone can be set manually for the CME server or you can set the DHCP 150 option on the remote DHCP and the phone will register.  Keep in mind that any firmware upgrades for the phone will be loaded from the remote CME TFTP router which may take a lot of time.  However this only happens on the rare occasions you upgrade you need to upgrade the phone firmware.

Hope this helps.