Remote Phone Best Practices and Limitations

Bandwidth

• Each PBX phone call utilizes about 80kbps of bandwidth. When you make a phone call from a remote phone, both the remote user and the location where the PBX system is located need this 80kbps of Internet speed. If either side of the phone call has a slow Internet connection at the time the call is taking place, the voice quality will suffer.

• Just because a remote user has a cable modem with 10MB of download speed, it does not mean that the voice call will be fine. Remember, the phone call is a symmetrical call, so we need 80kbps on the upload and download side. Most consumer Internet service, like cable modems and DSL, has very limited upload speeds (usually 256kbps to 512kbps).

• Now just because we have a remote user who has a 10MB download and 512kbps upload Internet connection, it still does not guarantee the phone call will not have problems. The way the Internet works by default is that bandwidth is shared with everything else the user is doing. If we are on a phone call and someone starts downloading a file or watching a video on YouTube, your Internet Service Provider (ISP) looks at both of these active connections as equal. The ISP lets them fight for the bandwidth and does not prioritize the voice traffic.  In the normal world of bandwidth usage, a slight delay in receiving a packet when downloading is never noticed since you are downloading a large file. Voice, on the other hand, is in real-time. Any delay or fighting for bandwidth will cause that portion of the phone call to be lost, causing breakup in voice quality. If this is happening for your users, you will want to look at upgrading the Internet at whichever end is having problems. You will also want to look into setting up routers with Traffic Shaping/Quality of Service (QoS), which prioritizes the voice traffic over all other traffic to help alleviate this issue. QoS settings are outside of the scope of our support. You should consult with your network system administrator for more options for QoS routers.

Firewalls

• If you are going to use phones that will be considered remote phones, then you will need to open ports on your firewall to allow the phones to connect to your PBX system. A remote phone is considered a phone that is not on your local area network (LAN) or Virtual Private Network (VPN).  Simply put, a remote phone is a phone that can not connect directly to the IP address that you have setup on your PBX system. 

• The ports you will need to open on your Firewall and direct to your PBX IP address are:

  • 5060 using protocol UDP for SIP- This is the signaling port that is used to talk with your phone.  When a call is sent to your phone, it informs your phone on port 5060 that it is sending a call and what audio port it will send the call on.

  • 10000-20000 using protocol UDP for RDP Stream- These are the ports that your phones use to transmit the outbound and inbound audio. Without these ports open, you will hear no audio when making or receiving calls.

  • 2001 using protocol TCP for Phone Feature Applications- This is the port that allows the phones to connect to your PBX system in order for the applications on the phone to communicate with your PBX system.

  • 69 for TFTP or 21 for FTP for phone updates- This is the actual port your phone uses to get firmware updates from your PBX system, to pull its config files, and to receive updates to config files for new applications and button layouts. Without this port open, your phone cannot get firmware updates or receive updates when the config file is updated for new features and enhancements.

It would be impossible for us to give step-by-step instructions on how to set up and configure your firewall to allow for remote phone support, since there are hundreds of different firewalls and routers on the market. You will need to consult with your system administrator of your network if you are unsure on how to open these ports. 

SIP ALG or FIXUP Settings

You will also want to make sure that all SIP ALG or SIP FIXUP is turned off, as this usually causes more problems with SIP than it helps. Most routers come with this feature ON from the manufacturer. Each manufacturer has their own names for this, and some of the common ones are:

• SIP ALG

• SIP Fixup

• SIP Markup

• SIP Translation

Issues with having more than one phone at the same remote location

• Are you having difficulty getting more than one phone at the same remote location to work reliably? The best solution for this it to have a VPN configured between the two locations so they operate like local phones on the same LAN.  Please contact your network system administrator for information on this option.

  • This is a very common issue with lots of routers, as each phone tries to connect to your PBX using port 5060 for registration. When more than one phone at the same remote location registers to the PBX phone system, they all register with the same external IP address. 

  • A good example to explain this issue: Let's say we have extensions 101 and 102 at the same remote location, and that remote location has an external IP address of 99.125.99.100.  When the phones register to your PBX phone system, they all show up and register with the IP address of 99.125.99.100. When your PBX phone system sends a call to the external IP address 99.125.99.100 for ext 101, the remote router gets confused on which phone to send the call to and the calls get lost or misrouted by your remote location router.