Specifications

MBG Engineering Guidelines, Release 8.0
4.4 Configuring MBG for Remote SIP Devices
Remote SIP Device Limitations
MBG cannot yet load-balance SIP devices. In general, resiliency for a SIP device can be achieved through
external DNS by configuring multiple “A” records for the FQDN of the MBG, or by configuring SRV records. Refer
to the documentation of the remote SIP devices for guidance on configuring resiliency.
Tuning Global Parameters
The default values for all parameters assume a Teleworking installation, with SIP devices being used over the
Internet. In a LAN context, these parameters will work correctly but may be slightly aggressive.
By default, MBG sends a SIP “Options” request to every connected device at an interval of 20s (“Options
keepalives”). The responses from these requests reset the idle timer for each connection. Each connection has a
300s (5 minutes) idle timeout, so the most important thing to remember is that the MBG server must see valid
SIP traffic from each device within the 300s interval. A device that times out due to inactivity is disconnected and
becomes out of service.
On a “quiet” network it is sufficient to disable gapped registration and raise the options interval to its maximum
value (180s at this time). If all remote SIP devices send their own keepalives or re-register at an interval less
than 300s, MBG's Options Keepalives can be turned off.
DNS Support
While SIP clients can address MBG by its IP address, Mitel recommends the use of a fully-qualified domain
name (FQDN) in the public Domain Name System (DNS) that resolves to the public IP of the MBG server.
Advantages:
• The IP address of the MBG server can be changed, and the clients will not need to be reconfigured.
• DNS can provide a certain level of resiliency in case an MBG server experiences any kind of service
outage. Simply configure the FQDN to resolve to multiple MBG servers. Please note that MBG cannot
control how a SIP device behaves when it receives multiple IP addresses in a DNS response.
Note: A remote SIP message will be recognized as being addressed to MBG if the IP in the URI is one that MBG
owns, or the FQDN in the URI either resolves to an IP that MBG owns, or is one of the configured “Allowed
URIs” in the “SIP options” section of the Configuration tab.
Warning: A SIP server requires functional DNS even if all devices are configured to use IP addresses
instead of FQDNs. MBG is no exception. Failure to provide MBG with a working DNS resolver or
preventing MBG from reaching the Internet DNS root servers can cause delays or failures in call setup.
4.5 Firewall Configuration for Remote SIP Devices
When MBG is deployed in the DMZ, the corporate firewall protecting the DMZ requires the following rules (in
addition to the common rules found in Firewalls (DMZ deployment)):
From the Internet to the MBG server:
• allow protocol UDP, destination port 5060 (and return traffic)
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