snom ONE Technical Manual - Atcom

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Deploying the snom ONE IP Telephone System
■ Use Short SIP Headers: Some SIP headers have a short form (e.g., the From header gets shortened
to F, the To header becomes T, and Via becomes V). Short headers have the advantage of
saving space in the messages, reducing overall probability of running into problems with maximum
message size in UDP. Although it is quite simple to support this, some devices do not support
short headers. For this reason, the system offers both short and long. In order to maximize interoperability,
keep the default value (long). If you are running into UDP packet fragmentation problems
(message size above 1492 bytes), switch to the short header form.
■ Listen to sip.mcast.net: SIP also has its own multicast group according to RFC 3261. A SIP
device usually knows where to send requests, but during bootup and configuration, a user agent
might want to locate the system with a multicast request. If this setting is turned on and you are
using user agents with the multicast detection feature, you can just plug the devices into the network
and they will get their configuration information automatically from the system if the system
PnP settings have been configured (see Chapter 19). Changing the Listen to sip.mcast.net setting
requires a system restart.
■ Allow domain admin to change trunks: In hosted environments, the service provider might want
to set up the trunks and hide this feature from domain administrators. If this feature is set to No,
domain administrators will not be able to edit or see the trunks.
■ Allow domain admin to change dial plans: If this feature is set to No, domain administrators
cannot change the dial plans or even view them from the web interface.
■ Allow domain admin to create or change accounts: If this feature is set to No, domain administrators
cannot create, change, or view accounts.
■ Allow domain admin to create or change ANI: If this feature is set to No, domain administrators
cannot create or change the ANI (automatic number identification). The ANI is used when the
system sends an outbound call on a trunk (see domain settings for more details).
■ Loopback detection: This setting applies only to multi-domain environments (for single-domain
environments, leave this setting on). When the system starts a call, that same call may come back
to the system and create a loop. This may happen if the call is for another caller on the system in
a multi-tenant environment. This is a dangerous situation because it might repeatedly initiate the
same call, ending up in many calls that take a lot of resources. Therefore, the system must detect
such a loop. In environments where an external SIP proxy routes the call from one snom ONE domain
to another, a simple loopback detection that is based on the call-ID is too pessimistic. Therefore,
in such environments, you might want to allow these calls and turn the loopback detection off
(see the Try Loopback setting on page 96).
■ Inband DTMF detection: When a user presses a key on the telephone, the system must be able
to understand the action. In telephony systems, this mechanism is typically called DTMF. In VoIP,
DTMF is usually sent “out of band” (RFC 2833) because it allows the system to easily detect the
tones in a fail-safe manner. However, not all devices support this method, and when this is the case,
the system must decode and analyze the media stream and perform this detection. Because this is
erroneous and costs additional CPU performance, it is strongly recommended that you not use this
feature and instead replace devices which do not support the out-of-band method with devices that
do. In-band and out-of-band can be compared to a T1 line that uses in-band signalling and a PRI
line that uses out-of-band signalling.
■ Remote SIP management: This setting allows the provider to send commands to the system (for
example, for rereading the configuration). It is useful in environments where the service provider
controls the system from a centralized location. By default, this setting is off, but if you are using
such an environment, this setting needs to be activated.
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