SIP Provider Gamma Telecom (UK) (kb4418)

The information in this article applies to:

  • SwyxWare 2015
  • SwyxWare 2013
  • SwyxWare 2011 R2

[ Summary | Information ]


Information und configuration hints for SIP provider Gamma Telecom (Great Britain/UK).


General information

Gamma Telecom is offering registerless SIP trunks. This means that the authentication is based on the public IP address of the SwyxWare server. Therefore, you need a static, public IP address from your ISP assigned to the SwyxWare server.

Gamma Telecom is operating with a number of different servers. Therefore it is not possible to preconfigure the Proxy Server in the "SIP" tab of the Trunkgroup Properties dialog. In this field, please enter the IP address that GammaTelecom has named you.

Due to the different servers, the predefined Number Formatting in the "profile" tab of the Trunkgroup Properties dialog might be wrong and need to be adjusted accordingly. The default setting in each case is "National".


During creation of the SIP Trunkgroup, the profile 'Gamma Telecom (UK)' must be selected.

In case that the SwyxWare server is running with a private IP address and the static, public IP address is provided by NAT gateway, it is necessary to configure a STUN server in the properties of the SIP trunk group, under the tab 'SIP'. A list of public STUN servers can e.g. be found at

GammaTelecom expects a Session interval of 600 (seconds) on outbound calls. The prevent reINVITES which would slow down the call establishment, underneath the registry key  HKLM\Software\Wow6432Node\Swyx\LinkMgr\CurrentVersion\Options two new DWORD values SipMinSessionTimerIntervalSeconds and SipSessionTimerIntervalSeconds  can be created with an assigned value of 600 (decimal). After creating this value, the LinkMgr service must be restarted.
Important: This setting will affect all SIP Trunks.

DTMF transmission
For sucessful DTMF transmission through a Gamma Telecom SIP trunk, it is necessary to adjust the DTMF parameters. On the SwyxWare server, underneath the registry key 

three new DWORDs with the following names and values have to be created:

DTMFGapDuration:    0x32 (HEX)
DTMFVolume:         0x7 (HEX)
DTMFToneDuration:   0x438 (HEX)

Afterwards, the LinkManager needs to be restarted.

Number format
To configure the requested number format on outbound calls, a special number replacement is necessary. In the field 'outbounf calling party number', the following replacement must be set: +44* -> *.

Important: The following instruction is not necessary when configuring a SwyxWare2013R3 or newer.
For Calling line identification on outgoing calls, depending on the configured Proxy server it might be necessary to send the own calling number in the P-Asserted-Identity header. You have to follow the instructions in Support of feature ClipNoScreening for SIP trunks (kb3905). In this case, the requested number format from Gamma Telecom must be considered.

The SIP trunk is named 'GammaTelecomTrunk'

The number range is +44 121 1234560 ... +44 121 1234569
Number format is 'National'

Create a new registry key


Within the newly created registry key, create new registry value of type String, name it SIPNetworkProvidedNumber
Given the number range and the number format above, set the value of the SIPNetworkProvidedNumber to "121123456".

Tested Features

  • Incoming/outgoing national calls
  • Incoming/outgoing international calls
  • Correct Calling Line Identification (CLI) on national and international calls
  • Holding and retrieving calls
  • Toggeling between two calls
  • Call transfer
  • Conferencing
  • Mutually supported codecs:
    • G.711a
    • G.711µ
    • G.729
    • T.38 for FAX negotiation
  • Incoming/outgoing DTMF signaling in accordance with via RFC2833
  • T.38 Negotiation and FAX transmission

CLIP No Screening is not supported by GammaTelecom.

Additional information

Occasionally, problems with correct CLI were observed with international calls.

Due to the different servers that Gamma Telecom is running, interoperability issues may occur, that are currently unknown.

Test dates:
10/09/2012 with SwyxWareV2011R2, QF3
12/07/2013 with SwyxWare2013
04/11/2014 with SwyxWare2015

Overview of tested SIP provider


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