Goals
- As per an OpenText partner, Skype just needs the SR140 SDP to indicate support for RFC2833. This feature is to enable the SR140 to indicate support for RFC2833 without the requirement to send out-of-band tones.
Background and strategic fit
RFC 2833 (RTP Payloads for DTMF Digits, Telephony Tones, and Telephony Signals) specifies an RTP payload format for carrying dual-tone multi frequency (DTMF) digits, and other line and trunk signals. Technically, RFC 2833 has been replaced by RFC 4733, but for the most part people call it 2833.
RFC 2833 is negotiated through Session Description Protocol (SDP). SDP is used to describe the voice stream (e.g. G.711) and it’s also used to inform the recipient that RFC 2833 is available. Specifically, it uses something called telephone-event.
Lync expects that the connecting endpoint will state that RFC 2833 is available or it will not accept the call regardless of what voice codec is available. To connect to Lync the SR140 will be required to add the following items into the SDP to show it supports RFC2833:
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-15
The SR140 will not be required to generate any outbound RFC2833 events.
Assumptions
Requirements
| # | Title | User Story | Importance | Notes |
|---|---|---|---|---|
| 1 | Keyword to enable feature | Add a new keyword to enable this feature into the SIP section of the callctrl.cfg file. In the future this keyword may be used to enable RFC2833 if the capabilities to do so has been added to the product. This parameter shall be an enabled/disabled setting and will default to false. | Must Have | Parameter Name TBD |
| 2 | Advertise support for RFC 2833 | When the feature is enabled, the outbound SDP will show support for RFC2833. It shall show support for events 0-15. a=rtpmap:101 telephone-event/8000 | Must Have | |
| 3 | No RFC2833 events | The SR140 is not required to generate any RFC2833 events. DTMF tones generated will not change from the current implementation. The tones will be sent as a part of the RTP audio stream. Support for generating RFC2833 or RC4733 events may be added at a future time but it is not a requirement for this feature request. | Must Have | |
| 4 | Documenation | The documentation for this feature shall state that this parameter only advises support for RFC2833 and that the product will not generate RFC2833 events. This parameter should be only enabled when advised by tech support. | Must Have |
References
- RFC 2833: RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals - http://www.ietf.org/rfc/rfc2833.txt
- RFC 4733 (obsoletes RFC 2833): RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals - http://www.ietf.org/rfc/rfc4733.txt
- RFC 4734 (updates RFC 4733): Definition of Events for Modem, Fax, and Text Telephony Signals - http://www.ietf.org/rfc/rfc4734.txt
- RFC 5244 (updates RFC 4733): Definition of Events for Channel-Oriented Telephony Signaling - http://www.ietf.org/rfc/rfc5244.txt
User interaction and design
Questions
Below is a list of questions to be addressed as a result of this requirements document:
| Question | Outcome |
|---|---|
Not Doing
- Sending RFC2833 Events
High Level Design Document
The HLD was combined with the HLD for RFC 2833 inbound support. It can be reached directly with this link.
Tasks Releated to Feature
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