Playing Tones as Announcements

The SBC Core supports playing announcements that are stored in G.711ULaw format. The SBC Core is enhanced to support playing compressed tones directly without allocating DSP resources by playing the tones from the pre-encoded files with various combinations of tones and codec types. The tone files are created for the required tone types with different codec combinations and stored as .wav files in the SBC. All these tones are stored with a ptime of 20 milliseconds.

The SBC Core is enhanced in this release with a new media profile, tonesAsAnnouncement, which includes the following parameters to configure the announcement file to play Local Ringback Tone (LRBT) for each codec entry:

• toneType
• codecType
• segmentId

The existing Tone Profile references the toneType in the tonesAsAnnouncement profile, whereas the new object toneCodecEntry references the codecType. With this enhancement, the user can associate default Tone Profile or can create a customized Tone Profile and assign it to the toneType of the toneAsAnnouncementProfile. The flag announcementBasedTones is included in toneAndAnnouncementProfile configuration to play ringback tones without using DSP resources.

The SBC supports playing tones for three groups of codecs. If the required tone playback falls under one of the following codecs and the flag annoucementBasedTones is enabled, the SBC must avoid allocating DSP resources and play a tone as an announcement. If the required tone playback does not fall under one of the following codecs and the flag annoucementBasedTones is enabled, the SBC does not fall back to the DSP mode and continues the call without playing the tones.

• G.711 (G.711ALaw and G.711ULaw)
• EVRC (EVRC, EVRC0, EVRCB, and EVRCB0)
  
• AMR-WB-BWE (9 variants)
  
  

The compressed tone files are stored in the standard .wav file format. The SBC uses the same naming convention for the compressed tone files as the announcement files. For example, in a sDDDDD.wav file, where DDDDD is a decimal number from 1 to 65,535, the decimal number represents the segment ID of the file.

The announcement and the tone files share the 5-bit segment ID space, and thus, every file name must have a unique segment ID. The compressed tone files are stored in the same directory path as the announcement files (/var/log/sonus/sbx/announcements). The tone file is played continuously until the tone is stopped due to a trigger.

The following table provides the .wav file mapping information for the application announcements:

LMSD - Tone Play Support

The SBC supports playing tones when an Alert-Info header is received in the Legacy Mobile Station Domain (LMSD) format (Alert-Info: <http:/LMSD/tone?sig-id=rt>). The SBC is enhanced to play the ringback tone without using DSP resources whenever it receives 180 with Session Description Protocol (SDP) answer with Alert-Info header (Alert-Info: <http:/LMSD/tone?sig-id=rt>). The Alert-Info header, present in the 180 ringing with SDP, carries the tone package information required by the SBC to play ringback tone. To support this feature, the existing LRBT framework is enhanced.  

The SBC supports generating LRBT when:

• The flag acceptAlertInfo is enabled on the egress TG.
• The provisional response is 180 ringing with SDP and the tone flavor is normal.
• The P-Com.DropEarlyMedia header is not present in the original INVITE.
• The SDP answer is received in 180 or in a previous provisional response (183).
• The 180 contains an Alert-Info header having sig-id = “rt” only (bt/ct does not play tone).
• The flag announcementBasedTone in the toneAndAnnouncementProfile associated with the ingress TG is enabled.

LMSD - Playing Tones Using Lock Down Preferred Codec

The SBC plays tones using the “lock down" preferred codec when the following flags are enabled:

• sendOnlyPreferredCodec (IPSP)

• honorRemotePrecedence (PSP)
• announcementBasedTones

The codec, which is used for playing tone towards the ingress leg, is based on whether the session is established as pass-through or transcoded. If the SBC receives SDP answer from the egress peer, the selected codec is the egress peer's preferred codec. However, the ingress peer's preferred codec is used to play the tone, if the session outcome is transcoding.

LMSD - Handling UPDATEs for the Tones

 The SBC is enhanced to stop playing ringback tones upon receipt of any of the following messages:

• UPDATE message with different SDP
• subsequent 183 with different SDP
• 200 OK with or without SDP

Call Flows

LMSD call flow where UPDATE is received with different SDP from egress:

LMSD Call Flow

LMSD call flow where announcement is played with locked down codec:

LMSD Call Flow

LMSD call flow where subsequent 18x (w/o SDP) received with Valid Alert-Info header (Early Media Case):

LMSD Call Flow

For more information on Tone and Announcement feature, refer to:

• Tone and Announcement Alarm for SBC SWe Cloud.
• Tone Codec Entry - CLI