A telephony engine of Smartswitch has a rich feature set.

VoIP audio

Supported protocols:

• RTP;
• RTCP;
• RTP DTMF (RFC2833)

Supported codecs:

• G729 (in proxy mode - G729AB, in transcoding mode - G729A);
• G723;
• GSM;
• G711 ulaw;
• G711 alaw;
• G726;
• ADPCM;
• LPC;
• slin;
• speex;
• iLBC;
• G722 (only proxy mode);

Supported modes:

• p2p (peer to peer). Is available for SIP channel;
• proxy. Is avaliable for all codecs. There is application level proxy mode available as well as proxy mode on the kernel level (Media Proxy);
• transcoding. Is vailable between any of the codecs, excluding G722. It's enabled automatically in the cases where in the process of session negotiation peers have chosen a codec scheme that requires transcoding.
• buffering (can be enabled optionally). You can define the duration of voice frame in milliseconds and system will buffer the stream according to the settings.
• reading DTMF from the voice stream (decoding tones on software DSP) - for G.711 ulaw/alaw family of codecs;
• voice recording to file from RTP stream. Supported file formats:
  • wav. Voice transcoding mode activates during this mode;
  • g729, g723, etc (all codec formats are supported). In case if file format doesn't match current selected channel format - trancoding mode is activated.
• playback from a file to an RTP stream. Supported file formats:
  • wav. Transcoding mode is activated;
  • mp3. Transcoding mode is activated;
  • g729, g723, etc (all codec formats are supported). In case if file format doesn't match currently chosen codec- transcoding mode is activated.
  • audio generation to RTP stream. Ringback generation.

DTMF

Supported protocols:

• RTP DTMF (RFC 2833);
• SIP INFO DTMF (RFC 2976) - for SIP channels;
• Cisco DTMF - for H.323 channels;
• H.245 DTMF - for H.323 channels;
• inband. For G.711 ulaw/alaw.

There is available automatic signalling protocol translation between all supported protocols.

Faxes

Supported protocols of data transmission:

• T.38 (UDPTL).
• inband (for G.711 ulaw/alaw).

For T.38 faxes there is supported switch back to voice mode after fax has been transmitted.

T.38 error correction modes:

• redundancy;
• FEC.

Available modes:

• proxy.There is available both application level proxy and kernel level proxy (Media Proxy);
• T.38 UDPTL transcoding. It happens in case if peers have incompatible error correction modes and/or buffer size;
• fax-server. Supported modes:
  • fax receival in T.38/inband mode with recording to .tiff file.
  • transmission of a fax in T.38/inband mode from a .tiff file.

Additionally there is supported:

• T.38 faxes under NAT;
• inband faxes under NAT;
• transmission of a T.38 fax to the audio RTP port (addiotional option for NAT support);
• options for fixups of T.38 implementation in attached equipment ;

VoIP signalling protocols

H.323

Supported protocols:

• H.323 v4;
• H.225;
• H.245;
• T.38;
• RAS.
• "fast start" procedure support;
• H.245 tunneling. Additional tunneling modes: cisco, QSIG;

Additionally:

• support for devices under NAT;
• manipulation with ToS bitfield of IP packets;
• RTP transmission modes: proxy, transcoding, passing through the jitter buffer;

There are 2 different stacks you can choose from:

• OpenH323;
• Objective Systems;

Both stacks can be used simultaneously and independently (to solve compatibility issues with the attached equipment).

SIP

Supported protocols:

• SIP v2;
• T.38.
• SIP INFO DTMF (RFC 2976);
• RFC 3261 (ACK, BYE, CANCEL, INVITE, OPTIONS, REGISTER);
• RFC 3265 (SUBSCRIBE, NOTIFY);
• RFC 3311 (UPDATE);
• RFC 3515 (REFER);
• RE-INVITE support.

Additionally:

• registration: inbound and outbound. There are configurable timeouts and number of registration attempts;
• support for devices under NAT;
• support for system installation under NAT;
• call hangup by RTP timeout;
• RTP transmission modes: direct (p2p) , proxy, transcoding, passing through the jitter buffer;
• video support;
• manipulation of ToS bitfield of IP packets;