VoIP Features

These features are configured in the IP Bearer Profile pane

 

Silence Suppression:

During a normal voice conversation, much of the time is wasted on silence from one or both ends. Ethernet bandwidth can be conserved if during these periods of silence RTP packets are sent with silence-encoded compressed payloads. The IMG Silence Suppression feature supports the concepts of Voice Activity Detection (VAD) and Comfort Noise Generation (CNG). When enabled Silence suppression will not send RTP traffic during periods of silence, saving bandwidth usage. At the beginning of a silence period, a single packet will be sent to the distant end to inform it that a period of silence is being entered, and that the distant end should begin to regenerate comfort noise to its TDM stream. Silence Suppression can be enabled or disabled on an established connection.

 

Note: This does not apply to EVRC or GSM-AMR as they have their own internal Silence Suppression scheme.

 

Note: For SIP calls silence suppression is enabled by default. In the default configuration the attribute is not sent unless it is specifically set to off. In the case of Fax reinvites if Silence Suppression is set to "off" the following line is included in the SIP SDP message:

 

a=silenceSupp:off - - - -

 

Echo Cancellation:

In compliance with ITU G.168-2000, this feature eliminates echo introduced by impedance mismatched hybrids on TDM channels.

 

VoIP Modules:

SLM-IPM-1001R (Rohs compliant Mindspeed Module) - Maximum Tail length is 128 milliseconds

SLM-IPM-1001 (non-Rohs compliant Mindspeed Module) - Maximum Tail length is 128 milliseconds

SLM-IPM-0001R (Rohs compliant EOL BroadCom Module) - Maximum Tail Length is 64 milliseconds

SLM-IPM-0001 (non-Rohs compliant EOL BroadCom Module) - Maximum Tail Length is 64 milliseconds

SLM-IPM-0001 (non-Rohs compliant EOL BroadCom Module) - Maximum Tail Length is 64 milliseconds

 

You may want to implement Echo Cancellation for tandem calls on trunks with echo or to clean an incoming signal before connecting to a media resource, such as a Voice Response Unit or Answering Machine Detection.

 

RTP Redundancy:

This feature provides RTP packet redundancy level 1 to guard against network packet loss. Refer to RFC 2198. This applies to RTP traffic in voice or fax/modem bypass calls. Note that Open Phone does not support RTP Redundancy. The IMG also supports changing the RTP payload type when redundancy is enabled

 

Note: This does not apply to EVRC, GSM-AMR or iLBC.

 

Fax:

Fallback to Fax Bypass:

The Fax Fallback feature is a backup mechanism to transmit a fax using Fax Bypass mode when T.38 cannot be negotiated successfully. This feature allows you to configure T.38 Fax Relay as the preferred type, and also allow Bypass Fax when T.38 is not supported by the remote end. The added negotiation will therefore reduce the call setup failure rate by increasing the content of the media offer.

In the event where the fallback scenario fails, the IMG will allow the voice call to proceed as if no negotiation had happened.

See the Fax Mode and Fax Bypass Codec fields in the IP Bearer Profile pane.

 

Fax Packet Redundancy:

RTP Redundancy is a method of overcoming packet loss by doubling packet payload without increasing the number of packets sent. This feature provides Fax packet redundancy to guard against network packet loss. Up to 3 levels are supported. Redundancy is applied to data and control T.38 packets. This is only applicable to Relay Fax Mode. This feature does not apply for the AMR or EVRC codecs.

If Fax Packet Redundancy is enabled then the IMG also supports changing the Payload Size.

See the Fax Mode and Fax Packet Redundancy fields in the IP Bearer Profile pane.

 

Modem Bypass:

If this feature is enabled the IMG switches to another codec when you are in a modem call. The codec that you switch to is specified in the Fax Bypass Codec field. For example, if you are using a low bit rate codec, such as G.729, a modem or fax call will probably not be successful. So in this case the IMG changes the codec to what is configured in the Fax Bypass Codec field.

This functionality is not supported for the AMR and EVRC codecs.

See the Modem Behavior field in the IP Bearer Profile pane.

 

Modem Disable:

If Modem Behavior is set to Disabled and Fax Mode is set to 'Enable Relay (T.38)', any detected data is assumed to be T.38 fax related. RTP will be shut down and then T.38 protocol will be started.

If Modem Behavior is set to Disabled and Fax Mode is set to 'Enable Bypass', any detected data is assumed to be fax related. RTP will switch to G711 ulaw/alaw and fax bypass will be started.

If Modem Behavior is set to Disabled and Fax Mode is set to 'Relay Fallback to Bypass', any detected data will be fax related. RTP will be shutdown and signaling will be decided through SIP signaling. (Whether to go to g.711 or T.38)

This feature was added in software 10.5.1 ER2 and is backwards compatible so that it is supported on both Mindspeed and Broadcom VoIP modules.

 

 

Digit Relay:

The IMG can propagate DTMF digits as In-Band, Packetized or via H.245 UII. The packet type can be changed for digit relay. See the Digit Relay and Digit Relay Packet Type fields in the IP Bearer Profile pane.

 

Note:If the Digit Relay field in the IP Bearer profiles object pane is set to DTMF Packetized then the telephone event message will be sent in the CDR otherwise the telephone event message will not be sent. See below

 

 Example of "telephone event" line in SDP

 

v=0

o=- 1643042763 1643042846 IN IP4 10.129.39.111

s=eyeBeam

c=IN IP4 10.129.39.111

t=0 0

m=audio 7118 RTP/AVP 0 3 8 18 5 101

a=alt:1 1 : A95B1E03 000000F5 10.129.39.111 7118

a=fmtp:101 0-15

a=rtpmap:101 telephone-event/8000

a=sendrecv

 

 

 

Media Inactivity Support:

The Media Inactivity feature was added to the IMG to inform the signaling layers (SIP and H323) when RTP has stopped flowing. The Initial Media Inactivity timer indicates that no RTP was ever received on the IP channel. The Media Inactivity Timer indicates that RTP has stopped flowing. When the signaling layers receive indications that these timers have expired, the signaling releases the channel. This feature resolves the problem where signaling gets out of sync and IP channels remain up with no one on the other side of the call. Media Inactivity Detection Support

 

 

RTP Change Upon Gratuitous ARP (10.5.0 ER2):

In Feature F-1485 the IMG will use ethernet information sent in a Gratuitous ARP from a Network Cluster to determine if the IP address information in the RTP streams going to and from the IMG needs to be updated. See RTP change on Gratuitous ARP link.