Rollin Luis
NETW320
Professor Antoniou

Week 2 HW assignment

Silent suppression is a technique used to improve bandwidth utilization of voice circuits. Through silence suppression, a mechanism senses periods of inactivity in a voice conversation and simply ceases sending data associated. Silent suppression can be enabled to monitor signals for voice activity so that when silence is detected for a specified amount of time, the application informs the Packet Voice Protocol and prevents the encoder output from being transported across the network. To help understand silence suppression technology, consider this example: Some people talk all the time. Even they have to take a breath and they sometimes listen and are quiet. On a phone call, it is quite common that there is silence in one direction of the call while there is speech carried in the other direction. The public switched telephone network does not take advantage of this condition. The PSTN opens up a path in both directions, between the speakers, and allocates 100% of the path capacity to the call, even when there is silence. Silent suppression is the application of this IP network principle to VoIP calls. When there is silence, you don't send voice packets full of silence. Silence suppression can save bandwidth, especially on IP trunks. The savings can be 40% to 50%. The packet-sending phone or gateway implements the VAD function in the codec. When you think of silent suppression think of it as speech door. It opens for speech and closes for silence. Silent suppression is advantageous for businesses, especially companies specializing in Internet voice applications and service providers, because it means networks and capacity are not being clogged with useless data. The silence suppression technology requires asynchronous movement of data, a very easy task for the Internet to handle. The result is a clear communication between two parties, but without nearly the amount of bandwidth that would otherwise be taken up. Traditional phone lines cannot take advantage of any type of suppression technology, so this technology has developed along with Internet voice communications. In the past, the entire channel through which the telecommunication was taking place was devoted to the conversation. That was not a problem because at that time the only function of the telecommunications system was to transmit voice data. The Internet transmits a wide variety of data, and with the greater demand for data transfer, the transmission speed can suffer. Slowing down a network of computers, essentially what the Internet is, is problematic for voice communication. It can lead to voice distortions, breaks and jumps between words, which could make effective communication all but impossible for the individuals trying to use it. Silence suppression can help that situation by effectively reducing the amount of bandwidth needed for voice calls to almost half of what would otherwise be required. Some disadvantages with silent suppression is background noise detection that may be difficult in some circumstances, relatively low speech level, or relatively high background noise level, for example. When silence suppression is active, the line appears to have gone dead at the other end of the call. For this reason, so-called comfort noise needs to be generated to compensate for the lack of background noise. The ingress end must therefore signal the egress end that silence suppression is in effect. For best results, the level of comfort noise being generated on egress should match that of the background noise at the ingress end. Speech activity detection must occur very quickly, otherwise clipping might occur. Thus, silence suppression is generally an optional feature on telephony devices. In some cases, it is automatically turned on based on the characteristics of a call.

References

Ellis, Juanita. Voice, Video, and Data Network Convergence: Architecture and Design, From VoIP to Wireless. Academic Press, 2003. VitalBook file. Bookshelf.

Silence Suppression. techtarget. Retrieved May 18, 2014, from the World Wide Web: http://searchunifiedcommunications.techtarget.com/tip/How-silence-suppression-saves-WAN-bandwidth