V7122 Gateway User Guide 247CHAPTER 8: T ELEPHONY C APABILITIESWorking with Supplementary ServicesThe gateway supports the following supplementary services: Call Hold / Retrieve (see Call Hold and Retrieve Features) Call Transfer (Call Transfer) Call Forward (doesn't initiate call forward, only responds to call forward request) Call WaitingThe gateway SIP users are only required to enable the Hold and Transfer features. The callforward (supporting 30x redirecting responses) and call waiting (receive of 182 response)features are enabled by default. Note that all call participants must support the specific usedmethod.When working with application servers (such as BroadSoft’s BroadWorks) inclient server mode (the application server controls all supplementary services andkeypad features by itself), the gateway’s supplementary services must bedisabled.Call Hold and Retrieve Features The party that initiates the hold is called the holding party, the other party is called theheld party. The gateway can't initiate the hold, but it can respond to hold request, and assuch it is a held party. After a successful hold, the held party should hear HELD_TONE, defined in thegateway's Call Progress Tones file. Retrieve can be performed only by the holding party while the call is held and active. After a successful retrieve the voice should be connected again. The hold and retrieve functionalities are implemented by REINVITE messages. The IPaddress 0.0.0.0 as the connection IP address or the string ‘a=inactive’ in the receivedREINVITE SDP cause the gateway to enter Hold state and to play held tone (configuredin the gateway) to the PBX/PSTN. If the string ‘a=recvonly’ is received in the SDPmessage, the gateway stops sending RTP packets, but continues to listen to theincoming RTP packets. Usually, the remote party plays, in this scenario, Music on Hold(MOH) and the gateway forwards the MOH to the held party.
