Yealink SIP-T48G Administrator's Manual

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Yealink SIP-T48G Administrator's Manual Manual pdf 14 page image

Microsoft Lync Edition Administrator’s Guide for SIP-T2_Series and T4_Series IP Phones2SIP provides capabilities to: Determine the location of the target endpoint -- SIP supports address resolution,name mapping, and call redirection. Determine media capabilities of the target endpoint -- Via Session DescriptionProtocol (SDP), SIP determines the “lowest level” of common services betweenendpoints. Conferences are established using only media capabilities that can besupported by all endpoints. Determine the availability of the target endpoint -- A call cannot be completedbecause the target endpoint is unavailable, SIP determines whether the calledparty is already on the IP phone or does not answer in the allotted number of rings.It then returns a message indicating why the target endpoint is unavailable. Establish a session between the origin and target endpoint -- The call can becompleted, SIP establishes a session between endpoints. SIP also supports mid-callchanges, such as the addition of another endpoint to the conference or the changeof a media characteristic or codec. Handle the transfer and termination of calls -- SIP supports the transfer of calls fromone endpoint to another. During a call transfer, SIP simply establishes a sessionbetween the transferee and a new endpoint (specified by the transferring party)and terminates the session between the transferee and the transferring party. Atthe end of a call, SIP terminates the sessions between all parties.SIP is a peer-to-peer protocol. The peers in a session are called User Agents (UAs). Auser agent can function as one of following roles: User Agent Client (UAC) -- A client application that initiates the SIP request. User Agent Server (UAS) -- A server application that contacts the user when a SIPrequest is received and that returns a response on behalf of the user.User Agent Client (UAC)The UAC is an application that initiates up to six feasible SIP requests to the UAS. The sixrequests issued by the UAC are: INVITE, ACK, OPTIONS, BYE, CANCEL and REGISTER.When the SIP session is being initiated by the UAC SIP component, the UAC determinesthe information essential for the request, which is the protocol, the port and the IPaddress of the UAS to which the request is being sent. This information can be dynamicand will make it challenging to put through a firewall. For this reason, it may berecommended to open the specific application type on the firewall. The UAC is alsocapable of using the information in the request URI to establish the course of the SIPrequest to its destination, as the request URI always specifies the host which is essential.The port and protocol are not always specified by the request URI. Thus if the requestdoes not specify a port or protocol, a default port or protocol is contacted. It may be