Chapter 2 SRG50 overview 23SRG50 Configuration GuideLocal modeIn the event of a WAN failure or the call server at the main office becomes unavailable, theIP Phones in normal mode revert to local mode automatically. In local mode, the IP usersconnected to the SRG are under the control of the SRG. When in local mode, main office callfeatures are not available to users attached to the SRG. The SRG offers a set of basic features forthe IP telephones, including access to the local PSTN, dialing emergency service numbers, andcalling local extensions. For a complete list of local mode features, see Features in local mode onpage 62. Local mode is illustrated in the figure Local mode on page 23.Figure 2 Local modeThe SRG handles all call processing. Calls between two IP telephones at the SRG are handledlocally as a simple station-to-station call. When an IP telephone initiates a local PSTN call, theSRG routes the call to a trunk that is connected to the local PSTN. Incoming DID calls are alsohandled by the SRG and terminated on the appropriate IP telephone set.In local mode, the IP telephones do not have access to the main office network over the VoIPtrunks. If alternate routes are configured, then calls can be made to the main office or other branchoffices using the available PSTN trunks.Several situations, described below, can cause the IP phone to be in local mode.Initial registrationWhen the IP telephone is installed, it first registers with the SRG, and is in local mode. When theSRG configuration at the main office and the SRG is complete the IP telephone is redirected to themain office, where it registers as a branch user and changes from local mode to normal mode.Note: The IP Phone KEM is supported on an SRG with normal mode IP Phones.It does not function with local mode or test local mode IP Phones.Branch office Main officeWAN connectivity lost,IP phonesIP phonesLocal modeSRGSoftwarephonesWLANhandsetsPSTN provides fallbackpollingSRG
