Chapter 1 Getting started 17Survivable Remote Gateway 50 Configuration GuideSRG50 operating modesThe SRG50 has two operating modes: normal and local.Normal modeIn normal mode (Figure 1), the SRG50 is connected to the main office call server over a WANusing VoIP trunks. From the perspective of the main office, the SRG50 is a branch office.Figure 1 Normal modeIP telephones connected at the SRG50 are registered with the main office call server and are undermain office control. They operate as branch user sets and have access to all telephony services andfeatures that the call server offers to IP telephones connected directly to the main office.When a branch user set initiates a local PSTN call, the main office sets up the call using the VoIPtrunks, which establishes a local media path. Emergency Services Access calls are similarly routedto the SRG50 PSTN. For main office callers, the SRG50 acts as a VoIP-PSTN gateway duringnormal mode.When call forwarding has been configured, incoming PSTN calls to the branch user set areforwarded over VoIP trunks to the main office, which terminates the call at the branch user.Similarly, calls from analog telephones connected to the SRG50 to the branch user set areforwarded to the main office over VoIP trunks, which then terminates the call at the branch user.Calls from the branch user set to the analog telephones at the SRG50 are routed over the VoIPtrunks to terminate at the analog telephone. In all these call scenarios, only signaling messages gothrough the VoIP trunk. The media path is set up directly between the branch user set and the voicegateway at the SRG50. This means that these calls do not use any WAN bandwidth between themain office and the branch office after calls are established.Branch office Main officeVoIP connection over WANIP phonesSRG50IP phonesNormal modeSoftwarephonesWLANhandsets
