332 CHAPTER 12: V IRTUAL CONNECTIONSsite code, there is no conflict between the extension dialed and anidentical extension number at the local site (Chicago). The choice of sitecodes is made by the person who configures the dial plans for the sites.See “Dial Plan Configuration” on page 334 for more information abouthow to set up VTLs in the dial plan.Conference CallsUsing VTLConnectionsUsers can set up conference calls over VTLs in much the same way thatthey set up conference calls with other users at their local site, or at a sitereachable by an external telephone line.■ On V3000, V3001R, or V5000 systems, you can have up to twelve4-person conference calls simultaneously.■ On NBX 100 systems, you can have up to four 4-person conferencecalls simultaneously.To make conference calls between sites, you must implement IGMP(Internet Group Management Protocol) on your network.Conference Calls Using Site-Unique ExtensionsIn Figure 20, a user in Chicago establishes a conference call with twousers in Atlanta and one user in Dallas as follows:1 Dial the first extension in Atlanta.2 After the user answers, press Conference and dial the second extensionin Atlanta.3 When the second user answers, press Conference again to connect allthree users.4 Press Conference again and dial the extension of the user in Dallas.5 When the fourth party answers, press Conference to connect all fourusers.Conference Calls Using Site CodesIn Figure 21, if you work in the Chicago office, to establish a conferencecall with two people in Atlanta and one person in Dallas:1 Dial the site code (62) and the first extension.2 After the first user answers, press Conference, dial the same site code(62) and the second extension in Atlanta.3 When the second Atlanta user answers, press Conference again toconnect all three users.
