All telephone calls, video conference calls take place over internet

• people identified by names or email addresses rather than phone numbers
• Can reach callee no matter where callee roams, no matter what IP device callee is currently using

Services:

1. SIP provides mechanisms for call setup

   • For caller to let callee know she wants to establish a call
   • Callee can agree on media type and encoding
   • End call

2. Determine current IP address of callee

   • map mnemonic identifier to current IP Address

3. Call Management:

   • Add new media streams during calls
   • Change encoding during call
   • Invite others
   • Transfer, hold calls