Emergency communication support on the Internet is an important task. In the event of an emergency, such as a disaster, accepting as many VoIP calls as possible in limited bandwidth is an important requirement. Another important requirement is providing high quality service for important communications (ex. 911 services in the US). But, for non-emergency communication, the number of sessions (calls) that can be supported is much more important than the quality of each session. SIP supports various kinds of media; not only voice but also video can be used. In a multimedia session, it is not necessary to guarantee quality of all media for normal communications in an emergency situation. So, packets that contain video data or high quality voice data can be dropped in a very congested network. Diffserv AF service is suitable to realize this kind of quality policy. We propose a scheme which provides high quality service for important VoIP communication sessions and minimum quality for normal sessions using Diffserv AF service and a call admission method based on observing VoIP flow information anda log of SIP messages.