问题描述：
英语翻译
The Session Initiation Protocol (SIP) is an application protocol,defined in RFC2543 [4],that is being designed by the
IETF MMUSIC (Multiparty Multimedia Session Control) working group to enable users to participate in multimedia
sessions,that is,to establish,modify and terminate multimedia sessions calls.MMUSIC working group [5] focus on
loosely coupled conferences as they exists today on the MBONE.One of the main issues in this area is related with
how to inform users about forthcoming sessions,media requirements,addresses,etc.There are two basic ways to
locate and to participate in a multimedia session:
· Advertisement.Sessions are advertised in various ways like email,web pages,newsgroups or a multicast
advertisements via Sessions Announcement Protocol (SAP) like in the MBONE.
· Invitation.Users are invited by others to participate by using the Session Initiation Protocol (SIP).
SIP has been proposed as a generic unicast and multicast initiation protocol and also as an IP Telephony call set-up
protocol.It is based on a client-server protocol.SIP clients send a Request Message for a service,and a server
handles the request,answering with a Response Message.SIP terminals can both generate and receive request as
they are composed by a User Agent Client (UAC) and a User Agent Server (UAS).
SIP terminals can establish voice calls directly without requiring any other element.Figure 6 shows an example in
which user1 calls user2 by sending an INVITE Request primitive containing user1 supported capabilities for receiving
audio and a UDP port (port 12345 and mlaw codec).When user2 receives INIVITE Request,he can establish a voice
channel to 12345 UDP port of user1 while he accepts the request by sending an OK Response message.In addition,
user2 response includes its own media capabilities,which are used by user1 to establish a voice channel (GSM codec
at 54321 port in the example) and send an ACK message to acknowledge user2’s response.In order to terminate the
connection,any of the parties can send a BYE Message,which must be acknowledged by an OK response.
The Session Initiation Protocol (SIP) is an application protocol,defined in RFC2543 [4],that is being designed by the
IETF MMUSIC (Multiparty Multimedia Session Control) working group to enable users to participate in multimedia
sessions,that is,to establish,modify and terminate multimedia sessions calls.MMUSIC working group [5] focus on
loosely coupled conferences as they exists today on the MBONE.One of the main issues in this area is related with
how to inform users about forthcoming sessions,media requirements,addresses,etc.There are two basic ways to
locate and to participate in a multimedia session:
· Advertisement.Sessions are advertised in various ways like email,web pages,newsgroups or a multicast
advertisements via Sessions Announcement Protocol (SAP) like in the MBONE.
· Invitation.Users are invited by others to participate by using the Session Initiation Protocol (SIP).
SIP has been proposed as a generic unicast and multicast initiation protocol and also as an IP Telephony call set-up
protocol.It is based on a client-server protocol.SIP clients send a Request Message for a service,and a server
handles the request,answering with a Response Message.SIP terminals can both generate and receive request as
they are composed by a User Agent Client (UAC) and a User Agent Server (UAS).
SIP terminals can establish voice calls directly without requiring any other element.Figure 6 shows an example in
which user1 calls user2 by sending an INVITE Request primitive containing user1 supported capabilities for receiving
audio and a UDP port (port 12345 and mlaw codec).When user2 receives INIVITE Request,he can establish a voice
channel to 12345 UDP port of user1 while he accepts the request by sending an OK Response message.In addition,
user2 response includes its own media capabilities,which are used by user1 to establish a voice channel (GSM codec
at 54321 port in the example) and send an ACK message to acknowledge user2’s response.In order to terminate the
connection,any of the parties can send a BYE Message,which must be acknowledged by an OK response.
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