Huawei U-SYS MRS6100 Technical Manual page 67

Technical Manual
U-SYS MRS6100 Media Resource Server
The host is a domain name defined globally or an IP address routable globally. The
local ID is composed of unique URI characters in the scope of host. Otherwise, the
local ID must be a globally unique value to ensure the global uniqueness of Call-ID.
Call-IDs are case-sensitive.
An example of Call-ID field :
Call-Id: call-973636852-4@182.20.20.105
182.20.20.105 is the IP address of a host. call-973636852-4 is a globally unique local
ID.
From
All requests and responses must contain the From field that indicates the initiator of
the request. The server duplicates this field from the request message to response
messages.
This field has a generic format:
From: display-name<SIP-URL>;tag=xxxx
The display-name is the character displayed on the user interface. The system will
use the display name Anonymous if the identity of the client remains hidden. The
display-name is optional. The tag is a string of hexadecimal numbers in which the
hyphen (-) can be added. When two user instances sharing the same SIP address
use the same Call-ID to initiate a call invitation, this tag is used for distinguishing
purposes. The tag value must be globally unique. A user should maintain the same
Call-ID and tag value in the whole process of a call.
An example of From field:
From: <sip:1000@182.20.20.105>;tag=1c17691
To
The To field specifies the logical recipient of the request. The format of the To field is
the same as that of the From field except that the first key is replaced by To. All
requests and responses must contain this field.
The tag parameter in the field distinguishes different user instances that are identified
by the same SIP URL. A proxy server can concurrently deliver several requests, and
the same request might reach different instances (home telephone, for example) of
the user. Because the instances might all respond to the request, it is required to use
the tag to distinguish the responses from different instances. The tag in the To field is
put by each instance in the response message.
Examples of To field:
To: <Sip:1000@182.20.50.1>
To: <sip:1001@182.20.50.1>;tag=62beb3ca
In SIP, the Call-ID, From, and To fields identify one call branch. When a proxy server
concurrently distributes requests, a call might have several call branches.
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Chapter 5 MGCP and SIP