When a header contains contact information, it is typically added using the 'SIP URI' format:
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A SIP URI is like an email address. In its simplest form, it appear as sip:content@hostname.
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The SIP URI can also indicate the target port: sip:content@hostname:port
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For some headers, the SIP URI can also include preferred display name. When that happens, the sip: part is enclosed in < > brackets. For example: display <sip:content@hostname>.
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Some line providers may use a different format called TEL URI. That takes the form tel:123456789.
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The system can use SIPS format which replaces sip: with sips:. This is used to indicate that the connection should use TLS from end to end. That is, every hop should use TLS.
