RFC 4566, "SDP: Session Description Protocol", July 2006

Note: This RFC has been obsoleted by RFC 8866

Errata ID: 4903
Status: Held for Document Update
Type: Technical
Publication Format(s) : TEXT
Reported By: Jxck
Date Reported: 2017-01-12
Held for Document Update by: Orie Steele
Date Held: 2024-04-01

Section 9 says:

   ; SDP Syntax
   session-description = proto-version
                         origin-field
                         session-name-field
                         information-field
                         uri-field
                         email-fields
                         phone-fields
                         connection-field
                         bandwidth-fields
                         time-fields
                         key-field
                         attribute-fields
                         media-descriptions

   connection-field =    [%x63 "=" nettype SP addrtype SP
                         connection-address CRLF]
                         ;a connection field must be present
                         ;in every media description or at the
                         ;session-level

   media-descriptions =  *( media-field
                         information-field
                         *connection-field
                         bandwidth-fields
                         key-field
                         attribute-fields )

It should say:

   ; SDP Syntax
   session-description = proto-version
                         origin-field
                         session-name-field
                         information-field
                         uri-field
                         email-fields
                         phone-fields
                         [connection-field]
                         bandwidth-fields
                         time-fields
                         key-field
                         attribute-fields
                         media-descriptions

   connection-field =    %x63 "=" nettype SP addrtype SP
                         connection-address CRLF
                         ;a connection field must be present
                         ;in every media description or at the
                         ;session-level

   media-descriptions =  *( media-field
                         information-field
                         *connection-field
                         bandwidth-fields
                         key-field
                         attribute-fields )

Notes:

in BNF of SDP,
connection-field itself is optional [0, 1], but media-description has multiple [0,) connection-field.
it seems conflict, because multiple of optional fields doesn't finish because multiple filed can't find when to end.

so change connection-field itself not optional (remove []) and, replace session-descriptions connection-field as optional.

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