RFC 3868 query regarding sequence number

Hi All,

 

I have a query regarding section 3.3.1 in RFC 3868
 
3.3.1.  Connection Oriented Data Transfer (CODT)
...
...
   |         Tag = 0x0107          |             Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Sequence Number                        |
...
...
     Parameters
     Routing Context               Mandatory
     Sequence Number               Optional *1
...
...
   NOTE *1:   This parameter is not present in case of Expedited Data
              (ED).
 
   Implementation note: For the CODT to represent DT1, DT2 and ED
   messages, the following conditions MUST be met:
 
   DT1 is represented by a CODT when:
     Sequence Number parameter is present (contains "more" indicator).
 
   DT2 is represented by a CODT when:
     Sequence Number parameter is present (contains P(S), P(R) and more
     indicator)
 
   ED is represented by a CODT with:
     Sequence Number parameter is not present
 
Here Sequence number is mentioned as a optional parameter. Can one assume
that is a message is received without a sequence number, then the message is
Expedited? Can a DT1 message not have a sequence number?
 
Thanks,
Sujay

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