title: CoAP, how to understand "Options"
body: <p>Formatting a CoAP packet</p>
  
  <p>[RFC 7252 CoAP][1]</p>
  
  <p>In RFC 7252 Section 3, Figure 7 the third row, bytes 9 ... 16 or maybe more, is the Options field. I am unable to find anything that specifies how long the options field is. I understand that it can change, but unlike the Token field who's length is specified by field TKL, I cannot recognize where the length of the Options is specified.</p>
  
  <p>Yes, I see sections 3.1 and 3.2 but am not able to understand what they are telling me.  The document states to reference the previous options.  OK, what do you do for the first message where there is no previous packet and no previous option?</p>
  
  <p>When my code needs to send a CoAP message, how do I determine what options can be sent?  What values must be loaded into the packet to send, for example, no options?</p>