6.1 Session Service Header

The Session Service header, as presented in RFC 1002, is as follows :

The FLAGS field breaks down further into:

The reserved bits are always supposed to be zero, and the E bit is an additional high-order bit which is prepended to the LENGTH field. Another way to look at the layout is like this:

We will stick with the latter, simpler format and ignore the FLAGS field, which is never really used.

The LENGTH field contains the number of bytes of payload, and the TYPE field is used to distinguish between the six different Session Service message types, which are:

0x00 == Session Message

0x81 == Session Request

0x82 == Positive Session Response

0x83 == Negative Session Response

0x84 == Retarget Session Response

0x85 == Session Keepalive

Each of these message types is explained below.