Segmented Header Formats

NJE headers for the DMTNET link driver and the DMTSNE session driver can be up to 32,767 bytes long. Headers longer than 256 bytes are transmitted as segmented headers, with each segment a maximum of 256 bytes long.

When segmented headers are transmitted, each segment contains a 4-byte control section that contains the length of that segment, a segment number, and a flag indicating if this is the last segment. The following is an example of segmented header formats.

 0                          2            3              4
+------------------------------------------------------+
| Segment Length           |  Unused    |  Seq. number |
|                          |            | and flag bit |
+------------------------------------------------------+

The remaining 252 bytes contain the actual header data.

For example, assume that you have a 600-byte header in the following format:

The figure contains a pictorial representation of the header. It begins with a control section that contains H'600' and flags, followed by a control section that contains H'320' and flags, followed by a general section (316 bytes), followed by a control section that contains H'276' and flags, followed by a subsystem section (272 bytes).

RSCS would send this header in the following form:

The figure contains a pictorial representation of the header, which is in three segments. The first segment begins with a control section that contains H'256', X'00', and X'80', followed by a control section that contains H'320' and flags, followed by 248 bytes of the general section. The second segment begins with a control section that contains H'256', X'00', and X'81', followed by 68 bytes of the general section, followed by a control section that contains H'276' and flags, followed by 180 bytes of the subsystem section. The third segment begins with a control section that contains H'96', X'00', and X'02', followed by 92 bytes of the subsystem section.