Introduction

This chapter describes the use of optional headers in Data Frames. It also describes some advanced functions defined in Fibre Channel for use in special circumstances.

Optional Headers

There are currently three possible optional headers in Fibre Channel Data Frames :

Network_Header: Used for including source and destination Name_Identifiers in a Sequence which can have a more general scope than the 3-byte Fibre Channel Address Identifiers, for addressing networks with different name spaces;

Association_Header: Used for addressing an Image, which is one of a process or group of processes which share a single N_Port and also used for associating Frames from different Exchanges together and for locating Exchange information when an X_ID field is invalidated; and

Device_Header: Used for including specific ULP header information.

A fourth header, termed the Expiration Security Header was defined, but since it wasn t being used, the space was reclaimed. If optional headers are present, they must be in the order listed as shown in Figure 13.1. A Frame may contain any or all of these headers, subject to the where present guidelines shown in Figure 13.2.

Figure 13.1: Placement of optional headers in Frame.

Figure 13.2: Summary of optional header usage.

The presence or absence of each of the four headers is indicated in bits 22 to 20 and 17 and 16 of the DF_CTL field in the Frame Header, as shown in Figure 13.2. If any particular optional header is present, the corresponding DF_CTL bit is set to...