Discussion of Classes of Service in ISM Book

Hi,

I doing final revision for my Information Storage Associate exam. Reading through Chapter 6 of the ISM book, I saw that Table 6-1 on p.138 describes the different classes of service for FC.

In this table, it states that Class 1 communication only uses EE_Credit for flow control.

However, if I turn to pp.282-283  of the EMC "Networked Storage Concepts and Protocols Techbook", it describes how Class 1 uses both EE_Credit and BB_Credit for flow control. In fact, on p. 282 of the techbook, it says:

    "BB_Credit is only used on the request frame and the ACK. Once the connection is established, flow control is controlled with End_to_End Credit."

Likewise, Fig. 155 on page 283 seems to show that both EE_Credit and BB_Credit are used in Class 1 sessions.

However, as I pointed out, Table 6-1 states that Class 1 communication only uses EE_Credit for flow control.

What is going on here?  I figure it is either a mistake or else a deliberate mistake or else a deliberate simplication (appropriate to this level of course).

Needless to say this is all very confusing!! I guess for the purposes of the exam, I should just stick to the information in Table 6-1.

Regards,

Bill Harpley