Understanding FCoE Architectural Constructs

[visitor68]

I am reading a book by Silvano Gai (I/O Consolidation in the Data Center). It's very informative, although I find some parts a bit confusing.

For one, I am trying to understand some of the functionality of the architectural components depicted in this image. This is a very ubiquitous diagram. I have seen it in many FCoE tutorials, so it's imperative that I understand it.

Perhaps someone smarter than me can help me understand it.

Specifically, I don't understand what is meant by the "Lossless Ethernet MAC" otherwise known as the "FCF-MAC".

Quoting from the book: "Each FCF-MAC is coupled with an FCoE Controller function. Each FCF-MAC  may be coupled with a Losseless Ethernet bridging element"

My guess is that an FCF-MAC is a L2 construct - a conceptual sublayer of the OSI model (as in MAC and LLC sub-layers) in which the semantics for the addressing scheme and media access primitives native to that layer exist. Moreover, it is "lossless" in that it also contains the software and hardware functionality to support PFC, ETS, DCBx.

If I got that part right, I really don't understand what is meant by the sentence I quoted from the book (read above). Moreover, why is the "Lossless Ethernet Bridging Element" optional? What exactly does it do?

Can anyone offer some insight, thoughts, analysis that can enhance my understanding? Sometimes it's really a challenge to read such documents without a live person next to you with whom to bounce ideas and share thoughts.

[doug.mtview]

FCF == FC Forwarder where MAC represents the FCoE Link End Point.  Lossless Ethernet uses IEEE bridge standards for no drop exchanges, such as 802.1Qbb, 802.1az, 802.1au where PFC == Priority Flow Control, etc.

[jrosenbl]

Consider the Nexus 5000 as an example.  It has all of the functions mentioned in the sentence you quoted.  The Nexus 5000 is both a Fibre Channel switch (it has the FCF function) and an Ethernet Switch bundled together.  Since it supports the DCB standards for lossless Ethernet its Ethernet Switch component is the aforementioned lossless Ethernet bridging element.  The N5K can switch Ethernet frames from one Ethernet port to another or FC frames from one FC port to another.  It can also switch FC frames to Ethernet ports by adding FCoE encapsulation and vice versa by de-encapsulating FCoE frames received from Ethernet ports and forwarding the payload FC frames to FC ports.   Does this help?