The 7-layer OSI model of networking is an enduringly powerful concept. It describes how to seperate the different hierarchies of networking activity, separate them and enable their interacting through interfaces. That way you can develop each layer without adversely affecting functions below you in the hierarchy whilst adding new functions or more performance at your own layer.

The seven layers are, from the wire or optical cable upwards:

1. Physical - the wire
2, Data link - data packet encoding and decoding
3. Network layer - switching and routing
4. Data transport - transfer of data between end systems
5. Session - establish, terminate and manage communication sessions between applications
6. Presentation - translates between application and network data formats
7. Application - provides application services for file transfers, e-mail, and other network software services.

A storage area network (SAN) switch or director is an element in a networking fabric and the OSI model can be used to describe what it does and how it is organised. Traditionally switches and directors have been lower layer items, not bothered about anything above layer 3.

For McData layering functions in the OSI way is fundamental to its development and strategy.

Jeff Vogel, McData's senior VP for corporate development and strategy, talked about this.

"Our extended value is in the layers above layer 2. It's a differentiator, (having) an architecture which lets us get to the upper layers quickly. Our customers don't have to reconstruct to benefit from this."

What McData has done is to create a specific box, an Application Services Module or ASM, that operates in the layer 4 to 7 area and interfaces to its switches and directors, operating at the layers 1 to 3 levels. The ASM is managed with the director it links to as a single unit and provides fabric application services such as storage virtualisation.

Vogel said: "Customers like this layered services strategy because it happens without affecting the lower layers." They don't have to replace or alter their director and switch setup to take advantage of the ASM-facilitated storage applications."

Where does iSCSI fit in the 7-layer model? Vogel says: "It's a layer 2 and3 infrastructure item. Nishan (Which McData acquired) provided this for us." He went on to characterise other things in 7-layer terms: "Layer 2 is the layer where switches (motherboard-based) and directors (backplane-based) exist. Layer 3 is for multi-protocol and distance technology. CNT gave us extension and Nishan brought us TCP/IP."

Other layer 3 applications are replication, virtual tape, continuous data protection, volume management and backup. "Things in the storage world like backup, replication and recovery make sense to do in the network That's where they'll eventually end up."

What McData has done is both to acquire companies and technologies to facilitate its advance up the 7-layer model and to partner so as to offer extended functionality to its customers. They can then make more use of the underlying fabric. Thus, for Wide Area File Services (WAFS), it is partnering Riverbed.

He explained that Nishan and CNT technology is being integrated for use in the remote sites in the WAFS area. "We'll see an OEM technology emerge first (Riverbed and ROC) for networking the remote and central sites. Then we'll incorporate our own technology."

"You'll start to see inter-fabric routing become part of our layer 2 infrastructure. Layer 2 stroke 3 integration drives cost out. It's about lowering cost and keeping the core attributes unaffected."

This is very similar to the way LANs scaled.

"The layer 4 through 7 area is all emerging value. This is where the profit is. You'll see us move through an OEM stage, possibly an acquisition."

Information lifecycle management
"ILM is very relevant. It gives customers a strategy for how they will build an intensive infrastructure. We won't get into ILM itself. We'll provide a foundation layer of good cost and performance. Applications shouldn't have to worry about disaster recovery and backup. We're building a more capable and resilient platform for our OEMs to enable them to offer ILM applications."

"We're moving up from layer 3. They're looking from layer 7 downwards with ILM. We meet in the middle."

Big directors
What about 512- (or 528-)port directors? "What's the problem you're trying to solve? Can you solve the problem with a 512-port chassis or a 2 by 256-port chassis? Go to the 512-port chassis if you need to run 512 ports at 4Gbit/s. Our customers aren't demanding that level of technology today. We'll build a 512-port product eventually."

"We'll build 4Gbit/s 256-port. We'll build 8Gbit/s 256-port. We'll build 8Gbit/s 512-port. Eventually we'll go bigger. Technology will migrate to where its cheapest to build and easiest to scale."

Vogel discussed over-subscription: "The Cisco528-port could provide variability of performance, etc. It adds overhead and cost."

Vogel contrasts the McData way with others': "Brocade and Cisco have radically different approaches. SANtap, for instance, is an inferior way of moving data because it contends for backplane performance."