The following writing is still related with the CCDE Practical exam that I took recently. IMHO, there are three types of designer for network infrastructure solution:
Designer for Solution: the one normally focuses on the high level solution, by considering customer business model, future growth and other non-technical stuff. The coverage of the design is usually broad, but not too deep, and the solution is for a complete infrastructure with all the supporting components, including the operational process and the operation management. Solution designer should be able to provide the high level topology network infrastructure with the technology to be used and the features need to be enabled, but neither is required to provide the details nor the exact hardware to be used. Characteristic and the features required from the hardware can be mentioned though, to make it easier for the hardware selection by later designer.
Designer for Pre-sales: similar with solution designer, but the coverage normally is less broad and more detail to support the sales activity. As example, while the solution designer may covers the whole infrastructure including the operational process, the pre-sales designer may cover only the data center but can provide the detailed topology for it. The pre-sales designer is the one who involves in the hardware selection, and she must ensure the hardware chosen can run the technology or features required in the solution. If there is capacity and future growth requirement in the design, it has to be considered as well during the hardware selection. The output expected from a pre-sales designer is high level design with the list of hardware required called Bill of Material.
Designer for Implementation: the one who focuses on the in-depth and bit level details of the design. Implementation designer must provide the low level design and make sure the solution can really be implemented using the hardware available. The list of hardware may have been decided by previous designer, so now it's time to make the solution really works. The coverage of the implementation designer can start from the physical topology and connection, module allocation in the hardware, IP addressing scheme, software to be used, up to the detailed configuration of each hardware. The technology and the features chosen may need to be adjusted accordingly based on the limitation from the hardware or the software architecture. And the configuration or the way to implement the technology or features is usually based on the best practices, lab testing or the previous experience in another networks.
One example when to use the different types of network designer is as follow: a solution designer is the one who builds the Request For Proposal (RFP) document for a complete solution including the operational support. So he stands on the customer side. A group of pre-sales designers, stand on the vendor side, can work to answer this RFP and each designer must provide the list of hardware for specific area that complies with the requirement. It is required for the pre-sales designer to submit the proposal explaining the high level design and how the proposed hardware can deliver the solution. And once the proposal is agreed, the hardware need to be ordered, and now it is time for the implementation designer to really make the solution works.
Which one of the designers is better? It depends.
As in the above example I mentioned, we can be the ones who set the direction of the new network infrastructure solution and technology to be used without having to know too much detail but instead must cover broader technology, we can be the ones who select the hardware and provide high level design to support the sales, or we can be the ones who work in low level design to implement the solution and configure the devices.
Sometimes a person must work as solution designer and pre-sales designer at the same time. And sometimes a person must even work as those three types!
Before I joined Cisco, I used to work as the solution designer, pre-sales and implementation designer role and my role may changed from one project to the other. Obviously at that time, as solution designer I gain benefit being outside Cisco because I was able to work even with the hardware from multiple vendors. But as implementation designer, I was not able to go deeper because I didn't have access to the detailed hardware and software architecture.
Since I joined Cisco Advanced Services about 3 years ago most of the time my focus has been in the implementation or after the list of hardware has been confirmed by the pre-sales designer. I must deal with the design limitation due to the hardware or software architecture. Most of my customers are Internet Service Provider or from Telecommunication industry. And in my last several projects I had to focus on the migration from the existing infrastructure to the new one, which means I have to deal more with the right methodology and the detailed procedures to transform the network without impacting the daily business of the customer.
The CCDE exam that I took few days ago covers the knowledge owned by the solution designer, and part of the pre-sales designer. It deals with the high level solution design. It is not required to know the limitation from the hardware, nor it is required to choose the hardware like what the pre-sales designer does. CCDE contents cover the different type of customer networks from different industry, from ISP to Retail, Financial, Media and so on. We don't need to know the in-depth and bit level details of the technology but we must know the reason why a particular technology is chosen in the solution.
So looking at the above facts, please allow me to make this statement even I haven't passed the exam to prove it: it is actually possible to just walk in to CCDE practical lab, without preparation, and pass it. As long as we have extensive experience with high level design for different type of networks. Plus we need the problem solving minded, the ability to capture only the related and important information, and a good stamina to stay focus with lots and lost of reading within 8 hours.
For me, if I really failed this attempt and need to take the exam again, at least now I know what to do. I need to get out from my current mindset that follows my current work where it is expected for me to focus in a very low level and detailed design, with a narrow technology area. I need to return back to my previous experience before I joined Cisco, when I used to support the pre-sales activities, and when I used to work with high level solution of multiple customer networks from different types of industry. Since my current work deals only with Service Provider networks, I may need to find some best practices documents, but not the in-depth implementation practices, but more like the high level design solution for different type of customer networks.
All of those will be necessary once I get the report 6-8 weeks from now, stating that I really fail. So let's just wait and see.