Need clarification on general switching process

[Tian NIE]

Hello all,

I was reading Cisco Express Forwarding (CEF) and several other articles or books online. But I am still confused on some subjects.

According to the first chapter of the CEF book, the switching process generally has three steps:

1. Getting the Packet off the Network Media
2. Switching the Packet
3. Transmitting the Packet

and, it's in the second step "Switching the Packet" that the author says:

"Now that the packet has been copied off the network media into a packet buffer on the router, it can be switched. A Cisco router can use two basic methods to switch packets:

• Hardware-based switching
• Software-based switching

Hardware-based switching exists in many different forms on Cisco routers, from the Cisco 12000 series and Cisco 6500 series, which use custom-designed ASICs, to the Cisco 10000, which uses a programmable ASIC called the Toaster to perform Parallel Express Forwarding (PXF). The following sections focus on software packet switching."

So here are my questions:

1. Do today's routers always go through the mentioned three steps to switch packets? (Which means that the packets are always DMA-ed in a packet buffer in the first place?)
2. Do today's routers' ASICs intervene only the second step? Or ASICs can and do intervene all three steps?
3. Where can I find reliable articles or books on the topic? Or is this topic supposed to be a pseudo-secret and only electrical engineers know what happens?

Thanks in advance for your responsible, reliable and clear replies!

[Joseph W. Doherty]

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Posting

Or is this topic supposed to be a pseudo-secret and only electrical engineers know what happens?

Actually how any particular device actually works is likely to be protected by patent, and beyond being protected by patent, is likely to be considered proprietary and a trade secret.

Hardware vendors will likely only reveal what they think will help sell their device vs. their competition.