Tuesday, September 29, 2009

What is Layer 2, and Why Should You Care?

I remember talking with a programmer one time about a simple web app I had created with my limited, self-taught knowledge. "Not bad," he said, "But all your logic is in the application layer." I nodded as if I knew what the heck he was talking about. Why should I care? It worked.

What I didn't know then was that back in 1977, some geeks, perhaps even bigger geeks than this guy who droned on about my application layer, got together and defined not one, not two, but seven layers to a computer network. Today, the work of this group, the Open System Interconnection (OSI) initiative, is the standard for network architect. The OSI Seven Layer Model describes, you guessed it, seven layers that any network must have: Application, Presentation, Session, Transport, Network, Data-Link, and Physical Layers.

So, what is layer 2? Layer 2 refers to the Data-Link layer. This is the layer of the network where data is transferred across the "Physical Layer"--cables, airwaves, routers, and LAN cards--from node to node in a Wide Area Network (WAN). So what, you might ask. I can send data from my computer to my sister's computer via email. What's the difference?

The difference is that, as you'll notice, the layer above Layer 2 is the Network itself. And, a subset of that network is something we all know and love: the Internet. WAN transmissions that remain on layer 2 never go to the internet. That email you sent your sister, however, did (provided you're not also office-mates with an Exchange server). If your data was a letter, Layer 2 describes your inter-office mail--no stamp, no postal worker, and it never leaves the building.

Finally, why do I care? Wireless broadband may seem like old hat to many of us. With a smart phone, tethering, and hot spots all over the city, we might not think twice about what layer our laptop is on when surfing the web on a layover at the airport. But what if instead of your laptop, it was a retail store's server... and instead of surfing the web, it was sending daily transaction reports or even credit card data for payment processing. Still think the layer is irrelevant? A layer 2 network means that cardholder data never hits the internet (a big no-no for PCI Compliance).

Accel Networks fixed wireless broadband services deliver broadband connection to your remote locations, not just for internet browsing, but for Layer 2 network purposes such as point-of-sale and other sensitive company data. Proving once again, "this ain't your average air card."

Labels: "Internet infrastructure", Fixed Wireless Broadband, Layer 2, OSI, PCI Compliance, PCI Compliant Broadband, PCI-DSS, WAN