• United States

Don’t neglect Layer 1

Jul 01, 20042 mins

* Lower-layer functions still vital

With all the attention garnered by the higher OSI layers, we sometimes forget that all seven layers are necessary for communications to work. So when troubleshooting, for example, don’t forget about the basic stuff.

Take power, for example.  We were recently reminded how important Layer 1 is to PCs and communications equipment when, after a week of troubleshooting, Joanie (with help) traced an intermittent problem to a lowly cabling issue.

We hear lots of talk about switches, firewalls, network monitors, traffic-shapers and other devices working at “Layers 4 – 7” these days. This gives the impression that anything below Layer 4 is old hat. 

But nothing could be further from the truth.

Let’s start by thinking about an “IP service.”  Indeed, IP (Layer 3) is perhaps the most visible layer from a management perspective.  Nevertheless, IP packets require a link layer (Layer 2) below them, often performed by either frame relay or PPP.  And the link layer requires a physical layer (Layer 1) below it, including connectors and cabling.

Years ago, the physical layer was at the forefront of the networking industry. The entire time-division T-1 multiplexing industry was based on intelligent control of Layer 1 parameters.  Various framing formats, including D4 framing and Extended Superframe Format, sit firmly at Layer 1.  Issues that seem positively ancient, such as bit density for T-1 lines, are Layer 1 issues.  But these constraints still must be met regardless of the upper-layer protocols in use.

As mentioned, Layer 1 also addresses connectors.  Both the physical and the electrical characteristics must be appropriately matched for communications to occur.  Just as you can’t plug a U.S.-format 110-volt appliance into a European 220-volt circuit without both a voltage adaptor and a physical plug adaptor, you have to make sure your communications connectors are appropriately matched. 

In fact, we still have a major issue on notebook computers in that an RJ-11 phone connector can physically go into the RJ-45 Ethernet adaptor.  Not only does this Layer 1 incompatibility not work; the ringing voltage on a phone line can wreck an Ethernet connector.

Bottom line?  It’s great to invest in innovation at the higher-layer protocols.  But if you ignore the lower layers, you’re likely to be building the proverbial house on shifting sand.