The first layer in the OS model or Layer one is the physical layer.
It defines how data is transmitted.
So in other words what state represents binary ones or binary zeros.
So media signal and binary transmission are defined at this layer the physical layer defines the electrical
mechanical procedural and functional specifications for the physical link or the physical layer.
This allows for interoperability to put that into plain English.
Here's an example.
RJ 45 connectors are used in ether net and you would plug an RJ 45 connector into the network interface
code of a P.C..
The standards associated with an RJ 45 interface are different to other interfaces such as a v 35 connection
which is used in some way and implementations so the physical characteristics of these interfaces and
the specifications for activating the connections are different on Ethernet.
As an example at Layer 2 ether 2 might be used but PDP or HDL C may be used at Layer 2 on a when interface.
The physical characteristics here are very different.
So things such as the pins the voltage the cable specifications and the devices that are supported may
vary copper.
As an example has a different physical characteristics and specifications when compared to fibre fibre
transmits light copper transmits electrical signals.
The physical infrastructure is very different and that needs to be standardised.
As an example a network engineer needs to know that he can connect and RJ 45 cable to a Dell laptop
or an HP laptop or a Cisco switch devices provided by different vendors specifications or standardised
so that network engineers could go out and purchase a cat 5 cable or CAT 6 cable with an RJ 45 connector
from a local network supplier and plug it in to any one of those devices without worrying about compatibility.
The physical specifications are laid out at layer one of the OSA model and thus we have interoperability
between different devices from different vendors because those vendors adhere to the standards at the
physical layer or layer one of the OS I model.
Once again a software developer working at least seven of the OS I model doesn't need to be concerned
with the physical characteristics of Ethernet or A.T.M. or DSL or RJ 45 cables or V 35 cables or fiber
optics and so forth and so on.
The developer adheres to the specifications at a layer 7 and network vendors providing networking equipment
or P.C. manufacturers providing pieces adhere to the standards at layer 1 to ensure interoperability
between networking devices.
The physical layer is often the easiest layer to identify because it's focused on physical devices with
physical cabling.
There are many major functions performed by this layer and they will vary depending on the physical
media.
So as an example Layer 1 specifications include cables specifications like maximum cable length electrical
specifications radio specifications including signal strength modulation techniques line coding but
synchronization and many other options.
You'll have to refer to the physical specifications of an individual media type such as Ethernet to
see the details and specifications for that individual media type.
Fibre is different to copper which is different to wireless which is different to DSL.
We're not going to concentrate on those here.
If you're planning on becoming a manufacturer you would have to adhere to the manufacturing requirements
for cabling and interfaces to ensure that you conform to the specifications so that interoperability
and standardization is ensured.