Physical layer represents a media that using for data transport from source to destination. Data is converted to bit level and ready to transfer via a physical media. The data conversion to bit level is accomplished by network hardware and software on computer (or network device).
I want to mention that where the physical layer used in real life, so I don’t give theoretical information at this post.
I try give two examples that we are using our real life frequently.
1- ADSL/VDSL Access
As you know, at the ADSL internet access, we separated our phone line into two parts with splitter which are carrying phone and ADSL signal. We connected phone part to our analog phone and ADSL part to our ADSL modem.
The splitter’s function is separating the two different frequencies (phone and ADSL) from each other
The technology called xDSL also and basically means transferring data over traditional phone lines. They have several variations like ADSL, VDSL, GSHDSL etc. The technology name is changed by data size transferred over phone line.
Let’s give an ADSL example on scheme;
As seen on the picture, our computer connects to internet via cable Ethernet or wireless network. Modem is connected nearest concentration point (DSLAM) with phone line. After DSLAM, the fiber optic lines are used for high-speed Ethernet (Gigabit, 10Gigabit or higher) connections.
The copper Ethernet cables, the air for transferring Wi-Fi signal and fiber optic cables for high speed connection are points as Layer 1 in real life.
2- Fiber Internet Access
The main difference between fiber access and ADSL is all communication is done over Ethernet. Usually service provide puts an Ethernet switch to the basement of the apartment and take a cat6 Ethernet cable to every flat in this apartment. We put this cat6 Ethernet cable to the router that given by service provider.
The internet access of the central switch at the bottom of apartment is done by high speed fiber Ethernet technologies. Last years’ service providers also give Ethernet connection to the home with fiber (fiber to home).
We connect our wired or wireless devices to our internet router that provided by service provider.
Let’s take look picture below;
The Ethernet cable that our computer connected, the Ethernet cable that our internet router connected to ISP switch and fiber optic cables that central switch connected to ISP’s backbone is physical layers of this example.