Hello sales2161
There are a whole series of characteristics and parameters that must be standardized and agreed upon by manufacturers and standards organizations at each layer of the OSI model. I’ve listed some parameters for some layers below, but these lists are by no means exhaustive.
On the physical layer, the parameters that are defined include the type of medium used and its characteristics. Copper, fiber, or wireless, including some minimum standard parameters of the medium defined by specific standards such as IEEE802.3 or 802.11 for example. These define things like type of copper used, type of glass used for fiber, minimum distance of physical cable, method of encoding (placement of bits on medium) and signalling (nature of the phenomenon traversing the medium such as voltage/light/EM waves). Physical layer also includes connector types, voltages, wavelengths, and signal strengths on the media. Most of these standards are not actually configurable on the devices, but are predetermined by the manufacturers for particular interfaces and components. Speed and duplex settings as you describe them are primarily an Ethernet issue and are found at the Datalink layer.
On the datalink layer, many more things can be configured, although some are built in. Configurable parameters include speed and duplex, and interface MTU, while interface types such as Ethernet, serial, and Wi-Fi are built in and cannot be modified. Physical addressing, logical link control operation and multiaccess mechanisms such as CSMA/CD and CSMA/CA and service protocols like STP, VTP, CDP, and DTP are all found within the datalink layer.
The network layer is where IP lives, and the parameters here are endless. IPv4, IPv6, routing protocols, routing mechanisms, GRE tunneling, VPNs, IPSec, and many others are agreements and standards that exist on this layer.
The transport layer similarly has many parameters including the protocol being used such as TCP, UDP, as well as other specialized protocols like RTP and RTCP. Addressing on this layer involves ports, and TCP in particular has reliability and error checking mechanisms that are agreements that take place at this level.
As we go higher, the number of parameters increase steadily, and when we reach the application layer, the detail becomes almost endless. Each application layer protocol has within it an enormous number of parameters that require negotiation in order for endpoints to function correctly.
Although by no means exhaustive, I hope this gives you an idea of the many agreements and parameters that must be in accord for communication to occur…
I hope this has been helpful!
Laz