What are the seven layers of the OSI Model and the order they are typically presented in?
Application, Presentation, Session, Transport, Network, Data Link, and Physical
What does the Physical Layer involve?
The Physical layer is everything about the physical connection from wires and jacks to electricity and light.
Takes into consideration the hardware used.
When we are discussing network interfaces, cabling, switches, or anything else hardware-related, we are talking about the physical layer
What does the Data Link Layer involve?
Above the Physical layer and describes how all of the data that has been flowing down from the top of the stack gets translated onto the physical transmission medium.
Handles error detection and correction if collisions occur on physical medium.
contains a set of addresses to ensure that systems can communicate with each another
While many protocols fall into the Data Link layer, the one most commonly used by people is the Ethernet (MAC)
What does the Network layer involve?
Manages network communication
Primarily this has to do with addressing traffic and ensuring it gets to where it is intended to go
Routing occurs at this layer
Layer three gets traffic from one network to another, which is in contrast to layer two, which is about getting traffic from one system to another on the same network. The addressing done at this layer is logical addressing
Internet Protocol happens at this layer and provides logical addressing and ability to aggregate addresses MAC addy's do not offer.
What does the Transport Layer do?
Depending on the protocol in use, the Transport layer may provide connection services as well as reliable delivery and the guaranteed ordering of messages.
Has 65,536 ports for both UDP and TCP.
Allows system to have multiple communication sessions open by connecting to a port and address combination (allows multiple communication simultaneously).
Is responsible for end-to-end communication.
Responsible for any reliability that may be required.
What does the Session layer do?
Handles sessions similar to a conversation.
Goal is to have a steady and coherent stream designed to accomplish a particular task.
Offers authentication and authorization as well.
NetBIOS is a protocol that falls under this layer and establishes identity and permissions and also makes sure the session stays open until it is no longer needed
If something happens at the lower layer like a wire falling out if the clip on the RJ45 cable has come loose, NetBIOS will ensure the session gets reestablished, assuming the connection is reestablished within a short period of time.
What does the Presentation layer do?
Responsible for representation of data.
XML and JPEG formats at this layer
This is where the data gets converted from a structured representation to strictly a series of bits and bytes
Encrypting and Decrypting are examples of functions that would happen here.
There is a certain amount of translation services performed at this layer because it frees the application up from having to be concerned with how data gets represented at the lower layers of the stack.
What does the Application layer do?
Is where the functions closest to the user exists.
Is responsible for generating and handling the data that goes to or comes from the lower layer.
SMTP, IMAP, and POP are application layer protocols responsible for users to send and receive e-mail.
The protocols specify how to direct the application on what to do with particular chunks of data.
What are the 4 layers of the TCP/IP model (from bottom up)
Link Layer (bottom)
What does the Link Layer do? (TCP/IP Model)
The Physical layer and the Data Link layer are both represented in the functionality of the Link layer from the TCP/IP model.
Once a chunk of data makes it through the Link layer, it is called a frame. The Link layer is responsible for formatting a frame and getting it out onto the wire.
Supports IP Encapsulation in Ethernet and related protocols.
The Link layer also handles the Address Resolution Protocol (ARP), which translates higher layer addresses to a Link layer address.
Prevents ARP floods and ensures cache is up-to-date by flushing when necessary.
What does the Internet Layer do? (TCP/IP Model)
Where the Internet Protocol resides.
Has two primary functions: 1.)choosing the next hop gateway, which means that it’s responsible for handling routing functions and 2.)reassembling fragmented IP datagrams.
Internet Control Messaging Protocol (ICMP) resides at this layer to provide error and diagnostic functionality.
Corresponds to Network layer in OSI model.
What does the Transport Layer do? (TCP/IP Model)
Handles end-to-end communication for systems.
The Transport layer makes sure, if it is necessary, that datagrams arrive intact and in order.
While IP does bear some of the burden of that end-to-end communication, IP is really a best effort delivery system and it doesn’t pay attention to whether datagrams arrive or not.
UDP and TCP are protocols for this layer.
UDP simply provides a datagram service. There is no reliability and no connection establishment. The datagrams are transmitted with absolutely no guarantee of their delivery or sequence when they arrive.
TCP, you are guaranteed, within reason, that datagrams will arrive at the other end and will arrive in the correct order.
What does the Application Layer do? (TCP/IP Model)
Two types of application protocols: 1.) Protocols that provide services to users directly (Telnet) 2.) Support protocols like Simple Network Management Protocol (SMNP) and Domain Name Services (DNS) Protocol.
Top three layers of the OSI model are covered in this layer of the TCP/IP model.
More focused on network components and less on aspects that deal more closely with users.
The two basic functions that IP is meant to implement are:
A) Addressing and Fragmentation
The first function of Internet Protocol (IP) is to provide _____ _____ by which systems can be accessed. These ____ ___ allows us to group systems together.