Week 0+1 - Main Questions Flashcards
Briefly describe and explain the responsibilities of the Physical Layer.
The physical layer is the lowest layer of the OSI model, it’s layer 1. The physical layer is responsible for raw unstructured bit stream data transmission between two nodes. It basically brings data to the physical medium (this can be wired or wireless). Among others, the physical layer defines cable types (quality / length), connectors (RJ45), radio frequency (in wireless networks) and other physical requirements. Devices that operates on this layer are hubs, repeaters.
Briefly describe and explain the responsibilities of the Application Layer.
The Application Layer is layer 7 of the OSI model. It serves as an interface for users and application processes to use network services. It is the top layer of the OSI model and therefore responsible for displaying received information like data and images to the user. It is a layer between user application and the underlying network. Whether you are sending an email or connecting to a website to fill out a form, you are interacting with the application layer.
Many common protocols operate on the application layer: HTTP, telnet, FTP, SMTP, DNS, etc.
Briefly describe and explain the responsibilities of the Network Layer.
The Network Layer (Layer 3 of the OSI model) is responsible for the source-to-destination delivery of packets, possibly across multiple networks. It is responsible for routing, packet forwarding and control of network congestion. Routers operate under this layer. It establishes, maintains and terminates connections across the network. Some of its functions include Logical Addressing (IP) and Routing. A Router helps choosing the path from A to B efficiently. Common protocols: IP; Devices that operates on this layer are: Routers.
What is needed in a server room?
Universal Power Supply, Raised floor, Raised ceiling, access control, climate control, Racks, Structured cabling, Video surveillance, Fire Suppression.
What is a router, and at what OSI layer does it operate?
A router is a networking device that works on OSI layer 3 (network layer). It establishes connectivity between multiple networks or network segments and it find paths for data packages between node A + B efficiently. Some routers have additional features implemented like DHCP services, packet filtering firewall or NAT.
What is a NIC and how is it used?
NIC stands for Network Interface Card. It is a piece of hardware that connects a device to a computer network. It allows a client to communicate with other clients on a network.
SMTP is a push protocol. Please explain.
SMTP stands for Simple Mail Transfer Protocol and is defined in RFC821. SMTP operates on OSI layer 7 (application layer) and is used for email transmission on the Internet, normally over TCP port 25.
SMTP is called a push protocol because it pushes the email for one mail server to the other and does not allow to pull a message from a remote server. If user A would like to send a message from his email client, the email client pushes the email to the outgoing mail server. The outgoing mail server stores the email and pushes the email on to the destination server (or another intermediary mail server).
Briefly describe and explain the responsibilities of the Transport Layer.
Network sends data on best effort, there is no guarantee that it arrives correct.
The transport layer provides a reliable communication between two endpoints, achieved by error / transmission control using checksums and sequence numbers. It makes sure that all data arrives, in correct order, without errors. Defines two main protocols: TCP (connection oriented) & UDP (connection less). With TCP packets will be resent and / or reassembled if errors occur.
Briefly describe and explain the responsibilities of the Session Layer.
This layer provides the protocols and means for two devices on the network to communicate with each other by creating and managing sessions.
It provides session establishment, maintenance and termination and session support. It allows/handles multiple simultanious sessions between two nodes by using ports. Unique session identification established by: sourceIP, sourcePORT, destIP, destPORT.
Briefly explain what a LAN is and the main function of it.
A LAN is a medium to which many nodes can be connected, on which every node has an address and which permits nodes connected to it to transfer messages to other nodes connected.
When you move the NIC cards from one PC to antoher PC, what happens to the MAC address?
NIC stands for Network Interface Card. It is a piece of hardware that connects a device to a computer network. It allows a client to communicate with other clients on a network.
The physical address, also known as MAC address (Media Access Control address), is a unique identifier given to each physical network adapter (NIC). The MAC address is burnt in to the NIC firmware.
So if you move the NIC card from PC-1 to PC-2, the physical address will also be moved from PC-1 to PC-2 as it is encoded into the NIC’s firmware.
Briefly describe and explain the responsibilities of the Data Link Layer.
The data link layer is layer 2 of the OSI model. Its main goal is sending and interpreting data signals on the physical medium between two nodes in an error free (collision detection on physical layer) way. The data link layer has two sub layers:
A. Logical Link Control: is responsible for flow and error control, frame synchronization.
B. Media Access Control: is responsible for physical addressing of nodes. These addresses are known as MAC addresses.
One specific protocol of the data link layer is Ethernet (it allows more than two nodes to be connected to a physical network). Devices that operates on this layer are: Switches.
How does TCP correct transmission errors?
By resending the data packets.
Briefly describe and explain the responsibilities of the Presentation Layer.
The Presentation layer formats and translates data for use by layers above and below so there is no misunderstanding due to different internal representations. It translate data from the application format to the network format, which is understandable/interoperable with any device. This is done by the Network Byte Order (Big endian).
Describe the difference between Symmetric-Key cryptography and Asymmetric-Key cryptography.
By using a Symmetric-Key cryptography the same secret key is used for the encryption AND decryption of the data. So sender and receiver must have the same secret key. Key exchange must be performed over a secure channel.
By using a Asymmetric-Key cryptography (also known as public key cryptography) a key pair is used to encrypt and decrypt the data. The key pair is often called Private & Public key. If a message is encrypted with one key (private key) the message can only be decrypted with the corresponding public key and vice versa. Therefore each party has two keys (public / private). The public key cannot be used to generate the corresponding private key.
Symmetric-Key encryption is much faster than asymmetric-key encryption but has the drawback of secret key exchange between all involved parties. A challenge in asymmetric key cryptography is definitely key management.
