Link Layer
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This layer is managed by Link... Maybe?.. Idk man, I just work here.
As discussed in the section on Encapsulation/Decapsulation, the Link Layer adds a final header/footer (or trailer) that provides information about the start/end of the packet. The frame data (Link header/footer) also provide information to enable packets to navigate within a local network before getting out to the Internet (if that's where they're headed). It deals with the transmission of data frames over a physical medium, such as Ethernet cables or wireless signals, within a local network.
Link Layer frame with header and footer encapsulating earlier headers and data (Credit: ScienceDirect.com)
Key Functions of the Link Layer:
Ethernet:
Ethernet is a widely used networking technology that operates at the Link Layer of the OSI model. It is commonly used in wired local area networks (LANs) and is known for its reliability and high data transfer rates. Ethernet uses a variety of cable types, including twisted-pair copper cables and fiber-optic cables, to transmit data between devices on the same network. Ethernet is prevalent in home and business networks, and is standardised by the IEEE (Institute of Electrical and Electronics Engineers) which ensures interoperability and compatibility among different devices and manufacturers.
Wi-Fi (802.11):
Wi-Fi, short for Wireless Fidelity, is a wireless networking technology that allows devices to connect to a local area network without the need for physical cables. It operates in the 2.4 GHz and 5 GHz frequency bands and is based on the IEEE 802.11 family of standards. Wi-Fi is commonly used for wireless internet access, allowing laptops, smartphones, tablets, and other devices to connect to the internet via wireless access points (routers). It provides the flexibility of mobility and is widely used in homes, offices, public spaces, and even in outdoor environments. Wi-Fi networks use various security protocols like WPA3 to protect data transmission and offer multiple Wi-Fi generations (e.g., 802.11ac, 802.11ax) with increasing speed and efficiency.
Switches and Routers:
Devices like switches and routers operate at the Link Layer or may span multiple layers. Switches are responsible for forwarding frames within a local network based on MAC addresses, enabling efficient communication between devices. Routers, which function at higher layers (typically the Network Layer), connect different local networks, allowing data to be transmitted between them.
Link Layer in the Internet Protocol Suite:
While the Link Layer deals with local network communication, it plays a vital role in the overall functioning of the Internet Protocol Suite. The Link Layer is the bridge between the upper-layer protocols (such as IP at the Network Layer) and the physical medium over which data is transmitted.
Tasks:
1) Explain the concept of "framing" in the Link Layer and why it's essential for data transmission.
2) What are MAC addresses, and why are they necessary in local network communication? Provide an example of a MAC address.
3) Discuss the challenges associated with MAC address exhaustion and potential solutions to extend the address space. (Compare this to the IPv4 IPv6 problem)
4) Name two different cable types used in Ethernet networks and briefly describe their advantages.
5) Differentiate between switches and routers in terms of their functions and the layers of the Internet Protocol Suite that they operate in.
- Framing: The Link Layer is responsible for dividing data packets from the upper layers into smaller frames suitable for transmission over the physical medium. Each frame typically includes a header and a trailer, which contain control information and error-checking mechanisms. (Have a look at the diagram on this page of the CS Field Guide, notice the different layers and how they relate).
- Media Access Control (MAC): The Link Layer includes a sublayer called the Media Access Control, which manages access to the shared communication medium in case of shared networks like Ethernet. It employs various protocols to determine which device can transmit data at a given moment to avoid data collisions.
- Addressing: Devices on the same local network are identified using Link Layer addresses, often referred to as MAC addresses (or sometimes as hardware or physical addresses). MAC addresses are unique identifiers burned into the network interface card (NIC) of each device. These addresses enable data to be delivered to the correct recipient within the local network. An example of an address is 00-B0-D0-63-C2-26, these addresses consist of 48-bits which gives us over 281 trillion addresses. This is a lot more than IPv4 but A LOT less than IPv6 and the current version is expected to only provide unique addresses until around the year 2100. There are plans to increase the length to 64-bits which give us the seemingly infinite addressing that IPv6 has.
- Error Detection and Correction: The Link Layer includes error-checking mechanisms to ensure the integrity of data frames during transmission. Common techniques include cyclic redundancy checks (CRC) to detect errors and retransmission of corrupted frames.
- Flow Control: Flow control mechanisms are implemented to manage the rate of data transmission between devices. This prevents data overload and congestion on the network.
Ethernet:
Ethernet is a widely used networking technology that operates at the Link Layer of the OSI model. It is commonly used in wired local area networks (LANs) and is known for its reliability and high data transfer rates. Ethernet uses a variety of cable types, including twisted-pair copper cables and fiber-optic cables, to transmit data between devices on the same network. Ethernet is prevalent in home and business networks, and is standardised by the IEEE (Institute of Electrical and Electronics Engineers) which ensures interoperability and compatibility among different devices and manufacturers.
Wi-Fi (802.11):
Wi-Fi, short for Wireless Fidelity, is a wireless networking technology that allows devices to connect to a local area network without the need for physical cables. It operates in the 2.4 GHz and 5 GHz frequency bands and is based on the IEEE 802.11 family of standards. Wi-Fi is commonly used for wireless internet access, allowing laptops, smartphones, tablets, and other devices to connect to the internet via wireless access points (routers). It provides the flexibility of mobility and is widely used in homes, offices, public spaces, and even in outdoor environments. Wi-Fi networks use various security protocols like WPA3 to protect data transmission and offer multiple Wi-Fi generations (e.g., 802.11ac, 802.11ax) with increasing speed and efficiency.
Switches and Routers:
Devices like switches and routers operate at the Link Layer or may span multiple layers. Switches are responsible for forwarding frames within a local network based on MAC addresses, enabling efficient communication between devices. Routers, which function at higher layers (typically the Network Layer), connect different local networks, allowing data to be transmitted between them.
Link Layer in the Internet Protocol Suite:
While the Link Layer deals with local network communication, it plays a vital role in the overall functioning of the Internet Protocol Suite. The Link Layer is the bridge between the upper-layer protocols (such as IP at the Network Layer) and the physical medium over which data is transmitted.
Tasks:
1) Explain the concept of "framing" in the Link Layer and why it's essential for data transmission.
2) What are MAC addresses, and why are they necessary in local network communication? Provide an example of a MAC address.
3) Discuss the challenges associated with MAC address exhaustion and potential solutions to extend the address space. (Compare this to the IPv4 IPv6 problem)
4) Name two different cable types used in Ethernet networks and briefly describe their advantages.
5) Differentiate between switches and routers in terms of their functions and the layers of the Internet Protocol Suite that they operate in.
