DATA LINK LAYER Flashcards
What role does the data link layer (Layer 2) play in the OSI model, and what are its main responsibilities?
The data link layer prepares network data for the physical network and is responsible for NIC to NIC communications. Its main responsibilities include enabling upper layers to access the media, encapsulating data into Layer 2 frames, controlling data placement and reception on the media, exchanging frames between endpoints, directing encapsulated data to the proper upper-layer protocol, and performing error detection.
Define what a node is in the context of computer networks, and provide examples of both end devices and intermediary devices.
In computer networks, a node is a device that can receive, create, store, or forward data along a communications path. Examples of nodes include end devices like laptops and mobile phones, as well as intermediary devices like Ethernet switches.
Why is the data link layer essential in computer networks, particularly for network layer protocols like IP?
Without the data link layer, network layer protocols such as IP would need to account for connecting to every type of media along a delivery path. The data link layer abstracts these details and provides a consistent interface for upper-layer protocols to access the media.
What is two sublayers?
The IEEE 802 LAN/MAN data link layer consists of the following two sublayers:
* Logical Link Control (LLC) - This IEEE 802.2 sublayer communicates between the
networking software at the upper layers and the device hardware at the lower layers. It
places information in the frame that identifies which network layer protocol is being used
for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6,
to use the same network interface and media.
* Media Access Control (MAC) – Implements this sublayer (IEEE 802.3, 802.11, or
802.15) in hardware. It is responsible for data encapsulation and media access control. It
provides data link layer addressing and it is integrated with various physical layer
technologies.
The LLC sublayer takes the network protocol data, which is typically an IPv4 or IPv6 packet, and
adds Layer 2 control information to help deliver the packet to the destination node.
The MAC sublayer controls the NIC and other hardware that is responsible for sending and
receiving data on the wired or wireless LAN/MAN medium.
What are the main functions provided by the MAC sublayer in data encapsulation?
The MAC sublayer provides frame delimiting to identify fields within a frame, addressing for source and destination, and error detection using a trailer to detect transmission errors.
How does the MAC sublayer manage media access control in network environments?
he MAC sublayer allows multiple devices to communicate over a shared (half-duplex) medium by controlling access. Full-duplex communications, however, do not require access control.
How does the MAC sublayer handle packet transmissions in different network environments, such as Ethernet LANs and serial links?
In Ethernet LANs with many hosts contending for access, the MAC sublayer resolves access. In serial links with only two devices, like routers, direct connection occurs, bypassing IEEE 802 MAC sublayer techniques. Routers encapsulate packets into appropriate frames and use suitable media access control methods for each link.
What functions does a router perform at the data link layer during packet exchange along a network path?
At each hop along the path, a router accepts a frame from a medium, de-encapsulates the frame, re-encapsulates the packet into a new frame, and forwards the new frame appropriate to the medium of that segment of the physical network.
How are data link layer protocols typically handled in comparison to protocols of upper layers in the TCP/IP suite?
Unlike upper layer protocols defined by RFCs, data link layer protocols are generally not defined by RFCs. The IETF maintains functional protocols and services for the TCP/IP protocol suite in the upper layers but does not define the functions and operation of the TCP/IP network access layer.
What does the data link layer do in relation to network data and physical networks?
The data link layer prepares network data for physical networks by understanding the logical topology of a network, determining what is necessary to transfer frames between devices.
What are the two types of topologies used to describe LAN and WAN networks?
The two types of topologies are physical topology and logical topology.
How is physical topology defined?
Physical topology identifies the physical connections between network devices, including intermediary devices like routers, switches, and access points. It may also include specific device locations such as room numbers and positions on equipment racks.
What is logical topology?
Logical topology refers to how a network transfers frames between nodes, identifying virtual connections using device interfaces and Layer 3 IP addressing schemes.
How does the data link layer interact with the logical topology of a network?
The data link layer governs data access to the media based on the logical topology, influencing the type of network framing and media access control used.
Describe the point-to-point topology commonly found in WANs.
It consists of a permanent link between two endpoints, offering a direct connection between them.
What is the WAN version of the star topology?
The WAN version of the star topology involves a central site connecting branch sites through point-to-point links, with branch sites unable to exchange data directly.
Explain the physical requirements and characteristics of a full mesh topology.
A full mesh topology requires every end system to be interconnected to every other system, offering high availability but incurring significant administrative and physical costs.
What are the features of a physical point-to-point topology?
Physical point-to-point topologies directly connect two nodes without sharing media with other hosts, often using protocols like Point-to-Point Protocol (PPP) for simplicity.
How does the logical data link protocol work in a point-to-point topology?
In a point-to-point topology, logical data link protocols are simple as all frames on the media can only travel to or from the two connected nodes.
How do intermediary devices affect the logical topology of a network?
Intermediary physical connections may not change the logical topology, as the logical point-to-point connection remains the same regardless of physical devices added to the network.
What are the characteristics of multiaccess LAN topologies?
Multiaccess LANs typically employ star or extended star topologies, with end devices interconnected using central intermediary devices such as Ethernet switches.
What advantages do star and extended star topologies offer?
They are easy to install, highly scalable, and facilitate troubleshooting due to their structured nature.
Give an example of Ethernet used in a point-to-point topology.
Two interconnected routers on an Ethernet LAN represent an example of Ethernet used in a point-to-point topology.
What is the role of the data link layer in network communication?
The data link layer prepares network data for the physical network, ensuring efficient transfer of frames between devices.
