Network Engineering M6

which are data link layer protocols?

802.11, Ethernet, PPP.

What method is used to manage contention-based access on a wireless network?

CSMA/CA. Carrier sense multiple access with collision avoidance (CSMA/CA) is used with wireless networking technology to mediate media contention. Carrier sense multiple access with collision detection (CSMA/CD) is used with wired Ethernet technology to mediate media contention. Priority ordering and token passing are not used (or not a method) for media access control.

Which data link layer media access control method does Ethernet use with legacy Ethernet hubs?

CSMA/CD. CSMA/CD is used by Ethernet networks using legacy Ethernet hubs. CSMA/CA is used by 802.11-based wireless networks.

what else does data link layer do?

Enables upper layers to access media. upper layer protocol is completely unaware of type of media that is used to forward the data. Accepts data, usually Layer 3 packets (i.e., IPv4 or IPv6), & encapsulates them into Layer 2 frames. Controls how data is placed & gotten on media. trades frames between endpoints over network media. Gets encapsulated data, usually Layer 3 packets, & directs them to proper upper-layer protocol. Performs error detection & rejects any corrupt frame.

what are IEEE 802 LAN/MAN standards specific to?

Ethernet LANs, wireless LANs (WLAN), wireless personal area networks (WPAN) & other types of local & metropolitan area networks.

Which organization defines standards for the network access layer (i.e., the OSI physical and data link layers)?

IEEE

Media Access Control (MAC)

Implements this sublayer (IEEE 802.3, 802.11, or 802.15) in hardware. responsible for data encapsulation & media access control. gives data link layer addressing & is integrated with different physical layer technologies.

Which two engineering organizations define open standards and protocols that apply to the data link layer?

International Telecommunication Union, Institute of Electrical and Electronics Engineers. IANA is responsible for overseeing and managing IP address allocation, domain name management, and protocol identifiers. The EIA is an international standards and trade alliance for electronics organizations, and is best known for its standards related to electrical wiring, connectors, and the 19-inch racks used to mount networking equipment. IEEE defines open standards and protocols that apply to the network access layer.

What are the two sublayers of the OSI model data link layer?

LLC, MAC. data link layer of the OSI model is divided into two sublayers: the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer.

What identifier is used at the data link layer to uniquely identify an Ethernet device?

MAC address. Ethernet frames are identified at the data link layer by their MAC addresses, which are unique to each NIC. IP addresses are used at the network layer, and TCP and UDP port numbers are used at the transport layer. Sequence numbers are fields in TCP headers.

What attribute of a NIC would place it at the data link layer of the OSI model?

MAC address. data link layer describes media access and physical addressing. The encoding of a MAC address on a NIC places it at that layer. Ports and cables are placed at the physical layer of the OSI model. IP addresses are placed at the network layer. The TCP/IP protocol stack describes a different model.

What kind of network would use point-to-point, hub and spoke, or mesh topologies?

WAN

What are two services performed by the data link layer of the OSI model?

accepts Layer 3 packets & encapsulates them into frames, gives media access control & performs error detection. data link layer is responsible for the exchange of frames between nodes over a physical network media. Specifically the data link layer performs two basic services: It accepts Layer 3 packets and encapsulates them into frames. It provides media access control and performs error detection. Path determination is a service provided at Layer 3. A Layer 2 switch builds a MAC address table as part of its operation, but path determination is not the service that is provided by the data link layer.

what layer 2 function does router perform?

accepts frame from medium, de-encapsulates frame, re-encapsulates packet into new frame.

what do full-duplex communications not need?

access control

Which media access control method is used in legacy Ethernet LANs?

carrier sense multiple access/collision detection

logical link control (LLC)

communicates between networking software at upper layers & device hardware at lower layers. places information in frame that tells which network layer protocol is being used for frame. This information allows multiple Layer 3 protocols like IPv4 & IPv6, to use same network interface & media.

what does MAC sublayer do?

controls NIC & other hardware that is responsible for sending & getting data on wired or wireless LAN/MAN medium. also gives data encapsulation. gives media access control, allowing multiple devices to communicate over shared (half-duplex) medium.

Which layer of the OSI model is responsible for specifying the encapsulation method used for specific types of media?

data link. Encapsulation is a function of the data link layer. Different media types require different data link layer encapsulation.

Which statement describes the half-duplex mode of data transmission?

data that is transmitted over network flows in 1 direction at time. data that is transmitted over the network can flow using one of three modes: Simplex - Data can only flow in one direction. Half-duplex - Data flows in one direction at a time. Full-duplex - Data flows in both directions at the same time.

which lists Layer 2 and Layer 3 address fields in the correct order?

destination NIC address, source NIC address, source IP address, destination IP address

what is node in computer networks?

device that can get, make, store, or forward data along communications path. can be either end device like laptop or mobile phone, or intermediary device like Ethernet switch.

what can each network environment that packets encounter as they travel from local host to remote host have?

different characteristics.

Which LAN topology is a hybrid topology?

extended star

what does MAC sublayer resolve?

fact that each network environment that packets encounter as they travel from a local host to a remote host can have different characteristics?

what kinds of data encapsulation does MAC sublayer give?

frame delimiting, addressing, & error detection.

frame delimiting

framing process gives important delimiters to identify fields in frame. These delimiting bits give synchronization between transmitting & receiving nodes.

addressing

gives source & destination addressing for transporting Layer 2 frame between devices on same shared medium.

responsibility of MAC sublayer?

gives way to get frame on & off media.

which duplex communication method is used in WLANs?

half-duplex

error detection

has trailer used to detect transmission errors.

What does data link layer add to Layer 3 packet to make frame?

header, trailer.

what is another name for OSI data link layer?

layer 2

what 2 sublayers do IEEE 802 LAN/MAN data link layer have?

logical link control (LLC) and media access control (MAC).

IEEE 802 LAN/MAN data link layer has which 2 sublayers?

logical link control, media access control

What is true concerning physical and logical topologies?

logical topologies refer to how network transfers data between devices. Physical topologies show the physical interconnection of devices. Logical topologies show the way the network will transfer data between connected nodes.

which topology shows networking device layer IP addresses?

logical topology

what do Ethernet LANs usually have?

many hosts contending for access on network medium.

media access control method used depends on which 2 criteria?

media sharing, topology

technician has been asked to develop a physical topology for a network that provides a high level of redundancy. Which physical topology requires that every node is attached to every other node on the network?

mesh. mesh topology provides high availability because every node is connected to all other nodes. Mesh topologies can be found in WANs. A partial mesh topology can also be used where some, but not all, end points connect to one another.

what would happen without data link layer?

network layer protocols like IP would have to make provisions for connecting to every type of media that could exist along delivery path. also, every time new network technology or medium was made IP, would have to adapt.

what does data link layer do?

prepares network data for physical network.

what is data link layer responsible for?

responsible for network interface card (NIC) to network interface card communications.

What type of physical topology can be created by connecting all Ethernet cables to a central device?

star. Devices connected to the Ethernet star topology connect to either a hub or a switch.

what does LLC sublayer do?

takes network protocol data, which is usually IPv4 or IPv6 packet, & adds Layer 2 control information to help send packet to destination node.

What is the function of the last field in a data link layer frame?

to determine whether frame experienced transmission errors.

Which is a function of the Logical Link Control (LLC) sublayer?

to identify which network layer protocol is being used. Defining the media access processes that are performed by the hardware and providing data link layer addressing are functions of the MAC sublayer. The data link layer accepts Layer 3 packets and packages them into data units that are called frames.

Although CSMA/CD is still a feature of Ethernet, why is it no longer necessary?

use of full-duplex capable Layer 2 switches. use of Layer 2 switches operating in full-duplex mode eliminates collisions, thereby eliminating the need for CSMA/CD.