Module 6 Cisco - Data Link Layer

. In contention-based multi-access networks,

, all nodes are operating in half-duplex.

ring

- End systems are connected to their respective neighbor forming this

What Layer 2 function does a router perform?

-Accepts a frame from a medium -de-encapsulates the frame -re-encapsulates the packet into a new frame

The media access control method used depends on which two criteria?

-Media Sharing -Topology

Examples of multiaccess networks that use controlled access include the following:

-legacy token ring -legacy ARCNET

What are the data link layer protocols?

802.11, ethernet, PPP

bus

All end systems are chained to each other and terminated in some form on each end. Infrastructure devices such as switches are not required to interconnect the end devices.

contention-based access

All nodes are operating in half-duplex, competing for the use of the medium. However, only one device can send at a time.

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

CSMA/CA

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

CSMA/CD

full-duplex

Data flows in both directions at the same time.

Which organization defines standards for the network access layer?

IEEE

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

ITU, IEEE

physical topology

Identifies the physical connections and how end devices and intermediary devices (i.e, routers, switches, and wireless access points) are interconnected. The topology may also include specific device location such as room number and location on the equipment rack. usually point-to-point or star.

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 IEEE 802 LAN/MAN data link layer consists of the following two sublayers:

LLC and MAc

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

LLC, MAC

What is another name for the OSI data link layer?

Layer 2

The IEEE 802 LAN/MAN data link layer consists of which two sublayers?

Logical Link Control Media Access Control

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

MAC Address

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

MAC address

addressing

Provides source and destination addressing for transporting the Layer 2 frame between devices on the same shared medium.

What is the responsibility of the MAC sublayer?

Provides the method to get the frame on and off the media

logical topology

Refers to the way a network transfers frames from one node to the next. This topology identifies virtual connections using device interfaces and Layer 3 IP addressing schemes.

Frame delimiting

The framing process provides important delimiters to identify fields within a frame. These delimiting bits provide synchronization between the transmitting and receiving nodes.

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.

frame start and stop indicator flags

Used to identify the beginning and end limits of the frame.

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

WAN

node

a device that can receive, create, store, or forward data along a communications path. can be either an end device such as a laptop or mobile phone, or an intermediary device such as an Ethernet switch.

cyclic redundancy check (CRC) value.

a logical summary of the contents of the frame. This value is placed in the frame check sequence (FCS) field to represent the contents of the frame.

hybrid

a variation or combination of any topology.

half-duplex

allows only one device to send or receive at a time on the shared medium

EIA

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.

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

carrier sense multiple action/collision detection

Layer 2 addresses are only used to

connect devices within the same shared media, on the same IP network.

data

contains the frame payload

There are two basic access control methods for shared media:

contention-based access, controlled access

simplex

data can only flow in one direction

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

data link

IEEE

defines open standards and protocols that apply to the network access layer.

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

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

point-to-point

directly connect two nodes

controlled access

each node has its own time to use the medium. These deterministic types of legacy networks are inefficient because a device must wait its turn to access the medium.

Which LAN topology is a hybrid topology?

extended star

QoS(Quality of service)

gives forwarding priority to certain types of messages, Voice over IP for example

Which duplex communication method is used in WLANs?

half-duplex

each frame type has three basic parts:

header, data, trailer

What does the data link layer add to a Layer 3 packet to create a frame?

header, trailer

this topology is a

hub and spoke

control

identifies special flow control services such as quality of service (QoS).

type

identifies the layer 3 protocol in the data field

Half-duplex communications exchange data

in one direction at a time

error detection

includes a trailer used to detect transmission errors

If the data must pass onto another network segment, an __________________, such as a router, is necessary.

intermediary device

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

it provides media access control and performs error detection, it accepts layer 3 packets and encapsulates them into frames

Path determination is a service provided at

layer 3

The data link layer address is only used for

local delivery

Which topology displays networking device layer IP addresses?

logical topology

The Internet Engineering Task Force (IETF)

maintains the functional protocols and services for the TCP/IP protocol suite in the upper layers, but they do not define the functions and operation of the TCP/IP network access layer.

This type of topology is a

mesh

Which physical topology requires that every node is attached to every other node on the network?

mesh

The data link layer is responsible for

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

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 data link layer prepares network data for the

physical network

The data link layer of the OSI model (Layer 2)

prepares network data for the physical network.

The MAC sublayer

provides data encapsulation through frame delimiting, addressing, and error detection.

mesh topology

provides high availability because every node is connected to all other nodes.

the IANA

responsible for overseeing and managing IP address allocation, domain name management, and protocol identifiers.

Full-duplex sends and receives data

simultaneously

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

star

Physical LAN topologies include:

star, extended star, bus, and ring.

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.

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

the use of full-duplex capable layer 2 switches

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

to determine whether the frame experienced transmission errors

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

to identify which network layer protocol is being used

Carrier sense multiple access with collision detection (CSMA/CD)

used with wired Ethernet technology to mediate media contention.

Carrier sense multiple access with collision avoidance (CSMA/CA)

used with wireless networking technology to mediate media contention.