data link layer term describing a device connected to a network
connection of devices on common media. Sometimes referred to as network segment
part of computer network that every device communicates with using the same physical medium
Network interface card (NIC)
computer hardware that allows the computer to connect to some networking cable
Logical link control (LLC)
the IEEE 802.2 standard that defines the upper sublayer of the Ethernet layer 2 specs
lower of the two sublayers of the IEEE standard for Ethernet
- refers to whether the performance of a device, attached to a particular type of LAN, can be accurately predicted
Carrier sense multiple access (CSMA)
media access methodology in which a node wishing to transmit listens for carrier wave before trying to send
signal on medium used to support the transmission of data
in Ethernet, the results of two nodes transmitting simultaneously
CCMA/collision avoid (CSMA/CA)
mechanism used to regulate the transmission of data onto network medium
communication that only allows one station to receive while the other station is transmitting
communication that allows receipt and transmission simultaneously
arrangement of nodes in a network and the physical connections between them
map of devices on a network representing how the devices communicate with each other
logical connection between devices in which the frames are passed between the devices
- an access method used with some LAN technologies by which devices access the media in a controlled manner
Cyclic redundancy check (CRC)
type of hash function (one way encryption) that's used to produce a small, fixed-sized checksum of a block of data, such as a packet or computer file
retransmission delay used with CSMA/CD when collision occurs
Association Identity (AID)
number used in 802.11 header to specify the session between a wireless client and the access point
Association resolution protocol (ARP)
method for finding a host's hardware address from its IPv4 network layer address
What are the 2 basic services the Data Link layer provides?
--Allows the upper layers to access the media using techniques such as framing --Controls how data is placed onto the media and is received from the media using techniques such as media access control and error detection
List and define the 4 specific terms associated with the Data Link layer?
Frame - The Data Link layer PDU Node - The Layer 2 notation for network devices connected to a common medium Media/medium (physical)* - The physical means for the transfer of information between two nodes Network (physical)** - Two or more nodes connected to a common medium
What happens the frame as moves from source to destination?
It changes based on the medium used
Define Media Access Control.
The technique used for getting the frame on and off media
What can the control information tell you?
--Which nodes are in communication with each other --When communication between individual nodes begins and when it ends --Which errors occurred while the nodes communicated --Which nodes will communicate next
List and define the three elements of a Data Link Layer Frame.
Data - The packet from the Network layer Header - Contains control information, such addressing, and is located at the beginning of the PDU Trailer - Contains control information added to the end of the PDU
List and define the 5 typical field types.
Start and stop indicator fields - The beginning and end limits of the frame Naming or addressing fields Type field - The type of PDU contained in the frame Quality - control fields A data field -The frame payload (Network layer packet)
What is the most common physical device that is used for the Data Link Layer?
Describe the two sublayers of the Data Link Layer.
The upper sublayer defines the software processes that provide services to the Network layer protocols. The lower sublayer defines the media access processes performed by the hardware.
What are the two functions of the Logical Link Control?
Frames the network layer packet Identifies the network layer protocol
What are the two functions of the Media Access Control?
Addresses the frame Marks the beginning and ending of each frame
What are the 4 organizations that define the Data Link standards?
International Organization for Standardization (ISO) Institute of Electrical and Electronics Engineers (IEEE) American National Standards Institute (ANSI) International Telecommunication Union (ITU)
What analogy is made with the media access control?
traffic rules that regulate the entrance of motor vehicles onto a roadway
What does the method that media access control uses depend on?
Media sharing - If and how the nodes share the media Topology - How the connection between the nodes appears to the Data Link layer
What are the two basic media access control methods for shared media?
Controlled - Each node has its own time to use the medium Contention-based - All nodes compete for the use of the medium
What are two examples of controlled media access?
Token Ring FDDI
What are two examples of contention-based media access?
Why can controlled media access be inefficient?
Device has to wait its turn to access the media
What logical and physical topologies are typically used in networks?
Point-to-Point Multi-Access Ring
Define point-to-point topology.
connects two nodes directly together
Define virtual circuit.
a logical connection created within a network between two network devices
Which type of topology is used to determine the media access control?
logical point-to-point topology
Define logical multi-access topology.
enables a number of nodes to communicate by using the same shared media
What are the three types of media access control can be used in a multi-access topology?
CSMA/CD, CSMA/CA, or token passing
How does a data flow in a ring network?
From node to node until it reaches the destination.
What are the three basic parts of a data link layer frame?
Header Data Trailer
What are the typical fields in the frame header?
Start Frame field - Indicates the beginning of the frame Source and Destination address fields - Indicates the source and destination nodes on the media Priority/Quality of Service field - Indicates a particular type of communication service for processing Type field - Indicates the upper layer service contained in the frame Logical connection control field - Used to establish a logical connection between nodes Physical link control field - Used to establish the media link Flow control field - Used to start and stop traffic over the media Congestion control field - Indicates congestion in the media
Which part the network (WAN/LAN) is the data link address used in delivering?
What is the difference between Data Link Address and Logical Address?
Data Link address only defines the machine it is not logically assigned
Does a point-to-point link need a data link address?
No it only has one place to go
Define error detection.
accomplished by placing a logical or mathematical summary of the bits that comprise the frame in the trailer
Define Frame Check Sequence.
used to determine if errors occurred in the transmission and reception of the frame
How could the CRC be correct and the frame contain errors?
The error bits could cancel each other out
Do all protocols support using the FCS to determine errors?
What Layer 2 protocols will we study in this course?
Ethernet Point-to-Point Protocol (PPP) High-Level Data Link Control (HDLC) Frame Relay Asynchronous Transfer Mode (ATM)
Which usually performs at a higher bandwidth, LAN or WAN?
What do Ethernet standards define?
Layer 2 Protocols and Layer 1 technologies
What is the data link address?
How is the data link address expressed?
48 bit Hexadecimal
What type of architecture does PPP use?
What are options available to use with PPP?
Authentication, compression, and multilink (the use of multiple physical connections).
What is the standard used for wireless LANs?
What services are supported by 802.11?
authentication, association (connectivity to a wireless device), and privacy (encryption)