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NETW202 Ch 7
OSI Data Link Layer
| Question | Answer |
|---|---|
| Address Resolution Protocol (ARP) | The method for finding a host's hardware address from its IPv4 network layer address. |
| Association Identity (AID) | A number used in the 802.11 header to specify the session between a wireless client and the access point. |
| Backoff | The retransmission delay used with CSMA/CD when a collision occurs. The algorithm forces each sender that detected the collisions to delay a random amount of time before attempting to retransmit. |
| Carrier Sense Multiple Access (CSMA) | Media access methodology in which a node wishing to transmit listens for a carrier wave before trying to send. If a carrier is sensed, the node waits for the transmission in progress to finish before initiating its own transmission. |
| Carrier | A signal on a medium used to support the transmission of data. Data is "carried" over the medium by modulation (combining the data signal with the carrier signal) |
| Collision | In Ethernet, the results of two nodes transmitting simultaneously. The signals from each device are damaged when they combine on the media. |
| CSMA/Collision Avoid (CSMA/CA) | A mechanism used to regulate the transmission of data onto a network medium. CSMA/CA is similar to CSMA/CD except the devices first request the right to send, which hopefully avoids collisions. CSMA/CA is used in 802.11 WLANS. |
| Cyclic Redundancy Check (CRC) | Hash function used to produce a small fixed-size checksum of a block of data such as a packet or computer file. CRC is computed and appended before transmission/storage & verified afterward by recipient to verify no changes have happened in transit |
| Deterministic | Refers to whether the performance of a device, attached to a particular type of LAN, can be accurately predicted (determined). Token Ring LANs are deterministic, but Ethernet LANs are non-deterministic. |
| Full-duplex | Communication that allows receipt and transmission at the same time. There are no collisions with full-duplex Ethernet transmissions. |
| Half-duplex | Communication that only allows one station to receive while the other station is transmitting. |
| Logical Link Control (LLC) | The IEEE 802.2 standard that defines the upper sublayer of the Ethernet Layer 2 specifications (and other LAN standards) |
| Logical network | A group of devices associated by the arrangement of a hierarchical addressing scheme. Devices in the same logical network that share a common network portion of their Layer 3 (Network) addresses. |
| Logical Topology | A map of the devices on a network representing how the devices communicate with each other. |
| Media Access Control (MAC) | The lower of the two sublayers of the IEEE standard for Ethernet. It is also the name of that sublayer (as defined by the IEEE 802.3 subcommittee) |
| Network Interface Card (NIC) | Computer hardware, typically used for LANs, that allows the computer to connect to some networking cable. Once connected to a medium, it will send/receive data as directed by the computer. |
| Network Segment | A part of a computer network that every device communicates with using the same physical medium. Network segments can be extended by hubs or repeaters. |
| Nodes | A data link layer term describing devices connected to the network. |
| Physical Network | The connection of devices on a common media. Also referred to as a network segment. |
| Physical Topology | The arrangement of the nodes in a network and the physical connections between them. |
| Token Passing | An access method used with some LAN technologies by which devices access the media in a controlled manner. This access to the LAN is managed using a small frame called a token. A device can send only when is has claimed the use of the token. |
| Virtual Circuit | A logical connection between devices in which the frames are passed between the devices. Virtual circuits are independent of the physical structure and may be established through multiple physical devices. |
| How does the data link layer prepare packets for transmission? | The data link layer prepares a packet for transport across the local media by encapsulating it with a header and a trailer to create a frame. |
| Describe four general data link layer media access methods. Suggest data communication environments in which these access methods can be appropriately implemented. | Controlled: Each node has its own time to use the medium, a ring topology. Contention-based: All nodes compete for the use of the medium, a bus topology. Half-duplex & Full-duplex. |
| Describe the features of a logical ring topology. | Each node receives a frame. If the frame is not addressed to the node, the frame is passed on to the next node. If there is no data transmitted, a signal (token) can be placed on the media. A node can place a frame on the media only when it has the token. |
| Name five Layer 2 protocols. | Ethernet, PPP, High-Level Data Link Control (HDLC), Frame Relay, and ATM. |
| List five header field types in data link frames. | Start Frame, Source/Destination Address, Priority/QoS, Type, Logical Link Control, Physical Link Control, Flow Control, Congestion Control. |
| If a node receives a frame and the calculated CRC does not match the CRC in the FCS, what action will the node take? | It will drop the frame. |
| Which of the following protocols are typically used in WANs? (Choose two) 802.11, Ethernet, HDLC, or PPP? | PPP & HDCL are designed as WAN protocols. |
| What are the contents of the data field in a frame? | The network layer PDU |
| Name a characteristic of contention-based MAC. | Nodes compete for the use of the medium. |
| Which of the following are common data link sublayers used in LANs? (Choose Two) Protocol data unit, Logic Link Control, MAC, Network Interface Card, Carrier Access Multiaccess? | Logic Link Control (LLC) is the upper sublayer & Media Access Control (MAC) is the lower sublayer. |
| Describe a characteristic of a virtual circuit. | Establishes a logical connection between two network devices. |
| Name three basic parts that are common to all data link layer frames. | Header, data, and trailer |
| Give a function performed by the data link layer. | Connects the network software to the network hardware. |
| Which of the following is true about the logical topology of a network? Is always multiaccess, Provides the physical addressing, Is determined by how the nodes in the network are connected, or Influences the type of MAC used in the network. | Influences the type of MAC used in the network. |
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