Module 2 NET 121

Logical address

A Network layer address that defines how data is sent from one network to another. Examples of logical addresses are IP and IPv6.

Positive acknowledgment with retransmission

A connection-oriented session that provides acknowledgment and retransmission of the data if it is not acknowledged by the receiving host within a certain time frame.

Data frame

A frame is the Protocol Data Unit encapsulation at the Data Link layer of the OSI reference model. A data frame encapsulates packets from the Network layer and prepares the data for transmission on a network medium.

Routing

A function of the Network layer that involves moving data throughout a network. Data passes through several network segments using routers that can select the path the data takes.

Protocol Data Unit (PDU)

A generic term used to describe the end product of a protocol. It can be thought of as the entire data structure handed down by a protocol to the protocol at the next lowest layer or the information placed on the network media by the Physical layer. A PDU will consist of the original user data and any upper-layer control information (headers and trailers) imposed by upper-layer protocols encapsulated by the control information of the protocol creating the PDU.

Virtual circuit

A logical circuit devised to ensure reliable communication between two devices on a network. Defined by a virtual path identifier/virtual channel (really the only time channel is used) identifier (VPI/VCI) pair, a virtual circuit can be permanent (PVC) or switched (SVC). Virtual circuits are used in Frame Relay and X.25. Known as virtual channel in ATM.

Frame

A logical unit of information sent by the Data Link layer over a transmission medium. The term often refers to the header and trailer, employed for synchronization and error control, that surround the data contained in the unit.

Hop count

A means of limiting the number of routers a packet can cross on the way to its destination. As a packet travels over a network through multiple routers, each router will increment the hop-count field in the packet by one as it crosses the router.

Acknowledgment (ACK)

A message confirming that the data packet was received. This occurs at the Transport layer of the OSI model.

Open Systems Interconnect (OSI)

A model defined by the ISO to categorize the process of communication between computers in terms of seven layers. The seven layers are Application, Presentation, Session, Transport, Network, Data Link, and Physical.

Routed protocol

A protocol (such as IP or IPv6) used to transmit user data through an internetwork. By contrast, routing protocols (such as RIP, IGRP, and OSPF) are used to update routing tables between routers.

Media Access Control (MAC)

A sublayer of the Data Link layer that controls the way multiple devices use the same media channel. It controls which devices can transmit and when they can transmit.

Logical Link Control (LLC)

A sublayer of the Data Link layer that provides an interface between the MAC sublayer and the Network layer.

Data packet

A unit of data sent over a network. A packet includes a header, addressing information, and the data itself. A packet is treated as a single unit as it is sent from device to device. Also known as a datagram.

Logical topology

A way that information can flow. The same as a physical topology except that the flow of information, rather than the physical arrangement, specifies the type of topology.

Layered architecture

An industry-standard way of creating applications to work on a network, which allows the application developer to make changes in only one layer instead of the whole program.

Data Terminal Equipment (DTE)

Any device that is located at the user end of a user-network interface and serves as a destination, a source, or both. DTE includes devices such as multiplexers, routers, protocol translators, and computers. The connection to a data network is made through data communication equipment (DCE) such as a modem, using the clocking signals generated by that device.

Data communication equipment (DCE)

Equipment that provides clocking to DTE equipment. DCE equipment starts at the CSU/DSU and is defined as a connection all the way to the provider's network.

True/False: A hub and a repeater operate at Layer 2 of the OSI model.

False

True/False: A hub and a switch operate at the same layer of the OSI model.

False

True/False: A hub and router operate at the same layer of the OSI model.

False

True/False: A packet-filtering firewall operates at the Network and Data Link layers of the OSI model.

False

True/False: A router and a bridge operate at the same layer of the OSI model.

False

True/False: The Transport layer converts digital data into electronic signals to be put on a wire.

False

Layer 3 switch

Functioning at the Network layer, a switch that performs the multiport, virtual LAN, data-pipelining functions of a standard Layer 2 switch but can also perform basic routing functions between virtual LANs.

At what layer of the Open Systems Interconnection (OSI) model does a router function?

Network

A packet-filtering firewall operates...e Network and Data Link layers of the OSI model.

Network and Transport

Flow control

Provides a means for the receiver to govern the amount of data sent by the sender. It prevents a sending host on one side of the connection from over owing the buffers in the receiving host—an event that can result in lost data.

Layers

Term used in networking to define how the OSI model works to encapsulate data for transmission on the network.

Session layer

The fifth layer of the OSI model, which determines how two computers establish, use, and end a session. Security authentication and network-naming functions required for applications occur here. The Session layer establishes, maintains, and breaks dialogs between two stations.

Transport layer

The fourth layer of the OSI model, which is responsible for checking that data packets created in the Session layer were received error free. If necessary, it also changes the length of messages for transport up or down the remaining layers.

Data Link layer

The second layer of the OSI model. It describes the logical topology of a network, which is the way that packets move throughout a network. It also describes the method of media access.

Physical layer

The sixth layer of the OSI model; responsible for formatting data exchange such as graphic commands and conversion of character sets. Also responsible for data compression, data encryption, and data stream redirection.

Presentation layer

The sixth layer of the OSI model; responsible for formatting data exchange such as graphic commands and conversion of character sets. Also responsible for data compression, data encryption, and data stream redirection.

International Organization for Standardization (ISO)

The standards organization that developed the OSI model. This model provides a guideline for how communications occur between computers.

Encapsulation

The technique used by layered protocols in which a layer adds header information to the Protocol Data Unit (PDU) from the layer above. As an example, in Internet terminology, a packet contains a header from the Data Link layer, followed by a header from the Network layer (IP), followed by a header from the Transport layer (TCP), followed by the application protocol data.

Network layer

This third layer of the OSI model. It is responsible for logical addressing and translating logical names into physical addresses. This layer also controls the routing of data from source to destination as well as the building and dismantling of packets.

True/False: A bridge is a network device that operates at Layer 2 of the OSI model.

True

True/False: A switch is a network device that operates at Layer 2 of the OSI model.

True