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35 Cards in this Set

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  • Back
What is a routable protocol
?
OSI
Open Systems Invconnection model - conceptual model that describes how data from an application on one computer can be transferred accross a network to an applicationon another computer.
What layer takes care of:

network cabling
physical
Peer-layer
Communication between identical layers on remote computers.
What layer takes care of:

Error detection on intra-networks.
datalink
How many layers in the OSI model and what are they?

All People Some Time Need Data Processing.
7 Layers

Application, Presentation, Session (Application Layers)

Transport, Network, Data Link, Physical (Data Transport Layers)
Advantages of the OSI model
· If a network conforms broadly to agreed standards, users are insulated against some of the adverse effects of technological change - equipment does not become obsolete quickly.
· It promotes modularization of network support software. Each module takes the form of a layer in the model and is responsible for providing selected services to the layer above.
· In theory any layer can be replaced by a new layer that provides the same services but in a different way, without affecting the user's view of the framework
What layer takes care of:

Routing packets
Network
What layer takes care of:

traffic congestion
network
Will every transmission use all the layers?
Not every transmision will use all application layers, but they will use all data transmision layers.
What layer takes care of:

encrypting data
presentation
Control data
contains specific instructions that indicate how the data should be handled.
What layer takes care of:

error correction
transport or datalink
Encapsulation
the process of enclosing the data in headers and trailers.
Headers and Trailers
Send control data
Decapsulation
process of removing the header and trailer from the original data.
What is the PDU called at:
Applicaiton Layer?
Transport Layer?
Network Layer?
Data Link Layer?

message
segment
packet
frame
Network
This layer makes certain that a packet sent from one device to another actually gets there in a reasonable period of time. Routing and flow control are performed here. This is the lowest layer of the OSI model that can remain ignorant of the physical network.
Physical Layer
Defines the physical link between sender and receiver. Specifies such parameters as voltage, data rates, maximum transmission distances, media type and media connectors.
Does not attach a header or trailer and does not interpert the data being transmitted.
Data Link Layer
provides for communication within an intranetwork or within a single network.
Physical addressing, network architecture, error detection, frame sequencing, flow control.
Transport
Makes sure the lower three layers are doing their job correctly, and provides a transparent, logical data stream between the end user and the network service s/he is using. This is the lower layer that provides local user services.
Network Layer
provides some functions nessacry for transmitting data through an internetwork such as a CAn, MAN, or WAN.
Presentation
Differences in data representation are dealt with at this level. For example, UNIX-style line endings (CR only) might be converted to MS-DOS style (CRLF), or EBCIDIC to ASCII character sets.
Application
Where the user applications software lies. Such issues as file access and transfer, virtual terminal emulation, interprocess communication and the like are handled here.
What layer takes care of:

Flow control
Intranetwork: Datalink

Internet: Transport
Connectionless protocol
The data communication method in which communication occurs
between hosts with no previous setup. Packets sent
between two hosts may take different routes. UDP is a
connectionless protocol. Also called packet switching.
Contrast circuit switching, connection-oriented.
Connection-oriented protocols
.
Cyclic Redundancy stack
Deals with error checking
Session
Communications between applications across a network is controlled at the session layer. Testing for out-of-sequence packets and handling two-way communication are handled here.
Physical
The nuts and bolts layer. Here is where the cable, connector and signaling specifications are defined.
Session Layer
establishes, manages, and terminates communication sessions between applications.
Transport Layer
responsible relaible internetwork data transprt. Transport layer protocols may implement one or more of the following:
Flow control, error detection and recovery, packet sequencing, connection managment.
PDU
Protocol data unit -
the data and headers/trailers added at each layer
Data Link
This layer deals with getting data packets on and off the wire, error detection and correction and retransmission. This layer is generally broken into two sub-layers: The LLC (Logical Link Control) on the upper half, which does the error checking, and the MAC (Medium Access Control) on the lower half, which deals with getting the data on and off the wire.
The LLC (Logical Link Control) is IEEE 802.2 Standard, and the MAC (Media Access Control) Layer is one of IEEE 802.3, .4, .5, .12, etc. standards or protocols.
In LANs, since you have several protocols defined in IEEE standards, it was decided to have a standard means of communicating with the Network Layer, but with the ability to communicate with different protocols communicating with the Data Link layer from below. The solution was to divide the Data Link layer into the layers LLC and MAC. The LLC provides services the the Network Layer, and uses the MAC layer to format frames and transmit frames using different protocols such as CSMA/CD (IEEE 802.3) or Token Ring (IEEE 802.5).
Presentation Layer
responsible for translating data formats between the applications on the commucating nodes. ie. translating ASCII characters used on a desktop to EBCIDIC used by mainframes.