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Q5. Match the following:
A. Application Layer 1. Responsible for co-ordinating communication between systems
B. Presentation Layer 2. Responsible for multiplexing upper-layer applications
C. Session Layer 3. Responsible for availability of intended communication partner
D. Transport Layer 4. Responsible for negotiating data transfer syntax
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A. A--->3; B--->4; C--->2; D--->1 B. A--->2; B--->4; C--->1; D--->4 C. A--->2; B--->3; C--->4; D--->1 D. A--->3; B--->4; C--->1; D--->2
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Correct answer: D
Explanation:
The OSI model model defines the idea interoperability between the network devices and software by dividing the functions of a protocol into different layers. This is useful for understanding, implementing, and troubleshooting the protocol stack. Layers 4-7 will deal with end to end communications between the data source and the destination where as the Layers 1-3 will deal with the communications between the devices found on the network.
1. Physical - This layer conveys the bit stream through the network at
the electrical and mechanical level. It provides the hardware means of sending
and receiving data on a carrier.
2. Data-Link - This layer encodes and frames data for transmission, in
addition to providing error detection and control. Because the data link layer
can provide error control, higher layers may not need to handle such services.
However, when reliable media is used, there is a performance advantage by not
handling error control in this layer, but in higher layers. Bridges operate at
this layer in the protocol stack.
3. Network - This layer creates the logical paths, known as virtual
circuits, for transmitting data from node to node. This layer includes routing
and forwarding. Routers operate at the network layer.
4. Transport - The transport layer provides quality service and accurate
delivery by providing connection oriented services between two end systems. It
controls the sequence of packets, regulates traffic flow, and recognizes
duplicate packets. The transport layer assigns packetized information a sequence
number that is checked at the destination. If data is missing from the packet,
the transport layer protocol at the receiving end arranges with the transport
layer of the sending system to have packets re-transmitted. This layer ensures
that all data is received and in the proper order.
5. Session - This layer manages the dialogue between end user processes.
Duplex or half duplex operation, establishing check pointing, termination and
restart procedures are found here. It deals with session and connection
coordination.
6. Presentation - This layer formats and encrypts data to be sent across
a network.
7. Application - This is the layer at which communication partners are
identified, user authentication and privacy are considered. Application services
are provided by this layer include file transfers (FTP), telnet, email, and
other network software services.
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