Homework3.docx - CNT 6885 DISTRIBUTED MULTIMEDIA SYSTEMS ASSIGNMENT 3 Problem 2 The ISO-OSI Reference Model has 7 layers What are these 7 layers Please


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CNT 6885 DISTRIBUTED MULTIMEDIA SYSTEMS ASSIGNMENT 3 Problem 2: The ISO-OSI Reference Model has 7 layers. What are these 7 layers? Please explain their functionality. Why do we usually have 4 layers only in actual implementations? OSI model Layer Protocol data unit (PDU) Function [6] Host layers 7 Application Data High-level APIs , including resource sharing, remote file access 6 Presentation Translation of data between a networking service and an application; including character encoding , data compression and encryption/decryption 5 Session Managing communication sessions , i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes 4 Transport Segment , Datagram Reliable transmission of data segments between points on a network, including segmentation , acknowledgement and multiplexing Media layers 3 Network Packet Structuring and managing a multi-node network, including addressing , routing and traffic control 2 Data link Frame Reliable transmission of data frames between two nodes connected by a physical layer 1 Physical Symbol Transmission and reception of raw bit streams over a physical medium Fig 1. OSI MODEL [4] 1. Physical Layer This layer is responsible for actual physical connection between two devices. The functions of the layer are: a. Bit synchronization: synchronizes the bits by providing a clock, which controls both sender and receiver. b. Bit rate control: defines the number of bits sent per second c. Physical topologies: the way different devices are arranged in the network d. Transmission mode: defines the way in which data flows between the two connected devices that are simplex, half duplex, full duplex. 2. Data Link Layer This layer is responsible for the node to node delivery of message. The functions of the layer are: a. Framing: provides the way to transmit a set of bits that are meaningful to the receiver. b. Physical Addressing: adds the physical address of the sender and receiver in the header of each frame c. Error Control: detects error and retransmits the lost or damaged frames. d. Flow control: coordinated the amount of data that can be sent before acknowledgment 3. Network Layer This layer works for the transmission of data from one host to another located in different networks. The functions of the layer are: a. Routing: determines the suitable route from the source to destination. b. Logical Addressing: for identification of devices uniquely on internetwork provides an addressing scheme. 4. Transport Layer This layer is responsible for end to end delivery of the complete message and provide acknowledgement of the successful transmission and re-transmission of the message. The functions of the layer are:
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a. Segmentation and Reassembly: breaks the message from session layer into small bits and reassembles the message at the destination.
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  • Fall '15
  • Johnathanliu

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