DCN_rpj11

DCN_rpj11 - 1 NT503 Data Communication& Networking LAN...

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Unformatted text preview: 1 NT503: Data Communication & Networking LAN architecture and protocols - I 2 Data Link Layer ¡ Data Link Layer is divided into two sub-layers, ¾ Logical Link Control (LLC) sub-layer ¾ Media Access Control (MAC) sub-layer ¡ Logical Link Control (LLC) sub-layer: ¾ Higher of the two data link layer sub-layers defined by IEEE standard 802.2 ¾ Offers connection-oriented as well as connection-less service ¾ Provides interface between network layer protocols (e.g. IP) and various 802 type networks (e.g. Ethernet, Token ring etc.) ¾ Provides a single format to the network layer by hiding the differences between 802 type networks 3 Logical Link Control (LLC) sub-Layer Network Layer LLC Data Link Layer MAC Physical Layer Network Layer Packet Packet Packet LLC LLC MAC MAC Data Link Layer 4 Functions of LLC sub-Layer ¡ Functions of LLC sub-layer: ¾ Flow control: ¢ to match speeds of sender and receiver ¢ Protocols used are stop-and-wait, sliding window, Go back N ¾ Error control: ¢ Deals with damaged, lost or duplicate frames, retransmission ¾ Provides various service options: ¢ unacknowledged or acknowledged service, ¢ acknowledged connection-oriented service ¾ Framing of bits: ¢ receive packets from IP layer, adds LLC header ¢ insert the structure into the payload field of an 802 frame. ¾ Provides interface to the network layer: ¢ isolates network layer from various network topologies 5 Functions of MAC sub-Layer ¡ Functions of MAC sub-layer: ¾ Provide access to the communication channel: ¢ Uses various contention based (e.g. pure ALOHA, slotted ALOHA, CSMA, CSMA/CD) as well as collision free protocols ¾ Error detection and correction: ¢ CRC/ checksum mechanism ¢ detect as well as correct the errors ¾ Assembly / de-assembly of frames: ¢ MAC layer attaches its header and trailer to the frame and passes the same to physical layer for transmission ¾ Provides interface between node’s logical link control and the network’s physical layer: ¢ MAC layer differs as per the network topology 6 TCP segments, IP datagrams, MAC frames 7 MAC frame format 8 MAC frame format (continued…..) ¡ LLC protocol data unit (PDU): SSAP – source service access point ¢ SSAP label (8-bit) identifies the sender’s protocol stack type DSAP – destination service access point ¢ DSAP label (8-bit) identifies destination’s protocol stack type LLC control field -...
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This note was uploaded on 07/15/2011 for the course ECO 2023 taught by Professor Mr.raza during the Summer '10 term at FAU.

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DCN_rpj11 - 1 NT503 Data Communication& Networking LAN...

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