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Data link layer

Data link layer. The Data Link layer of a model typically has the following responsibilities: 1. Creates a frame 2. Creates an error-free logical connection Error control Flow control 3. Makes sure the receiver stays synchronized with the incoming data stream. Flow Control.

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Data link layer

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  1. Data link layer Data Communication and Computer Networks The Data Link layer of a model typically has the following responsibilities: 1. Creates a frame 2. Creates an error-free logical connection Error control Flow control 3. Makes sure the receiver stays synchronized with the incoming data stream.

  2. Flow Control Data Communication and Computer Networks • Ensuring the sending entity does not overwhelm the receiving entity: • Preventing buffer overflow. • Propagation time. • Transmission time.

  3. Error Control Data Communication and Computer Networks Detection errors Lost frames Damaged frames Automatic repeat request

  4. Network layer Data Communication and Computer Networks • Layer 3. The network layer is responsible: • The delivery of individual packets from the original source to the final destination . • Logical addressing: if the packet passes the network boundary we need another addressing system to help (source to destination) connection. • Routing : route or switch the packet to final destination. • Source-to-destination delivery (End-to-End).

  5. Internet Protocol Data Communication and Computer Networks • Provides information about how and where data should be delivered • Subprotocol that enables TCP/IP to internetwork • To internetwork is to traverse more than one LAN segment and more than one type of network through a router • In an internetwork, the individual networks that are joined together are called subnetworks

  6. Internet Protocol cont. Data Communication and Computer Networks • IP is an unreliable, connectionless protocol, which means it does not guarantee delivery of data • Connectionless • Allows protocol to service a request without requesting verified session and without guaranteeing delivery of data

  7. Position of IP in TCP/IP protocol suite Data Communication and Computer Networks

  8. Datagram Data Communication and Computer Networks • A packet in the IP layer is called a datagram, a variable-length packet consisting of two parts: header and data. • The header is 20 to 60 bytes in length and contains information essential to routing and delivery.

  9. IP datagram Data Communication and Computer Networks

  10. IP datagram fields Data Communication and Computer Networks • VER - version numbers, 4 and 6 • HLEN - header length in 4-byte words. Value of 5 means 20 byte header • DS (differentiated services or Service type ) -

  11. IP datagram fields cont. If you want to send a packet with a special type of service, use one of the 5 bit sets. Data Communication and Computer Networks Precedence bits - never used. Similar to PRI bits in IPv6. TOS (Type of Service) bits -

  12. IP datagram fields cont. Data Communication and Computer Networks If we call these 8 bits Differentiated Services (and not the older Service Type), then the first six bits are called code-points

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