The document discusses reliable transmission in data links, focusing on flow control mechanisms like acknowledgements and timeouts, specifically the stop-and-wait and sliding window protocols. It highlights that the stop-and-wait protocol involves waiting for an acknowledgment before sending the next frame, while the sliding window protocol allows sending multiple unacknowledged frames with assigned sequence numbers. Furthermore, the document touches on media access control, detailing its significance within local area networks (LANs) and their characteristics such as speed and minimal wiring.

1. FLOW CONTROL

2. Reliable Transmission
• CRC is used to detect errors.
• Some error codes are strong enough to correct errors.
• The overhead is typically too high.
• Corrupt frames must be discarded.
• A link-level protocol that wants to deliver frames reliably must
recover from these discarded frames.
• This is accomplished using a combination of two fundamental
mechanisms
• Acknowledgements and Timeouts

3. Protocols used in Flow control
• Stop and wait protocol
• Sliding window protocol

4. Stop and Wait Protocol
• Idea of stop-and-wait protocol is straightforward
• After transmitting one frame, the sender waits for an acknowledgement before
transmitting the next frame.
• If the acknowledgement does not arrive after a certain period of time, the
sender times out and retransmits the original frame

5. Stop and Wait Protocol

6. Problems with Stop and wait Protocol
• Problems due to lost packet
• Problems due to lost ack
• Problems due to delayed Ack

7. Sliding Window Protocol

8. Sliding Window Protocol
• Sender assigns a sequence number denoted as SeqNum to each frame.
• Assume it can grow infinitely large
• Sender maintains three variables
• Sending Window Size (SWS)
• Upper bound on the number of outstanding (unacknowledged) frames that the sender can transmit
• Last Acknowledgement Received (LAR)
• Sequence number of the last acknowledgement received
• Last Frame Sent (LFS)
• Sequence number of the last frame sent

9. Media Access Control

10. • Data Link layer has two sub layers
• Logical Link Layer Sublayer
• Media Access Control Sublayer
Media Access Control Sublayer
• Implemented on the hardware layer
• To responsibility of the sublayer
• Data encapsulation
• Media Access Layer

11. LAN
• A LAN is a network that is used for communicating among computer
devices, usually within an office building or home
• LAN’s enable the sharing of resources such as files or hardware
devices that may be needed by multiple users
• Is limited in size, typically spanning a few hundred meters, and no
more than a mile
• Is very fast, with speeds from 10 Mbps to 10 Gbps
• Requires very little wiring, typically a single cable connecting to each
device
• Has lower cost compared to MAN’s or WAN’s