Computer Networks - Issues in Datalink Layer (Access Control, Error Control, Framing, Link Control...)

2. Issues in Data Link Layer
• The main job of the data link layer is to make the
communication on the physical link reliable &
efficient.
Issues,
– Provide interface to the network layer services.
– Framing
– Flow Control
– Error Control
– Synchronization
– Link Configuration Control.

3. Issues in Data Link Layer
Services provided to Network layer
 Virtual Communication
 Actual Comunication

4. Types of services provided to the Network Layer,
 Unacknowledged Connectionless service
 Acknowledged Connectionless service
 Acknowledged Connection oriented service
Framing
• Translation of physical layer’s raw bits into a larger
aggregate (or) discrete units called frames.
• Here beginning and end of the data are marked to
recognize the frame & used in synchronization.
Issues in Data Link Layer

5. Synchronization
• Receiver must know, when the data begins & when it
ends and also receiver should be able to distinguish
between each bit in the frame of data.
Flow Control
• Refers to the mechanisms that make sure that the
sending station cannot overwhelm the receiving
station.
• Preventing the buffer overflow.
 Eg., Sliding Window.
Issues in Data Link Layer

6. Error Control
• All transmission media have potential for
introduction of errors.
• Error control mechanisms can detect as well as
correct errors.
Link Configuration Control
• Link Topology
 Physical arrangement of the connection between the
devices.
• Link Duplexity
 Simplex – only one device can transmit to other. (ie.,
one direction transmit)
Issues in Data Link Layer

7.  half duplex – Both device can transmit to each other, but
not simultaneously.
 full duplex – Both device can transmit simultaneously.
Issues in Data Link Layer