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 Layer 1 of the TCP/IP protocol stack: Network
Access Layer (NAL). Functions, performed on the
layer. МАС address in Ethernet networks.
 The Internet Protocol Suite (commonly known as TCP/IP) is the set of communications
protocols used for the Internet and other similar networks.
 Transmission Control Protocol (TCP) and the Internet Protocol (IP)
 The Internet Protocol Suite may be viewed as a set of layers. Each layer solves a set of
problems involving the transmission of data, and provides a well-defined service to the
upper layer protocols based on using services from some lower layers.
 The TCP/IP model consists of four layers. This layer architecture is often compared with
the seven-layer OSI Reference Model. From lowest to highest, these are
• the Network Access Layer,
• the Internet Layer,
• the Transport Layer,
• and the Application Layer
 The TCP/IP Network Access Layer can
encompass the functions of two lower layers
of theOSI reference Model:
Data Link, and Physical.
Data Link Layer
Prepare Network layer packets for transmission and to control access to the physical media.
Supporting & Connecting
to upper layer services
The Data Link layer provides a means for exchanging data
over a common local media.
The Data Link layer performs two basic services:
 Allows the upper layers to access the media using
techniques such as framing
 Controls how data is placed onto the media and is received
from the media using techniques such as media access
control and error detection
 The Data Link layer is responsible for the exchange of
frames between nodes over the media of a physical
Connecting upper layer services to
the media
 In many cases, the Data Link layer is embodied as a
physical entity, such as an Ethernet network interface
card (NIC), which inserts into the system bus of a
computer and makes the connection between running
software processes on the computer and physical
 The technique used for getting the frame on and off
media is called the media access control method.
 Media Access Control (MAC) provides Data Link layer
addressing and delimiting of data according to the
physical signaling requirements of the medium and
the type of Data Link layer protocol in use.
 Address the frame
 Mark the beginning and ending of the frame
Media Access Control Methods
There are two basic media access control methods for shared media:
 Controlled - Each node has its own time to use the medium
When one device places a frame on the media, no other device can do so until the frame
has arrived at the destination and has been processed by the destination.
 Contention-based - All nodes compete for the use of the medium
When the device attempting to transmit sees that the media is busy, it will wait and try
again after a short time period.
Media access control protocols for non-shared media require little or no
control before placing frames onto the media. Such is the case for
point-to-point topologies.
 Half-Duplex
 Full-Duplex
Logical vs. Physical Toplogy
The Frame
 Header - Contains control information, such addressing
(48-bit MAC)
 Data - The packet from the Network layer
 Trailer - Contains control information added to the end of
the PDU, such addressing (48-bit MAC)
Physical Layer
 controls how data is placed on the communication media
 encode the binary digits that represent Data Link layer
frames into signals and to transmit and receive these
signals across the physical media
 create the electrical, optical, or microwave signal that
represents the bits in each frame
Physical Layer
Fundamental Principles
The three fundamental functions of the Physical layer are:
 The physical components
 Data encoding
 Signaling
Data Carrying Capacity
Data transfer : Bandwidth, Throughput and Goodput
Types of Physical Media