Purpose of the Data Link Layer

Describe the purpose and function of the data link layer in preparing communication for transmission on specific media.

The Data Link Layer

• The Data Link layer is responsible for communications between end-device network interface cards.
• It allows upper layer protocols to access the physical layer media and encapsulates Layer 3 packets (IPv4 and IPv6) into Layer 2 Frames.
• It also performs error detection and rejects corrupts frames.

IEEE 802 LAN/MAN Data Link Sublayers

IEEE 802 LAN/MAN standards are specific to the type of network (Ethernet, WLAN, WPAN, etc).

The Data Link Layer consists of two sublayers. Logical Link Control (LLC) and Media Access Control (MAC).

• The LLC sublayer communicates between the networking software at the upper layers and the device hardware at the lower layers.
• The MAC sublayer is responsible for data encapsulation and media access control.

Providing Access to Media

Packets exchanged between nodes may experience numerous data link layers and media transitions.

At each hop along the path, a router performs four basic Layer 2 functions:

• Accepts a frame from the network medium.
• De-encapsulates the frame to expose the encapsulated packet.
• Re-encapsulates the packet into a new frame.
• Forwards the new frame on the medium of the next network segment.

Data Link Layer Standards

Data link layer protocols are defined by engineering organizations:

• Institute for Electrical and Electronic Engineers (IEEE).
• International Telecommunications Union (ITU).
• International Organizations for Standardization (ISO).
• American National Standards Institute (ANSI).

Other related topics

Other useful information

• Full CCNA Course
• CCNA Certificate Information
• 200-301 CCNA Exam Questions and Solutions
• 200-301 CCNA Exam Topics