MAC layer and Llczi layer

1. What is the Mac Sublayer and the LLC sublayer of the data link layer?

The main functions of the MAC sub-layer include the encapsulation/uninstallation of data frames, the addressing and recognition of frames, the reception and transmission of frames, the management of links, the difference of frames

Error control, and so on. The existence of Mac sub-layer shields the difference of different physical link types;

Among the many functions of the Mac sub-layer, a very important feature is the right to use the quorum media, that is, when the site can be used to communicate

Quality. In fact, LAN technology is a carrier-listening multi-access with conflict detection (Carrier sense Multiple access/

Collision DETECTION,CSMA/CD) This media access method.

The LLC Sublayer is responsible for providing services to its upper layers;

The LLC is developed on the basis of high-level Data link control (Hdlc:high-level data-link control) and uses a subset of the HDLC specification. The LLC defines three types of data communication operations:

Type 1: no connection. This method of sending information is usually not guaranteed to be received.
Type 2: Connection oriented. This approach provides four services: connection establishment, acknowledgment and acknowledgment response, error recovery (via request for re-sending of received erroneous data), and sliding window (factor: 128). The data transfer rate can be improved by changing the sliding window.
Type 3: No connection acknowledgment response service.
The LLC no connection service of type 1 specifies a static frame format and supports running network protocols. The Transport Layer network protocol is typically used in service Type 1 mode.

In the Windows 2000 Network Architecture, the LLC Sublayer is implemented by the transport driver, and the Mac Sublayer is implemented by a network interface card (NIC: NIC).


The LLC for type 2 is a connection-oriented service that supports reliable data transfer and is used in LAN environments where the network layer and transport layer protocols are not required to be invoked.

2. Why is only the LAN link layer divided into two sub-tiers?
802.3 (local area network) is a shared medium, and the WAN is dedicated (usually point-to-point) there is no media conflict problem

MAC layer and Llczi layer