Understanding the network.pdf - Back to Home

802.3u. The IEEE standardization process usually takes a few years, so quite often,
there will be competing "proprietary" versions of the same base technology in the
marketplace. Although these technologies might provide the same functionality,
they are usually incompatible. For more information about the IEEE 802 committee,
you can check out their Web site at
http://grouper.ieee.org/groups/802/index.html.
802.2 Logical Link Control
In the discussion of the OSI-RM in Chapter 1, "Understanding Networking
Concepts," the IEEE variation of the OSI-RM Layer 2 was also introduced. Under the
IEEE/OSI variation, Layer 2 is split in half so that the lower half is the media access
layer. The media access layer controls Layer 2 source and destination addressing,
transmission signaling and encoding (framing), and error and data flow control. The
upper half of the IEEE/OSI Layer 2 variation is the Logical Link Control (LLC)
interface. The IEEE subcommittee 802.2 is responsible for the development of the
LLC specification. The LLC layer is used by the MACs (and some other protocols,
such as FDDI) to provide an interface between Layer 3 protocols and the Layer 2
MAC protocols.
The LLC standard has two interfaces (see Figure 4.1). The first is theNetwork/ LLC
interface, which defines the interface between the LLC and the Layer 3 protocol. The
second is the LLC/MAC interface, which handles communication between the LLC
and the MAC sublayer. These interfaces allow the LLC to interpret and generate
commands between the Layer 3 network protocol and Layer 2 transmission protocol.
This communication includes data flow control, error detection and recovery, and
the exchange of Layer 2 and Layer 3 address information. Although the MAC is
responsible for the transmission of the Layer 3 data between end-stations, it is the
responsibility of the LLC to ensure that data is delivered to the "service" or
application for which it is intended. It accomplishes this through the use of Service
Access Points.