Unlike the protocols of the upper layers of the TCP/IP suite, data link layer protocols are generally not defined by Request for Comments (RFCs). Although the Internet Engineering Task Force (IETF) maintains the functional protocols and services for the TCP/IP protocol suite in the upper layers, the IETF does not define the functions and operation of that model's network access layer.
Specifically the data link layer services and specifications are defined by multiple standards based on a variety of technologies and media to which the protocols are applied. Some of these standards integrate both Layer 2 and Layer 1 services.
The functional protocols and services at the data link layer are described by:
- Engineering organizations which set public and open standards and protocols.
- Communications companies which set and use proprietary protocols to take advantage of new advances in technology or market opportunities.
Engineering organizations that define open standards and protocols that apply to the data link layer include:
- Institute of Electrical and Electronics Engineers (IEEE)
- International Telecommunication Union (ITU)
- International Organization for Standardization (ISO)
- American National Standards Institute (ANSI)
The table in the figure highlights various standard organizations and some of their more important data link layer protocols.