The level of access to the network is the lowest level in the hierarchy of TCP/IP protocols. Protocols at this level allow the system to transmit data to other devices in a directly connected network. This level defines how the network is used to transfer an IP datagram. Unlike parental protocols, Network Access Layer protocols need to know the details of the underlying network (package structure, addressing, etc.) in order to properly format the transferred data to meet network constraints. The level of access to the TCP/IP network can include the functions of the lower three levels of the OSI reference model (network, data link and physics). For network protocols to work, they must be encoded into the software, either as part of the computer`s operating system (OS), or as an application, or in computer hardware. Most modern operating systems have integrated software services, prepared for the implementation of certain network protocols. Other applications, z.B. Web browsers, are designed with software libraries that support all the protocols needed for the application function. In addition, support for TCP/IP and routing protocols is implemented in direct hardware to improve performance. The reliable provision of data on the underlying physical network is processed by the Data Link layer. TCP/IP rarely creates protocols in the data interconnection layer. Most CFRs that refer to the data interconnection layer explain how ip can use existing data interconnection protocols.
SLIP is used for point-to-point series connections with TCP/IP. SLIP is used for dedicated series connections and sometimes also for DF purposes. SLIP is useful for allowing host and router mixes to communicate with each other. For example, the host host, host router and router are common SLIP network configurations. SLIP is just a package frame protocol: it defines a sequence of characters that frame IP packets on a serial line. It does not offer address, package type identification, error detection or correction, or compression mechanisms. Opening TCP/IP protocols requires an open standard development process and publicly available standard documents. Internet standards are developed by the Internet Engineering Task Force (IETF) at public meetings. The protocols developed in this process are published in the form of requests for Comments (RFCs).  As the title “Request for Comments” indicates, the style and content of these documents are much less rigid than in most standard documents. RFCs contain a wide range of interesting and useful information and are not limited to the formal specification of data communication protocols.
There are three basic types of CFRs: Standards (STD), Current Best Practices (BCP) and Informational (FYI). Each time a new protocol is implemented, it is added as a result of the protocol. The organization of protocol collections is considered monolithic, as all protocols are stored at the same address and overlap. Network protocols are defined rules that prescribe how data is formatted, transferred and captured so that computer network devices — from servers and routers to terminals — communicate independently differences in their infrastructures, designs or underlying standards.