NFS Architecture and Protocols

NFS consists of seven layers of protocols that correspond to the layers of the Open System Interconnection (OSI) model.

Table 11.1 OSI Layers and NFS Protocols

The Physical layer controls how data is physically transmitted across the network. The Data Link layer provides transfer of data that is combined into frames. Ethernet is the standard implementation of these two layers.

The Network layer is concerned with getting the data from one host to another on the network. The Internet Protocol (IP) is an implementation of this layer.

IP must get the packets to the correct destination. It is not concerned with data reliability or with data order. It can fragment packets that are too large. The Internet Protocol uses unique IP addresses to identify hosts

The Transport Layer, which is responsible for data flow and data reliability, is implemented by using UDP or TCP.

Transmission Control Protocol (TCP) provides reliable, ordered delivery of data packets and is stateful. TCP keeps track of the order of information and resends missing data. This protocol is best for long network connections, such as file transfer.

User Datagram Protocol (UDP) is a simple, connectionless protocol that does not ensure the order or the completeness of the datagrams. It is stateless and is best for short connections such as remote procedure calls.

The Session Layer is concerned with the exchange of messages between devices. NFS uses the Remote Procedure Call (RPC) protocol.

The Presentation Layer is concerned with the exchange of data types between heterogeneous systems. NFS uses the External Data Representation (XDR) protocol. This protocol specifies the format to which the data must be converted before being sent. Once received, the data is then reconverted.

For more information about the OSI model of networking, see "OSI Model" in the TCP/IP Core Networking Guide.

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