Internet Protocol Suite

The set of network communication protocols that are specified by the IETF, and approved as Internet Standards by the IESG, within the oversight of the IAB. (See: OSIRM Security Architecture. Compare: OSIRM.)

Usage: This set of protocols is popularly known as "TCP/IP" because TCP and IP are its most basic and important components.

For clarity, this Glossary refers to IPS protocol layers by name and capitalizes those names, and refers to OSIRM protocol layers by number.

Tutorial: The IPS does have architectural principles [R1958], but there is no Internet Standard that defines a layered IPS reference model like the OSIRM. Still, Internet community literature has referred (inconsistently) to IPS layers since early in the Internet's development [Padl].

This Glossary treats the IPS as having five protocol layers -- Application, Transport, Internet, Network Interface, and Network Hardware (or Network Substrate) -- which are illustrated in the following diagram:

OSIRM Layers Examples IPS Layers Examples

Message Format: P2 [X420] Message Format: ARPA (RFC 822) +----------------+ +-------------+ |7.Application | P1 [X419] | Application | SMTP (RFC 821) +----------------+ - - - - - - | | |6.Presentation | [I8823] | | +----------------+ - - - - - - | | |5.Session | [I8327] +-------------+ +----------------+ - - - - - - | Transport | TCP (RFC 793) |4.Transport | TP4 [I8073] | | +----------------+ - - - - - - +-------------+ |3.Network | CLNP [I8473] | Internet | IP (RFC 791) | | +-------------+ | | | Network | IP over IEEE +----------------+ - - - - - - | Interface | 802 (RFC 1042) |2.Data Link | +-------------+ | | LLC [I8802-2] - Network - The IPS does | | MAC [I8802-3] - Hardware - not include +----------------+ - (or Network - standards for |1.Physical | Baseband - Substrate) - this layer. +----------------+ Signaling [Stal] + - - - - - - +

The diagram approximates how the five IPS layers align with the seven OSIRM layers, and it offers examples of protocol stacks that provide roughly equivalent electronic mail service over a private LAN that uses baseband signaling.

• IPS Application Layer: The user runs an application program. The program selects the data transport service it needs -- either a sequence of data messages or a continuous stream of data -- and hands application data to the Transport Layer for delivery.

• IPS Transport Layer: This layer divides application data into packets, adds a destination address to each, and communicates them end-to-end -- from one application program to another -- optionally regulating the flow and ensuring reliable (error- free and sequenced) delivery.

• IPS Internet Layer: This layer carries transport packets in IP datagrams. It moves each datagram independently, from its source computer to its addressed destination computer, routing

  the datagram through a sequence of networks and relays and selecting appropriate network interfaces en route.

• IPS Network Interface Layer: This layer accepts datagrams for transmission over a specific network. This layer specifies interface conventions for carrying IP over OSIRM Layer 3 protocols and over Media Access Control sublayer protocols of OSIRM Layer 2. An example is IP over IEEE 802 (RFD 1042).

• IPS Network Hardware Layer: This layer consists of specific, physical communication media. However, the IPS does not specify its own peer-to-peer protocols in this layer. Instead, the layering conventions specified by the Network Interface Layer use Layer 2 and Layer 3 protocols that are specified by bodies other than the IETF. That is, the IPS addresses inter-network functions and does not address intra-network functions.

The two models are most dissimilar in the upper layers, where the IPS model does not include Session and Presentation layers. However, this omission causes fewer functional differences between the models than might be imagined, and the differences have relatively few security implications:

• Formal separation of OSIRM Layers 5, 6, and 7 is not needed in implementations; the functions of these layers sometimes are mixed in a single software unit, even in protocols in the OSI suite.

• Some OSIRM Layer 5 services -- for example, connection termination -- are built into TCP, and the remaining Layer 5 and 6 functions are built into IPS Application-Layer protocols where needed.

• The OSIRM does not place any security services in Layer 5 (see: OSIRM Security Architecture).

• The lack of an explicit Presentation Layer in the IPS sometimes makes it simpler to implement security in IPS applications. For example, a primary function of Layer 6 is to convert data between internal and external forms, using a transfer syntax to unambiguously encode data for transmission. If an OSIRM application encrypts data to protect against disclosure during transmission, the transfer encoding must be done before the encryption. If an application does encryption, as is done in OSI message handling and directory service protocols, then Layer 6 functions must be replicated in Layer 7. [X400, X500].

The two models are most alike at the top of OSIRM Layer 3, where the OSI Connectionless Network Layer Protocol (CLNP) and the IPS IP are quite similar. Connection-oriented security services offered in OSIRM Layer 3 are inapplicable in the IPS, because the IPS Internet Layer lacks the explicit, connection-oriented service offered in the OSIRM.