OSI vs TCP/IP: Which OSI Layers Are Added? Session & Presentation | AI Research

OSI vs TCP/IP: Which OSI Layers Are Added? (Session & Presentation)

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Nov 4, 2026

The OSI (Open Systems Interconnection) and TCP/IP models describe network communication using layers, but they group responsibilities differently. In common textbook mappings, TCP/IP combines the OSI “Session”, “Presentation”, and “Application” functions into a single “Application” layer, whereas OSI keeps Session, Presentation, and Application as separate layers. Therefore, the OSI layers added when comparing OSI to TCP/IP are:

(iii) Session layer
(ii) Presentation layer
(and together with OSI Application layer inside TCP/IP’s single Application layer)

So, among your options, the correct choice is: (iv) Both session layer and presentation layer.

Key idea: [keyword]{def="OSI model"){def="Open Systems Interconnection reference model with 7 layers"} and keyword{def="Internet protocol suite reference model with fewer layers, often 4"} differ mainly in how application-related responsibilities are grouped. Session layer and Presentation layer exist distinctly in OSI, but are folded into TCP/IP’s Application layer. Application layer is present in both—just differently structured.

This structure and mapping are widely documented in networking references that compare the OSI layered architecture to the TCP/IP layered architecture.

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OSI vs TCP/IP Layers (Session/Presentation/Application Mapping)

Where Session & Presentation “go” in TCP/IP

In the OSI model:

Session layer (Layer 5) handles session establishment, maintenance, and teardown, plus synchronization points.
Presentation layer (Layer 6) handles data representation: syntax/format conversion (e.g., encoding/serialization), and typically encryption/compression-related concerns.
Application layer (Layer 7) exposes network services to user applications.

In the common TCP/IP conceptual model:

The Application layer is described as covering application-level protocols and “application service” functionality—commonly including what OSI splits into Session + Presentation + Application.

So when you “compare OSI to TCP/IP,” you effectively notice that OSI provides extra separation: OSI isolates Session and Presentation as distinct layers, whereas TCP/IP does not.

Layer Responsibilities (OSI separation vs TCP/IP combination)

Session responsibilities

OSI Layer 5

Dialog management, synchronization, and orderly session control."

Presentation responsibilities

OSI Layer 6

Data translation/encoding, representation, and crypto-related transformations."

Application responsibilities

OSI Layer 7

Protocol services used by applications (e.g., HTTP-like behavior)."

Single Application layer

TCP/IP model grouping

Typically merges OSI’s Session + Presentation + Application into one umbrella layer."

How to answer the multiple-choice question

1
Step 1
Understand that TCP/IP’s Application layer commonly subsumes OSI’s Session (Layer 5) and Presentation (Layer 6) functions.
2
Step 2
Since OSI splits responsibilities into more layers, the ‘extra’ ones (compared to TCP/IP) are the ones TCP/IP does not keep separate.
3
Step 3
Session alone? Presentation alone? Both? The correct selection is the option that matches the two OSI layers that TCP/IP typically combines: Session + Presentation.
4
Step 4
Choose (iv) Both session layer and presentation layer.

Visual summary: OSI vs TCP/IP layer grouping

Conclusion: Both session layer and presentation layer are the OSI layers that are “added” as separate layers compared to the TCP/IP model grouping.

Exam shortcut

If the question asks which OSI layers are added compared to TCP/IP, think: TCP/IP keeps fewer application layers → OSI’s Session + Presentation are the ones split out.

Be careful about “4-layer vs 5-layer” TCP/IP views

Different textbooks draw TCP/IP slightly differently (e.g., “Application/Transport/Internet/Link” or variants). But the common teaching mapping is that OSI Session & Presentation are not kept separate in TCP/IP—they’re absorbed into the single Application layer.

Common FAQs

Knowledge Check

Question 1 of 4

Q1Single choice

Which OSI layers are typically considered ‘added’ when comparing OSI to the TCP/IP model?

(i) Application layer

(ii) Presentation layer

(iii) Session layer

(iv) Both session layer and presentation layer

Explore Related Topics

OSI Model

The OSI model is a seven‑layer framework that defines data flow, encapsulation, and troubleshooting across networks.

Layers 1‑7 progress from raw bits to user services; examples include Ethernet, IP, TCP, and HTTP.
Encapsulation adds a header (and optional trailer) at each layer: $Payload + Header_n + Trailer_n$ , ending as bits.
The model enables layered troubleshooting; e.g., Layer 3 problems involve routing/IP, Layer 7 involve application protocols.
Compared to TCP/IP, OSI splits functions into more layers; Session and Presentation map into TCP/IP’s Application layer.

OSI Protocol Layers: Identifying the Incorrect Layer–Function Pair

Functions of the OSI Session Layer: Session Establishment and Synchronization

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