TCP/IP vs OSI: Which Layer Corresponds to the OSI Transport Layer?
In the OSI model, the Transport layer is responsible for end-to-end communication using ports and protocols like TCP/UDP. In the TCP/IP model, the closest equivalent is the Host-to-host layer (often also described as the transport layer in TCP/IP literature). It maps most directly to OSI’s transport functions (TCP/UDP, ports, reliability/ordering semantics), rather than to the OSI network layer (Network layer).2
So for your multiple-choice options, the correct answer is:
- (ii) Host-to-host
Footnotes
-
TCP/IP Model Overview - Explains the four TCP/IP layers and typical responsibilities (application, host-to-host/transport, internet, network access). ↩
-
OSI vs TCP/IP Model Mapping - Provides a direct mapping between OSI layers and TCP/IP layers, including transport ↔ host-to-host. ↩
OSI Model vs TCP/IP Model (Layer Mapping)
Key concept mapping (what “equivalent” means here)
“Equivalent” doesn’t mean identical naming, but rather matching responsibilities:
-
Host-to-host handles transport semantics:
- TCP provides reliable, connection-oriented byte streams
- UDP provides connectionless datagrams
These align with OSI transport layer goals (end-to-end delivery, ports, segmentation/reassembly, and transport features).2
-
The Internet layer aligns with OSI’s network layer: it focuses on IP addressing and routing, not transport reliability/ports.2
-
The Network access layer corresponds to OSI’s data link/physical layers (framing and link-level transmission).2
Footnotes
-
TCP/IP Model Overview - Explains the four TCP/IP layers and typical responsibilities (application, host-to-host/transport, internet, network access). ↩ ↩2 ↩3
-
OSI vs TCP/IP Model Mapping - Provides a direct mapping between OSI layers and TCP/IP layers, including transport ↔ host-to-host. ↩ ↩2 ↩3
Pick the TCP/IP layer equivalent to the OSI Transport layer
- 1Step 1
Transport layer provides end-to-end communication using ports and transport protocols (e.g., TCP/UDP).
- 2Step 2
In TCP/IP, the layer that provides end-to-end delivery semantics using TCP and UDP is the Host-to-host layer.2
Footnotes
-
TCP/IP Model Overview - Explains the four TCP/IP layers and typical responsibilities (application, host-to-host/transport, internet, network access). ↩
-
OSI vs TCP/IP Model Mapping - Provides a direct mapping between OSI layers and TCP/IP layers, including transport ↔ host-to-host. ↩
-
- 3Step 3
Internet layer is primarily IP routing; Network access is local link framing—neither matches transport semantics.2
Footnotes
-
TCP/IP Model Overview - Explains the four TCP/IP layers and typical responsibilities (application, host-to-host/transport, internet, network access). ↩
-
OSI vs TCP/IP Model Mapping - Provides a direct mapping between OSI layers and TCP/IP layers, including transport ↔ host-to-host. ↩
-
- 4Step 4
Therefore, the correct option is (ii) Host-to-host.
Pro Tip
If the question mentions TCP/UDP, ports, end-to-end delivery, or reliability, you’re in the territory of the Host-to-host layer in TCP/IP (OSI Transport equivalent).
Common confusion
Don’t pick Internet just because it handles packets—IP routing belongs to OSI’s network layer, not OSI’s transport layer (which handles end-to-end transport semantics).
Responsibility alignment (OSI Transport → TCP/IP layer)
Scores reflect functional alignment to OSI Transport responsibilities (end-to-end delivery, ports, TCP/UDP).
Transport layer: end-to-end delivery, ports, segmentation/reassembly, TCP/UDP semantics.
Multiple-choice walkthrough
Knowledge Check
What layer in the TCP/IP stack is equivalent to the transport layer of the OSI model?