ITPEC FE Subject A October 2025 Question 25
Between LAN systems that are different from the transport layer upward in the OSI basic reference model, which of the following is a device that performs protocol conversion?
Explanation
Gateway — the device that converts protocols when two networks differ from the transport layer upward.
Each relay device works up to a certain OSI layer and can only bridge differences up to that layer:
- •Repeater — layer 1, regenerates the electrical signal.
- •Bridge — layer 2, forwards frames by MAC address.
- •Router — layer 3, forwards packets by network address.
- •Gateway — layers 4 to 7, converts between different protocols at the transport layer and above.
Answer (b)
Why not others:
- •(a) Bridge — works only at the data link layer and needs the same protocols above it on both sides.
- •(c) Repeater — works only at the physical layer and just amplifies the signal.
- •(d) Router — relays at the network layer; it does not convert transport-layer or application protocols.
Key rule: A relay device must reach the highest layer at which the two networks differ: layer 1 repeater, layer 2 bridge, layer 3 router, layer 4 and above gateway.
Networks · AI-written, may contain errors
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