ITPEC FE Morning April 2020 Question 31
Which device performs protocol conversion between different types of networks, functioning at the layers of transport and above in the OSI basic reference model?
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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