Which device enables communication between devices on one IP network and devices on a different IP network (possibly with protocol translation or policy control)?

Introduction / Context:
Interconnecting dissimilar or separate networks often requires an intermediate device that understands both sides. While routers move packets between IP subnets, the broader term “gateway” historically denotes a device that connects different networks and can perform translation, policy enforcement, or application mediation.

Given Data / Assumptions:

• Two networks are distinct at Layer 3 or above.
• Communication requires crossing a boundary (addressing, policy, or protocol differences).

Concept / Approach:
A gateway connects networks and may translate between protocols or simply route between IP subnets while applying access control, NAT, or application proxies. In many enterprise diagrams, the default gateway is the router interface that leads off the local subnet.

Step-by-Step Solution:

Verification / Alternative check:
Network hosts are configured with a “default gateway” IP for off-subnet traffic. Security gateways also implement firewalls, NAT, or application proxies to govern cross-network communication.

Why Other Options Are Wrong:

• Multiplexer: shares a medium among inputs; not inter-networking.
• T-switch: not a standard inter-networking device.
• Modem: adapts signals to access media; not a cross-network policy/forwarding element by itself.
• None: incorrect because gateways fulfill the requirement.

Common Pitfalls:
Equating “gateway” strictly with “router”: routers are a common form of gateway, but gateways may also perform translation beyond pure IP routing.

Final Answer:
Gateway