Networks, Devices, and Paths

A computing device is any physical artifact that can run a program -- computers, tablets, servers, routers, and smart sensors all qualify. A computer network is a group of interconnected computing devices capable of sending or receiving data. A computing system is a broader term: a group of computing devices and programs working together for a common purpose. A network is a type of computing system.

Communication between two devices requires a path -- a sequence of directly connected computing devices from sender to receiver. Routing is the process of finding that path. On the Internet, routing is dynamic: it is not predetermined. Routers make forwarding decisions in real time based on current network conditions, not a fixed plan established in advance.

Bandwidth is the maximum amount of data a network can transmit in a fixed amount of time, measured in bits per second (bps, Mbps, Gbps). Bandwidth is a capacity limit, not a speed guarantee. A highway with 6 lanes has more bandwidth than one with 2 lanes, but traffic and distance still affect travel time.

Protocols: The Rules That Make the Internet Work

A protocol is an agreed-upon set of rules that specify the behavior of a system. Without shared protocols, two devices from different manufacturers couldn't communicate at all. The Internet's power comes from using open (nonproprietary) protocols -- rules that anyone can implement, not locked to a specific vendor.

Open protocols mean:

• Any manufacturer can build a device that connects to the Internet
• New devices can join without central permission or coordination
• Competition drives improvement without fragmentation
• The system is scalable -- it can grow to accommodate billions of new devices

Key protocols you need to know for the AP exam:

Packet Switching: How Data Actually Travels

Data on the Internet travels as a data stream broken into chunks called packets. Each packet contains two things:

1. A chunk of the actual data (a portion of the email, image, or video)
2. Metadata for routing -- source address, destination address, packet sequence number, and information for reassembly

Why packet switching instead of a dedicated end-to-end connection (circuit switching)?

• Efficiency: The network capacity is shared. When you're not actively transmitting, those resources are available to other users.
• Resilience: Each packet can take a different route. If one path fails, packets reroute automatically.
• Scalability: Adding new devices doesn't require reserving dedicated channels for every possible pair of communicators.

The Internet vs The World Wide Web

This distinction is tested directly on the AP exam. Students consistently confuse these two things.

How Routing Works

When a packet enters the network, each router it reaches makes a forwarding decision: which neighboring router should receive this packet next to move it closer to the destination? This decision is based on the packet's destination IP address and the router's current routing table (a map of known paths).

Because routing is dynamic, two consecutive packets from the same email may travel completely different physical routes. They're identified by destination IP address and reassembled at the endpoint using sequence numbers embedded in their metadata.

AP Exam Spotlight

BI4 MCQ questions are primarily conceptual -- no code to trace. The most common question types:

1. Network diagram: Given a diagram showing connections between devices, identify a valid path from A to B, or identify which devices are directly connected.
2. Packet questions: Why might packets arrive out of order? What does packet metadata contain? What happens when a packet doesn't arrive?
3. Protocol identification: Which protocol handles reliable delivery (TCP)? Which protocol does the WWW use (HTTP)?
4. Internet vs WWW: Which statement correctly distinguishes them?

Practice MCQs

Predict your answer before clicking. These questions match AP exam difficulty and phrasing.