Computer Networks

A network layer groups responsibilities such as physical signaling, addressing, transport, or application behavior. The OSI model is a reference framework with seven layers.

A browser request is encoded into application data, carried by transport and Internet headers, then framed for the local link.

Describe the broad task of the network layer and the transport layer when sending a web request.

The network layer routes packets between networks using addresses. The transport layer provides process-to-process delivery, with TCP or UDP behavior depending on the application.

An IP address identifies a network interface. A subnet prefix divides the address into a network portion and a host portion; DNS maps names to records such as IP addresses.

A laptop sees a destination outside its local prefix and sends the packet to its default gateway after resolving the service name.

Explain what the prefix `/24` tells you and what a default gateway is used for.

A `/24` uses the first 24 address bits as the network prefix. A default gateway is the router used for destinations without a more-specific local route.

A switch forwards frames within a local link using link-layer addresses. A router forwards packets between networks using network-layer addresses and routing information.

In a home network, a switch connects devices on the local LAN while the wireless router forwards outbound traffic toward the internet provider.

Trace a packet from a laptop to a remote server through a home gateway, naming the roles involved.

The laptop sends a frame to its gateway, the gateway routes the IP packet onward, and intermediate routers select next hops until the destination network receives it.

TCP provides a reliable, ordered byte stream with connection setup and recovery behavior. UDP sends independent datagrams without TCP's delivery guarantees.

A file download usually relies on TCP delivery; a live voice call may prefer low delay and tolerate an occasional lost packet.

For a time-sensitive multiplayer game update, compare TCP and UDP trade-offs without assuming one is always correct.

UDP avoids waiting for retransmission of stale data, which can help latency. The game must handle loss, ordering, and security as needed; some systems instead use TCP or modern secure transports.

An application protocol defines message formats and interactions for a service. Examples include HTTP for web transfers, DNS for name lookup, and SMTP for sending email.

If a domain resolves but a secure web request fails, DNS may be working while the server, certificate, route, or TLS configuration still needs checking.

A user can ping an IP address but not open a domain. Name a likely first check and one follow-up.

Check DNS resolution for the domain. If it resolves, test the application port and inspect the browser/network error to distinguish service availability from certificate or HTTP issues.