Paper 1 Computer Networks Answers

These answers correspond to Paper 1 Computer Networks Drills.

Answer 1: LAN vs WAN

• The 40 computers in one lab form a LAN because they are within a small local area and are usually managed by one organisation.
• The link between campuses 12 km apart is a WAN because it connects networks over a wider geographical area, using a service provider link.

Mark points:

• identifies the lab network as LAN;
• gives small/local area or single-organisation management as reason;
• identifies the campus link as WAN;
• gives wider geographical area or provider link as reason.

Common weak answer:

• saying LAN means wireless and WAN means wired. LAN/WAN is about scale and coverage, not just cable type.

Answer 2: Intranet

The staff site is an intranet because it is private to the college’s staff and requires staff login. The internet is the wider public network where the main college website can be accessed by public users.

Mark points:

• intranet is private/internal to an organisation;
• internet is publicly accessible/global by comparison.

Common weak answer:

• saying an intranet is not a website. An intranet can provide private web pages or services.

Answer 3: IP Address

The destination IP address identifies the server or network interface that the packet should be routed to.

Mark points:

• 1 mark for identifying the destination host/interface for routing.

Common weak answer:

• saying the IP address identifies only the web page. The address identifies the network destination, not a specific page.

Answer 4: DNS

1. The browser needs the IP address for www.example.edu.
2. It sends a DNS lookup request for the domain name.
3. DNS returns 198.51.100.42.
4. The browser uses that IP address to connect to the web server.

Mark points:

• domain name is looked up;
• DNS maps name to IP address;
• correct IP address 198.51.100.42 is returned;
• browser uses the IP address to connect to the server.

Common weak answer:

• saying DNS sends the web page to the browser. DNS resolves names; the web server sends the web page.

Answer 5: Protocol

Both programs need the same protocol so they interpret each message in the same way. For GET:42, both sides must agree that GET is the command and 42 is the identifier; otherwise one program may parse or respond to the message incorrectly.

Mark points:

• protocol provides agreed communication rules or message format;
• links the rule to correct interpretation of COMMAND:ID.

Common weak answer:

• saying a protocol is needed only for security. Protocols are broader communication rules.

Answer 6: Packet Switching

The message is split into smaller packets:

1: HEL
2: LOW
3: ORL
4: D

Each packet can be sent separately and carries sequencing information. The packets may arrive in a different order. At the destination, the sequence numbers are used to reorder the packets and reassemble:

HEL + LOW + ORL + D = HELLOWORLD

Mark points:

• message is split into packets;
• packets carry sequence numbers or ordering information;
• packets may travel or arrive separately;
• destination reorders and reassembles the original message.

Common weak answer:

• saying each packet must take exactly the same route. Packet switching allows packets to be routed independently.

Answer 7: Router

Two roles:

• A router forwards packets from the school LAN towards another network, such as the internet.
• It uses destination IP address/routing information to choose the next hop for a packet.

Mark points:

• forwards packets between networks;
• uses addressing/routing information to choose where to send packets next.

Common weak answer:

• saying a router stores all websites. It forwards network traffic; it is not a web server.

Answer 8: Client Server

The browser is the client because it sends the search request. The web server is the server because it receives the request, processes the search, and returns matching book records.

Mark points:

• client sends request;
• server processes request and returns response.

Common weak answer:

• saying the larger computer is always the server. Client/server roles depend on request and response behavior.

Answer 9: Socket

The socket endpoint is identified by:

IP address: 127.0.0.1
port: 5000

Mark points:

• 1 mark for IP address;
• 1 mark for port number.

Common weak answer:

• giving only the IP address. Multiple services can run on the same host using different ports.

Answer 10: TCP/IP Layers

Responsibility	Layer
HTTP request for a web page	application
TCP reliable delivery between programs	transport
IP addressing and routing between networks	internet
transmission over the local network medium	network access / link

Mark points:

• application for HTTP;
• transport for TCP delivery;
• internet for IP addressing/routing;
• network access/link for local transmission.

Common weak answer:

• placing IP at the application layer. IP belongs to the internet layer.