AS Computer Science 9618: Client-Server, DNS and Network Hardware

GreenLeaf Dental Clinic runs a small office network. Patient appointment records are centrally stored and updated only on a dedicated file server kept in the back office; no other computer on the network keeps its own copy of this data. The receptionist's computer displays a patient's appointment record by requesting it from this file server whenever it is needed.

(a) State whether retrieving a patient's appointment record in this way uses the client-server model or the peer-to-peer model, identifying which computer in the scenario is the client and which is the server. [2]

(b) The clinic's system administrator has also registered the domain name portal.greenleafdental.example.com for the file server, so that other devices do not need to know its IP address directly. Describe how a device converts this domain name into the correct IP address before it can actually contact the server. [3]

(c) Inside the clinic, a switch connects the reception computer and the back-office file server together on the wired LAN, and a router connects this LAN on to the clinic's ISP and the wider internet. State one function performed by the router that is not performed by the switch. [2]

(d) The clinic is adding a new computer at the reception desk and must decide whether to connect it to the network with a wired Ethernet cable run to the switch, or wirelessly through the clinic's wireless access point. Explain one advantage and one disadvantage of choosing the wired connection instead of the wireless connection for this new computer. [4]

Part (a): Client or server?

Retrieving a patient’s appointment record like this uses the client-server model, not the peer-to-peer model, because the two computers play clearly unequal, fixed roles rather than acting as equal peers.

The client is the receptionist’s computer. It is the device that initiates the request for a resource.
The server is the back-office file server. It is the device that stores the appointment records and centrally provides them in response to a request, while no other computer keeps its own copy.

[2 marks]: [1] for correctly stating “client-server”, [1] for correctly identifying both the client (reception computer) and the server (file server).

Part (b): Resolving the domain name with DNS

A domain name such as portal.greenleafdental.example.com is easy for people to remember, but data can only actually be routed across a network using IP addresses. Converting between the two is the job of the Domain Name System (DNS):

The device that wants to contact the file server sends a request to a DNS server, asking for the IP address that corresponds to the domain name portal.greenleafdental.example.com.
The DNS server looks up this domain name in its own records. If it does not hold a matching record itself, it queries further DNS servers until the correct IP address is found.
The matching IP address is returned to the requesting device.
The device can now use this IP address to actually locate and contact the file server, since the domain name alone cannot be used to route data across the network.

[3 marks]: [1] for identifying that a DNS server is involved, [1] for describing the domain-name-to-IP-address lookup, [1] for the matching IP address being returned to the requesting device so the connection can be made.

Part (c): Switch vs router

A switch only forwards data between devices that are already connected to the same local network, here, between the reception computer and the file server. It has no awareness of, and no connection to, any network beyond the clinic’s own LAN.

A router, in contrast, connects the clinic’s local network to a different network entirely, the ISP’s network and, through it, the wider internet, and directs (routes) data between the clinic’s network and these external networks. Without the router, the reception computer and file server could still exchange data with each other through the switch, but neither of them could reach anything outside the clinic, including any remote service the clinic relies on.

[2 marks]: [1] for stating a genuine router-only function (connecting to/routing data to an external network such as the internet), [1] for correctly contrasting it with the switch’s more limited role (only forwarding data within the existing local network).

Part (d): Wired vs wireless connection

Advantage of the wired connection. A wired Ethernet cable run directly to the switch is generally more reliable and provides higher, more consistent bandwidth than a wireless connection. It is not affected by physical obstructions such as walls, by distance from the wireless access point, or by other wireless devices competing for the same radio signal, all of which can slow down or interrupt a wireless connection.

Disadvantage of the wired connection. It requires a physical cable to be run all the way from the new reception desk back to the switch. This is far less flexible than simply connecting wirelessly, and can be more disruptive and expensive to install. Particularly if the desk is not already close to existing cabling and new cable has to be laid through walls or under flooring.

[4 marks]: [2] for a correctly explained advantage tied to a genuine wired-versus-wireless trade-off (such as reliability, consistent bandwidth or freedom from interference), [2] for a correctly explained disadvantage tied to a genuine trade-off (such as installation cost, cabling effort or lack of flexibility).

Final answers

(a) Client-server model, client: the reception computer; server: the back-office file server.
(b) The requesting device queries a DNS server, which looks up the domain name and returns the matching IP address, allowing the device to contact the file server directly.
(c) The router routes data between the clinic’s network and external networks (such as the internet); the switch only forwards data between devices already on the same local network.
(d) Advantage: a wired connection is more reliable and offers more consistent bandwidth. Disadvantage: it needs a physical cable run to the desk, which is less flexible and can be more costly to install.