| Date | November 2017 | Marks available | 6 | Reference code | 17N.1.SL.TZ0.12 |
| Level | SL | Paper | 1 | Time zone | no time zone |
| Command term | Explain | Question number | 12 | Adapted from | N/A |
Question
A wireless local area network (WLAN) is used to extend access to a school’s wired local area network.
The advantages of this WLAN are user-mobility and economical access points.
The concept of packet data transmission is used within this network.
Figure 1 shows the simplified structure of a data packet.
Figure 1: The structure of a data packet
Identify one hardware component of the WLAN, other than computers.
Outline two disadvantages of this WLAN.
Identify three ways in which the network administrator can reduce the risk of unauthorized access to confidential data.
Define the term protocol.
With reference to Figure 1, explain how data is transferred by packet switching.
Markscheme
Award up to [1 max].
Wireless router/modem;
Access points;
Switch;
Wireless repeater/extender/booster;
Award [1] for identifying a disadvantage and [1] for an expansion, for two disadvantages up to [4 max].
Data transfer will decrease (compared with a wired LAN);
Because the number of computers using the network increases;
(and because) WLAN has lower bandwidth than a wired LAN;
Less data security;
As devices from outside the school can access the network/intercept transmissions;
More easily open to misuse;
As teacher/administrator cannot directly monitor a specific student/teacher/ machine;
Intermittent connectivity due to physical barriers (walls);
Results in low transfer/speed and may hinder operations.
Note: Accept any reasonable points, provided they are appropriately elaborated.
Award up to [3 max].
Give each user appropriate login details/passwords;
Different access rights for students, teachers, school administrators (file-level and share-level security);
All passwords and files should be encrypted;
Use the latest WiFi protocol/WPA2;
Require MAC address authentication;
Password protect the documents;
Note: the focus of the question is on confidential data (firewalls not accepted)
Set of rules for data transmission;
Award up to [6] as follows:
Award up to [3 max] for a general description of how data is transferred by packet switching. ([1 max] if this general description is very simplistic and refers to just the Header/Data/Trailer already shown in the question paper).
Award up to [3 max] for added detail that references the contents of the given data packet in the answer.
Example of general description
Data is organized in specially formatted units (data packets) which are routed from source to destination using network switches and routers;
Network switches and routers determine how best to transfer the packet between a number of intermediate devices (routers and switches) on the path to its destination (rather than flowing directly over a single wire on the path to its destination);
Data packets are reassembled at the destination;
Example of referencing content
Addresses have to be in a standard format so that each switch/routing station recognizes the address;
Address of sender identifies the sending computer, so that any packets not received can be re-requested;
Address of receiver identifies intended recipient so it can be forwarded on correctly;
The protocol used must be identified so that the correct rules are followed;
Size of packet / size of fields in packet – All packets/fields must have the same size so that the data can be reassembled;
Sequence number so that packets can be reassembled in correct order;
Transmission codes to show whether the data packet is transmitted or re-transmitted;
Control bits, to maintain the integrity of the data by ensuring that the data received is the same as the data sent;
Error checking code – when an error is detected, an algorithm either corrects the error or requests that the packet is resent;
