FIT3165/FIT4165 Tutorial #7 TCP/IP Layered Architecture
Week 8 – Semester 1 – 2022
14 April 2022
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Updated by Dr. , Rosanna F. Alam and , April 2022.
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Instructions
1. Students work individually to solve this week’s exercise.
2. Each student must answer the following review Q’s and complete the practical tasks
given in part 2.
Review Questions
1. Assume the propagation delay in a broadcast network is 5 microseconds and the frame transmission time is 10 microsecond.
a) How long does it take for the first bit to reach the destination?
b) How long does it take for the last bit to reach the destination after the first bit has
c) How long is the network involved with this frame transmission (vulnerable to
collision)?
The last bit is 10 μs behind the first bit.
a) It takes 5 μs for the first bit to reach the destination.
b) The last bit arrives at the destination 10 μs after the first bit.
c) The network is involved with this frame for a total of (5 + 10) microsec = 15 μs.
Frame takes 10 μs to be assembled on the communication link; it’s called transmission delay.
2. Four stations are connected to a hub in a transitional Ethernet network. The distances between the hub and the stations are 300m, 400m, 500m and 700m respectively. What is the length of this network and when we need to calculate TP?
For calculating Tp= (propagation delay) we need to consider the maximum length of frame transmission between any two stations. In this case, the maximum length is 500 + 700 = 1200 m.
So Tp = propagation delay is the amount of time it takes for the head of the signal to travel from the sender to the receiver. It can be computed as the ratio between the link length and the propagation speed over the specific medium.
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Tp = propagation delay =(1200 meters/2 x 10^8 meters/sec) = 6 μs (microsec).
3. What are the common Standard Ethernet implementations?
The common traditional Ethernet implementations are 10Base5, 10Base2, 10- Base-T, and 10Base-F.
4. What is a VLAN? Define the purpose of VLAN and how VLAN helps companies save time and money?
A VLAN is when a group of workstations within a LAN that can communicate with each other as though they were on a single, isolated LAN.
A VLAN provides broadcast packets sent by one of the workstations to all the others in the VLAN. Broadcasts sent by one of the workstations in the VLAN will not reach any workstations that are not part of that VLAN. The workstations can all communicate with each other without needing to go through a gateway. The workstations can communicate with each other using non-routable protocols.
The purpose of VLANs is to split flat networks into VLANs to reduce congestion on a large LAN. In a flat LAN, every packet that any device puts onto the wire is sent to every other device on the LAN. As the number of workstations on the typical LAN grew, they started to become hopelessly congested; there were just too many collisions, because most of the time when a workstation tried to send a packet, it would find that the wire was already occupied by a packet sent by some other device. A VLAN saves time and money because re-configuration is done through software. Physical reconfiguration is not necessary.
5. In ATM, what is the relationship between TPs, VPs, and VCs?
A Transmission Path (TP) is the physical connection between a user and a switch or between two switches.
It is divided into several VPs (virtual paths), which provide a connection or a set of connections between two switches.
VPs in turn consist of several VCs (virtual circuits) that logically connect two points.
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6. A simple parity check bit, which is normally added at the end of the word (changing a 7-bit ASCII character to a byte), cannot detect even numbers of errors. For example, two, four, six, or eight errors cannot be detected in this way. A better solution is to organize the characters in a table and create row and column parities. The bit in the row parity is sent with the byte, the column parity is sent as an extra byte (Figure below). EVEN PARITY is used!
Show how the following errors can be detected?
a. An error at (R3, C3).
b. Two errors at (R3, C4) and (R3, C6).
c. Three errors at (R2, C4), (R2, C5), and (R3, C4).
d. Four errors at (Rl, C2), (Rl, C6), (R3, C2), and (R3, C6).
The following shows the errors and how they are detected.
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7. This problem shows a special case in checksum handling. A sender has two data items to send: (4567)16 and (BA98)16. What is the value of the checksum?
The sum in this case is (FFFF)16 and the checksum is (0000)16. The problem shows that the checksum can be all 0s in hexadecimal. It can be all Fs in the hexadecimal only if all data items are all 0s, which makes no sense.
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Practical Tasks
Activity 1: Build the following network with routers connecting multiple LANs together. Use static routing and default route option in the routers to ensure connectivity between the LANs.
(i) Two company routers are connected to a router named Internet playing the role of the Internet. The company network is divided into client and server subnets. Build the network as shown in the figure 1 and use the following IP addressing scheme given below.
Network address
Address Range
Company A Clients
10.0.0.0/24
10.0.0.1 – 10.0.0.254
Company A Servers
10.0.1.0/24
10.0.1.1 – 10.0.1.254
Company B Clients
172.16.1.0/24
172.16.1.1 – 172.16.1.254
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Company B Servers
172.16.2.0/24
172.16.2.1 – 172.16.2.254
Company B – Internet
10.0.4.0/30
10.0.4.1 – 10.0.4.2
Company A – Internet
10.0.2.0/30
10.0.2.1 – 10.0.2.2
(ii) Use the “ip route add” command in the routers to add static routing information for the packets to reach hosts from one submit to another. The routing configuration should allow any host from any network to reach any other host in any network. (i.e. ip route add {NETWORK/MASK} via {GATEWAYIP} )
(ii) The Internet router must be the default gateway for both the company networks. Use the “Default Route” option in the router configuration window to add the default route configurations. An example command is given below.
ip route add default via 10.0.4.1
Here, we are adding a path to the router’s routing table where it states that any packet for which the router doesn’t know which direction to forward should be forwarded to the node having the IP address 10.0.4.1.
(iii) Run the simulation and check network connectivity by using the ping command to reach any host from any other. If you have any problem in reaching full connectivity, you may use the “ip route show” command in the routers to check the routing information that the router holds and add appropriate commands to the static routing table.
©2022, Faculty of IT, Monash University
Activity 2: Use DHCP to assign IP addresses to the PCs in the LANs. Configure and enable DHCP server applications in the routers and the DHCP client application in the PCs. Use the “ifconfig” command at the command prompt to check PC IP configurations.
Remove the IP addresses from the clients and the servers. We will use DHCP to assign IP addresses to these hosts. Company-A and Company-B routers will be configured to act as
DHCP servers.
(i) Configure DHCP servers in the company-A and company-B routers using the IP addressing scheme given in the activity 1. You can use the DHCP server configuration example given below as a guideline.
subnet 10.0.4.0 netmask 255.255.255.0 {
range 10.0.4.127 10.0.4.254;
default-lease-time 600; option routers 10.0.4.2;
(ii) Enable DHCP client service on servers and clients.
(iii) Run the simulation and check the clients’ and servers’ IP configuration using
“ifconfig” command in the command prompt. You may check network connectivity by using the ping command to reach any host from any other.
©2022, Faculty of IT, Monash University
Extra theory questions try on your own time:
8. Can two hosts in two different networks have the same link-layer address (MAC address)?
The answer is theoretically yes. A link-layer address has a local jurisdiction. This means that two hosts in different networks can have the same link-layer address, although this does not occur today because each NIC has a unique MAC address. The Ethernet address is 6 bytes (48 bits), normally written in hexadecimal notation, with a colon between the bytes. For example, the following shows an Ethernet MAC address: 4A:30:10:21:10:1A.
4A:30:10:00:00:00 ====> 4A:30:10:FF:FF:FF
The maximum devices for this prefix is 224 combinations = 16777216, 16-million possible devices, This means that the manufacturer can use this prefix to produce this amount of devices, but it doesn’t mean that he already manufactured them all or he had a plan to do. And if This Manufacturer used all possible devices for this prefix he had to buy a new prefix from the IEEE to manufacture extra devices.
9. Do we need a multiple access protocol when we use the DSL service provided by the telephone company to access the Internet? Why?
We do NOT need a multiple access protocol in this case. The DSL provides a dedicated point-to-point connection to the telephone exchange office.
10. Why is there no need for CSMA/CD on a full-duplex Ethernet LAN?
In a full-duplex Ethernet, each station is connected to the switch and the media is divided into two channels for sending and receiving. No two stations compete to access the channels; each channel is dedicated.
11. How is the preamble field different from the SFD (Start Frame Delimiter) field in an Ethernet frame?
©2022, Faculty of IT, Monash University
The preamble is a 56-bit field (101010……….10) that provides an alert and timing pulse. It is added to the frame at the physical layer and is not formally part of the frame. SFD (Start Frame Delimiter, flag 10101011) is a one-byte field that serves as a flag.
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