tasks
1. Identify all protocols related to the frames and
Ans - name all the protocals you find under each of the frames , which are as folllows :
a.Ehternet II (2)
b.hTTP
c.Internet protocal
d.Transmission protocal
e.User diagram protocal
f.smb
g.microsoft windows browser protocal
a. Using Wikipedia give a one-sentence description of each protocol you can find in
the recorded frames.
b.hTTP - what is this and where it is used, as an example - http is used in web, ftp for file transfer protocal
c.Internet protocal - The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP established Internet by routing and conveying messages over the network boundries.
d.Transmission protocal - The Transmission Control Protocol (TCP) is one of the core protocols of the Internet protocol suite (IP), and is so common that the entire suite is often called TCP/IP. TCP provides reliable, ordered and error-checked delivery of a stream of octets between programs running on computers connected to a local area network, intranet or the public Internet. Keeping track of the data/package sent by IP on the internet.
e.User diagram protocal -The User Datagram Protocol (UDP) is one of the core members of the Internet protocol suite (the set of network protocols used for the Internet)
. With UDP, computer applications can send messages, in this case referred to as datagrams,
to other hosts on an Internet Protocol (IP) network without prior communications to set up special transmission channels or data paths.
b. Expand the Ethernet II frames, and for each determine the value of the “Type”
field. What do these “Type” values mean?
IPV4 IPV6 explained
2. Identify, in all recorded Ethernet II frames, different source (Src) and destination (Dst)
MAC (physical) addresses.
a. How many different addresses have you found?
b. Give their hexadecimal and textual interpretation wherever available.
c. Explain why some addresses are repeated over and over again.
3. What is the shortest and longest Ethernet frame r
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Knowledge Base :
IP - IP PROTOCOL DEALS WITH ROUTER, HELPS TWO COMPUTERS TO CONNECT, ITS A ROUTABLE PROTOCAL,
TCP - Tramsmission Control Protocol
If you are connected to a non routable network, then all the computer is connceted to which is a risk.
With IP you can seperate comoputers and then with router you can put a boundary and goes to a sub protocol / sub network. Sub networks using routers are accessable using routable protocol (IP).
IP - is about routing information, communication. when computers are connected / found they starts communication.....here TCP comes in to say what protocol should be used for communication.
Wndowing...is the process by which with the client computer sends the data to the other pc.
cpmputer sends packets in groups.
Computer 1 sends packet 1 to compouter 2. Computer 2 sends ack to computer 1.
Once that is received, comp 1 sends 2 packets to comp 2.
comp2 says - i received packet 3.
comp1 says - i m gonna send packet 4,5,6,7 (it doubles everytime)
comp2 says - i got packet 7!
as long as this keeps happenning, comp1 starts sending double chuncks of information
When it gets to 128 packets and something happens and data gets messed up. Comp 2 only receives only 2 of those in order. THen comp 2 will say, the last packet i recveid was 1023.
Comp 1 will go back and send 1023rd packet
comp 2 says i received 1023rd packet
comp 1 then sends two and so on.....repeates the cycle
Exanping the window and closing that back again.....
small increaments and huge increaments
Why windowing is huge problem...real time communication has to happen real time --IP4 could cause problem with thsi windowing process.
1,2,4,,8 packets are not enough to support a real time communication process.
Ip connects two computers
TCP contorls the transmission once computers are connected.
TCP takes place at the transport layer.
Every device needs an IP address in the network.
Subnet mask is a way to segment a network so that any other computer can not access or could connect to each other. Subnet mask takes care of this.
Default gateway- is the router for the sub network you are on.
Lets say your pc is looking for a website, it will first to to the local network. if it cant find that, it will go to the default gateway. Then to router and the router will direct it to get the website you are looking for.
when my comp looks for www.cnn.com it actually looks for the ip address.
DNS (domain name server) comes in to the pay here.
www.cnn.com = 123.12.124.12
my computer talks to DNS server and DNS tells to my comp , cnn.com is www.cnn.com = 123.12.124.12
then my pc looks for 123.12.124.12 in the loacl network, if it cant find that it goes to the default gateway to look for the IP address.
Domain name > DNS Server > tells the ip address > computer then looks for the website using the IP address
DHCP - dynamic host control protocol
Without an IP address a comp cant do anything.
Static IP address, Dynamic address.
TCP IP IPV4
when computers are communication using TCP IP, data are transmitted in chunks.
Dynamic IP address - means when the pc connects to the net work it will call out DHCP server, DHCP server will give your pc an IP address , DNS server and all the related things to connect in Network with other clients and servers.
DHCP process - pc > calls out > i need an ip address > DHCP > 192.458.125.12 > what is the default gate way > what is the dns server >
DHCP server will give all this to your pc with a lease time, which will say for how long your pc can have the dynamic IP address.
lets say its 4 days.
half way through your pc tries to renew the lease automatically.
DHCP says, no problems
The lease is renewed for anoher 4 days.
Then again PC contact DHCP......so on.
If your computer cant contact before the half life, DHCP waits for the rest half of the time / lease period.
50% mark...
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PORTS - Different ports get used for diff purposes -
FTP 21 port no
SMPT 25
DNS 53
Http 80
POP3 110
https 443
Remote port 8080
Wire Shark -
Query:
ip.dst == 192.168.0.195 (my ip add or my friends)
ip.src == 192.168.0.195
APPLY
More query:
tcp port == 80
If a virus is designed for a port , say 7124 you go :
tcp port == 7124 - if you find something - good luck as you are attacked by the virus, lol
if nothing, you are fine
This is how you track down whats happening in the network
Purpose of IP and MAC explained
Purpose of IP and Merc
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FIT5135 Data Communications
Review Questions and Lab Preparation – V1.1
Lecture Topic: Data Link Layer
Review Questions
Use these questions to review the important material from the Topic Notes and chapter 4 of the prescribed textbook.
The review should take place in your own time. Where possible you should work with your colleagues.
You can discuss your answers with your tutor in the week 5 tutorial
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1. What are the functions of the data link layer?
The Data Link layer performs a number of separate activities, including:
Data Link Layer Functions
The following are the key tasks performed at the data link layer:
Logical Link Control (LLC): Logical link control refers to the functions required for the establishment and control of logical links between local devices on a network. As mentioned above, this is usually considered a DLL sublayer; it provides services to the network layer above it and hides the rest of the details of the data link layer to allow different technologies to work seamlessly with the higher layers. Most local area networking technologies use the IEEE 802.2 LLC protocol.
Media Access Control (MAC): This refers to the procedures used by devices to control access to the network medium. Since many networks use a shared medium (such as a single network cable, or a series of cables that are electrically connected into a single virtual medium) it is necessary to have rules for managing the medium to avoid conflicts. For example. Ethernet uses the CSMA/CD method of media access control, while Token Ring uses token passing.
Data Framing: The data link layer is responsible for the final encapsulation of higher-level messages into frames that are sent over the network at the physical layer.
Addressing: The data link layer is the lowest layer in the OSI model that is concerned with addressing: labeling information with a particular destination location. Each device on a network has a unique number, usually called a hardware address or MAC address, that is used by the data link layer protocol to ensure that data intended for a specific machine gets to it properly.
Error Detection and Handling: The data link layer handles errors that occur at the lower levels of the network stack. For example, a cyclic redundancy check (CRC) field is often employed to allow the station receiving data to detect if it was received correctly.
Source
2. What is media access control and why is it important?
MAC addresses are required to make a local Ethernet (or wifi) network function. They allow a network device to attract the attention of a single directly connected device, even though the physical connection is shared. This can be important when thousands of devices are connected together within a single organisation. They serve no function on the wider internet.
Media Access Control address (MAC address) is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification
MAC address is a unique number which is necessary for communication between computers in network.
Media Access Control and is a unique identifier for your network card/interface, aka the "MAC address". These addresses are important because you can configure other devices, like a wireless router, to only allow network interfaces with specific MAC addresses to connect.
This is one way to protect your home wireless network from being used by the neighbors but it is, of course, not foolproof. There are tools you can use to spoof a MAC address, so it's not 100% effective, but its a pretty good start for home networks. There is a link below with more technical info re: MAC addresses.
IP address is like mobile PHONE number(Can change and will contain only numbers)
MAC address is like mobile EMI number(will be fixed and contains alphabets and numbers)
According to IEEE Std 802-2001 section 6.2.3 "MAC sublayer", the primary functions performed by the MAC layer are:[1]
*Frame delimiting and recognition
*Addressing of destination stations (both as individual stations and as groups of stations)
*Conveyance of source-station addressing information
*Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sublayer
*Protection against errors, generally by means of generating and checking frame check sequences
*Control of access to the physical transmission medium
Source
3. Under what conditions is media access control unimportant?
4. Compare and contrast roll call polling, hub polling (or token passing), and contention.
5. Which is better, controlled access or contention? Explain.
6. Define two fundamental types of errors.
7. Discuss the distribution of errors on a transmission link.
8. Is there any difference in the error rates of lower speed lines and of higher speed lines?
9. Briefly define noise.
10. Describe four types of noise. Which is likely to pose the greatest problem to network managers? .
11. How do amplifiers differ from repeaters?
12. What are three ways of reducing errors and the types of noise they affect?
13. Describe three approaches to detecting errors, including how they work, the probability of detecting an error, and any other benefits or limitations.
14. Briefly describe how even parity and odd parity work.
15. Briefly describe how checksum works.
16. How does cyclical redundancy checking (CRC) work?
17. How does forward error correction work? How is it different from other error correction methods?
18. Under what circumstances is forward error correction desirable?
19. Using diagrams for illustration compare and contrast stop-and-wait ARQ and continuous ARQ.
20. Describe the frame layouts for HDLC, Ethernet, and PPP.
21. What is transmission efficiency?
22. What is meant by the term “overhead bits’?
23. Are stop bits necessary in asynchronous transmission? Explain using a diagram.
24. Under what conditions does a data link layer protocol need an address?
25. Are large frame sizes better than small frame sizes? Discuss.
26. What media access control technique does your tutorial class use?
27. Show how the word “Hi” would be sent using asynchronous transmission using even parity (make assumptions about the bit patterns needed). Show how it would be sent using Ethernet.
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