Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

COURSES NETWORK+ > SECTION 3 : OSI MODEL > Flashcards

SECTION 3 : OSI MODEL Flashcards

1
Q

What is the acronym of OSI

A

Open system Interconnections Model.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Difference between OSI Model and TCP/IP model ?

A

The TCP/IP model is closer to reality while the OSI model is mostly theoretical and could be applied to every networks.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the order of the 7 layers ?

A

From bottom to top :
Physical
Data link
Network
Transport
Session
Presentation
Application
(please do not throw sausage pizza away)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How do we call data when it comes to layers ?

A

7 - 6 - 5 : Data
4 : Segments
3 : packets
2 : frames
1 : bits
(Do Some People Fear Birthday)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Sum up briefly the physical layer

A

Where transmission of bits across the notwork occurs and includes physical and electrical network characteristics

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is transition modulation ?

A
  1. One way to electrically or optically represent a binary 1 or 0 is to use the transition between a voltage level (for example, going from a state of no voltage to a state of voltage, or vice versa, on a copper cable) or the transition of having light or no light on a fiber optic cable to represent a binary 1.
  2. Similarly, a binary 0 is represented by having no transition in a voltage level or light level from one time period to the next. This approach of representing binary digits is called state transition modulation.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain bits representation in fiber

A

Light on = 1
Light off = 0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the two main wiring standards operating at layer 1 ?

A

TIA/EIA-568A and TIA/EIA-568B

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is communication synchronized ?

A

It is a layer 1 issue. Asynchronously and synchronously.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does synchronous communication mean ?

A

Uses à reference clock to coordinate transmissions between receivers and senders.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How can the bandwidth of the cable be utilized ?

A

There are two ways :
Broadband
Baseband

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What are thé différence between broadband and baseband ?

A

Broadband : divides bandwidth into separate Channel (TV cable -200 channels).
Baseband : use all available frequencies on a medium to transmit data all of the time. Ex: telephone. Baseband uses a référence clock. That’s why we can’t have two phonecalls. A wire home ethernet Network is the same they use all the frequency of a cable.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How can we get more out of a limited Network?

A

Different mechanisms :
TDM - time division multiplexing | each session takes a turn, using Time slots, to Share the medium between all users.
STDM - StatTDM | dynamically allocate the time based on an as-needed basis. More efficient.
FDM - Frequency division miltiplexing | divides the medium into channels based on frequencies and each session is teansmitted over a different Channel. Similar to broadband !!

Multiplexing is getting more out of a limited network. It allows multiple people to use a baseband connections at the sametime

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the devices that operate at layer 1 ?

A

Cables (ethernet, fiber and so on)
Wireless things (Bluetooth, NFC, WIFI)
Infrastructure devices (hub, WAP, Mediaconverter)
Layer 1 devices only repeat bits.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Define the basic principle of layer 2 ?

A

This layer packages up the bits into frames and transmits those frames on the network.
Layer 2 devices view networks logically.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is a MAC adress ?

A

Physical adressing system of a device which operates on a logical topology. It uses a 48 bit physical adressing to any network interface card (NIC). The first half bits will identify the producer. Thé other is a unique value.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is logical link control (LLC)?

A
  1. Provides connection services and allows acknowledgment of receipt of messages.
  2. The most basic form of flow control.
  3. It also provides basic error control functions (data frame not received, corrupted data frames and so on). Since we are talking about 1 and 0, it will add up and the last bit must be even or odd to determine if it was good or not.

Operates at layer 2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How is communication synchronized across layer 2 ?

A

Isochronous : network devices use a common reference clock and create time slots for transmission (cf. Multiplexing).

Synchronous : network devices agree on clocking method to indicate beginning and end of frames and can use control characters.

Asynchronous : they reference their own internal clocks and uses start and stop bits.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the devices of layer 2 ?

A

Switches that can learn ports and devices. NIC and bridges too.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Basic principle of layer 3?

A

Forwards traffic with logical adresses. (Routing).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What does switching mean ?

A

It means routing (layer3).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How should data be forwarded or routed at layer 3?

A
  • packet switching
  • circuit switching
  • message switching
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is packet switching ?

A

Thé most commonly used.

Data is divides into packets and then forwarded. Packets will be switched from place to place. Every time it can get another route.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is circuit switching ?

A

Dedicated communication link is established between two devices.

A phone call creates a temporary connection that all data uses.

For thé entire phone call, it uses the same paru.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is message switching ?

A

Data is divided into messages which may be stored and then forwarded.

Similar to packet switching but it can be stored.

It operates at layer 3.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is route discovery and selection ?

A

Manually configured as a static route or dynamically through a routing protocol.

Routers will maintain a routing table. Using RIP, OSPF or EIGRP. Routing protocols help us décide how data will flow.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Principle of dynamic routing ?

A

Routers consistantly talk to each other to find the best path.

28
Q

What are connection services ?

A

Augment layer 2 connection services to imprévue reliability.

More flow control and packet reordering allows to reorder the packets.

29
Q

What is ICMP ?

A

Sends error messages and operational information to an IP destination. Thé most used message is Ping. Ping tells if the packets were received and in How much time. Used for troubleshooting.

Traceroute is more or les the same but uses many ping to locate the servers.

30
Q

What are the devices that operate at layer 3?

A
  • routers and multilayer switches.
  • multilayer combines switch of layer 2 and routers of layer 3. Multilayerswitch is considérered a layer 3 device.
  • ICMP
  • Ipv4
31
Q

What is the data type of the transport layer ?

A

We deal with segments and datagram.

32
Q

What are the two protocols of the layer 4?

A

TCP : connection oriented protocol that is a reliable way to transport segments accros thé network.

UDP :

33
Q

Explain TCP handshake.

A

The client will send a syn packet then thé server will send a syn+ack and the client will send back an ack. The transmission of data will then begin. It’s like certified mail.

34
Q

Explain UDP.

A

Connectionless protocol that is an unreliable way to transport segments across thé Network. If we use UDP it’s datagram. If the datagrams are dropped thé sender is unaware. Good for audio and vidéo streaming. Increase the performance.

35
Q

Compare TCP and UDP

A

Reliable (three way handshake) \ unreliable

Connection-oriented \ connectionless

Segment retransmission and flow control through windowing \ no windowing

Segment sequencing \ no sequencing (if they arrive in different order it will be broadcasted so)

Acknowledge segments \ no acknowledgment

36
Q

What is windowing ?

A

Allows thé clients to adjust the amount of data in each segments.

Sends less data with decreased retransmissions.

For instance à download says 20 min remaining then five and so on. This is windowing. The window adjusts to send more segment according to the bandwidth.

Window opens up —> less segments with more data (it’s good)

We speed up and slow-down.

37
Q

What is buffering ?

A

Occurs when devices allocate memory to store segments if bdwt isn’t readily available.

Routers have a special memory and store segments for instance. If the network is congested it will keep information to send it later.

For instance if three routers send 210 MB/s to a router and if it can only send 50 mb there is a bottleneck. Router will keep in its buffer.

There is a possibility in some network (see picture). Some devices do not operate at their full capabilities.

38
Q

Layer 4 devices?

A

TCP and UDP.
Wan accelerator (?)
Load balancer and firewalls
If we block a port 80 over TCP it’s layer4.

39
Q

What is the session layer ? (L5)

A

Keeps conversations separate to prevent intermingling of data.

40
Q

What are the three phases of a session?

A
  1. Set Up
  2. Maintain
  3. Tear down
41
Q

What is session set up ?

A

Checking of user credentials and assigning numbers to sessions to help identify them.

42
Q

Maintain a session

A

Transferring data over and over again allows a session to be maintained.
If we have a break ==> reestablish connection (“can you repeat ? “)
Acknowledge receipt ==> “did you understand ?”

43
Q

Tear down session

A

Ending of a session after the transfer is done or when the other party disconnects.
When one party is not getting the information, the session is being torn down.

44
Q

Layer 5 devices ?

A

H.323 and NetBios

45
Q

What is H.323 ?

A

H.323 is used to set up, maintain and tear down voice and video connections. it operates over the RTP (real time protocol). ==> like facetime, skype or youtube.
RTP is related to streaming audio and streaming video.

46
Q

What is NetBIOS ?

A

Used to share files over a network. Windows uses it a lot.

47
Q

What is layer 6 ?

A

The presentation layer formats the data to be exchanged and secures that data with proper encryption. (data formatting and encryption). The presentation layer translates information in a way that the application layer understands. It also translates information from the application layer to the session layer.

48
Q

What is data formatting ?

A

Data is formatted by the computer to have compatibility between different devices.

ASCII for instance, or GIF or JPG, PNG and so on.

49
Q

What is ASCII ?

A

It ensures data is readable and provides proper data structure. It allows us to negotiate data transfer over layer 7.

50
Q

What is encryption ?

A

Used to scramble the data in transit to keep it secure from prying eyes and provide data confidentiality.

For instance TLS. It create an encrypted tunnel.

51
Q

What are layer 6 devices or protocols ?

A
  • Scripting languages
  • Standard text
  • Pictures
    -Movie files
  • ERncryption algorithms
52
Q

What is the Application layer ?

A

Provides application-level services where users communicate with the computer.
We talk about low level applications like file transfer or network transfer.

53
Q

What are application services ?

A

Application services are the things that unites communicating components from more than one network application. For instance POP3 or Imap are low level application but Microsoft Outlook is not.

54
Q

What is service advertisement ?

A

this is where application can send out announcements to other devices on the network to state the service they offer.
for instance a printer alerts that it can be used for printing.

55
Q

What are layer 7 devices ?

A

Email applications, web browsing, DNS, HTTP, Pop3 IMAP, FTP, FTPS, SFTP or TELNET and SSH.

56
Q

What is Wireshark ?

A

Wireshark allows to inspect packet in-depth. It is used for troubleshooting, forensics and pentest.

57
Q

What is encapsulation ?

A

Process of putting headers (and trailers) around the data.
if we move down the OSI layers from 7 to 1 we encapsulate. If we move up we decapsulate.

58
Q

What is protocol Data Unit ?

A

A single unit of information transmitted in a computer network.
In the real world we use PDUs to transmit data. They are called L7PDU or L4PDU. They follow the name of data used for every layers.

59
Q

what is the cinematic of encapsulation ?

A

We take the data from the application layer and wrap it with the headers of each layer. At layer 4 we add our source and destination ports. At layer 3 we add our source and destination IP addresses. At layer 2 we add our source and destination MAC addresses. At layer 1 we transmit our layer 2 frames as a series of 1 and 0. When it is received by the other device it will decapsulate by reading the ethernet header. If the destination MAC is correct it will decapsulate everything. Or else it will be sent to the default gateway. It can decapsulate the following header until the right host is found. The right host will decapsulate everything.

60
Q

What is the TCP header ?

A

It contains 20 bytes (source port, destination port, sequence number, acknowledgment number, control flags)

61
Q

What are the control flags of a TCP header ?

A

SYN : used to synchronize connection during the three-way handshake.
ACK : used during the handhsake but also used to acknowledge the successful receipt of packets.
FIN : tear down the virtual connections created by the handshake and the syn flags.
RST : used when a client or server receives a packet that was not expecting during the current connection.
PSH : Used to ensure data is given priority and is processed at the sending or receiving ends
URG: simiar to PSH and identifies incoming data as urgent. PSH is used by the sender. URG violates the packets priority order.

62
Q

What is the UDP header ?

A

smaller than TCP because it is a connectionless (8bit).
source port : same than TCP
destination pot : idem
length :
checksum : not a mandatory field but it can be used to provide some validation that the UDP data was well received.

63
Q

Where does ethernet header operate ?

A

Layer 2.
in the ethernet header, we find the destination and source MAC addresses, the EtherType and the VLAN tag (optional).
The Ethertype field is used to indicate which protocol is encapsulated in the payload of that frame.

64
Q

What is the minimum bytes for an ethernet payload ?

A

42 Bytes if VLANs are being used and 46 bytes if no VLANs are being used.

65
Q

What is the MTU ?

A

when you send a pyaload there is a maximum size. By default ethernet uses an MTU of 1500 bytes as a maximum. If you have a payload that is larger you need to use a jumbo frame larger than 1500 bytes.

COURSES NETWORK+ (7 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions