open system interconnection in computer network

open system interconnection in computer network

1. Network+ Guide to Networks
5
th
Edition
Chapter 2
Networking Standards and the OSI
Model

2. Figure 2.1 Flow of data through the OSI model

3. Mnemonics for the OSI Model
•Bottom Up
–Please
–Do
–Not
–Throw
–Sausage
–Pizza
–Away
•Top Down
–All
–People
–Seem
–To
–Need
–Data
–Processing

4. Application Layer
•Top (seventh) OSI model layer
•No software applications
•Protocol functions
–Facilitates communication
•Between software applications and lower-layer network
services
–Network interprets application request
–Application interprets data sent from network

5. Presentation Layer
•Protocol functions
–Accept Application layer data
–Formats data to make it understandable to different
applications and hosts
•Examples
–Text encoding methods ASCII and ANSI
–Compression methods like JPEG and MP3
–Data encryption and decryption

6. Session Layer
•Protocol functions
–Coordinate and maintain communications between two nodes
•Session
–Connection for ongoing data exchange between two parties
•Example: between Web browser client and Web server
•Functions
–Establishing and keeping alive communications link
•For session duration
–Determining if communications ended
•Determining where to restart transmission
–Terminating communications

7. Transport Layer
•Protocol functions
–Accept data from Session layer
–Provides flow control, segmentation, and error
control
•Primary Transport Layer Protocols: TCP and UDP

8. Transport Layer
•TCP
•Connection-oriented
–Establishes a connection before transmitting data
–Three-way handshake
SYN
SYN/ACK
ACK

9. Transport Layer
•TCP
–Require acknowledgements from receiver to ensure
data was received correctly
–Checksum
•Unique character string allowing receiving node to
determine if arriving data unit exactly matches data unit
sent by source
•Ensures data integrity
Send data, wait for ACK
ACK
Send more data, wait for ACK

10. Transport Layer
•UDP: A connectionless protocol
–Do not establish connection with another node before
transmitting data—no handshake
–Make no effort to ensure data is delivered free of
errors
–Faster than connection-oriented protocol
–Useful when data must be transferred quickly, such as
streaming music or video

11. Transport Layer
•Segmentation
–Breaking large data units received from Session layer
into multiple smaller units called segments
–Increases data transmission efficiency
•MTU (maximum transmission unit)
–Largest data unit network will carry
–Ethernet default: 1500 bytes
–Discovery routine used to determine MTU

12. Transport Layer (cont’d.)
•Reassembly
–Process of reconstructing segmented data units
•Sequencing
–Method of identifying segments belonging to the
same group of subdivided data

13. Transport Layer (cont’d.)
Figure 2-2 Segmentation and reassembly

14. Network Layer
•Packet formation
–Transport layer segment is encapsulated by a Network
layer packet
•Network layer adds logical addressing information—IP
address
•Routing
–Determine path from point A on one network to point B
on another network
•Routing considerations
–Delivery priorities, network congestion, quality of
service, cost of alternative routes

15. Network Layer
•Common Network layer protocol
–IP (Internet Protocol)
•Fragmentation
–Network layer protocol (IP) subdivides Transport layer
segments received into smaller packets
–This is usually avoided by adjusting the Maximum
Segment Size in the Transport layer, because it
makes data transfer inefficient
•Link Ch 2e

16. Data Link Layer
•Function of protocols
–Divide data received into distinct frames for
transmission in Physical layer
–Add Physical address to the frame: MAC addresses
like 00-30-48-82-11-BD
•Frame
–Structured package for moving data
•Includes raw data (payload), sender’s and receiver’s
physical addresses, error checking and control
information

17. Data Link Layer (cont’d.)
•Frames may be damaged as they pass through the
Physical layer, so the Data Link layer has error-
checking
–Error checking
•Frame check sequence
•CRC (cyclic redundancy check)
•Possible glut of communication requests
–Data Link layer controls flow of information
•Allows NIC to process data without error

18. Data Link Layer (cont’d.)
•Two Data Link layer sublayers
–LLC (Logical Link Control) sublayer
–MAC (Media Access Control) sublayer
•MAC address components
–Block ID
•Six-character sequence unique to each vendor
–Device ID
•Six-character number added at vendor’s factory
•MAC addresses frequently depicted in hexadecimal
format

19. Example of MAC Address
•Whole MAC address: 00-30-48-82-11-BD
–Block ID
•00-30-48
•Identifies the vendor
–Device ID
•82-11-BD
•Different for each NIC from the same vendor
•If two NICs have the same MAC address, they have
problems networking
–This can happen with cheaply made refurbished NICs,
or with copied virtual machines

20. Data Link Layer (cont’d.)
Figure 2-5 The Data Link layer and its sublayers

21. Data Link Layer (cont’d.)
Figure 2-6 A NIC’s Mac address

22. Finding Your MAC Address
•Start, CMD, Enter
•IPCONFIG /ALL
•Scroll up to see the first entry
MAC Address (also
called "Physical
Address")
IP Address

23. Physical Layer
•Functions of protocols
–Accept frames from Data Link layer
–Generate signals as changes in voltage at the NIC
•Copper transmission medium
–Signals issued as voltage
•Fiber-optic cable transmission medium
–Signals issued as light pulses
•Wireless transmission medium
–Signals issued as electromagnetic waves

24. Physical Layer (cont’d.)
•Physical layer protocols responsibility when
receiving data
–Detect and accept signals
–Pass on to Data Link layer
–Set data transmission rate
•Devices operating at Physical layer
–Hubs and repeaters
•NICs operate at both Physical layer and Data Link
layers

25. Applying the OSI Model
Table 2-1 Functions of the OSI layers

26. iClicker QuestionsiClicker Questions

27. Which OSI layer creates electrical Which OSI layer creates electrical
signals which travel along an Ethernet signals which travel along an Ethernet
cable?cable?
A.Session, Presentation, or Application
B.Transport
C.Network
D.Data Link
E.Physical
1 of 5

28. Which OSI layer tears down a Which OSI layer tears down a
connection after a period of inactivity?connection after a period of inactivity?
A.Application
B.Presentation
C.Session
D.Transport
E.Network, Data Link, or Physical
2 of 5

29. Which OSI layer encrypts and decrypts Which OSI layer encrypts and decrypts
data sent with secure protocols like data sent with secure protocols like
HTTPS?HTTPS?
A.Session, Presentation, or Application
B.Transport
C.Network
D.Data Link
E.Physical
3 of 5

30. Which OSI layer assigns addresses likeWhich OSI layer assigns addresses like
00-50-56-C0-00-0100-50-56-C0-00-01
to the data?to the data?
A.Session, Presentation, or Application
B.Transport
C.Network
D.Data Link
E.Physical
4 of 5

31. Which OSI layer assigns addresses like Which OSI layer assigns addresses like
147.144.51.101147.144.51.101
to the data?to the data?
A.Session, Presentation, or Application
B.Transport
C.Network
D.Data Link
E.Physical
5 of 5

32. iClicker QuestionsiClicker Questions
Review

33. Which item below is a MAC Which item below is a MAC
address?address?
A.147.144.1.2
B.94112
C.1005HA
D.00-12-11-XY-9Q-01
E.00-11-15-A3-B2-2E
1 of 5

34. Which OSI layer is also called Which OSI layer is also called
Layer 2?Layer 2?
A.Session, Presentation, or Application
B.Physical
C.Network
D.Data Link
E.Transport
2 of 5

35. Which OSI layer routes packets Which OSI layer routes packets
across the Internet?across the Internet?
A.Layer 5, 6 or 7
B.Layer 4
C.Layer 3
D.Layer 2
E.Layer 1
3 of 5

36. Which OSI layer maintains a list of Which OSI layer maintains a list of
remote servers that your computer is remote servers that your computer is
currently connected to?currently connected to?
A.Layer 5, 6 or 7
B.Layer 4
C.Layer 3
D.Layer 2
E.Layer 1
4 of 5

37. Which OSI layer sends radio Which OSI layer sends radio
signals out your Wi-Fi signals out your Wi-Fi
Interface?Interface?
A.Session, Presentation, or Application
B.Transport
C.Network
D.Data Link
E.Physical
5 of 5