ch2_v1Computer Networks engineering notes.ppt

Very good and detaiped notes on computer network for college semester exams semester 5.

1. 2.1
Chapter 2
Network Models
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2. 2.2
2-1 LAYERED TASKS
Weusetheconceptoflayersinourdailylife.Asan
example,letusconsidertwofriendswhocommunicate
throughpostalmail.Theprocessofsendingalettertoa
friendwouldbecomplexiftherewerenoservices
availablefromthepostoffice.
Sender, Receiver, and Carrier
Hierarchy
Topics discussed in this section:

3. 2.3
Figure 2.1 Tasks involved in sending a letter

4. 2.4
2-2 THE OSI MODEL
Establishedin1947,theInternationalStandards
Organization(ISO)isamultinationalbodydedicatedto
worldwideagreementoninternationalstandards.AnISO
standardthatcoversallaspectsofnetwork
communicationsistheOpenSystemsInterconnection
(OSI)model.Itwasfirstintroducedinthelate1970s.
Layered Architecture
Peer-to-Peer Processes
Encapsulation
Topics discussed in this section:

5. 2.5
ISO is the organization.
OSI is the model.
Note

6. 2.6
Figure 2.2 Seven layers of the OSI model

7. 2.7
Figure 2.3 The interaction between layers in the OSI model

8. 2.8
Figure 2.4 An exchange using the OSI model

9. 2.9
2-3 LAYERS IN THE OSI MODEL
Inthissectionwebrieflydescribethefunctionsofeach
layerintheOSImodel.
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
Topics discussed in this section:

10. 2.10
Figure 2.5 Physical layer

11. 2.11
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note

12. 2.12
Figure 2.6 Data link layer

13. 2.13
The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

14. 2.14
Figure 2.7 Hop-to-hop delivery

15. 2.15
Figure 2.8 Network layer

16. 2.16
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note

17. 2.17
Figure 2.9 Source-to-destination delivery

18. 2.18
Figure 2.10 Transport layer

19. 2.19
The transport layer is responsible for the delivery
of a message from one process to another.
Note

20. 2.20
Figure 2.11 Reliable process-to-process delivery of a message

21. 2.21
Figure 2.12 Session layer

22. 2.22
The session layer is responsible for dialog
control and synchronization.
Note

23. 2.23
Figure 2.13 Presentation layer

24. 2.24
The presentation layer is responsible for translation,
compression, and encryption.
Note

25. 2.25
Figure 2.14 Application layer

26. 2.26
The application layer is responsible for
providing services to the user.
Note

27. 2.27
Figure 2.15 Summary of layers

28. 2.28
2-4 TCP/IP PROTOCOL SUITE
ThelayersintheTCP/IPprotocolsuitedonotexactly
matchthoseintheOSImodel.TheoriginalTCP/IP
protocolsuitewasdefinedashavingfourlayers:host-to-
network,internet,transport,andapplication.However,
whenTCP/IPiscomparedtoOSI,wecansaythatthe
TCP/IPprotocolsuiteismadeoffivelayers:physical,
datalink,network,transport,andapplication.
Physical and Data Link Layers
Network Layer
Transport Layer
Application Layer
Topics discussed in this section:

29. 2.29
Figure 2.16 TCP/IP and OSI model

30. 2.30
2-5 ADDRESSING
Fourlevelsofaddressesareusedinaninternetemploying
theTCP/IPprotocols:physical,logical,port,andspecific.
Physical Addresses
Logical Addresses
Port Addresses
Specific Addresses
Topics discussed in this section:

31. 2.31
Figure 2.17 Addresses in TCP/IP

32. 2.32
Figure 2.18 Relationship of layers and addresses in TCP/IP

33. 2.33
InFigure2.19anodewithphysicaladdress10sendsa
frametoanodewithphysicaladdress87.Thetwonodes
areconnectedbyalink(bustopologyLAN).Asthe
figureshows,thecomputerwithphysicaladdress10is
thesender,andthecomputerwithphysicaladdress87is
thereceiver.
Example 2.1

34. 2.34
Figure 2.19 Physical addresses

35. 2.35
Mostlocal-areanetworksusea48-bit(6-byte)physical
addresswrittenas12hexadecimaldigits;everybyte(2
hexadecimaldigits)isseparatedbyacolon,asshown
below:
Example 2.2
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.

36. 2.36
Figure2.20showsapartofaninternetwithtworouters
connectingthreeLANs.Eachdevice(computeror
router)hasapairofaddresses(logicalandphysical)for
eachconnection.Inthiscase,eachcomputeris
connectedtoonlyonelinkandthereforehasonlyone
pairofaddresses.Eachrouter,however,isconnectedto
threenetworks(onlytwoareshowninthefigure).So
eachrouterhasthreepairsofaddresses,oneforeach
connection.
Example 2.3

37. 2.37
Figure 2.20 IP addresses

38. 2.38
Figure2.21showstwocomputerscommunicatingviathe
Internet.Thesendingcomputerisrunningthree
processesatthistimewithportaddressesa,b,andc.The
receivingcomputerisrunningtwoprocessesatthistime
withportaddressesjandk.Processainthesending
computerneedstocommunicatewithprocessjinthe
receivingcomputer.Notethatalthoughphysical
addresseschangefromhoptohop,logicalandport
addressesremainthesamefromthesourceto
destination.
Example 2.4

39. 2.39
Figure 2.21 Port addresses

40. 2.40
The physical addresses will change from hop to hop,
but the logical addresses usually remain the same.
Note

41. 2.41
Example 2.5
Aportaddressisa16-bitaddressrepresentedbyone
decimalnumberasshown.
753
A 16-bit port address represented
as one single number.