The OSI Model and the TCP/IP Protocol Suite 1 Example 1 Assum - PowerPoint PPT Presentation

The OSI Model and the TCP/IP Protocol Suite 1

Example 1 Assum Assume Mar aria ia an and Ann are are nei neighb hbors ors wi with th a lo lot of of comm common ideas eas. Howev However, er, Mar Maria ia sp speaks eaks only ly Sp Spanish ish, and and Ann nn spea speaks ks only ly En Engli lish sh. Sin ince both both hav have le learn arned ed the the sign sign la langu guage age in in their their ch childho ldhood, od, they they en enjo joy meetin meeting in in a cafe cafe a coupl couple of of days days per per we week ek and and exc excha hang nge the their ir ide deas as us using ng signs signs. Occasiona Occasionall lly, y, they they als lso use use a bili iling ngua ual dict dictionary ionary. Com Commun munica icati tion on is is face face to to face face and and Ha Happens in in one one layer as as shown wn in in the followi wing ng Figure re. 2

Example 2 No Now assume assume that that An Ann has has to to mov ove to to ano another ther tow town bec ecaus ause of of her er job job. Be Before fore she she mov moves, es, the the two two meet meet for for the the la last st time time in in the the same cafe sam cafe. Al Alth thou ough gh both oth are are sad, d, Mar Maria sur surprises prises Ann nn whe when sh she opens opens a packet acket th that at contains contains tw two smal small mac machines hines. The The first first mac machine hine can scan scan and and tran transform sform a let etter ter in in Eng Engli lish to to a secret secret co code de or or vice vice versa versa. Th The other other mach machine ne can can sca can and and tr trans nslate ate a lett etter er in in Span Spanis ish to to the the same same secr ecret et code code or or vice vice versa versa. An Ann takes takes the the first first mach machin ine; Mar Maria ia keeps eps the the sec econ ond on one. The The two two friends fr iends can can sti till commun communica icate te using using the the sec secret ret code, code, as as shown shown in in Figure. 3

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Topics Discussed in the Section  Hierarchy  Layer 0: Tranport the letter  Layer 1: drop in the mailbox  Layer 2: Translate to secret code  Layer 3: Write letter  Services  Sender site: uses the services of the layer below it  Receiver site: provide service to the layer above it 5

THE OSI MODEL Es Estab tablis lishe hed in in 19 1947, the the Int Inter erna nation tional al Sta Stand ndar ards ds Or Organ ganiza izatio tion (I (ISO) SO) is is a multi multinat nation ional al body body ded dedica icated ted to to wor world ldwide wide ag agre reem emen ent on on in inter ternati ational onal st stan anda dards ds. Almos Al most thr hree ee-fou fourth rths of of co coun untri tries es in in the the worl world are re repre re prese sente nted in in the the ISO SO. An An ISO SO sta standa ndard rd tha that cover covers al all as aspe pect cts of of ne networ twork co comm mmun unic icati ation ons is is the the Open Systems Interconnection (OSI) mod model el. It It was as first first intro rodu duce ced in in the late 1970 1970s. 6

The OSI model 7

OSI layers 8

Layered Architecture  Organization of the layers  Layer 1,2,3 --- network support layers  Layer 5,6,7 --- user support layers  Layer 4 --- link the two subgroups and ensure the format is compatible. 9

An exchange using the OSI model 10

Layered Architecture  Encapsulation:  The data part of a package at level N is carrying the whole packet (data + overhead) from level N+1 11

Physical Layer  Physical characteristics of interfaces and media  Representation of bits  Data rate  Synchronization of bits  Line configuration  Physical topology  Mesh topology; star topology; ring topology; bus topology  Transmission mode  Simplex mode; half-duplex mode; full-duplex mode 12

Note The physical layer is responsible for moving individual bits from one (node) to the next. 13

Data Link Layer  Framing  Physical addressing  Flow control  Error control  Access control 14

Network Layer  Logical addressing  Routing 15

Transport Layer  Service-point addressing  Segmentation and reassembly  Connection control  Flow control  Error control 16

Session Layer  Dialog control  Synchronization 17

Presentation Layer  Translation  Encryption  Compression 18

Application Layer  Network virtual terminal  File transfer, access, and management (FTAM)  E-mail services  Directory services 19

Summary of OSI Layers 20

TCP/IP PROTOCOL SUITE Th The TC TCP/IP P/IP pr protoco otocol su suite ite was as deve develo loped ed pr prior or to to the the OSI OSI mode odel. The Theref refore ore, the the lay layers ers in in the the TC TCP/I P/IP pr proto otoco col su suite ite do do not not match match ex exac actly tly with ith tho those se in in the the OSI SI mod model el. The The origi origina nal TCP TCP/IP /IP pr proto otoco col suite suite was was def define ined as as fou four so software ftware lay layers ers bui built lt upon upon th the ha hard rdwar are. Toda Today, y, ho howev wever er, TCP/IP TCP/IP is is tho thoug ught ht of of as as a fiv five-la layer yer mod odel el with ith the the lay ayer ers na named ed si simila milarly rly to to the ones ones in in the OSI SI model. 21

TCP/IP and OSI model 22

A private internet 23

Communication at the physical layer Source Destination Legend A R1 R3 R4 B Physical Physical layer layer Link 3 Link 6 Link 5 Link 1 011 ... 101 0 11 . . . 1 01 011 ... 101 011 ... 101 24

Note The unit of communication at the physical layer is a bit. 25

Communication at the data link layer Source Destination D Data H Header Legend A B R1 R3 R4 Data link Data link Physical Physical Link 6 Link 5 Link 1 Link 3 H2 D2 Frame D 2 F r a H m 2 e H2 D2 H2 D2 Frame Frame 26

Note The unit of communication at the data link layer is a frame. 27

Communication at the network layer Source Destination D Data H Header Legend A B R1 R3 R4 Network Network Data link Data link Physical Physical H3 D3 Datagram D3 H3 Datagram 28

Note The unit of communication at the network layer is a datagram. 29

Communication at transport layer A B Source Destination D Data H Header Legend Transport Transport R1 R3 R4 Network Network Data link Data link Physical Physical H4 D4 Segment H4 D4 Segment 30

Note The unit of communication at the transport layer is a segment, user datagram, or a packet, depending on the specific protocol used in this layer. 31

Communication at application layer A B Application Source Destination D Data H Header Application Legend Transport Transport R1 R3 R4 Network Network Data link Data link Physical Physical D5 D5 Message D5 D5 Message 32

Note The unit of communication at the application layer is a message. 33

ADDRESSING Fo Four ur le levels vels of of addr addres esse ses ar are used used in in an an inter interne net employ mploying ing the the TC TCP/I P/IP pro protoc tocols ols: phy physic sical al add addres ress, s, logic lo ical al add addre ress ss, po port rt address, address, and and ap appl plic icati ation on- sp spec ecifi ific add addre ress ss. Ea Each ch ad addr dres ess is is re relate ated to to a one one layer er in in the TC TCP/ P/IP archit hitec ecture re. 34

Addresses in the TCP/IP protocol suite 35

physical addresses 1 packet 87 10 Data 87 10 Data accepted 4 36

logical addresses 33 99 A P Data 20 10 A P Data 20 10 A P Data Physical addresses changed 95 66 A P Data 95 66 A P Data 33 99 A P Data Physical addresses changed 37

Note The physical addresses will change from hop to hop, but the logical addresses remain the same. 38

port numbers Sender Receiver A P Data Data a j Data a j Data A P a j Data A P a j Data H2 A P a j Data H2 A P a j Data Internet 39

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