Not for distribution to students Layered Standards ...CSIE/ycliaw/BDC/02_Layered.pdf · Not for distribution to students Not for distribution to students 13 25 Figure 2-19: OSI and

Not for distribution to students

Not for distribution to students 1

Layered StandardsArchitectures

Chapter 2

Panko’s Business Data Networks andTelecommunications, 5th editionCopyright 2005 Prentice-Hall

2

Breaking up large tasks into smaller tasks andassigning tasks to different individuals is common in allfields

Specialization in standards design (EEs for physicallayer, application specialists for application layer, etc.)

Simplification in standards design for individualstandards

If you change a standard at one layer, you do not haveto change standards at other layers

Why Layers



OSI, TCP/IP, and Other StandardsArchitectures

4

ISO/OSI Model

OSI(Open Systems Interface) Model :developed by ISO

International Organization for Standardization

Open system means thatit can communicate with any other systems thatfollows the specified standards (semantics,syntaxs, timing)

seven layers



5

ISO/OSI Model, Continued

第七層應用層

第六層展示層

第五層會議層

第四層傳輸層

第三層網路層

第二層資料連結層

第一層實體層

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HTTP, SMTP



7

ISO/OSI Model - Application Layer Downward

The application layer governs how two applications workwith each other, even if they are from different vendors

8

ISO/OSI Model - Presentation LayerDownward



9

ISO/OSI Model - Session LayerDownward

10

ISO/OSI Model - Transport LayerDownward



11

ISO/OSI Model - Network LayerDownward

12

ISO/OSI Model - Data Link LayerDownward



13

ISO/OSI Model - Physical LayerDownward and Upward

SerDes: Serialize and Deserialize

14

ISO/OSI Model - Data Link LayerUpward



15

ISO/OSI Model - Network LayerUpward

16

ISO/OSI Model - Transport LayerUpward



17

ISO/OSI Model - Session LayerUpward

18

ISO/OSI Model - Presentation LayerUpward



19

ISO/OSI Model - Application LayerUpward

20




21

TCP/IP Model

22

TCP/IP Model, Continued



23

OSI and TCP/IP

OSI TCP/IP

StandardsAgency(ies)

ISO (InternationalOrganization for Standardization)

ITU-T (InternationalTelecommunicationsUnion—TelecommunicationsStandards Sector)

IETF (InternetEngineering TaskForce)

24

OSI and TCP/IP, Continued

OSI TCP/IP

Dominance Nearly 100% at physical and datalink layers

70% to 80% at theInternet and transportlayers. Also strongat the application layer

Documents areCalled

Various Mostly RFCs (requestsfor comment)



25

Figure 2-19: OSI and TCP/IP, Continued

Do not confuse OSI (the architecture) with ISO(the organization)

The acronyms for ISO and ITU-T do not matchtheir names, but these are the official namesand acronyms

26

Figure 2-20: The Hybrid TCP/IP-OSIArchitecture

TCP/IP OSI Hybrid TCP/IP-OSI Broad Purpose

Application

Application

Presentation

Session

Application(Layer 5) Applications

Transport

Internet

Transport

Network

Transport (Layer 4)

Internet (Layer 3)Internetworking

Use OSI Standards Here

Data Link

Physical

Data Link (Layer 2)

Physical (Layer 1)

Communicationwithin a singleLAN or WAN



27

Figure 2-20: The Hybrid TCP/IP-OSIArchitecture, Continued

Notes:

The Hybrid TCP/IP-OSI Architecture is used on theInternet and dominates internal corporate networks

OSI standards are used almost universally at thephysical and data link layers (which governcommunication within individual networks)

TCP/IP is used for 70% to 80% of all corporatetraffic at the internet and transport layers and isused heavily at the application layer.

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Figure 2-7: TCP/IP-OSI Architecture

Device-deviceconnection

Physical (1)

Transmission across asingle network (LAN orWAN)

Frame delivery across anetwork

Data Link (2)

Packet delivery acrossan internet

Internet (3)

Transmission across aninternet

Host-hostcommunication

Transport (4)

Application-applicationinterworking

Application-applicationinterworking

Application (5)

General PurposeSpecific PurposeLayer



29

Figure 2-7: TCP/IP-OSI Architecture, Continued

Physical and Data Link Layer StandardsGovern Communication Through a SingleNetwork

LAN or WAN

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Physical Layer

Physical layer standards govern transmissionbetween adjacent devices connected by atransmission medium

Switch X1

Physical LinkA-X1

Host A



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Data Link Layer

Data link layer standards govern thetransmission of frames across a singlenetwork—typically by sending them throughseveral switches along the data link

Data link layer standards also govern frameorganization, timing constraints, andreliability

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Figure 2-8: Physical and Data Link LayerStandards

Host A

Mobile ClientStation

ServerStation

Switch

SwitchX2

Switch X1

Switch

Data LinkA-R1

Physical LinkA-X1

PhysicalLink

X1-X2

Router R1

PhysicalLink

X2-R13 Physical Link

1 Data Link2 Switches



33


Internet and Transport Layers

An internet is a group of networks connectedby routers so that any application on anyhost on any network can communicate withany application on any other host on anyother network

Internet and transport layer standardsgovern communication across an internetcomposed of two or more single networks

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Internet Layer

Internet layer standards govern thetransmission of packets across aninternet—typically by sending them throughseveral routers along the route

Internet layer standards also govern packetorganization, timing constraints, andreliability



35

Figure 2-9: Internet and Data Link LayerStandards

Host B

Host A

Network XNetwork Y

Network Z

R1

R2

Data Link A-R1

Data Link R2-B

DataLink

R1-R2Route A-B

3 Data Links: One per Network1 Route per Internet

36

Figure 2-9: Internet and Data Link LayerStandards, Continued

Host A

Mobile ClientStation

ServerStation

Switch

SwitchX2

SwitchX1

Switch

Data LinkA-R1

Router R1

PacketFrame X

Network X

RouteA-B

Details inNetwork X

Frame X Destination Addresses:Packet: Host B (Destination Host)

Frame: Router R1



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Router R1

Router R2

Packet

Frame Y

ToNetwork X

ToNetwork Z

Network Y

Data LinkR1-R2

RouteA-B

Details inNetwork Y

Frame Y Destination Addresses:Packet: Host B (Destination Host)

Frame: Router R2

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Host B

Mobile ClientStations

SwitchZ1

SwitchX2

SwitchZ2

Switch

Packet

Frame Z

Network Z

Router R2

Router

Data LinkR2-B

Details inNetwork Z

Frame Z Destination Addresses:Packet: Host B (Destination Host)

Frame: Host B



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Frames and Packets

In an internet with hosts separated by Nnetworks, there will be:

2 hosts

One route (between the two hosts)

N frames (one in each network)

N-1 routers (change frames between each pair ofnetworks)

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Transport Layer

Transport layer standards govern aspects ofend-to-end communication between two endhosts that are not handled by the data linklayer

These standards also allow hosts to worktogether even if the two computers are fromdifferent vendors and have different internaldesigns



41

Figure 2-10: Internet and Transport LayerStandards

Transport Layerend-to-end (host-to-host)

TCP is connection-oriented, reliable

Internet Layer(usually IP)

hop-by-hop (host-router or router-router)connectionless, unreliable

Router 1 Router 2 Router 3

Client PC Server

Data Link Layer

Data Link Layer Data Link Layer

Data Link Layer

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Application Layer

The application layer governs how twoapplications work with each other, even ifthey are from different vendors



43

Transport and Application Layer Standards

Transport Layerend-to-end (host-to-host)

(Client PC – Server)Client PC Server

App A App B App C App D

Application Layer(App B – App C)

Most hosts are multitasking machinesthat run multiple applications simultaneously.

Hosts need to communicate; So do pairs of applications

44

Figure 2-21: OSI Session Layer

Network orInternet

Client PC Server

Transport Layer

Session Layer(Manages a series of transactions)App

1App

2App

3App

4



45

Figure 2-21: OSI Session Layer, Continued

OSI Session LayerManages a series of transactions closely

If there is a connection break, only have toretransmit transactions since the last rollback point

TCP/IP Has No Session LayerThe few applications that need to managetransaction series closely provide their ownmechanisms

In HTTP, cookies provide continuity acrossapplications

46

Figure 2-22: OSI Presentation Layer

Presentation Layer(Transfer Syntax C)App 2

InternalSyntax A

App 3Internal

Syntax B

Presentation standards also includecompression standards and

data formatting standards (jpeg, etc.)



47

Figure 2-22: OSI Presentation Layer, Continued

OSI Presentation LayerTransfer syntax

Layer for application standards, such as jpeg

TCP/IP Has No Presentation LayerMIME at least allows the sender to indicate theformat of file delivered in a message

48

Other Major Standards Architectures

IPX/SPXUsed by older Novell NetWare file servers

Popular option for newer Novell NetWare fileservers

SNA (Systems Network Architecture)Used by IBM mainframe computers

AppleTalkUsed by Apple Macintoshes



Messages

50

Figure 2-1: How Standards GovernInteractions

StandardsGovern the Exchange ofMessages

Messages must begoverned by strict rules

Semantics

Syntax

Timing網路傳輸協定要素網路傳輸協定要素



51

Figure 2-1: How Standards GovernInteractions, Continued

Message Semantics (Meaning)

訊息所代表的意義

Only a few message types areallowed because computers do nothave the intelligence to handleopen-ended communication

In HTTP, request and responsemessages

52

Figure 2-2: Hypertext Transfer Protocol(HTTP) Interactions

Client PC Webserver

Browser WebserverApplication

1.HTTP Request Message

Asking for a File

2.HTTP Response Message

Delivering the File



53


Message Syntax (Organization)

訊息格式需事先制定

Rigidly structured

In HTTP, lines of text(Figure 2-3)

Most lines are of the form“Keyword: Information”

54

Figure 2-3: Syntax of HTTP Request andResponse Messages

[CRLF]Carriage return and line feed (starts a new line)

HTTP Request MessageGET /reports/project1/final.htm HTTP/1.1[CRLF]

Host: voyager.cba.Hawaii.edu[CRLF]



55

Figure 2-3: Syntax of HTTP Request andResponse Messages, Continued

HTTP Response MessageHTTP/1.1 200 OK[CRLF]

Date: Tuesday, 20-MAR-2004 18:32:15 GMT[CRLF]

Server: name of server software[CRLF]

MIME-version: 1.0[CRLF]

Content-type: text/plain[CRLF]

[CRLF]

File to be downloaded

56


Message Syntax (Organization)General Message Organization (Figure 2-4)

Primary components

Data Field (content to be delivered)

Header (everything before the data field)

Trailer (everything after the data field)

Header and trailer are further divided into fields



57

Figure 2-4: General Message Organization

Trailer Data Field

Header

OtherHeaderField

AddressField

Data Field

Message without a trailer

Message with a trailer

58

Figure 2-4: General Message Organization,Continued

Header

Message with only a header

e.g. TCP supervisory messages are pure headers



59


Message Timing Constraints

When may a process transmit? Atany time? Only when some eventhappens?

Turn-taking in conversations

In client/server computing, servercannot respond unless it receives arequest

Many more complex examples exist(for instance, in TCP later in thischapter)

Connection-Oriented andConnectionless Protocols



61

Figure 2-5: Connectionless andConnection-Oriented Protocols

Message(No Sequence Number)

Connectionless Protocol

A B

Message 1 (Seq. Num = A1)

Message 2 (Seq. Num = A2)

Close Connection

Connection-OrientedProtocol

Open ConnectionA B

Message 3 (Seq. Num B1)

62

Figure 2-5: Connectionless andConnection-Oriented Protocols, Continued

Client PCBrowser

WebserverWebserver Application

HTTP Request

No OpeningsNo Closings

Connectionless



63

Connection-Oriented

Open

Communication

Acknowledgement

Close

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Figure 2-6: Transmission Control Protocol(TCP) Session

1. SYN (Open)

2. SYN, ACK (1) (Acknowledgment of 1)

3. ACK (2)

Client PCTransport Process

WebserverTransport Process

Open(3)

TCP 3-Way Connection Open

Connection-Oriented



65

Figure 2-6: Transmission Control Protocol(TCP) Session, Continued

4. Data = HTTP Request

5. ACK (4)



CarryHTTPReq &Resp

(4)6. Data = HTTP Response

7. ACK (6)

Request-ResponseCycle for Data Transfer

66




CarryHTTPReq &Resp

(4)

8. Data = HTTP Request (Error)

9. Data = HTTP Request (No ACK so Retransmit)

10. ACK (9)

11. Data = HTTP Response

12. ACK (11)

Error Handling

timeout



67


If acknowledgements are not sent by thereceiver, the sender retransmits the TCPsegment

This gives reliability

Note: An ACK may be combined with the nextmessage if the next message is sent quicklyenough

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Close(4)

13. FIN (Close)

14. ACK (13)

15. FIN

16. ACK (15)

4-Way Close



Syntax Examples

70

Octets

Field lengths may be measured in octets

An octet is a group of eight bits

In computer science, an octet is called a byte

Octet



71

…

Figure 2-12: Ethernet Frame

Preamble (7 octets) 10101010 …

Start of Frame Delimiter(1 octet) 10101011

Destination Ethernet (MAC) Address (48 bits)

Source Ethernet (MAC) Address (48 bits)

Length (2 octets) Length of Data Field

72

Figure 2-12: Ethernet Frame, Continued

Data Field(variablelength)

PAD (added if data field < 46 octets)

Frame Check Sequence (32 bits)

LLC Subheader(usually 7 octets)

UsuallyIP Packet



73


> 46 bytes

≥ 64 bytes, ≤ 1500 bytes

74


Sender computes the frame check sequencefield value based on contents of other fields

Receiver recomputes the field value

If the values match, there have been no errors

If the values do not match, there is an errorThe receiver simply discards the frame

Unreliable: error detection but not errorcorrection

Frame Check Sequence (32 bits)



75

Figure 2-13: Ethernet Switching Decision

Switching TablePort Host 10 A1-44-D5-1F-AA-4C13 B2-CD-13-5B-E4-6515 C3-2D-55-3B-A9-4F16 D4-47-55-C4-B6-9F

UTP

UTPfrom

Port 15

UTPUTP

Ethernet Switch

A1-44-D5-1F-AA-4C B2-CD-13-5B-E4-65

D4-47-55-C4-B6-9F

C3-2D-55-3B-A9-4F

Frame To C3… Frame To C3…

76

Figure 2-14: Internet Protocol (IP) Packet



VerticalCommunication

78

Figure 2-15: Layered Communication onthe Source Host

ApplicationProcess

HTTPMessage

TransportProcess

HTTPMessage

TCPHdr

Encapsulation of HTTP Messagein Data Field of TCP Segment



79

Figure 2-15: Layered Communication on theSource Host, Continued

When a layer process (N) creates a message,it passes it down to the next-lower-layerprocess (N-1) immediately

The receiving process (N-1) will encapsulatethe Layer N message, that is, place it in thedata field of its own (N-1) message

80

Figure 2-15: Layered Communication onthe Source Host, Continued

TransportProcess

HTTPMessage

TCPHdr

InternetProcess

HTTPMessage

TCPHdr

IPHdr

Encapsulation of TCP Segmentin Data Field of IP Packet



81


InternetProcess

HTTPMessage

TCPHdr

IPHdr

Data LinkProcess

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Encapsulation of IP Packetin Data Field of Ethernet Frame

82


Data LinkProcess

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Physical Process



83


The following is the final frame for a packet carryingan HTTP message on an Ethernet LAN

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

L5 L4 L3 L2L2

84


SMTPMessage

TCPHdr

IPHdr

PPPHdr

PPPTrlr

L5 L4 L3 L2L2

The following is the final frame for a packet carryingan SMTP (e-mail) message on PPP telephone modem connection

Note: HTTP is NOT the application layer message, as it is in webservice.

PPP replaces Ethernet.



85


TCPHdr

IPHdr

EthHdr

EthTrlr

The following is the final framefor a packet carrying a supervisory TCP segment:

L4 L3 L2L2

Supervisory TCP segments are initiated by the Transport layer process(Layer 4), so Layer 5 is not involved.

TCP supervisory messages consist entirely of headers. The headercarries supervisory information, so no TCP data field exists in supervisoryTCP messages.

86

Figure 2-16: Decapsulation on theDestination Host

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Data LinkProcess

Physical Process



87

Figure 2-16: Decapsulation on theDestination Host, Continued

HTTPMessage

TCPHdr

IPHdr

EthHdr

EthTrlr

Data LinkProcess

InternetProcess

HTTPMessage

TCPHdr

IPHdr

Decapsulation of IP Packetfrom Data Field of Ethernet Frame

88


InternetProcess

HTTPMessage

TCPHdr

IPHdr

TransportProcess

HTTPMessage

TCPHdr

Decapsulation of TCP Segmentfrom Data Field of IP Packet



89


TransportProcess

HTTPMessage

TCPHdr

ApplicationProcess

HTTPMessage

Decapsulation of HTTP Messagefrom Data Field of TCP Segment

90

Sample Frame - captured using sniffer

Ethernet Frame

PPPOEIP

TCP

HTTP



91

Figure 2-17: Layered End-to-End Communication

Int

App

DL

Trans

Phy

SourceHost

DestinationHost

Switch 1 Switch 2 Router 1 Switch 3 Router 2

Source andDestinationHosts Have

5 Layers

SwitchesHave Two

Layers---

Each SwitchPort

Has OneLayer

RoutersHave Three

Layers---

Each RouterPort

Has TwoLayers

92

Figure 2-18: Protocols

Protocols are standards that governinteractions between hardware and softwareprocesses at the same layer but on differenthosts

Int

App

DL

Trans

Phy

SourceHost

DestinationHost


Hypertext Transfer Protocol



93

Figure 2-18: Protocols, Continued

Int

App

DL

Trans

Phy

SourceHost

DestinationHost


Hypertext Transfer Protocol

Transmission Control Protocol

Internet Protocol

94

Figure 2-24: Characteristics of ProtocolsDiscussed in the Chapter

Layer ProtocolConnection-Oriented/Connectionless

Reliable/Unreliable

Strong / WeakTimingConstraints

5 (App) HTTP Connectionless Unreliable Weak

4 (Trans) TCP Connection-oriented Reliable Strong

3 (Internet) IP Connectionless Unreliable Weak

2 (DL) Ethernet Connectionless Unreliable Weak



95

Topics Covered

OSI model 第七層應用層

第六層展示層

第五層會議層

第四層傳輸層

第三層網路層

第二層資料連結層

第一層實體層

96

Topics Covered

Layered Standards ArchitecturePhysical layer (between adjacent devices)

Data link layer (across a switched network)

Internet layer (across an internet)

Transport layer (host-to-host)

Application layer (application-to-application)



97

Topics Covered

Other Standards ArchitecturesIPX/SPXSNAAppleTalk

98

Topics Covered

Standards govern the semantics, syntax andtiming of message exchanges

Data field, header, and trailerHeader and trailer subdivided into fields

HTTP: Text request and response messages

Connection-oriented versus connectionless

TCP connections3-way opens, data exchanges, 4-way closes



99

Topics Covered

ReliabilityIn TCP, receiver sends ACKs

Senders retransmit non-acknowledged segments

TCP/IP-OSI ArchitectureOSI is 100% dominant at Layers 1 and 2

TCP/IP is 70% to 80% dominant at Layers 3 and 4

TCP/IP is used heavily at Layer 5

100

Topics Covered

Ethernet PacketSource and destination addresses are 48 bits longSwitches base output port decisions on 48-bitEthernet addressesUnreliable: if detects an error, drops the frame

Internet Protocol (IP)32-bit addressesShow 32 bits on each lineUnreliable: checks headers for errors but discards



101

Topics Covered

Vertical Communication on the Source HostLayer process send message to the next-lower layer

Encapsulation

Final frame

Vertical Communication on the DestinationHost

Decapsulation and passing up

102

Topics Covered

Not All Devises Have All LayersHosts: all five

Routers: three

Switches: two

ProtocolsStandards that govern interactions betweenhardware and software practices at the same layerbut on different hosts