复旦大学：《计算机网络 Computer Networking》课程教学资源（PPT课件讲稿）Network Standards Layered Architectures

Network standards Layered Architectures Chapter 2 Updated january 2009 XU Zhengchuan Fudan University

Network Standards Layered Architectures Chapter 2 Updated January 2009 XU Zhengchuan Fudan University

Message Standards (Protocols)

1. Message Standards (Protocols)

Figure 2-1: Standards Govern the Exchange of Messages Standards Rules of operation that allow two hardware or software processes to work together Even if they are from different vendors Standards govern the exchange of messages Messages must be governed by strict rules Because computers are not intelligent Message

2-3 Figure 2-1: Standards Govern the Exchange of Messages • Standards – Rules of operation that allow two hardware or software processes to work together – Even if they are from different vendors • Standards Govern the Exchange of Messages – Messages must be governed by strict rules – Because computers are not intelligent Message

Figure 2-1: Standards Govern the Exchange of Messages(Continued Standards govern Syntax Syntax the organization of the message Human example: Susan thanked Tom This sentence has a subject-verb-object syntax Standards Govern Semantics Semantics: The meaning of the message Human example:“ Susan thanked tom” Humans understand the meaning of this easily

2-4 Figure 2-1: Standards Govern the Exchange of Messages (Continued) • Standards Govern Syntax – Syntax: the organization of the message – Human example: “Susan thanked Tom” – This sentence has a subject-verb-object syntax • Standards Govern Semantics – Semantics: The meaning of the message – Human example: “Susan thanked Tom” – Humans understand the meaning of this easily

FIgure2-2:HypertextTransferProtocol(http) Interactions Http Request Message Asking for a File Browser Webserver Application。 Client Pc Webserver Http Response mEssage delivering the File or gIvIng an error message Semantics in Http Which governs the Web 2-5

2-5 Figure 2-2: Hypertext Transfer Protocol (HTTP) Interactions Client PC Webserver Browser Webserver Application 1. HTTP Request Message Asking for a File 2. HTTP Response Message delivering the File or giving an error message Semantics in HTTP, which governs the Web

FIgure 2-3: Syntax of Http Request and Response Messages °[CRLF] Carriage return and line feed (starts a new line) Http Request Message Get /reports/project 1/final. htm Http/1.1[CrlF GET is the method(others exist) Next comes the path to the file to be retrieved Lastcomestheversionofthehttpstandard Host: voyager. cba. Hawaii. edu[CRLFI The host to be sent the request message 2-6

2-6 Figure 2-3: Syntax of HTTP Request and Response Messages • [CRLF] – Carriage return and line feed (starts a new line) • HTTP Request Message – GET /reports/project1/final.htm HTTP/1.1[CRLF] • GET is the method (others exist) • Next comes the path to the file to be retrieved • Last comes the version of the HTTP standard – Host: voyager.cba.Hawaii.edu[CRLF] • The host to be sent the request message

Figure 2-3: Syntax of Http Request and Response Messages, Continued Syntax is Http Response Message very rigid Http/1.1 200 OkicrLf Date: Tuesday, 20-JAN-2006 18: 32: 15 GMT[] Server: name of server software[CRLF MIME-version: 1.0[CRLF] Content-type: text/plain[Crlf [] File to be downloaded(byte stream) Syntax of fields (ines) after first line Keyword: Content /CRLFI 2-7

2-7 Figure 2-3: Syntax of HTTP Request and Response Messages, Continued • HTTP Response Message – HTTP/1.1 200 OK[CRLF] – Date: Tuesday, 20-JAN-2006 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 (byte stream) • Syntax of fields (lines) after first line: – Keyword : Content [CRLF] Syntax is very rigid

Test Your Understanding ·P100 2-8

2-8 • Test Your Understanding • P 100

Figure 2-1: Standards Govern the Exchange of Messages continued General Message Syntax Organization General Message Organization(Figure 2-4) Primary parts of messages Data Field (content to be delivered) Header(everything before the data field) Trailer(everything after the data field The header and trailer act like a delivery envelope for the data field Trailer Data Field Header 2-9

2-9 Figure 2-1: Standards Govern the Exchange of Messages, Continued • General Message Syntax (Organization) – General Message Organization (Figure 2-4) – Primary parts of messages • Data Field (content to be delivered) • Header (everything before the data field) • Trailer (everything after the data field) – The header and trailer act like a delivery envelope for the data field. Trailer Data Field Header

Figure 2-1: Standards Govern the Exchange of Messages, Continued General Message Syntax(Organization) Header and trailer are further divided into fields Trailer Data Field Header Other Message with Header Destination all three parts Field Address Field is Used by Switches and routers ike the Address on an envelope 2-10

2-10 Figure 2-1: Standards Govern the Exchange of Messages, Continued • General Message Syntax (Organization) – Header and trailer are further divided into fields Trailer Data Field Header Other Header Field Destination Address Field is Used by Switches and Routers Like the Address on an Envelope Message with all three parts