Bài giảng Mạng máy tính: Chương 2b

ươ

ế

ng 2 (ti p). ứ ầ ứ

Ch ụ Giao th c t ng ng d ng (application layer)

ị Đoàn Th Thu Hà

Discussion

 Web programming with ASP.

 Visual Basic programming.

 Object oriented programming.

 Event driven programming.

 Component driven programming.

 TCP Socket programming.

 Simple web server.

Chapter 2. The Application Layer 2 1-6/2005

Ch2. The Application Layer

ộ ố

ắ

ệ 2.1. M t s khái ni m và nguyên t c.

2.2. Web & Hyper Text Transfer Protocol.

2.3. Web design and HTTP, Web programming.

2.4. File Transfer Protocol.

2.5. Electronic Mail Protocols.

2.6. Domain Name System.

Chapter 2. The Application Layer 3 1-6/2005

2.4. FTP File Transfer Protocol

file transfer

FTP client

FTP server

FTP user interface

user at host

remote file system

local file system

ề ả ệ

 Truy n/t

i t p (to/from remote host).

 Client/server model

ề ả

ầ

 Client: đ a ra yêu c u truy n t

 Server = remote host.

 FTP: RFC 959

Chapter 2. The Application Layer 4 1-6/2005

FTP: control & data connections

TCP control connection port 21

TCP data connection port 20

FTP client

FTP server

 FTP s d ng TCP. ử ụ

ử ụ

ế

ờ

ồ

ạ

 FTP s d ng đ ng th i 2 liên k t TCP t

ổ i 2 c ng:

ề

ệ

ổ

 TCP control connection, port 21: trao đ i các thông đi p đi u

ể

khi n (commands, responses…).

ề ả ệ

 TCP data connection, port 20: truy n t

i t p.

ữ ạ

ệ

 FTP l u gi

tr ng thái client trong phiên làm vi c (state

vs. HTTP is stateless).

Chapter 2. The Application Layer 5 1-6/2005

ổ

FTP: Quá trình trao đ i/truy n t

ề ả i

TCP control connection port 21

client

server

TCP data connection port 20

ạ ổ

i c ng 21.

ạ ổ

 FTP server nghe t

i c ng 21.

ử

ể

ậ

ầ G i user & password đ đăng nh p.

ề

ấ

ậ

ể ể ắ ầ

ế ậ

ổ

 FTP client yêu c u k t n i v i FTP server qua TCP t ế ố ớ

ượ đ

c thi

ế ữ ệ

ở c l nh truy n t p, nó m liên k t d li u (data

ệ ượ

ế

 FTP server ch p nh n, liên k t đi u khi n (control connection) ế t l p. Quá trình trao đ i có th b t đ u.

ậ ượ ệ ớ i client, t p đ

ề ệ ề c truy n qua liên k t này.

ế ữ ệ

ắ

ỗ

 Khi server nh n đ connection) t

ề ỉ ử ụ

ộ ệ ề

ể ế k t ch s d ng đ truy n m t t p).

 Sau khi truy n xong m t t p, server ng t liên k t d li u (m i liên ộ ệ

Chapter 2. The Application Layer 6 1-6/2005

FTP commands, responses

Lệnh (commands), phúc đáp (responses) được truyền dạng ASCII

Sample commands:  sent as ASCII text over control

Sample return codes  status code and phrase (as in

channel

HTTP)

current directory

 331 Username OK, password required  125 data connection  USER username  PASS password  LIST return list of file in

 RETR filename retrieves

already open; transfer starting  425 Can’t open data

(gets) file

connection

 452 Error writing

 STOR filename stores (puts) file onto remote host

file

Chapter 2. The Application Layer 7 1-6/2005

FTP clients & servers

file transfer

FTP client

FTP server

FTP user interface

user at host

remote file system

local file system

 Microsoft FTP Service  …

 Commandbased client:  Windows FTP command.  Linux FTP command.

 GUI clients

 Windows Commander.  CuteFTP, WS_FTP…

Chapter 2. The Application Layer 8 1-6/2005

CuteFTP

Chapter 2. The Application Layer 9 1-6/2005

Ch2. The Application Layer

ộ ố

ắ

ệ 2.1. M t s khái ni m và nguyên t c.

2.2. Web & Hyper Text Transfer Protocol.

2.3. Web design and HTTP, Web programming.

2.4. File Transfer Protocol.

2.5. Electronic Mail Protocols.

2.6. Domain Name System.

Chapter 2. The Application Layer 10 1-6/2005

2.5. Electronic Mail

user agent

mail server

ạ

user agent

ầ Ba thành ph n chính:  User agents (mail clients)  So n, đ c th (messages). ư ọ  Vd: Outlook, Eudora, Netscape

SMTP

Messenger...

mail server

user agent

SMTP

user agent

mail server

 Mail servers  L u tr , x lý th . ư ữ ử ư  Vd: Exchange, MDeamon…

user agent

outgoing message queue

user agent

 Simple Mail Transfer Protocol (SMTP).  Post Office Protocol (POP).  Internet Mail Access Protocol (IMAP).  HTTP.

user mailbox

 Protocols

Chapter 2. The Application Layer 11 1-6/2005

Alice  Bob

ử

ạ

ủ ế

4) Mail server c a Alice g i th qua liên k t TCP.

ử ụ i “to”:

ử ớ g i t

1) Alice s d ng UA so n th , đ/c bob@yahoo.com.

ư ủ 5) Mail server c a Bob c t th

ấ ư c vào hòm th

ư ế ứ

ủ

ậ ượ nh n đ ủ c a Bob.

ợ

ử 2) Alice’s UA g i th đ n mail ư ượ server c a Alice, b c th đ ế x p vào hàng đ i (message queue).

ể ấ

ư ừ

6) Bob dùng UA đ l y th t ư ề ồ ọ server v r i đ c th .

ủ

ế

ở

3) Mail server c a Alice m liên k t

ớ

ủ

TCP t

i mail server c a Bob.

mail server

user agent

mail server 3

user agent Outlook

5 yahoo.com

Yahoo! Mail hua.edu.vn

Chapter 2. The Application Layer 12 1-6/2005

SMTP (Simple Mail Transfer Protocol)

ế

ể ử

 S d ng liên k t TCP (port 25) đ g i mails:

ử ụ T sender’s mail client t ớ ừ i sender’s mail server. T sender’s mail server t ớ ừ i receiver’s mail server.

 Ba pha:

ắ

ổ

B t tay (handshaking/greeting). Trao đ i messages. K t thúc. ế

 Command/response: commands: ASCII. responses: status code & phrase.

Chapter 2. The Application Layer 13 1-6/2005

SMTP: sample interaction (C: client; S: server)

S: 220 yahoo.com C: HELO hau.edu.vn S: 250 Hello hau.edu.vn, pleased to meet you C: MAIL FROM: S: 250 alice@hau.edu.vn... Sender ok C: RCPT TO: S: 250 bob@yahoo.com ... Recipient ok C: DATA S: 354 Enter mail, end with "." on a line by itself C: Hi Bob! C: Would you like to play tennis this evening? C: . S: 250 Message accepted for delivery C: QUIT S: 221 yahoo.com closing connection

Chapter 2. The Application Layer 14 1-6/2005

SMTP: more

ử ụ

ế

ề

ộ

đi p.ệ

ả ượ

ệ

 SMTP s d ng persistent connection: m t liên k t, nhi u thông

ạ c mã hoá d ng ASCII 7

bit (USASCII).

ấ

ở CRLF.CRLF

ể ứ CRLF.CRLF  c n ầ

 Thông đi p (k c n i dung th ) ph i đ ể ả ộ

ộ ố ữ ệ ể ả

ữ ệ

ị ả

ệ

ế

mã hoá đ đ m b o không có d li u nào trùng v i ký hi u k t thúc message (vd: base64).

ớ

 Đánh d u k t thúc msg b i ế  M t s d li u nh phân (vd: picture) có th ch a ớ

ử ụ

ề

ỗ

ộ

 HTTP: pull protocol <> SMTP: push protocol.  Cùng s d ng ASCII (command/req/resp/status code).  HTTP: m i obj ch a trong m t msg <> SMTP: cho phép nhi u obj (text,

ứ ộ

picture…) trong m t msg (multipart msg). Chapter 2. The Application Layer

 So sánh v i HTTP:

15 1-6/2005

Mail message format

ứ

ổ

SMTP: giao th c trao đ i email msg

(exchange msgs).

header

RFC 822: standard for text message

format:

blank line

body

 To:  From:  Subject:

Khác v i ớ smtp commands (MAIL FROM, RCPT TO,…)!

 Header lines, vd:

 The “message”.  ASCII

 Body

Chapter 2. The Application Layer 16 1-6/2005

MIME (Multipurpose Internet Mail Extension)

ặ

ớ

ể

 RFC 822: text msg, g p khó khăn v i multimedia.  MIME: RFC 2045, RFC 2056.  So v i RFC 822, MIME thêm vào các header lines đ mô

ớ ả ộ

ủ n i dung c a email msg.

MIME version

method used to encode data

multimedia data type, subtype, parameter declaration

From: alice@hau1.edu.vn To: bob@yahoo.com Subject: Picture of yummy crepe. MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Type: image/jpeg

encoded data

base64 encoded data ..... ......................... ......base64 encoded data

Chapter 2. The Application Layer 17 1-6/2005

MIME: Content types

Content-type: type/subtype; parameters

Chapter 2. The Application Layer 18 1-6/2005

MIME: Encoding types

Content-Transfer-Encoding: Encoding type

Chapter 2. The Application Layer 19 1-6/2005

MIME: Multiple objects mail message

From: alice@hau.edu.vn To: bob@yahoo.com Subject: Picture of yummy crepe. MIME-Version: 1.0 Content-Type: multipart/mixed; boundary=StartOfNextPart --StartOfNextPart Content-Transfer-Encoding: quoted-printable Content-Type: text/plain

Dear Bob, Please find a picture of a crepe. --StartOfNextPart Content-Transfer-Encoding: base64 Content-Type: image/jpeg

base64 encoded data ..... ......................... ......base64 encoded data --StartOfNextPart

Chapter 2. The Application Layer 20 1-6/2005

The received mail message

ậ

ỗ

ể ượ

ề

ể

 Received:  Returnpath:  Mail có th đ

c chuy n qua nhi u server khác nhau (forward).

 Server thêm vào dòng header m i khi nh n th : ư

Received: from hamburger.edu by sushi.jp; 12 Oct 98 15:30:01 GMT Received: from crepes.fr by hamburger.edu; 12 Oct 98 15:27:39 GMT From: alice@crepes.fr To: bob@hamburger.edu Subject: Picture of yummy crepe. MIMEVersion: 1.0 ContentTransferEncoding: base64 ContentType: image/jpeg

base64 encoded data ....... ........................................ .......base64 encoded data

Chapter 2. The Application Layer 21 1-6/2005

ớ

ể

ị

Hi n th full headers v i Y! Mail

2.General Preference

1.Mail Options

3.Messages: Show all…

Chapter 2. The Application Layer 22 1-6/2005

Mail access protocol

SMTP

user agent

access protocol

user agent

receiver’s mail server

sender’s mail server

ứ ử

ớ i server. ứ

ậ

ừ

 SMTP: giao th c g i mail t  Mail access protocol: giao th c nh n mail t

server.

 POP (Post Office Protocol): RFC 1939. TCP Port 110.  IMAP (Internet Mail Access Protocol): RFC 1730. TCP port 143.  HTTP: Hotmail, Yahoo!...

Chapter 2. The Application Layer 23 1-6/2005

POP3 protocol

[1] Authorization phase  client commands:

 user: declare username  pass: password

 server responses  +OK  -ERR

[1]

[2] Transaction phase, client:  list: list message numbers  retr: retrieve message by number  dele: delete

ổ

ượ ậ

[3] Update phase:  Quit  nh ng thay đ i (dele) đ

c c p

ữ nh tậ

[2]

[3]

S: +OK POP3 server ready C: user bob S: +OK C: pass hungry S: +OK user successfully logged on C: list S: 1 498 S: 2 912 S: . C: retr 1 S: S: . C: dele 1 C: retr 2 S: S: . C: dele 2 C: quit S: +OK POP3 server signing off

Chapter 2. The Application Layer 24 1-6/2005

POP3 (more) and IMAP

ế ộ

ữ

ộ

ạ

IMAP4  L u tr toàn b msg t

More about POP3  Ch đ “download and c):

ư server.

ổ

i dùng t

ầ ữ

ướ delete” (xem vd tr  Msg b xoá khi thoát. ị  Không th nh n msg l n n a. ậ ể

ể

 Cho phép ng ứ ư ữ ư ụ

ữ ạ l

c gi

ữ

ườ ạ ch c l u tr trên server (t o th m c, di chuy n msg…)  L u tr ng thái gi a các phiên

ề ầ ừ

ề

 Msg đ  Có th nh n msg nhi u l n t ậ ể nhi u client.

ư ụ ự ạ

t o.

ữ

ạ

ạ ư (state):  Th m c t  Các msgs đã di chuy n.ể

 “Downloadandkeep”: ượ i server.

ệ

các phiên làm vi c (stateless).

 Không l u tr ng thái gi a

Chapter 2. The Application Layer 25 1-6/2005

Ch2. The Application Layer

ộ ố

ắ

ệ 2.1. M t s khái ni m và nguyên t c.

2.2. Web & Hyper Text Transfer Protocol.

2.3. Web design and HTTP, Web programming.

2.4. File Transfer Protocol.

2.5. Electronic Mail Protocols.

2.6. Domain Name System.

Chapter 2. The Application Layer 26 1-6/2005

2.6. DNS (Domain Name System)

Mr Binh HTTP (Internet Explorer)

From: Đ.V.Bình To: Phòng ĐT

www.hau.edu.vn

www.hau.edu.vn => 203.162.8.82

203.162.8.82

Phòng ĐT => H.101

DNS client DNS servers

ỉ

ị

ượ ử ụ

ể

ạ

ộ

ị

Ms Nam

c s d ng đ xác đ nh m t nút trong m ng

ử ụ

TCP/IP: 203.162.8.82  khó nh !ớ  S d ng tên (host name) song song v i IP address.

ớ  DNS (RFC 1034, RFC 1035, RFC 2136):

ể

 Chuy n host name

 IP address.

 Đ a ch IP (32 bit) đ

Chapter 2. The Application Layer 27 1-6/2005

2.6. DNS (Domain Name System)

Chapter 2. The Application Layer 28 1-6/2005

DNS services

ự ế ớ

ị

ng tác tr c ti p v i users mà cung ng trình khác (HTTP,

ươ DNS không t ươ ụ ấ c p các d ch v cho các ch ụ ộ ầ ứ FTP…) thu c t ng ng d ng:

 Host name  IP (hostname to IP resolve).  Host aliasing. ộ

ể

 M t máy tính có tên chính th c và có th có bí danh (alias). ứ

 Mail server aliasing.

 @hau1.edu.vn  mail server address = ?

i)ả

ể

c cung ượ

i do l

 Load distribution (phân tán t  M t d ch v web (cnn.com, yahoo.com…) có th đ ụ ể ượ ả ề i nhi u server có IP khác nhau đ phân tán t ườ ử ụ i s d ng cao.

ộ ị ấ ạ c p t ng

Chapter 2. The Application Layer 29 1-6/2005

Domain name servers

Root DNS Servers

poly.edu DNS servers

umass.edu DNS servers

pbs.org DNS servers

yahoo.com DNS servers

amazon.com DNS servers

t IP c a

ỏ

ủ www.amazon.com thì: ố ỉ ủ com DNS servers  h i Root DNS servers.

ế Vd: client mu n bi  Tìm đ a ch c a ị  amazon.com  com DNS servers.  www.amazon.com  amazon.com DNS servers.

org DNS servers edu DNS servers com DNS servers

Chapter 2. The Application Layer 30 1-6/2005

Internet domain name space

vn

 Host name: www.hau1.edu.vn;

 Domain name (tên mi n):ề

ề ậ

 Mi n = t p h p các nút m ng có ợ cùng m t nút cha trong s đ trên.

 Vd:  hau1.edu.vn; yahoo.com; yale.edu.  Subdomain: cs.yale.edu;

mail.hau1.edu.vn  vn: Vietnam.  edu: education.  hau: Hanoi Agricultural University.  www: máy ch world wide web. ủ  mail: máy ch mail. ủ

ạ ơ ồ ộ

Chapter 2. The Application Layer 31 1-6/2005

Internet domain name space

Chapter 2. The Application Layer 32 1-6/2005

Internet domain name space

Chapter 2. The Application Layer 33 1-6/2005

Internet domain name space



Chapter 2. The Application Layer 34 1-6/2005

Internet domain name space

Chapter 2. The Application Layer 35 1-6/2005

DNS: Root name servers

k RIPE London (also Amsterdam, Frankfurt)

i Autonomica, Stockholm (plus 3 other locations)

a Verisign, Dulles, VA c Cogent, Herndon, VA (also Los Angeles) d U Maryland College Park, MD g US DoD Vienna, VA h ARL Aberdeen, MD j Verisign, ( 11 locations)

m WIDE Tokyo

e NASA Mt View, CA f Internet Software C. Palo Alto, CA (and 17 other locations)

13 root name

servers worldwide

b USC-ISI Marina del Rey, CA l ICANN Los Angeles, CA

ể

ầ ớ

ử

 Khi local name server không th chuy n host name

 IP, g i yêu c u t

i root

srv.

ế

ể

ạ

ạ ớ authoritative name server n u ch a th ánh x đ/c ngay. ạ ử ề ừ authoritative name server. ế ấ ả ế

 root name server:  Liên l c v i  L y k t qu ánh x g i v t ả  Tr k t qu v cho ả ề

local name server.

Chapter 2. The Application Layer 36 1-6/2005

TLD and Authoritative Servers

ệ

ề

ị

 Toplevel domain (TLD) servers: ch u trách nhi m v các

ả

mi n ề com, org, net, edu… và uk, fr, ca, jp…  Network Solutions: qu n lý com TLD servers.  Educause: qu n lý edu TLD servers.

ố ượ

ế ế

ả ượ

 Authoritative DNS servers:  M i host trong m ng mu n đ

c bi

t đ n ph i đ

c khai báo

ộ

ạ ỗ ớ v i m t authoritiative DNS server.

 DNS servers c a các t

ạ ch c ánh x hostname

 IP cho các

ủ ủ ổ ứ

ổ ứ ch c đó (vd: web, mail…).

hosts c a t

ể ượ

ả

ở

ổ ứ

ấ

ị

 Có th đ

c qu n lý b i các t

ụ ch c hay nhà cung c p d ch v .

Chapter 2. The Application Layer 37 1-6/2005

Local name server

ủ

ả

ộ

 Thu c qu n lý c a ISP (ISP, company, university…).

ộ

ủ

ế

ố

ộ

ướ

t IP c a m t host nào đó, tr

 Khi m t host mu n bi ỏ

tiên, nó “h i” local name server.

ế

ả ằ

 Không nh t thi

ế t ph i n m trong ki n trúc DNS servers

ấ ộ ậ (đ c l p).

ườ

ủ

ấ

 “G n” máy tính c a ng

i s d ng nh t nên th

ầ ượ

ầ

ấ

ỏ

ườ ử ụ ỗ c “h i thăm” đ u tiên m i khi có truy v n DNS.

 Xem Windows Local DNS: ipconfig

Chapter 2. The Application Layer 38 1-6/2005

DNS example

Chapter 2. The Application Layer 39 1-6/2005

DNS example 1

ầ

root name server

Tình hu ngố : host surf.eurecom.fr c n đ/c IP c a ủ gaia.cs.umass.edu

2 4

ạ ớ

1. Liên l c v i local DNS server: dns.eurecom.fr

3 5

ạ ớ 2. dns.eurecom.fr liên l c v i root name server (n u c n)

local name server dns.eurecom.fr

Authorititive name server dns.umass.edu

1 6

gaia.cs.umass.edu

ế ầ 3. root name server liên l c ạ v i ớ authoritative name server: dns.umass.edu (n u ế c n)ầ

requesting host surf.eurecom.fr

Chapter 2. The Application Layer 40 1-6/2005

DNS example 2

root name server

6 2

Root name server có th :ể  Không bi t ế authoritative

name server (ans).

 Bi

t ế intermediate name

3 7

ể

server (ins)  T ins có th tìm ra ans ừ

local name server dns.eurecom.fr

intermediate name server dns.umass.edu 5

4 1 8

authoritative name server dns.cs.umass.edu

requesting host surf.eurecom.fr

gaia.cs.umass.edu

Chapter 2. The Application Layer 41 1-6/2005

DNS example 3

root name server

ỏ

iterated query 2

ượ

i ng

ị ả

c h i ch u t

recursive query:  A h i B, B h i C, C h i ỏ ỏ ồ ả ờ c D,… r i tr l i.ạ l  Server đ ượ ỏ ấ ặ n ng g p đôi?

local name server dns.eurecom.fr

intermediate name server dns.umass.edu 6

1 8

authoritative name server dns.cs.umass.edu

iterative query:  DNS server đ ộ

ỏ

ượ ỏ c h i ợ g i ý h i m t server khác.

requesting host surf.eurecom.fr

gaia.cs.umass.edu

 “I don’t know this name, 1-6/2005

but ask this server”

Chapter 2. The Application Layer 42

DNS: caching & updating

ỗ

ậ ượ ượ ẽ ượ ư ạ

ứ ầ c yêu c u tra c u ụ ụ i ph c v c l u l

ữ

ầ ờ

ả

ờ

ả

ượ

 M i khi DNS server nh n đ c s đ IP, IP mà nó tìm đ ế ứ cho nh ng l n tra c u ti p theo. Timeout: th i gian h t h n (sau m t kho ng th i gian, ộ ế ạ ị ươ ứ ng ng b xoá). ườ c cache t ng đ ậ

b n ghi cache t TLD servers th ơ ế ậ