Networked Applications Chapter 11 Panko s Business Data Networks

Application Architectures

Application Architectures • An application architecture is the design decision about which network host or hosts to use to do the processing work in an application 3

Figure 11 -1: Simple Terminal-Host System All Processing is done on the host. Host gets overloaded: slow response. Extensive network traffic: expensive. Dumb Terminal Direct Modem Dumb Terminal Wire C onnect ion Telephone Network Modem Host 4

Client/Server Computing • The client does at least some of the work • Made possible by growing client processing power (PCs) • Two versions – File server program access – Request/response processing 5

Figure 11 -2: Client/Server Computing File Server Program Access 1. Program Stored on File Server 2. Program Downloaded to Client PC When Called 3. Program Executed on Client PC! Only useful for small programs (e-mail, word processing, etc. ) Because clients do not get very large 6

Figure 11 -2: Client/Server Computing Client/Server Processing with Request-Response Cycle Request Message Client Program Response Message Does Light I/O and Post-Download Processing Client PC Server Program Does Heavy Database and Other Heavy Processing Server Highly scalable: Use larger server as number of clients increases 7

Figure 11 -3: Web-Enabled Application (E-Mail) HTTP Request Message Client is Browser Client PC HTTP Response Message Server Program Form of client server processing that uses browsers as clients Almost all client PCs now have browsers. No need to install new software. E-Mail Server 8

E-Mail

Figure 11 -4: E-Mail • Importance of E-Mail Expanded List – Universal service on the Internet – Attachments make e-mail a general file delivery mechanism – Messages with inappropriate content, viruses, worms, spam, adware, spyware, and other abuses 10

Figure 11 -5: E-Mail Standards 2. SMTP To Send 1. SMTP To Sender’s Mail Server Sending E-Mail Client Receiver’s Mail Server Simple Mail Transfer Protocol (SMTP) is used to transmit mail in real time to a user’s mail server or between mail servers Receiving E-Mail Client Sender-initiated 11

Figure 11 -5: E-Mail Standards Sender’s Mail Server Sending E-Mail Client Receiver’s Mail Server POP or IMAP to download mail to receiver when the receiver is next capable of downloading mail. POP or IMAP To Receive Receiving E-Mail Client Receiver-initiated 12

Figure 11 -5: E-Mail Standards Sender’s Mail Server Receiver’s Mail Server Message Body Format Standard Sending E-Mail Client Message RFC 822 or 2822 HTML body UNICODE Receiving E-Mail Client 13

Figure 11 -4: E-Mail • E-Mail Standards – Message body standards • Receiver must understand sender’s message • RFC 822 and RFC 2822 for all-text bodies • HTML bodies with fancy text and graphics • UNICODE for non-English language characters 14

Figure 11 -6: Interactions in the Simple Mail Transfer Protocol (SMTP) Actor SMTP Message Comment Client SMTP Process None Connects to server Via TCP Server SMTP Process Client SMTP Process Server When a TCP connection 220 Mail. Panko. Com Ready is opened, the server signals that is is ready. Client asks to begin HELO Voyager. cba. Hawaii. edu Sending a message. Gives own identity. Server signals that it 250 Mail. Panko. Com Is ready to begin Receiving a message. 15

Figure 11 -6: Interactions in the Simple Mail Transfer Protocol (SMTP) Actor SMTP Message Comment Client MAIL FROM: Bob@ voyager. cba. hawaii. edu Client identifies the sender (mail author, not SMTP process). Server 250 OK Accepts author. However, May reject mail from others. Client RCPT TO: Ray@Panko. com Identifies first mail recipient. Server 250 OK Accepts first recipient 16

Figure 11 -6: Interactions in the Simple Mail Transfer Protocol (SMTP) Actor SMTP Message Comment Client RCPT TO: Lee@Panko. com Identifies second mail Recipient. Server 550 No such user here Does not accept second Recipient. However will deliver to first recipient. Client DATA Message will follow. Server 354 Start mail input; end with <CRLF> Gives permission to send message. 17

Figure 11 -6: Interactions in the Simple Mail Transfer Protocol (SMTP) Actor SMTP Message Comment Client When in the course … The message. Multiple lines Of text. Ends with line Containing only a single Period: <CRLF> Server 250 OK Server accepts message. Client QUIT Requests termination of Session. Server 221 Mail. Panko. Com Service Closing transmission channel End of transmission. Server None Closes TCP connection. 18

Sample SMTP Exchange • S: HELO pc-ycc R: 250 euler. im. ncnu. edu. tw Hello …, pleased to meet you • S: MAIL FROM: Smith@Alpha. ARPA R: 250 OK • S: RCPT TO: Jones@Beta. ARPA R: 250 OK • S: RCPT TO: Green@Beta. ARPA R: 550 No such user here • S: DATA R: 354 Start mail input; end with <CRLF> S: Blah blah…. S: …etc. S: <CRLF> R: 250 OK • S: QUIT 19

POP 3 Post Office Protocol - Version 3 • RFC 1939 / Std 53 • To retrieve emails from server (POP 3 server) • Three states – Authorization State – Transaction State – Update State 20

POP 3 Commands • Authorization State – USER username – PASS password • Update State – QUIT – APOP name digest • Transaction State – STAT – LIST [msg. No] – RETR msg. No – DELE msg. No – NOOP – RSET – TOP msg. No line – UIDL [msg. No] 21

S: C: S: S: C: S: +OK POP 3 server ready <1896. 697170952@dbc. mtview. ca. us> USER mrose +OK User name accepted, password please PASS pwd 999 +OK Mailbox open, 2 messages (320 octets) STAT +OK 2 320 LIST +OK 2 messages (320 octets) 1 120 2 200. RETR 1 +OK 120 octets <the POP 3 server sends message 1>. DELE 1 +OK message 1 deleted QUIT +OK dewey POP 3 server signing off (maildrop empty) 22

RFC 822 • Defines format for text messages via electronic mail • Used by SMTP as accepted mail format • Specifies both envelope and contents • Includes a variety of headers that can be included in the message header lines 23

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Received: By Open. Mailer; Thu, 15 Jun 2006 09: 41: 13 +0800 (CST) From: "Yen-Cheng" <ycc 123@ms 6. hinet. net> Reply-To: ycc 123@ms 6. hinet. net Subject: A test mail for BDC 2006 Message-ID: <1150335673. 27009. ycchen@ncnu. edu. tw> To: "=? big 5? B? MS 2 zry. Cr 27/+IKb. Rrn. Y=? =" <ycchen@ncnu. edu. tw> Cc: ycchen@im. ncnu. edu. tw Date: Thu, 15 Jun 2006 09: 41: 13 +0800 (CST) RFC 822/2822 MIME-Version: 1. 0 Return-Path: ycc 123@ms 6. hinet. net Disposition-Notification-To: "Yen-Cheng" <ycc 123@ms 6. hinet. net> X-Priority: 1 X-MSMail-Priority: High Content-Type: text/plain; charset=big 5 Content-Transfer-Encoding: quoted-printable Headers Hi, This=20 mail=20 is=20 just=20 to=20 say=20 hello. So, =20 Hello! Fred=20 Chen --=3 D=3 DMailed=20 via=20 NCNU=20 E-Mail=3 D=3 D-- 25

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Limitations of SMTP and RFC 822 • Cannot transmit executables or binary files without conversion into text through non-standard programs (e. g. UUENCODE) • Cannot transmit diacritical marks • Transfers limited in size • Gateways do not always map properly between EBCDIC and ASCII • Cannot handle non-text data in X. 400 messages • Not all SMTP implementations adhere completely to RFC 821 (tabs, truncation, etc) 28

MIME (Multipurpose Internet Mail Extensions) • Intended to resolve problems with SMTP and RFC 822 • Specifies five new header fields, providing info about body of message • Defines multiple content formats • Defines encodings to enable conversion of any type of content into transferable form 29

MIME • Multipurpose Internet Mail Extensions (MIME) – System for identifying format of a file. • Used in e-mail attachments • Used in HTTP downloads and other applications – Examples (Top-Level Media Type/Specific Type) • Text/Plain (plain ASCII text) • Image/JPEG (JPEG graphic file) • Octet/Stream (un-interpreted bytes for application) • Application/Postscript (Postscript application data) 30

MIME Header Fields • MIME-Version: Indicates compliance with RFCs 1521 and 1522 • Content-Type: Describes data in sufficient detail for Content-Type receiver to pick method for representation • Content-Transfer-Encoding: Indicates type of Content-Transfer-Encoding transformation used to represent content • Content-ID: Used to uniquely identify MIME entities Content-ID • Content-Description: Plain text description for use Content-Description when object is not readable 31

MIME Content Types • Seven major types: Text, Multipart, Message, Image, Video, Audio, Application • Fourteen subtypes • Text provides only plain subtype, but a richtext subtype is likely to be added • Multipart indicates separate parts, such as text and an attachment • MIME types are used by web servers, as well 32

Content Types • Text – Plain • Multipart – Mixed, Parallel, Alternative, Digest • Message – RFC 822, Partial, External-body • Image – jpeg, gif • Video – mpeg • Audio – Basic • Application – Postscript, octet stream 33

multipart/mixed. . . From: "Yen-Cheng Chen" <ycchen@ncnu. edu. tw> To: <ycchen@im. ncnu. edu. tw> Subject: test mail! Date: Wed, 22 May 2002 14: 27: 07 +0800 MIME-Version: 1. 0 Content-Type: multipart/mixed; boundary="----=_Next. Part_000_0047_01 C 2019 E. 69 F 32 C 40“ Status: This is a multi-part message in MIME format. ------=_Next. Part_000_0047_01 C 2019 E. 69 F 32 C 40 Content-Type: text/plain; charset="big 5" Content-Transfer-Encoding: 7 bit Start of Body! Yen-Cheng ------=_Next. Part_000_0047_01 C 2019 E. 69 F 32 C 40 Content-Type: text/plain; name="a. txt" Content-Transfer-Encoding: 7 bit Content-Disposition: attachment; filename="a. txt“ This is the first and only one line of the file. ------=_Next. Part_000_0047_01 C 2019 E. 69 F 32 C 40 -- 34

Content-Transfer-Encoding • Reliable delivery across wide range of environments • Content transfer encoding field – Six values – Three (7 bit, 8 bit, binary) no encoding done • Provide info about nature of data • Quoted-printable – Data largely printable ASCII characters – Non-printing characters represented by hex code • Base 64 – Maps arbitrary binary input onto printable output • X-token – Named nonstandard encoding 35

Quoted-printable Content-Type: text/plain; charset="big 5" Content-Transfer-Encoding: quoted-printable 一年=365天 =A 4@=A 6~=3 D 365=A 4=D 1 暨南大學 =BA[=ABn=A 4 j=BE=C 7 A=B A=3 DB 36

Content-Transfer-Encoding • Content-Transfer-Encoding: base 64 24 bits 0 0 0 0 Radix-64 0~63 A~Za~z 0~9+/ 32 bits 37

HTML and HTTP

Figure 11 -7: HTML and HTTP Browser 1. HTTP Request Webserver Application 2. HTTP Response Webserver Client PC HTML Document 39

Figure 11 -8: Downloading a Complex Webpage with Two Graphics Files HTML Document Browser Client PC Webserver Application Webserver As Displayed 2 Graphics Files Webpage Consists of Three Files Rendered as a Single Page On-Screen 40

Figure 11 -8: Downloading a Complex Webpage with Two Graphics Files 1. HTML Document Browser Client PC As Displayed HTML Document Webserver Application 2 Graphics Files Webserver Download Requires 3 HTTP Request-Response Cycles; Downloads HTML Page First It has Tags to Identify Other Files 41

Figure 11 -8: Downloading a Complex Webpage with Two Graphics Files 2. Browser Client PC As Displayed 3. Webserver Application 2 Graphics Files Webserver Based on Tags in HTML Document, Browser Requests Downloads of Remaining Graphics or Other Files Browser Renders Combined Webpage on Screen 42

Figure 11 -8: Downloading a Complex Webpage with Two Graphics Files • Quiz: Your browser downloads a webpage with three graphics images, a sound sequence, and a Java applet. How many files will your browser have to download? 43

HTTP Messages • Requests – Client to server • Responses – Server to client • Request line • Response line • General header • Request header • Response header • Entity body 44

Hyper. Text Transfer Protocol (HTTP) http: //www. im. ncnu. edu. tw: 80/~ycchen/ http: //www. im. ncnu. edu. tw/~ycchen/www/test. cgi? var 1=123&var 2=value 2 File Transfer Protocol (FTP) ftp: //ftp. ncnu. edu. tw/Java. Download/Docs/ ftp: //anonymous: guest@ftp. ncnu. edu. tw/ ftp: //ycchen@www. im. ncnu. edu. tw/ Gopher Protocol (Gopher) gopher: //gopher. nsysu. edu. tw/11/traveler/train Electronic Mail (Mailto) mailto: username@ncnu. edu. tw? subject=Hello! Usenet News (News) news: tw. bbs. rec. travel news: * Telnet to Remote Host (Telent) telnet: //bbs. ee. cycu. edu. tw/ telnet: //guest@bbs. ncnu. edu. tw/ URL: Uniform Resource Locator Host-Specific File Names (File) 45 file: ///C|/My Documents/ URL Examples

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15 sec, at most 100 requests 47

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Figure 11 -9: Examples of HTTP Request and Response Messages • HTTP Request Message – GET /panko/home. htm HTTP/1. 1[CRLF] – Host: voyager. cba. hawaii. edu[CRLF] • Notes: – CRLF: carriage return and line feed • Two ASCII characters • Start a new line – Beyond the first line, each line is a field • Variable name: value 51

Figure 11 -9: Examples of HTTP Request and Response Messages • HTTP Response Message – HTTP/1. 1 200 OK[CRLF] – Date: Tuesday, 20 -JAN-2004 18: 32: 15 GMT[CRLF] – Server: name of server software[CRLF] – MIME-version: 1. 0[CRLF] – Content-type: text/plain[CRLF] – File to be downloaded 52

Figure 11 -9: Examples of HTTP Request and Response Messages • File to be Downloaded – HTML documents are plain text files • Only use keyboard characters • Use the ASCII code to represent them – Many other files are arbitrary strings of bytes • Graphics files • Sound files • Etc. • Come after the blank line following the response header 53

MIME New Not in Book • Multipurpose Internet Mail Extensions (MIME) – System for identifying format of a file. • Used in e-mail attachments • Used in HTTP downloads and other applications – Examples (Top-Level Media Type/Specific Type) • Text/Plain (plain ASCII text) • Image/JPEG (JPEG graphic file) • Octet/Stream (un-interpreted bytes for application) • Application/Postscript (Postscript application data) 54

MIME: . mht/. mhtml New Not in Book • IE 5 introduced the new 'Web Archive' format for storing web pages, which have the extension MHT. • The 'Web Archive' saves a web page as a single document complete with all images. • The format is a standard mime/multipart e-mail message. • . mht . eml 55

E-Commerce

Figure 11 -10: Electronic Commerce Functions Browser Webserver Application E-Commerce Server Customer PC External Bank Internal Warehouse Database 57

Figure 11 -10: EC Functions • Webserver Functionality, Plus… • E-Commerce functionality – – – Online catalog Shopping cart Checkout, including payment Customer resource management (CRM) Links to External Systems • Credit card number checking • Bank settlement 58

Figure 11 -10: EC Functions • E-Commerce functionality – Links to internal systems • Accounting • Pricing • Warehousing (Product Availability) • Shipment • Etc. 59

Figure 11 -11: Application Server (3 -Tier Architecture Client PC with Browser 1. Form Webserver Application 2. Server Data Mainframe Server of External Company Database Server 60

Figure 11 -11: Application Server (3 -Tier Architecture Client PC with Browser Webserver 3. Mainframe Query and Application Response Server Mainframe CICS and other matters (3) Database Server of External Company 61

Figure 11 -11: Application Server (3 -Tier Architecture Client PC with Browser Webserver Application Server 4. DB Server Mainframe Query and Response 5. External Query/ Response Database Sever Interactions (4, 5) Application program interfaces (API) Both internal and external database hosts Database Server of External Company 62

Figure 11 -12: E-Commerce Security Subnet for Internal Hosts (Little or No Access From Outside) Ethernet Switch DMZ Subnet (Easy Access from Outside) Customer DMZ: Subnet for Externally-Facing Servers Marketing Client Accounting Server E-Commerce Server 63

Figure 11 -12: E-Commerce Security SSL/TLS provides protection against eavesdroppers Customer E-Commerce Server 64

Software as a Service (SAS)

Figure 11 -13: Software as a Service (SAS) Ordinary Webservice HTTP Request Browser Client PC HTTP Response Webserver Application Webserver HTML or Other Document Ordinary webservice was created to download documents 66

Figure 11 -13: Software as a Service (SAS) SOAP Request Message (Parameters/ Calling Properties) Program Client PC Service Object SOAP Response Message Numerical Answer Other Computer 67

Figure 11 -13: Software as a Service (SAS) HTTP Request Client PC SOAPCapable Browser HTTP Response SOAP Message Using XML Syntax Service Object Webserver -Interface Properties Methods SOA requests are sent to a service object via HTTP They are sent as SOAP messages written in XML 68

Figure 11 -14: Simple SOAP Request and Response • Simple Object Access Protocol (SOAP) • Carried in HTTP request or response message • Formatted using XML Syntax – Similar to HTML syntax but the sender and receiver can create new tags that they can then use in transactions, such as <price>$33</price> HTTP Header SOAP Body 69

Figure 11 -14: Simple SOAP Request and Response • Situation – There is a pricing object that returns the price if another object sends the part number, quantity, and shipping type (rush, etc. ) on an interface – Objects can be on different computers Request (Part. Num, Quantity, Shipping. Type) Sending Object Pricing Object Response (Price) 70

Figure 11 -14: Simple SOAP Request and Response • SOAP Request Message HTTP Request Header pointing to program <? xml version=“ 1. 0”> <BODY> <Quote. Price xmlns=“Quote. Interface”> <Part. Num>QA 78 d</Part. Num> <Quantity>47</Quantity> <Shipping. Type>Rush</Shipping. Type> </Quote. Price> </BODY> Note: xmlns specifies an XML namespace for the object 71

Figure 11 -14: Simple SOAP Request and Response • SOAP Response Message HTTP Response Header <? xml version=“ 1. 0”> <BODY> <Quote. Price xmlns=“Quote. Interface”> <Price>$750. 33</Price> </Quote. Price> </BODY> 72

Figure 11 -15: Universal Description, Discovery, and Integration (UDDI) Server for SAS Client PC UDDI Functions: 2. SOAP Interaction 1. Server with UDDI the Identified Request for Service Object Information, Response Interaction Between UDDI Servers to Fulfill a Request UDDI Server White Pages By name Yellow Pages By type Green Pages Details of how to use, payment, etc. UDDI Server 73

Perspective on SAS New: Not In Book • Benefits of SAS – Offers a way to standardize interactions between objects over the Internet – Can make distributed computing far simpler once Web services standards are fully developed • Concerns – High overhead (very chatty) – Standards immaturity – Security is embryonic 74

Peer-to-Peer Computing

Figure 11 -16: Traditional Client/Server Application Client PC Advantage: Central Control Client PC Disadvantages: Network Overload at Server Underused Client Power Central Control Server Does Heavy Processing Work 76

Figure 11 -17: Simple Peer-to-Peer (P 2 P) Application Request Client PC Response Benefits: End User Freedom No Network Bottleneck at Serve Uses Client Capacity Better Client PC Problems: Transient Presence of Clients Transient Client IP Addresses Security (No Central Control) 77

P 2 P Applications • Direct service, although most P 2 P systems use facilitating servers for some of the work Peer Peer 78

Figure 11 -18: Gnutella: Pure P 2 P with Viral Networking Gnutella Client (ABC) 1. Init or Search Message Gnutella Client (Carol) 2. Init or Search Message 3. Init or Search Message Gnutella Client (DEF) 3. Init or Search Message 4. P 2 P File Download HTTP Request-Response Gnutella Cycle Client (XYZ) Gnutella Client (GHI) 79

Figure 11 -19: Napster Index Server 1. Uploads List Of Available Files When Connects Client A 2. Search Query 3. Response File List of Available Files From All Current Clients Client B 4. Large P 2 P Download Client C 80

Figure 11 -20: Use of Servers in Instant Messaging Pure P 2 P IM Ongoing Communication Client PC A Client PC B In pure P 2 P IM, there are no servers. The clients communicate directly. Finding each other can be difficult because of DHCP. 81

Figure 11 -20: Use of Servers in Instant Messaging Use of a Presence Server 1. Presence Information Client PC C 3. Ongoing Communication 2. Presence Information Client PC D Clients register with presence servers. Presence servers notify other clients as appropriate. Clients use this information to communicate directly. 82

Figure 11 -20: Use of Servers in Instant Messaging Use of a Relay Server All Communication Goes through the Relay Server Client PC E Presence Information Client PC F Relay servers route all IM messages. This permits security filtering and other services. It limits privacy because the relay server sees everything. 83

Figure 11 -21: SETI@Home Client PC Processor Sharing 1. I am idle. Give me work. 2. Here is work to do 3. I am busy now. Here are my results. Idle Client PC With SETI@home Screen Saver Program SETI@home Server No Interaction Busy Client PC With SETI@home Screen Saver Program 84

Perspective on Application Architectures • Driven primarily by the evolution of client processing power • Terminal-Host: Client processing power was uneconomical • Client/Server: Client PCs could handle some of the load • P 2 P: Clients have rich power to do most things 85

Topics Covered

Topics Covered • Application Architectures – Terminal-host – Client/server • File server program access • Client/server processing with request/response cycle – Peer-to-peer (P 2 P) – Evolution of architectures driven by growing desktop computer power 87

Topics Covered • E-Mail – Sending: Simple Mail Transfer Protocol (SNMP) – Retrieving: POP and IMAP – Document format standards: RFC 822/2822, HTML, and UNICODE – Viruses, worms, and Trojan horses • Where to do antivirus filtering? – Spam 88

Topics Covered • HTTP and HTML – Webpages consist of an HTML document and multiple graphics, etc. files – Message transfer: HTTP • Multiple downloads for the multiple files in a webpage – MIME 89

Topics Covered • E-Commerce – E-Commerce : webservice with additional functionality – Webserver interacts with customer browser – Application server interacts with back-end databases, passes webified response to the webserver for delivery to the customer – DMZ and SSL/TLS security 90

Topics Covered • Software as a Service (SAS) – Regular webservice: retrieve stored files – SAS: use HTTP and extended HTML to handle programto-program interactions on different machines – SOAP request message passes parameters to a service object on another machine – SOAP response message brings the reply – SOAP messages are written in XML 91