تجارت الکترونیک سیار جلسه پنجم مدرس : دکتررامین کریمی

2-2 Application Software Platform (OS + Hardware) Application Program Interface (API) Application Software Platform (OS + Hardware) Application Program Interface (API) Application process Inter-process Communication  Platform Services  Graphics  Data Interchange  Data Management  User Interface  Software Engineering  Communication Services Application Agent

2-3 Distributed Applications = Network Applications: Platform (OS + Hardware) Application Software (Client Part) Platform (OS + Hardware) Communication Software & Hardware Application Software (Server Part) Client (user) AgentServer Agent CommunicationNetwork Client Agents Examples: – Internet Explorer, Opera – MS’s Outlook, Netscape’s Messenger, Eudora Server Agents Examples: – Internet Information Sever, Appachi – SQL query engines, … Application Program Interface (API) System Application

2-4 Application Software Presentation User Interface Business (Application Logic) Data (Database Access) Layered Application Model-1 Application Model – Presentation: The client agent remains focused on presenting information to or receiving input from the user. – User Interface: User’s access to the application logic via client agent. It can be dynamical and configured by user. It is build on the top of the user interface control. – Dynamic User Interface: Customizing the look (example: Customizing the content ( examples: my.yahoo.com, )my.yahoo.comwww.exite.com

2-5 Business Rules (Application Logic) – Units of processing or algorithms that represents concept of importance to the organization using database. Data (Database Access) – Logic to connect to database; access/manipulate data held within databases. Layered Application Model-2 User Interface Presentation Business (Application Logic) Data (Database Access) Core Business Services Business Processes User Interface Control and Related Logic Application Interface Control and Related Logic Application Interface Presentation User Interface

2-6 User Interface Presentation Business (Application Logic) Database Layered Application: 3-Tier Client/Server Model Client Workstation (rich client) Application Sever Data (Data Access and Storage) CommunicationNetwork Mobile Client Workstation (thin client) User Interface Presentation Data Server Run by Client Agent Runs by Application Server Agent Runs by Database Server Agent Run by Client Agent user

2-7 “Logical Tiers vs Physical Tiers Application Model – Logical Tiers Presentation User Interface Business Data – Physical Tiers Client workstation Application server Data Base Presentation Client Workstation User Interface Business (Application Logic) Application Server Data (Database Access) Database

4-8 Caching Example (1) Assumptions average object size = L= 100,000 bits avg. request rate from institution’s browser to origin serves = a= 15reqs/sec delay from Internet router to any origin server and back to router = 2 sec Consequences utilization on LAN = 15% utilization on LAN = 15% utilization on access link=100% utilization on access link=100% total delay = Internet delay + access delay + LAN delay = 2 secs + minutes + 20 msecs origin servers public Internet institutional network R=10 Mbps LAN R=1.5 Mbps access link Traffic Intensity on the LAN = 15*100,000/10Mbps=15% Traffic Intensity on the access link = 15*100,000/1.5Mbps=100%

4-9 Link delay Traffic intensity La/R Average queuing delay (secs) 100% 15% 60% 20 msecs 160 msecs

Hit Rate and Miss Rate Hit Rate : تعداد درخواست هایی که در کش موجود می باشد. Miss Rate : تعداد درخواست هایی که در کش موجود نمی باشد.

4-11 Possible solution increase bandwidth of access link to, say, 10 Mbps Consequences utilization on LAN = 15% utilization on access link = 15% total delay = Internet delay + access delay + LAN delay = 2secs + 20msecs + 20msecs often a costly upgrade Caching Example (2) origin servers public Internet institutional network 10 Mbps LAN 10 Mbps access link Traffic Intensity on the access link = 15*100,000/10Mbps = 15% Traffic Intensity on the LAN = 15*100,000/10Mbps = 15%

4-12 Install cache suppose hit rate is 0.4 Consequence 40% requests will be satisfied almost immediately 60% requests satisfied by origin server utilization of access link reduced to 60%, resulting in delays (say 160 msec) total delay = Internet delay + access delay + LAN delay = 0.6×(2secs+160msecs+20msecs) + 0.4×20msecs = secs Caching Example (3) origin servers public Internet institutional network 10 Mbps LAN 1.5 Mbps access link institutional cache Traffic Intensity on the access link = 0.6*15*100,000/1.5Mbps = 60% Traffic Intensity on the LAN = 15*100,000/10Mbps = 15%