Clients and servers Client An application that initiates peer-to-peer communication, e.g. web browser Easier to build than servers s System privileges usually unnecessary Server Program that waits for incoming communication requests from a client CSIE NTUT TANAN
CSIE, NTUT, TAIWAN 6 Clients and Servers • Client * An application that initiates peer-to-peer communication, e.g. web browser * Easier to build than servers * System privileges usually unnecessary • Server Program that waits for incoming communication requests from a client
Privilege and complexity Server software often needs to access to objects that Os protects Server can not rely on the usual OS check since its privilege status allow to access any file Security issues Authentication authorization Data Security Privacy Protection CSIE NTUT TANAN
CSIE, NTUT, TAIWAN 7 Privilege and Complexity • Server software often needs to access to objects that OS protects • Server can not rely on the usual OS check since its privilege status allow to access any file • Security issues: – Authentication – Authorization – Data Security – Privacy – Protection
Privilege and complexity The combination of special privileges and concurrent operation usually makes servers more difticult to design and implementation CSIE NTUT TANAN
CSIE, NTUT, TAIWAN 8 Privilege and Complexity • The combination of special privileges and concurrent operation usually makes servers more difficult to design and implementation
Standard v.s. Nonstandard Client Software Standard application services Defined by TCP/IP Assigned well-known, universally recognized protocol port Non-standard application services All other services which is not standard Or, locally-defined application services CSIE NTUT TANAN
CSIE, NTUT, TAIWAN 9 Standard v.s. Nonstandard Client Software • Standard application services – Defined by TCP/IP – Assigned well-known, universally recognized protocol port • Non-standard application services – All other services which is not standard – Or, locally-defined application services
Standard v.s. Nonstandard Client Software Standard application service examples Remote login teLnEt protocol E-mail client, SmtP or Pop protocol File transfer client, FTP protocol Web browser Http protocol Non-standard application service examples Music or video transfer Voice communication Distributed database access CSIE NTUT TANAN
CSIE, NTUT, TAIWAN 10 Standard v.s. Nonstandard Client Software • Standard application service examples – Remote login, TELNET protocol – E-mail client, SMTP or POP protocol – File transfer client, FTP protocol – Web browser, HTTP protocol • Non-standard application service examples – Music or video transfer – Voice communication – Distributed database access