Addressing processes ■to receive messages, identifier includes both IP process must have identifier address and port numbers host device has unique 32- associated with process on bit IP address host. Q:does IP address of host example port numbers: on which process runs ·HTTP server:80 suffice for identifying the ·mail server:25 process? to send HTTP message to ■Ano,many processes gaia.cs.umass.edu web can be running on same server: host IP address:128.1 19.245.12 。port number:80 ■more shortly.. Application Layer2-11
Application Layer2-11 Addressing processes ▪ to receive messages, process must have identifier ▪ host device has unique 32- bit IP address ▪ Q: does IP address of host on which process runs suffice for identifying the process? ▪ identifier includes both IP address and port numbers associated with process on host. ▪ example port numbers: • HTTP server: 80 • mail server: 25 ▪ to send HTTP message to gaia.cs.umass.edu web server: • IP address: 128.119.245.12 • port number: 80 ▪ more shortly… ▪ A: no, many processes can be running on same host
App-layer protocol defines types of messages open protocols: exchanged, ■defined in RFCs e.g.,request,response allows for interoperability message syntax: ·eg,HTTP,SMTP what fields in messages how fields are proprietary protocols: delineated e.g.,Skype message semantics meaning of information in fields rules for when and how processes send respond to messages Application Layer2-12
Application Layer2-12 App-layer protocol defines ▪ types of messages exchanged, • e.g., request, response ▪ message syntax: • what fields in messages & how fields are delineated ▪ message semantics • meaning of information in fields ▪ rules for when and how processes send & respond to messages open protocols: ▪ defined in RFCs ▪ allows for interoperability ▪ e.g., HTTP, SMTP proprietary protocols: ▪ e.g., Skype
What transport service does an app need? data integrity throughput some apps (e.g.,file transfer,some apps (e.g., web transactions)require multimedia)require 100%reliable data transfer minimum amount of other apps(e.g.,audio)can throughput to be tolerate some loss “effective'” other apps("elastic apps") timing make use of whatever some apps (e.g.,Internet throughput they get telephony,interactive security games)require low delay tobe“effective' encryption,data integrity, Application Layer2-13
Application Layer2-13 What transport service does an app need? data integrity ▪ some apps (e.g., file transfer, web transactions) require 100% reliable data transfer ▪ other apps (e.g., audio) can tolerate some loss timing ▪ some apps (e.g., Internet telephony, interactive games) require low delay to be “effective” throughput ▪ some apps (e.g., multimedia) require minimum amount of throughput to be “effective” ▪ other apps (“elastic apps”) make use of whatever throughput they get security ▪ encryption, data integrity, …
Transport service requirements:common apps application data loss throughput time sensitive file transfer no loss elastic no e-mail no loss elastic no Web documents no loss elastic no real-time audio/video loss-tolerant audio:5kbps-1Mbps yes,100's video:10kbps-5Mbpsmsec stored audio/video loss-tolerant same as above interactive games loss-tolerant few kbps up yes,few secs text messaging no loss elastic yes,100's msec yes and no Application Layer2-14
Application Layer2-14 Transport service requirements: common apps application file transfer e-mail Web documents real-time audio/video stored audio/video interactive games text messaging data loss no loss no loss no loss loss-tolerant loss-tolerant loss-tolerant no loss throughput elastic elastic elastic audio: 5kbps-1Mbps video:10kbps-5Mbps same as above few kbps up elastic time sensitive no no no yes, 100’ s msec yes, few secs yes, 100’ s msec yes and no
Internet transport protocols services TCP service: UDP service: reliable transport between unreliable data transfer sending and receiving between sending and process receiving process flow control:sender won't does not provide:reliability, overwhelm receiver flow control,congestion congestion control:throttle control,timing, sender when network throughput guarantee, overloaded security,or connection does not provide:timing, setup, minimum throughput guarantee,security Q:why bother?Why is connection-oriented:setup there a UDP? required between client and server processes Application Layer2-15
Application Layer2-15 Internet transport protocols services TCP service: ▪ reliable transport between sending and receiving process ▪ flow control: sender won’ t overwhelm receiver ▪ congestion control: throttle sender when network overloaded ▪ does not provide: timing, minimum throughput guarantee, security ▪ connection-oriented: setup required between client and server processes UDP service: ▪ unreliable data transfer between sending and receiving process ▪ does not provide: reliability, flow control, congestion control, timing, throughput guarantee, security, or connection setup, Q: why bother? Why is there a UDP?