Network edge: connectionless service Goal: data transfer Apps using TCP: between end systems r Http(wWw), Ftp m same as before (file transfer), Telnet r UDP -User datagram (remote login), SMTP Protocol [RFc 768]: (email) Internet's connectionless service m unreliable data Apps using UDP: transfer r streaming media, teleconferencing m no flow control Internet telephony m no congestion control 1: Introduction 11
1: Introduction 11 Network edge: connectionless service Goal: data transfer between end systems m same as before! r UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service m unreliable data transfer m no flow control m no congestion control App’s using TCP: r HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email) App’s using UDP: r streaming media, teleconferencing, Internet telephony
The Network Core 无法显示该图片 r mesh of interconnected routers r the fundamental question: how is data transferred through net? ● m circuit switching: dedicated circuit per call: telephone net placket-switching: data sent thru net in discrete" chunks 1: Introduction 12
1: Introduction 12 The Network Core r mesh of interconnected routers r the fundamental question: how is data transferred through net? m circuit switching: dedicated circuit per call: telephone net m packet-switching: data sent thru net in discrete “chunks
Network Core: Circuit Switching End-end resources reserved for call" link bandwidth switch capacity r dedicated resources: no sharin r circuit-like (guaranteed) performance r call setup required 1: Introduction 13
1: Introduction 13 Network Core: Circuit Switching End-end resources reserved for “call” r link bandwidth, switch capacity r dedicated resources: no sharing r circuit-like (guaranteed) performance r call setup required
Network Core: Circuit Switching network resources r dividing link bandwidth g, bandwidth Into pieces divided into pieces" m frequency division r pieces allocated to calls m time division r resource piece idle if not used by owning call (no sharing dividing link bandwidth into pieces frequency division m time division 1: Introduction 1
1: Introduction 14 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” r pieces allocated to calls r resource piece idle if not used by owning call (no sharing) r dividing link bandwidth into “pieces” m frequency division m time division r dividing link bandwidth into “pieces” m frequency division m time division
Circuit Switching: TDMA and TDMA Example FDMA 4 users■■□■ frequency time TDMA frequency time 1: Introduction 15
1: Introduction 15 Circuit Switching: TDMA and TDMA FDMA frequency time TDMA frequency time 4 users Example: