The Network Core ☒无法显示该图片， 口meSh(网眼、编织)of interconnected routers 口the fundamental(基本的) question:how is data transferred through net? ÷circuit switching: dedicated circuit per call:telephone net packet-switching:data sent thru net in discrete(离散的) “chunks" Introduction 1-16
Introduction 1-16 The Network Core ❑ mesh（网眼、编织） of interconnected routers ❑ the fundamental （基本的） question: how is data transferred through net? ❖ circuit switching: dedicated circuit per call: telephone net ❖ packet-switching: data sent thru net in discrete（离散的） “chunks
Network Core:Circuit Switching End-end resources reserved for "call" link bandwidth,switch capacity dedicated resources: no sharing ▣circuit-like (guaranteed) performance ▣call setup required Introduction 1-17
Introduction 1-17 Network Core: Circuit Switching End-end resources reserved for “call” ❑ link bandwidth, switch capacity ❑ dedicated resources: no sharing ❑ circuit-like (guaranteed) performance ❑ call setup required
Network Core:Circuit Switching network resources dividing link bandwidth (e.g.,bandwidth) into "pieces" divided into "pieces" *frequency division pieces allocated to calls *time division resource piece idle if not used by owning call (no sharing) Introduction 1-18
Introduction 1-18 Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces” ❑ pieces allocated to calls ❑ resource piece idle if not used by owning call (no sharing) ❑ dividing link bandwidth into “pieces” ❖ frequency division ❖ time division
Circuit Switching:FDM and TDM Example: FDM 4 users 口■ frequency time TDM frequency time Introduction 1-19
Introduction 1-19 Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:
Numerical example刨 How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots/sec *500 msec to establish end-to-end circuit Let's work it out! Introduction 1-20
Introduction 1-20 Numerical example(数例) ❑ How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? ❖ All links are 1.536 Mbps ❖ Each link uses TDM with 24 slots/sec ❖ 500 msec to establish end-to-end circuit Let’s work it out!