Advanced Computer Networks: Lecture 2. This lecture will cover the following: multiplexing and statistical multiplexing; inter-process communication; IPC abstractions; abstract channel functionality; performance metrics; bandwidth versus latency; bandwidth requirements; protocol interfaces;...
CS716 Advanced Computer Networks By Dr. Amir Qayyum Lecture No. 2 Multiplexing • Physical links/switches must be shared among users – (synchronous) TimeDivision Multiplexing (TDM) – FrequencyDivision Multiplexing (FDM) L1 R1 Multiple flows on a single link L2 L3 R2 Switch Switch R3 Do you see any problem with TDM / FDM ? Statistical Multiplexing • • • • Ondemand timedivision, possibly synchronous (ATM) Schedule link on a perpacket basis Buffer packets in switches that are contending for the link Packets from different sources interleaved on link … Do you see any problem ? Statistical Multiplexing • An application needs to breakup its message in packets, and reassemble at the receiver • Fair allocation of link capacity: FIFO, roundrobin or QoS • If congestion occurs at a switch buffer may overflow, packets may be lost … Enough … ? • A network is delivering packets among a collection of computers • How application processes communicate in a meaningful way ? • Hide network complexity by implementing the common services once InterProcess Communication • Turn hosttohost connectivity into processtoprocess communication, making the communication meaningful • Fill gap between what applications expect and what the underlying technology provides Host Host Application Host Abstraction for applicationlevel communication Channel Application Host Host IPC Abstractions • Semantics and interface depend on applications • Message stream • Request/Reply – distributed file systems • file servers (FTP) – digital libraries / HTTP • information retrieval – video ondemand – video conferencing • reliable ? • prioritized ? • delay/bandwidth guarantees ? • • • • • • delay sensitive twoway frame flow 1/4 NTSC = 352x240 pixels (352 x 240 x 24)/8=247.5KB 30 fps = 7500KBps = 60Mbps 10fps + compression