Advanced Computer Networks: Lecture 38 - Dr. Amir Qayyum

Advanced Computer Networks: Lecture 38. This lecture will cover the following: real time applications; taxonomy of applications; integrated services: resource reservation protocol (RSVP); mechanisms to support integrated services; integrated services example; flow specification components;...

CS716 Advanced Computer Networks By Dr. Amir Qayyum 1 Lecture No. 38 Real Time Applications • Require “deliver on time” assurances – Must come from inside the network Microphone Sampler A D converter Buffer D A Speaker ã Exampleapplication(audio) Samplevoiceonceevery125às Eachsamplehasaplaybacktime Packetsexperiencevariabledelayinnetwork Add constant factor to playback time:  playback point Real Time Application Example: Live­Source Audio • One byte per 125 microseconds • Delay between speaker & listener  should be fixed • Each packet has “playback time”  based on delay • But network delay is variable Real Time Application Example: Live­Source Audio • Solution – Fix delay at 95­99% mark on distribution – i.e. delay by which 95­99% of packets  arrive • Some packets (1­5%) still lost, but tolerable • Early packets are buffered until playback  time Playback Buffer Sequence number Packet arrival Packet generation Playback Network delay Buffer Time Example Distribution of Delays 90% 97% 98% Packets (%) 99% 50 100 150 200 Delay (milliseconds) Taxonomy of Applications Taxonomy Applications Real time Tolerant Adaptive Delayadaptive Nonadaptive Elastic Intolerant Rate-adaptive Interactive Interactive bulk Nonadaptive Rateadaptive Asynchronous Elastic Applications • Old data are useful, just not as good – Interactive applications (e.g. ssh,  rlogin, telnet) – Bulk transfers (e.g. http, ftp) – Asynchronous interaction (e.g. e­mail) 10 Token Bucket 23 Per­Router (Router­Centric)  Mechanisms • Admission Control – Decide if a new flow can be supported – Answer depends on service class – Not the same as policing • Packet Processing – Classification: associate each packet with  the appropriate reservation – Scheduling: manage queues so each packet  receives the requested service 24 Reservation Protocol • Called signaling in ATM • Proposed Internet standard: RSVP – Consistent with robustness of today’s  connectionless model – Uses soft state (refresh periodically) – Designed to support multicast (can specify  number of speakers) – Receiver­oriented • RSVP uses two messages – PATH transmitted by source every 30 sec – Destination responds with RESV message • Requirements must be merged for multicast 25 26 RSVP – Receiver Oriented Layered  Multicast • RSVP addresses disparate delay requirements • Can different rates be supported? 27 RSVP ­ Solution • Break data into ordered layers • Deliver subset of layers to each receiver 28 Integrated Services –  Scalability Issue • Per­flow monitoring at routers requires  per­flow state information at routers • An OC­48 link can carry 39,000 audio  streams at 64 Kbps each 29 Differentiated Services • Problem with IntServ: scalability • Goal: use small number of classes to  provide scalable solution • Idea: support two classes of packets – Premium (like first­class) – Best­effort, regular (like bulk mail) • Diffserv proposes 6 bits of IP ToS  field (64 classes) 30 Differentiated Services Questions • Who is allowed to set the premium bit? – Typically an ISP – What about an individual customer or  application? • How do routers react to such a  classification? – IETF has specified per­hop behavior 31 Differentiated Services • Mechanisms – Packets: ‘in’ and  ‘out’ bit – Edge routers: tag  packets – Core routers: RIO     (RED with in and  out) P(drop) 1.0 MaxP AvgLen Min out Min in Max out 32 Maxin Differentiated Services • Expedited forwarding – Per­hop behavior – Must strictly limit use – Mechanisms • Strict priority • Weighted fair queuing (WFQ) with  large weights for expedited forwarding 33 Differentiated Services • Assured forwarding – Per­hop behavior – Like RED but with “in” and “out”  packets (RIO) – Does not reorder packets – Weighted RED generalizes to greater  than two (2) classes • Edge routes can mark packets as “in” or  “out”  34 QoS in ATM • Similar to RSVP • Five service classes – Constant bit rate (CBR) – Variable bit rate (VBR) – real­time – Variable bit rate (VBR) – non­real­time – Unspecified bit rate (UBR) – like best effort – Available bit rate (ABR) – like best effort +  ATM’s congestion control 35 RSVP versus ATM (Q.2931) • RSVP – Receiver generates reservation – Soft state (refresh/timeout) – Separate from route establishment – QoS can change dynamically – Supports receiver heterogeneity 36 RSVP versus ATM (Q.2931) • ATM – Sender generates connection request – Hard state (explicit delete) – Concurrent with route establishment – QoS is static for life of connection  (except ABR) – Uniform QoS to all receivers 37 .. .Lecture? ?No.? ?38 Real Time Applications • Require “deliver on time” assurances – Must come from inside the network... Taxonomy Applications Real time Tolerant Adaptive Delayadaptive Nonadaptive Elastic Intolerant Rate-adaptive Interactive Interactive bulk Nonadaptive Rateadaptive Asynchronous Elastic Applications