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Special Topics on Wireless Ad-hoc Networks

Special Topics on Wireless Ad-hoc Networks. Lecture 11: Quality of Services on Wireless Networks. University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani. Univ. of Tehran. 1. Covered topics. How to support real-time applications on wireless network? References

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Special Topics on Wireless Ad-hoc Networks

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  1. Special Topicson Wireless Ad-hoc Networks Lecture 11: Quality of Services on Wireless Networks University of Tehran Dept. of EE and Computer Engineering By: Dr. Nasser Yazdani Univ. of Tehran Wireless Ad hoc NetworkingWireless Ad Hoc Networks 1

  2. Covered topics • How to support real-time applications on wireless network? • References • Chapter 6 of the book • “Protection and Guarantee for Voice and Video Traffic in IEEE 802.11e Wireless LANs” by Yang Xiao, Haizhon Li and Sunghyun Choi. Univ. of Tehran Wireless Ad hoc Networking 2

  3. Outline • Quality of Service • QoS on IP networks: • Integrated Services • Differentiated Services • QoS on Wireless Link • QoS Routing • Cross layer Design Univ. of Tehran Wireless Ad hoc Networking 3

  4. What is QoS? • Many views. User Satisfaction, etc. • Some applications require “deliver on time” assurances • must come from inside the network • Example application (audio) • sample voice once every 125us • each sample has a playback time • packets experience variable delay in network • add constant factor to playback time: playback point Sampler , Microphone Buffer , A D D A converter Speaker Wireless Ad hoc Networking

  5. Applications? • Elastic (delay-tolerant) • Tolerate delays and losses • Can adapt to congestion • Non-elastic (Real-Time) • Needs some kind of guarantee from network • Main Question? How guarantee Delay and losses • End to End, is it enough? • In the Network • QoS Parameters • Bandwidth • Latency • Jitter • Loss Wireless Ad hoc Networking

  6. Utility Curve Shapes U U Elastic Hard real-time BW BW Delay-adaptive U BW Wireless Ad hoc Networking

  7. General view • QoS depends on all layers. • Cross layer problem? • It is a hard problem • It needs some kind of state maintenance in contrast to IP design philosophy. Wireless Ad hoc Networking

  8. What we should do? • Maximize User Satisfaction (U) • Mechanism? • Best effort is not enough • Isolate traffics and flows • Active queue management • Policing • Say no for some traffics • Admission control Wireless Ad hoc Networking

  9. Two Broad Approach Integrated ServicesDifferentiated Services Wireless Ad hoc Networking

  10. Integrated Service • Enhancing IP Service Model • Add QoS service classes • Explicit resource management at IP level • Per flow state maintained at routers which is • used for admission control and scheduling • set up by signaling protocol, users explicitly request their needs. • This is done with RSVP protocol Wireless Ad hoc Networking

  11. Integrated Services Example • Achieve per-flow bandwidth and delay guarantees • Example: guarantee 1MBps and < 100 ms delay to a flow Path RSVP Message Receiver Sender Wireless Ad hoc Networking

  12. Integrated Services Example • Allocate resources - perform per-flow admission control Receiver RESV RSVP Message Sender Wireless Ad hoc Networking

  13. Integrated Services Example • Install per-flow state Receiver Sender Wireless Ad hoc Networking

  14. Integrated Services Example • Install per flow state Receiver RESV RSVP Message Sender Wireless Ad hoc Networking

  15. Integrated Services : Data Path • Per-flow classification Receiver Sender Wireless Ad hoc Networking

  16. Integrated Services : Data Path • Per-flow buffer management Receiver Sender Wireless Ad hoc Networking

  17. Integrated Services Example • Per-flow scheduling Receiver Sender Wireless Ad hoc Networking

  18. Service Types • Multiple service classes • Service can be viewed as a contract between network and communication client • end-to-end service • other service scopes possible • Three defined services • Best-Effort for (best-effort or elastic) • Guaranteed Service for hard real-time (“Real-Time applications”) • Controlled Load for soft real-time (“tolerant” applications) Wireless Ad hoc Networking

  19. Flowspec • Rspec: describes service requested from network • controlled-load: none • guaranteed: delay target • Tspec: describes flow’s traffic characteristics • average bandwidth + burstiness: token bucket filter • token rate r • bucket depth B • must have a token to send a byte • must have n tokens to send n bytes • start with no tokens • accumulate tokens at rate of r per second • can accumulate no more than B tokens Wireless Ad hoc Networking

  20. Per-Router Mechanisms • Admission Control • decide if a new flow can be supported • answer depends on service class and policy • 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 Wireless Ad hoc Networking

  21. What is the Problem? • Intserv can support QoS, but • Too complex • Not scalable • Queuing & scheduling • Classification speed • Hardware Restriction • DiffServ aims at providing QoS with simple mechanisms so that it scales and can be deployed. • push the complexity to the “edges” of the network. • Provide weaker guarantee Wireless Ad hoc Networking

  22. DiffServ Architecture • Ingress routers (Edge Routers) • Perform per aggregate shaping or policing (Behavior Aggregate) • Mark packets with Code Points, each CP represent a Class of Service (DSCP DiffServ Code Point) • Core routers • Implement Per Hop Behavior (PHB) for each DSCP • Process packets based on DSCP DS-2 DS-1 Egress Ingress Egress Ingress Edge router Core router Wireless Ad hoc Networking

  23. Differentiated Service (DS) Field • DS filed reuse the first 6 bits from the former Type of Service (TOS) byte • The other two bits are proposed to be used by ECN 0 5 6 7 DS Field 0 4 8 16 19 31 Version HLen TOS Length Identification Flags Fragment offset IP header TTL Protocol Header checksum Source address Destination address Data Wireless Ad hoc Networking

  24. Per Hop Behavior (PHB) • Define behavior of individual routers rather than end-to-end services • Two PHBs • Assured Forwarding (AF, A type) • Expedited Forwarding (EF, P type) • Plus, best-effort service! Wireless Ad hoc Networking

  25. DiffServ Implementations • Two important proposals • RIO Mechanism (1 service) • The Scalable Share Differentiation architecture (SSD) • Two-Bit architecture • RFC (2475) Wireless Ad hoc Networking

  26. Two-Bit Architecture • Proposes three different levels of service: • Premium Service. • Assured Service. • Best Effort Service. • Two-bit architecture: • Packets get differentiated by two bits in their header. • Premium bit (P-bit) • Assured Service bit (A-bit) Wireless Ad hoc Networking

  27. RFC 2475: Overall Architecture • Classifiers: • Multifield Classifier (MF) • Behavior Aggregate Classifier (BA) Wireless Ad hoc Networking

  28. Traffic Conditioning • Schedulers: Work-conserving or Non-work-conserving • Traffic conditioning uses Non-work-conserving ones • Implementations • Leaky Bucket • Token Bucket • Hybrid approaches • Leaky-Token Bucket • Dual Token Bucket Wireless Ad hoc Networking

  29. Leaky Bucket • Smoothes traffic and generates constant rate b bits r b/s Wireless Ad hoc Networking

  30. Token Bucket Filter • Described by 2 parameters: • Token rate r: rate of tokens placed in the bucket • Bucket depth b: capacity of the bucket • Operation: • Tokens are placed in bucket at rate r • If bucket fills, tokens are discarded • Sending a packet of size P uses P tokens • If bucket has P tokens, packet sent at max rate, else must wait for tokens to accumulate Wireless Ad hoc Networking

  31. Token Bucket Operation Tokens Tokens Tokens Overflow Packet Packet Not enough tokens  wait for tokens to accumulate Enough tokens  packet goes through, tokens removed Wireless Ad hoc Networking

  32. Token Bucket • On the long run, rate is limited to r • On the short run, a burst of size b can be sent • Token Bucket 3 possible uses • Shaping • Delay pkts from entering net (shaping) • Policing • Drop pkts that arrive without tokens • Metering (Marking) • Let all pkts pass through, mark ones without tokens Wireless Ad hoc Networking

  33. QoS Issues on wireless Dynamically varying network topology Imprecise state information Lack of central coordination Error-prone shared radio channel Hidden terminal problem Limited resource availability Insecure medium Univ. of Tehran Wireless Ad hoc Networking 33

  34. Different approaches MAC layer Network Layer Cross Layer Univ. of Tehran Wireless Ad hoc Networking 34

  35. Flexible QoS Model for MANETs (FQMM) • FQMM is the first QoS Model proposed in 2000 for MANETs by Xiao et al. • The model can be characterized as a “hybrid” IntServ/DiffServ Model since • the highest priority is assigned per-flow provisioning. • the rest is assigned per-class provisioning. • Three types of nodes again defined • Ingress (transmit) • Core (forward) • Egress (receive) Wireless Ad hoc Networking

  36. QoS Signaling • Signaling is used to reserve and release resources. • Prerequisites of QoS Signaling • Reliable transfer of signals between routers • Correct Interpretation and activation of the appropriate mechanisms to handle the signal. • Signaling can be divided into “In-band” and “Out-of-band”. • Most papers support that “In-band” Signaling is more appropriate for MANETs. Wireless Ad hoc Networking

  37. In-band VS Out-of Band Signaling • In-band Signaling, network control information is encapsulated in data packets + Lightweight • Not Flexible for defining new Service Classes. • Out-of-band Signaling, network control information is carried in separate packets using explicit control packets. • Heavyweight • signaling packets must have higher priority to achieve on time notification => can lead to complex systems. + Scalability. Signal packets don’t rely on data packets + We can have rich set of services, since we don’t need to “steal“ bits from data packets Wireless Ad hoc Networking

  38. INSIGNIA – MANETs QoS Signaling • INSIGNIA is the first signaling protocol designed solely for MANETs by Ahn et al. 1998. • Can be characterized as an “In-band RSVP” protocol. • It encapsulates control info in the IP Option field (called now INSIGNIA Option field). • It keeps flow state for the real time (RT) flows. • It is “Soft State”. The argument is that assurance that resources are released is more important than overhead that anyway exists. In-band { RSVP { Wireless Ad hoc Networking

  39. INSIGNIA – OPTION Field • Reservation Mode (REQ/RES):indicates whether there is already a reservation for this packet. • If “no”, the packet is forwarded to INSIGNIA Module which in coordination with a AC may either: grant resources  Service Type = RT (real-time). deny resources Service Type = BE (best-effort). • If “yes”, the packet will be forwarded with the allowed resources. • Bandwidth Request (MAX/MIN): indicates the requested amount of bandwidth. Wireless Ad hoc Networking

  40. INSIGNIA – Bottleneck Node • During the flow reservation process a node may be a bottleneck: The service will degrade from RT/MAX -> RT/MIN. • If M2 is heavy-loaded it may also degrade the service level to BE/MIN where there is actually no QoS. Wireless Ad hoc Networking

  41. INSIGNIA is just the signaling protocol of a complete QoS Architecture. INSIGNIA Drawbacks. Only 2 classes of services (RT) and (BE). Flow state information must be kept in mobile hosts. To realize a complete QoS Architecture we also need many other components as well as a Routing Protocol (e.g. DSR, AODV, TORA). INSIGNIA Wireless Ad hoc Networking

  42. Routing is an essential component for QoS. It can inform a source node of the bandwidth and QoS availability of a destination node We know that AODV is a successful an on-demand routing protocol based on the ideas of both DSDV and DSR. We also know that when a node in AODV desires to send a message to some destination node it initiates a Route Discovery Process (RREQ). QoS Routing and QoS for AODV Wireless Ad hoc Networking

  43. QoS for AODV was proposed in 2000 by C. Perkins and E. Royer. The main idea of making AODV QoS enabled is to add extensions to the route messages (RREQ, RREP). A node that receives a RREQ + QoS Extension must be able to meet the service requirement in order to rebroadcast the RREQ (if not in cache). In order to handle the QoS extensions some changes need to be on the routing tables AODV current fields. Destination Sequence Number, Interface, Hop Count, Next Hop, List of Precursors AODV new fields. (4 new fields) 1)Maximum Delay, 2) Minimum Available Bandwidth, 3) List of Sources Requesting Delay Guarantees and 4) List of Sources Requesting Bandwidth Guarantees QoS for AODV Wireless Ad hoc Networking

  44. QoS for AODV - Delay • Handling Delay with the Maximum Delay extension and the List of Sources Requesting Delay Guarantees. • Example shows how the with the Maximum Delay extension and the List of Sources Requesting Delay Guarantees are utilized during route discovery process. Wireless Ad hoc Networking

  45. QoS for AODV - Bandwidth • Handling Bandwidth is similar to handling Delay requests. • Actually a RREQ can include both types. • Example shows how the with the Minimum Available Bandwidth extension and the List of Sources Requesting Bandwidth Guarantees are utilized during route discovery process. Wireless Ad hoc Networking

  46. QoS for AODV - Loosing QoS • Loosing Quality of Service Parameters if after establishment a node detects that the QoS can’t be maintained any more it originates a ICMP QOS_LOST message, to all depending nodes. == > Reason why we keep a List of Sources Requesting Delay/Bandwidth Guarantees. • Reasons for loosing QoS Parameters. • Increased Load of a node. • Why would a node take over more jobs that it can handle? Wireless Ad hoc Networking

  47. Yang Xiao Haizhon Li Sunghyun Choi Protection and Guarantee for Voice and Video Traffic in IEEE 802.11e Wireless LANs

  48. Goal: Provide two level mechanism to enhance IEEE 802.11e (QoS) • First Level • Tried-and-known Method (ETD) • Early protection method (ENB) • That is to enhance admission control of 802.11e • Protect the existing voice and video flow from the new and other existing voice and video flows • The Second Level • That is to reduce influences on collisions by data traffic, and more fully utilize the channel capacity • To protect the existing voice and video flow from the best effort traffic

  49. Motivation • Admission control is not good enough • Admission control is good only when the traffic load is not heavy • Data traffics have influences on QoS flows due to collisions • Even though much of the channel capacity can be used many best-effort traffic degrade the existing voice/video flow since many data transmissions cause many collisions

  50. IEEE 802.11 DCF Each station check whether the medium is idle before attempting to transmit if (idle for DISF period) transmit immediately else (busy for the medium) a. wait until the medium becomes idle b. id the channel stays idle during DIFS period start a backoff process by selecting a backoff counter (BC) Backoff Process For (each slot time) if (medium is idle) BC is decremented else frozen backoff process if(BC == 0) the frame is transmitted

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