Tema 3.- Redes inalámbricas Ad Hoc. Quality of Service (QoS)

Transcription

1 Tema 3.- Redes inalámbricas Ad Hoc. Quality of Service (QoS)! Introducción! QoS in IP based Networks! QoS in MANETs! Propuestas del Grupo GRC " Arquitectura DACME Redes Inalámbricas Máster Ingeniería de Telecomunicación, Universidad de Málaga QoS in MANETs Redes Inalámbricas 2 Introduction # The evolution of the Multimedia Technology and the Commercial Interest of Companies to reach civilian applications have made QoS in MANETs an unavoidable task. # QoS and Overhead are synonyms $!. The idea of providing QoS in MANETs is not to extinct Overhead but to keep it as low as possible. # MANETs : 3 new problems! % Dynamic Topology. % Bandwidth Constrains. % Limited Processing & Storing capabilities of Devices. # What happens with QoS in Wire-based Networks?. Can we port ideas / protocols to MANETs? A Glance At QoS in Mobile Ad-Hoc Networks:

2 Redes Inalámbricas 3 How do we measure the QoS? # Some mostly used QoS attributes % Available Bandwidth % Probability of packet loss % Delay variance (jitter, unpredictable delay) % end-to-end delay (Accumulation of jitter along the path) % Power consumption or battery charge % Service coverage area The QoS Metrics # QoS Metrics can be defined in terms of one of the parameters or a set of parameters in varied proportions Redes Inalámbricas 4 # QoS definition QoS Definition % The collective effect of service performance which determines the degree of satisfaction of a user of a service. & The United Nations Consultative Committee for International Telephony and Telegraph (CCITT) Recommendation E.800 Video frame without QoS Support Video frame with QoS Support

3 Redes Inalámbricas 5 Principles for QOS Guarantees (I) # Consider a phone application at 1Mbps and an FTP application sharing a 1.5 Mbps link. % Bursts of FTP can congest the router and cause audio packets to be dropped. % Want to give priority to audio over FTP. # PRINCIPLE 1: Marking of packets is needed for router to distinguish between different classes; and new router policy to treat packets accordingly. Redes Inalámbricas 6 Principles for QOS Guarantees (II) # PRINCIPLE 2: provide protection (isolation) for one class from other classes. % Applications misbehave (audio sends packets at a rate higher than 1Mbps assumed above). % Require Policing Mechanisms to ensure sources adhere to bandwidth requirements; Marking and Policing need to be done at the edges:

4 Redes Inalámbricas 7 Principles for QOS Guarantees (III) # PRINCIPLE 3: While providing isolation, it is desirable to use resources as efficiently as possible. # Alternative to Marking and Policing: allocate a set portion of bandwidth to each application flow; can lead to inefficient use of bandwidth if one of the flows does not use its allocation. Redes Inalámbricas 8 Principles for QOS Guarantees (IV) # PRINCIPLE 4: Need a Call Admission Process; application flow declares its needs, network may block call if it cannot satisfy the needs. % Remember: Cannot support traffic beyond link capacity

5 Redes Inalámbricas 9 # How is QoS achieved? % Over Provisioning. Add plentiful capacity to the network. & Easy! (e.g. upgrade from 10Mb to 100Mb) & Can be done gradually. & But we remain at 1 service class (best effort) again. QoS in IP Based Networks % Network Traffic Engineering. Make the Network more sophisticated! (e.g. Traffic Classes, Connection Admission Control, Policy Managers, ) & Reservation-based Engineering. (e.g. RSVP/IntServ, ATM) & Reservation-less Engineering. (e.g. DiffServ) Used in today s Differentiated Services» IPv4 TOS octect» IPv6 traffic Class octect Redes Inalámbricas 10 Integrated Services # Attempt to modify Internet service model to support diverse application requirements # Any data flow that desires better than best-effort delivery requests and reserves resources at routers along the path % RSVP is the recommended reservation protocol # If insufficient resources are available, the flow is denied admission into the network # Each router % Maintains reservation state for each flow % Classifies every packet and decides forwarding behavior % Monitors the flow to ensure that it does not consume more than the reserved resources # Advantages % Enables fine-grained QoS and resource guarantees # Disadvantages % Not scalable, harder to administer

6 Redes Inalámbricas 11 Differentiated Services # Moves admission control and flow monitoring to the edge of the network # Edge nodes classify and mark packets to receive a particular type of service % Diff Serv Code Point (DSCP) & Packet is marked in the Type of Service (TOS) in IPv4, and Traffic Class in IPv6. % Finite set of DSCPs defined # Interior nodes determine the type of service for forwarded packets based on their DSCP values # Advantages % More scalable % No per-flow state % Easier to administer # BIG ADVANTAGE: % No state info to be maintained by routers! # Disadvantages % Cannot provide the same per-flow guarantees as IntServ Redes Inalámbricas 12 QoS in MANETs # A lot of work has been done in supporting QoS in the Internet, but unfortunately none of them can be directly used in MANETs because of the bandwidth constraints and dynamic network topology of MANETs. # To support QoS, the link state information such as delay, bandwidth, cost, loss rate, and error rate in the network should be available and manageable. # However, getting and managing the link state information in MANETs is very difficult because the quality of a wireless link is apt to change with the surrounding circumstances. # The resource limitations and the mobility of hosts make things more complicated. # Hard QoS guarantee is not possible in MANETs % Adaptive QoS % Service Differentiation

7 Redes Inalámbricas 13 Why QoS is Hard in Mobile Ad Hoc Network? # Dynamic Network Topology % Flow stop receiving QoS provisions due to path disconnections % New paths must be established, causing data loss and delays # Imprecise state information % Link state changes continuously % Flow states change over time # No central control for coordination # Error-Probe shared medium # Hidden terminal problem # Limited resources availability % Bandwidth, battery Life, Storage, processing capabilities # Insecure medium Redes Inalámbricas 14 Main issues # The main issues to consider to achieve good quality are: % MAC level QoS: IEEE e required to differentiate from bandwidth greedy best-effort traffic % Admission control: to avoid more connections than the MANET can handle % Increase routing effectiveness: even by using layer-2 aware routing protocols such as AODV or DSR, video transmission gaps are still too large to be handled by a video codec # For video streaming % Also ' H.264 codec tuning:

8 Redes Inalámbricas 15 QoS Signalling Terminology # Signaling is used to reserve and release resources. # Prerequisites of QoS Signalling % Reliable transfer of signals between routers % Correct Interpretation and activation of the appropriate mechanisms to handle the signal. & It means that signaling must be understandable and implemented by the rest of the nodes # Signaling can be divided into In-band and Out-of-band % In-band: integrated in data packets % Out-of-band: explicit use of control packets. Performance? & This packets should have higher priority & RSVP is an example of out-of-band signaling Is the facto signaling protocol for IntServ # Most papers support that In-band Signaling is more appropriate for MANETs. Redes Inalámbricas 16 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. Version Hdr Len Prec TOS Identification Flags TTL Protocol Source Address Destination Address Options 32 bits (Shaded fields are absent from IPv6 header) Total Length Fragment Offset Header CheckSum Padding # 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

9 Redes Inalámbricas 17 # QoS Routing QoS in MANETs, an Integrated Vision % QoS enabled routing (AODV/OLSR) % CEDAR(Core-Extraction Distributed Ad-hoc Routing) % Ticket based Probing (distributed QoS routing) % Predictive Location-Based QoS Routing Protocol % Bandwidth Routing Protocol % Trigger-Based Distributed QoS Routing Protocol % On-Demand QoS Routing Protocol % QoS-Enabled Ad Hoc On-Demand Distance Vector Routing Protocol % On-Demand Link-state Multipath QoS Routing Protocol % Asynchronous Slot Allocation Strategies % Redes Inalámbricas 18 QoS Routing # 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). Mona Ghassemian, King s College, September 2003

10 Redes Inalámbricas 19 # QoS information is added to the RREQ packet # Intermediate nodes forward the RREQ only if they have sufficient resources to meet the QoS requirement # Resource information is updated in the RREQ by intermediate nodes # Destination sends resource information back to source in the RREP message QoS-Extensions of AODV: Basic Idea S RREQ RREP D Redes Inalámbricas 20 QoS for AODV - Delay # Handling Delay with the Maximum Delay extension and the List of Sources Requesting Delay Guarantees. % RREQ includes delay % Each node has its NODE_TRANSVERSAL_TIME # Example shows how the with the Maximum Delay extension and the List of Sources Requesting Delay Guarantees are utilized during route discovery process. 1 ingress A RREQ1 delay=100 2 x RREQ2 delay=10 RREP1 delay=80 core B Traversal_time= 3 0 cache delay(b->d)=80 RREQ1 delay=70 RREP1 delay=50 core C Traversal_time= 5 0 cache delay(c->d)=50 RREQ1 delay=20 =TraversalTime + delay RREP1 delay=0 egress D

11 Redes Inalámbricas 21 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. ingress A 1 RREQ1 min_bandwidth=10kbps 2 RREQ2 minband=80k x RREP1 bandwidth=50 core B Available_Bandwidth = 100K cache band(b->d)=50 RREQ1 min_bandwidth=10kbps RREP1 bandwidth=50 core C Available_Bandwidth = 50K cache band(c->d)=50 RREQ1 min_bandwidth=10kbps min{inf,50} RREP1 bandwidth=inf egress D Redes Inalámbricas 22 ingress A 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? cache delay(b->d)=80 QOS_LOST core B Traversal_time= 3 0 cache delay(b->d)=80 QOS_LOST core C Traversal_time= 5 0 cache delay(c->d)=50 egress D

12 Redes Inalámbricas 23 Propuestas del Grupo GRC: Arquitectura DACME # Previous proposals have strong requirements: % All terminals must be equipped with the same software and similar hardware % All terminals must perform QoS related tasks % If some of the terminals do not offer QoS support, the whole QoS framework fails or there is severe malfunctioning # None of the previous proposals has taken into consideration that: % The bandwidth reservation process is NP-hard % QoS at the MAC layer is fundamental % Multipath routing algorithms can offer important benefits % The MANET paradigm is based on user cooperation, but in most cases we can not force users to cooperate Redes Inalámbricas 24 Propuestas del Grupo GRC: Arquitectura DACME! Propuestas del Grupo GRC % Arquitectura DACME Multipath routing algorithm [1] TCP/UDP IP MDSR IEEE e IEEE g DACME Distributed admission control Prioritized channel access

13 Redes Inalámbricas 25 # Only two: DACME - Requirements % All stations that have IEEE e interfaces should map the IP packet's TOS to a MAC-level Access Category (basic requirement to achieve good performance) % Sources and destinations of QoS traffic should implement DACME (Distributed Admission Control for MANET Environments) Redes Inalámbricas 26 DACME - Admission control # DACME makes periodic end-to-end network measurements using probes # Intermediate stations are not aware of DACME's tasks % DACME uses UDP/IP # Decisions on whether to admit, maintain or drop a QoS flow are based on DACME's periodic measurements and the QoS requirements of each specific flow

14 Redes Inalámbricas 27 DACME architecture # 1. The application registers with DACME, indicating the source and destination port, the destination's IP address and the QoS requirements # 2. DACME periodically sends probes to assess available bandwidth on the path # 3. The port state is set to up or down according to current network conditions # 4. The packet filter module is responsible for enforcing accept/reject decisions, and also for changing the packet's TOS field if accepted Redes Inalámbricas 28 # General simulation setup: % ns-2 discrete event simulator % Radio interfaces are IEEE g/e enabled Performance evaluation % Scenarios are sized 1900x400 m2 and composed by 50 nodes % Radio range is of 250 meters (4 hops between nodes on average) % Nodes move according to the random way-point model at a constant speed of 5 m/s % Comparison between DSR & MDSR routing protocols % Simulation time is of 300 seconds for each experiment % DACME source/destination pairs have a DACME agent attached

15 Redes Inalámbricas 29 # 4 Video sources and 3 Voice sources regulated by DACME % Video sources generate CBR traffic at 1 Mbit/s in the Video AC % Voice sources: & VoIP streams simulated using a Pareto On/Off distribution & both burst and idle time set to 500 ms & shaping factor used is 1.5, average data rate is of 100 kbit/s % Sources are turned off in the same order they were turned on # 4 background traffic sources % Traffic is negative-exponentially distributed Traffic % Variable traffic loads; load share per AC is: 50% to the Video AC, 25% to Besteffort AC, 25% to Background AC % These sources are active all the time Redes Inalámbricas 30 Performance in terms of throughput/losses # On average the throughput of DACME-regulated sources is much more stable (always close to the source data rate of 1 Mbit/s) # Voice sources do not generate constant data-rate traffic # In terms of packet losses we achieve very significant improvements

16 Redes Inalámbricas 31 Performance in terms of end-to-end delay # In terms of average end-to-end delay, DACME allows achieving much lower values than its non-dacme counterpart Redes Inalámbricas 32 Routing overhead and traffic acceptance rate # In terms of routing overhead, DACME reduces it by avoiding routing collapse situations # In terms of traffic acceptance rate: % high data-rate sources (video) are more penalized