Quality of Service QoS in Data Networks Raj Jain Washington University in Saint Louis Saint Louis MO 63130 Jain cse wustl edu These slides are available on line at http www cse wustl edu jain cse574 06 Washington University in St Louis CSE574s 9 1 2006 Raj Jain Overview QoS Mechanisms ATM QoS Integrated services RSVP Differentiated Services Multiprotocol Label Switching MPLS Comparison of different QoS approaches QoS over Wireless Washington University in St Louis CSE574s 9 2 2006 Raj Jain Quality of Service Service Movie Song Telephone Call FTP Quality of Service Picture quality Color quality sound quality For network based services service quality may depend upon Throughput Min max average rate Delay Max delay delay variation Jitter Packet Loss Rate Reliability Links going up down Each layer PHY MAC IP TCP and application has to have mechanisms to guarantee QoS Washington University in St Louis CSE574s 9 3 2006 Raj Jain QoS Components 1 Signaling 3 4 2 Admission control Shaping Policing 5 Classification Scheduling 6 8 Routing Buffer Mgmt 9 Traffic Monitoring 7 Drop Policies and feedback Washington University in St Louis CSE574s 9 4 2006 Raj Jain QoS Components 1 Signaling Users need to tell negotiate their QoS requirements with the network 2 Admission Control Network can deny requests that it can not meet 3 Shaping Traffic is smoothed out so that it is easier to handle 4 Policing Ensuring that the users are sending at the rate they agreed to 5 Marking Classification Packets are classified based on the source destination TCP ports application 6 Scheduling Different flows get appropriate treatment 7 Drop Policies Low priority packets are dropped 8 Routing Packets are sent over paths that can meet the QoS 9 Traffic Management Sources may be asked to reduce their rates to meet the loss rate and delay guarantees Washington University in St Louis CSE574s 9 5 2006 Raj Jain Traffic Shaping Altering the traffic characteristics of a given flow is called traffic shaping The source must shape its traffic prior to sending it to network so it does not violate traffic contract Shaper Leaving traffic with desired characteristics Arriving traffic with undesired characteristics Washington University in St Louis CSE574s 9 6 2006 Raj Jain Token Bucket Shaper Tokens arrive periodically at Average Rate Token Incoming Traffic Washington University in St Louis Bucket Size K Server CSE574s 9 7 Shaped Traffic 2006 Raj Jain Traffic Policing Users violating the traffic contract can jeopardise the QoS of other connections The network must protect well behaving users against such traffic violations Policing functions are deployed at the edge entry of the network Conforming traffic admitted into network Policer Arriving traffic Non conforming traffic dropped Washington University in St Louis CSE574s 9 8 2006 Raj Jain Peak Rate Policing with Leaky Bucket Enforces sustained rate and maximum burst size Requires only one counter counter is decremented to a minimum of zero at the avg rate counter is incremented by one to a maximum of a limiting value for each packet arrival An arriving packet is nonconforming if counter is at its limit Washington University in St Louis CSE574s 9 9 Incoming Packets Rejected Accepted 2006 Raj Jain Queuing and Scheduling for QoS Classification Incoming Packets Drop Policy Scheduling Buffer Allocation Packets from multiple flows are queued at a given transmission link To give different QoS multiple queues may be used Buffer allocation scheduling and drop policies for each queue are set to provide different QoS Washington University in St Louis CSE574s 9 10 2006 Raj Jain ATM Networks PBX 1 PBX 3 5 2 3 ATM cells are fixed size 48 byte payload 5 byte header IP packets can be segmented into ATM cells at entry to ATM connection and reassembled at the end Each cell has a circuit number Virtual Circuit Id VCI Circuit number determines the cell s queuing and forwarding Circuits have be set up before use Circuits are called Virtual Circuits VCs Multiple VCs can be grouped in to a virtual path VP Washington University in St Louis CSE574s 9 11 2006 Raj Jain ATM Service Categories Constant Bit Rate CBR Throughput delay delay variation guaranteed Real Time Variable Bit Rate rt VBR Average Throughput delay delay variation guaranteed Non Real Time Variable Bit Rate nrt VBR Throughput guaranteed Unspecified Bit Rate UBR No Guarantees Best Effort Available Bit Rate ABR Minimum Throughput Very low loss Feedback Guaranteed Frame Rate GFR Minimum Throughput Frame based guarantee ATM also has Rate shaping Connection Admission control CAC Policing and QoS based routing PNNI Washington University in St Louis CSE574s 9 12 2006 Raj Jain Service Class and QoS Parameters Service Class Traffic Parameter QoS Parameter CBR PCR maxCTD CDV CLR rt VBR PCR SCR MBS maxCTD CDV CLR nrt VBR PCR SCR MBS CLR ABR PCR MCR CLR network specific UBR PCR No QoS CDV Cell delay variation CLR Cell Loss Rate CTD Cell Transfer Delay Washington University in St Louis PCR Peak Cell Rate SCR Sustained avg Cell Rate MCR Minimum Cell Rate MBS Maximum Burst Size CSE574s 9 13 2006 Raj Jain ATM QoS Issues Can t easily aggregate QoS VP VCs Can t easily specify QoS What is the CDV required for a movie Signaling too complex Need Lightweight Signaling Need Heterogeneous Point to Multipoint Variegated VCs Need QoS Renegotiation Need Group Address Need priority or weight among VCs to map DiffServ and 802 1D Washington University in St Louis CSE574s 9 14 2006 Raj Jain Integrated Services Best Effort Service Like UBR Controlled Load Service Performance as good as in an unloaded datagram network No quantitative assurances Like nrt VBR or UBR w minimum cell rate MCR Guaranteed Service rt VBR Firm bound on data throughput and delay Delay jitter or average delay not guaranteed or minimized Every element along the path must provide delay bound Is not always implementable e g Shared Ethernet Like CBR or rt VBR Washington University in St Louis CSE574s 9 15 2006 Raj Jain RSVP Resource ReSerVation Protocol Internet signaling protocol Carries resource reservation requests through the network including traffic specs QoS specs network resource availability Sets up reservations at each hop Traffic Spec Network Traffic Spec Sender Receiver QoS Spec Available Resources AdSpec Washington University in St Louis CSE574s 9 16 2006 Raj Jain RSVP Messages S1 S2 R1 R2 R4 R3 H5 H4 H3 S1 R1 R4 H5 H4 S2 R2 R3 H3 Sources send PATH messages to the multicast address Contain
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