Transcript ppt
QoS ( Intserv & Diffserv) BY ANJALI KULKARNI YI-AN CHEN QoS • Current Internet offers best effort service only • As the Internet is the ubiquitous communications infrastructure, there is a clear need for providing differentiated classes of service to network traffic What is Intserv • Service differentiation in the Internet • Focuses on individual packet flows • Each flow requests specific levels of service from network • Levels of service quantified as a minimum service rate, or a maximum tolerable end-to-end delay or loss rate • Network grants or rejects the flow requests, based on availability of resources and the guarantees provided to other flows Interserv • Best effort service • Real time service • Controlled link sharing Multi-entity link-sharing Multi-protocol link-sharing Multi-service sharing Framework of IS Model • • • • Packet scheduler Admission control Classifier Reservation setup protocol(RSVP) RSVP • Path messages Phop, Sender template, Tspec, Adspec • Resv messages Reservation style, Filter specification, Rspec, Tspec • PathErr, PathTear, ResvErr, ResvTear, ResvConf Messages Processing and Propagation of Path Messages by Network Routers • Update the path state entry • Set cleanup timer • Create and forward Path message Any change to stored path state or a change in the set of outgoing interfaces in the data forwarding path Every refresh period timeout interval RSVP Host Router RSVP Application RSVP proc. RSVP Routing Process Polcy ctrl RSVP Pocess Data Admis sion ctrl classifier Packet Scheduler Classifier Data packet scheduler Polcy ctrl. admis sion ctrl. Data RSVP Filters Sender Selection Distinct Shared Explicit Fixed-Filter (FF) Style Share-Explicit (SE) Style Wildcard None Defined Wildcard-Filter (WF) Style Factors Impeding Deployment of Intserv/RSVP • Use of per-flow state and per-flow processing raises scalability concerns for large network • The necessary policy control mechanisms have only recently become available What is Diffserv • Based on a model where traffic entering a network is classified , possibly conditioned at the boundaries of the network, and assigned to different service classes • Here, we avoid complexity and maintenance of per-flow state information in core nodes and push unavoidable complexity to the network edges What is Diffserv • Provide scalable service differentiated in the internet that can be used to permit differentiated pricing of internet service • Separate packet forwarding model from routing model Terminology • • • • • • Per Hop Behavior(PHB) DS Domain( e.g. ISP, intranet) DS Boundary Node(Egress & Ingress) DS Interior Node DS Codepoint(DSCP) DS Behavior Aggregate Terminology • Bandwidth Broker (BB) Logical entity, can be mapped to a single or multiple physical entity A logical entity residing in each administrative domain managing internal demands & resources according to some policy database (who can do what where and when) Setting up & maintaining bilateral agreement with neighbor domains Terminology • SLA(SLS) & TCA(TCS) Customer/Provider boundaries Service Level Agreement A set of parameters and their values which together define the service offered to a traffic stream by a DS domain Traffic Conditioning Agreement A set of parameters and their values which together specify a set of classifier rules and traffic profile SLA Logical View of Packet Classifier and Traffic Conditioner Meter Packets classifier Marker Shaper/ Dropper Terminology • Classifier •BA Classifier •MF Classifier • Traffic Profile Specifies the temporal properties of a traffic stream selected by a classifier. It provides rules for determining whether a particular packet is inprofile or out-of-profile Terminology • Traffic Conditioner •Meter •Marker •Host Marking •Router Marking •Shaper •Dropper Service Taxonomy • Quantitative Service Traffic offered at service level A will be delivered with low latency • Qualitative Service 90% of in profile traffic delivered at service level B will experience of no more than 50 msec latency • Relative Quantification Service Traffic with drop precedence AF12 has a higher probability of delivery than traffic with drop precedence AF13 Assured Forwarding (AF) Class • As long as aggregate traffic from some sites connecting to internet does not exceed the subscribed information rate, forward packets with high probability • AF PHB group - Forwarding of IP packets in N independent AF classes. Within each class, an IP packet is assigned M different levels of drop precedence • Queuing and discard behavior Expedited Forwarding (EF) Class • Providing low loss, low latency, low jitter, assured bandwidth, end-to-end service through DS domains • EF PHB A router uses policing and shaping mechanism to ensure that the maximum arrival rate of a traffic aggregate is less than its minimum departure rate Working within a Domain Edge Router Source Core Router BB DS Domain Dest. Working within a Domain • Step 1 Source sends request message to first hop router • Step 2 First hop router sends request to BB, which sends back either a accept or reject • Step 3 If accept, either source or first hop router will mark DSCP and start sending packets Working within a Domain • Step 4 Edge router checks compliance with SLA and does policing. Excess packets are either discarded or marked as low priority to comply with the SLA • Step 5 Core routers will just look at DSCP and decide PHB Intra-Domain Resource Allocation Architecture Edge Router-BB Communication • BB contains the flow database containing information regarding flows requesting increased level of service . It contains ingress/egress interface, resources requested, start/finish time • BB sends the TCA to the domain’s edge routers Edge Router-BB Communication • COPS is used for this. BB’s COPS server TCA to COPS client residing at edge router • COPS client translates these commands to parameters understood by forwarding path via the Forwarding path driver(FPD) Interdomain Communication Functions of BB • Negotiation of SLAs with BBs of neighboring domains • Translation of SLAs into one or several TCAs for edge devices • Delivery of the TCAs to the edge routers of the administered domain, using one of many proposed protocols Steps in Interdomain Communication • Assumption Needs of domain 1 towards domain 3 are satisfied by a 64kb/s flow of premium traffic • Step 1 BB1 learns internally that a 64kb/s SLA is needed • Step2 BB1 requests the SLA from BB2, BB2 performs admission control Steps in Interdomain Communication • Step 3 If the request is admitted, BB2 sends a TCA derived from the SLA requested to R2( it’s administered edge router) • Step 4 BB2 responds positively to BB1. This TCA models the traffic to be transferred from domain1 via R2 Steps in Interdomain Communication • Step 5 A similar TCA is sent by BB1 to it’s administered edge router R1 instructing it to allow the given traffic to flow out to domain 2 • Step 6 BB2 may request more premium resources from BB3 to aggregate the new premium traffic demand to the existing SLA between BB2 and BB3 Multicasting in DS Domain • Neglected Reservation Subtree Problem (NRS) • Heterogeneous Multicasting Groups • Dynamic of Arbitrary Sender Change NRS Interface A Routing Interface C replication Ingress egress Interface B Interface D ingress egress Multicast packet replication in a DS router NRS cont. Multicast branch with reservd bandwidth Interior Router Multicast branch without reserved Boundary Router Sender Receiver DS domain DS domain NRS cont. Multicast branch with reservd bandwidth Interior Router Multicast branch without reserved Boundary Router Sender Receiver DS domain DS domain Heterogeneous Multicasting Groups • Participants requesting a best effort quality only should also be able to participate in a group communication which otherwise utilises a better service class • Support heterogeneous groups with different service classes in a consistent way Dynamics of Arbitrary Sender Change • A sender resource must be reserved seperately if simultaneous sending delivery trees are used Security Consideration • Theft of service • Denial of service 2 Bit Differentiated Services Architecture for the Internet • Premium service Premium service levels are specified as a desired peak bit rate for a specific flow • Assured service • Best-effort service Block Diagram of First Hop Router Input Functionality Markers to Implement the 2 Different Services Border Router Input Interface Profile Meters Router Output Interface for 2-bit Architecture Statically Configured Example with no BB Messages Exchanged • All allocations are statically preallocated through purely bilateral agreements between users. This negotiation is done by human repreentatives of each domain • BBs perform function to allocate profile within their local domain End-to-End Example with Static Allocation End-to-End Static Allocation eg. with no Remaining Allocation First Step in End-to-End Dynamic Allocation Example Second Step in End-to-End Dynamic Allocation Example Third Step in End-to-End Dynamic Allocation Example Fourth Step in End-to-End Dynamic Allocation Example Final Step in End-to-End Dynamic Allocation Example Intserv Operation over Diffserv S IS Domain DS Domain IS Domain D Intserv Operation over Diffserv • Selecting an appropriate PHB for the requested service • Performing appropriate policing at the edges of Diffserv region • Exporting Intserv parameters from the Diffserv region • Performing admission control on the Intserv requests Statically Provisioned Diffserv Network Region • RSVP messages carried transparently through the Diffserv network region • The corresponding service level is determined by the Intserv to Diffserv mapping discussed previously RSVP -Aware Diffserv Network Region • Signaling between the Diffserv network region and network elements outside it Comparison of Intserv & Diffserv Architectures Intserv Granularity of service differentiation State in routers(e.g. scheduling, buffer management) Traffic Classification Basis Type of service differentiation Individual Flow Admission Control Required Signaling Protocol Required(RSVP) Diffserv Per Flow Aggregate of flows Per Aggregate Several header fields DS Field Deterministic or statistical guarantees Absolute or relative assurance Required for absolute differentiation Not required for relative schemes Comparison of Intserv & Diffserv Architectures Coordination for service differentiation Scope of Service Differentiation Scalabilty Network Accounting Network Management Interdomain deployment Intserv Diffserv End-to-End Local (Per-Hop) A Unicast or Multicast Anywhere in a path Network or in specific paths Limited by the number Limited by the of flows number of classes of service Based on flow Based on class characteristics and QoS usage requirement Similar to Circuit Similar to existing Switching networks IP networks Multilateral Bilateral Agreements Agreements