Post on 13-Jan-2016
description
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 sharingMulti-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
• Resv messages
• PathErr, PathTear, ResvErr, ResvTear, ResvConf Messages
Phop, Sender template, Tspec, Adspec
Reservation style, Filter specification, Rspec, Tspec
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
Appli-cation RSVP
proc.Polcyctrl
class-ifier
PacketScheduler
Admissionctrl
Classifierpacket
scheduler
admissionctrl.
RoutingProcess
RSVPPocess
Polcyctrl.
Data
RSVP RSVP
Data Data
RouterHost
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 boundariesService 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
classifier
Meter
MarkerShaper/Dropper
Packets
Terminology
• 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 in-profile or out-of-profile
•BA Classifier
•MF Classifier
Terminology
• Traffic Conditioner
•Meter
•Marker
•Shaper
•Dropper
•Host Marking
•Router Marking
Service Taxonomy
• Quantitative Service
• Qualitative Service
• Relative Quantification Service
Traffic offered at service level A will be delivered with low latency
90% of in profile traffic delivered at service level B will experience of no more than 50 msec latency
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
BB
Source
Dest.
Edge Router
Core Router
DS Domain
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
Ingress
ingress
egress
egress
Routing
replication
Interface A
Interface B
Interface C
Interface D
Multicast packet replication in a DS router
NRS cont.
Sender
DS domain DS domain
Interior Router
Boundary Router
Receiver
Multicast branch with reservd bandwidth
Multicast branch without reserved
NRS cont.
Sender
DS domain DS domain
Interior Router
Boundary Router
Receiver
Multicast branch with reservd bandwidth
Multicast branch without reserved
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 thr
ough 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
IS Domain DS Domain IS DomainS 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 DiffservGranularity of servicedifferentiation
Individual Flow Aggregate offlows
State in routers(e.g.scheduling, buffermanagement)
Per Flow Per Aggregate
Traffic ClassificationBasis
Several header fields DS Field
Type of servicedifferentiation
Deterministic orstatistical guarantees
Absolute orrelativeassurance
Admission Control Required Required forabsolutedifferentiation
Signaling Protocol Required(RSVP) Not required forrelative schemes
Comparison of Intserv & Diffserv Architectures
Intserv Diffserv Coordination for service differentiation
End-to-End Local (Per-Hop)
Scope of Service Differentiation
A Unicast or Multicast path
Anywhere in a Network or in specific paths
Scalabilty Limited by the number of flows
Limited by the number of classes of service
Network Accounting Based on flow characteristics and QoS requirement
Based on class usage
Network Management Similar to Circuit Switching networks
Similar to existing IP networks
Interdomain deployment
Multilateral Agreements
Bilateral Agreements