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