Quality of Service Frameworks

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Quality of ServiceFrameworks

• Hamed Khanmirza
• Principles of Network
• University of Tehran

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What is QoS?

• The capability to control traffic handling
  mechanisms in the network such that the network
  meets the service needs of certain applications
  and users subject to network policies.
• Applications
• Elastic (delay-tolerant)
• Tolerate delays and losses
• Can adapt to congestion
• Non-elastic (Real-Time)
• Needs some kind of guarantee from network
• QoS Parameters
• Bandwidth
• Latency
• Jitter
• Loss

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Utility Curve Shapes
U
U
Elastic
Hard real-time
BW
BW
Delay-adaptive
U
BW
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Integrated Services
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Service characteristic

• Enhancing IP Service Model
• Add QoS service classes
• Explicit resource management at IP level
• Per flow state maintained at routers which is
• used for admission control and scheduling
• set up by signaling protocol, users explicitly
  request their needs.
• This is done with RSVP protocol

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Integrated Services Example

• Achieve per-flow bandwidth and delay guarantees
• Example guarantee 1MBps and lt 100 ms delay to a
  flow

Receiver
Path RSVP Message
Sender







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Integrated Services Example

• Allocate resources - perform per-flow admission
  control

Receiver
RESV RSVP Message
Sender







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Integrated Services Example

• Install per-flow state

Receiver
Sender







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Integrated Services Example

• Install per flow state

Receiver
RESV RSVP Message
Sender







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Integrated Services Example Data Path

• Per-flow classification

Receiver
Sender











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Integrated Services Example Data Path

• Per-flow buffer management

Receiver
Sender











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Integrated Services Example

• Per-flow scheduling

Receiver
Sender











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Service Types

• Multiple service classes
• Service can be viewed as a contract between
  network and communication client
• end-to-end service
• other service scopes possible
• Three defined services
• Best-Effort for (best-effort or elastic)
• Guaranteed Service for hard real-time (Real-Time
  applications)
• Controlled Load for soft real-time (tolerant
  applications)

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Differentiated Services
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What is the Problem?

• Goal providing support for wide variety of
  applications
• Interactive TV, IP telephony, on-line gamming
  (distributed simulations), VPNs, etc
• Problem
• Best-effort cannot do it
• Intserv can support all these applications, but
• Too complex
• Not scalable
• Queuing scheduling
• Classification speed
• Hardware Restriction
• DiffServ aims at providing QoS with simple
  mechanisms so that it scales and can be deployed.
• push the complexity to the edges of the
  network.
• Provide weaker guarantee

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DiffServ Architecture

• Ingress routers (Edge Routers)
• Perform per aggregate shaping or policing
  (Behavior Aggregate)
• Mark packets with Code Points, each CP represent
  a Class of Service (DSCP DiffServ Code Point)
• Core routers
• Implement Per Hop Behavior (PHB) for each DSCP
• Process packets based on DSCP

DS-2
DS-1
Ingress
Egress
Egress
Ingress
Edge router
Core router
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Differentiated Service (DS) Field
0
5
6
7
DS Filed
0
4
8
16
19
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Version
HLen
TOS
Length
Identification
Flags
Fragment offset
IP header
TTL
Protocol
Header checksum
Source address
Destination address
Data

• DS filed reuse the first 6 bits from the former
  Type of Service (TOS) byte
• The other two bits are proposed to be used by ECN

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Per Hop Behavior (PHB)

• Define behavior of individual routers rather than
  end-to-end services
• Two PHBs
• Assured Forwarding (AF, A type)
• Expedited Forwarding (EF, P type)
• Plus, best-effort service!

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EF PHB (Premium)

• Provides the abstraction of a virtual pipe
  between an ingress and an egress router
• Network
• No loss
• low delay jitter
• User
• Send traffic based on SLA
• Excess traffic is delayed, and dropped when
  buffer overflows
• Signaling, admission control may get more
  elaborate in future (DiffServ/RSVP)

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Assured Forwarding PHB

• Possible service
• strong assurance for traffic within profile
• Out-of-profile traffic will be marked as lower
  class (i.e. BE)
• Network
• lower loss rate than best-effort
• In case of congestion best-effort packets are
  dropped first
• User sends no more assured traffic than its
  profile
• If it sends more, the excess traffic is converted
  to best-effort
• IETF defines AF as (RFC 2477)
• 4 classes
• Each with 3 drop precedence
• Order of packets must be preserved

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Provisioning Configuration

• To provide network QoS, some configuration and
  provisioning is required
• Provisioning
• Static and long-term management tasks
• Enhancing network equipment
• Interface definition
• Link speed and BW
• Configuration
• Dynamic and short-term tasks
• Direct manipulation of traffic handling mechanisms

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Service Level Agreement Policy

• Agreements/service provided within a domain
• Service Level Agreement (SLA) with ISP
• Policy
• A high level description of the quality and
  efficiency objectives to be met by the network
• Policy is set by SLA

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Example of an SLA

• Traffic submitted by customer c1
• and marked with DSCP EF
• and destination address in subnet 2.x.x.x
• and conforming to profile p1
• Will be delivered to egress point B with
• latency not exceeding 100ms and a
• drop-probability less than 0.1
• Traffic submitted by customer c1
• and marked with DSCP EF
• and destination address in subnet 2.x.x.x
• and not conforming to profile p1
• Will be discarded

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Example of an SLA

• Traffic submitted by customer c1
• and marked with DSCP EF
• and destination address in subnet 3.x.x.x
• and conforming to profile p2
• Will be delivered to egress point C with
• latency not exceeding 100ms and a
• drop-probability less than 0.1
• Traffic submitted by customer c1
• and marked with DSCP EF
• and destination address in subnet 3.x.x.x
• and not conforming to profile p2
• Will be discarded

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Example of an SLA

• Traffic submitted by customer c1
• and marked with DSCP EF
• and destination address not in subnet 2.x.x.x
• and destination address not in subnet 3.x.x.x
• Will be discarded
• Traffic submitted by customer c1
• and not marked with DSCP EF
• Will be delivered with best-effort service
• P1
• Conforming traffic must not exceed 64kbps over
  any 5msec interval
• P2
• Conforming traffic must not exceed 128kbps over
  any 2.5msec interval

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Pushed vs. Signaled
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Components of Policy System
Functional Layers No physical
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Distributed Data Store - Directory
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Interior Provisioning
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Assured Service

• Large spatial granularity service
• Theoretically, user profile is defined
  irrespective of destination
• This makes service very useful, but hard to
  provision
• Over provision?

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Multicast Problems in DiffServ

• Multicast
• Problem
• Dynamic trees
• Solutions
• Different DSCP
• Some determined tree structure
• Remarking and shaping at boundaries

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DiffServ Implementations

• Two important proposals
• RIO Mechanism (1 service)
• The Scalable Share Differentiation architecture
  (SSD)
• Two-Bit architecture
• RFC (2475)

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Two-Bit Architecture

• Proposes three different levels of service
• Premium Service.
• Assured Service.
• Best Effort Service.
• Two-bit architecture
• Packets get differentiated by two bits in their
  header.
• Premium bit (P-bit)
• Assured Service bit (A-bit)

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Leaf Router Input Functionality
Marker 1
Flow 1
Marker N
Flow N
Arriving packet
MF Packet classifier
Forwarding engine
Clear AP bits
Best effort
classify packets based on packet header
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Markers in Leaf Routers
Drop on overflow
Packet output
Wait for token
Set P bit
Packet input
No token
token
Packet output
Packet input
Test if token
Set A bit
RIO is applied here
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Red with In or Out (RIO)

• Similar to RED
• With two separate probability curves
• In (of profile)
• Out (of profile)
• Out class has
• lower Minthresh, so packets are dropped from this
  class first
• Based on queue length of all packets
• In Class
• As avg queue length increases, in packets are
  also dropped
• Based on queue length of only in packets

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Output Forwarding

• 2 queues
• High Priority EF packets
• Lower priority queue implements RED In or Out
  scheme (RIO)
• Usually scheduling scheme is Strict Priority

EF
P bit set?
High-priority Q
Send Packet
AF
If A bit set incr a_cnt
Low-priority Q
If A bit set decr in_cnt
RIO queue management
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Intra Domain Behavior

• Each domain is assigned a Bandwidth Broker (BB)
• Usually, used to perform ingress-egress bandwidth
  allocation
• BB is responsible to perform admission control in
  the entire domain
• BB not easy to implement
• Require complete knowledge about domain
• Single point of failure, may be performance
  bottleneck
• Designing BB still a research problem

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Example

• Achieve end-to-end bandwidth guarantee

BB
BB
BB
receiver
sender
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RFC 2475 Overall Architecture

• Classifiers
• Multifield Classifier (MF)
• Behavior Aggregate Classifier (BA)

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Traffic Conditioning

• Schedulers
• Work-conserving
• Non-work-conserving
• Traffic conditioning uses Non-work-conserving
  ones
• Implementations
• Leaky Bucket
• Token Bucket
• Hybrid approaches
• Leaky-Token Bucket
• Dual Token Bucket

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Leaky Bucket

• Smoothes traffic and generates constant rate

b bits
r b/s
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Token Bucket Filter

• Described by 2 parameters
• Token rate r rate of tokens placed in the bucket
• Bucket depth b capacity of the bucket
• Operation
• Tokens are placed in bucket at rate r
• If bucket fills, tokens are discarded
• Sending a packet of size P uses P tokens
• If bucket has P tokens, packet sent at max rate,
  else must wait for tokens to accumulate

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Token Bucket Operation
Tokens
Tokens
Tokens
Overflow
Packet
Packet
Not enough tokens ? wait for tokens to accumulate
Enough tokens ? packet goes through, tokens
removed
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Token Bucket

• On the long run, rate is limited to r
• On the short run, a burst of size b can be sent
• Token Bucket 3 possible uses
• Shaping
• Delay pkts from entering net (shaping)
• Policing
• Drop pkts that arrive without tokens
• Metering (Marking)
• Let all pkts pass through, mark ones without
  tokens

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Comparison
Best-Effort
Diffserv
Intserv

• Per aggregation isolation
• Per aggregation guarantee

• Connectivity
• No isolation
• No guarantees

• Per flow isolation
• Per flow guarantee

Service

• End-to-end

• Domain

• End-to-end

Service Scope
Complexity

• No set-up

• Long term setup

• Per flow setup

Scalability

• Highly scalable
• (nodes maintain only routing state)

• Scalable (edge routers maintains per aggregate
  state core routers per class state)

• Not scalable (each router maintains per flow
  state)