Part 2 Differentiated Services

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Part 2Differentiated Services
2
Differentiated Services principles

• Status
• Work undertaken in 97
• IETF WG since Jan98 ("Diffserv")
• Several RFCs, including
• RFC 2475 An Architecture for Differentiated
  Services
• Rationale
• Reservation-based schemes require state
  maintenance at every hop, thus don't scale
• Stateless techniques in the core may provide
  differentiated services if all packets are
  marked (1) with a "preference treatment
  attribute"

(1) Marking pkts also called coloring
3
Diffserv Guiding Principles
States

• Push all the states at the edge
• All the states
• All per-flow work, including
• marking
• policing
• and/or shaping

flows
flows
Stateless core
flow
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Diffserv Guiding Principles (cont)

• "Packet Marking" used by "DS-capable" routers to
  apply differential packet treatment
• Within core network
• all packets are marked
• all packets with identical marking treated
  equivalently (they form a class, called
  "Differentiated-services behavior aggregate (BA)
  ")

5
Fast packet classification
Packet header

• At core nodes
• (DS Interior nodes)
• Differentiation mark (1)
• mapped
• to node behaviors (2)
• (1) called DS codepoint
• (2) called per-hop-behavior PHB

Diff Mark
Logical representation of DSCP to Behavior
mapping
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What is a Behavior?
Packet header

• In practice Behavior
• (i.e. differential treatment)
• Combination of
• Output Queue scheduling
• Packet dropping policy

Diff Mark
Queue scheduling
Packet Dropping
7
Types of classifiers
Packet header

• Multi-field (MF) classifier
• classifies on combination of (one or more) header
  fields
• boundary routers
• (in general, region boundary only)
• Behavior Aggregate (BA) classifier
• classifies on DS codepoint only
• Interior routers

S
D
Prot
Classification
CodePoint
Classification
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Who may mark the packets first?

• Host ...
• But generally
• Leaf Router

H
Pkt
M
Domain
H
Pkt
Pkt
D
M
Leaf router
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Current Class Sets (PHB Groups)

• Expedited Forwarding (EF) service (Jacobson,
  Nichols, Zhang)
• Assured Forwarding (AF) service (Clark,
  Wroclawsky, Fang)

10
Assured vs. Expedited in Diffserv

• Expedited
• Absolute assurance
• May emulate Virt. leased lines
• Excess traffic strictly dropped Traffic shaped
• Assumes expedited is a small of total network
  capacity
• 1 codepoint

• Assured
• Statistical assurance
• Emulates unloaded network
• Excess traffic either re-marked and sent, or
  dropped
• Loose assumption on of total network capacity
• 12 codepoints

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Implementing Packet Marking

• Principle
• No need to change IP packet header, just refine
  meaning of existing fields
• IPv4
• Provided with a mechanism for packet priority
  marking, the Type of Service (ToS) octet
• IPv6
• Provided with Traffic Class octet

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DS field coding (RFC 2474)

• DS field coded in
• IPv4 ToS octet
• IPv6 Traffic Class octet
• 6-bit field to code the DS code point (DSCP
  field)

DS Field IPv4 ToS octet IPv6 Traffic Class
octet
CU
DSCP
Currently Unused
DS CodePoint
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RSVP and Diffserv differences
Diffserv
RSVP

• Simply marks traffic

• Provisions resources for Network Traffic

• Signaling and resource handling invoked at every
  node

• Marking at the edge only

• Per-flow state in every node

• No state in the core

• Heavy Multi Field classification

• Light classification

• Requires host QoS-awareness

• Host can be Diffserv unaware

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RSVP and Diffserv cooperation
H

• Several models proposed
• Diffserv
• as transit
• between RSVP domains

RSVP
R
Transit is RSVP unaware
Diffserv
R
RSVP
H

• Diffserv RSVP aggregation
• as transit
• between RSVP domains

Transit is Agg-RSVP aware
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Diffserv as Transit

• DS domain contains pure Diffserv routers
• Edge routers
• are RSVPDiffserv capable
• perform QoS mapping between RSVP classes and
  Diffserv classes
• Fixed problems
• RSVP problem of multi-field classification in the
  core
• flows marked with DSCP
• traffic is fast classified

H
RSVP Domain
Transit routers are RSVP unaware
R
D
DS Domain
D
R
RSVP Domain
H
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Diffserv as Transit (cont)

• RSVP egress
• RSVP signaling
• Traffic shaping
• Packet marking
• Device RSVPDiffserv capable

H
RSVP Domain
R
R
DS Domain
R

• Diffserv core routers
• Operate on DSCP
• Carry RSVP messages transparently

R
RSVP Domain
R
H
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On transparent transport of path/resv

• path/resv traverse transparently the Diffserv
  cloud
• This simply means that
• they are ignored as RSVP control messages
• thus, they are treated as regular Diffserv pkts
• This does not mean that path/resv have to be
  carried in a tunnel

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Diffserv as Transit (cont)
H
RSVP Domain

• Remaining problems
• No capacity admission control in the Diffserv
  core
• Route stability, QoS routing

R
R
DS Domain
R
RSVP Domain
R
H
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Diffserv Aggregated RSVP as Transit

• Fixed problems
• RSVP problem of multi-field classification in the
  core
• flows marked with DSCP
• traffic is fast classified
• Capacity admission
• No per flow state, reduced signaling overhead
• Remaining problems
• Route stability, QoS routing

H
RSVP Domain
Reservations made for aggregates of flows
R
D
DS Domain
R
R
D
R
RSVP Domain
H
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Intserv-Diffserv Service class mappings

• Possible default mapping model
• aggregate individual Intserv flows to Diffserv
  classes

Intserv individual flows
Best Effort
Assured
Expedited
Diffserv service classes
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Major Diffserv IETF RFCs and drafts

• An Architecture for Differentiated Services
• RFC 2475 (Category Informational) Dec 1998
• Differentiated Services Quality of Service Policy
  Information Base
• draft-ietf-diffserv-pib-00.txt March 2000
• Definition of the Differentiated Services Field
  in the IPv4, IPv6 headers
• RFC 2474 December 98
• Assured Forwarding PHB Group
• RFC 2597 June 99
• An Expedited Forwarding PHB
• RFC 2598 June 99
• A conceptual Model for Diffserv Routers
• draft-ietf-issll-Diffserv-model-03.txt, May 2000

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End of Part 2 Differentiated Services