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Part 2 Differentiated Services

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Emulates unloaded network. Excess traffic either re-marked and sent, or dropped ... May emulate 'Virt. leased lines' Excess traffic strictly dropped; Traffic shaped ... – PowerPoint PPT presentation

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Title: Part 2 Differentiated Services


1
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
4
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
6
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
8
Who may mark the packets first?
  • Host ...
  • But generally
  • Leaf Router

H
Pkt
M
Domain
H
Pkt
Pkt
D
M
Leaf router
9
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

11
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

12
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
13
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

14
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
15
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
16
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
17
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

18
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
19
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
20
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
21
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

22
End of Part 2 Differentiated Services
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