Title: Part 2 Differentiated Services
1 Part 2Differentiated Services
2Differentiated 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
3Diffserv 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
4Diffserv 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)
")
5Fast 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
6What 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
7Types 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
8Who may mark the packets first?
- Host ...
-
- But generally
- Leaf Router
-
H
Pkt
M
Domain
H
Pkt
Pkt
D
M
Leaf router
9Current Class Sets (PHB Groups)
- Expedited Forwarding (EF) service (Jacobson,
Nichols, Zhang) - Assured Forwarding (AF) service (Clark,
Wroclawsky, Fang) -
10Assured 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
11Implementing 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
12DS 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
13RSVP and Diffserv differences
Diffserv
RSVP
- Provisions resources for Network Traffic
- Signaling and resource handling invoked at every
node
- Per-flow state in every node
- Heavy Multi Field classification
- Requires host QoS-awareness
- Host can be Diffserv unaware
14RSVP 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
15Diffserv 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
16Diffserv 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
17On 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
18Diffserv 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
19Diffserv 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
20Intserv-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
21Major 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
22End of Part 2 Differentiated Services