Transcript DiffServ

DiffServ
QoS in internet
Elon Rot , Itay Poleg
Presentation for ATM Networks course
(EE-046992)
DiffServ: 26/06/05
Why do we need QoS ?
• IP revolution - from “IP over everything” to
“everything over IP”
• Current Internet guarantee: Best Effort only.
• Some applications require more:
– Guarantee delay, jitter
– Guarantee bandwidth
– Guarantee loss rate
(VoIP, Conference-Calls, VPN, VOD…)
• Although QoS is available in lower layers
(ATM, FR, Ethernet) we need a media
independent IP QoS
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Little History
• An 8 bit field in the IP-header
– Seems like a good idea for future use.
• Lots of initial research in the late 80s and early 90s.
– Often takes a telecommunications view of the network.
• ATM QoS and Integrated services were developed
based on these results (1995).
– Focus on per-flow, hard QoS.
– Effort was driven by perceived application needs.
• In the last years (from 1998), the focus has shifted
towards Differentiated services.
– Focus is on QoS for flow aggregates, e.g., all the flows
belonging to one customer.
• From 2000 , you can buy a router that support DiffServ
(Cisco)
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What is needed to support QoS
• Between the network and its clients - Traffic
contract
– Traffic specification/desired QoS/supported
QoS
• At network edge:
–
–
–
–
Signaling and admission control
Packet classification/marking
Traffic shaping
Traffic policing
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What is needed to support QoS
• At routers:
– Classification and scheduling
– Smart Routing
– Buffer management.
– Traffic monitoring
– Traffic reshaping
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Different QoS approaches
• Per flow Vs. aggregate
– More groups leads to:
more flexibility, more admission,
more routers resources
• Statistical Vs. Deterministic guarantee
– Sometimes statistical
are not enough
– Deterministic more complex, less utilization
• End-to-End Vs. Per-Hope-Behavior
– User see E2E
– PHB is simpler to implement
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IntServ
• Per-flow QoS guarantees
• Reservation of resources using RSVP
• Two service models:
– controlled-load service: performance is as
good as unloaded network
– guaranteed service: firm bound of throughput
and delay
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IntServ drawbacks
• Scalability
– RSVP support along the path
– Maintaining “soft” reservations
• Complexity
– Support for each flow
– Need to administrate allocations
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What is DiffServ?
• Aggregate connections flows to different
classes
• Different demand can be guaranteed to
each class
• Guarantees implementations are per hop
behavior
• Each flow gets required services
statistically
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DiffServ architecture
Edge Routers:
Usually work at lower rate
Therefore can implement more functionality
like marking & shaping traffic
Core Routers:
Usually work at high rate
So we want packet handle to be fast and simple
(using the classifications)
Per-class service
DiffServ architecture
• Edge routers
– Each flow is handled separately, and each
packet is marked according to the SLA
• Core routers
– Deals with classes (rather then flow) so can
be more simple.
– Each router still need to manage buffering and
scheduling
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Traffic Conditioner Block (TCB)
Classification: selects a packet in a traffic stream
based on the content of some portion of the
packet header
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Traffic Conditioner Block (TCB)
Metering: checks whether the traffic falls within
the negotiated profile.
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Traffic Conditioner Block (TCB)
Marking: marks packet to a particular DS
behavior aggregate
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Traffic Conditioner Block (TCB)
Shaper/Droper: delays if necessary and then
forwards or discards the packets .
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Classification
• How to mark?
6 bit it the IP header.
• Remainder – IP header
bit # 0
7 8
version
header
length
15 16
ToS
24
total length (in bytes)
Identification
time-to-live (TTL)
23
0
D M
F F
protocol
Fragment offset
header checksum
source IP address
destination IP address
options (0 to 40 bytes) (Not used)
4 bytes
• Type Of Service field
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31
ToS field
• IP-v4
0
1
2
3
Precedence
Priority
• DS-Field
1
0
2
Class Selector
Codepoints
4
5
6
Type of Service
One hot field for :
Delay,cost,throughput,
reliability
3
4
5
Differentiated Services
Codepoint (DSCP)
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6
7
0
Must be
zero
7
Currently
Unused
PHB
• Externally observable forwarding treatments at a
single node
• PHB can be described in relative or absolute
terms
• PHBs are typically implemented by means of
buffer management and packet scheduling
• All packets with the same DSCP are treated the
same, Four types of classes available:
–
–
–
–
Default
Class-Selector
Expedited Forwarding (EF)
Assured Forwarding (AF)
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PHB types
• Default PHB:
– Traditional best effort treatment.
– Must be implemented
– Used for unsupported DSCP
• Class-Selector PHB
The DSCP (6 bit)
pattern is: 000000
The DSCP (6 bit)
pattern is: xxx000
– Backward compatibility
– Eight possible combinations (including default)
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PHB types
The DSCP (6 bit)
pattern is: 101110
• Expedited Forwarding PHB
– Providing low loss, low latency, low jitter,
assured bandwidth, end-to-end service through
DS domains
– Implies isolation: guarantee for the EF traffic
should not be influenced by the other traffic
classes
– Non-conformant traffic is dropped or shaped.
– Possible service: providing a virtual wire
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PHB types
• Assured Forwarding (AF):
– A method by which Behavior Aggregates can be given
different forwarding assurances.
– The intent is that it will be used to implement services
that differ relative to each other (e.g., gold, silver,…).
– AF defines 4 classes with some bandwidth and buffers
allocated to them.
– Within each class, there are three drop priorities, which
affect which packets will get dropped first if there is
congestion.
– Non-conformant traffic is remarked.
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AF table
The DSCP (6 bit) pattern is: xyzab0
xyz is the class: 001-class1 ; 010-class2 ; 011-class3 ; 100-class4
ab is the drop precedence: 01-low ; 10-medium ; 11-high
Class
Class 1
Class 2
Class 3
Class 4
001010
(AF11)
001100
(AF12)
001110
(AF13)
010010
(AF21)
010100
(AF22)
010110
(AF23)
011010
(AF31)
011100
(AF32)
011110
(AF33)
100010
(AF41)
100100
(AF42)
100110
(AF43)
Drop
precedence
Low
Drop
Medium
Drop
High
Drop
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Service
• A service describes the overall treatment of a
customer’s traffic within a DS domain.
– Customers see services, not PHBs.
• To support a service, many components must
work together:
– Mapping of service to PHBs, traffic conditioning,
network provisioning, PHB-based forwarding.
• Services in the DiffServ architecture is defined in
the form of Service Level Agreement (SLA).
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Putting it all together
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Conclusion
• Diffserv provides:
– Internet Class Of Service: several ToS
guaranteed in each DS domain.
– Using PHB to achieve the requirements.
– Provisioning of network resources
according to SLAs
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Advantage
– Scalability
• No dynamic change of state
Saves communication between routers
• Can be deployed for specific domain independently
– Simple
• Relatively low number of states
Using a stateless approach that minimize the need of nodes to
remember anything about flows
• Divide load on routers, edge vs. core
edge routers – a few strong and expensive routers
core routers – a lot simple and chip
• No signaling
– Easily adjustable to SLAs
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Disadvantages
– Not real end-to-end QoS:
• Only PHB – which are not easily map to E2E
• Limited number of classes – can’t isolated specific
flow.
• Inside aggregate each flow get the same (only
statistic guarantees)
– Routing independent mechanism
– Admission control:
• Fairly static
• Manually or with another mechanism
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Diffserv-aware-MPLS
• DiffServ enable scalable network design with
multiple CoS.
• MPLS enable path protection and restoration
(create an end-to-end specific path)
• Combine those two protocols give us the ability to
give strict E2E QoS guarantees while optimizing the
use of network resource
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Diffserv-aware-MPLS
LSP 1 (AF1)
Ingress node
(TCB)
LSP 2 (AF3)
Core router
(LSR)
With both Diffserv
& MPLS support
LSP 3 (EF)
Support Diffserv
and MPLS
Incoming Traffic
LSP 4 (default)
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References
• Internet Architecture and Protocols EE-046000
http://www.ee.technion.ac.il/courses/046000/
• Cisco
www.cisco.com/warp/public/cc/pd/iosw/ioft/iofwft/prodlit/difse_wp.htm
• QoS - by: ANJALI KULKARNI YI-AN CHEN
www.cse.buffalo.edu/~qiao/cse620/present_2000/presentation.ppt
• IEFT RFCs 2474, 2475, 2598, 3270
www.ietf.org/rfc.html
• MPLS DiffServ-aware Traffic Engineering
http://www.juniper.net/solutions/literature/white_papers/200048.pdf
DiffServ: 26/06/05
DiffServ
QoS in internet
Elon Rot , Itay Poleg
Presentation for ATM Networks course
(EE-046992)
DiffServ: 26/06/05