technische quality of service universitÄt ilmenau · basic functions to provide qos admission...
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TECHNISCHE UNIVERSITÄTILMENAU
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Quality of Service
QoS requirementsQoS in networksBasic QoS mechanismsQoS in IP networks
IntServDiffServMPLS
Wireless Internet 2Andreas Mitschele-Thiel 6-Apr-06
QoS Basics
QoS attributes:data rate (throughput)error rate (packet loss)delay (latency)delay variation (jitter)
Mechanisms to ensure QoS?reservation of „dedicated“ resources for a connection (e.g. CS voice, IntServ/RSVP)differentiation (e.g. priorization) of the use of a shared resource by different connections (e.g. DiffServ)overprovisioning, i.e. dimensioning of the network such that all offered (or accepted) traffic can be handled (e.g. Ethernet LAN)
Basic functions to provide QoSadmission control (possibly including resource reservation)traffic classificationtraffic conditioning (traffic shaping and policing)schedulingoverload control
Goal of QoS-enabled networks:
Enable predictable service delivery to certain classes or types of traffic independent of other factors, e.g. other traffic or link conditions
Goal of QoS-enabled networks:
Enable predictable service delivery to certain classes or types of traffic independent of other factors, e.g. other traffic or link conditions
Wireless Internet 3Andreas Mitschele-Thiel 6-Apr-06
QoS Requirements – User (end-to-end) Requirements
Summary of applications in terms of requirements
Errortolerant
Errorintolerant
Conversational(delay <<1 sec)
Interactive(delay approx.1 sec)
Streaming(delay <10 sec)
Background(delay >10 sec)
Conversationalvoice and video Voice messaging Streaming audio
and video Fax
E-mail arrivalnotificationFTP, still image,
paging
E-commerce,WWW browsing,Telnet,
interactive gamesAcce
ptab
le e
rror
rate
Delays requirements
Wireless Internet 4Andreas Mitschele-Thiel 6-Apr-06
End User Performance RequirementsConversational/real-time services
Medium Application Degree of symmetry
Data rate
Key performance parameters and target values
End-to-end One-wayDelay
DelayVariation within a call
Information loss
Audio Conversatio-nal voice
Two-way 4-25 kb/s
<150 msecpreferred<400 msec limit
< 1 msec
< 3% FER
Video Videophone Two-way 32-384 kb/s
< 150 msecpreferred<400 msec limitLip-synch : < 100 msec
< 1% FER
Data Telemetry- two-way control
Two-way <28.8 kb/s
< 250 msec N.A Zero
Data Interactive games
Two-way < 1 KB < 250 msec N.A Zero
Data Telnet Two-way(asymmetric)
< 1 KB < 250 msec N.A Zero
Source: UMTS standards
FER: Frame Error Rate
Wireless Internet 5Andreas Mitschele-Thiel 6-Apr-06
End User Performance RequirementsInteractive services
Medium Application Degree of symmetry
Data rate
Key performance parameters and target values
One-wayDelay
DelayVaria-tion
Information loss
Audio Voice messaging
Primarilyone-way
4-13 kb/s
< 1 sec for playback < 2 sec for record
< 1 msec
< 3% FER
Data Webbrowsing- HTML
Primarily one-way
< 4 sec /page
N.A Zero
Data Transaction services – high priority e.g. e-commerce, ATM
Two-way < 4 sec N.A Zero
DataE-mail(server access)
PrimarilyOne-way
< 4 sec N.A Zero
Wireless Internet 6Andreas Mitschele-Thiel 6-Apr-06
End User Performance RequirementsStreaming services
Medium Application Degree of symmetry
Data rate
Key performance parameters and target values
One-wayDelay
DelayVaria-tion
Information loss
Audio High quality streaming audio
Primarily one-way
32-128 kb/s
< 10 sec < 1 msec
< 1% FER
Video One-way One-way 32-384 kb/s
< 10 sec < 1% FER
Data Bulk data transfer/retrieval
Primarily one-way
< 10 sec N.A Zero
Data Still image One-way < 10 sec N.A Zero
Data Telemetry- monitoring
One-way <28.8 kb/s
< 10 sec N.A Zero
Wireless Internet 7Andreas Mitschele-Thiel 6-Apr-06
Architectural Requirements
IP-based networks are still expected to increase in
the number of hosts
the number and variety of applications
the capacity of the network infrastructure
This growth is expected to continue for the foreseeable future
=> Need for a scaleable architecture supporting service differentiation
Goal of a QoS enabled network architecture:
Enable predictable service delivery to certain classes or types of traffic regardless of what other traffic is flowing through the network during periods of congestion
Wireless Internet 8Andreas Mitschele-Thiel 6-Apr-06
QoS in Networks – End-to-end QoS
ISP
Backbone Network
Backbone Network
LAN or wireless
End-to-end QoS
Edge-to-edge QoSEdge-to-edge QoS Edge-to-edge QoSEdge-to-edge QoS
... ...RouterLink
Network-layer QoS depends on
routers along the path
characteristics of each link´s technology (layer 1 and 2)
Data Link layer QoS
Wireless Internet 9Andreas Mitschele-Thiel 6-Apr-06
Edge-to-edge QoS
Processing delays experienced within each routerTransmission delays across each link (fairly predictable)
Introduced within routers by unrelated traffic passing through shared resources at congestion points (queueing delays)
Routers provide only finite buffering capacity (congestion points)
Latency
Jitter
Packet loss
FIFO Queue
Port n
Port m
„Best-Effort“ RouterYn pps
Ym pps
Output PortX pps
...
Dominant influence of routers on achieved network-level QoS
Wireless Internet 10Andreas Mitschele-Thiel 6-Apr-06
QoS-aware Router
A queue for each class of trafficQueue managementDifferent packet discard functions
Queues must share finite capacity of output link → scheduler
Classification of packets (Traffic classes)
Port mYm pps
Classify
....
Port nYn pps
Output PortX pps
Schedule
Queue
Queue
Queue
Queue
Queue
Queue
Wireless Internet 11Andreas Mitschele-Thiel 6-Apr-06
Scalable QoS Architecture
Design of a good QoS architecture is generally non-trivial
Edge routers: complex but slower software implementation being able to classify and independently queue hundreds of traffic classes
Core routers: speed-optimized hardware implementation of a limited number of queues for handling all traffic classes
Capacity problem:
Needed granularity is available at the edges, but not in the core!
Multiple traffic classes have to share queues within the core routers
To reduce unpredictable mutual interference in the core, a level of predictabilitymust be imposed on the traffic before entering the core
Solution: Edge routers manipulate the temporal characteristics of individual traffic classes
Wireless Internet 12Andreas Mitschele-Thiel 6-Apr-06
Basic QoS Mechanisms – Traffic Shaping and Policing
Traffic ShapingPlacing an upper bound on the maximum bandwith available to a traffic class
PolicingIf too many packets arrive in a given time interval, some are simply dropped
MarkingPackets are marked if they exceed a burstiness threshold
The core can schedule such packets with lower priority
In case of transit congestion, marked packets are dropped first
ReorderingWithin one queue unmarked packets are scheduled before marked ones
Wireless Internet 13Andreas Mitschele-Thiel 6-Apr-06
Metering
Policing and Marking share a common component – a metering function detecting whether a packet is „in“ or „out of profile“
Example: Token Bucket Meter
Tokens are added with some fixed rate X (tokens per second)
Token Bucket with fixed depth of Y
tokens
Whenever a packet arrives, one token is removed from the bucket
and the packet is marked to be „in profile“Data
Packet 1Data
Packet 2Data
Packet 3Data
Packet 4Data
Packet 5Data
Packet 6
Whenever a packet arrives and no token is available in the bucket,
the packet is marked to be „out of profile“
Wireless Internet 14Andreas Mitschele-Thiel 6-Apr-06
Metering
Policing and Marking share a common component – a metering function detecting whether a packet is „in“ or „out of profile“
Example: Token Bucket Meter
Allows a small degree of burstiness
Enforces a lower average rate limit
Arriv
al R
ate
( pps
)
Elapsed Time
„in profile“ „in profile“„out of profile“
Wireless Internet 15Andreas Mitschele-Thiel 6-Apr-06
Packet Dropping
Ran
dom
Ear
ly D
etec
tion
(RE
D)
Dro
ppin
g
Prob
abilit
y
Average Occupancy
100%
1
maxp
minth maxth
Never drop
Non-zero and
increasing likelyhood
of drop
Always drop
Dro
ppin
g
Prob
abilit
y
Average Occupancy
100%
1
maxp
minth maxth
Never drop
Non-zero and
increasing likelyhood
of drop
Always drop
Wei
ghte
d R
ando
m
Ear
ly D
etec
tion
min1thmin2th max1thmax2th
Marked Packets
Regular Packets
different dropping probabilitiesfor different traffic (TOS field)
Wireless Internet 16Andreas Mitschele-Thiel 6-Apr-06
QoS in IP Networks – IP Packet Marking (TOS Field)
Packet Marking assigns a priority level to each packet
Devices supporting traffic priorisation can use this information to provide traffic shaping capabilities enabling QoS
In IP-based networks this priority level is stored in the Type of Service (TOS) field (8 bits) of the IP header:
Type of Service field
Precedence field: denotes the importance or priority of a packet
TOS field: denotes how a device should handle the tradeoff between throughput, delay, reliability and cost to provide the appropriate service for a packet
MBZ field: must be zeroBit: 0 1 2 3 4 5 6 7
There is no standard for interpreting the TOS field in the IP header!
Wireless Internet 17Andreas Mitschele-Thiel 6-Apr-06
Advanced Network Services
Integrated Services (IntServ, or IS)
Differentiated Services (DiffServ, or DS)
Multiprotocol Label Switching (MPLS)
A number of concepts are common to each of these network models
Wireless Internet 18Andreas Mitschele-Thiel 6-Apr-06
links
Common Concepts
Network architectures comprise
edge routers
core routers
Wireless Internet 19Andreas Mitschele-Thiel 6-Apr-06
Common Concepts
Edge routers
accept customer traffic into the network
characterize, police, and/or mark traffic, being admitted to the network
may decline requests signaled by outside sources (admission control)
Wireless Internet 20Andreas Mitschele-Thiel 6-Apr-06
Common Concepts
Core routers
provide transit packet forwarding service between other core and/oredge routers
differentiate traffic insofar as necessary to cope with transient congestion within the network
Wireless Internet 21Andreas Mitschele-Thiel 6-Apr-06
Integrated Services (IntServ, or IS)
Two classes of applications are supported by IntServ:
Real-time applications
Traditional applications expecting a service best described as best effort „under unloaded conditions“
IntServ architecture focuses on supporting individual applications by
per flow traffic handling at every hop along an applications end-to-end path
an a-priori signaling of each flow‘s requirements (setup of the flow)
An IntServ flow (a common QoS treatment) is defined as a stream of packets with common
source address, destination address and port number
Signaling in the IntServ architecture to set up the flow is supported by the ReSerVation Protocol (RSVP)
Wireless Internet 22Andreas Mitschele-Thiel 6-Apr-06
IntServ – Service Models
IntServ defines these service models:
Controlled Load
• Approximates the behavior visible to applications receiving best-effort service „under unloaded conditions“ (private best effort)
• Supports nominal end-to-end latency bounds
• There is some likelihood of moderate to extreme jitter
Guaranteed Service
• Datagrams will arrive within the guaranteed delivery time
• Datagrams will not discarded due to queue overflow(provided that the flow‘s traffic stays within its specified traffic parameters)
Best Effort
Wireless Internet 23Andreas Mitschele-Thiel 6-Apr-06
IntServ – Network Model
Before a flow is allowed to use the network resources it is subjected to admission control of each network element along the proposed path (local per hop decision)A flow is admitted only when each network element along the path indicates it can support the request
Network elements on the edge of the network limit an applications capability to inject traffic exceeding its negotiated traffic profile (possibly rate shaping)
Each router on the established path maintains state information on the flow
Wireless Internet 24Andreas Mitschele-Thiel 6-Apr-06
Token Bucket: Rate (bytes/s) and
size (bytes)
Peak data rate
Minimum policed unit
Maximum packet size
IntServ – Reservation Protocol
Path
message
Path
message
Path
message
Path
message
Path
message
Path
message
Path messagefrom Sender
contains Traffic Specification
that profiles the flow to be sent
Each RSVP-enabled router installs Path state and forwardsPATH message to
next hop on route to receiver
Receiver cannot make a
reservation request until it receives PATH
message
RESV messagecontains resource
reservation request
RESV
message
RESV
message
RESV
message
RESV
message
RESV
messageRESV
message
The RESV message goes upstream following the
Source Route provided in PATH message. EachRSVP-enabled router makes the requested
reservation
Sender
Receiver
Wireless Internet 25Andreas Mitschele-Thiel 6-Apr-06
IntServ – Reservation Protocol
RSVP is receiver-initiated (receiver of data flow is responsible for the initiation of the resource reservation)
RSVP supports heterogeneous receivers in a multicast group
multicast group membership changes dynamically
→ reservation must be renewed
multicast group members „switch channels“
[Compare to sender-initiated approach: the sender would be responsible for resource reservation for all multicast group members!]
Periodic Path messages are forwarded along the routing trees provided by the routing protocol (routing from source to sinks based on regular IP mechanism)
Reservation refresh messages are forwarded along the sink trees (based on state information maintained by each router) to maintain current reservation state (identical to first request)
Wireless Internet 26Andreas Mitschele-Thiel 6-Apr-06
IntServ – Summary
Pros
Provides the highest possible level of QoS
Cons
Each flow must be handled and maintained by each router on the data path even in the core network (scalability problem: consider that millions of flows have to be managed by a Gigabit router)
Signaling overhead due to RSVP soft-state behavior
Shortest path routing (OSPF) may not be optimal
No fairness, i. e. fair distribution of limited resources among aspirants
Violation of IP principle to keep individual states of connections in the edges (hosts) only
Wireless Internet 27Andreas Mitschele-Thiel 6-Apr-06
Differentiated Services (DiffServ, or DS)
DS Boundary Node
DS Interior Node
DS Ingress Node
DS Egress Node
DS Domain
Edge-and-core architecturecomplex decision making is pushed to the edgesedge-to-edge services are built from a small set of core router behaviors
Terminology
Ideas:
alternative to the high complexity of the IntServ architecture
incremental improvements on the best-effort service model
remove complexity from the core nodes => scalability
Wireless Internet 28Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Traffic ClassificationEdge-and-core architecture requires mapping of a wide variety of traffic into a restricted set of core router behaviors within the DS Ingress Node
Wide variety of end-to-end
services
Restricted set of core router behaviors
PHBs
DS Ingress Node
Two primary types of DiffServ classifiers (applied in ingress node):Behavior Aggregate (BA)
packet classification solely based on DiffServ field (Differentiated Services Code Point – DSCP values) in IP header (former TOS field)
Multi-Field (MF)packet classification based on multiple fields of the header, e.g.
source and destination addressessource and destination portsprotocol ID
Within a DiffServ domain many microflows will share a single DSCP
Wireless Internet 29Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Traffic ConditioningTraffic conditioning:
Meteringmonitoring if traffic meets the profile (based on classification)
Markingsetting of the DS field
Classifier BA/MF
Marker
Meter
Shaper / Dropper
Traffic Profile
Traffic Conditioner
Router
Shaper/dropper queueingpriority degradation or dropping where negotiated rate is exceeded
Wireless Internet 30Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Per-hop Behaviors (PHBs)
PHBs are a description of the externally observable forwarding behavior of a DS node applied to a particular Behavior Aggregate (BA):
resources (buffer, bandwith, ...)
priority relative to other PHBs
relative observable traffic characteristics (delay, loss, ...)
→ no constraints with respect to implementation!
PHBs are indicated by specific values in the DSCP
PHBs are building blocks for edge-to-edge services
Note: DiffServ allows to map multiple DSCP values onto the same PHB
Two PHBs have been standardized by IETF:
Expedited Forwarding (EF)
Assured Forwarding (AF)
(Class Selector Per-hop Behaviors)
Wireless Internet 31Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Expedited Forwarding (EF) PHBEF PHB requests every router along the path to service EF packets at least as fast as the rate at which EF packets arrive
Rate shape or police EF traffic on entry to the DS Domain, to limit the rates at which EF traffic may enter the network core
Configure the EF packet-servicing interval at every core router to exceed the expected aggregate arrival rate of EF traffic
EF packet-servicing intervals must be unaffected by the amount of non-EF traffic waiting to be scheduled at any given instant
Output Port
ScheduleQueue
Queue
Queue
Queue
Queue
Queue
DSCP (locally mapped onto EF PHB)
Other PHBs
0 01 1 11
EF PHB is a building block for low-losslow-latencylow-jitter
edge-to-edge services
Wireless Internet 32Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Assured Forwarding (AF) PHBGroup of PHBs for building edge-to-edge services
Relative bandwidth availability
Packet drop characteristics
Output Port
Queue
Queue
Queue
Queue
Queue Assignment
Drop Weighting
n 0n m mn
Per Queue RED-like
Packet Dropper
Parameters (drop probabilities, queue sizes, scheduling parameters) are assigned by the network operator allowing him to build desired end-to-end services
Wireless Internet 33Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Two-tier Architecture
DS Egress Node
To permit services which span across domains
Establish Service Level Agreements (SLA) including Traffic Conditioning Agreements – TCA
Common service provisioning policy
DS Ingress Node DS Domain
DS Ingress Node
DS Egress Node
DS Domain
DS Ingress Node
DS Egress Node
DS Domain
Resource Management is performed at two levels
Inside administrative domainsBetween neighboring domains (Bandwidth Broker – BB)
BB
BBBB
Concatenation of bilateral agreements leads to end-to-end QoS delivery paths But: Agreements are bilateral only!
SLA 1
SLA 2
Wireless Internet 34Andreas Mitschele-Thiel 6-Apr-06
DiffServ – Summary
Wide variety of services
Easy introduction of new services in already existing DS enablednetworks
Decoupling of services from application in use
Avoid per-microflow or per-customer state handling within core network nodes => scalability
Interoperability with old network nodes
Supports incremental deployment
Division of forwarding path and management plane
Wireless Internet 35Andreas Mitschele-Thiel 6-Apr-06
Multi-Protocol Label Switching (MPLS)
Convergence of connection-oriented forwarding techniques and the Internet routing protocols
MPLS is not primarily a QoS mechanism!
Important tool for backbone providers
Allows traffic engineering of non-shortest-path routes within a network
Simplifies the mechanics of packet processing within core routers
Provides high-speed tunnels between non-label-switched domains
Make DiffServ architecture more reliable!
Wireless Internet 36Andreas Mitschele-Thiel 6-Apr-06
MPLS
MPLS Edge MPLS EdgeMPLS Core
MPLS Domain
Customer B
Customer C
Customer A
Customer A
Customer A
Customer C
Customer B
Customer B
Label switched Router
Edge LSR
Label = 17
Label = 10
Label = 200
Label = 35
Label = 17
Label = 17
On each physical link, a Label Switched Path (LSP) is represented by a particular label
One LSP may be represented by different labels on other links along its path
Association between actual label values and LSP at any hop is created on-demand by the Label Distribution Protocol (LDP)
Wireless Internet 37Andreas Mitschele-Thiel 6-Apr-06
MPLS – Forward Equivalence Class (FEC)
Forward Equivalence Class (FEC)A group of packets that share the same requirements for their transport (e.g. with the same forwarding treatment, over the same path)
LabelA label identifies the Label Switched Path (LSP) a packet should traverse
The Label is carried or encapsulated in a Layer-2 header
Comparison of DiffServ- and MPLS-based forwarding
IP Dest. Addr. IP (L3) Dest. Label
FEC (QoS)
DiffServ (Core handling)
MPLS (Core handling)
MPLS (Edge handling)
DiffServ (Edge handling)
DSCP (QoS)DSCP (QoS)Label
IP Dest. Addr.
…
Wireless Internet 38Andreas Mitschele-Thiel 6-Apr-06
MPLS – Label Switched Paths (LSP)
Label Switched Paths (LSPs)Hop-by-hop routing
• each LSR independently selects the next hop for a given FEC(method is similar to that currently used in IP networks)
Explicit routing (ER)
• a kind of source routing: Ingress LSR specifies the list of nodes through which the ER-LSP traverses
• specified path could be non-optimal (Traffic Engineering)
• resources may be reserved to ensure QoS
Label Switched Path MergingTwo or more incoming labels map to a single downstream label at a core LSR
Traffic belonging to the same FEC but entering from different Ingress LSRs are merged onto a single LSP at some point in the middle of the network
Wireless Internet 39Andreas Mitschele-Thiel 6-Apr-06
AdvantagesMPLS forwarding can be done by simple switches
Only label lookup and replacement must be performed
Not necessary to analyze the network layer header (e.g. IP header) within the MPLS enabled network
A packet is assigned to a FEC only once when entering the networkInformation carried in the packet header can be used for FEC mapping (incoming port, ...)
FEC mapping can become more and more complicated without any impact on the routers that only forward labeled packets
MPLS provides explicit routing (traffic engineering)
The label may represent a combination of the FEC, a class of service and other forwarding criteria
MPLS is applicable to any network layer protocol
MPLS can support a hierarchical routing design (label stack)
FECs can range from „IntServ“ to „DiffServ“
Virtual Private Network support
Wireless Internet 40Andreas Mitschele-Thiel 6-Apr-06
No distinction between packets within the network
(if no resources are available packets are queued or dropped)
Minimalist counterpart to IntServ, throwing out everything that isn‘t
essential to the provision of some aggregate service
levels
Summary 1
Relative QoS level
Best effort
Best effort
Activated by: -
Packet Marking
Packetmarking
Net
Each packet is marked with a request for a type of
service; nodes select routing paths and/or forwarding behaviors to satisfy the
service request
Integrated Services
Integrated Services (RSVP)
Net + App
First attempt of IETF to develop a service model that supports
per-flow QoS guarantees; requires complex architecture along any edge-to-edge path
Differentiated Services
Differentiated Services
Net Net
Multiprotocol Label Switching
MPLS
Can build upon Diffserv and adds support for explicitly
constructed, non-shortest-path routing of traffic
Wireless Internet 41Andreas Mitschele-Thiel 6-Apr-06
Summary 2 – Apply a mix of techniques to provide E2E QoS
IntServ
(Transit Network)
DS DomainDS Domain
DS DomainMPLS
IntServ
IntServ
(Transit Network)
IntServ in the access network DiffServ/MPLS in the backbone
Wireless Internet 42Andreas Mitschele-Thiel 6-Apr-06
QoS on the Air Interface
QoS has to be provided end-to-endbut, different mechanisms may be used on different parts of the end-to-end connectionapplication of the mechanisms to the air interface
reservation(IntServ)
differentiation(DiffServ)
overprovisioning
UMTS provides a mix (variety) of the techniques in different parts (levels) of the system
=> appropriate where the amount of resources and the number of connections is small and the QoS requirements are hard
=> appropriate where a large number of connections has to be handled or QoS requirements are moderate
=> appropriate where resources are abandon(typically not true for air interface) or traffic volume is known (may hold for access network)