QoS Protocols & Architectures by Harizakis Costas.
Post on 20-Dec-2015
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Presentation Flow
QoS defined QoS protocols :
– RSVP, DiffServ, MPLS, SBM
QoS architectures QoS and multicast environments Protocol comparison … … conclusions !
IP-based Networks - Internet Today
Internet today– Provides “best effort” data delivery– Complexity stays in the end-hosts– Network core remains simple– As demands exceeds capacity, service degrades
gracefully (increased jitter etc.)
Delivery delays cause problems to real-time applications
QoS Defined
The goal :Provide some level of predictability and control beyond the current IP “best-effort” service
Fundamental principleLeave complexity at the “edges” and keep network “core” simple
QoS Metrics
Performance attributes– Service availability– Delay– Delay variation (jitter)– Throughput– Packet loss rate
Vary according to Service Level Agreement (SLA)
Service Level Agreements (SLA)
QUALITY OF SERVICE PARAMETERS
Service Level Application Priority Mapping
1 Non-critical data Similar to Internet today No minimum information rate
guaranteed
Best-effort delivery Unmanaged performance
2 Mission-critical data VPN outsourcing, e-
commerce Similar to ATM VBR
Low loss rate Controlled delay and delay
variation
3 Real time applications Video streaming, voice,
videoconferencing
Low loss rate Low delay and delay variation
QoS Protocol Classification
QoS can be achieved by :– Resource reservation (integrated services)– Prioritization (differentiated services)
QoS can be applied :– Per flow (individual, uni-directional streams)– Per aggregate (two or more flows having something
in common)
QoS Protocols
ReSerVation Protocol (RSVP)
Differentiated Services (DiffServ)
Multi Protocol Labeling Switching (MPLS)
Subnet Bandwidth Management (SBM)
RSVP - Resource Reservation
Attributes– The most complex of all QoS technologies– Closest thing to circuit emulation on IP networks– The biggest departure from “best-effort” IP service
Provides the highest level of QoS in terms of : – Service guarantees– Granularity of resource allocation– Detail of feedback to QoS-enabled applications
RSVP - Integrated Services
Enables integrated services (IntServ)
IntServ types– Guaranteed : as close as possible to a dedicated
virtual circuit– Controlled Load : equivalent to best-effort service
under unloaded conditions
RSVP - Implementation
Sender– PATH message containing
traffic specification (bitrate, peak rate etc.)
Receiver– RECV message containing
the reservation specification (guaranteed or controlled) the filter specification (type of packets that the reservation
is made for)
RSVP - Queuing
IntServ uses a token-bucket model to characterize I/O queuing
Token bucket attributes– Token rate– Token bucket depth– Peak rate– Minimum policed size– Maximum packet size
RSVP - Conclusions
Reservations are “soft” – Periodic refresh is necessary
It is a network (control) protocol – Works in parallel to TCP and UDP
APIs are required to specify flow requirements Reservations are receiver-based Has to maintain a state for each flow Multicast reservations
– Merged at replication points, difficult to understood algorithms have to be used though
DiffServ- Prioritization
Description– Applied on flow aggregates– Services requirements are classified – Classification is performed at network ingress points– A predefined per-hop behavior (PHB) is applied to
every service class– Traffic is smoothed according to PHB applied
DiffServ- Traffic Classes
Two traffic classes are available : – Expeditied Forwarding (EF) - 1 codepoint
Minimizes delay and jitter Provides the highest QoS Traffic that exceeds the traffic profile is discarded
– Assured Forwarding (AF) - 12 codepoints 4 classes, 3 drop-precedences within each class Traffic that exceeds the traffic profile is not delivered with
such high probability
DiffServ- Implementation
Classifier
MeterMarker
Conditioner
Maps DSCPs toPHBs
MaintainsDSCP
mappings andassociations
with localpolicies
Accumulatesstatistics
Applies thedefined PHB(scheduling)
DiffServ- Implementation
Type of ServicePrecedence
RFC 1122Must
BeZero
IP Type of Service (TOS)
0 32 4 5 6 71
MBZ
RFC 1349
DiffServ codepoints (DSCPs) redefine the Type-of-Service (ToS) IPv4 field
Precedence bits are preserved Type-of-Service bits are NOT
DSCP
Class Selector Unused
0 32 4 5 6 71
Differenciated ServicesCodepoint (DSCP)
CU
DiffServ- Conclusions
Traffic classes are equivalent to IP precedence service descriptors
– DiffServ unaware routers pass-through DiffServ traffic
Easy to be implemented / integrated even into the network core.
Proper classification can lead to efficient resource allocation and though improved QoS
MPLS - Label Switching
Used to establish fixed bandwidth routes (similar to ATM virtual circuits)
Resides only on routers and is protocol independent Traffic is marked at ingress and unmarked at egress
boundaries Markings are used to determine next router hop (not
priority)
The aim is to simplify the routing process …
MPLS - Implementation
Label Value Exp . S TTL
8320 1
20-bits : Label value used for lookup 8-bits : Time-To-Live
1-bit : Bottom of Label Stack
3-bits : Reserved
The 1st hop router, using the header information (destination address etc.) attaches a label and forwards the packet
Every MPLS-enabled router uses the label as an index to a table defining the next hop and label
MPLS - Conclusions
Labels can be “stacked” – This allows MPLS “routes within routes”
Label Distribution Protocol (LDP)– Distributes labels across MPLS-enabled routers– Ensures they agree on the meaning of labels– Usually transparent to network managers
Implication : – Define a policy management that distributes labels
SBM - Subnet Bandwidth Management
A top-to-bottom QoS approach Applies to the Data Link Layer (OSI layer 2) Makes LAN topologies (e.g. Ethernet) QoS-
enabled Fundamental requirement
– All traffic must pass through at least one SBM-enabled switch
SBM - Implementation
SBM Modules– Bandwidth Allocator (BA)
Hosted on switches Performs admission control
– Requestor Module (RM) Resides in every end-station Maps Layer 2 priority levels and the higher-layer QoS
protocol parameters
SBM - Conclusions
Much like the RSVP protocol Makes the traditional Ethernet, QoS aware Introduces an additional indirection in the
routing mechanism 8-level priority value
QoS Architectures
Application
Physical
Data Link
Network
Transport
Session
Presentation
Top-
to-B
otto
m Q
oS
Host A
Application
Physical
Data Link
Network
Transport
Session
Presentation
Host B
RSVP
DiffServ
SBM
QoS-enabledApplication
QoS API
SBM
RSVP RSVPDiffServ and MPLS
End-to-End QoS
Protocol Comparison
QoS Net App Description
most x Provisioned resources end-to-end (leased lines)
x x RSVP Guaranteed (provides feedback to application)
x x RSVP Controlled Load (provides feedback to application)
x MPLS (Multi-Protocol Label Switching)
x x DiffServ applied at network ingress appropriate to RSVP service level for that flow
x x DiffServ or SBM applied on per-flow basis by source application
x DiffServ applied at network core ingress
x Fair queuing applied by network elements (e.g. WFQ, RED)
least Best effort service
Multicast Environments
RSVP – Heterogeneous receivership makes reservation merging a
difficult task
DiffServ– Its relative simplicity makes it a better fit for multicast support
MPLS– Work is underway, no standards have emerged yet
SBM – Explicit support for multicast
Conclusions
Complexity at the edges – simple network core– Limit RSVP’s use on the backbone– Instead use the DiffServ
DiffServ is a perfect complement for RSVP
ToDo :– Performance attributes for each class still missing– Interworking solution for mapping IP CoS to ATM QoS
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