Transcript MPLS Forum Tutorials - Systems and Computer Engineering

Class of Service (CoS)
&
Quality of Service (QoS)
Sources:
MPLS Forum
V. Alwayn, Advanced MPLS Design and Implementation, Cisco Press
E. W. Gray, MPLS Implementing the Technology, Addison Wesley
B. Davie and Y. Rekhter, MPLS Technology and Applications, Morgan Kaufmann
E. Osborne and A. Simha, Traffic Engineering with MPLS, CiscoPress
Slide 3-1
What exactly is CoS ?
•
Class of Service (CoS):



Groups of flows with same level of treatment
Traffic differentiation or the ability to treat packets differently based
on the application or packet’s importance or priority
Service-level depends on state of the network and relative priority

•
Example: 802.1p (Ethernet): No resources allocated per call, but
differentiation of service level through priority. Relative priority, i.e. If
network is congested service WILL degrade.
CoS is the ability of network devices to prioritize best-effort
traffic



No guarantees, highest class traffic get priority over other traffic
when congestion happens
No connections maintained end-to-end
No per-flow state information maintained
Slide 2
Class of Service
•
How many classes?

Service provider specific. Example: Sprint has 4 classes (once)

Class A Premium Traffic: reserved for latency-sensitive applications
only, e.g., VoIP or Video over IP.

Class B Critical Traffic: highest class for data applications, e.g.,
financial transactions

Class C Business Traffic: second class for data applications, e.g.
database applications.

Class D Standard Traffic: This class is the default class, all traffic not
prioritized in the above queues will be serviced in this class. Typical
traffic for this queue is web browsing.

Bandwidth allocation recommendations (depends on ISPs):
 35% for VoIP, 25% for class B, 15% for class C, 25% for class D
Slide 3
What exactly is QoS ?
•
Quality of Service (QoS)



Mechanisms that allow network managers to contorl the mix of
bandwidth, delay, jitter, and packet loss
Hard allocation of resources
What you pay for is what you get

•
QoS is the ability to guarantee transmission characteristics
end-to-end, not a device feature




•
Example: Connection set-up in an ATM network which allocates a fixed
amount of resources
Bandwidth, maximum end-to-end delay, maximum delay variation
Signaling and end-to-end connections may be required
Granularity and state information on a per flow basis
Prioritization of service classes, bandwidth allocation, and congestion
aviodance
Evolution of standards:



Best Effort Service: 1981
Integrated Services (IntServ): 1997
Differentiated Services (DiffServ):
1998
Slide 4
IP QoS – group discussion
•
•
2-minute competition
Identify types of policies/mechanisms in support of IP
QoS

Control policies


Admission control, policy control, congestion control,
conditioning policy (between networks)
Data or packet policies



marking, classification
policing, dropping policy
Queuing / scheduling policy
 LLQ, Priority Queuing
 WFQ, CBWFQ
 Hybrid
 Adaptive queuing Slide 5
The QoS Pendulum
Time
No state
Aggregated
state
Best Effort
DiffServ
Per-flow state
IntServ / RSVP
1. The original IP service
2. First efforts at IP QoS
3. Seeking simplicity and scale
4. Bandwidth Optimization & e2e SLAs
((IntServ+DiffServ+ Traffic Engineering))
Slide 6
IP QoS over MPLS
• Service providers that offer IP services over an
MPLS backbone must support IP QoS over their
MPLS infrastructure – IP QoS over MPLS VPNs
or MPLS traffic engineered paths.
• MPLS can offer IP QoS services more efficiently
over a range of platforms, including ATM LSRs.
• Some useful QoS capabilities such as
guaranteed-bandwidth LSPs can be supported
over MPLS networks.
Slide 7
Integrated Services
(IntServ)
Slide 3-8
What is IntServ ?
• An architecture allowing the delivery of the required
level of QoS to real-time applications
• Introduces a circuit-switched model to IP
• A signalling-based system where the endsystem
has to request the required service-level
• RSVP – one of the signaling protocols of choice
• A way of providing end-to-end QoS, state
maintenance (for each RSVP flow and
reservation), and admission control at each NE
Slide 9
The IntServ Model
Signalling required by end-stations
for Resource-Reservation (RSVP)
Sender
Receiver
Slide 10
The IntServ Model –
Connection Set-Up
Step 1: RSVP Path
Step 2: RSVP RESV
Step 3: Data
Sender
Receiver
Slide 11
IntServ Characteristics
•
•
Introduces the model of connections or flows
•
IntServ also defines a reservation spec called Rspec, which requests
specific QoS levels and ther reservation of resources.
•
Requires the following to verify that traffic conform to its Tspec:
Defines a traffic specification called Tspec, which specifies the kind of
application traffic that ingresses the network.



Known QoS requirements
Signalling protocol (i.e., RSVP)
Significant enhancements on network element:





Admission control
Policy control
Packet classification and marking
Packet scheduling and queuing
Packet dropping policy
Slide 12
IntServ Summary
• Provides the means for real-time applications
over IP
• Introduces a connection / flow approach
• Uses RSVP as signalling mechanism
• Requires the end-station / application to signal for
QoS
• Requires network elements to maintain
connection state
Slide 13
MPLS Implementation of IntServ
• Path setup, including bandwidth reservation, is
the same as before
• In operational mode,


Ingress: associates all packets associated with a FEC
and assign them to a particular LSP.
Tandom node: when a packet arrives, it looks up the
label in its table and recognizes all the QoS-related
mechanisms associated with the packet, such as
policing and queuing. The IP header needs not be
examined.
Slide 14
IP Precedence
• Main problem with IntServ:

The IntServ RSVP per-flow approach to QoS is not
scalable and adds complexity to implementation.
• Solution?:

IP precedence simplifies it by adopting an aggregate
model for flows by classifying various flows into
aggregated classes and providing the appropriate
QoS for the classified flows.
Slide 15
Differentiated Services
(DiffServ)
Slide 3-16
What is DiffServ
• An architecture for implementing scalable,
stateless service differentiation
• A service defines significant characteristics of
packet transmission in one direction across a set
of one or more paths in the network
• Examples of characteristics:



Delay
Jitter
Packet loss
Slide 17
DiffServ Architecture
Each router participates in providing a packet its class of
service. This is called as “Per Hop Behaviour (PHB)”.
Slide 18
Classification of Packets
• What parameters can be used for classification?

Source/destination IP addresses
 Incoming/outgoing interface
 IP precedence values, DSCP value
 ….
Slide 19
The DiffServ Model
Differentiated Services Domain
(DS Domain)
DS Boundary Nodes
(Ingress / Egress)
DS Interior Nodes
Slide 20
The DiffServ Model
Chacteristics of per-hop-behaviors
(PHB) defined per DS Domain
IP packets crossing a link and requiring
same DiffServ behavior are referred to
as Behavior Aggregate (BA)
Traffic Classification and
Conditioning between DS Domains
Contiguous DS Domains
can be grouped into DS Regions
Slide 21
DiffServ Service Concepts
Service = Conditioning + Behaviors
DS
Domain
Conditioning at
ingress devices
Per-hop behaviour in
transit nodes
Slide 22
DiffServ Service Classes or
Per Hop Behaviors (PHB)
•
Describes the forwarding behavior applied to an
aggregate of flows
•
The means a network-node allocates resources to meet a
behavior aggregate
•
Per Hop Behaviors are implemented (on each router) via:

Queue management and scheduling


Scheduling


Buffer size, Queue depth, Over-subscription policy
Scheme to determine which queue to service when link is available
Congestion management and avoidance

Optimize resource utilization
Slide 23
DiffServ Service Classes
IP Packet with
DiffServ Fields
Version Hdr Len
4 bit
4bit
0
1
2
TOS
1byte
3
4
Total Len
2bytes
5
DSCP
6
more IP Hdr …
7
CU
DiffServ Field (DSCP) defines Per-Hop
Behavior (PHB) (i.e., marking)
The remaining two unused bits in the TOS byte are
used for TCP ECN which is defined in RFC3168.
Slide 24
DiffServ Service Classes
0
0
1
0
2
3
4
5
6
7
0
0
0
0
unused
Best Effort DSCP
The common best effort forwarding behavior available in all routers
Network will deliver these packets whenever resources available
Node should make sure that these packets don’t get ‘starved’
Packets with an unidentified DSCP should also receives this PHB
Slide 25
DiffServ Service Classes
0
1
Class
2
3
4
5
Drop
Precedence
6
7
Assured Forward
(AF) DSCP
unused
Class – specifies the PHB that packet is to receive. AF is a method of providing
low packet loss, but it makes minimal guarantees about latency.
AF1 – 001
AF2 – 010
AF3 – 011
AF4 – 100
Drop Precedence - marks relative importance of a packet within a given class.
010 low
100 medium
110 high
Slide 26
DiffServ Service Classes
0
1
1
0
2
3
4
5
6
7
1
1
1
0
unused
Expedited Forward
(EF) DSCP
These packets must be policed at ingress
Non conforming packets are discarded
These packets must be shaped on egress
These packets should receive Priority Queuing or LLQ (Premium Service
PHB)
Slide 27
DiffServ Service Classes
Summary
Best Effort DSCP
•Best Effort Service
•Client gets available Resources only
Assured Forward
(AF) DSCP
•Specified Forwarding Behavior
•Specified Drop Precedence
Expedited Forward
(EF) DSCP
•Priority Delivery
•Must adhere to “traffic contract”
Slide 28
How Is A DiffServ Service
Established?
DS
Domain 1
DS
Domain 2
DS Administrators set up DS-capable routers within their
domain for conditioning and PHB per service class
Slide 29
DS
Domain 3
How Is A DiffServ Service
Used?
DS
Domain 1
DS
Domain 2
Source now sends traffic marked for Gold service level
NO SIGNALLING OR STATE IS INVOLVED
Slide 30
DS
Domain 3
Service Classes Are Locally
Significant
• Service for a given DiffServ category (e.g., Gold) is not necessarily the
same in Domain 2 as in Domain 1
• Interdomain agreements must be brokered to ensure E2E QoS
DS
Domain 1
DS
Domain 2
DS
Domain 3
Policy-driven approach is seen as a good mechanism to achieve
end to end consistency
Slide 31
DiffServ Characteristics
• DiffServ is a relatively simple and coarse method to
provide differentiated Classes of Service.
• Offers a small well defined set of building blocks
from which several services may be built.
• Flows (stream of packets with a common
observable characteristics) are conditioned at the
network ingress and receive a certain forwarding
treatment per hop behavior within the network.
• Multiple queuing mechanisms offer differentiated
forwarding treatments.
Slide 32
DiffServ Summary
• Model consists of a set of Differentiated Services
Domains (Policy / Management Domain)
• Interconnections of DS Domains require Traffic
Classification and Conditioning
• DiffServ deals with aggregates of flows assigned
to a PHB
• DiffServ operates stateless and does not require
signalling
• DiffServ is a refined CoS mechanism
Slide 33
MPLS and DiffServ
Slide 3-34
MPLS and DiffServ – Basic
Operation
Packet‘s forwarded according to Destination
Address (DA) and DiffServ Control Point (DSCP)
IWF
MPLS enabled Network
with DIffServ capabilities
DiffServ enabled Network
Slide 35
MPLS and DiffServ – Basic
Operation
Packet‘s forwarded along an LSP based
on Label that identfies a specific FEC
IWF
MPLS enabled Network
with DIffServ capabilities
DiffServ enabled Network
Slide 36
MPLS and DiffServ – Basic
Operation
MPLS provides Traffic Engineering
in addition to CoS/QoS
IWF
MPLS enabled Network
with DIffServ capabilities
DiffServ enabled Network
Slide 37
DSCP to MPLS Mapping (1)
DiffServ DSCP
Drop
Precedence
Class
0
1
2
3
4
unused
12 possible combinations
5
• Class – specifies the PHB that packet is to receive




AF1 – 001
AF2 – 010
AF3 – 011
AF4 – 100
• Drop Precedence - marks relative importance of a
packet within a given class



001 low
010 medium
011 high
Slide 38
DSCP to MPLS Mapping (2)
• What to map?


DSCP has 6 bits
MPLS header?
• How to map?
Slide 39
DSCP to MPLS Mapping (3)
DiffServ DSCP
Drop
Precedence
Class
0
1
2
3
4
unused
5
MPLS Label
EXP
0
1
2
• E-LSP – the MPLS ‘shim’ EXP field maps PHBs
using only the drop precedence field of the DSCP
Slide 40
DSCP to MPLS Mapping
DiffServ DSCP
Drop
Precedence
Class
0
1
2
3
4
unused
5
DSCP
0
•
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15
PSC - PHB Scheduling Class
L-LSP – the DSCP is completely used to map LSPs
for a single FEC / BA pair
Slide 41
E-LSP and L-LSP
• PSC = PHB Scheduling Class (PSC)
• E-LSP (<= 8 PHB)



EXP-Inferred-PSC LSP
A single LSP can support up to eight BA’s
EXP (3-bits) maps LSP using drop precedence (3-bits)
• L-LSP (<= 64 PHB )



Label-Only-Inferred-PSC LSP
A separate LSP for a single FEC / BA (OA) pair
Label maps LSP using DSCP (6-bits)
• Defined for both CR-LDP and RSVP-TE
Slide 42
Label Request Message
Label Request
Message Length
Message ID
LSPID TLV
Explicit Route TLV (optional)
Traffic Parameters TLV (optional)
Pinning TLV (optional)
Resource Class TLV (optional)
Pre-emption TLV (optional)
Diff-Serv TLV (optional)
Slide 43
DiffServ TLV for E-LSP CR-LDP
Diff-Serv (0x901)
T
Length
Reserved
Mapnb(4)
Map 1
.
Mapnb
Map Entry Format
Reserved (13)
EXP (3)
Slide 44
PHBID (16)
DiffServ TLV for L-LSP CR-LDP
Diff-Serv (0x901)
T
0
Length
Reserved
1
2
3
4
5
6
7
PSC
8
DSCP
PSC
Slide 45
9
10
11
12
13
14
15
MPLS – DiffServ Interworking
Behavior Aggregate (BA) get‘s
mapped to LSP by LER.
(multiple possible scenarios)
Packet classified by Destination
and DiffServ Code Point
(i.e., Class of Service)
IWF
MPLS enabled Network
with DIffServ capabilities
DiffServ enabled Network
Slide 46