Qos and Mpls

8/14/2019 Qos and Mpls

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QoS v MPLS

Tutor: Lu Thanh Tr

Email: [email protected]


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QoS (Quality of Service)

There is really a need for QoS (RFC1633)? NO

Bandwidth is infinite thanks to the emergence of new

transmission technologies, the installation of new cables

Difficult to implement a QoS approach

Applications can adapt

YES

Bandwidth demand increases exponentially while supplied

bandwidth increases linearly Applications only adapt as the available bandwidth varies in

a limit range

By supplying different QoS, ISPs can get more benefit


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Players in the QoS

ISP, Internet Service

Providers utilize their resources to

the maximum get as many subscribers

as they can

Subscribers get as much bandwidth

as they can from ISP

reliable connection zero down time if

possible


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Service Level Agreement (SLA)

Service Level Agreement. The SLA is a contract between the service provider and the

customer. The SLA can be applied to a customer, a group of

customer, to a group of business.

SLA consist of:Availability

Services offered

Service Guarantees

Responsibilities

Auditing the service

Pricing


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QoS Characteristics

Service availability

Delay

Delay variation

Throughput

Packet loos rate


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QoS Characteristics

Latency Latency or a propagation time is referred to the time it takes to send a message

from the sender until to the time the receiver receives.

Router Latency Its the time it takes to the router to retransmit the packet that it had received

from the time it had arrived to the router.

Jitter (Delay variation) Refers to the variation in time duration in all packets in stream taking the same

route. For instance, when sending a video or audio stream over the networkand the packets dont arrive in the order that was sent on a timely basis. This

creates a distortion of the signal, which is very harmful to multimedi

a.


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QoS Characteristics

Bandwidth Bandwidth is the ideal capacity that the network can operate. The networks

never work on ideal maximum capacity since there are negative factors that

cause deterioration of the quality of the network. Such as factors can be

transmission delay, noise and etc.

Packet Loss Packet loss takes in place when we are experiencing congestion on our

network. In the event of the congestion the network can discard this packet,

which are defined by this parameter.

Service Availability Availability is the reliability of the users connection to the Internet service.

To be able to do this we use Service Level Agreement (SLA).


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Integrated Services - motivation

Many applications are sensitive to the effects of delay, jitter and

packet loss

The existing Internet architecture provides a best effort service

All traffic is treated equally (FIFO queuing). Currently there is no

mechanism for distinguishing between delay sensitive and best effort

traffic. IPv4 TOS is not widely implemented.

Aim of IntServ WG: to specify the enhanced services needed in the

Internet service model to support the integration of real-time and

classical data traffic.


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Integrated Services Architecture

Integrated Services (IntServ) expands congestion

control to include reservation of resources:

Signalling through Resource Reservation Protocol (RSVP)Specification of traffic characteristics and QoS

Admission control

Policing and shaping of traffic

Scheduling of flow packets


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Key Components

QoS routing agent Admission control

Reservation setup agent

Resource reservation table

Flow identification Packet scheduler

Data plane

Control plane


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Control Plane sets up resource reservation

Data plane forwards data packets based on reservationstate.

To setup reservation, app first characterizes its traffic flow

and specifies QoS requirements : referred to as flowspecification

The reservation setup request is then sent to the network.


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Router upon getting the request, interacts with QoSrouting agent to find the next hop.

It then coordinates with the admission control moduleto determine if there are sufficient resources to meetthe requested resources.

Once reservation set up is successful, the informationfor the reserved flow is installed into the resourcereservation table.

Information in the resource reservation table is used toconfigure flow identification module and the packetscheduling module in the data plane.


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Route Selection

IntServ does not specify any route selection

of its own.

It relies on existing routing protocols toforward its control packets further.

Obviously a more efficient routing protocol

which can find a path that is likely to have

sufficient resources is desired.


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Reservation Setup

To setup reservation a reservation set up

protocol is needed that goes hop by hop

along the path to install the reservation state

in the routers.

The reservation protocol must also deal with

changes in the network topology.

In IntServ, RSVP has been developed as theresource reservation protocol.


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Admission Control

In order to provide guaranteed resources for

reserved flows, a network must monitor its

resource usage and admit a new flow only if it

has sufficient resource.

It has two functions : to determine if a new

flow reservation can be set up based on the

admission control policies and to monitor andmeasure the available resources.


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Admission Control (Contd)

Two basic approaches:Parameter based

Measurement based


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Measurement based

Admission control module measures the

actual traffic load and uses that info while

admitting a new flow.

Since traffic sources are not static, this

method is probabilistic in nature.

So cannot be used to provide tight

guarantees.Measurements can be done in a number of

ways


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Measurement Based (contd)

Exponential averaging : New estimate = (1-w) * old estimate +

w * new measurement

Time window approach: Average arrival rate is measured over a sampling interval. At the

end of measuring period the highest average is used as the

estimated rate.

If there are n sampling intervals in a measurement period T and

Ci is the average measured over sampling interval I, thenestimated rate = max [C1, C2, ., Cn]


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Flow Identification

Router must examine every incoming packet

and decide whether the packet belongs to

one of the reserved flows.

IP flow is identified by src addr, dest addr,

proto ID, src port, dst port : five-tuple.

These five fields of the incoming packet is

compared against the five-tuple of all theflows in the reservation table for flow

identification.


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Tx

Rx

1) Tspec (sender traffic spec)

ADSpec (services, possibly modified by routers)

2) Tspec (reservation traffic spec)

RSpec (reservation service request)

Service class



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Fluid Model Scheduling

If an element approximates the fluid model then the service

received will be the same as a wire with bandwidth equal to

the service rate.

Aim is to isolate traffic flows from each other. D=b/R

Fluid model scheduler with service

rate, R.

Tx Rx

RxTxwire with bandwidth R


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Relationship between service, traffic,

loss and delay bounds

time

traffic service

traffic arrival

busy period

backlog

bits


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Traffic Specification

To date, one general traffic specification parameter has been

defined (RFC 2215): TOKEN_BUCKET_TSPEC

Consists of: float r token rate (bytes/sec)

float b bucket depth (bytes)

float p peak rate (bytes/sec)

unsigned m minimum policed unit (bytes)

unsigned M maximum packet size (bytes)

RSPEC consists of:R requested rate (bytes/sec)

S delay slack

(microseconds)


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Service Categories

Guaranteed Service Mathematically provable upper bound on queuing

delay, assured data rate, no loss

Hard real-time applications

Controlled Load Approximates best-effort service under unloaded

conditions

Adaptive real-time applications

Best effort


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FIFO

First Arrival, First Transmission simple to implement! Completely dependent on arrival time No notion of priority or allocated buffers No space in queue, packet discarded

Used in, e.g., IP Internet

Arrival

Full?

Discard

N

Y

Processor

Queue

Departure


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Weighted Robin Round

if only one arrival queue -> it gets full bandwidth if n arrival queues -> each gets 1/n of bandwidth Each queue has a priority

Arrival queues

Transmission queue

Round robin


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Assign:

33%/66%

Q1

Q2

Q3

example: A T3 trunk with 500 connections, each connection has mean packet

length 500 bytes: 250 with weight 1, 250 with weight 10

Each packet takes 500 * 8/45 Mbps = 88.8 microseconds Round time =2750 * 88.8 = 244.2 ms


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Problems with Weighted Round Robin

Unfair if packets are of different length or weightsare not equal

With variable size packets and different weights,

need to know mean packet size in advance

Can be unfair for long periods of time


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Suggestion: Weighted Fair Queuing (WFQ)

Deals better with variable size packets and weights:

assign a relative weight to each queue ( higher priority queues get

a larger piece of the pipe).

the weight is a relative value--not a guaranteed bandwidth rate!

Actual bandwidth for each queue at any given moment depends

on # of queues using the pipe and on the relative weights of each

of those queues.

By default, WFQ favors lower-volume traffic flows overhigher-volume ones (for example, a routine e-mail

over a large FTP download).


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Suppose, in each round, the server served one bit

from each active connection (GPS)

ComputeR=Round number= the number ofrounds already completed (can be fractional)

for each packet, Compute f=finish number= round

number when a packet will complete its service

Serve packets in order of finish numbers

WFQ Algorithm


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WFQ Computation

a packet of lengthp arriving to an empty queue when the round number is R,

Ideally, it will complete service when the round number is => f =R + p

(independent of the number of other connections!)

a packet arrives to a non-empty queue, and the previous packet has a finish

number off, will have a finish number=> f =(previous) f+p

Problem: we need to determine is the connection active? if not, what is the current round number?

Solution:Redefine round numberas

a real-valued variable that increases at a rate inversely

proportional to the number of currently active connections


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Delay-Earliest Due Date (Delay-EDD)

Delay-EDD prescribes how to assign deadlines to packets

Earliest-due-date = packet with earliest deadline selected

Deadline = expected arrival time + delay bound

Implementation: A source is required to send slower than itspeak rate

Bandwidth at scheduler reserved at peak rate

Each packet gets a hard delay bound

Delay bound is independentof bandwidth requirement

but reservation is at a connections peak rate

Implementation requires per-connection state and a priority queue


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Rate-controlled scheduling

A class of disciplines two components: regulator and scheduler

incoming packets are placed in regulator where they wait

to become eligible

then they are put in the scheduler Regulatorshapes the traffic, scheduler provides

performance guarantees


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Virtual Clock(L. Zhang, 1991)

Scheduling of packets based on when packets would havebeen sent if TDM were used.

Timers VC (flow monitoring) and auxVC (packet scheduling)

On packet arrival both timers are advanced to next packet

eligibility time. After a set number of packets (AI*AR), VC is compared to a

real-time clock (RTC). IfVC > RTC restrict flow

IfVC < RTC, VC=RTC (prevent higher rate in subsequent

interval)

VC updates are packet based. AuxVC avoids saving credits


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Guaranteed Service


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Guaranteed Service

Provides guaranteed bandwidth and strict

bounds for delay.

Intended for apps that require highest

assurance on bw and delay : mission criticalapps, intolerant playback apps.

Can be viewed as a virtual circuit with

guaranteed bw. Provides bounds on maximal queuing delay.


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Tx

Rx

1) Tspec (sender traffic spec)

ADSpec (services, possibly modified by routers)

2) Tspec (reservation traffic spec)

RSpec (reservation service request)Service class



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Guaranteed Service (contd)

Apps invoke guaranteed service by specifying a traffic

descriptor (TSpec) and a service spec (RSpec) to the

network.

TSpec describes traffic sources with followingparameters: Bucket rate (r) : rate at which tokens arrive.

Peak rate (p) : max rate for packet transmission

Bucket depth (b) : size of token bucket Min policed unit (m) : any packet with size lass than m will be

counted as size m.

Max packet size (M) : Max packet size accepted.


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Delay calculation

Given the TSpec and RSpec the worst case

end-to-end queuing delay for a flow can be

calculated.

Assume a fluid model and traffic source is

constrained by token bucket params (r, b, p)

If p is very large compared to R and r, then

the worst case queuing delay = AB = b/R.


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Delay Calculation(Contd)

b

R

r

O

A B

time

bits


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If p is comparable to R and r, then the worst

case delay is AC =

b (p R) / R (p r) (p > R r)


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b

R

r

O

F E

p

A C

B D


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Delay calculation (Contd)

In real network fluid model does not apply.

So two error terms are introduced: Error term C is rate

dependent and represents the delay that a packet

experiences due to rate parameter and packet length(store and forward model).

Error term D is rate independent : delay due to route

lookup, flow identification.

End-to-end sums of C and D over a path are Ctot andDtot


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Delay calculation (Contd)

Incorporating the error terms and packet

lengths, the worst-case queuing delay :

[(b M) (pR) / R(p-r)] + [(M+Ctot)/R] + D

tot

(p > R r)

[(M + Ctot) / R] + D

tot(R p r)


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Policing and Shaping

Traffic flows that receive guaranteed servicemust conform to the token bucket and peakrate params over all periods.

For any period T, the amount of data sentcannot exceed M + Min (pT, rT+b-M).Packets smaller than min policing unit m arecounted as m.

Policing is done at the edge of the network bycomparing the traffic to the agreed TSpecparams.


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Policing and Shaping

Shaping is done at all heterogeneous branch

points and all merging points.

Heterogeneous branch point is a spot where

a multicast distribution tree has multiple

outgoing branch that have different TSpecs.


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Controlled load service


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Controlled load service

Strict bw assurance and delay bound comes at a price: resources have to be reserved for the worst case.

For some apps a service model with less strictguarantees and lower cost would better serve their

needs. End-to-end behavior somewhat vague. A very high percentage of packets will be successfully

delivered by the network to the receivers. The transit delay experienced by a very high

percentage of packets will not greatly exceed mindelay.


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Resource Reservation

Protocol (RSVP)


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RSVP

A resource reservation protocol defined for

IntServ.

Used by hosts to communicate service

requirements to the network and by routers in

the network to establish reservation state

along a path


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Basic Features

Simplex Reservation :Makes reservation only in one direction.

Treats sender as logically distinct from a receiver

For two way communication, the two ends must

establish reservation for both directions.

Receiver Oriented

Receivers of a flow initiates and maintains theresource reservation.


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Basic Features (Contd)

Routing IndependentDesigned to operate with current and future unicast

and multicast routing protocols

The path for a flow is done separately by routingprotocols

Policy IndependentRSVP transports and maintains traffic control and

policy control parameters that are opaque to RSVPControl params are passed to relevant controlmodules for processing.


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Soft StateRSVP maintains soft states providing graceful

support for dynamic membership changes and

automatic adaptation to routing changes.Reservation state has a timer associated with the

state. When timer expires, the state is

automatically deleted.

RSVP periodically refreshes the reservation state

to maintain the state along the paths.


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Reservation StyleRSVP provides several reservation models or

styles to fit a variety of applications

Can be used to share a reservation among trafficstreams from multiple senders or to select a

particular sender.


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Data Flows

RSVP defines a session to be a data flow

with a particular destination and transport

layer protocol.

RSVP session defined by the triple

(destAddr, ProtoId, [dstPort]).


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Reservation Model

RSVP reservation request consists of a flowspec

together with a filter spec.

flowspec specifies a desired QoS

Filterspec along with a session specifies a flow. Flowspec used to set params in the nodes packet

scheduler

Filterspec used to set the params of the packet

classifier.


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Reservation Model (Contd)

Flowspec include a service class (guaranteed

or controlled load) and two sets of numeric

params RSpec (desired QoS) and a TSpec

(describes traffic).


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Protocol Overview

(1) (2) (3)

(4)(5)(6)

PATH

RESV


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Protocol Overview (contd)

Sender 1

Sender 2

Receivier B

Receiver A

R R

RR

R

PATH

PATH

PATH

PATH

RESV

RESV

RESV

RESV


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Protocol Overview (Contd)

Two primary RSVP msgs : PATH and RESV

PATH msgs are sent from source towards the receivers. Used to pass characteristics of the path.

Installspath state in each node along the way

Includes IP address of previous hop (needed to send RESV msg)

Sender template : sender IP address and port

Sender Tspec : traffic spec of sender

After receiving PATH msg receiver can request a reservation

by sending RESV msg.


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Protocol Overview (Contd)

RESV must follow the exact same reverse

path upstream.

They create reservation state in each node

along the paths

After receiving RESV msg sender can start

sending data packets.


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PATH Message

Contains previous hop, sender template,

sender TSpec and the AdSpec.

Sender template contains info that along with

Session uniquely identifies the flow. It has same format as filterspec.

Sender TSpec characterizes the traffic that

sender will generate.


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PATH Message (Contd)

AdSpec is an optional element in PATH msg :

used to carry OPWA (One Pass with

Advertising)

Passed to local traffic control at each node, whichreturns an updated AdSpec, the updated version

is then forwarded in PATH msg downstream.


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RESV Message

Sent by receivers towards sender along

reverse direction of PATH msg to request

reservation.

Contains info about reservation style,flowspec object and filterspec object.

Flowspec includes a service class,

reservation spec (RSpec) that defines thedesired QoS and a traffic spec (TSpec) that

describes the traffic flow.


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RSVP Message Formats


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g

(Contd)

Version : 4 bitsProtocol version number : Current version is 1

Flags : 4 bitsReserved

Msg Type: 8 bits 1 = Path

2 = ResvRSVP checksum: 16bits

RSVP Message Formats


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g

(Contd)

Send_TTL: 8bits IP TTL value with which the message was sent

RSVP length : 16bitsTotal length of the RSVP message in bytes

including the common header.


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Object Formats

Every RSVP object consists of one or more

32-bit words with a one-word header with the

following format:

Length (in bytes) Class-Num C-type

0 1 2 3

Object contents


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Object Formats (contd)

Length : length of the object in bytes

Class-Num : Identifies the object class.SESSION

FLOWSPEC

SENDER_TSPEC

C-type : Object type unique within Class-Num.


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RESV message

::=

[]

[]

[] []

::= |


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PATH Tear message

::=

[]

[]

Path Tear is initiated by sender or by path

state timeout.

Deletes matching Path state. Travel downstream towards all receivers


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RESV Tear message

::= [] []

Resv Tear is initiated by receiver or by resvstate timeout.

Deletes matching resv state. Travels upstream towards all matching

senders.


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PATH Error message

::=

[]

[]

[]Reports error in processing PATH msg

Travel upstream towards sender


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RESV Confirm message

::=

[]

Sent to acknowledge reservation request

Sent when RESV_CONFIRM object is

present in RESV message.Sent to receiver host from sender.


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Reservation Styles

Reservation request includes a set of options

that are collectively called reservation style.

Decides whether distinct reservation for each

upstream sender or else make a singlereservation that is shared among selected

senders.


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Reservation Styles (Contd)

sender selection Reservation:

distinct shared

Explicit Fixed filter (FF) Shared explicit(SE)

wildcard Not defined Wildcard filter (WF)


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Reservation Style (Contd)

Wildcard-filter (WF) style Implies shared reservation and wild card sender

selection

All receivers share a single reservation whosesize is the largest of the resource requests from

the receivers; all upstream senders can use the

reservation.

Can be represented as WF (*, {Q}), where * is thewildcard sender and Q is the flowspec.


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Fixed-filter (FF) styleDistinct reservation and explicit sender selection.

Distinct reservation established for specific

senderCan be represented as FF (S

1(Q

1), S

2(Q

2), ..)


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Shared explicit (SE) styleShared reservation but explicit sender selection

Creates a single reservation shared by specific

sendersRepresented as SE((S

1, S

2, ., S

n) {Q}).


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Example

S1

S2, S3

R1

R2

R3

(a)

(d)

(c)

(b)


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Wildcard-Filter

Sends Reserves Receives

(c) WF(*{4B})

(d) WF(*{3B})

WF(*{2B})

(c) *{4B}

(d) *{3B}

WF(*{4B}) (a)

WF(*{4B}) (b)


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Fixed-Filter


(c) FF(S1{4B}, S2{5B})

(d) FF(S1{3B}, S3{B}) FF(S1{B})

(c)S1{4B}

S2{5B}

(d)S1{3B}S3{B}

FF(S1{4B}) (a)

FF(S2{5B}, S3{B}) (b)


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SE-Filter


(c) SE(S1,S2{B})

(d) SE(S1, S3{3B}) SE(S2{2B})

(c)(S1,S2){B}

(d)(S1,S2,S3){3B}

SE(S1{3B}) (a)

SE(S2,S3{3B}) (b)


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OPWA

Basic reservation model in RSVP is one pass. It is not possible to determine characteristics

of the path or whether the path is able to

support the desired QoS.Other model, OPWA (One Pass with

Advertising) is more sophisticated which usesAdSpec.

Sender includes an AdSpec in its PATH msgto collect info about the path.

OPWA (Contd)


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OPWA (Cont d) Receiver can use information in the AdSpec to determine

end-to-end characteristics of the path and calculate end-to-

end delay. Has three components :

Default general parameters Guaranteed service fragment Controlled load service fragment

Default general parameters Min path latency : sum of fixed delay along the path in addition to

queuing delay. Path bandwidth : min bandwidth of the path Integrated services hop count : total number of hops that are capable

of supporting IntServ.

Global break bit : set to 0 by sender. Set to 1 if any node along thepath does not support RSVP

Path MTU : MTU of the path.

OPWA (Contd)


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OPWA (Cont d)

Guaranteed service fragment includes Ctot,

Dtot, Csum, Dsum and optional values thatoverride default general params

Controlled load service fragment does not

require any extra data, but may containoptional values that override default general

params.


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Flow Identification

An important module in the data plane. In an integrated services network, a router

has to extract the five tuple from an incoming

packet and compare it against the reservationtable to see if it belongs to a reservedflowPacket processing has to happen very fast

(on OC12 link (622 Mbps), it is of the order of

micro seconds).Flow Identification should happen at a high

speed.

C


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Design Choices

Trade off between speed vs spaceOne extreme is direct memory lookup

Single memory access

Requires high storageFive-tuple is 104 bits long

Other extreme is binary searchEfficient in terms of storage spaceBut relatively slow

Compromise is to use hashing based scheme

H hi b d h


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Hashing based scheme

0

N

Hash table

Collision resolution table

Reservation table

0

M

H hi b d h


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XOR folding of source and destination IP address H(.) = A

1xor A

2xor . A

n

Aiis the substring with i bit to i+m bit of the 64-bit string

No need to get fourth layer info (port) XOR folding of destination IP address and

Destination port Suitable for web-based application where the source addr

and source port may be the same for flows, but destinationaddr and destination port may be different

H hi b d h


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XOR folding of the five tupleLikely to perform better for scheme that uses the

full five tuple.

Similar to other schemes except that 104 bits areused in hash calculation

H hi b d h


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32-bit CRC has been widely used for error detection

in communication systems Known for exploiting the randomness in traffic well

CRC32 of five tuples as hash function Double hashing

Used to significantly reduce collision rate

If there is a collision with first hashing function, a second

hashing function is used Probability of collision with two hashing function is low

More complex because of two level of hashing.

RSVP summary


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RSVP summary

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 understoodalgorithms have to be used though

I tS R f


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IntServ References

R. Braden, D. Clark, S. Shenker, Integrated Services in

the Internet Architecture: an Overview, RFC1633

J. Wroclawski, The Use of RSVP with IETF Integrated

Services, RFC2210.

J. Wroclawski , Specification of the Controlled-Load

Network Element Service, RFC2211

S. Shenker, C. Patridge, R. Guerin, Specification of

Guaranteed Quality of Service, RFC2212

R. Braden, L.Zhang et. al., Resource ReservationProtocol (RSVP), RFC2205.

DiffServ - Prioritization


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DescriptionApplied on flow aggregates

Services requirements are classified

Classification is performed at network ingresspoints

A predefined per-hop behavior (PHB) is applied

to every service class

Traffic is smoothed according to PHB applied


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DiffS I l t ti


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DiffServ - Implementation

C l a s s i f i e r

M e t e r M a r k e r

C o n d i t i o n e r

M a p s D S C P s t oP H B s

M a i n t a i n s

D S C P

m a p p i n g s a n d

a s s o c i a t i o n s

w i t h l o c a l

p o l i c i e s

A c c u m u l a t e s

s t a t i s t i c s

A p p l i e s t h ed e f i n e d P H B

( s c h e d u l i n g )

DiffS I l t ti


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DiffServ - Implementation

T y p e o f S e r v i c eP r e c e d e n c e

R F C 1 1 2 2 M u s tB e

Z e r o

I P T y p e o f S e r v i c e ( T O S )

0 32 4 5 6 71

M B Z

R F C 1 3 4 9

DiffServ codepoints (DSCPs) redefine the Type-of-Service (ToS) IPv4 field

Precedence bits are preserved Type-of-Service bits are NOT

D S C P

C l a s s S e l e c t o r U n u s e d

0 32 4 5 6 71

D i f f e r e n c i a t e d S e r v i c e s

C o d e p o i n t ( D S C P )

C U

DiffServ - Conclusions


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105

Traffic classes are equivalent to IP precedence

service descriptors DiffServ unaware routers pass-through DiffServ traffic

Easy to be implemented / integrated even into thenetwork core.

Proper classification can lead to efficient resource

allocation and though improved QoS


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MPLSImplementation


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- Implementation

L a b e l V a l u e E x p . S T T L

832 0 1

2 0 - b i t s : L a b e l v a l u e u s e d f o r l o o k u p 8 - b i t s : T i m e - T o - L i v e

1 - b i t : B o t t o m o f L a b e l S t a c k

3 - b i t s : R e s e r v e d

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 atable defining the next hop and label

MPLS - Conclusions


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Labels can be stackedThis allows MPLS routes within routes

Label Distribution Protocol (LDP)

Distributes labels across MPLS-enabled routersEnsures they agree on the meaning of labelsUsually transparent to network managers

Implication :Define a policy management that distributes

labels


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Documents

Qos and Mpls