ecn based admission control for inter-provider...

1CFP Inter-Provider QoS Mtg 01/28/05 @ MIT, Nortel Real-Time ECN usage for Inter-Provider QoS, Kwok Ho Chan & Jozef Babiarz

ECN Based Admission Control for Inter-Provider QoS

Kwok Ho Chan, Jozef BabiarzCTO Office, Nortel NetworksJanuary 28, 2005


Overview

> Provide session admission control for real-time inelastic flows like voice, video and multimedia end-to-end including across inter-provider links.

> Use per service class Explicit Congestion Notification (ECN) marking to notify the end-system (or proxy) of congestion level along the path that the session/flow will take.

> During session setup, end-system (or proxy) perform verification of path status (verify connectivity and congestion level),

• i.e., for VoIP, • end-system (or proxy) sends early media or RTP probes, • ECN-capable routers mark ECN bits of EF packets based on congestion or traffic

level they measure.

> Application running in the end-system or network server makes the decision to admit or not admit the new session based on ECN marking.


Defined SLAs for End-to-End Service

• Customer “A” has SLA with SP “A” for access and transport using “Telephony”service class and service agreement with Application Provider

• Customer “B” has SLA with SP “C” for access and transport using “Telephony”service class and service agreement with Application Provider

• SP “A” has SLA with SP “B” for transport using “Telephony” service class• SP “C” has SLA with SP “B” for transport using “Telephony” service class• Application Provider has agreement with SP “A” to use “Telephony” service class

SP A SP B SP C

CS

CommunicationServer

Customer “A”

ApplicationProvider

Customer “B”

QoS TransportSLA

QoS TransportSLAQoS A

ccess

SLA

QoS AccessSLA

Servic

e Agre

ement

Service Agreement


Admission Control

On reception of call request message from Terminal “A” :1. Terminal “B”, generates and sends RTP Request probe packets to Terminal “ A”2. If rate in the Telephony service class > than “a”, ECN bit 7 set to ‘1’3. Upon receiving Request probe packets, Terminal “A” replies with RTP Response probe

packets to Terminal “B”, echoing the received ECN bits in probe payload4. If rate in Telephony service class > than “a”, ECN bit 7 set to ‘1’5. If Response probe packets ECN=‘00’ Terminal “B” will start alerting the user (Ring phone)

SP A SP B SP C

CS

CommunicationServer

Terminal“A”

Terminal “B”

Signaling or ControlECN

CapableECN

Capable

QoS TransportSLA

QoS TransportSLA


SLA Bandwidth Diagram for ECN SAC

BW available for

other services if voice is not

using it1st Traffic Level

(ECN ‘01’)

2nd Traffic Level (ECN ‘11’)

BW reserved& guaranteed

for VoIP

BW = 100%

BW assigned for other services

BW borrowedfrom other services

All calls areadmitted Only higher priority or emergency calls are

admitted

Voice Traffic

Other Traffic

Minimumdelta is one call

time


Status> Extensions to ECN for use with Real-Time inelastic traffic

like VoIP, video and multimedia streaming applications are proposed in IETF

• http://www.ietf.org/internet-drafts/draft-babiarz-tsvwg-rtecn-02.txt• Planning to update the above draft to include ECT(0) marking• Companion draft to define generic RTP probe format (March IETF)• Framework draft explaining how ECN mechanism is used for

admission control of VoIP. (March IETF?)

> For more information please contact Joe Babiarz email [email protected] Chan email [email protected]


Backup Slides

End to End Session Admission Control Using ECN Marker and RTP Probe

Jozef BabiarzOct. 21, 2004


Session Admission Control

> Session admission control (SAC) is a mechanism to block new real-time inelastic flows like voice and videoconferencing when the network resources are at capacity and the admission of additional flows would degrade the service quality to established users.

> ECN SAC is a probe based approach during session (call) setup to determine if there is sufficient bandwidth for a new session to be admitted.

> The ECN SAC concept can also be extended and used to control admission control of priority sessions (i.e., E911, etc.) as well for session preemption. (Note covered in this presentation).


Key Features of ECN SACProbing verifies

• Connectivity path between the two end points• Availability of bandwidth along the path end-to-end in the IP

network • Measures total round trip delay (RTT)

Works for all real-time flows• VoIP• Video conferencing• Video and audio streaming applications

Can be used with any signaling method• SIP, H.323, MGCP, H.248, UNISTIM, ASPEN, etc.

Only VoIP SIP scenarios are discussed in this presentation


The DiffServ (DS) Field is an 6-bit field in the IP header and is defined in RFC 2474.

Version HLen DS field LengthIdentification Fragment offsetFlags

Source addressDestination address

TTL Protocol Header checksum

0 4 8 15 31

Data

IPHeader

DSCP0 5 6 7

ECN1 2 3 4

- The first six bits contain the DiffServ Code Points (DSCP).- The two least significant bits (LSBs) of the DiffServ Field (bits 6 & 7) are used

for Explicit Congestion Notifications (ECN). RFC 3168 defines the incorporation of ECN and usage for TCP flows.

Explicit Congestion Notification (ECN) bits

6 & 7

DiffServ Field & Explicit Congestion Notification


Architecture

Telephony Service• Expedited Forward (EF) PHB used for VoIP• Packet marking for VoIP (IP telephony)

• EF DSCP is used for VoIP payload• EF DSCP is used for probe packets sent during call setup• CS5 DSCP is used for SIP signaling

• ECN bits are used to explicitly convey status of bandwidth usageend-to-end in the network for packets in the Telephony service class (in both directions)

Video Conferencing Service • CS4 DSCP is used for inelastic flows

• Probe packets marked with CS4 DSCP are sent during session setup• etc.


Architecture (cont.)

Flow Measurement is Performed• Per Service Class (e.g., EF marked packets)• On selected routers (ingress and/or egress ports)• Measure the aggregated flow rate (token bucket or other method)• Mark ECN bit if rate is exceeded

No State Information is Kept in Router

-12nd Traffic Level(2nd Level of Congestion)

1-1st Traffic Level(1st Level of Congestion)

00Not Congested

Bit 7

Bit 6

Traffic Load Status in the Network

The table below summarizes the meaning of the ECN bits in the DS Field of IP Header from routers perspective


Accesslink

Accesslink

CS

BW limitedcore link

IP Network

On reception of call request message from Client A :• Client B, generates and sends RTP Request probe packets to Client A• If EF rate > than “a”, ECN bit 7 set to ‘1’• Upon receiving Request probe packets, Client A replies with RTP Response probe packets to Client B, echoing the received ECN bits• If EF rate > than “a”, ECN bit 7 set to ‘1’• If Response probe packets ECN=‘00’ Client B will start alerting the user (Ring phone)

SIP Client A

SIP Client B

Communication Server

SAC Procedure

ECN Capable

ECN Capable


Link Bandwidth Diagram for ECN SAC

BW available for

other services if voice is not

using it1st Traffic Level

(ECN ‘01’)

2nd Traffic Level (ECN ‘11’)

BW reserved& guaranteed

for VoIP

BW = 100%

BW assigned for other services

BW borrowedfrom other services

All calls areadmitted Only higher priority or emergency calls are

admitted

Voice Traffic

Other Traffic

Minimumdelta is one call

time


SummaryProbe packets provide information on

• Connectivity• BW available along the path in both directions• Round Trip Delay (RTT)

IP end-point (SIP Client) examines this information and if parameters are met, session is admitted and alerting is done by the end-point

Also, the end-point sends the obtained information to the communication server (B2BUA) via normal signaling

1

10

Bit 7

Session preemption condition(if supported)

Block admission of regular calls(Admit emergency or higher

priority calls)

Admit all calls

Action taken by End-Point

12nd Traffic Level(2nd Level of Congestion)

01st Traffic Level(1st Level of Congestion)

0Not Congested

Bit 6Traffic Load Status in the Network

Note: Forwarding BW of Telephony service class is configured to support normal calls + emergency calls


INVITE SDP1

180 Ringing

200 OK SDP 2

ACK

INVITE SDP1

180 Ringing

200 OK SDP 2

ACK

RTP Response Probe

RTP Request Probe

Media

INVITE SDP1

180 Ringing

200 OK SDP 2

ACK

Session Admission Control“Session Admitted” Scenario

Client BNetwork BNetwork A Network C

2. The presence of the option tag “ecn-probe”within the INVITE request prompts Client B to initiate a Request/Response Probe Packet transaction.

B2BUA 1 B2BUA 2

100 Trying100 Trying

Client A

1. Client A includes a Require header field with the option tag “ecn-probe”in the initial INVITE request.

SIP INVITE Request

INVITE sip:343-3756;[email protected];user=phone SIP/2.0 Via: SIP/2.0/TCP clientA. wrightpatterson.af.com:5060;branch=z9hG4bK74b43 Max-Forwards: 70Route: From: John ;tag=9fxced76sl To: Call-ID: [email protected]: 1 INVITE Contact: Require: ecn-probe Resource-Priority: normalContent-Type: application/sdpContent-Length: 143

100 Trying


INVITE SDP1

180 Ringing

200 OK SDP 2

ACK

INVITE SDP1

180 Ringing

200 OK SDP 2

ACK

RTP Response Probe

RTP Request Probe

Media

INVITE SDP1

180 Ringing

200 OK SDP 2

ACK

Client A Client BNetwork BNetwork A

B2BUA 1 B2BUA 2


Session Admission Control“Session Admitted” Scenario - continued

3. If the RTP Response Probe indicates that the level of congestion along the network path is below the predefined threshold then call processing proceeds as normal.




0 4 8 15 3111DSCP




0 4 8 15 3100DSCP

Note: the ECN bit value of “00.”

IPRTP UDP IPRTP UDP

100 Trying

Network C


INVITE SDP1 R-P: normal

503 Service Unavailable

ACK



ACK

RTP Response Probe

RTP Request Probe



ACK

Client A Client BNetwork BNetwork A

B2BUA 1 B2BUA 2


Session Admission Control- “Session Blocked” Scenario- Resource-Priority: Normal

1. If the ECN bit values in the RTP Response Probe indicate that the level of congestion between the two clients is above the predefined threshold, then Client B will send a 503 “Service Unavailable”response upstream to Client A. This action will terminate call setup.




0 4 8 15 3111DSCP




0 4 8 15 3101DSCP

Note: the ECN bit value of “01.”IPRTP UDP IPRTP UDP

2. The 503 Response message prompts client A to provide the appropriate “all circuits” busy alerting to the associated user.

100 Trying

Network C

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