1、 ATIS-1000011 ETS PACKET PRIORITY FOR IP NNI INTERFACES USE OF EXISTING DIFFSERV PER HOP BEHAVIORS TECHNICAL REPORT The Alliance for Telecommunication Industry Solutions (ATIS) is a technical planning and standards development organization that is committed to rapidly developing and promoting techni
2、cal and operations standards for the communications and related information technologies industry worldwide using a pragmatic, flexible and open approach. Over 1,100 participants from more than 350 communications companies are active in ATIS 23 industry committees and its Incubator Solutions Program
3、. NOTE - The users attention is called to the possibility that compliance with this standard may require use of an invention covered by patent rights. By publication of this standard, no position is taken with respect to whether use of an invention covered by patent rights will be required, and if a
4、ny such use is required no position is taken regarding the validity of this claim or any patent rights in connection therewith. ATIS-1000011, ETS Packet Priority for IP NNI Interfaces Use of Existing DiffServ Per Hop Behaviors Is an ATIS Standard developed by the Signalling, Architecture, and Contro
5、l (SAC) Subcommittee under the ATIS Packet Technologies and Systems Committee (PTSC). Published by Alliance for Telecommunications Industry Solutions 1200 G Street, NW, Suite 500 Washington, DC 20005 Copyright 2007 by Alliance for Telecommunications Industry Solutions All rights reserved. No part of
6、 this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. For information contact ATIS at 202.628.6380. ATIS is online at . Printed in the United States of America. ATIS-1000011 Technical Report on ETS PACK
7、ET PRIORITY FOR IP NNI INTERFACES USE OF EXISTING DIFFSERV PER HOP BEHAVIORS Secretariat Alliance for Telecommunications Industry Solutions Approved October 2006 Abstract This Technical Report provides guidelines for the application of existing Differentiated Service (DiffServ) Per Hop Behaviors (PH
8、B) and their associated DiffServ Code Points (DSCP) when Emergency Telecommunications Service (ETS) Voice over IP (VoIP) packets are transported in the media stream at Network-Network Interfaces (NNI). Given the current situation involving a single Expedited Forwarding DSCP for all real-time service
9、s, it is recommended that public carriers utilize a local/experimental DSCP to differentiate ETS VoIP traffic from other real-time traffic at NNI interfaces between carriers. The local/experiment DSCP assignment can be determined based on Service Level Agreements between the carriers. ATIS-1000011 i
10、i FOREWORD The Alliance for Telecommunication Industry Solutions (ATIS) serves the public through improved understanding between carriers, customers, and manufacturers. The Packet Technologies and Systems Committee (PTSC) - formerly T1S1 - develops and recommends standards and technical reports rela
11、ted to services, architectures, and signaling, in addition to related subjects under consideration in other North American and international standards bodies. PTSC coordinates and develops standards and technical reports relevant to telecommunications networks in the U.S., reviews and prepares contr
12、ibutions on such matters for submission to U.S. ITU-T and U.S. ITU-R Study Groups or other standards organizations, and reviews for acceptability or per contra the positions of other countries in related standards development and takes or recommends appropriate actions. Suggestions for improvement o
13、f this document are welcome. They should be sent to the Alliance for Telecommunications Industry Solutions, PTSC Secretariat, 1200 G Street NW, Suite 500, Washington, DC 20005. At the time it approved this document, PTSC, which is responsible for the development of this Technical Report, had the fol
14、lowing members: R. Hall, PTSC Chair J. Zebarth, PTSC Vice-Chair C. Underkoffler, ATIS Chief Editor P. Tarapore, PTSC Technical Editor Organization Represented Name of Representative AcmePacket Kevin KlettAlcatel USA Inc. Ken Biholar AT and possibly even at intranetwork core interfaces. At the same t
15、ime, traffic volumes during emergency conditions have been known to increase significantly, with the bulk of the increase coming from residential voice calls as the affected population seeks help or tries to establish the safety of family and friends during these conditions. To summarize, emergency
16、conditions result in diametrically opposite outcomes for a network depleted network resources particularly at UNI and NNI interfaces along with a significant surge of incoming real-time voice traffic. Differentiated Services 2, 3, & 4enable the implementation of scalable service differentiation in I
17、P networks. This differentiation is achieved by aggregating traffic types (e.g., real-time telephony, high throughput data, etc.) into one of three Per Hop Behavior (PHB) categories whereby packet streams of similar traffic types are classified and treated appropriately in router queues. These PHBs
18、are: Best Effort (BE): This is the default forwarding behavior available in existing routers. Packets in this behavior aggregate are not subject to any specified assurances and the network will deliver as many of these packets as possible as quickly as feasible, subject to network policy conditions
19、and constraints. Assured Forwarding (AF): This PHB provides a means to offer different levels of forwarding assurances for IP packet streams that do not have very stringent delay, jitter, or loss requirements (e.g., high throughput data). Four AF PHB classes have been defined where each 5Depending o
20、n the severity of the emergency, even core interfaces may experience diminished resources and bottlenecks. 2 ATIS-1000011 AF class has a certain amount of forwarding resources (queue buffer space and bandwidth) allocated. Within each AF class, packets are marked with one of three possible drop prece
21、dence levels, indicating the priority with which the packets will be dropped in case of congestion. Expedited Forwarding (EF): This PHB is intended to provide a forwarding behaviour that provides assurances of low delay, low packet loss, and low jitter services such as that required to support real-
22、time telephony. Packet streams intended for this PHB are suitably “marked” and they encounter queues which are typically empty or which are very sparsely populated. The intent is to keep queue occupation low relative to buffer space, thus minimizing delay and delay variation. This is achieved by ens
23、uring that service rates at the EF queues exceed the arrival rates. Due to the stringent requirement of low delay, jitter, and loss, and the lack of reasons to do otherwise, the EF PHB currently has a single class defined. Thus, all real-time telephony calls are currently handled by this PHB regardl
24、ess of the type of the call ETS or non-ETS. Attempts to classify various IP-based service types into the defined PHBs have been made based on the performance and QoS characteristics of the traffic type in question. The ITU-T Recommendation Y.1541 5provides a mapping between user applications, networ
25、k performance QoS classes, and DiffServ PHBs. In the IETF, work is in progress that attempts to group specific traffic types to individual Per Hop Behaviors based on performance and QoS characteristics 6. However, the priority of a critical emergency service is not discussed in either of these afore
26、mentioned guidelines. ATIS documents 7have provided some guidance on the criticality of IP-based service in the form of a priority related to admission control and resource reservation. Three broad classes High, Normal, and Best Effort have been defined with the recommendation that High Priority be
27、exclusively reserved for emergency services such as ETS. It is straightforward to note that all Best Effort priority services can be mapped to the Best Effort PHB. For services in the Assured Forwarding PHB, the presence of four AF classes - each with drop precedence values - can provide the means t
28、o meet priority requirements for these services. It is the Expedited Forwarding PHB that is of concern when attention is turned to the requirement to support Emergency Services in practice, there is only one EF class for all real-time telephony traffic regardless of whether calls are High Priority E
29、TS calls or Normal Priority non-ETS calls. This inability of the single EF PHB to distinguish ETS voice calls from other voice calls only becomes significant during emergency conditions. Recall the likely state of the network during such conditions discussed earlier - depleted network resources part
30、icularly at UNI and NNI interfaces along with a significant surge of incoming real-time voice traffic. These conditions may overwhelm the potentially depleted resources available for the EF PHB, such that the arrival rates at the EF queues may increase significantly beyond the service rates at these
31、 queues. The resulting dropped packets in addition to added delay and jitter - may impact the ETS calls, just when they are in urgent need of successful treatment. Given this severe constraint of a single EF PHB Class, the following recommendation is proposed as a way for service providers to recogn
32、ize ETS voice calls at NNI interfaces: At NNI interfaces between public domain carriers, assign a local/experimental DiffServ Code Point (DSCP) to ETS VoIP service based on SLA agreements, and continue to utilize the existing EF PHB DSCP for non-ETS VoIP service. 3 ATIS-1000011 In conclusion: 1. Thi
33、s recommendation should be adopted as part of the interconnection agreements between public domain, service providers to define how DiffServ PHB Code Points will be applied to ETS and non-ETS VoIP calls at NNI interfaces. 2. This recommendation should be adopted on the understanding that it is a tem
34、porary solution, due to the existing constraint of the currently specified single EF PHB Class for all VoIP telephony services regardless of their priority requirements. Provision should be made for the adoption of new operating guidelines when available, thereby allowing for the separation of ETS a
35、nd non-ETS VoIP traffic. 3. This recommendation does not dictate how ETS and non-ETS traffic is to be carried within service providers networks. It is understood that how service providers carry ETS and non-ETS traffic, with respect to PHB treatment, may depend upon the providers capabilities and preferences. 4
