Configuration Guide - QoS

Transcription

1 Release: Document Revision: NN A Rev01

2 Release: 5.3 Publication: NN Document Revision: Document status: Standard Document release date: 30 March 2009 Copyright 2009 Nortel Networks All Rights Reserved. Printed in Canada, India, and the United States of America LEGAL NOTICE While the information in this document is believed to be accurate and reliable, except as otherwise expressly agreed to in writing NORTEL PROVIDES THIS DOCUMENT "AS IS" WITHOUT WARRANTY OR CONDITION OF ANY KIND, EITHER EXPRESS OR IMPLIED. The information and/or products described in this document are subject to change without notice. Nortel, the Nortel logo, and the Globemark are trademarks of Nortel Networks. All other trademarks are the property of their respective owners. ATTENTION For information about the safety precautions, read "Safety messages" in this guide. For information about the software license, read "Software license" in this guide.

3 Contents About this document...1 Issue 5.3 (30 March 2009) Nortel Networks Inc. i

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5 About this document About this document Overview This chapter describes the organization of this document, product version, intended audience, conventions, and update history. Related versions The following table lists the product versions related to this document. Product Name Nortel Secure Router 8000 Series Secure Router Version V200R005 Intended audience The intended audiences of this document are: Network operators Network administrators Network maintenance engineers Organization This document consists of four chapters and is organized as follows. Chapter Description 1 QoS Overview Introduces the function and implementation of QoS. 2 HIC QoS Configuration Describes the Diff-Serve model, the implementation and configuration of QoS on the HIC. Issue 5.3 (30 March 2009) Nortel Networks Inc. 1

6 About this document Nortel Secure Router 8000 Series Chapter 3 FIC QoS Configuration Appendix A Abbreviations and Acronyms Description Describes the implementation and configuration of QoS on the FIC, including traffic shaping, limit rate on the interface, convergence management, convergence avoidance, link efficiency mechanism, class-based QoS, frame relay QoS, ATM QoS, MPLS QoS, VLAN QoS and TE QoS. Lists the abbreviations and acronyms used in this volume. Conventions Symbol conventions The symbols that may be found in this document are defined as follows. Symbol Description Indicates a hazard with a high level of risk that, if not avoided, will result in death or serious injury. Indicates a hazard with a medium or low level of risk which, if not avoided, could result in minor or moderate injury. Indicates a potentially hazardous situation that, if not avoided, could cause equipment damage, data loss, and performance degradation, or unexpected results. Indicates a tip that may help you solve a problem or save time. Provides additional information to emphasize or supplement important points of the main text. General conventions Convention Times New Roman Boldface Italic Courier New Description Normal paragraphs are in Times New Roman. Names of files, directories, folders, and users are in boldface. For example, log in as user root. Book titles are in italics. Terminal display is in Courier New. 2 Nortel Networks Inc. Issue 5.3 (30 March 2009)

7 About this document Command conventions Convention Boldface Italic Description The keywords of a command line are in boldface. Command arguments are in italics. [ ] Items (keywords or arguments) in square brackets [ ] are optional. { x y... } Alternative items are grouped in braces and separated by vertical bars. One is selected. [ x y... ] Optional alternative items are grouped in square brackets and separated by vertical bars. One or none is selected. { x y... } * Alternative items are grouped in braces and separated by vertical bars. A minimum of one or a maximum of all can be selected. [ x y... ] * &<1-n> Optional alternative items are grouped in square brackets and separated by vertical bars. Many or none can be selected. The parameter before the & sign can be repeated 1 to n times. A line starting with the sign is comments. GUI conventions Convention Boldface Description Buttons, menus, parameters, tabs, windows, and dialog titles are in boldface. For example, click OK. > Multi-level menus are in boldface and separated by the ">" signs. For example, choose File > Create > Folder. Keyboard operation Format Key Key 1+Key 2 Key 1, Key 2 Description Press the key. For example, press Enter and press Tab. Press the keys concurrently. For example, pressing Ctrl+Alt+A means the three keys should be pressed concurrently. Press the keys in turn. For example, pressing Alt, A means the two keys should be pressed in turn. Issue 5.3 (30 March 2009) Nortel Networks Inc. 3

8 About this document Nortel Secure Router 8000 Series Mouse operation Action Click Double-click Drag Description Select and release the primary mouse button without moving the pointer. Press the primary mouse button twice continuously and quickly without moving the pointer. Press and hold the primary mouse button and move the pointer to a certain position. Update history Updates between document versions are cumulative. Therefore, the latest document version contains all updates made to previous versions. Updates in Issue 01 ( ) This document is the first commercial release. 4 Nortel Networks Inc. Issue 5.3 (30 March 2009)

9 Contents 1 QoS Overview Introduction Traditional packets transmission application New applications requirements Congestion causes, impact and countermeasures Congestion Occurrence Congestion results Countermeasures Traffic control technologies Realization of QoS on the Secure Router Issue 5.3 (30 March 2009) Nortel Networks Inc. i

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11 Figures Figure 1-1 Schematic diagram of traffic congestion Issue 5.3 (30 March 2009) Nortel Networks Inc. iii

12 Contents 1 QoS Overview Introduction Traditional packets transmission application New applications requirements Congestion causes, impact and countermeasures Congestion Occurrence Congestion results Countermeasures Traffic control technologies Realization of QoS on the Secure Router Issue5.3 (30 March 2009) Nortel Networks Inc. i

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14 Figures Figure 1-1 Schematic diagram of traffic congestion Issue5.3 (30 March 2009) Nortel Networks Inc. iii

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16 1 QoS Overview 1 QoS Overview About this chapter The following table shows the contents of this chapter. Section Description 1.1 Introduction This section describes the basic concept of QoS. 1.2 Traditional packets This section describes the feature and mode of traditional transmission application services. 1.3 New applications requirements This section describes the feature of new services and requirements for QoS. 1.4 Congestion causes, impact This section describes the cause and countermeasures and countermeasures against congestion 1.5 Traffic control technologies 1.6 Realization of QoS on the Secure R This section describes the technologies to solve congestion. This section describes the realization of QoS on the SR8000. Issue 5.3 (30 March 2009) Nortel Networks Inc. 1-1

17 1 QoS Overview Nortel Secure Router 8000 Series 1.1 Introduction Quality of Service (QoS) measures the performance of service providers in meeting client s requirements. Instead of giving accurate marks, QoS evaluation stresses analyzing the service performance to guide service improvement. In the internet, QoS evaluates the packet delivery capability of the services. QoS evaluates different services from different aspects. During packet transmission, QoS evaluates the performance according to delay, delay jitter and packet loss ratio, and other requirements. 1.2 Traditional packets transmission application In a traditional IP network, the router treats all packets identically and handles them according to the First In First Out (FIFO) policy. During forwarding, the router assigns resources to the packets in the order of arrival. All the packets share the network and bandwidth resources of the router. How many resources packets can receive depends on the time they arrive. This service model is called as Best-Effort, which delivers packets to their destination as possible as it can, without any assurance and guarantee for delivery delay, jitter, and packet loss ratio. The Best-Effort model is suitable for applications insensitive to bandwidth and delay performance, such as WWW, File Transfer Protocol (FTP) and New applications requirements With the rapid development of the network, more and more networks are connected to the internet. More and more users use the internet as a platform for data transmission and implement various applications. Service providers also want to develop new services for more profits. Apart from traditional applications such as WWW, and FTP, users expand services on the internet, with services such as e-learning, telemedicine, videophone, videoconference and video on demand. Enterprise users who want to connect their branches in different areas through VPN technologies can implement some transactional applications such as accessing corporation databases or managing remote devices through telnet. All these new applications put forward special requirements for bandwidth, delay, and jitter. For example, videoconference and video on demand need the guarantee of high bandwidth, low delay and low jitter. Critical tasks such as transaction and Telnet stress on low delay and prior handling in case of congestion. New emerging services put higher requirement in the service capability of the IP network. Other than simply delivering packets to their destination, users want to get better services, for example, providing user-specific bandwidth, reducing packet loss ratio, managing and avoiding network congestion, regulating network traffic and configuring the priority of packets. 1-2 Nortel Networks Inc. Issue 5.3 (30 March 2009)

18 1 QoS Overview 1.4 Congestion causes, impact and countermeasures Network congestion is a key factor in degrading the service quality of traditional networks. Congestion refers to reduced and delayed service rates because of the relative shortage of resources. This section introduces the knowledge concerning congestion: Congestion Occurrence Congestion results Congestion results Congestion Occurrence In complex environments, congestion is likely to occur. Consider Figure 1-1 as an example. Figure 1-1 Schematic diagram of traffic congestion 100M 100M 10M 100M 100M Traffic congestion on interfaces operating at different speeds 100M Traffic congestion on interfaces operating at the same speed Packets enter a router from a high-speed link and are forwarded over a low-speed link. Packets enter a router from several interfaces at the same speed and are forwarded through an interface at the same speed as well. If packets arrive at a line rate, congestion occurs because of the bottleneck of link bandwidth. Any resource shortage during normal packet forwarding, such as the lack of assignable processor time, buffer and memory, can cause congestion. In addition, congestion can occur as the arriving traffic is not managed efficiently and exceeds the assigned network resources Congestion results Congestion may cause the following negative results: Increasing the delay and jitter of packet transmission Packet re-transmission due to long delay Decreasing the efficient network throughput and wasting network resources Consumption of too many network resources (memory in particular) due to intensified congestion and even resources deadlock and system breakdown by irrational resources assignment Issue 5.3 (30 March 2009) Nortel Networks Inc. 1-3

19 1 QoS Overview Nortel Secure Router 8000 Series Countermeasures Congestion causes the traffic fail to receive network resources in time, and degrade the service performance. Congestion is common in packet switching and complex environments with multiple services. Increasing network bandwidth to solve resources shortage but does not solve all the congestion problems. A more effective method is to improve the functions of traffic control and resource allocation at the network layer, and to provide distinguished services for applications with different service requirements. During resources allocation and traffic control you can control the direct or indirect factors that cause network congestion to a greater extent. When congestion occurs, resources allocation should be balanced according to the application s requirements. Thus, the influence of congestion on QoS can be reduced to the minimum. 1.5 Traffic control technologies Traffic classification, traffic policing, traffic shaping, congestion management and congestion avoidance are foundations for a network to provide distinguished services. Traffic classification: identifies the object according to certain matching rules. Traffic policing: manages or controls the specifications of particular traffic that enters a router. If the traffic exceeds the specification, some controls or punishment measures can be taken to protect commercial benefits of carriers and prevent network resources from being damaged. Traffic shaping: is a traffic control measure of actively adjusting the output speed of traffic. It can enable the traffic to adapt the network resources supplied by the downstream router to prevent the unwanted packet dropping and congestion. Congestion management: handles the resources competition during network congestion. It stores packets in the queue first, and then takes a dispatching algorithm to assign the forwarding sequence of packets. Congestion avoidance: monitors the use of status of network resources, and actively drops packets when congestion becomes worse. In this way, it can solve network overload. Among these technologies, traffic classification identifies the prerequisite for differentiated services, which identifies the interested packet with a certain matching rule. Traffic policing, traffic shaping, congestion management and congestion avoidance implement management over network traffic and allocate resources in different aspects respectively to realize differentiated services. In general, a router performs the following QoS functions: Traffic classification and marking Traffic policing and traffic shaping Congestion management Congestion avoidance 1.6 Realization of QoS on the Secure Router 8000 There are different configurations of QoS on the FIC and the HIC of the Secure Router Nortel Networks Inc. Issue 5.3 (30 March 2009)

20 1 QoS Overview For the configuration of QoS on the HIC, refer to QoS configuration on the HIC. For the configuration of QoS on the FIC, refer to QoS configuration on the FIC. Issue 5.3 (30 March 2009) Nortel Networks Inc. 1-5

21 Contents 1 Introduction to HIC Principle of QoS for HIC IP QoS models IP QoS type Supports of lower layer network for IP QoS Interoperability of various IP QoS models Diff-serv architecture model Overview Diff-Serv networking Definitions of Diff-Serv service categories Technologies used for implementing Diff-Serv model MPLS QoS MPLS CoS MPLS VPN QoS QoS processing in MPLS domain HQoS Introduction Principles of HQoS Introduction to the QoS implementations for HIC Upstream configuration Downstream configuration HIC QoS configuration Configuring QoS-based simple traffic classification Establishing the configuration task Enabling simple traffic classification Configuring the mapping table Between DSCP and CoS Configuring QoS-based complex traffic classification Establishing the configuration task Configuring the matching rules for a class Configuring traffic behavior Configuring the class-based policy Issue 5.3 (30 March 2009) Nortel Networks Inc. i

22 3.2.5 Applying the policy on an interface Checking the configuration Configuring an internal traffic policy Establishing the configuration task Configuring an internal traffic policy Checking the configuration Configuring traffic shaping Establishing the configuration task Configuring traffic shaping Configuring GTS queue statistics Checking the configuration Configuring congestion avoidance Establishing the configuration task Setting parameters according to the CoS of packets Setting parameters according to the protocol type of packets Checking the configuration Configuring MPLS QoS Establishing the configuration task Mapping from DSCP to EXP on the MPLS ingress Mapping from EXP to DSCP on the MPLS egress Configuring the mapping table between EXP and CoS Checking the configuration Configuring HQoS Establishing the configuration task Configuring HQoS Configuring HQoS on MP-group interface Checking the configuration Configuration examples Example for the bandwidth guarantee based on simple traffic classification Example for the bandwidth guarantee based on complex traffic classification Example for configuring the traffic policing Example for configuring HQoS Configuring HQoS on a VPN ii Nortel Networks Inc. Issue 5.3 (30 March 2009)

23 Figures Figure 2-1 Schematic diagram of the Diff-Serv network structure Figure 2-2 DS field and ToS field Figure 2-3 Traffic classification and traffic control Figure 2-4 Dropping probability curve of RED algorithm Figure 2-5 Mapping between DSCP and EXP Figure 2-6 Figure of the original congestion management principles Figure 3-1 Networking diagram of QoS Figure 3-2 Networking diagram for configuring HQoS on a VPN Issue 5.3 (30 March 2009) Nortel Networks Inc. iii

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25 Tables Table 1-1 Working mode of Secure Router 8012 router Table 1-2 Types of the interface module that plug into the slots of the Secure Router Table 2-1 Code points of AF Table 2-2 The corresponding relations between the IPv4 precedence and the CSCP Table 2-3 Mapping table of the default DSCP and service types Table 2-4 HQoS statistics items of the traffic Table 3-1 The default mapping table of the DSCP and CoS Table 3-2 Mapping table of the packet protocol and the bandwidth Table 3-3 The default RED parameter list for classes of service Table 3-4 The default RED parameters for various services Table 3-5 The default mapping relationship from DSCP to EXP Table 3-6 The default mapping relationship from EXP to DSCP Table 3-7 The default mapping table of the EXP and CoS Issue 5.3 (30 March 2009) Nortel Networks Inc. v

26 Contents 1 Introduction to HIC Issue 5.3 (30 March 2009) Nortel Networks Inc. i

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28 Tables Table 1-1 Working mode of Secure Router 8012 router Table 1-2 Types of the interface module that plug into the slots of the Secure Router Issue 5.3 (30 March 2009) Nortel Networks Inc. iii

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30 1 Introduction to HIC 1 Introduction to HIC For details of HIC, refer to Nortel Secure Router8000 Series Hardware Description and Nortel SecureRouter8012 Series Hardware Description. Hi gh speed Interface Card (HIC) contains the following cards: 2-port 10/100Base-TX FE electrical interface module (RT-HIC-2FE) 4-port 10/100Base-TX FE electrical interface module (RT-HIC-4FE) 8-port 10/100Base-TX FE electrical interface module (RT-HIC-8FE) 2-port 10/100Base-TX FE optical interface module (RT-HIC-2FE-SFP) 4-port 10/100Base-TX FE optical interface module (RT-HIC-4FE-SFP) 8-port 10/100Base-TX FE optical interface module (RT-HIC-8FE-SFP) 1-port 1000Base Ethernet optical interface module (RT-HIC-1GE) 2-port 1000Base Ethernet optical interface module (RT-HIC-2GE) 1-port unchannelized POS/155M optical interface module (RT-HIC-1POS) 2-port unchannelized POS/155M optical interface module (RT-HIC -1POS) 4-port unchannelized POS/155M optical interface module (RT-HIC -2POS) 4-port unchannelized POS/155M optical interface module (RT-HIC-4POS) 1-port channelized POS optical interface E1 module (RTP1CPE1) 1-port channelized POS optical interface T1 module (RTP1CPT1) 16-port channelized POS E1 module 16 (RTP116CE1) 16-port channelized POS T1 module 16 (RTP116CT1) 1-port ATM 155M optical interface module (RTP1A1CFF) 2-port ATM 155M optical interface module (RTP1A2CFF) 4-port ATM 155M optical interface module (RTP1A4CFF) High speed card IPSec module (RT-HIC-HPSEC) For the Secure Router 8002, slots 1 and 2 support HIC. For the Secure Router 8004, slots 1, 2 and 4 support HIC. For the Secure Router 8008, slots 1, 2 and 4 support HIC. For the Secure Router 8012, slots 1, 2, 3, 4, 5 and 7 support HIC, but the module type of the plugged in HIC depends on the working mode of the router. Issue 5.3 (30 March 2009) Nortel Networks Inc. 1-1

31 1 Introduction to HIC Nortel Secure Router 8000 Series Secure Router 8012 router has two working modes: common mode and extended mode. When changing the working modes from the extended mode (6HIC) to the common mode, pull out the HIC interface modules on slots 1, 3, 5 and 7 (3HIC). Table 1-1 shows how to decide the working mode of the router. T able 1-1 Working mode of Secure Router 8012 router Working Mode Common mode Extended mode Conditions The router runs in the common working mode when the following interface modules are plugged in slot 1: RT-HIC-2FE, RT-HIC-4FE, RT-HIC-8FE, RT-HIC-2FE-SFP, RT-HIC-4FE-SFP, RT-HIC-8FE-SFP, RT-HIC-1GE, RT-HIC-2GE, RT-HIC-POS, RT-HIC-2POS, RT-HIC-4POS, RT-HIC-ATM, RT-HIC-2ATM, RT-HIC-4ATM, RTP116CE1, RTP116TE1, RTP1CPE1, RTP1CPT1, RTP1A2CFF, RTP1A4CFF, RT-HIC-HPSEC. The router runs in the extended working mode when the following interface modules are plugged in any of the 1, 3, 5 and 7 slots: RTP116CE1, RTP116CT1, RTP1CPE1, RTP1CPT1, RTP1A1CFF, RT-HIC-1POS HIC. The Secure Router 8012 searches the type of the interface mode and determines its working mode when the system is initialized or upon the hot swapping of the interface module. Table 1-2 shows the types of the interface module that plugin the slots of the Secure Router Nortel Networks Inc. Issue 5.3 (30 March 2009)

32 1 Introduction to HIC Table 1-2 Types of the interface module that plug into the slots of the Secure Router 8012 Working Mode Slot ID 1 2, 4 3, 5, 7 6, 8 Common mode (3HIC) The HIC interface modules that can be plugged in: RT-HIC-2FE RT-HIC-4FE RT-HIC-8FE RT-HIC-2FE-SFP RT-HIC-4FE-SFP RT-HIC-8FE-SFP Any HIC/FIC interface module can be plugged in. The HIC interface module cannot be plugged in; any FIC interface module can be plugged in. The HIC interface module cannot be plugged in; any FIC interface module can be plugged in. RT-HIC-1GE RT-HIC-2GE RT-HIC-2POS RT-HIC-4POS RTP1A2CFF RTP1A4CFF RT-HIC-HPSEC Extended mode (6HIC) The HIC interface modules that can be plugged in: RTP116CE1 RTP116CT1 RTP1CPE1 RTP1CPT1 RTP1A1CFF RT-HIC-1POS Any HIC/FIC interface module can be plugged in. The HIC interface modules that can be plugged in: RTP116CE1 RTP116CT1 RTP1CPE1 RTP1CPT1 RTP1A1CFF The HIC interface module cannot be plugged in; any FIC interface module can be plugged in. RT-HIC-1POS Issue 5.3 (30 March 2009) Nortel Networks Inc. 1-3

33 Contents 2 Principle of QoS for HIC IP QoS models IP QoS type Supports of lower layer network for IP QoS Interoperability of various IP QoS models Diff-serv architecture model Overview Diff-Serv networking Definitions of Diff-Serv service categories Technologies used for implementing Diff-Serv model MPLS QoS MPLS CoS MPLS VPN QoS QoS processing in MPLS domain HQoS Introduction Principles of HQoS Introduction to the QoS implementations for HIC Upstream configuration Downstream configuration Issue 5.3 (30 March 2009) Nortel Networks Inc. i

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35 Figures Figure 2-1 Schematic diagram of the Diff-Serv network structure Figure 2-2 DS field and ToS field Figure 2-3 Traffic classification and traffic control Figure 2-4 Dropping probability curve of RED algorithm Figure 2-5 Mapping between DSCP and EXP Figure 2-6 Figure of the original congestion management principles Issue 5.3 (30 March 2009) Nortel Networks Inc. iii

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37 Tables Table 2-1 Code points of AF Table 2-2 The corresponding relations between the IPv4 precedence and the CSCP Table 2-3 Mapping table of the default DSCP and service types Table 2-4 HQoS statistics items of the traffic Issue 5.3 (30 March 2009) Nortel Networks Inc. v

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39 2 Principle of QoS for HIC 2 Principle of QoS for HIC About this chapter T he following table lists the contents of this chapter. Section Description 2.1 IP QoS models This section describes the basic concepts of the IP QoS model. 2.2 Diff-serv architecture This section describes the service class and related model technology of the Diff-Serv model. 2.3 MPLS QoS This section describes the principles of implementing QoS in MPLS. 2.4 HQoS This section describes the origin, principle and application of HQoS. 2.5 Introduction to the QoS implementations for HIC This section describes the methods of implementing QoS of HIC. Issue 5.3 (30 March 2009) Nortel Networks Inc. 2-1

40 2 Principle of QoS for HIC Nortel Secure Router 8000 Series 2.1 IP QoS models IP QoS type Integrated service model IP QoS models specify the modes of packet delivery services. Depending the specified QoS features of these modes, network carriers can sign service agreements with customers when planning and designing QoS of networks and routers. The section contains the contents as follows: IP QoS type Supports of lower layer network for IP QoS Interoperability of various IP QoS models The Integrated Service (Int-Serv) model features submission of a request to the network before sending a packet. This signaling implements the request and one instance is Resource Reservation Protocol (RSVP). An application program informs the network of its QoS requirements (such as delay, bandwidth, packet loss ratio and other indices) through the RSVP signaling protocol. After receiving a resource reservation request, the network node on the transmission path implements admission control to determine whether to reserve resource for the application according to the authentication of a user and availability of resource. Once the resource allocates for an application, the network makes a commitment to satisfy the QoS requirements of this application as long as the traffic parameters controls the range of the packet of this application. The network nodes on the reserved path can execute packet classification, traffic policing, and low delay queue scheduling (for example, WFQ) to commit the requirement of the application. Often in combination with multicast, real-time multimedia applications that need a guarantee of bandwidth and low delay, such as videoconferencing, video on demand, use the Int-Serv model. Int-Serv adopting the RSVP protocol has defined two types of services: Guaranteed Service provides a guaranteed bandwidth and delay to satisfy the requirement of an application. For example, VoIP application can reserve 10Mbit/s bandwidth and requires delay no longer than one second. Controlled-Load Service can provide QoS similar to that of Best-Effort without network overload even if a network is overloaded, guaranteeing low delay and low packet loss ratio for some applications. Int-Serv provides good end-to-end QoS delivery service but poor scalability. The router must maintain some necessarysoft state information for each resource reservation. When combined with the multicast application, the router still has to regularly send requests for resources and path update information to the network to support multicast members to enter or exit dynamically, consuming many processors and memory resources of the router. When a network expands, the cost of maintenance increases greatly, causing a poor performance of the router when it is processing packets. Int-Serv is not applicable to the backbone network centered with traffics. 2-2 Nortel Networks Inc. Issue 5.3 (30 March 2009)

41 2 Principle of QoS for HIC Differentiated service model The application adopting the Diff-Serv model does not need to send a request to the network before transmitting a packet, which is different from Int-Serv. It informs a network node of its QoS requirement through the QoS parameter carried in the IP packet header. This information identifying a QoS requirement is just like an in-band signaling, which is then analyzed by various routers on the packet propagation path to know the service requirement category of a packet. When providing services, Diff-Serv provides the same service policy for the packets of the same requirement category. Diff-Serv model takes traffic aggregate (the packet set having the same QoS requirement category) as the service objects to classify the traffic of packets in terms of coarse granularity. Thus, if packets are correctly labeled with service class, the downstream router needs only to recognize them instead of complex traffic classification. Based on the features, Diff-Serv does not have the heavy arising from maintaining the great soft state information of each flow. Thus, Diff-Serv is of good scalability and is applicable to the backbone network. The next chapter describes the Diff-Serv model in detail Supports of lower layer network for IP QoS Lower layers such as LAN, X.25, ATM, which encapsulates IP packets and transmit them construct the IP network architecture. Various link technologies also have different effects on delay and jitter. In addition, if the lower layer network is one of switching networks such as X.25, frame relay or ATM, the exchange of the intermediate node processes the packet of the link layer during the encapsulating and transferring of a packet. The QoS requirement at the IP layer may not be understood and IP QoS may be damaged during congestion. To solve this problem, a mechanism at the lower layer must simulate the IP QoS model at the higher layer, and the IP QoS requirement can receive when the packet at the layer 2 arrives. Mapping the IP QoS parameter to the parameter for traffic control at the second layer. MPLS technology can be used to effectively support the Diff-Serv model Interoperability of various IP QoS models You must allow the interoperation of the IP QoS model for the IP packet to maintain or gain necessary QoS guarantee when it transmits between networks adopting different IP QoS models. For example, to extend the range of QoS and implement the end-to-end QoS delivery, the edge of a network adopts Int-Serv and Diff-Serv model in a backbone network. In this case, the interoperation must support between Int-Serv and Diff-Serv processing modes such as RSVP in Diff-Serv domain and the mapping between the services of Int-Serv and Diff-Serv. If adjacent areas adopt the same IP QoS model,(such as Diff-Serv model), but different ISPs manage it, the QoS parameters of the same service category in these two areas are not necessarily the same because of differences in areas such as history and security policy. Convert corresponding QoS parameters when an IP packet passes these areas. 2.2 Diff-serv architecture model Diff-Serv is an IP QoS model that is applicable to the backbone network and can satisfy multiple service requirements. Issue 5.3 (30 March 2009) Nortel Networks Inc. 2-3

42 2 Principle of QoS for HIC Nortel Secure Router 8000 Series Overview This section describes what you need to learn before configuring the Diff-Serv and lists related references, including: Overview Diff-Serv networking Definitions of Diff-Serv service categories Technologies used for implementing Diff-Serv model This model defines eight kinds of standard forwarding services, such as: Expedited Forwarding (EF), Assured Forwarding (AF) and so on. In the Diff-Serv system, users can apply for services at different levels with the Diff-Serv field of packet marking. The first 6 bits of Diff-Serv field are Differentiated Services CodePoint (DSCP) and the group of the packets with the same DSCP value is called Behavior Aggregate (BA). A router reserves the mapping of DSCP to Per-Hop Behaviors (PHB, the behaviors satisfying a forwarding requirement, such as traffic policing, traffic shaping, queue management and other QoS behaviors). When a packet enters a router, a DSCP classifies it into a BA and forwarded by a specific PHB. With QoS services, the network border router and the internal router put different emphasis on their functions and cooperate with each other like an integer. Diff-Serv makes the border router implement complex traffic classification and traffic control. The router is mainly responsible for complex traffic classification, marking DSCP for a packet, supervision of traffic access rate, access control. The internal router in an area is mainly responsible for simple traffic classification and traffic control of BA. This avoids the complex traffic classification and traffic control based on Per-stream in the Int-Serv model, which enables the forwarding operations within a DS network to be performed effectively. RFC2474 and RFC2475 have defined respectively the architectures of DS field and Diff-Serv model. RFC2597 has defined AF PHB and RFC2598 EF PHB. 2-4 Nortel Networks Inc. Issue 5.3 (30 March 2009)

43 2 Principle of QoS for HIC Diff-Serv networking Figure 2-1 Schematic diagram of the Diff-Serv network structure DS node DS Region Border node DS domain Non-DS domain The network node that implements the Diff-Serv function is called a DS node. The DS domain is made up of a group of connected DS nodes that use the same service policy and implements the same PHB group set. A DS region is made up of a group of adjacent DS domains. DS nodes include border DS node and internal DS node. The former connects one DS domain and other DS domains or non-ds domains, while the latter is only responsible for connecting the border DS node and other internal nodes in the same DS domain. Both types of nodes can select corresponding PHB to perform forwarding according to the DSCP of a packet. The border DS node implements traffic control according to the Traffic Conditioning Agreement (TCA) made between domains. The internal DS node needs only to implement simple traffic classification and traffic control of BA based on DSCP. The border DS node acts as both the ingress node and egress node of DS domain. A packet enters the DS domain from the ingress node and flows out of it from the egress node Definitions of Diff-Serv service categories DS field and DS codepoint DS fields are the Type of Service (ToS) field in IPv4 and the Traffic Class field in IPv6. As shown in Figure 2-2, DS CodePoint (DSCP) uses the first six bits (bits 0-5) s and reserve the last two bits (bits 6 and 7). The first three bits (bits 0-2) is the Class Selector CodePoint (CSCP), representing a category of DSCP. Issue 5.3 (30 March 2009) Nortel Networks Inc. 2-5

44 2 Principle of QoS for HIC Nortel Secure Router 8000 Series Figure 2-2 DS field and ToS field IPv4 ToS Precedence D T R C 0 CSCP DS Field unused DSCP Standard PHB DSCP selects the corresponding PHB in each network node. Per-hop Behavior (PHB) describes the visible behavior that a DS node acts upon data stream clustering. A network administrator can configure the mapping relation between DSCP and PHB. If a packet that DSCP cannot identify (e.g., the mapping not defined in PHB) is received, the node forwards it using the default PHB (that is, Best-Effort, DSCP=000000). Each DS node must support this default PHB. The IETF defines the following three standard PHBs: Expedited Forwarding (EF) Assured Forwarding (AF) Best-Effort (BE). (default PHB). 1. EF PHB EF is forwarding processing where any Diff-Serv node sends the information flow rate that is equal to or higher than the set rate. EF PHB cannot be remarked in the DS field. You are allowed remarking only at the edge node. You are required a new DSCP (different mappings of DSCP to PHB can be selected for different DS domains) to adapt to the features of EF PHB. Whenever you adopt the tunneling technology mark an external packet as EF. EF PHB simulates the forwarding effect of Virtual Leased Line in the DS domain and provides the forwarding service with low packet loss rate, low delay and high bandwidth. 2. AF PHB AF satisfies the following requirements: Traffic allowed to exceed the specifications ordered whenever bandwidth services are ordered with ISP. Ensuring forwarding quality for traffic that does not exceed the ordered specifications. Traffic exceeding specifications is forwarded at a lower QoS level instead of being discarded. The following four categories define AF: AF1, AF2, AF3 and AF4. Each category of AF service packets can further divide into three different dropping priorities. AF code point AFij means that AF category is i (1<= i <= 4) and drop precedence is j (1<= j<=3). When providing AF services, the carriers allocate different bandwidth resources to each category of AF. 3. BE PHB BE PHB is the traditional IP packet delivery service that focuses on the reach ability and has no other requirements. All the routers must support BE PHB. 2-6 Nortel Networks Inc. Issue 5.3 (30 March 2009)

45 2 Principle of QoS for HIC Recommended DSCP There may be user-defined mapping of DSCP to PHB in different DS domains. RFC recommends code points for BE, EF, AFij and Class Selector Code points (CSCP) as shown in Table 2-1. CSCP is designed to be compatible with the IPv4 precedence model. BE: DSCP= EF: DSCP= AFij code point Table 2-1 Code points of AF - Low drop precedence, j=1 Medium drop precedence, j=2 High drop precedence, j=3 AF(i=4) AF(i=3) AF(i=2) AF(i=1) If j=1, green color marks the packet i; if j=2, yellow color, and if j=3, red color. For packet color concepts, refer to the related descriptions in the section srtcm and trtcm algorithms. The packets of a same AF category have the same first three bits. The values are as follows: AF1=001, AF2=010, AF3=011 and AF4=100. The 3rd and 4th bits stand for discarding priority and they occupy three values, that is, 01, 10 and 11. The bigger a value is, the higher the discarding priority. CSCP When Diff-Serv standards are made, consider the backward compatibility with the priority domain in IPv4. DSCP=xxx000 is taken as Class Selector Code points. The higher the code point value is, the lower the PHB forwarding delay is. An IPv4 precedence corresponds to a CSCP. In the implementation of the Secure Router 8000, the corresponding relations by default are shown in Table 2-2. Table 2-2 The corresponding relations between the IPv4 precedence and the CSCP IPv4 precedence CSCP (binary) CSCP (decimal) Corresponding service BE AF1 green AF2 green AF3 green AF4 green EF Issue 5.3 (30 March 2009) Nortel Networks Inc. 2-7

46 2 Principle of QoS for HIC Nortel Secure Router 8000 Series IPv4 precedence CSCP (binary) CSCP (decimal) Corresponding service EF EF Other code points All DSCPs correspond to BE except for the preceding DSCPs Technologies used for implementing Diff-Serv model Basis of traffic conditioning Traffic classification Service Level Agreements (SLA) is a service agreement signed between customers and service providers. SLA includes many parts, for example, charging protocol, in which the technical description part is Service Level Specification (SLS). The SLS focuses on Traffic Conditioning Specification (TCS) that describes the detailed parameters of each service level. These parameters include: Detailed performance parameters such as expected bandwidth, discarding rate and delay. Topological logic range for services provided (ingress and egress points). Traffic profiles for services needed, for example, token bucket parameter. How to process the information flow which is out-of-profile. Marking services provided. Shaping services provided. The traffic parameters of TCS (such as average rate, peak rate, committed burst size, and maximum burst size) are the major basis of traffic control in the Diff-Serv network. Behavior Aggregate (BA) is the packet set with the same DSCP. Traffic classification of BA is indispensable whenever Diff-Serv provides bandwidth-guaranteed services for BA. Users can mark DSCP or the border router in the form of value-added service provision. The border router of Diff-Serv is responsible for such access control functions as traffic policing (which can be implemented for the traffic of a specific user), defense against attacks by theft and denial of service and traffic filtering. The border router is required to support complex traffic classification to identify more specific traffic. Traffic policing and traffic shaping In the Diff-Serv architecture, traffic conditioner implements the functions of traffic policing and shaping. A Traffic conditioner consists of four parts: meter, marker, shaper and dropper as shown in Figure 2-3. Meter measures traffic and judges whether the information flow conforms to the definition of traffic profile in TCS., The traffic conditioner then performs such actions as marker, shaper and dropper according to the traffic measurement results. Markerre-marks the DSCP of a packet and then sends the re-marked packet to a specific BA. It may: 2-8 Nortel Networks Inc. Issue 5.3 (30 March 2009)

47 2 Principle of QoS for HIC Degrade the out-of-profile information traffic as another different PHB according to SLS. Or ensure the availability of DSCP in a domain Shaper controls the traffic flow not to exceed the committed specification with a storage buffer that can buffer the received traffic. Dropper drops some packets during traffic policing to make the traffic comform to the traffic specifications. Setting the buffer of the Shaper to 0 or a small value can implement the dropper. Figure 2-3 Traffic classification and traffic control Meter Packets Classifier Marker Shaper/ Dropper Diff-Serv shifts a great number of traffic control operations to the border router of Diff-Serv network. PHB forwarding operations are performed effectively as the Secure Router 8000 only implements traffic control on BA. PHB forwarding operations conforms to the requirement of a core network for high-speed forwarding. Because the border router needs only to process limited low-speed user access, traffic control is implemented effectively on it. Traffic control can protect the network resource of ISP and provide value-added services. For example, it can be used for marking and traffic shaping. Subject to the Diff-Serv MIB requirement, Diff-Serv router must support traffic control on both the input interface and output interface. srtcm and trtcm algorithms A Single Rate Three Color Marker (srtcm) algorithm in RFC 2697 and a Two Rate Three Color Marker (trtcm) algorithm in RFC 2698 meters the traffic. The packets are marked green, yellow or red according to the metering result. In the case of AF service, the packet is re-marked with different drop precedence according to the metering result and the packet color. Both srtcm and trtcm algorithms use two token buckets to meter the arriving pacekts, and allow the traffic burst of certain levels, but focus on different points. The srtcm emphasizes on the packet burst size, while the trtcm on the burst rate. The srtcm and the trtcm can operate in one of two modes: Color-Blind mode and Color-Aware mode, of which the Color-Blind mode is very common. The following describes these two algorithms. 1. srtcm Algorithm The srtcm uses two token buckets to meter the traffic, which update the tokens at the Committed Information Rate (CIR) and whose sizes are Committed Burst Size (CBS) and Excess Burst Size (EBS). In this example, these two buckets are called bucket C and bucket E respectively. Tc and Te represent the token counts in the buckets, and if intiated, they are equal to CBS and EBS respectively. CBS is smaller than EBS. Both Tc and Te update with CIR times per second, and every update follows the rules below: Issue 5.3 (30 March 2009) Nortel Networks Inc. 2-9

48 2 Principle of QoS for HIC Nortel Secure Router 8000 Series Congestion avoidance If Tc < CBS, then Tc is incremented by 1, else If Te < EBS, then Te is incremented by 1, else Neither Tc nor Te is incremented. In the color-blind mode, the following rules meter the arriving packet (suppose size B): If Tc-B >= 0, the packet is marked green and Tc is decremented by B, else If Te-B >= 0, the packet is marked yellow and Te is decremented by B, else The packet is marked red, and neither Tc nor Te is decremented. In the blind-aware mode, the following rules meter the arrriving packet (suppose size B): If the packet is pre-colored green and Tc-B >= 0, the packet is marked green and the Tc is decremented by B, else If the packet is pre-colored green or yellow and Te-B >= 0, the packet is marked yellow and Te is decremented by B, else The packet is marked red, and neither Tc nor Te is decremented. 2. trtcm Algorithm The trtcm algorithm has two token update rates, Committed Information Rate (CIR) and Peak Information Rate (PIR). In this example, the two token buckets are bucket C and bucket P, whose sizes are CBS and PBS respectively. Tc and Tp represent the token count in the bucket, and if initinized, Tc and Tp are equal to CBS and PBS respectively. Tc is updated CIR times per second and Tp is updated PIR times per second. One token is incremented every update unless the bucket is full. In the color-blind mode, the following rules meter the arrriving packet (suppose size B): If Tp-B < 0, the packet is marked red, else If Tc-B < 0, the packet is marked yellow and Tp is decremented by B, else The packet is marked green, and both Tc and Tp are decremented by B. In the Blind-Aware mode, the following rules meter the arrriving packet (suppose size B): If the packet is pre-colored red or Tp-B < 0, the packet is marked red, else If the packet is pre-colored yellow or Tc-B < 0, the pacekt is marked yellow and Tp is decremented by B, else The packet is marked green, and both Tc and Tp are decremented by B. When congestion occurs or is intensified, the Diff-Serv adopts a specific queuing and packet discarding strategy for the tradeoff of resource allocation for traffics (EF, AF, etc.) of different service levels. For example, a possible implementation may be to discard all the packets marked with red color, forward with BE policy the packets marked with yellow color and forward those marked with green color with low discard-probability. Because Diff-Serv mainly provides guaranteed bandwidths for BA data stream, adopting the queuing mechanism defined in advance can control resource allocation. In addition, during intensified congestion, the packets with different priorities in AF service must be represented with different discarding probabilities. This is implemented through internal setting instead of user configurations. Diff-Serv is advantageous in terms of configuration and maintenance. The Secure Router 8000 drops the packets at the input interface according to the packet precedence and at the output interface according to the protocol type of the packet Nortel Networks Inc. Issue 5.3 (30 March 2009)

49 2 Principle of QoS for HIC Setting the drop threshold value and the maximum dropping probability according to Class of Service (CoS) of Packets RED applies congestion avoidance policies on packets with different CoSs (the first three bits of DSCP) based on the drop probability curve (as shown in Figure 2-4). When the average queue length exceeds the lower limit Minth, RED starts to discard packets at a certain probability. The longer average queue is, the larger drop probability is applied. When the average queue length exceeds the higher limit Maxth, or is between Maxth and the largest queue length (that is the buffer length), the packets are discarded at the maximum drop probability MaxP. If the average queue length exceeds the buffer length, all packets out of the buffer are discarded. Figure 2-4 Dropping probability curve of RED algorithm P 1 MaxP 0 Minth Maxth Q-Length Q When configuring the RED algorithm, you need to specify the CoS of packets and specify lower and higher limit of average queue and the maximum dropping probability. Setting the drop threshold value and maximum dropping probability of different protocol types For packets with different protocol types, implement a congestion avoidance strategy by using RED algorithm that is based on the drop probability curve (as shown in Figure 2-4). Specify the protocol type of packets and set the lower and higher limit of average queue and the maximum drop probability during RED algorithm configuration. For the adaptive traffic (for example, TCP traffic), the source can adjust the rate automatically in case of network congestion and packet timeout. The packet drop conditions can be decreased when configuring the parameters. For example, the drop probability can decrease under the same queue threshold. 2.3 MPLS QoS MPLS QoS is implemented by containing the DS of the IP packet within the MPLS label. The section contains: MPLS CoS MPLS VPN QoS QoS processing in MPLS domain Issue 5.3 (30 March 2009) Nortel Networks Inc. 2-11