QoS Technology White Paper

Transcription

1 QoS Technology White Paper Keywords: Traffic classification, congestion management, congestion avoidance, precedence, differentiated services Abstract: This document describes the QoS features and related technologies supported by the S9500E series routing switches. It covers traffic classification, congestion management, congestion avoidance, traffic policing, and traffic shaping, and briefly describes a typical QoS solution. Flexible implementations of the QoS features enable network carriers and industry users to provide differentiated services on any IP networks. Acronyms: Acronym Full spelling ACL AF BE CE DP DSCP EF EPCL HoL IDC In CAR IPCL LP MPLS Out CAR P PE PHB QoS SP Access Control List Assured Forwarding Best Effort Customer Edge Drop Precedence Differentiated Services Code Point Expedited Forwarding Egress Policy Control List Head of the line Blocking Internet Data Center In Committed Access Rate Ingress Policy Control List Local Precedence Multi-protocol Label Switching Out Committed Access Rate Provider Provider Edge Per-Hop Behavior Quality of Service Strict Priority Hangzhou H3C Technologies Co., Ltd. 1/19

2 Acronym Full spelling ToS TS VPN WRED WRR Type of Service Traffic Shaping Virtual Private Network Weighted Random Early Detection Weighted Round Robin Hangzhou H3C Technologies Co., Ltd. 2/19

3 Table of Contents Overview 4 Background 4 QoS Service Models 4 Introduction to DiffServ 4 Advantages and Disadvantages of DiffServ 5 Congestion: Causes, Impacts, and Countermeasures 5 Causes 5 Impacts 6 Countermeasures 6 Benefits of the QoS Implementation of the S9500E 6 S9500E QoS Technology Implementation 8 QoS Implementation Process 8 Traffic Classification 8 Overview 8 Traffic Classification Fields 8 QoS Policy Components 9 Priority Marking and Priority Mapping 9 Packet Precedence 9 Implementation of Priority Marking and Priority Mapping 11 Traffic Policing 12 Overview 12 Traffic Policing Models 12 How Packets Are Handled with Traffic Policing 14 Congestion Management 14 Queue Scheduling Overview 14 Queue Scheduling Modes 14 Congestion Avoidance 15 Traffic Shaping 16 Packet Buffer Sharing 16 Application Scenarios 17 References 19 Hangzhou H3C Technologies Co., Ltd. 3/19

4 Overview Background On traditional IP networks, each device treats all packets equally and handles them using the first in first out (FIFO) policy. It delivers packets to their destinations with best effort, without any guarantee for reliability or latency. The Internet has been growing fast along with networking technologies. More and more business applications have been emerging on the Internet with different service requirements. Real-time applications, Voice over IP (VoIP) and video services for example, require low transmission delay. Contrarily, and FTP applications are not sensitive to transmission delay. To provide different services for diversified users and applications, the network must conquer the drawback of best-effort service to classify and identify traffic flows. To this end, Quality of Service (QoS) technology was introduced. QoS Service Models The following are the three QoS service models most often discussed: Best-effort service model: The simplest service model providing no guarantee for latency, reliability, or any other performance indices. Integrated services (IntServ) model: A multiple services model that can accommodate various QoS requirements. In this model, an application must request a specific kind of service from the network before it can send data. The request is made by RSVP signaling. This model has only limited use at present. Differentiated services (DiffServ) model: A multiple services model that can satisfy diverse QoS requirements. This model is a widely used QoS solution for IP backbone networks. The QoS technology described in the following sections is based on DiffServ. Introduction to DiffServ Different from IntServ, DiffServ does not request resource reservation from devices before having an application send out packets. Instead of maintaining the status of each flow, the network provides specific services according to the DiffServ type of each packet. The DiffServ type of a service flow is represented by the Differentiated Services Code Point (DSCP) filed in the IP header. On a DiffServ network, each device performs Per-Hop Behaviors (PHB) specific to DSCP precedence values. The following shows the commonly defined PHBs: Expedited Forwarding (EF) PHB: The EF PHB is mainly used for preferential services sensitive to delay, jitter, or packet loss. This class of service typically runs at a relative constant rate and requires fast forwarding within the device. Assured Forwarding (AF) PHB: The AF PHB provides assured delivery service as long as the traffic does not exceed the maximum permitted bandwidth. Once the maximum permitted bandwidth is exceeded, the AF PHB is divided into four classes, each using three drop priorities and assigned appropriate bandwidth. The IETF defines four separate queues to transmit AF1x, AF2x, AF3x, and AF4x services. The combination of classes and drop priorities yields 12 AF PHBs. Hangzhou H3C Technologies Co., Ltd. 4/19

5 Best Effort (BE) PHB: The BE PHB is mainly used for services insensitive to delay, jitter, or packet loss. The following are two DiffServ implementations on MPLS networks: On an Ethernet network, the MPLS packet has a shim between Layer 2 (the data link layer) data and Layer 3 (the network layer) data. The unused EXP filed containing three bits in the shim is extended to indicate the queue scheduling and packet dropping priority. On an ATM or FR network, the MPLS packet has no shim. Instead, labels are used. Each FEC and QoS combination, rather than each FEC, is assigned a label. Based on the label carried in each received MPLS packet, an MPLS-capable device identifies which label to send with the packet in place of the incoming label and which service is to apply. Three MPLS DiffServ tunneling modes are described in RFC 3270, including Uniform, Pipe, and Short Pipe. Advantages and Disadvantages of DiffServ DiffServ is easy to implement with excellent scalability, because it comprises only a finite number of service levels, and thus the number of status information fields is small. However, DiffServ can hardly provide flow-based end-to-end quality guarantee. Although the IETF defines a DSCP value for each standard PHB, vendors may customize their DSCP-to-PHB mappings. This results in interoperability issues between DiffServ networks provided by different vendors. When multiple DiffServ networks are interconnected, the same DSCP-to-PHB mappings must be maintained for them. Congestion: Causes, Impacts, and Countermeasures Network congestion is a major factor contributed to service quality degrading on a traditional IP network. Congestion is a situation where extra delay is introduced because the forwarding rate decreases due to insufficient resources. Causes Congestion easily occurs in complex packet switching circumstances on the Internet. Figure 1 shows two common cases: Figure 1 Traffic congestion example scenario As shown in the figure, congestion is very likely to occur in either of the following two cases: The traffic enters a device from a high speed link and is forwarded over a low speed link. Hangzhou H3C Technologies Co., Ltd. 5/19

6 Packet flows arrive at a device through several incoming interfaces and are forwarded out one outgoing interface, whose rate is smaller than the total rate of the incoming interfaces. Impacts Congestion may bring these negative results: Increased delay and jitter during packet transmission Decreased network throughput and resource use efficiency Network resource (memory in particular) exhaustion and even system breakdown Packet loss It is obvious that congestion hinders resource assignment for traffic and thus degrades service performance. Congestion is unavoidable in switched networks and multi-user application environments. To improve the service performance of your network, you must address the congestion issues. Countermeasures A simple solution for congestion is to increase network bandwidth. It is in no way ultimate however, because you cannot increase network bandwidth infinitely. A more effective solution is to provide DiffServ for different applications through traffic control and resource allocation. In this way, resources can be used more properly. During resources allocation and traffic control, the direct or indirect factors that might cause network congestion should be controlled to reduce the probability of congestion. Once congestion occurs, resource allocation should be performed according to the characteristics and demands of applications to minimize the impacts of congestion. QoS evaluates the ability of a network to forward packets of different services. Generally, QoS performance is measured with respect to bandwidth, delay, jitter, and packet loss ratio during packet forwarding process. To meet the requirements, the S9500E series routing switches (hereinafter referred to as the S9500E) provide the following QoS features: Traffic classification Priority marking Traffic policing Congestion management Congestion avoidance Traffic shaping Queue buffer sharing Benefits of the QoS Implementation of the S9500E The QoS implementation of the S9500E delivers these benefits: Delivering powerful traffic classification capability. The S9500E provides powerful ACL functions. It supports ACL rules for up to 80 bytes of the first 128 bytes in packets. In addition, the S9500E can comprehensively identify and classify packets based on more fields than commonly used Layer 2 to Layer 4 fields of packets. Meanwhile, you can configure traffic classification rules of different effective scopes specific to actual implementations. Both ingress and egress ACLs are supported on the S9500E. Hangzhou H3C Technologies Co., Ltd. 6/19

7 Organizing traffic classification rules in policies. You can specify the occasions where a policy applies, such as globally, on a VLAN, or on an interface, as needed. Supporting dynamically modifying currently effective QoS policies and ACL policies. As the modification procedure does not affect traffic matching, there is no risk of temporary security black holes. Delivering comprehensive priority marking and support for priority mapping tables. Providing inbound/outbound traffic policing, and supporting the single-rate three-color algorithm and two-rate three-color algorithm with fine-grained rate values and burst sizes. The control granularity varies with value ranges. The control granularity refers to the minimum rate unit that can be controlled by the traffic policing function. The support for variable granularities makes traffic policing more practical. Supporting congestion management algorithms Strict Priority (SP) and Weighted Round Robin (WRR) queuing and providing congestion management profile configuration to facilitate congestion management and configuration. Supporting congestion avoidance algorithms such as Tail-Drop and Weighted Random Early Detection (WRED), and allowing you to query the congestion avoidance algorithm result (dropping or forwarding a packet) in real time. Hangzhou H3C Technologies Co., Ltd. 7/19

8 S9500E QoS Technology Implementation QoS Implementation Process Figure 2 QoS implementation flow chart Port-based QoS Trusting packet priority Trusting port priority Obtaining priority parameters according to priority mapping tables Flow-based QoS Traffic classification based on Layer 2 through Layer 4 information Traffic classification based on user defined fields Traffic policing Priority marking Dropping red packets Traffic accounting Port QoS RX IPCL In CAR TX O ut CAR EPCL Scheduler Traffic policing Priority marking Dropping red packets Traffic accounting Flow-based QoS Traffic classification based on Layer 2 through Layer 4 information Bandwidth scheduling management Bandwidth guarantee Traffic shaping on the outgoing interface Traffic shaping for output queues Traffic Classification Overview Traffic classification uses certain match criteria to identify packets with specific characteristics. It is the basis for providing differentiated services for network services. For different classes of traffic, you can configure different QoS parameters. You can simply define match criteria by using the packet precedence bits in the type of service (ToS) field of the IP packet header, or define a class for packets with fields in Layer 2 through Layer 4 packet headers (MAC address, IP address, and service port number for example). Traffic Classification Fields You can classify packets based on the fields in Layer 2 to Layer 4 packet headers, such as the source MAC address, destination MAC address, 802.1p priority, VLAN ID, Ethernet protocol type, VPNinstance, and EXP. Hangzhou H3C Technologies Co., Ltd. 8/19

9 In addition, you can specify fields other than those commonly used for traffic classification by specifying their offsets to the header of a particular layer. This allows for more comprehensive match criteria. QoS Policy Components A QoS policy involves three components: class, traffic behavior, and policy. Class Classes are sets of match criteria used to identify traffic. A class is identified by a class name. The relationship between the criteria in a class can be AND or OR. AND: The device considers a packet belongs to a class only when the packet matches all the criteria in the class. OR: The device considers a packet belongs to a class if the packet matches any of the criteria in the class. Traffic behavior A traffic behavior defines a set of QoS actions for packets. Policy A policy associates a class with a traffic behavior. You can configure multiple class-to-behavior associations in a policy. A QoS policy can take effect only after it is applied to an object, which can be the system in the global scope, a VLAN or an interface. Priority Marking and Priority Mapping For QoS purposes, packets are assigned priorities, which determine their forwarding priorities and treatment. Priority marking and priority mapping enables a device to set or change the priority of traffic to handle different network situations. Packet Precedence Packet precedence identifies the scheduling weight or forwarding priority of a packet. Different types of packets have different precedence types. 1) 802.1p priority 802.1p priority is in the Layer 2 Ethernet frame header and applicable to occasions where Layer 3 header analysis is not needed and QoS must be assured at Layer 2. Hangzhou H3C Technologies Co., Ltd. 9/19

10 Figure Q tagged Ethernet frame header As shown in Figure 3, the 4-byte 802.1Q tag header comprises the two-byte tag protocol identifier (TPID), whose value is 0x8100, and the two-byte tag control information (TCI). The first three bits of the TCI is the p priority. Figure 4 presents the format of the 802.1Q tag header. Figure Q tag header 2) IP precedence and DSCP value The combination of IP precedence and DSCP value represents the IP packet precedence. The ToS field of the IP header contains eight bits, of which the first three bits (0 to 2) represent IP precedence from 0 to 7. According to RFC 2474, the ToS field of the IP header is redefined as the differentiated services (DS) field, where a DSCP value is represented by the first six bits (0 to 5). Figure 5 IP precedence and DSCP value 3) EXP value The EXP value represents the precedence of MPLS packets. Hangzhou H3C Technologies Co., Ltd. 10/19

11 Figure 6 MPLS label structure In addition to packet precedence, the S9500E also uses local precedence (LP) and drop precedence (DP) for QoS purposes. These two types of precedence have only local significance. Local precedence determines in which output queue a packet is to be put for forwarding. Packets in a high priority queue are processed preferentially. A higher local precedence represents a higher priority queue. Drop precedence represents the drop probability of a packet. Packets with higher drop precedence are dropped preferentially. Local precedence and drop precedence are the basis of congestion management and congestion avoidance. Implementation of Priority Marking and Priority Mapping Priority marking is to set a particular precedence value for packets. The S9500E supports marking 802.1p priority, EXP value, DSCP value, local precedence, and drop precedence for inbound packets, and 802.1p priority, DSCP value, and EXP value for outbound packets. Upon receiving a packet flow on an interface, the device assigns packet precedence according to the priority trust mode of the interface. The priority trust mode can be: Untrust mode By default, the priority trust mode of an interface is untrust mode. In this mode, the device assigns QoS parameters for incoming packets on the interface based on the port priority rather than any precedence carried in the packets. The unstrust mode is suitable for edge ports. Trust DSCP mode In trust DSCP mode, the device searches the DSCP-to-priority mapping tables to obtain the set of QoS parameters (802.1p or EXP value, DSCP value, local precedence, and drop precedence) for each incoming packet based on the DSCP value in the packet. For a packet to be sent out the device, if it is to be VLAN tagged, the obtained 802.1p priority is used in the VLAN tag; if it is to be encapsulated with an MPLS label, the obtained EXP value is used in the label; if it is an IP packet and the trust DSCP mode is configured with the override keyword, the obtained DSCP is used in the IP header in place of the original DSCP value carried in the packet. For non-ip packets, the untrust mode applies if DSCP of packets is trusted. Trust 802.1p mode In trust 802.1p mode, the device searches the 802.1p-to-priority mapping tables to obtain the set of QoS parameters (802.1p or EXP value, DSCP value, local precedence, and drop precedence) for each incoming packet based on the 802.1p priority in the packet. For a packet to be sent out the device, if it is to be VLAN tagged and the trust 802.1p mode is configured with the override keyword, the obtained 802.1p priority is used in the VLAN tag in place of Hangzhou H3C Technologies Co., Ltd. 11/19

12 the original 802.1p priority; if it is to be encapsulated with an MPLS label, the obtained EXP value is used in the label; if it is an IP packet, the obtained DSCP value is used in the IP header. For non VLAN-tagged packets, the untrust mode applies if 802.1p priority of packets is trusted. Trust EXP mode In trust EXP mode, the device searches the EXP-to-priority mapping tables to obtain the set of QoS parameters (802.1p or EXP value, DSCP value, local precedence, and drop precedence) based on the EXP value of packets. For a packet to be sent out the device, if it is to be VLAN tagged, the obtained 802.1p priority is used in the VLAN tag; if it is to be encapsulated with an MPLS label, the obtained EXP value is used in the label. For non-mpls packets, the untrust mode applies if the MPLS EXP field of packets is trusted. Trust auto mode In trust auto mode, QoS parameter assignment is based on packet precedence. Unlike in other trust modes, the device can select the precedence to use depending on packet type in trust auto mode. For Layer 2 packets, 802.1p priority is used; for Layer 3 packets, IP precedence is used preferentially; for MPLS packets, EXP is used preferentially. Traffic Policing Overview One typical application of traffic policing is to supervise the specification of certain traffic entering a network and limit it within a reasonable range, or to "discipline" the extra traffic. In this way, the network resources and the interests of the carrier are protected. For example, you can limit bandwidth for HTTP packets to less than 50% of the total. If the traffic of a certain session exceeds the limit, traffic policing can drop the packets or reset the IP precedence of the packets. Traffic policing is widely used in policing traffic entering the networks of internet service providers (ISPs). It can classify the policed traffic and take pre-defined policing actions on each packet depending on the evaluation result: Forwarding the packet if the evaluation result is conforming. Dropping the packet if the evaluation result is excess. Forwarding the packet with its IP precedence re-marked if the evaluation result is conforming. Traffic Policing Models The S9500E supports two traffic policing models, single-rate three-color model and two-rate threecolor model. Hangzhou H3C Technologies Co., Ltd. 12/19

13 Figure 7 Single-rate three-color traffic policing process CIR Overflow CBS EBS Packets(B) B < Tc No B < Te No Yes Yes Conforming Excess Violating Mark priorities, Accounting Mark priorities, Accounting Mark priorities, Accounting Drop Figure 8 Two-rate three-color traffic policing process PIR CIR PBS CBS Packets(B) B > Tp No B > Tc No Yes Yes Violating Excess Conforming Mark priorities, Accounting Drop Mark priorities, Accounting Mark priorities, Accounting As shown in Figure 7 and Figure 8: In the single-rate model, the peak rate (CIR) is defined for only the conforming traffic. When the CBS bucket overflows, extra tokens are put into the EBS bucket. In the two-rate model, the peak rate (CIR and PIR) is set for the conforming traffic and the excess traffic respectively, thus adapting to different scenarios. Hangzhou H3C Technologies Co., Ltd. 13/19

14 Traffic policing supports ingress traffic policing and egress traffic policing independently. How Packets Are Handled with Traffic Policing With traffic policing, packets are marked green, yellow, or red. You can configure the device to remark IP precedence and perform traffic accounting for green and yellow packets, drop red packets or re-mark their IP precedence, and perform traffic accounting for red packets. Traffic accounting collects statistics in bytes or packets depending on your configuration. You can use the statistics to analyze traffic policing performance. Priority re-mark modifies the priority of a packet. You can perform the action to increase the precedence of green packets and decrease the precedence of yellow or red packets so that devices at the next level can process them correctly. For the purpose of priority re-mark, colored priority mapping tables are maintained. Congestion Management Congestion occurs on an interface where the arrival rate of packets is faster than the sending rate. Without congestion management, high priority packets may fail to be served prior to low priority packets because the first in first out (FIFO) mechanism is adopted. Queue Scheduling Overview The S9500E delivers congestion management based on the hardware queue scheduling mechanism. The process is as follows: 1) Each packet is assigned a local precedence during the QoS processing within the device. 2) The device puts the packets to the output queues specific to their local precedence values. 3) The outgoing interface selects a queue based on the scheduling mechanism and sends out the packets in the queue. Figure 9 shows the queue scheduling mechanism. Figure 9 Queue scheduling mechanism Control Video Voice Queue scheduler Data Mirror Queue Scheduling Modes Queue scheduling modes SP and SP+WRR are supported. By default, all ports use SP queuing. Hangzhou H3C Technologies Co., Ltd. 14/19

15 SP queuing schedules queues strictly according to the descending order of priority. It sends packets in the queue with the highest priority first. When the queue with the highest priority is empty, it sends packets in the queue with the second highest priority, and so on. WRR queuing schedules all queues in turn to ensure that every queue can be served for a certain time. Assume there are four output queues on a 1000 Mbps interface. WRR assigns each queue a weight value (40, 30, 20, and 10) to decide the proportion of resources assigned to the queue. In this way, the queue with the lowest priority is assured of 100 Mbps of bandwidth at least, thus avoiding the disadvantage of SP queuing that packets in low-priority queues may fail to be served for a long time. With SP+WRR queuing, you can assign some of the output queues to the SP scheduling group and the others to the WRR scheduling group. On a port, the queues in the SP scheduling group are scheduled preferentially; when no packet is to be sent in the queues in the SP scheduling group, the queues in the WRR scheduling group are scheduled. The queues in the SP scheduling group are scheduled according to the strict priority of each queue, while the queues in the WRR queue scheduling group are scheduled according the weight of each queue. To perform SP+WRR queuing on a port, you first create a scheduling policy, then specify the scheduling relationship for queues in the policy, and then apply the policy to the port. Congestion Avoidance One proactive approach to improving network performance is to avoid congestion before it occurs to deteriorate network performance. Congestion avoidance involves port-level flow control, switch fabriclevel flow control, tail drop, and WRED. Port-level flow control With port-level flow control, when the buffer of an incoming port is getting full due to congestion on an outgoing port for example, the incoming port sends out flow control frames to the peer device to inform it to stop sending packets. When the available buffer size of the incoming interface increases to a certain level after congestion on the outgoing interface is removed, the incoming interface informs the peer device to resume sending of packets. This feature prevents packets from being discarded on the device. Switch fabric-level flow control The S9500E uses the switch fabric structure. Before cross-card or cross-chip packets are sent to the switch fabric, they are cached in the virtual output queues (VoQs), where they wait for being scheduled and sent by the chip. To which VoQ a packet is assigned depends on its forwarding type, destination, and priority. When the switch fabric port is overloaded, link-level flow control Xoff messages are generated and sent to the chip. Upon receiving the Xoff messages, the chip stops scheduling or sending packets, and packets are buffered in the VoQs. When the switch fabric port can send these buffered packets, Xon messages are sent to the chip scheduler. Upon receiving the Xon messages, the scheduler takes packets out of the VoQs, encapsulates them in cells, and transmits the cells in the switch fabric. Before the scheduler delivers packets to the switch fabric, it first takes the packets out of the VoQs, breaks the packets into fragments and encapsulates the fragments in cells. When the switch fabric is congested, some fragments of a packet may be lost. As the switch fabric does not have the retransmission mechanism, the peer chip cannot re-assemble the packet and the received cells are Hangzhou H3C Technologies Co., Ltd. 15/19

16 rendered useless. This causes waste of switch fabric bandwidth. The problem is known as head of line (HOL) blocking. On the S9500E, the HOL blocking issue is addressed by using VoQs in conjunction with link-level flow control. Tail drop Tail drop is a traditional packet drop policy. With tail drop, when the length of a queue reaches the maximum threshold, all the newly arriving packets are dropped. Such a policy results in global TCP synchronization. That is, if packets from multiple TCP connections are dropped, these TCP connections concurrently go into the state of congestion avoidance and slow start to reduce traffic, but traffic peak occurs later. Consequently, network traffic jitters all the time. WRED WRED is used to avoid global TCP synchronization. WRED avoids global TCP synchronization by randomly dropping packets. Thus, when the sending rates of some TCP sessions slow down after their packets are dropped, other TCP sessions remain at high sending rates. As there are always TCP sessions at high sending rates, link bandwidth is efficiently utilized. Traffic Shaping Traffic shaping is typically used to restrict outgoing traffic and burst traffic of a specific connection from a certain network. Thus, packets are sent out at an even rate. Traffic shaping is usually implemented with buffers and token buckets. Packets are first buffered in a buffer and then scheduled by the token bucket to leave at an even rate. The S9500E supports interface-based traffic shaping and queue-based traffic shaping. The difference between traffic policing and traffic shaping is that packets to be dropped with traffic policing are retained in a buffer or queue with traffic shaping. When there are enough tokens in the token bucket, the buffered packets are sent at an even rate. Traffic shaping may result in additional delay while traffic policing does not. Packet Buffer Sharing The S9500E uses the switch fabric architecture for forwarding, and schedules packets on two layers. Congestion may occur on each layer. When congestion occurs, packets are buffered. To improve resource use efficiency, the S9500E provides a resource sharing technology. Hangzhou H3C Technologies Co., Ltd. 16/19

17 Figure 10 Schematic diagram for resource sharing Switch fabric Shared pool Dedicated queues Dedicated queues Shared pool Ingress packet processor Egress packet processor As shown in Figure 10, there is a queue resource manager for the switch fabric port on the ingress packet processor and a queue resource manager for the egress port on the egress packet processor. In a switching fabric forwarding architecture without resource sharing technology, the queue resources of each switch fabric port or egress port are dedicated and cannot be borrowed. This may create the situations where a congested port cannot get buffer or queue resources while the buffer or queue resources on the other ports are idle. To improve resource use efficiency, the S9500E introduced the resource sharing pool to allow a percentage (configurable as required) of the resources to be shared. A port can use not only its dedicated resources but also the resources in the shared pool. Application Scenarios The S9500E is applicable to enterprise networks, MANs, and data centers. This section describes a QoS configuration example for enterprise network applications. Categories of the network applications on an enterprise network Generally, enterprise network applications are categorized into the following services: Voice services: Voice traffic is delay-sensitive and needs to be prioritized during transmission. Voice traffic has strict requirements for network performance, including packet loss less than 1%, delay within 200 ms, and small bandwidth jitter for each call. Video is categorized into this service category. Real-time services: Real-time services are strict applications that are the core businesses of an enterprise. They feature strong interactivity and are sensitive to packet loss and delay. ERP applications and asset applications are two examples of real-time services. Hangzhou H3C Technologies Co., Ltd. 17/19

18 Batch services: Batch services are accessed by a small number of users. They are not sensitive to packet loss or delay, and usually operate for several hours every time. Massive file transfer and backup belongs to batch services. Best-effort services: The default data traffic type is called best effort. Best effort services have no definite bandwidth requirements and often play the supporting roles in the enterprise operation. and common Internet accesses are examples of best effort services. Undefined QoS services: New applications can be classified as undefined QoS services. The preceding types of service are provided by application providers. Actually, various control protocols such as the spanning tree protocols and routing protocols also exist to maintain network interconnectivity. Network control protocols are the basis of network interconnection. Figure 11 A typical enterprise network Access types Internal accesses on the enterprise network Internal accesses on the enterprise network include the personnel access to various servers (such as the DNS server, server, file server, and ERP server), servers access to the storage devices, and share access between terminal users. External accesses on the enterprise network External accesses on an enterprise network include inter-vpn video conferencing, video on demand (VoD), VoIP, and Internet access. All traffic of internal accesses and external accesses is sent to the distribution-layer and core-layer switches. The QoS control methods of the S9500E can play an important role in congestion Hangzhou H3C Technologies Co., Ltd. 18/19

19 management, congestion avoidance, providing the maximum buffer, and improving bandwidth use efficiency to the maximum extent. Recommended configurations Configure an MQC policy on the S9500E to classify traffic by packet type into various classes and perform traffic policing and priority marking for each class of packets. Traffic policing is used to control the maximum access bandwidth. Priority marking is used to set different priority values for different types of packets, so that they are processed differently when they are forwarded in the device and scheduled on the egress interface. Prioritize packets of VoIP, VoD, internal access, Internet access, and other accesses in the descending order. References RFC 1349, Type of Service in the Internet Protocol Suite RFC 1633, Integrated Services in the Internet Architecture: an Overview RFC 2211, Specification of the Controlled-Load Network Element Service RFC 2212, Specification of Guaranteed Quality of Service RFC 2215, General Characterization Parameters for Integrated Service Network Elements RFC 2474, Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers RFC 2475, An Architecture for Differentiated Services RFC 2597, Assured Forwarding PHB Group RFC 2598, An Expedited Forwarding PHB (Per-Hop Behavior) RFC 2697, A single rate three color marker RFC 2698, A two rate three color marker RFC 3270, Multi-Protocol Label Switching (MPLS) Support of Differentiated Services IEEE 802.1Q-REV/D5.0 Annex G Copyright 2009 Hangzhou H3C Technologies Co., Ltd. All rights reserved. No part of this manual may be reproduced or transmitted in any form or by any means without prior written consent of Hangzhou H3C Technologies Co., Ltd. The information in this document is subject to change without notice. Hangzhou H3C Technologies Co., Ltd. 19/19