QoS

One of the most recent advances in networking is a result of work by vendors and independent software vendors (ISVs) for implementing techniques to improve the QoS on networks. These techniques are designed to improve the service quality of applications, especially when users are accessing the applications, which typically reside in a data center, across a WAN, or through a VPN connection across the Internet. QoS is implemented differently depending on the vendor and the device type you are configuring for QoS. For example, Cisco Systems implements QoS in release 12.0 of its IOS operating system for switches, routers, and remote access servers. Microsoft implements QoS in Windows 2000. Together, businesses can take advantage of QoS at almost every access point within a network.

Benefits of QoS

QoS is quickly becoming an important component of large, distributed networks. As voice and data networks converge, QoS becomes increasingly important because a Network Administrator will need to set higher priority for voice over IP (VoIP) traffic than traditional IP data traffic. For businesses to leverage their existing data network investments for voice and videoconferencing, the QoS must be near 100 percent, as is the case with today's traditional voice networks.

QoS enables businesses to maximize their network investments. QoS allows Network Administrators to set service levels for applications, users, groups and computers by establishing rules of priority on systems and network devices. QoS techniques control allocation of network bandwidth to applications so that higher-priority, or delay-sensitive applications, such as an Enterprise Resource Planning (ERP) or videoconferencing application, can achieve the service level that they require to run efficiently.

Realizing the full benefits of QoS requires an end-to-end approach. In other words, to fully implement QoS, a Network Administrator should implement QoS parameters from one end (the host computer) of the network to the other end of the network (the client machine residing in a branch office over a 128K frame relay link) and all points in between.

Consider the following example: A Windows 2000 Server runs SQL Server 7.0 and a packaged sales force automation application. It resides on a Compaq ProLiant server that is located in a corporate data center in Dallas, Texas. The company's distributed sales force must review, approve, and submit all orders by the 28th of each month. On the 28th of each month, the entire sales force dials-in to the corporate network using their laptops that run Windows 2000 Professional with an IPSec client for VPN connectivity through a local ISP. Because the sales force is distributed and uses the corporate VPN heavily during this time, a Network Administrator might want to implement QoS so that the orders are submitted on time, without having to contend with other corporate traffic, such as HTTP for Web browsing.

In this example, the goal was to guarantee a service level, implementing QoS for the application and for the network ensures that the orders are received before month-end closing. To implement QoS, the server running the application and the network devices connecting the server to the client need to detect the application traffic type and/or IP addresses of the server and clients and then direct the application traffic to a set of queues. These queues would then have an associated priority level that defines the rate at which the application data is submitted to the network and the rate at which the application traffic travels through the network. The Windows 2000 SQL Server would define a higher priority to the queue that stores the sales force automation application traffic, and the network devices connecting the server to the clients (for example, switch in the data center and the VPN router) would be configured with QoS priority so that the sales force automation application traffic is serviced with higher priority than other traffic types.

Windows 2000 QoS

QoS is implemented in Windows 2000 in several ways. For traffic prioritization, QoS is implemented using 802.1p, DIFFSERV, INTSERV, and others. This chapter focuses on 802.1p, DIFFSERV, and INTSERV. Because most LANs are based on IEEE 802 technologies, such as Ethernet, Token-ring, and FDDI, 802.1p is an important technique for implementing QoS. 802.1p is a technique that leverages part of the layer-2 (Media Access Control address) header of an 802 packet. This header field can be assigned eight levels of priority, which are then leveraged by switches, routers, and network adapters to assign service levels based on queuing priorities. DIFFSERV, on the other hand, is a layer-3 implementation of QoS that defines a priority level in the header of an IP packet called the DIFFSERV codepoint (DSCP). Routers can be configured for DIFFSERV QoS so that a consistent service level can be established from one point in the network to another. DIFFSERV is not as widely adopted as 802.1p, however, DIFFSERV is gaining momentum because it can sustain service levels for low-latency applications, such as videoconferencing. INTSERV is a QoS technique that defines a guarantee of service or a controlled load.

For example, configuring a series of routers in a WAN with INTSERV can produce a guaranteed level of performance in terms of latency. QoS can be set so that latency does not exceed 20ms, or a controlled load in terms of volume, which could mean all conversations between a client and server will comprise no less than 256Kbps throughput. Unlike 802.1p and DIFFSERV, INTSERV does not rely on an underlying queuing priority; it defines a service level control to an INTSERV class on each device. In other words, a router that supports INTSERV QoS service classes.

Implementing QoS on networks is typically accomplished using a set of protocols, policies, and management tools. QoS can be implemented using Resource Reservation Protocol (RSVP ) and Subnet Bandwidth Manager (SBM ) protocol. Each protocol provisions network resources are based on the QoS techniques (802.1p, DIFFSERV, and INTSERV) and the priorities defined by each technique. Windows 2000 implements QoS by leveraging Active Directory and group polices. In this way, a Network Administrator can use a customizable and familiar interface (such as MMC) and set QoS on any number of computers, users, and groups. In addition, Microsoft and Cisco have worked together to create Cisco Network Services for Active Directory (CNS/AD) . CNS/AD will extend a Network Administrator's ability to assign policy to include Cisco network devices using Active Directory and group policies. CNS/AD eliminates the problem of having to have two different QoS technologies from two different vendors working together. Consequently, QoS is much easier to put in place.

One consideration when designing a QoS infrastructure for your environment is that not all computers, network interface cards, and routers will support the Network Driver Interface Specification (NDIS) version needed to implement QoS. NDIS version 5 is required to implement QoS on Windows 2000. This might require an upgrade to the network interface cards or other hardware in your network environment.

To implement QoS on Windows 2000, you must install the QoS admission control service through Windows 2000 setup. After it is installed, a MMC snap-in is created that allows a Network Administrator to assign QoS on an enterprise-wide basis or by subnetwork settings. Enterprise settings take the form of QoS settings to any authenticated user, or unauthenticated users. For example, you can apply a controlled load or a guaranteed service level to any authenticated user based on packets sent and received with certain flow limits on a single conversation or aggregated for all conversations. Settings include data rates in Kbits/sec, peak data rates in Kbits/sec, or duration in minutes. The default policy setting for data rate is 500Kbits/sec and full media speed (100Mbps) for peak data rates.

To implement QoS on a subnet, simply add the subnetwork's IP address and mask to the QoS admission control MMC snap-in, and then assign configuration to each subnet. Like with enterprise settings, it is possible assign traffic settings based on data rate, peak data rates, aggregate data rates and peak aggregate data rates. However, with subnetwork QoS settings, these settings are assigned to servers instead of users. It is possible to set logging for RSVP signaling and specify the log file location, number of log files, and log file size. In addition, you can initiate accounting and define additional advanced settings for election priorities on servers. QoS admission control for Windows 2000 can be installed for a domain tree or a number of domain trees in an Active Directory forest.

Figure 14.2 illustrates how you can implement QoS for 802.1p and INTSERV QoS techniques using RSVP signaling to control the amount of network resources allocated (and guaranteed) to the server and the sales users. Keep in mind that this example depicts using a third-party router and switch that also supports these QoS techniques so that end-to-end QoS can be realized. Also note that this example assumes QoS can be implemented at the ISP; an important point if you plan to implement QoS over a VPN, especially for videoconferencing and other low-latency applications.

QoS is becoming increasingly important. Application service providers, for example, must be able to establish a guaranteed service level to their customers, which often comes at a high price because of the overhead involved in implementing QoS. Because QoS is a technique that assigns priority and policy to a network, a QoS-enabled network will require more planning and more overhead to achieve the service goals defined by the business and implemented by the Network Administrators. Generally speaking, the more a Network Administrator is willing to accept overhead in their network, the greater the ability to implement QoS. This translates to planning. If you require QoS on your network, expect that you will have to assess your network environment's capability and capacity to set and maintain the service level defined by your application and business environment.

With Windows 2000 support for QoS, enterprises and service providers can now implement QoS techniques on Windows 2000 platforms and establish service level guarantees for users and applications. Look for more QoS techniques to be implemented in Windows 2000. Because Active Directory can be easily leveraged to apply QoS policy throughout an enterprise, you can expect network vendors and ISVs to include Active Directory schema modifications and MMC snap-ins to support their network devices and network-aware applications.

One of the most important aspects of QoS in Windows 2000 is that the service is integrated into Active Directory. This integration means that Windows 2000 provides an application-aware network infrastructure. Through the QoS Application Programming Interface (API), vendors can update existing applications and develop future applications to communicate with network components to request the bandwidth needed for the applications to function properly. For example, telephony and video applications can utilize Active Directory-based policies to request more bandwidth for users in a specific OU when they access a videoconferencing application.