Chapter 9 - Current QoS Functionality Available in Network Equipment
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In this section, we discuss the current state of implementation of QoS functionality in different types of network equipment.
As described, Windows hosts provide a broad range of QoS functionality, including signaling, policy, marking and traffic shaping. Host functionality integrates marking and shaping behavior with signaling and policy and presents a unified mechanism-independent API to applications. In addition, traffic control is directly accessible to network management applications. In general, RSVP signaling is available on Windows 2000 and Windows 98. Traffic control (including marking and scheduling) is available only on Windows 2000.
Various Unix and Linux implementations provide a range of QoS functionality including RSVP signaling, diffserv marking and sophisticated scheduling algorithms. However, these are generally not abstracted into a unified API and are not integrated with network policy in a manner that can provide a full range of quality of guarantees.
All major router vendors support per-conversation RSVP signaling in varying degrees on some subset of their products1. In general, RSVP admission control may be configured separately from the traffic handling mechanisms on these routers. This enables network administrators to mix and match per-conversation admission control with either aggregate or per-conversation traffic handling. SBM client functionality is available from several router vendors.
Router vendors are in the process of implementing functionality to translate intserv requests to diffserv service levels. A major router vendor is demonstrating DCLASS functionality based on network policies.
Those routers providing RSVP support also provide the corresponding per-conversation traffic handling mechanisms. In addition, most router vendors provide a simple form of diffserv today, by their ability to group traffic for different treatment based on values in the IP precedence field or TOS field of packet headers.
Most router vendors provide SNMP monitoring (and in certain cases configuration) of QoS functionality. Several vendors provide CLI or CLI-like interfaces to this functionality. A small number of router vendors provide COPS interfaces to corresponding policy servers, which may be used to apply both signaled and provisioned QoS. Provisioned QoS interfaces are more common today than signaled QoS interfaces, however increasing numbers of routers are adding support for management of signaled QoS via COPS.
Signaling and SBM Functionality
Several switch vendors support varying degrees of SBM functionality and are able to act as DSBMs on shared subnets. Some switches return a TCLASS object in response to host signaling.
High-end and midrange switches support 802.1p today. This is a relatively new standard and so legacy switches generally will not support 802.1p. It is unlikely that low-end LAN devices, (such as the dumb hubs common in many offices) will support 802.1p. Many newer routers will mark 802.1p headers in packets they submit to a LAN. Windows 2000 hosts will do so if the network card driver is 802.1p capable and enabled for 802.1p marking. Note that the IEEE has yet to standardize a mechanism for automatically negotiating 802.1p functionality. As a consequence, it is possible to incorrectly configure senders and receivers so that they are unable to communicate. It is generally recommended that network administrators deploy 802.1p on a subnet wide basis.
QoS policy today focuses on top-down provisioned QoS. Network administrators may use existing policy servers to configure QoS parameters in network devices to prioritize aggregated traffic based on addresses or ports. For example, traffic from the engineering department may be given priority over traffic from the marketing department, based on different source IP subnet addresses. This type of policy is very broad, or coarse-grain, as opposed to, for example, per-application or per-user policy. Such policy is usually configured independently in each network device with little effort to integrate policies across devices.
High-end policy management vendors are developing more integrated policy-based management, using a central data-store to push consistent configuration information to multiple devices. In addition, RSVP-capable routers are being extended to recognize RSVP policy elements and to communicate directly with directory based policy data, using LDAP, or indirectly, via COPS and emerging policy servers.
Standard policy schemas for policy data are currently under definition in the IETF. These address both configured and signaled QoS. While the majority of commercially available policy management systems today provide schemas for provisioned QoS, Microsoft's Active Directory and ACS provide a schema for signaled QoS.
|1||At least one major router vendor is also in the process of implementing aggregate RSVP signaling.|