Medianet Reference Guide - Cisco

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Cisco QoS Toolset Chapter 4 Medianet QoS Design Considerations Admission Control Tools Interactive applications—particularly voice and video applications—often require realtime services from the network. As these resources are finite, they must be managed efficiently and effectively. If the number of flows contending for such priority resources were not limited, then as these resources become oversubscribed, the quality of all realtime flows would degrade—eventually to the point of unusability. Note Admission Control (AC) is sometimes also referred to as Call Admission Control (CAC); however, as applications evolve, not all applications requiring priority services are call-oriented, and as such AC is a more encompassing designation. Admission control functionality is most effectively controlled an application-level, such as is the case with Cisco Unified CallManager, which controls VoIP and IP video and/or TelePresence flows. As such, admission control design is not discussed in detail in this document, but will be deferred to application-specific design guides, such as the Cisco Unified Communications design guides and/or the Cisco TelePresence design guides at www.cisco.com/go/designzone. As discussed previously, media applications are taxing networks as never before. To that end, current admission control tools are not sufficient to make the complex decisions that many collaborative media applications require. Thus, admission control continues to be an field for extended research and development in the coming years, with the goal of developing multi-level admission control solutions, as described below: • The first level of admission control is simply to enable mechanisms to protect voice-from-voice and/or video-from-video on a first-come, first-serve basis. This functionality provides a foundation on which higher-level policy-based decisions can be built. • The second level of admission control factors in dynamic network topology and bandwidth information into a real-time decision of whether or not a media stream should be admitted. These decisions could be made by leveraging intelligent network protocols, such as Resource Reservation Protocol (RSVP). • The third level of admission control introduces the ability to preempt existing flows in favor of “higher-priority” flows. • The fourth level of admission control contains policy elements and weights to determine what exactly constitutes a “higher-priority” flow, as defined by the administrative preferences of an organization. Such policy information elements may include—but are not limited to—the following: – Scheduled versus ad hoc—Media flows that have been scheduled in advance would likely be granted priority over flows that have been attempted ad hoc. – Users and groups—Certain users or user groups may be granted priority for media flows. – Number of participants—Multipoint media calls with larger number of participants may be granted priority over calls with fewer participants. – External versus internal participants—Media sessions involving external participants, such as customers, may be granted priority over sessions comprised solely of internal participants. – Business critical factor—Additional subjective elements may be associated with media streams, such as a business critical factor. For instance, a live company meeting would likely be given a higher business critical factor than a live training session. Similarly, a media call to close a sale or to retain a customer may be granted priority over regular, ongoing calls. 4-28 Medianet Reference Guide OL-22201-01
Chapter 4 Medianet QoS Design Considerations Enterprise Medianet Strategic QoS Recommendations Note It should be emphasized this is not an exhaustive list of policy information elements that could be used for admission control, but rather is merely a sample list of possible policy information elements. Additionally, each of these policy information elements could be assigned administratively-defined weights to yield an overall composite metric to calculate and represent the final admit/deny admission control decision for the stream. • The fifth level of admission control provides graceful conflict resolution, such that—should preemption of a media flow be required—existing flow users are given a brief message indicating that their flow is about to be preempted (preferably including a brief reason as to why) and a few seconds to make alternate arrangements (as necessary). A five-level admission control model, deployed over a DiffServ-enabled infrastructure is illustrated in Figure 4-23. Figure 4-23 Five-Level Admission Control Model Deployed Over a DiffServ Infrastructure Business and User Expectations Business Graceful Conflict Resolution Policy Information Elements Policy Intelligence Network Intelligence Admission Control DiffServ Infrastructure Technical 225081 Thus, having laid a foundational context by reviewing QoS technologies, let us turn our attention to Cisco’s strategic QoS recommendations for enterprise medianets. Enterprise Medianet Strategic QoS Recommendations As media applications increase on the IP network, QoS will play a progressively vital role to ensure the required service level guarantees to each set of media applications, all without causing interference to each other. Therefore, the QoS strategies must be consistent at each PIN, including the campus, data center, branch WAN/MAN/VPN, and branch. Also, integration will play a key role in two ways. First, media streams and endpoints will be increasingly leveraged by multiple applications. For example, desktop video endpoints may be leveraged for desktop video conferencing, Web conferencing, and for viewing stored streaming video for training and executive communications. OL-22201-01 Medianet Reference Guide 4-29
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Medianet Reference Guide - Cisco

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