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2014 Edition, August 2014

Complete Document

Requirements for the Mission Critical Priority and QoS Control Service

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Description / Abstract:

Scope (Informative)

Priority and QoS refers to the access and control of system resources; especially with respect to a wireless broadband network. While the lion's share of attention is paid in this specification to wireless broadband network resources, this specification is not limited thereto. Transport network, backhaul, and interconnected systems are all considered.

The public safety broadband network is a challenging environment. Various types of users (e.g., first responders, second responders, etc.) with various disciplines (police, fire, EMS , etc.) and all types of applications (voice, video, data) all share the same resources. This creates an unprecedented environment for the management of resources for a public safety system. Conventional LMR systems have dedicated resources for Push-to-Talk, and there is traditionally only limited sharing of a system between disciplines. Trunked LMR systems improve sharing between disciplines, but still don't have to share resources like LTE all-IP users.

Priority, as used herein, refers to the ability for a given user to access and obtain resources from the broadband network. Once a user has been granted resources by the system, quality of service (QoS) refers to the specific attributes (e.g., latency, packet loss rate) that govern the experience of content exchange with the user. Users of the public safety broadband network need a consistent and deterministic service for real-time management of priority and QoS.

Commercial cellular network operators typically offer elevated priority to premium customers on a statically assigned basis (i.e., the customer's priority only changes with changes in their subscription level). While this is sufficient for commercial use, public safety users require priority services that are situational. The sheriff at a traffic stop does not require the same priority on the broadband network as a patrolman exchanging gunfire at a bank robbery. Preemption of lower-priority resources is essential in order to provide resources to the highest priority incidents.

Mission critical communications require immediate access to resources. Many factors can impact the resources available to a given traffic flow: number of users, number of incidents, distance to cell antenna, interference, etc. Further, many factors can contribute to wireless congestion at a cell. For this reason, Priority and QoS capabilities for public safety need to consider the dynamic situational aspects of responders. It is insufficient to statically assign a priority to a given responder that will be sufficient for all situations.

Another important aspect of priority and QoS is that it is based on the user and not a given device. In the commercial cellular world, users obtain a personal device and that device and its telephone number are assumed to be associated with a user. In the public safety world, devices are re-used across shifts (e.g., tablets, radios, fire trucks, etc.). It is not realistic to assume that all public safety broadband devices are personally issued. For example, an incident commander can pick up a shared laptop belonging to her agency and sign-in, or can be assigned to a vehicle having a fixed-mount laptop in the vehicle. Therefore, public safety priority and QoS needs to be derived for a user also taking into account the application(s) that he/she is currently invoking, and applied to the devices currently being used by the user. The type of user is one of many factors affecting a Subscriber's overall priority and QoS state. See sections 3.1.3 and 3.1.4 for more information.

Responders are trained today with procedures that have taken decades to perfect. Any service provided to responders has to complement their existing workflow. This service attempts to avoid distracting a user from the mission by requiring him/her to enter a broadband maintenance terminal or to become aware of the broadband network's detailed prioritization parameters. In this specification, prioritization is integrated into usage patterns familiar to the user (e.g., the emergency button).

Applications can be deployed by various domains utilizing the network. For example, telephony might be deployed nationally and push-to-talk might be deployed regionally by a state (e.g., in a separate APN). The priority and QoS capabilities described herein are intended to consistently govern resources for all applications, regardless of the entity (national, regional, local) that is operating the application. This specification defines a Priority and QoS Control Service (PQCS) to address these complex and varied needs. The PQCS:

• Allows Subscribers, other users, and other services to control and coordinate dynamic priority changes;

• Translates a coherent model of PS state (responder emergency, etc.) to service effecting controls in a Subscriber's transport network;

• Is consistent with the principles expressed by the NPSTC Local Control Task Group [4] the Priority and QoS Task Group [3] and the Broadband Data Protocol Standards Overview [5]; and,

• Supports "all IP" broadband networks (e.g., LTE). The PQCS does not support circuit-switched networks.

Scope (Normative)

This document pertains to the control of Priority and Quality of Service (QoS) for communications on a wireless broadband network using Internet Protocols (IP). This document describes requirements for a mission critical Priority and QoS Control Service for a wireless broadband network. The network and its resources are assumed to be shared by different classes of users, and different types of applications. Prioritization is the ability to determine which resource requests should be granted and which granted resources should be discontinued or preempted. This document includes requirements to determine a user's default priority on the broadband network, and also provides requirements for dynamic prioritization changes to meet situational needs. Quality of Service is the ability to ensure that IP packet flows associated with different applications satisfy performance objectives needed for the applications to operate. The requirements contained herein allow an operator to define consistent and deterministic policies to moderate usage of the shared wireless broadband network. Requirements are further provided for end-users and applications to dynamically influence policy selection.