Next Generation Network Priority Service (NGN-PS)

Next Generation Network Priority Service (NGN-PS) allows National Security/Emergency Preparedness (NS/EP) users to make priority calls/sessions using public networks. When you enable the NGN-PS feature on a DSR Node, ingress messages received from Diameter Peer Nodes are examined to determine if they qualify for priority treatment based upon a set of rules. These rules, established by Standards Development Organizations, have various groups working on what is broadly called Emergency Telecommunications Services (ETS).

ETS is intended to be used by qualified and authorized users, for example, emergency service personnel, only during times of emergency situations and network congestion. ETS access:

Is limited to key personnel and those with leadership
Is provided end-to-end priority treatment beyond that offered to the general public
Can include priority call/session set-up, access to additional resources (alternate routing), and exemption from restrictive network traffic management controls.

Note:

If NGN-PS is disabled after being enabled, then DSR does not disable NGN-PS, but an alarm alerts the user that the runtime state and administrative state for NGN-PS are not in synch.

NGN-PS support is comprised of two major functions:

Identifying messages which require NGN-PS, which is based on subscription information stored in databases that is downloaded to entities that perform priority marking of transactions by way of AVPs.
- The following messages are candidates for NGN-PS treatment:
  - Cx/Dx LIR & LIA
  - Cx/Dx SAR & SAA
  - Dh/Sh UDR & UDA
  - Gx CCR-I & CCA-I
  - Gx RAR & RAA
  - Rx AAR & AAA
If a message qualifies for priority treatment, it is considered inviolable. An inviolable message cannot be blocked, rejected, or discarded by any ingress or egress control functions due to internal resource congestion or exhaustion.

Note:

NGN-PS messages must receive priority treatment both at the Diameter Application signaling layer and IP-layer.

The priority level for violable messages is defined as a number between zero and three, where zero has the lowest and three has the highest violable message priority. NGN-PS messages have a priority level of four.

Note:

After a message becomes inviolable, its priority cannot be modified during the lifetime of that message within a DSR node. After an ingress Request message is marked as inviolable, all messages associated with that transaction are also marked as inviolable. Similarly, Answer messages associated with inviolable transactions are made inviolable.

You can enable any of the following diameter interfaces for NGN-PS support:

Gx, Rx, Cx/Dx and Dh/Sh

NGN-PS messages are identified by the contents of a particular AVP for well-known set of order pairs. Most non-Gx NGN-PS messages can be identified by the presence of an AVP; Gx NGN-PS message identification requires more complex rules based upon AVP content and user-provided configuration data.

Identifying Messages for Priority Treatment

Congestion control procedures use message priorities and congestion levels to determine which messages to shed/divert when congestion exists. Lowest priority messages are assigned a priority of 0, and the highest priority messages are assigned a value of 3. Because inviolable messages must be provided a higher treatment versus violable message, the existing four priority values of 0 through 3 are reserved for violable messages, and message priority of 4 is reserved for inviolable messages.

A message is considered inviolable if:

The message priority is greater or equal to the Minimum Inviolable Priority value. See Diameter System Options elements. NGN-PS messages received from Diameter Peer Nodes are identified and tagged as inviolable before DSR ingress congestion controls are applied.
Answer priority is equal to the Maximum of Request Priority and Minimum Answer Priority value. See Diameter System Options elements.

Identifying NGN-PS Messages

NGN-PS specifications identify a well-defined and limited number of messages that are candidates for priority treatment. Inviolable messages are exempt from discard and bypass all ingress and egress throttling controls. These messages typically represent a small portion of message traffic, and you can configure this function to avoid abuse. For information about limiting the percentage of the maximum engineered DA-MP ingress message rate, see Diameter System Options elements NGN-PS Maximum Message Rate Percent.

When NGN-PS is disabled, a DSR Node does not search for ingress NGN-PS messages. When NGN-PS is enabled, the DSR Node measures the ingress rate of NGN-PS which are marked as inviolable and, if the NGN-PS Maximum Message Rate Percent value has not been reached, DSR is allowed to tag NGN-PS messages received from Diameter Peer Nodes.

Identifying Non-Gx NGN-PS Messages

Sh/Dh and Cx/Dx messages are tagged based on the presence of Session-Priority AVP value in Diameter messages. Rx messages are identified as NGN-PS if the MPS-Identifier AVP value in Diameter message is the same as the Rx MPS-Identifier value in Diameter System Options elements.

Identifying Gx NGN-PS Messages

Gx NGN-PS messages are identified by both the content of AVPs, as well as user-configurable data.

The reserved NGN-PS priority levels are network-specific and user-configurable. See Gx NGN-PS Identifier in Diameter System Options elements.

The ARP AVP is not a top-level AVP, which means that it is always embedded within another Grouped AVP. The ARP AVP can be embedded in one of the following top-level grouped AVPs within the Gx message:

Default-EPS-Bearer-QoS AVP
Charging-Rule-Install AVP
Usually, ARP is stored in the Default-EPS-Bearer-QoS AVP. For Gx RAR messages, if a Default-EPS-Bearer-QoS AVP cannot be located, DSR searches for up to three (3) instances of the Charging-Rule-Install AVP looking for a Priority-Level assigned to a NGN-PS user.

Priority treatment of Gx CCR-I and CCA-I messages is only required if Advance Priority is enabled in the your network. If your network supports one of the two mutually exclusive advance priority types, you can select which one to enable. See Gx Advance Priority Type in Diameter System Options elements.