ALI Query Service

Document Information
Full name: 

NENA ALI Query Service Standard

Document type: 


Standard number: 

04-005 v1

Document description: 

This document defines the NENA XML ALI Query Service (AQS) that specifies new protocols between the PSAP and the Next Generation Emergency Services Network (NGESN). It provides the rationale behind the AQS and how it relates to the current ALI protocol. It also provides an overview of implementation alternatives (bindings) described in detail within the document.

This document describes specifications that overcome the following limitations of the existing ALI

  • Low-level character-based protocol supporting query request, query response and broadcast
  • message concepts
  • ALI data is limited to 511 characters
  • The ALI data representation uses position-dependent encoding
  • Mostly delivered over slow asynchronous links (as low as 1200 bps)

Here are some of the advantages of AQS over the standing ALI protocol:

  • Based on self-describing messages, defined by a formal XML syntax (schema).
    The advantage here is more expressive power and validation capability.
  • Message exchange patterns are formally defined (WSDL1)
    The advantage here is having an implementation (protocol) independent specification of the
    AQS interface (e.g. supporting Application Programming Interfaces)
  • Each type of query is represented by a specific message definition
    The advantage here is the explicit and non-ambiguous statement of supported query requests
  • The query key can support other forms beyond “NPA NXX TN”, such as SIP URL.

As with any evolving technology, operations at the PSAP must adapt to manage the new evolving standard. Examples are:

  • Most of these protocols assume TCP/IP connections to the PSAP.
  • By delivering XML to the PSAP, the PSAP administrator, or a third party, must define how
    the XML data is represented to the Call Taker.
Committee Information
Committee Name(s): 

Technical – CPE

Committee type: 


Document Dates


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ALI Query Service.pdf 933.71 KB