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SBC – Southwest Public Safety
VoIP i2 Architecture
Part I
The IP Domain
The Interim VoIP Architecture for Enhanced 9-1-1 Services (i2)
document was the primary source of information used to create this
presentation.
This NENA STANDARD is published by National Emergency
Number Association (NENA) as a guide for the designers and
manufacturers of systems that are used for the purpose of processing
emergency calls.
VoIP i2 Architecture
The following slide has the IP Domain graphically
depicted, where you will see several functional
elements and where they fit within this schema.
Click on any of the VoIP functional elements to
be magically transported to a place presenting the
element definition and a short explanation of how it
fits in the VoIP I2 Architecture.
There is a short quiz at the end of the presentation
concerning some of the components of the VoIP
architecture.
To proceed to the quiz section,
PSTN
IP domain
Routing Proxy &
Redirect server(s)
Call server/
proxy server
Used for
contingency routing
Emergency Services
Provider Network
PSTN
Gateway
v6
ESGW(s)
v4
v5
E9-1-1
Selective
Router(s)
v4
v1
VoIP
End
Point
IP Domain
v2
v2
v0
Layer 2
Location
Download
mechanisms
VPC
VPC
VPC
Layer 3/Layer 7
Location
Download
v3
v9
LIS
v7
v7
v-e2
ESZ
RDB
RDO
SRDB
ALI
ALIDB
DB
v8
MSAG
VDB DBMS
v9
PSAP
So Sorry!
This element is not a discussion item in this particular
PowerPoint show.
Information concerning only the VoIP elements in the IP
domain are presented in this show.
Please return and select one of those functional elements.
VoIP Endpoint
The term VoIP endpoint is used to refer to the
endpoint IP Device that is used to originate an
emergency call.
To return to I/P overview click here
Location Information Server
The LIS serves as a repository for location information.
Location information is in the form of civic address or
geo-spatial location attributes correlated with a particular
physical location.
The LIS is configured with mappings between individual
location information and a logical representation of the
physical locations with which they are associated.
This set of associations is called a
“Wiremap.”
Location Information Server (cont.)
The “wiremap” in the LIS is assumed to be configured
and maintained by the entity that provides/maintains the
physical or logical access facility for endpoint equipment.
This might be an IT administrator for an enterprise, or an
Internet Service provider or an access provider in nonenterprise/residential VoIP markets.
The administrator/owner of the LIS is responsible for
creating and maintaining this wiremap, and for ensuring
that the civic location data is MSAG-validated.
Location Information Server
(cont.)
A given endpoint can be associated with a physical
location that is mapped to a particular address (civic or
geo), and the address is downloaded from the LIS to the
endpoint.
The LIS may also support assignment of a location
query key, to a particular instance of an address, to
support subsequent queries for the address.
Validation Database
The VDB contains information that describes the
current, valid civic address defined by the Emergency
Services Network Provider’s MSAG.
The VDB should have the capability to receive a
validation request containing a civic address consisting of
data elements included in the civic Location Object (LO)
and be able to determine if this civic address is a valid
address.
Validation Database (cont.)
The VDB will return a response indicating that a
given LO is a valid address or an error response.
The VDB may be distributed across multiple
databases, for example, with different VDB’s serving
different regional areas; however, there will be one
primary source of validation data for any given
geographic area or address.
Location Object (LO)
The LO is used to refer to the current position of a VoIP
endpoint that originates an emergency call.
The LO may be:
Geo location – latitude, longitude, elevation or floor, and the
datum which identifies the coordinate system used.
Civic location – a set of objects that describe detailed street
address information.
Call Server/Proxy Server
The term Call Server is used to refer to the entity in
a private or public IP domain that provides service to
endpoints in an emergency caller’s home domain and
that works with the servers and other elements in the
IP domain used to support emergency services call
routing in the i2 solution.
The Call Server may use SIP (Switched Internet
Protocol) or some other VoIP signaling protocol within
its own serving domain.
Call Server/Proxy Server (cont.)
A proxy server primarily plays the role of routing,
which means its job is to ensure that a request is sent to
another entity "closer" to the targeted user.
Proxies are also useful for enforcing policy (for
example, making sure a user is allowed to make a
call).
A proxy interprets, and, if necessary, rewrites
specific parts of a request message before forwarding.
Redirect Server/Call Relay Server
A call relay server is a redirect server that
generates redirect responses to requests it receives,
redirecting the client to contact an alternate set of
URIs to route the call to the call center with which
VoIP Service Provider has an arrangement.
Call Server/Proxy signals callback number as
calling number/ANI for the call.
Uniform Resource Identifier
URI is an Internet protocol element consisting of a
short string of characters that conform to a certain
syntax.
The string comprises a name or address that can be
used to refer to a resource. It is a fundamental component
of the World Wide Web.
For example, the URL http://www.wikipedia.org/ is a URI
that identifies a resource (Wikipedia's home page) and
implies that a representation of that resource is obtainable
via HTTP from a network host named www.wikipedia.org.
Emergency Service Zone (ESZ)
Routing Data Base (RDB)
The ERDB contains routing information associated
with each ESZ in a serving area.
It supports the boundary definitions for ESZs and the
mapping of civic address or geospatial coordinate
location information to a particular ESZ.
Emergency Service Zone Routing
Data Base (cont.)
For each ESZ, the ERDB contains:
1. one Emergency Services Routing Number (ESRN)
associated with the primary Selective Router (SR)
that serves the ESZ and
2. one routing Emergency Services Number (ESN)
that uniquely identifies the ESZ in the context of
that SR.
Emergency Service Zone Routing
Data Base (cont.)
When an emergency call is originated, and location
information is received from the VoIP Positioning
Center (VPC), the ERDB will identify the ESZ and
routing information associated with the received
location information, and will provide to the VPC:
1. ESRN,
2. the routing ESN,
3. the Contingency Routing Number (CRN - if available) and
optionally,
4. the administrative ESN.
Emergency Service Zones
When the response areas of the
agencies are overlaid, they form
geographic zones, each served
by a combination of Police, Fire
and EMS agencies.
These Zones are called Emergency
Service Zones (ESZ’s). Each ESZ
contains the set of street addresses
served by the agencies.
Root Discovery Operator
The RDO is responsible for:
 maintaining and making available the identities
of the key VDB and ERDB functions in the
network.
 ensuring that updated versions of the data with
specific activation and expiry times are available.
Root Discovery Operator
The RDO is also responsible for:
 consolidating the discovery information as
received by all VDB and ERDB operators,
 negotiating coordinated activation and expiry
intervals, and
 making this consolidated information available
for access over the interface.
Validation Data Base (cont.)
The VDB will return a response indicating that a
given Location Object (LO) is a valid address or an
error response.
The VDB may be distributed across multiple
databases, for example, with different VDBs serving
different regional areas; however, there will be one
primary source of validation data for any given
geographic area or address.
The VoIP Positioning Center
VPC is the element that provides routing information
to support the routing of VoIP emergency calls, and
cooperates in delivering location information to the
PSAP over the existing ALI DB infrastructure.
The information provided includes:
 Callback information, when available and
 a Location Object or Location Key.
The VPC may also receive other information
about the call, such as Voice Server Provider
(VSP) identification information.
The VoIP Positioning Center (cont.)
The VPC uses the received location information with
other locally stored information that enables it to
determine the appropriate ERDB to query for the
routing instructions.
The VPC uses the received location information to
request routing information from the ERDB that is
associated with the caller’s location.
The VPC may also obtain information from the
ERDB to assist in contingency routing.
Emergency Services Gateway
The ESGW is the signaling and media interworking
point between the IP domain and conventional trunks
to the E9-1-1 SR that use either Multi-Frequency
[MF] or Signaling System #7 [SS7] signaling.
The ESGW uses the routing information provided
in the received call setup signaling to select the
appropriate trunk (group) and proceeds to signal call
setup toward the SR using the ESQK to represent the
Calling Party Number/Automatic Number
Identification (ANI) information.
Public Switched Telephone Network
PSTN is the world's collection of interconnected
voice-oriented public telephone networks, both
commercial and government-owned.
PSTN is the aggregation of circuit-switching
telephone networks that has evolved from the days of
Alexander Graham Bell.
Quick Quiz
The following five review questions are
designed to help you remember some of the
important components of the IP Domain and
their function within the VoIP architecture.
Click on the response that you feel best answers
the question. The correct answer will highlight.
1. The term VoIP endpoint is used to refer to:
a)
the termination point of a VoIP call.
b)
a repository for location information.
c)
the element that provides routing information to
support the routing of VoIP emergency calls.
d)
the endpoint IP Device that is used to originate an
emergency call.
2.
A server is a network element that receives
requests in order to service them and sends back
responses to those requests.
One of these is NOT an example of a server
used in SIP domains :
a) proxies,
b) VoIP Positioning Centers
c) redirect servers,
d) registrars
3.
The Emergency Routing Database (ERDB) is the
element that provides routing information to
support the routing of VoIP emergency calls, and
cooperates in delivering location information to
the PSAP over the existing ALI DB infrastructure.
a) TRUE
b) FALSE
The ERDB contains the routing information associated
with each ESZ in a serving area.
The VoIP Positioning Center (VPC) is the element that
provides routing information to support the routing of
VoIP emergency call. The VPC supports access to the
routing data in the ERDB.
4.
The VoIP Positioning Center (VPC) is a key element in
the VoIP architecture. The following statements are all
true about the function of the VPC except for one.
Which statement is not a function of the VPC?
a. The VPC uses the received location information with other
locally stored information that enables it to determine the
appropriate ERDB to query for the routing instructions.
b. The VPC uses the routing information provided in the received
call setup signaling to select the appropriate trunk (group).
c. If the VPC receives a Location Key, the VPC obtains the
location information from the identified LIS.
The Emergency Services Gateway (ESGW) uses
the routing information provided in the received call
setup signaling to select the appropriate trunk.
5.
The Validation Database (VDB) contains information
that describes the current, valid civic address space
defined by the Emergency Services Network Provider’s
MSAG.
“Once queried, The VDB will return a response
indicating that a given location is a valid address
or reply with an error response”.
a) TRUE
b) FALSE
SBC – Southwest Public Safety
VoIP i2 Architecture The IP Domain is Part 1 in
the VoIP i2 Architecture PowerPoint series.
See VoIP i2 Architecture 9-1-1 Call Routing for an
explanation of the basic routing of a VoIP call.
Frank Abbenhaus