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H.323 Gatekeepers
Lucent Technologies - elemedia
Agenda
• Introduction
• Overview of Gatekeeper Functions
• Why are Gatekeepers Useful?
• Gatekeeper Concepts
• Signalling Models
• Gatekeeper Operations
• Signalling Flows
• Policy/Service Examples
• Gatekeepers and H.323v2
• Beyond H.323v2
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INTRODUCTION
H.323 Components
•
•
•
•
Terminal
Gateway (GW)
Gatekeeper (GK)
Multipoint Control Unit (MCU)
– Multipoint Controller (MC)
– Multipoint Processor (MP)
Terminal 1
Terminal 2
MC
Gatekeeper 1
Gatekeeper 2
MC
Gatekeeper 3
MC
MP
LAN
Gateway 1
MC
Gateway 2
Gateway 3
MC
MP
MCU 1
MC
MP
MCU 2
MC
GW, GK & MCU can be a single device 3
INTRODUCTION
Gatekeeper in H.323
• Gatekeepers are optional
• Mandatory functions if present:
– Address translation (routing) to determine destination
address of H.323 endpoint for a call
– Admission control to determine whether to allow
endpoints to originate and terminate calls
– Bandwidth control to, at a minimum, process
bandwidth requests (can be a null function)
– Zone management
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INTRODUCTION
Gatekeeper in H.323 (contd.)
• Gatekeeper optional functions:
– Call control signalling to handle directly the Q.931
signalling between the H.323 endpoints
– Call authorization using some policy (e.g. subscription
status)
– Bandwidth management to process bandwidth requests
using some policy (e.g. based on current conditions)
– Call management to process call requests using some
policy (e.g. based on endpoint status)
– Gatekeeper management information (MIB)
– Bandwidth reservation for terminals not capable of
performing it
– Directory services
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INTRODUCTION
Why are Gatekeepers Useful?
• Centralized Management
– Authentication, routing, call detail recording, etc.
• Isolate Endpoints from Network Internals
– Knowledge of naming structures, gateway routing
algorithms, etc, stays in network
• Interface to New and Existing Network Databases
– LDAP directories, RADIUS servers, SCPs, etc.
• Interfaces to Other H.323 Networks
– Calls between service providers
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INTRODUCTION
Gatekeeper Standards
• Standards specify the communications between
H.323 entities and Gatekeepers (RAS messages)
• Standards specify the services a Gatekeeper
must provide
BUT
• Standards DO NOT specify how the Gatekeeper
should provide those services
• Standards DO NOT fully specify how
Gatekeepers locate other Gatekeepers
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CONCEPTS AND FUNCTIONS
H.323 ZONE
• Simply defined as the collection of H.323 devices
managed by a single gatekeeper
• Boundaries of a zone can be based on
administrative, naming structure, geographic,
engineering (or other) criteria
• Calls between endpoints in a zone handled by a
single gatekeeper
• Calls between endpoints in different zones might
involve gatekeepers from both zones
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CONCEPTS AND FUNCTIONS
Gatekeeper Components
Network Based Information
and Control
Policy
Features &
Services
Protocol Procedures:
RAS, Q.931, H.245, H.450
Protocols:
• TCAP/SS7
• LDAP
• SNMP
• RADIUS
• et al.
Management
Endpoint &
Conference
State Data
Q.931/ASN Encode/Decode and Transport
H.323
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SIGNALLING MODELS
Signalling Models
• The signalling model determines which protocol
messages pass through the gatekeeper, and which
pass directly between the two endpoints
• The more messages that are routed between the
gatekeeper, the more informational and control it
has -- and more load and responsibility
• The gatekeeper ultimately decides the signalling
model
• Media never passes through the gatekeeper
function (although a proxy could be co-located on
same host)
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CONCEPTS AND FUNCTIONS
Signalling Models
Notes:
• The following signalling model scenarios
show calls between a PC terminal and a
PSTN gateway, but generally apply to any
call between two H.323 endpoints
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SIGNALLING MODELS
Direct Endpoint Call Signalling
Terminal
Call Signalling (Q.931)
Gateway
Call Control (H.245)
Media Stream (RTP)
Address Translation
Admission Control
GK
Bandwidth Control
(RAS)
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SIGNALLING MODELS
Direct Endpoint Call Signalling
• Gatekeeper participates in call admission but has
limited direct knowledge of connected calls
• Due to limited involvement, single gatekeeper can
process large number of calls
• Limits service management functions: gatekeeper
cannot determine call completion rates, for
example
• Limits centralized security: gatekeeper cannot
validate Q.931 message fields (e.g. caller’s ID)
• Limits call detail recording function: gatekeeper
depends on endpoint(s) for call duration
information, for example
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SIGNALLING MODELS
Gatekeeper Routed Call Signalling (Q.931)
Terminal
Gateway
Call Control (H.245)
Media Stream (RTP)
Address Translation
Admission Control
GK
Bandwidth Control
(RAS)
Call Signalling (Q.931)
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SIGNALLING MODELS
Gatekeeper Routed Call Signalling (Q.931)
• Gatekeeper aware of connection state of call but
not media usage (no access to H.245 signalling)
• More load on gatekeeper as it must process Q.931
messages and maintain Q.931 signalling channel
• Service management functions can include
connection statistics but not media usage
• Gatekeeper can validate Q.931 message
parameters such as calling party information
• Call detail recording functions enhanced by direct
knowledge of connection state
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SIGNALLING MODELS
Direct Endpoint Call Signalling w/UUIE
Terminal
Call Signalling (Q.931)
Gateway
Call Control (H.245)
Media Stream (RTP)
Address Translation
Admission Control
GK
Bandwidth Control
Q.931 UUIE Notification (v2)
(RAS)
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SIGNALLING MODELS
Direct Endpoint Call Signalling w/UUIE
• Hybrid between direct call signalling and
gatekeeper routed signalling
• Q.931 messages do not flow through the
gatekeeper, but gatekeeper is notified of Q.931
content in RAS messages.
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SIGNALLING MODELS
Gatekeeper Routed Call Signalling (Q.931/H.245)
Terminal
Gateway
Media Stream (RTP)
Address Translation
Admission Control
GK
Bandwidth Control
(RAS)
Call Signalling (Q.931)
Call Control (H.245)
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SIGNALLING MODELS
Gatekeeper Routed Call Signalling (Q.931/H.245)
• Gatekeeper aware of connection state of call and
media channels in use (can audit bandwidth usage)
• Highest load on gatekeeper as it must process
Q.931 and H.245 messages and maintain the
corresponding signalling channels
• Service management functions can include
connection and media usage statistics
• Call detail recording functions further enhanced
by direct knowledge of media usage
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GATEKEEPER OPERATIONS
Gatekeeper Operations and Policy
Notes:
• List of parameters in messages is not inclusive
• Parameter names displayed as follows:
– Required parameters shown in bold
– Optional parameters shown in italic
– Version 2 parameters shown in blue
(bold or italic)
• LDAP/TCAP message content is paraphrased for
illustration
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GATEKEEPER OPERATIONS
Endpoint/GK Discovery
(1) Who is my GK?
Endpoint
(2) I can be your GK
(1) GRQ
GK
(2) GCF/GRJ
GatekeeperRequest:
requestSeqNum
rasAddress
endpointType
gatekeeperIdentifier
endpointAlias
GatekeeperConfirm:
requestSeqNum
gatekeeperIdentifier
rasAddress
alternateGatekeeper
et al.
et al.
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GATEKEEPER OPERATIONS
Endpoint/GK Discovery Processing
• Discovery can be multicast (most useful for LAN
environments) or unicast based on endpoint
configuration data
• Possible acceptance criteria to be used by
gatekeeper:
– IP address (or IP subnet) of endpoint
– Gatekeeper ID supplied by endpoint
– Aliases supplied by endpoint
– Gatekeeper load
• Gatekeeper might need to consult external database
(e.g. LDAP directory)
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GATEKEEPER OPERATIONS
Endpoint/GK Registration
(1) Here are my aliases and IP address
(2) OK
(1) RRQ
Endpoint
GK
(2) RCF/RRJ
RegistrationRequest:
requestSeqNum
callSignalAddress
RegistrationConfirm:
requestSeqNum
terminalAlias
terminalAlias
timeToLive
endpointIdentifier
endpointIdentifier
willRespondToIRR
keepAlive
willSupplyUUIEs
et al.
alternateGatekeeper
timeToLive
preGrantedARQ
et al.
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GATEKEEPER OPERATIONS
Endpoint/GK Registration Processing
• Gatekeeper might authenticate endpoint
– H323v1 must use ad hoc/proprietary methods such as
supplied aliases, IP address, etc.
– H.323v2 can use encrypted password or certificates
• Gatekeeper might authorize endpoint
– Validate list of supplied aliases
• Associate aliases with the IP address for later location
• Gatekeeper assigns and returns Endpoint ID to be
used in subsequent messages
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GATEKEEPER OPERATIONS
Example: Reservation Authorization via LDAP
Needs to authorize
aliases
Register: johnDoe
+13141592654
RRQ
GK
RCF/RRJ
LDAP SEARCH:
Filter:
e164=13141592654
AND h323ID=johnDoe
LDAP SEARCH RESULT:
Entry:
e164=13141592654
h323ID=johnDoe
status=active
LDAP Directory containing
subscriber data
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GATEKEEPER OPERATIONS
Call
Admission
(1) Can I call +1323931245
(2) Yes, contact this IP address
using 16 Kb/sec?
(1) ARQ
GK
Endpoint
(2) ACF/ARJ
AdmissionRequest:
requestSeqNum
callModel
endpointIdentifier
destinationInfo
destCallSignalAddress
srcInfo
bandwidth
conferenceID/callID
willSupplyUUIEs
et al.
AdmissionConfirm:
requestSeqNum
bandwidth
callModel
destCallSignalAddr
irrFrequency
willRespondToIRR
uuiesRequested
et al.
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GATEKEEPER OPERATIONS
Call Admission Processing
• Gatekeeper might authenticate endpoint to ensure
it is registered and check if it is authorized to make
call
• Gatekeeper must determine call model
– Endpoint can ask for preference but gatekeeper will decide
• Gatekeeper might check for bandwidth
• If direct signalling, gatekeeper supplies destination
endpoint address (discussed later)
• If gatekeeper routed signalling, it supplies its own
address and can defer routing
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GATEKEEPER OPERATIONS
Example: Admission Authorization via SS7
Admit: johnDoe
Calling card: 271828182+8459
Needs to authorize
calling card number
ARQ
GK
ACF/ARJ
TCAP QUERY:
Invoke:
Provide Value
Digits = 271828182
Pin=8459
TCAP END:
Return Result:
Record Status Indicator
Service Control Point containing
calling card info (e.g. LIDB in
the US)
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GATEKEEPER OPERATIONS
Q.931 Setup
(1) Connect me to
+108061998
Endpoint
(2) Determine
gateway
SETUP
(2) Start PSTN
origination
SETUP
GK
SETUP message IEs:
Bearer capability IE
Display IE
Calling party number IE
Called party number IE
GW
User-to-user IE:
h245Address
sourceInfo
destinationAddr
conferenceID
callIdentifier
fastStart
fastCap
et al.
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GATEKEEPER OPERATIONS
Setup Processing
• Gatekeeper associates Setup with previous
admission using Conference ID
• Destination determined using Calling Party
Number or destination alias(es)
• External databases might be consulted to
determine destination endpoint:
– Map full destination alias to a terminal
– Map leading digits of E.164 number to gateway(s)
• Setup message is forwarded to destination
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GATEKEEPER OPERATIONS
Example: Endpoint Location Via LDAP
(1) Connect me to
+14142135624
Endpoint
(2) Query LDAP
Directory
SETUP
(3) Start PSTN
origination
SETUP
GK
LDAP SEARCH:
Filter: E164=1414
OR E164=1414213
GW
LDAP SEARCH RESULT:
IP=192.168.26.68 STATE=IS
IP=192.168.26.102 STATE=IS
LDAP
DIRECTORY
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GATEKEEPER OPERATIONS
Example: Endpoint Location Via SS7
(1) Connect me to
8001732050
Endpoint
(2) Freephone!
(3) Start PSTN
- Query SCP
origination
- Translate E.164
SETUP
SETUP
GK
TCAP QUERY:
Invoke:
Provide Instructions
Digits=8001732050
et al.
GW
TCAP END:
Invoke:
Connect:
Digits=2236067977
et al.
SCP PROVIDING
FREEPHONE SERVICE
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GATEKEEPER OPERATIONS
Remaining Call Setup
Gatekeeper
Terminal
Gateway
CALL PROCEEDING
CALL PROCEEDING
ARQ
ACF
ALERTING
ALERTING
CONNECT
CONNECT
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GATEKEEPER OPERATIONS
Remaining Call Setup Processing
• Gatekeeper processes terminating admissions
request doing potential authorization and
bandwidth checks
• Gatekeeper primarily a “pipe” for Q.931 messages
but might authorize some fields (e.g. Display)
• Gatekeeper substitutes its own address in
“h245address” fields if it wishes to route H.245
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GATEKEEPER OPERATIONS
Stable Call Processing
• Gatekeeper verifies calls are “alive” using one of
the following techniques:
– Wait for periodic IRRs (as requested in the ACF)
– Periodically send an IRQ, expecting an IRR
– Periodically send a Q.931 Status Enquiry, expecting a Status
• Gatekeeper might receive bandwidth changes requests
(BRQ) and must allow (BCF) or deny (BRJ) the
request
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GATEKEEPER OPERATIONS
Call Teardown
Gatekeeper
Terminal
Gateway
RELEASE COMPLETE
RELEASE COMPLETE
DRQ
DRQ
DCF
DCF
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GATEKEEPER OPERATIONS
Call Teardown Processing
• Gatekeeper processes Release Complete, noting the
time and forwards it to the other endpoint
• Gatekeeper processes DRQ from both endpoints
and releases any allocated bandwidth
• Gatekeeper might create call detail record for the
call, recording endpoint information and Connect
and Release times for example
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H.323v2 and Gatekeepers
H.323v2 Features Related to Gatekeeper
• Authentication Framework
–
–
–
–
Tokens (password or certificate based) for RAS
TLS (certificate based) for Q.931
Negotiated H.245 security
H.323 defines the framework - need profiles to nail down
specific choices of algorithms
• Mechanism to specify alternative gatekeepers to
endpoints
• Registration “keep alive” similar to conference IRR
“keep alive”
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H.323v2 and Gatekeepers
H.323v2 Features Related to Gatekeeper
• RAS Transport Improvements
– IRR ACK/NAK
– Request In Progress (RIP) to ask for more time
• Signalling changes
– Excuse endpoints from Admission Requests
– Fast call setup / tunneled H.245
– Gatekeeper can request Q.931 information be forwarded to
it on direct routed calls
• H.450 Services
– Call transfer and call forwarding
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Beyond H.323v2
Beyond H.323v2: Network Management
• Definition of Management Information Bases (MIB) for
H.323 protocols and devices under development
• Gatekeepers can provide large amount of centralized
management information and control
Network
Management
Station
SNMP/
CMIP
Gatekeeper
Gateway
MCU and others
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Beyond H.323v2
Beyond H.323v2: Inter-gatekeeper
Communication
• Current H.323 standards do not provide an interzone model that scales well for large networks
• Inter-gatekeeper protocols being discussed to
enable gatekeepers to efficiently locate one another
to route calls to non-local address
• Hierarchical arrangements with “clearinghouse”
gatekeepers have been proposed
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