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H.323 Gatekeepers: Overview, Functions, and Applications

This article provides an introduction to H.323 gatekeepers, their functions, and why they are useful in managing H.323 networks. It covers topics such as signalling models, gatekeeper operations, policy/service examples, and their role in H.323v2.

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H.323 Gatekeepers: Overview, Functions, and Applications

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  1. H.323 Gatekeepers Lucent Technologies - elemedia

  2. 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

  3. INTRODUCTION H.323 Components • Terminal • Gateway (GW) • Gatekeeper (GK) • Multipoint Control Unit (MCU) • Multipoint Controller (MC) • Multipoint Processor (MP) Terminal 1 Terminal 2 Gatekeeper 1 Gatekeeper 2 Gatekeeper 3 MC MC MC MP LAN Gateway 1 Gateway 2 Gateway 3 MCU 1 MCU 2 MC MC MP MC MP MC GW, GK & MCU can be a single device

  4. 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 allowendpoints to originate and terminate calls • Bandwidth control to, at a minimum, process bandwidth requests (can be a null function) • Zone management

  5. 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

  6. 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

  7. 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

  8. CONCEPTS AND FUNCTIONS H.323 ZONE • Simply defined as the collection of H.323 devices managed by a singlegatekeeper • 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

  9. Features & Services Policy Management Endpoint & Conference State Data Protocol Procedures: RAS, Q.931, H.245, H.450 Q.931/ASN Encode/Decode and Transport CONCEPTS AND FUNCTIONS Gatekeeper Components Protocols: • TCAP/SS7 • LDAP • SNMP • RADIUS • et al. Network Based Information and Control H.323

  10. 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)

  11. 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

  12. SIGNALLING MODELS Direct Endpoint Call Signalling Terminal Gateway Call Signalling (Q.931) Call Control (H.245) Media Stream (RTP) Address Translation Admission Control Bandwidth Control (RAS) GK

  13. 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

  14. SIGNALLING MODELS Gatekeeper Routed Call Signalling (Q.931) Terminal Gateway Call Control (H.245) Media Stream (RTP) Address Translation Admission Control Bandwidth Control (RAS) GK Call Signalling (Q.931)

  15. 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

  16. SIGNALLING MODELS Direct Endpoint Call Signalling w/UUIE Terminal Gateway Call Signalling (Q.931) Call Control (H.245) Media Stream (RTP) Address Translation Admission Control Bandwidth Control Q.931 UUIE Notification (v2) (RAS) GK

  17. 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.

  18. SIGNALLING MODELS Gatekeeper Routed Call Signalling (Q.931/H.245) Terminal Gateway Media Stream (RTP) Address Translation Admission Control Bandwidth Control (RAS) GK Call Signalling (Q.931) Call Control (H.245)

  19. 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

  20. 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

  21. GATEKEEPER OPERATIONS Endpoint/GK Discovery (1) Who is my GK? (2) I can be your GK (1) GRQ Endpoint GK (2) GCF/GRJ GatekeeperRequest: requestSeqNum rasAddress endpointType gatekeeperIdentifier endpointAlias et al. GatekeeperConfirm: requestSeqNum gatekeeperIdentifier rasAddress alternateGatekeeper et al.

  22. 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)

  23. GATEKEEPER OPERATIONS Endpoint/GK Registration (2) OK (1) Here are my aliases and IP address (1) RRQ Endpoint GK (2) RCF/RRJ RegistrationRequest: requestSeqNum callSignalAddress terminalAlias timeToLive keepAlive endpointIdentifier willSupplyUUIEs et al. RegistrationConfirm: requestSeqNum terminalAlias endpointIdentifier alternateGatekeeper timeToLive willRespondToIRR preGrantedARQ et al.

  24. 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

  25. 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 containingsubscriber data

  26. GATEKEEPER OPERATIONS Call Admission (1) Can I call +1323931245 using 16 Kb/sec? (2) Yes, contact this IP address (1) ARQ GK Endpoint (2) ACF/ARJ AdmissionRequest: requestSeqNumcallModel endpointIdentifierdestinationInfo destCallSignalAddress srcInfo bandwidth conferenceID/callID willSupplyUUIEs et al. AdmissionConfirm: requestSeqNum bandwidth callModel destCallSignalAddrirrFrequencywillRespondToIRR uuiesRequested et al.

  27. 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

  28. 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)

  29. GATEKEEPER OPERATIONS Q.931 Setup (1) Connect me to +108061998 (2) Determine gateway (2) Start PSTN origination Endpoint SETUP SETUP GK GW SETUP message IEs: Bearer capability IE User-to-user IE: Display IEh245Address Calling party number IE sourceInfo Called party number IEdestinationAddr conferenceID callIdentifier fastStart fastCap et al.

  30. 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

  31. GATEKEEPER OPERATIONS Example: Endpoint Location Via LDAP (2) Query LDAP Directory (3) Start PSTN origination (1) Connect me to +14142135624 Endpoint SETUP SETUP GK GW LDAP SEARCH:Filter: E164=1414 OR E164=1414213 LDAP SEARCH RESULT: IP=192.168.26.68 STATE=IS IP=192.168.26.102 STATE=IS LDAP DIRECTORY

  32. GATEKEEPER OPERATIONS Example: Endpoint Location Via SS7 (2) Freephone! - Query SCP - Translate E.164 (3) Start PSTN origination (1) Connect me to 8001732050 Endpoint SETUP SETUP GK GW TCAP END: Invoke: Connect: Digits=2236067977 et al. TCAP QUERY: Invoke: Provide Instructions Digits=8001732050 et al. SCP PROVIDING FREEPHONE SERVICE

  33. GATEKEEPER OPERATIONS Remaining Call Setup Gatekeeper Gateway Terminal CALL PROCEEDING CALL PROCEEDING ARQ ACF ALERTING ALERTING CONNECT CONNECT

  34. 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

  35. 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

  36. GATEKEEPER OPERATIONS Call Teardown Gatekeeper Gateway Terminal RELEASE COMPLETE RELEASE COMPLETE DRQ DRQ DCF DCF

  37. 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

  38. 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”

  39. 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

  40. 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

  41. Beyond H.323v2 Beyond H.323v2: Inter-gatekeeper Communication • Current H.323 standards do not provide an inter-zone 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

  42. Internet Multimedia Communications Software ... integrating voice, fax, data and video ... integrating voice, fax, data and video For information on elemedia’s H.323 Gateway Toolkits and H.323 Gatekeeper Toolkits, please contact us at: +1 732-949-2184 888-elemedia (1-888-353-6334) (U.S. and Canada) Email: elemedia@lucent.com http://www.elemedia.com

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