Cisco Voice Gateways And Gatekeepers

by Mallory, David; Salhoff, Ken; Donohue, Denise

• ISBN13: 9781587052583
• ISBN10: 158705258X
• Edition: 1st
• Format: Hardcover
• Copyright: 2006-08-17
• Publisher: Cisco Press

Summary

Cisco Voice Gateways and Gatekeepers Understanding and configuring GW/GK in complex VoIP networks Denise Donohue, CCIEreg; No. 9566 David Mallory, CCIE No. 1933 Ken Salhoff, CCIE No. 4915 Deployments of voice over IP (VoIP) networks continue at a rapid pace. Voice gateways are an essential part of VoIP networks, handling the many tasks involved in translating between transmission formats and protocols and acting as the interface between an IP telephony network and the PSTN or PBX. Gatekeepers and IP-to-IP gateways help these networks scale. Gatekeepers provide call admission control, call routing, address resolution, and bandwidth management between H.323 endpoints including Cisco IOSreg; voice gateways and Ciscoreg; Unified CallManager clusters. IP-to-IP gateways allow VoIP calls to traverse disparate IP networks. Cisco Voice Gateways and Gatekeepers provides detailed solutions to real-world problems encountered when implementing a VoIP network. This practical guide helps you understand Cisco gateways and gatekeepers and configure them properly. Gateway selection, design issues, feature configuration, and security and high-availability issues are all covered in depth. The abundant examples, screen shots, configuration snips, and case studies make this a truly practical and useful guide for anyone interested in the proper implementation of gateways and gatekeepers in a VoIP network. Emphasis is placed on the accepted best practices and common issues encountered in real-world deployments. Cisco Voice Gateways and Gatekeepers is divided into four parts. Part I provides an overview of an IP voice network. Part II is dedicated to voice gateways, including discussions of Media Gateway Control Protocol (MGCP); H.323; Session Initiation Protocol (SIP); voice circuit options; connecting to the PSTN, PBX, and IP WAN; dial plans; digit manipulation; route selection; class of restriction; Survivable Remote Site Telephony (SRST) and MGCP fallback; digital signal processor (DSP) resources; and Tool Command Languaue (Tcl) scripts and Voice XML (VXML). Part III addresses voice gatekeepers, including detailed deployment and configuration. Part IV is dedicated to IP-to-IP gateways. "With this book, the authors provide an in-depth look at the breadth of voice gateway features and capabilities, as well as providing voice gateway configuration guidance." -Christina Hattingh, Access Technology Group, Cisco Systemsreg; Denise Donohue, CCIEreg; No. 9566, is a design engineer with AT&T. She is responsible for designing and implementing data and VoIP networks for SBC and AT&T customers. David L. Mallory, CCIE No. 1933, is a technical education consultant with Cisco Systems, supporting Cisco voice certifications. Prior to this role, David was a systems engineer supporting several global enterprise customers. Ken Salhoff, CCIE No. 4915, is a systems engineer with Cisco Systems. Ken has been specializing in voice technologies at Cisco for the past six years. bull; bull;Understand the pros and cons of MGCP, H.323, and SIP, how they implement call signaling and describe call flow, and how to configure each protocol bull;Learn the various analog and digital voice circuit options used to connect a VoIP network to the PSTN bull; bull;Configure and troubleshoot PSTN, PBX, and IP WAN connections bull;Build scalable dial plans and understand the different types of dial peers bull;Understand the various ways gateways control called and calling phone numbers bull;Examine call admission control (CAC) techniques bull; bull;Configure Class of Restrictions (CoR) for both inbound and outbound calls bull;Deploy and troubleshoot SRST and MGCP fallba

Author Biography

Denise Donohue, CCIE No. 9566, is a design engineer with AT&T. She is responsible for designing and implementing data and VoIP networks for SBC and AT&T customers. Prior to that, she was a Cisco instructor and course director for Global Knowledge. Her CCIE is in Routing and Switching.

David L. Mallory, CCIE No. 1933, is a technical education consultant with Cisco Systems, Inc. supporting Cisco voice certifications. Prior to this role, David was a systems engineer supporting several global enterprise customers. David has presented on voice gateways and gatekeepers at Networkers and has achieved four CCIE certifications: Routing and Switching, WAN Switching, Security, and Voice.

Ken Salhoff,CCIE No. 4915, is a systems engineer with Cisco Systems, Inc. Ken has been specializing in voice technologies with Cisco for the past six years. In the systems engineering role, Ken has supported several global enterprise customers using Cisco voice technologies. Ken has achieved two CCIE certifications: Routing and Switching, and Voice.

 

Table of Contents

Foreword	xxiv
Introduction	xxvi
Part I Voice Gateways and Gatekeepers	3	(20)
Gateways and Gatekeepers	5	(18)
The Role of Voice Gateways	5	(3)
Types of Voice Gateways	7	(1)
Routers	7	(1)
Standalone Voice Gateways	7	(1)
Switch Modules	8	(1)
The Role of Voice Gatekeepers	8	(2)
The Role of IP-to-IP Gateways	10	(1)
Introduction to Voice Protocols	11	(3)
Media Gateway Control Protocol	11	(1)
H.323	12	(1)
Session Initiation Protocol	12	(1)
Skinny Client Control Protocol	13	(1)
Real-Time Transport Protocol	14	(1)
Call Control Agents	14	(2)
Cisco CallManager	14	(1)
Cisco CallManager Express	14	(1)
SIP Proxy Server	15	(1)
Cisco Enterprise Gateway	15	(1)
PBX with Toll Bypass	15	(1)
Deployment Scenarios	16	(2)
Single Site Deployment	16	(1)
Multisite with Centralized Call Control	17	(1)
Multisite Deployment with Distributed Call Control	17	(1)
Case Study: Introduction	18	(3)
Chapter Review Questions	21	(2)
Part II Gateways	23	(434)
Media Gateway Control Protocol	25	(28)
Introduction to MGCP	26	(2)
Pros	27	(1)
Cons	28	(1)
MGCP Operation	28	(5)
MGCP Messages	29	(2)
Registering with CallManager	31	(2)
Call Flow with MGCP	33	(4)
Call Flow Between Analog Phones	33	(2)
ISDN Connections with Backhaul	35	(2)
MGCP Fallback	37	(1)
Dial Plan Considerations	37	(1)
Implementing MGCP Gateways	37	(10)
Basic MGCP Gateway Configuration	38	(1)
Configuring MGCP Fallback	39	(1)
Assigning an MGCP Source IP Address	39	(1)
Configuring MGCP PRI and BRI Backhaul	39	(1)
Enabling Multicast Music on Hold	40	(1)
Configuring Cisco CallManager	40	(5)
Configuring CallManager Redundancy	45	(1)
Configuring DTMF Relay	46	(1)
Securing MGCP Gateways	47	(1)
Troubleshooting Tools	47	(2)
Case Study: Configuring an MGCP Gateway	49	(2)
Review Questions	51	(2)
H.323	53	(26)
H.323 Specifications	53	(1)
H.323 Network Components	54	(2)
H.323 Gateways	55	(1)
H.323 Gatekeepers	55	(1)
H.323 Terminals	55	(1)
Multipoint Control Units	56	(1)
H.323 Proxy Servers	56	(1)
Call Flow	56	(2)
H.323 Fast Start	56	(2)
H.323 Protocol Pros and Cons	58	(1)
Pros	58	(1)
Cons	59	(1)
When to Use H.323	59	(1)
Dial Plan Considerations	60	(1)
Implementing H.323 Gateways	61	(11)
Voice Class Configuration	62	(2)
Voice Service VoIP Configuration	64	(1)
Toll Bypass	65	(2)
Defining H.323 Gateways on CallManager	67	(2)
Redundancy	69	(1)
DTMF Relay	70	(2)
Securing H.323 Gateways	72	(1)
Troubleshooting Tools	72	(1)
Case Study: Configuring an H.323 Gateway	73	(3)
Review Questions	76	(3)
Session Initiation Protocol	79	(36)
Description of SIP	79	(9)
SIP Functional Components	81	(1)
SIP Messages	82	(6)
SIP Call Flow	88	(7)
Call Flow Between Two SIP Gateways	88	(2)
Call Flow Using a Proxy Server	90	(2)
Call Flow Using Multiple Servers	92	(1)
Call Flow Using Cisco CallManager 5.x	93	(2)
SIP Pros and Cons	95	(1)
Pros	95	(1)
Cons	96	(1)
When to Use SIP	96	(1)
Dial Plan Considerations	96	(1)
Implementing SIP Gateways	97	(12)
SIP Dial Peer Configuration	98	(1)
SIP UA Configuration	98	(3)
SIP Voice Service Configuration	101	(1)
Toll Bypass	102	(1)
Registering with CallManager	102	(1)
Configuring a SIP Trunk with CallManager 4.x	102	(3)
Configuring a SIP Trunk with CallManager 5.x	105	(2)
Configuring the Gateway for a CallManager Trunk	107	(1)
DTMF Relay	107	(2)
Securing SIP Gateways	109	(1)
Allowing H.323 to SIP Connections	110	(1)
Troubleshooting Tools	110	(1)
Case Study: Configuring SIP Between a Gateway and CallManager 5.x	111	(2)
Review Questions	113	(2)
Circuit Options	115	(30)
Circuit Signaling	115	(1)
Analog Circuits	116	(10)
FXS/FXO	116	(1)
FXS	117	(1)
FXO	117	(1)
FXO Power Failover	117	(1)
FXS/FXO Supervisory Signaling	117	(1)
Address Signaling	118	(1)
FXS-DID	119	(1)
Informational Signaling	119	(1)
Caller ID	120	(1)
Supervisory Disconnect	121	(1)
CAMA	122	(1)
E&M	123	(1)
Type I Signaling	124	(1)
Type II Signaling	124	(1)
Type III Signaling	124	(1)
Type IV Signaling	125	(1)
Type V Signaling	125	(1)
Address Signaling	126	(1)
Digital Circuits	126	(16)
T1	127	(2)
Channel-Associated Signaling	129	(1)
E&M Signaling	129	(1)
Feature Group D	130	(1)
E1	131	(1)
E1 R2	131	(1)
Line Signaling	131	(1)
Inter-Register Signaling	132	(2)
ISDN	134	(1)
ISDN Switch Configuration	134	(2)
ISDN Call Signaling	136	(2)
Information Elements	138	(1)
Address Types	139	(1)
NFAS	140	(1)
QSIG	141	(1)
Echo Cancellation	141	(1)
Review Questions	142	(3)
Connecting to the PSTN	145	(38)
PSTN Circuit Selection Overview	145	(2)
Supported Analog Connection Types	146	(1)
Supported Digital Connection Types	147	(1)
Analog Trunks	147	(11)
Configuring FXO Connections	147	(2)
Verifying and Troubleshooting	149	(1)
Caveats and Restrictions	150	(1)
Media Gateway Control Protocol	150	(2)
Configuring DID Connections	152	(2)
Verifying and Troubleshooting	154	(1)
Caveats and Restrictions	154	(1)
Configuring Centralized Automated Message Accounting Connections	154	(2)
Verifying and Troubleshooting	156	(1)
Caveats and Restrictions	157	(1)
Digital Trunks	158	(21)
Configuring E1/T1 Physical Layer Connections	158	(1)
Verifying and Troubleshooting	159	(3)
Configuring ISDN PRI Trunks	162	(2)
MGCP	164	(1)
Verifying and Troubleshooting	165	(3)
Configuring E1 R2 Trunks	168	(3)
MGCP	171	(1)
Verifying and Troubleshooting	171	(1)
Configuring T1 CAS Trunks	172	(2)
MGCP	174	(1)
Verifying and Troubleshooting	174	(1)
Configuring ISDN BRI Trunks	175	(2)
MGCP	177	(1)
Verifying and Troubleshooting	178	(1)
Case Study: Add an E1 R2 Connection to the Leeds Gateway	179	(2)
Review Questions	181	(2)
Connecting to PBXs	183	(36)
Analog Trunks	184	(6)
Configuring FXO/FXS Connections	184	(2)
MGCP	186	(1)
Configuring E&M Trunks	187	(1)
Verifying and Troubleshooting	188	(2)
Digital Trunks	190	(17)
Configuring E1/T1 Physical Layer Connections	190	(1)
Clocking	191	(4)
Verifying and Troubleshooting	195	(1)
Configuring ISDN PRI Trunks	196	(2)
Verifying and Troubleshooting	198	(3)
MGCP	201	(2)
Verifying and Troubleshooting	203	(1)
Q Signaling	204	(2)
Configuring E1 R2 or T1 CAS Trunks	206	(1)
Configuring Transparent Common Channel Signaling	207	(6)
Case Study: Implementing a Cisco Voice Gateway at the Shanghai Office	213	(4)
Review Questions	217	(2)
Connecting to an IP WAN	219	(56)
Applications for Connecting to an IP WAN	219	(1)
Design Considerations	220	(1)
Quality of Service	221	(28)
Using Class Maps to Classify Traffic	222	(1)
Classifying at Layer 4	222	(3)
Classifying at Layer 3	225	(1)
Classifying at Layer 2	226	(1)
Using Policy Maps	227	(5)
Mapping to MPLS Classes	232	(7)
Link Fragmentation and Interleave	239	(1)
Multilink PPP	240	(2)
Frame Relay FRF.12 Fragmentation	242	(2)
Frame Relay Fragmentation Using MLPoFR	244	(1)
MLPoATM	245	(1)
Compression	246	(2)
AutoQos	248	(1)
Providing Fax and Modem Services	249	(11)
Providing Fax Services	250	(1)
Configuring Cisco Fax Relay	251	(1)
Configuring T.38 Fax Relay for MGCP Gateways	252	(2)
Configuring T.38 Fax Relay for H.323 and SIP Gateways	254	(1)
Configuring Super G3 Fax Relay	255	(1)
Configuring Fax Passthrough	256	(1)
Configuring Fax Passthrough for MGCP Gateways	256	(1)
Configuring Fax Passthrough for H.323 and SIP Gateways	257	(1)
Providing Modem Services	258	(1)
Configuring Cisco Modem Relay	258	(1)
Configuring Modem Passthrough	259	(1)
Security	260	(6)
Securing Voice Media and Signaling	261	(1)
Securing Voice Media with Secure RTP	261	(2)
Securing Voice Signaling with IPsec	263	(1)
Securing Voice Signaling with TLS	263	(1)
V3PN	264	(1)
NAT and VoIP	265	(1)
Firewalls and VoIP	265	(1)
Case Study: Using a T1 Link as a Tie Line	266	(6)
Review Questions	272	(3)
Dial Plans	275	(28)
Numbering Plans	276	(5)
Private Numbering Plans	276	(1)
Private Numbering Plan Design Considerations	276	(2)
PSTN Numbering Plans	278	(1)
North American Numbering Plan	279	(1)
UK National Numbering Plan	279	(2)
Overlapping Numbering Plans	281	(2)
Building a Scalable Dial Plan	283	(1)
Dial Peers	283	(2)
Inbound Versus Outbound Dial Peers	284	(1)
Call Legs	284	(1)
Dial Peer Matching	285	(13)
Inbound Dial Peer Matching	285	(3)
Outbound Dial Peer Matching	288	(1)
direct-inward-dial Is Not Configured	288	(1)
direct-inward-dial Is Configured	289	(1)
Verifying Dial Peers	289	(2)
Outbound Dial Peer Targets	291	(1)
Trunk Groups	291	(2)
Dial Peer Hunting	293	(1)
POTS Versus VoIP Outbound Dial Peers	293	(1)
Dial Peer Operational Status	294	(1)
Dial Peers Versus Cisco CallManager	295	(3)
Case Study: Configuring PSTN Access	298	(2)
Review Questions	300	(3)
Digit Manipulation	303	(24)
Basic Digit Manipulation	303	(3)
Digit Stripping	304	(1)
Forward Digits	305	(1)
Prefix Digits	306	(1)
Number Expansion	306	(1)
Voice Translation Rules and Profiles	307	(10)
Creating Voice Translation Rules	308	(1)
Building Regular Expressions	309	(1)
Using Regular Expressions When Rerouting a Call over the PSTN	310	(2)
Using Regular Expressions to Delete Specific Digits	312	(1)
Using Regular Expressions with Sets and Replacement Digits	312	(1)
Using Regular Expressions to Change the Call Type or Numbering Plan	313	(1)
Creating Voice Translation Profiles	314	(1)
Applying Voice Translation Profiles	314	(1)
Blocking Calls Using Voice Translation Rules and Profiles	315	(1)
Testing Voice Translation Rules	316	(1)
Manipulating Caller ID	317	(1)
CLID Commands	317	(1)
Station ID Commands	318	(1)
Order of Operation in Digit Manipulation	318	(2)
Troubleshooting Digit Manipulation	320	(1)
Case Study	321	(2)
Review Questions	323	(4)
Influencing Path Selection	327	(38)
Hunt Groups	328	(4)
Using the preference Command	328	(1)
Using the huntstop Command	329	(1)
Using Digit Manipulation	330	(2)
Using Trunk Groups	332	(1)
Tail-End Hop-Off	333	(1)
Call Admission Control	334	(25)
Local CAC Mechanisms	336	(1)
Physical DS0 Limitation	336	(1)
Maximum Connections	336	(1)
Local Voice Busyout	337	(1)
Measurement-Based CAC Mechanisms	337	(1)
IP SLA	338	(1)
Calculated Planning Impairment Factor and Mean Opinion Scores	338	(2)
Configuring IP SLA	340	(2)
IP Service Assurance Agent and Response Time Reporter	342	(2)
PSTN Fallback	344	(2)
Advanced Voice Busyout	346	(1)
Resource-Based CAC Mechanisms	346	(1)
Local Gateway Resources	346	(1)
Gatekeeper Zone Bandwidth	347	(1)
Resource Availability Indication	348	(1)
Resource Reservation Protocol	348	(1)
Gateway-Controlled RSVP	349	(2)
Configuring Gateway-Controlled RSVP	351	(1)
CallManager-Controlled RSVP with RSVP Agent	352	(2)
Configuring RSVP Agent	354	(4)
RSVP and the IntServ/DiffServ Model	358	(1)
Incorporating RSVP into the Voice Network	358	(1)
POTS-to-POTS Call Routing Considerations	359	(1)
Case Study: Implementing Gateway-Controlled RSVP	360	(2)
Review Questions	362	(3)
Configuring Class of Restrictions	365	(16)
COR Overview	365	(1)
COR Operation	366	(1)
Implementing COR	367	(3)
Assigning COR Lists with SRST	370	(1)
Assigning COR Lists with Cisco CallManager Express	371	(1)
Assigning COR Lists to SIP Phones with CallManager Express	372	(1)
Restricting Inbound Calls	372	(2)
Case Study: Implementing COR for Miami	374	(5)
Review Questions	379	(2)
SRST and MGCP Gateway Fallback	381	(30)
SRST Overview	381	(2)
Fallback Time	382	(1)
Restoral Time	383	(1)
Configuring SRST	383	(4)
Gateway Configuration	383	(3)
CallManager Configuration	386	(1)
Dial Plan Considerations	387	(3)
Planning	387	(1)
H.323 Gateways	388	(1)
MGCP Gateways	388	(1)
Direct Extension Dialing	389	(1)
Configuring SRST Dial Plan Patterns	389	(1)
SRST Features	390	(7)
Auto Attendant	390	(1)
Maximum Line Appearances	391	(1)
Conferencing	391	(1)
Transferring Calls	391	(1)
Transfer-Pattern	391	(1)
Consultative Transfers	392	(1)
Forwarding Calls	392	(1)
Voice-Mail Integration	393	(1)
Integrating with CUE	393	(1)
Integrating with a Centralized Voice-Mail System	393	(3)
Music on Hold	396	(1)
SIP SRST	397	(1)
Configuring SIP Registrar Server	397	(1)
Configuring a Voice Register Pool	397	(1)
Call Preservation	398	(1)
Secure SRST	399	(4)
Configuring Secure SRST	399	(4)
MGCP Gateway Fallback	403	(1)
Configuring MGCP Gateway Fallback	404	(1)
Verifying and Troubleshooting SRST	404	(1)
Verifying and Troubleshooting MGCP Gateway Fallback	405	(1)
Case Study: Integrating SRST with an Analog Voice-Mail System	405	(3)
Review Questions	408	(3)
DSP Resources	411	(28)
Need for DSP Resources	411	(1)
Determining the DSP Resources Required	412	(12)
DSP Types	413	(1)
PVDM Versus PVDM2	414	(1)
Voice Termination	414	(4)
Codec Complexity	418	(1)
Configuring Codec Complexity	419	(1)
Flex Complexity	420	(1)
DSP Sharing	421	(1)
Enabling DSP Sharing	422	(1)
Transcoding and MTP Resources	422	(1)
Conference Bridge Resources	423	(1)
Configuring DSP Resources	424	(10)
Configuring Transcoding and Conferencing (C549)	425	(4)
Configuring Enhanced Transcoding and Conferencing (C5510)	429	(5)
Transcoding for CallManager Express	434	(1)
Case Study: Add DSP Resources to the Miami Gateway	435	(2)
Review Questions	437	(2)
Using Tcl Scripts and VoiceXML	439	(18)
Tcl IVR and VoiceXML Application Overview	439	(3)
Programming Resources	441	(1)
Sample Applications	442	(2)
Auto Attendant	442	(1)
Basic ACD	443	(1)
Fax Detect	443	(1)
T.37 Store and Forward Fax	443	(1)
Malicious Call ID	443	(1)
Cisco Voice Portal	444	(1)
Embedded Event Manager	444	(1)
Downloading Tcl Scripts from Cisco.com	444	(1)
Configuring the Gateway to Use a Tcl Script	445	(3)
Initializing Tcl Scripts and Specifying Parameters	445	(1)
Applying TclScripts	446	(1)
Configuring Inbound Applications	446	(1)
Configuring Outbound Applications	446	(1)
Tcl Packages and Parameter Namespaces	446	(1)
Tcl Parameters in Cisco IOS Release 12.3(14)T and Above	447	(1)
Order of Parameter Precedence	448	(1)
Upgrading to Cisco IOS Release 12.3(14)T and Later	448	(1)
Implementing the AA Tcl Script	448	(2)
Creating Audio Files	450	(1)
Restrictions and Caveats	451	(1)
Case Study: Implementing ACD Application	451	(3)
Review Questions	454	(3)
Part III Gatekeepers	457	(92)
Deploying Gatekeepers	459	(26)
Gatekeeper Functionality	459	(2)
Gatekeeper Signaling	461	(8)
RAS Signaling	461	(3)
Gatekeeper Discovery Process	464	(2)
H.323 Call Flows Using Gatekeepers	466	(2)
Gatekeeper Update Protocol	468	(1)
Gatekeeper Transaction Message Protocol	469	(1)
E.164 Number Resolution	469	(3)
Zone Prefixes	470	(1)
Technology Prefixes	471	(1)
Gatekeeper Call Routing Process	472	(1)
Call Admission Control	472	(4)
Gatekeeper Deployment Models	476	(5)
Redundancy	476	(2)
Resource Availability Indicator	478	(1)
Directory Gatekeeper	479	(2)
Gatekeepers with CallManager	481	(1)
Security with Gatekeepers	482	(1)
Tokenless Call Authentication	483	(1)
Review Questions	483	(2)
Gatekeeper Configuration	485	(64)
Configuring Basic Gatekeeper Functionality	485	(13)
Configuring Gatekeeper Zones	486	(1)
Configuring Gateways to Use H.323 Gatekeepers	487	(2)
Technology Prefixes	489	(1)
Configuring Zone Prefixes and Dial Peers	490	(4)
Dynamic Prefix Registration	494	(2)
Configuring Call Admission Control	496	(2)
Multiple Gatekeeper Configurations	498	(2)
Configuring Directory Gatekeepers	500	(3)
Troubleshooting Gatekeepers	503	(5)
Registration Issues	503	(2)
Call Routing Issues	505	(3)
CallManager and Gatekeepers	508	(5)
Configuring a CallManager Gatekeeper Trunk	508	(5)
Gatekeeper Redundancy	513	(15)
Hot Standby Routing Protocol	513	(3)
Gatekeeper Clustering	516	(4)
Load Balancing	520	(1)
Troubleshooting Gatekeeper Clustering	521	(1)
Configuring Resource Availability Indicator	522	(6)
Configuring Gatekeeper Security	528	(8)
Troubleshooting Gatekeeper Security	530	(6)
Case Study: Deploying Gatekeepers to Assist in Migration to VoIP	536	(10)
Review Questions	546	(3)
Part IV IP-to-IP Gateways	549	(28)
Cisco Multiservice IP-to-IP Gateway	551	(26)
IP-to-IP Gateway Overview	551	(1)
Cisco Multiservice IP-to-IP Gateway	552	(4)
Architecture	553	(1)
Media-Handling Modes	554	(1)
Protocol Support	555	(1)
SIP Networks	555	(1)
H.323 Networks	555	(1)
Protocol Interworking	556	(1)
Basic Configuration	556	(4)
Via-Zones	558	(2)
IP-to-IP Gateway Features	560	(10)
Video Support	560	(1)
Address Hiding	561	(1)
Security	562	(1)
H.323 Deployments	562	(1)
SIP Deployments: Transport Layer Security	562	(1)
Digest Authentication	562	(1)
DTMF Interworking	563	(1)
Fax Support	564	(1)
Quality of Service	565	(1)
Call Admission Control	565	(1)
RSVP-Based CAC	565	(1)
Max Connections-Based CAC	565	(1)
IP Call Capacity-Based CAC	565	(1)
Thresholds Based on CPU, Memory, and Total Calls	566	(2)
Transcoding	568	(1)
VXML and Tcl Scripts	568	(1)
Billing	568	(1)
show Commands	569	(1)
debug Commands	569	(1)
Case Study: Providing Enterprise VoIP Trunking to VoIP Service of the Service Provider	570	(4)
CallManager Configuration	571	(3)
Review Questions	574	(3)
Appendix A Answers to Chapter-Ending Review Questions	577	(22)
Index	599

Excerpts

Preface Foreword Cisco IOS routers have shipped with voice interface cards since 1997, and after this capability was available the term voice gateway became part of the VoIP vernacular, seemingly overnight. The voice interfaces allowed routers to provide a critical interconnectivity link between the traditional data IP networks and the traditional voice (PSTN, PBXs, and key systems) networks. With this technology, the industry widely built toll bypass networks during the late 1990s: Enterprises connected their PBXs at different sites with VoIP "trunks" instead of with TIE lines or the PSTN, and service providers leveraged IP backbone networks to offer calling-card services and cut-rate long-distance and international calling. VoIP did not fascinate the popular imagination of the likes of Jeff Pulver of Voice-on-the Net (VON) and other industry observers until end-user-visible devices, such as IP phones, and IP-based applications brought the technology to the forefront. Voice gateway technology is still the pale sibling of the IP telephony world that creates no buzz, and yet it is also the workhorse of every single VoIP network. Even as VoIP endpoints become ever more prevalent in businesses and residences, voice gateways still provide critical interconnectivity with billions of traditional PSTN and PBX voice endpoints, without which companies cannot operate their communications networks. Although the idea of a voice gateway is conceptually simple enough--itrs"s a demarcation between two networks and translates the protocols from one (the TDM world) to the other (the IP world)--the technology has become increasingly sophisticated and the features more intertwined over the years. Choosing the "right" voice gateway and configuring the "right" set of features for a particular network is no longer the task for the uninitiated. The question I hear most frequently is whether to deploy MGCP, H.323, or SIP gateways. Cisco gateways are protocol agnostic and support all of these protocols and several variations thereof, and the answer to the question posed is not a simple one: The optimal network design depends on a large number of considerations. Some protocols and designs are better suited to particular types of networks, partly owing to the architecture of the protocols themselves and partly due to the features that have been chosen for implementation over the years. A Cisco Press book with comprehensive coverage focused entirely on voice gateway technology and features was a long time coming, and at last with this book, the authors provide an in-depth look at the breadth of voice gateway features and capabilities, as well as providing voice gateway configuration guidance. The book explains the major VoIP protocols, MGCP, H.323, and SIP, their structure and operation, and the considerations to choose among them. It discusses in detail the PSTN and PBX circuit connection technologies and choices. There are often multiple connection choices on the central office or PBX switch as well as on the voice gateway side of the circuit, and which of these would provide the features, cost points, and manageability that are optimal for your network might not be obvious at first glance. The book goes on to provide insights into many other areas of gateway selection and deployment, including the myriad choices in carrying fax and modem traffic over IP, dial plan features and digit manipulation tools, call admission control capabilities to keep voice traffic off the IP network when it does not have the quality levels to carry it, a review of DSP technology and operation, and an examination of IP connectivity implications and QoS features required to carry voice traffic with decent quality. Later chapters in the book also include discussions on pure IP-oriented topics such as TCL and VXML applications capabilities, confe