vocaltec ss7 solution white paper

VocalTec ArchitectureA Standards-based Platform for IP Telephony

______________________________________________________________________________________

VocalTec SS7 Solution

White PaperRelease 1.4

January 2001

VocalTec Communication

VocalTec SS7 Solution Page 1

Information in this document is subject to change without notice. This document may not bereproduced or transmitted in any form or by any means without the express written permission ofVocalTec Communications Ltd.

© 2001 VocalTec Communications Ltd. All rights reserved.

VocalTec®, VocalTec Gatekeeper, VocalTec Telephony Gateway and VocalTec NetworkManager are trademarks or registered trademarks of VocalTec Communications Ltd.All other trademarks are the property of their respective owners.

SS7 White Paper, 3rd edition – January 2001

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Publication number: VTWP- SS7 -01-2001-V3-R1-E



ContentsContentsIntroduction..........................................................................................................4

Overview ...................................................................................................................................... 4

SS7 Network ................................................................................................................................ 4

SS7 Advantages .......................................................................................................................... 5

SS7 Market .................................................................................................................................. 5

SS7 Technology/ Network Elements ........................................................................................... 5

SS7 Signaling Points ................................................................................................................... 6

Service Switching Point (SSP) ................................................................................................. 6

Signal Transfer Point (STP) ..................................................................................................... 6

Service Control Point (SCP)..................................................................................................... 6

SS7 Network Availability .......................................................................................................... 6

SS7 Signaling Links Types....................................................................................................... 7

SS7 Protocol Stack .................................................................................................................. 8

Message Transfer Part............................................................................................................. 8

ISDN User Part (ISUP)............................................................................................................. 9

Telephone User Part (TUP)...................................................................................................... 9

Signaling Connection Control Part (SCCP).............................................................................. 9

Transaction Capabilities Applications Part (TCAP).................................................................. 9

ISUP Call Flow ....................................................................................................................... 10

VocalTec’s SS7 Solution ....................................................................................11

VocalTec’s SS7 Solution ....................................................................................11

SS7 Introduction......................................................................................................................... 11

Migrating to SS7..................................................................................................................... 11

VocalTec SS7 Architecture .................................................................................................... 11

VocalTec SS7 Signaling Gateway.......................................................................................... 11

SS7 Configurations .................................................................................................................... 12

Non-Associated SS7 Configuration........................................................................................ 12

Associated SS7 Configuration................................................................................................ 13

Multiple Media Gateways Configuration................................................................................. 14

Redundant Signaling Gateways Configuration ...................................................................... 14

SS7 Solution Details .................................................................................................................. 15

Signaling Gateways Features ................................................................................................ 15

Network Redundancy/Availability ........................................................................................... 15



Signaling Gateway hook-ups ................................................................................................. 17

Media Gateway hook-ups....................................................................................................... 17

Support for Multiple Gateways ............................................................................................... 17

SS7 Management ...................................................................................................................... 18

Phone To Phone Call Flow ........................................................................................................ 19

Supported Services under SS7.............................................................................................. 16

Supported SS7 Standards...................................................................................................... 16

Supported SS7 Flavors .......................................................................................................... 16

Glossary..............................................................................................................20

Figures

Figure 1 - SS7 Signaling Points....................................................................................................... 6Figure 2 - SS7 Network Design for Availability................................................................................ 7Figure 3 - SS7 Signaling Link Types ............................................................................................... 7Figure 4 - SS7 Protocol stack.......................................................................................................... 8Figure 5 - SS7 ISUP Call Flow ...................................................................................................... 10Figure 6 - VocalTec SS7 Architecture ........................................................................................... 11Figure 7 - Associated Configurations ............................................................................................ 12Figure 8 - Associated Configurations ............................................................................................ 13Figure 9 – Multiple Media Gateways Configurations..................................................................... 14Figure 10 – Redundant Signaling Gateways Configurations ........................................................ 14Figure 12 – Phone-to-Phone Call Flow ......................................................................................... 19

Tables

Table 1 - ISUP Call Setup Messages............................................................................................ 10Table 2 - Supported SS7 Standards.............................................................................................. 16Table 3 - Supported SS7 Flavors .................................................................................................. 17



IntroductionIntroduction

OverviewSS7, also referred to as out-of-band signaling, is the common channel signaling protocolused for call handling within the Public Switched Telephone Network (PSTN). SS7 is theunderlying data communications protocol used by telephone networks to control call set-upand call routing, and to provide services such as caller ID and CLASS features. SS7 offerstelephone network management functions that are faster and more reliable, by managingvoice circuit functions on a separate, fully redundant data network.

SS7 was designed in the late 1970s and early 1980s for exchanging call control informationbetween the various network switches and databases in the PSTN. It replaces an earlierCommon Channel Inter-office Signaling system (CCIS, or SS6 in ITU terms) and offersseveral important advantages, including greater speed and flexibility. SS7 is now widelydeployed and is used to support services such as ISDN (Integrated Services Digital Network).

The global SS7 standard defined by ITU allows for national variants. Variants are defined bythe national Telecommunications Companies (Telcos). There may be more than one nationalvariant. ANSI is the international SS7 standard for T1 lines and ETSI is the standard for E1lines.

The SS7 standard allows network elements in the PSTN to exchange information over adigital signaling network to support wireless (cellular) call setup, routing and control.

SS7 NetworkAn SS7 network is a packet network operating in parallel with the public switched telephonenetwork. SS7 networks are designed for extremely high reliability using traditional telephonecompany techniques, i.e., providing full redundancy. An IP Network (such as the Internet)achieves high availability with routing protocols that route around failures. An SS7 networkachieves high availability by having two or more copies of everything — every router andevery connection (link). SS7 networks are typically engineered so that no link is loaded tomore than 40 percent of its capacity. In the event of a link failure, the remaining link can carryall the traffic with margin to spare.

SS7 network signaling uses relatively small messages that are efficiently packed. SS7typically runs on 64-Kbps links. Since the messages are extremely compact, a single 64-Kbps-link set (that is, pair of links) is capable of carrying the message traffic for over 50,000calls per hour.

SS7 allows a single flag byte between packets to denote both the end of the precedingpacket and the beginning of the next packet. It requires the constant transmission andreception of small “fill-in” signal units (packets), which can bombard an HDLC processor withinterrupts. And, with SS7, one must constantly monitor the error rate on each to identify linksthat may need to be removed from service. In combination, these features generally requirespecial-purpose hardware and/or firmware rather different from that used with Ethernet, X.25,or traditional IP transports.

The SS7 network is basically a packet network that controls the operation of the PSTN andprovides access for new services in the traditional telephone network.



SS7 AdvantagesThe advantages of using SS7 (over other PSTN signaling systems) are numerous:

• Faster call set-up, answer detection and call tear down

• One signaling channel can perform signaling for thousands of voice channels

• Increased information associated with the call

• Ability to reduce telecommunications costs by purchasing high capacity trunks

• Ease of upgrade to new services

• Suitable for mobile applications and wireless services

• Efficient and secure Telecommunications

• A high level of call security is provided through the monitoring of traps and callinformation

SS7 MarketA growing numbers of service providers around the globe, from the major Local ExchangeCarriers (LECs) and Inter Exchange Carriers (IXCs), to the wireless operators, mobileoperators and smaller carriers, are opening up for those vendors who can connect to the SS7network. In addition, corporate users are gaining indirect access to SS7 networks viagateway services offered by the major IXCs. As an example, a corporation with multiple,geographically dispersed call centers can improve operating efficiency by using their owncomputers and an SS7 gateway to specify routing for their inbound traffic on a call-by-callbasis. SS7 is the interface to connect this new application logic to the traditional circuit-switched network.

The following Telephony service providers commonly use SS7:

• International and long distance carriers

• Local carriers

• Large Internet Telephony Service Providers (ITSPs)

SS7 Technology/ Network ElementsSS7 messages are sent at 56-64 Kbps on bi-directional channels called signaling links. EachSS7 signaling link can support up to 4096 calls. Actual numbers depend on the network loadand type of equipment. Out-of-band signaling allows for faster call setup and more efficientuse of the voice channel. Out-of-band signaling also supports Intelligent Network (IN)services, which require signaling to network elements without voice trunks (e.g., databasesystems).

Each signaling point is uniquely identified by a numeric point-code. These include:

• Origination Point-Code (OPC) – address on the network of the originator of the signal

• Destination Point-Code (DPC) – used to identify the destination point on the network

Each signaling point uses a routing table (e.g., based on prefixes) to select the appropriatesignaling path for each message.



SS7 Signaling Points

Figure 1 - SS7 Signaling Points

A typical SS7 network consists of the following signaling points:

Service Switching Point (SSP)

The SSP is a switch that originates, terminates, or tandems (transfers) calls. The SSP is usedto set up, manage and release voice channels and to complete calls.

The SSP may send query messages to a centralized database (SCP), e.g. to map a toll-free1-800/888 virtual number to an actual number. The purpose of these queries is to enhancethe functionality of the SSP by providing external information (such as routing information forthe 800/888 destination mapping).

A tandem SSP tunnels the call information to the outgoing trunk, while a terminating SSP(which ends the SS7 signaling section of the call) does not. A terminating SSP is for example,when the call continues over a PRI line or an analog line to a customer. An SSP can beterminating for one call and tandem for another destination (the call goes through to anotherSSP or CO). An SSP can be tandem for all calls.

Signal Transfer Point (STP)

An STP acts as a hub or router for SS7 messages (including call setup, management andteardown messages, call information and all database queries). This improves networkutilization and alleviates the need for a meshed network.

An STP can also act as a firewall to screen SS7 messages exchanged with other networks.For that purpose it may perform global title translation – translating OPCs and DPCs betweenSS7 sub-networks.

Service Control Point (SCP)

An SCP provides application services (such as 1-800 mapping). An SCP usually drives adatabase to hold the permanent data. The SCP services, known as Service ControlFunctions (SCF), provide data in response to queries.

SS7 Network Availability

SS7 network elements (such as SCPs, STPs and links) commonly appear in mated pairconfigurations (e.g., a pair of STPs serve a PBX), so that there is always an alternative routefor traffic in the event that one element fails. Elements are often placed at separategeographical locations. Each site is physically connected to at least two other sites. A link-set



is the group of links that service the same connection between points A and B. If one of thelinks (in a link-set) fails, the signaling traffic is rerouted over another link in the set. Traffic isalso load-balanced among all links in the link-set. Error correction and retransmission allowfor continued service in the event of any signaling point or link failure.

Telephone

Telephone

TelephoneTelephone

Signaling Link

Subscriber Line

Voice TrunkSSP

STP

SCP

Network 1 Network 2

Telephone

Figure 2 - SS7 Network Design for Availability

SS7 Signaling Links Types

Figure 3 - SS7 Signaling Link Types

The following signaling links are based on the SS7 signaling network:

• A Link – access link; between the SCP/SSP and STP

• B Link - bridge link, between STP and STP (quad B links between networks)



• C Link – cross link; between STP and STP (mated pair). This is used only when an STPhas no other route available to a destination signaling point due to link failure(s)

• D Link - diagonal link; between secondary STP pair (e.g., local or regional) and primarySTP pair (e.g., inter-network gateway)

• E Link - extended link; between the SCP/SSP and STP

• F Link - fully associated link; connects two signaling endpoints in association with thevoice trunks. F links are commonly used in networks without STPs

The VocalTec SS7 Architecture supports both A-links and F-Links

SS7 Protocol Stack

Hardware and software functions of the SS7 protocol are divided into functional abstractionscalled “levels”. These levels map loosely to the Open Systems Interconnect (OSI) 7 layermodel.

Figure 4 - SS7 Protocol stack

Message Transfer Part

The message transfer part (MTP) is divided into three levels:

• MTP Level 1 - defines the physical, electrical, and functional characteristics of the digitalsignaling link. Examples are: E-1 (2048 kb/s; 32 * 64 kb/s channels), T-1 (1536 kbps; 24* 64 kb/s channels) and V.35 (64 kb/s).

• MTP Level 2 - Ensures accurate end-to-end transmission of a message across asignaling link. Flow control, message sequence validation, and error checking. If there isan error on a signaling link this layer ensures that the message (or set of messages) isretransmitted.

• MTP Level 3 - provides message routing between signaling points in the SS7 network.MTP Level 3 re-routes traffic away from failed links and signaling points and controlstraffic when congestion occurs.



ISDN User Part (ISUP)

Protocol used to set-up, manage, and release trunk circuits that carry voice and databetween terminating line exchanges. Used for both ISDN and non-ISDN calls.

Telephone User Part (TUP)

TUP is an older variant of ISUP. In some parts of the world (e.g., China, Brazil), TUP is usedto support basic call setup and tear-down. TUP handles analog circuits only. In mostcountries, ISUP has replaced TUP for call management.

Signaling Connection Control Part (SCCP)

Provides connectionless and connection-oriented network services and Global TitleTranslation (GTT) capabilities above MTP Level 3. SCCP is used as the transport layer forTCAP-based services.

Transaction Capabilities Applications Part (TCAP)

Supports the exchange of non-circuit related data between applications across the SS7network. TCAP is provided over SCCP.

TCAP Example – Service

Queries and responses sent between SSPs and SCPs are carried in TCAP messages, e.g.,to determine the routing number associated with a dialed 800 number and to check thepersonal identification number (PIN) of a calling card user.

TCAP Example – Roaming

In mobile networks (IS-41 and GSM), TCAP carries Mobile Application Part (MAP) messagessent between mobile switches and databases to support user authentication, equipmentidentification, and roaming.

When a mobile subscriber roams into a new mobile switching center (MSC) area, theintegrated visitor location register (VLR) requests service profile information from thesubscriber's home location register (HLR) using mobile application part (MAP) informationcarried within TCAP messages.



ISUP Call Flow

Figure 5 - SS7 ISUP Call Flow

The following table describes the ISUP Call Setup messages illustrated above.

Message Description

IAM Initial address Message – contains the dialed E164 number address.

ACM Address Complete Message – voice channel open and setup is completed.

ANM Answer Supervision Number Message – the destination user answered.

REL Release Message - release the call.

RLC Release Complete Message – call release complete.

Table 1 - ISUP Call Setup Messages



VocalTec’s SS7 SolutionVocalTec’s SS7 Solution

SS7 Introduction

Migrating to SS7

VocalTec’s SS7 solution is based on the VocalTec architecture, a standards-based multi-service IP Telephony platform in which VocalTec Telephony Gateways provide the bridgebetween the IP domain and the PSTN realm. The VocalTec Telephony Gateways interface tothe regular (non-SS7) PSTN world for both voice and signaling. When connecting to an SS7PSTN network, the signaling trunks carry SS7 control messages. Supporting the SS7interface is accomplished by adding the VocalTec SS7 Signaling Gateways, which acts asthe signaling front-end.

VocalTec SS7 Architecture

The VocalTec Telephony Gateways (VGW 120 or VGW 2000) act as media gatewayshandling the voice trunks. The VocalTec SS7 Signaling Gateways acts as signaling gatewaysproviding the signaling translation from SS7 to Media Gateway call control. SS7 support isprovided by VocalTec SS7 Signaling gateways, which function as SS7 transit exchangeand/or outgoing international gateway exchange.

Service Provider Network Operating Center

Figure 6 - VocalTec SS7 Architecture

VocalTec SS7 Signaling Gateway

VocalTec SS7 Signaling Gateway is an essential component of the VocalTec SS7 solution.VocalTec SS7 Signaling Gateways process SS7 stacks - including Message Transfer Part(MTP) level 2/3 and TUP or ISUP messages – and convert them to SS7 over IP messages.The signaling gateway connects to the traditional SS7 PSTN via E1/T1 or V.35. A Signalinggateway can connect to multiple VocalTec Telephony (media) Gateways over the IP network.



SS7 Configurations

Non-Associated SS7 Configuration

SSPVGW w/ SS7

PCM (E1/T1)

VoIP

Signaling (ISUP over IP)

SS7 ISUP

Signaling GW

VGW

Single SpanSingle Span

SSPVGW w/ SS7

PCM (E1/T1)VoIP


SS7 ISUP

Signaling GW

VGW

Quad SpanQuad Span

Figure 7 – Non-Associated Configurations

In this configuration the signaling and PCM packets (audio) are carried via two separatetrunks. Signaling passes directly to the signaling gateway, which is connected to the mediagateway over IP. PCM packets pass directly to the media gateway.

In the trunk used for signaling, one or more channels carry the signaling data (depending onconfiguration). The other channels are unused. In SS7 terms, the signaling trunk is known asan "A-Link" (See SS7 Signaling Links Types on page 7 in this document). It is possible totransmit more than one signaling channel over a trunk or multiple trunks for creating link-sets.Having the signaling go through a separate media, allows supporting 31/24 voice circuits ineach E1/T1.



Associated SS7 Configuration

SSPVGW w/ SS7

PCM (E1/T1)

VoIP


PCM +

SS7 ISUPSignaling GW

VGW

Single SpanSingle Span

SSPVGW w/ SS7

PCM (E1/T1)

VoIP

PCM (E1/T1)


PCM +

SS7 ISUPSignaling GW

VGW

Quad SpanQuad Span

Figure 8 - Associated Configurations

This configuration shows the signaling trunk used to transfer both PCM audio and SS7signaling. In SS7 terms, this trunk is known as an "F-Link" (See SS7 Signaling Links Typeson page 7 in this document ).

On the mixed signaling/PCM trunk, PCM and signaling pass through the signaling gateway.The signaling gateway separates the signaling channel from the PCM channels. The PCM isthen sent over a PCM trunk to the media gateway, while the signaling travels over IP to themedia gateway for call control. In configurations with more than one voice trunk, only onetrunk carries mixed PCM + Signaling packets. The other (PCM only) trunks go directly fromthe SSP to the media gateway. The mixed trunk supports 30/23 voice circuits (may be less ifmultiple circuits are used for SS7 signaling). The PCM only trunks support 31/24 voicecircuits in each E1/T1.



Multiple Media Gateways Configuration

SSP

VoIP

VGW(s)

VGW w/ SS7

PCM (E1/T1)

Signaling

PCM +

SS7 ISUP

Signaling GW

VoIP

VoIP PCM (E1/T1)

PCM (E1/T1)

Figure 9 – Multiple Media Gateways Configurations

In a configuration with multiple media gateways, the Signaling Gateway routes the signalinginformation to the proper media gateway according to the trunk configuration.

Redundant Signaling Gateways Configuration

POP B

POP A

STP A

STP B

Figure 10 – Redundant Signaling Gateways Configurations



SS7 Solution Details

Signaling Gateways Features

The Signaling Gateway configuration determines the link-set division, the individual links,user parts (ISUP/TCAP and the variant that is running on each link set), the point-code, andadditional configuration parameters.

The signaling gateway supports the following features:

• Supports E1/T1 interfaces (V.35 line can be supplied on demand). Support up to 24signalling trunk interfaces (depending on type of SS7 Signaling gateway model)

• Supports multiple distributed hosts (media gateways) - up to 128 hosts (connecting morethan 32 media gateways requires a proxy)

• Supports fault tolerance, high availability and redundancy, through Load sharing signalinggateways. Supports multiple link redundancy, signaling card redundancy and signalinggateway redundancy

• Supports ITU-T and ANSI standards as well as over 20 country variants. Other variantscan be provided upon request

• Support for ISUP, including Basic call control, Circuit Management (circuits un/blocking,circuit groups and resetting circuits)

• Supports supplementary services

• Functions as SS7 transit exchange and/or outgoing international gateway exchange

• Supports multiple SS7 standards (see Table 2 - Supported SS7 Standards Table)

• Alarm capabilities on all MTP levels 1-3 and on ISUP

Network Redundancy/Availability

Network redundancy is implemented at the following levels:

• Link level

• Having every two elements connected using two or more links, which together can bedefined as a link set – thus providing fail over.

• Having each node (such as STP) connect with two other nodes thus providing failover via an alternate node. If one link or node fails then the other links on the link setcan take over the load.

• Board level – The signaling gateway can have up to 12 signaling boards. Board failuregenerates the same effect as link failure – causing other links in the link-set to take over.

• Signaling gateway level redundancy – two signaling gateways can act in a load-sharing mode. If one of the signaling gateways fails, then the other can take over. Allactive calls remain intact.



Supported Services under SS7

All VocalTec services are all supported within the VocalTec SS7 architecture, including:

• Phone-to-Phone, Fax-to-Fax

• Post Paid and Pre-paid Calling card

• Web-to-Phone, PC-to-Phone

• Virtual Private Networks (VPN)

• Interdomain (IDM)

Supported SS7 Standards

SS7 Standard Description SupportedQ.700-Q.709 T1.111.3 - ANSI Messaging Transfer Part (MTP) YesQ.710 PBX Application --Q.711-Q.716 T1.112- ANSI Signaling Connection Control Part (SCCP) YesQ.721-Q.725 Telephone User Part (TUP) YesQ.730 ISDN Supplementary Services YesQ.741 Data User Part (DUP) --Q.761- Q.766T1. 113- ANSI 1988/1992

ISDN User Part (ISUP) Yes

Q.771-Q.775 T1.114- ANSI Transaction Capabilities Application Part(TCAP)

--

Q.791- Q.795 Monitoring, Operations, and Maintenance PartialQ.780- Q.785 Test Specifications Yes

Table 2 - Supported SS7 Standards

Supported SS7 Flavors

VocalTec SS7 architecture supports the following country variants. Other variants can beprovided upon request.

Country SS7 Flavor DetailsArgentina ITU ISUPAustralia BTNUP + ITU ISUPBelgium ITU ISUPCanada ITU ISUPChile ITU ISUPChina ITU ISUP TUP versionFrance ITU ISUP French TUPGermany ITU ISUPHong Kong ITU ISUPHungary ITU ISUPIndonesia ITU ISUPIsrael ITU ISUPItaly ITU ISUPJapan MTP (Q.701), Signaling Network (Q.704)KoreaNew Zealand BTNUP + ITU ISUPNetherlands ITU ISUPPeru ITU ISUP



Country SS7 Flavor DetailsPortugal ITU ISUPSingapore ITU ISUPSouth Africa ITU ISUPSpain ITU ISUPSweden ITU ISUPTaiwan ITU ISUPUK BTNUP + ITU ISUPUnited Emirates ITU ISUPUSA ANSI ISUP

Table 3 - Supported SS7 Flavors

Signaling Gateway hook-ups

Connection with SSP(s) and/or STP(s)

The signaling gateway connects to the SS7 network over E1/T1/V.35 lines using the ITU-TISUP protocol (ANSI-ITU and TUP can be supported upon request). The physical connectionis over T1/E1. V.35 can be provided upon request.

Connection with Media Gateway

The signaling gateway can be connected to media gateways as follows:

• IP connection only – This connection type is used in a non-associated SS7 mode (A-Link). The signaling is transmitted over a dedicated trunk (E1/T1) from the PSTN to theSignaling Gateway. The signaling is then transmitted from the Signaling Gateway to themedia gateway over an IP connection.

• IP connection + E1/T1 trunk – This connection type is used in a full-associated SS7mode (F-Link). The trunk used for signaling is also used to pass PCM audio (thetimeslots, besides those used for signaling, are used for audio). The Signaling Gatewayperforms a drop & insert function, extracting/inserting the signaling timeslot. The signalingis transmitted to the media gateway over IP. The audio is passed through (withoutmodification) to an outgoing trunk that carries the PCM to the media gateway.

Media Gateway hook-ups

The connection between the switch and the gateway is a regular PCM E1/T1 connection forvoice timeslots. The switch can pass voice lines that have no signalling directly to thegateway and visa versa.

Support for Multiple Gateways

If connected via the Ethernet, each gateway is considered as a Signaling gateway host. Asingle Signaling Gateway can support up to 128 media gateway hosts (connecting more than32 gateways requires a proxy).



SS7 ManagementThe Signaling gateway needs no direct management since it is part of the Media gateway. Allmanagement take place from the VNM as part of the Media Gateway management.

SS7 Monitoring

All SS7 alarms are displayed on the Media Gateway machine console as well as on the VNM.

Two types of alarms are generated:

• Internal alarms – these are generated by the internal stacks/engines/application. Forexample, when the NIC reports a lost connection, the PCM interface reports CRC erroron one of the channels.

• External alarms – these are received via the interfaces and report problems. Forexample, VGK reports login denied or the SS7 network reports lost trunksynchronization.

The Signaling Gateway is a logical part of the Media Gateway. It relays any problems (suchas internal problems) or errors (such as SS7 network errors) to the Media Gateway it isconnected to.

SS7 Configuration

SS7 configuration is available through the media gateway configuration. When the mediagateway uses an SS7 signaling connection to the PSTN, a special SS7 configuration tabprovides control over SS7 related aspects. The following SS7 parameters can be configuredusing VNM for a specific media gateway:

• VGW host ID - this identifies the specific media gateway when more than one mediagateway is connected to the same signaling gateway. The first media gateway isnumbered zero (0), the next one is numbered one (1) and so on.

• SIU IP address – Defines the signaling gateway IP address to enable communicationbetween the media gateway and the signaling gateway.

• Channel mapping - when the signaling gateway transports voice as well as signaling,sometimes the channels on the trunk from the SS7 network are mapped to anotherchannel number on the trunk between the signaling gateway and the VGW. When thishappens, there is a need to inform the VGW of this mapping. This mapping data is usedby VGW to match messages received from the Telephony interface in the VGW tomessages received from the SS7 network.

• Additional SS7 parameters – these are for advanced use only (e.g., gateway timeouttimers).

The SS7 network configuration does not require daily maintenance unless deployment ischanged (e.g., add trunks, change point codes, etc). All other low level SS7 parameters canbe configured via TELNET (over IP), FTP (over IP) or a VT-100 Terminal connected directly(RS-232) to the signaling gateway, which uses its own command-line configuration. Low-levelparameters should only be modified by field technicians only.



Phone To Phone Call Flow

Phone A STPSignalingGateway Gatekeeper STP Phone B

IAM

Dial

ARQ

ACF

Set-up

ARQ

ACF

IAM

Answer

Ring

ANM

Connect

ANM

Voice

ACM

ACM

SignalingGateway

Figure 11 – Phone-to-Phone Call Flow

1. The user picks up the phone and dials the destination number.

2. The PSTN switch routes the call to the gateway using ISUP Initial Address Message.

3. The gateway sends an Address Complete Message back to the PSTN and passes thedestination number to the gatekeeper using the RAS ARQ message.

4. The gatekeeper authenticates and authorizes the call, responding with ACF messagethat includes the destination gateway IP address.

5. The gateway sends a H.225 Setup message to the destination gateway.

6. The termination gateway requests admission from the gatekeeper (RAS ARQ message).

7. The gatekeeper grants permission for the call (RAS ACF message).

8. The termination gateway sends an IAM message to the PSTN.

9. The switch sends a ring signal to the phone.

10. When the user picks up the phone, the switch sends an ANM to the originating gateway.

11. The termination gateway sends a Connect message to the originating gateway (bothgateway’s send IRR (call start) message to the VGK).

12. The originating gateway sends an ANM message to the origination switch.

13. Voice connection is established through the Audio trunk.



GlossaryGlossaryAIN Advanced Intelligent Network - a separate data network that provides the telephone

network with advanced call control and enhanced services features (American version ofIN).

ANI Automatic Number Identification - provides the called party with the calling party’s number.

CCS7 Common Channel Signaling 7 - European name for SS7.CLASS Customer Local Area Signaling Services - a Bellcore definition of local calling services

including call forwarding, caller ID, and call waiting. CO equipment is usually marked withCLASS number, such as CLASS 4 or CLASS 5. This number defines what kind ofservices this CO offers.

DNIS Dialed Number Identification Service - This is a feature that provides the destinationnumber. It is used by the 800-services for real-destination resolution. However DNIS isalso available for other non-800 services (e.g. premium-rate-service).

IN Intelligent Network - a separate data network to provide the telephone network withadvanced call control and enhanced services features all IN services require SS7signaling as underlay foundation. However SS7 does not imply IN and vice versa.

INAP Intelligent Network Application Part - an IN application layer.

ISUP ISDN User Part - an SS7 layer which supports implementation of ISDN.IXC Inter Exchange Carrier - a long distance phone company.

LEC Local Exchange Carrier - the local phone company.

MTP Message Transfer Part - lower layers of the SS7 protocol stack (physical, link network).

OPC Origination Point Code – address on the network of the originator of the signal.

DPC Destination Point Code – used to identify the destination point on the network.SCP Service Control Point - an IN definition of a control element, typically a database which is

used to determine how to handle the call.

SCCP Signaling Control Connection Part - an SS7 protocol layer, which provides data servicesused to support TCAP and other higher-level layers.

SLK Signaling Link - the physical transmission line connecting the individual node in an SS7Network.

SP Signaling Point - an SS7 signaling point.

SS7 Signaling System 7 - the international data communications protocol standard whichsupports advanced telephone services and IN.

SSP Service Switching Point - an IN definition for an originator or terminator of calls and SS7messages, typically a central office (CO).

STP Signal Transfer Point - an IN definition for a network node in an SS7 network that does notterminate calls.

TCAP Transaction Capabilities Application Part - a higher-level SS7 protocol layer, whichsupports transaction-based applications.

VOIP Voice Over Internet Protocol. A standard term referring to transferring voice over the openInternet or IP networks.

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