SAS Technical Note Ver. 6.2

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Multi-Service Business Gateways

VoIP Media Gateways

SIP Protocol

July 2011

Document # LTRT-29802

Technical NoteStand-Alone Survivability (SAS) Application


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Technical Note Contents

Document #: LTRT-29802 3 July 2011

Table of Contents

1 Introduct ion ......................................................................................................... 7

2 SAS Operating Modes ......................................................................................... 9

2.1 SAS Outbound Mode ............................................................................................. 102.1.1 Normal State ............................................................................................................ 102.1.2 Emergency State ..................................................................................................... 11

2.2 SAS Redundant Mode ........................................................................................... 12

2.2.1 Normal State ............................................................................................................ 122.2.2 Emergency State ..................................................................................................... 132.2.3 Exiting Emergency State and Returning to Normal State ....................................... 14

3 SAS Routing ...................................................................................................... 15

3.1 SAS Routing in Normal State ................................................................................. 15

3.2 SAS Routing in Emergency State .......................................................................... 17

4 SAS Configuration ............................................................................................ 194.1 General SAS Configuration .................................................................................... 19

4.1.1 Enabling the SAS Application .................................................................................. 194.1.2 Defining Common SAS Settings .............................................................................. 20

4.1.2.1 Configuring SAS Parameters ...................................................................204.1.2.2 Configuring SAS Proxy Set ......................................................................22

4.2 Configuring SAS Outbound Mode .......................................................................... 23

4.3 Configuring SAS Redundant Mode ........................................................................ 24

4.4 Configuring Gateway Application with SAS ........................................................... 25

4.4.1 Gateway with SAS Outbound Mode ........................................................................ 254.4.2 Gateway with SAS Redundant Mode ...................................................................... 28

4.5 Advanced SAS Settings ......................................................................................... 304.5.1 Manipulating URI user part of Incoming REGISTER ............................................... 304.5.2 Manipulating Destination Number of Incoming INVITE ........................................... 324.5.3 SAS Routing Based on SAS Routing Table Rules .................................................. 334.5.4 Blocking Calls from Unregistered SAS Users.......................................................... 364.5.5 Configuring SAS Emergency Calls .......................................................................... 374.5.6 Adding SIP Record-Route Header to SIP INVITE ................................................... 384.5.7 Replacing Contact Header for SIP Messages ......................................................... 38

5 Viewing Registered SAS Users ........................................................................ 39

6 Maximum SAS Regis tered Users ..................................................................... 41

6.1 SAS Cascading ...................................................................................................... 41


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Technical Note 4 Document #: LTRT-29802

Stand-Alone Survivability

List of Figures

Figure 2-1: SAS Outbound Mode in Normal State (Example) ................................................................ 10Figure 2-2: SAS Outbound Mode in Emergency State (Example) ......................................................... 11Figure 2-3: Example of SAS Redundant Mode in Normal State ............................................................ 12Figure 2-4: SAS Redundant Mode in Emergency State (Example) ....................................................... 13

Figure 3-1: Flowchart of INVITE from UA's in SAS Normal State .......................................................... 15Figure 3-2: Flowchart of INVITE from Primary Proxy in SAS Normal State ........................................... 16Figure 3-3: Flowchart for SAS Emergency State ................................................................................... 17Figure 4-1: Enabling SAS in Applications Enabling Page ...................................................................... 19Figure 4-2: Common SAS Settings in SAS Configuration Page ............................................................ 21Figure 4-3: Defining UAs' Proxy Server in Proxy Sets Table Page ........................................................ 22Figure 4-4: Defining SAS Outbound Mode in SAS Configuration Page ................................................. 23Figure 4-5: Defining SAS Redundant Mode in SAS Configuration Page ............................................... 24Figure 4-6: Enabling Proxy Server for Gateway Application in Proxy & Registration Page ................... 25Figure 4-7: Defining Proxy Server for Gateway Application in Proxy Set Page ..................................... 26Figure 4-8: Disabling user=phone in SIP URL in SIP General Parameters Page ................................. 27Figure 4-9: Enabling Proxy Server for Gateway Application in Proxy & Registration Page ................... 28Figure 4-10: Defining Proxy Servers for Gateway Application in Proxy Set Page ................................. 29

Figure 4-11: Disabling user=phone in SIP URL in SIP General Parameters Page ............................... 29Figure 4-12: Manipulating User Part in Incoming REGISTER in SAS Configuration Page ................... 31Figure 4-13: Manipulating INVITE Destination Number in IP to IP Inbound Manipulation Page ........... 32Figure 4-14: Defining SAS Routing Rules in IP2IP Routing Page ......................................................... 33Figure 4-15: Blocking Unregistered SAS Users in SAS Configuration Page ......................................... 36Figure 4-16: Defining SAS Emergency Numbers in SAS Configuration Page ....................................... 37Figure 5-1: Viewing Registered SAS Users in SAS Registered Users Page ......................................... 39Figure 6-1: SAS Cascading Using SAS Routing Table - Example......................................................... 42Figure 6-2: SAS Cascading Using SAS Redundancy Mode - Example ................................................. 43

List of TablesTable 4-1: SAS IP2IP Routing Table Parameters .................................................................................. 33Table 6-1: Max. SAS Registered Users per Device .............................................................................. 41


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Technical Note Notices


Notice

This document describes the Stand-Alone Survivability (SAS) application.

Information contained in this document is believed to be accurate and reliable at the time ofprinting. However, due to ongoing product improvements and revisions, AudioCodes cannotguarantee the accuracy of printed material after the Date Published nor can it acceptresponsibility for errors or omissions. Updates to this document and other documents as wellas software files can be viewed by registered customers athttp://www.audiocodes.com/downloads.

Copyright 2011 AudioCodes L td. All rights reserved.

This document is subject to change without notice.

Date Published: July-10-2011

TrademarksAudioCodes, AC, AudioCoded, Ardito, CTI2, CTI, CTI Squared, HD VoIP, HD VoIPSounds Better, InTouch, IPmedia, Mediant, MediaPack, NetCoder, Netrake, Nuera, OpenSolutions Network, OSN, Stretto, TrunkPack, VMAS, VoicePacketizer, VoIPerfect,VoIPerfectHD, What's Inside Matters, Your Gateway To VoIP and 3GX are trademarks orregistered trademarks of AudioCodes Limited. All other products or trademarks areproperty of their respective owners. Product specifications are subject to change withoutnotice.

WEEE EU Directive

Pursuant to the WEEE EU Directive, electronic and electrical waste must not be disposed

of with unsorted waste. Please contact your local recycling authority for disposal of thisproduct.

Customer Support

Customer technical support and service are generally provided by AudioCodes'Distributors, Partners, and Resellers from whom the product was purchased. For technicalsupport for products purchased directly from AudioCodes, or for customers subscribed toAudioCodes Customer Technical Support (ACTS), [email protected].

Abbreviations and Terminology

Each abbreviation, unless widely used, is spelled out in full when first used.
http://www.audiocodes.com/downloadshttp://www.audiocodes.com/downloadsmailto:[email protected]:[email protected]:[email protected]:[email protected]://www.audiocodes.com/downloads


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Reader's Notes


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Technical Note 1. Introduction


1 IntroductionAudioCodes Stand-Alone Survivability (SAS) application has been specifically designedand developed to eliminate single, point-of-failure issues for enterprises employing acentralized, hosted IP-PBX or IP Centrex network. Even during a communication failurewith the enterprise's IP-PBX or IP Centrex entities (e.g., disconnection of Internet / WAN orproxy server), SAS ensures continuous telephony communication for the enterprisetelephony users (SIP user agents). During such a communication failure, SAS maintainsvoice call service capabilities for calls between UAs (i.e., internal calls), and for callsbetween UAs and the PSTN (if the device is connected to the PSTN network).

Notes:

Throughput this document, the term user agent(UA) refers to theenterprise's LAN phone user (i.e., SIP telephony entities such as IPphones).

Throughout this document, the term proxy or proxy serverrefers to thecentralized IP Centrex or IP-PBX of the enterprise.

Throughout this document. the term SAS refers to the SAS applicationrunning on the device.


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Reader's Notes


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Technical Note 2. SAS Operating Modes


2 SAS Operating ModesThe device's SAS application can be implemented in one of the following main modes:

Outbound Proxy:In this mode, SAS receives SIP REGISTER requests from theenterprise's UAs and forwards these requests to the external proxy (i.e., outbound

proxy). When a connection with the external proxy fails, SAS enters SAS emergencystate and serves as a proxy, by handling internal call routing for the enterprise's UAs -routing calls between UAs and if setup, routing calls between UAs and the PSTN.

Redundant Proxy:In this mode, the enterprise's UAs register with the external proxyand establish calls directly through the external proxy, without traversing SAS (or thedevice per se'). Only when connection with the proxy fails, do the UAs register withSAS, serving now as the UAs redundant proxy. SAS then handles the calls betweenUAs, and between the UAs and the PSTN (if setup). This mode is operational onlyduring SAS in emergency state. This mode can be implemented, for example, forproxies that accept only SIP messages that are sent directly from the UAs.

Note: It is recommended to implement the SAS outbound mode.


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2.1 SAS Outbound Mode

This section describes the SAS outbound mode, which includes two states - normal andemergency.

2.1.1 Normal State

In normal state, SAS receives REGISTER requests from the enterprise's UAs and forwardsthem to the external proxy (i.e., outbound proxy). Once the proxy replies with a SIP 200OK, the device records the Contact and address of record (AOR) of the UAs in its internalSAS registration database. Therefore, in this mode, SAS maintains a database of all theregistered UAs in the network. In addition, SAS continuously maintains a keep-alivemechanism toward the external proxy, using SIP OPTIONS messages. The figure belowillustrates the operation of SAS outbound mode in normal state:

Figure 2-1: SAS Outbound Mode in Normal State (Example)

Enterprise

LAN

IP

Network

IPCentrex

Server

Enterprise

IP-Phones

Normal State

AudioCod es Device

Running SAS Application


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2.2 SAS Redundant Mode

In SAS redundant mode, the enterprise's UAs register with the external proxy and establishcalls directly through it, without traversing SAS (or the device per se'). Only whenconnection with the proxy fails, do the UAs register with SAS, serving now as the UAs

redundant proxy. SAS then handles the calls between UAs, and between the UAs and thePSTN (if setup).

This mode is operational only during SAS in emergency state.

Note: In this SAS deployment, the UAs (e.g., IP phones) must support configurationfor primary and secondary proxy servers (i.e., proxy redundancy), as well ashoming. Homing allows the UAs to switch back to the primary server from thesecondary proxy once the connection to the primary server returns (UAscheck this using keep-alive messages to the primary server). If homing is notsupported by the UAs, you can configure SAS to ignore messages receivedfrom UAs in normal state (the 'SAS Survivability Mode' parameter must be

set to 'Always Emergency' / 2) and thereby, force the UAs to switch back totheir primary proxy.

2.2.1 Normal State

In normal state, the UAs register and operate directly with the external proxy.

Figure 2-3: Example of SAS Redundant Mode in Normal State

Enterprise

LAN

IPNetwork

IPCentrex

Server

Enterprise

IP-Phones

Normal State

AudioCodes Device



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Technical Note 2. SAS Operating Modes


2.2.2 Emergency State

If the UAs detect that their primary (external) proxy does not respond, they immediatelyregister to SAS and start routing calls to it.

Figure 2-4: SAS Redundant Mode in Emergency State (Example)

Enterprise

LAN

IP

Network

IPCentrex

Server

Enterprise

IP-Phones

Emergency

State

Aud ioCodes Device


PSTN


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2.2.3 Exiting Emergency State and Returning to Normal State

Once the connection with the primary proxy is re-established, the following occurs:

UAs:switch back to operate with the primary proxy.

SAS:ignores REGISTER requests from the UAs, forcing the UAs to switch back tothe primary proxy.Note:This is only applicable if the 'SAS Survivability Mode' parameter is set to'Always Emergency' (2).


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Technical Note 3. SAS Routing


3 SAS RoutingThis section provides flowcharts describing the routing logic for SAS in normal andemergency states.

3.1 SAS Routing in Normal StateThe flowchart below shows the routing logic for SAS in normal state for INVITE messagesreceived from the UAs.

Figure 3-1: Flowchart o f INVITE from UA's in SAS Normal State


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The flowchart below shows the routing logic for SAS in normal state for INVITE messagesreceived from the external proxy.

Figure 3-2: Flowchart of INVITE from Primary Proxy in SAS Normal State


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Technical Note 3. SAS Routing


3.2 SAS Routing in Emergency State

The flowchart below shows the routing logic for SAS in emergency state.

Figure 3-3: Flowchart for SAS Emergency State


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Reader's Notes


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Technical Note 4. SAS Configuration


4 SAS ConfigurationSAS supports various configuration possibilities, depending on how the device is deployedin the network and the network architecture requirements. This section provides step-by-step procedures on configuring the SAS application, using the device's Web interface.

The SAS configuration includes the following:General SAS settings - common to all deployment types (see Section4.1on page19)

SAS outbound mode (see Section4.2 on page23)

SAS redundant mode (see Section4.3 on page24)

Device running the Gateway application together with the SAS application (seeSection4.4 on page25)

Optional, advanced SAS features (see Section4.5 on page30)

4.1 General SAS Configuration

This section describes the general configuration required for the SAS application. This

configuration is applicable to all the SAS modes.

4.1.1 Enabling the SAS Application

Before you can begin configuring SAS, you need to enable the SAS application on thedevice. Once enabled, the device's Web interface provides the SAS pages for configuringSAS.

Note: The SAS application is available only if the device is installed with the SASSoftware Upgrade Key. If your device is not installed with the SAS feature,please contact your AudioCodes representative.

To enable the SAS application:

1. Open the 'Applications Enabling' page (Configuration tab VoIP menuAppl ications Enabling Appl ications Enabling).

2. From the 'Enable SAS' drop-down list, select 'Enable'.

Figure 4-1: Enabling SAS in Applications Enabling Page

3. Click Submit.

4. Save the changes to the flash memory with a device reset; after the device resets, theSASmenu appears and you can now begin configuring the SAS application.

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4.1.2 Defining Common SAS Settings

The common SAS settings include configuring the various SAS parameters and definingthe Proxy Set ID for the SAS proxy.

4.1.2.1 Configur ing SAS Parameters

The procedure below describes how to configure SAS settings that are common to all SASmodes.

To configure common SAS settings:

1. Open the 'SAS Configuration' page (Configuration tab VoIP menu SASStand Alone Survivability).

2. Define the port used for sending and receiving SAS messages. This can be any of thefollowing port types:

UDP port - defined in the 'SAS Local SIP UDP Port' field

TCP port - defined in the 'SAS Local SIP TCP Port' field TLS port - defined in the 'SAS Local SIP TLS Port' field

Note: This SAS port must be different to the device's local gateway port (i.e., thatdefined for the 'SIP UDP/TCP/TLS Local Port' parameter in the 'SIP GeneralParameters' page - Configurationtab VoIPmenu SIP DefinitionsGeneral Parameters).

3. In the 'SAS Default Gateway IP' field, define the IP address and port (in the formatx.x.x.x:port) of the device (i.e., Gateway application). Note that the port of the device isdefined by the parameter 'SIP UDP Local Port' (refer to the note in Step2 above).

4. In the 'SAS Registration Time' field, define the value for the SIP Expires header that issent in the 200 OK response to an incoming REGISTER message when SAS is inemergency state.

5. From the 'SAS Binding Mode' drop-down list, select the database binding mode:

0-URI:If the incoming AOR in the REGISTER request uses a 'tel:' URI or'user=phone', the binding is done according to the Request-URI user part only.Otherwise, the binding is done according to the entire Request-URI (i.e., user andhost parts - user@host).

1-User Part Only: Binding is done according to the user part only.

You must select '1-User Part Only' in cases where the UA sends REGISTERmessages as SIP URI, but the INVITE messages sent to this UA include a Tel URI.

For example, when the AOR of an incoming REGISTER is sip:[email protected],SAS adds the entire SIP URI (e.g., sip:[email protected])to its database (when theparameter is set to '0-URI'). However, if a subsequent Request-URI of an INVITEmessage for this UA arrives with sip:[email protected] user=phone, SAS searches itsdatabase for "3200", which it does not find. Alternatively, when this parameter is set to'1-User Part Only', then upon receiving a REGISTER message withsip:[email protected], SAS adds only the user part (i.e., "3200") to its database.Therefore, if a Request-URI of an INVITE message for this UA arrives withsip:[email protected] user=phone, SAS can successfully locate the UA in its database.


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Figure 4-2: Common SAS Settings in SAS Configuration Page

6. In the 'SAS Proxy Set' field, enter the Proxy Set used for SAS. The SAS Proxy Setmust be defined only for the following SAS modes:

Outbound mode:In SAS normal state, SAS forwards REGISTER and INVITEmessages received from the UAs to the proxy servers defined in this Proxy Set.

Redundant mode and only if UAs don't support homing :SAS sends keep-alive messages to this proxy and if it detects that the proxy connection hasresumed, it ignores the REGISTER messages received from the UAs, forcingthem to send their messages directly to the proxy.

Define the SAS Proxy Set ID, as described in Section4.1.2.2.

Note: Do not use Proxy Set ID 0.

7. Click Submitto apply your settings.

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5

3

4

2


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4.1.2.2 Configuring SAS Proxy Set

The procedure below describes how to configure the SAS Proxy Set ID, which defines theaddress of the UAs' external proxy. This needs to be configured only if you specified theSAS Proxy Set in the 'SAS Configuration' page (see Section4.1.2.1,Step6).

To configure the SAS Proxy Set:

1. Open the 'Proxy Sets Table' page (Configuration tab VoIP menu ControlNetworks Proxy Set Table).

2. From the 'Proxy Set ID' drop-down list, select the required Proxy Set ID.

Notes:

The selected Proxy Set ID number must be the same as that specified inthe 'SAS Proxy Set' field in the 'SAS Configuration' page (see Section4.1.2.1,Step6).

Do not use Proxy Set ID 0.

3. In the 'Proxy Address' field, enter the IP address of the external proxy server.

4. From the 'Enable Proxy Keep Alive' drop-down list, select 'Using Options'. Thisinstructs the device to send SIP OPTIONS messages to the proxy for the keep-alivemechanism.

Figure 4-3: Defining UAs' Proxy Server in Proxy Sets Table Page

5. Click Submitto apply your settings.

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4

3


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4.2 Configuring SAS Outbound Mode

This section describes how to configure the SAS outbound mode. These settings are inaddition to the ones described in Section4.1 on page19.

Note: The VoIP CPEs (such as IP phones or residential gateways) need to bedefined so that their proxy and registrar destination addresses and ports arethe same as that configured for the device's SAS IP address and SAS localSIP port. In some cases, on the UAs, it is also required to define SAS as theoutbound proxy, meaning that messages sent by the UAs include the hostpart of the external proxy, but are sent (on Layer 3/4) to the IP address / UDPport of SAS.

To configure SAS outbound mode:


2. From the 'SAS Survivability Mode' drop-down list, select 'Standard'.

Figure 4-4: Defining SAS Outbound Mode in SAS Configuration Page

3. Click Submit.

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4.3 Configuring SAS Redundant Mode

This section describes how to configure the SAS redundant mode. These settings are inaddition to the ones described in Section4.1 on page19.

Note: The VoIP CPEs (such as IP phones or residential gateways) need to bedefined so that their primary proxy is the external proxy and the redundant proxy destination addresses and port is the same as that configured for thedevice's SAS IP address and SAS SIP port.

To configure SAS redundant mode:


2. From the 'SAS Survivability Mode' drop-down list, select one of the followingdepending on whether the UAs support homing (i.e., they always attempt to operatewith the primary proxy, and if using the redundant proxy, they switch back to theprimary proxy whenever it's available):

UAs support homing:Select 'Always Emergency'. This is because SAS doesnot need to communicate with the primary proxy of the UAs; SAS serves only asthe redundant proxy of the UAs. When the UAs detect that their primary proxy isavailable, they automatically resume communication with it instead of with SAS.

UAs do not support homing:Select 'Ignore REGISTER'. SAS uses the keep-alive mechanism to detect availability of the primary proxy (defined by the SASProxy Set). If the connection with the primary proxy resumes, SAS ignores themessages received from the UAs, forcing them to send their messages directly tothe primary proxy.

Figure 4-5: Defining SAS Redundant Mode in SAS Conf iguration Page

3. Click Submit.

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4.4 Configuring Gateway Appl ication with SAS

If you want the device to run both the Gateway and SAS applications, the configurationdescribed in this section is required. The configuration steps depend on whether theGateway application is operating with SAS in outbound mode or SAS in redundant mode.

Note: The Gateway application must use the same SAS operation mode as the SIPUAs. For example, if the UAs use the SAS application as a redundant proxy(i.e., SAS redundancy mode), then the Gateway application must do thesame.

4.4.1 Gateway with SAS Outbound Mode

The procedure below describes how to configure the Gateway application with SASoutbound mode.

To configure Gateway application wi th SAS outbound mode:

1. Define the proxy server address for the Gateway application:

a. Open the 'Proxy & Registration' page (Configurationtab VoIPmenu SIPDefinitions submenu Proxy & Registration).

b. From the 'Use Default Proxy' drop-down list, select 'Yes'.

Figure 4-6: Enabling Proxy Server for Gateway Application in Proxy & Registration Page

c. Click Submit.

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2. Disable use of user=phone in SIP URL:

a. Open the 'SIP General Parameters' page (Configurationtab VoIPmenu

SIP Definitionssubmenu General Parameters).

b. From the 'Use user=phone in SIP URL' drop-down list, select 'No'. This instructsthe Gateway application to not use user=phonein the SIP URL and therefore,REGISTER and INVITE messages use SIP URI. (By default, REGISTERmessages are sent with sip uriand INVITE messages with tel uri.)

Figure 4-8: Disabling user=phone in SIP URL in SIP General Parameters Page

c. Click Submit.

2.b


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Figure 4-10: Defining Proxy Servers for Gateway Application in Proxy Set Page

i. Click Submit.

2. Disable use of user=phone in SIP URL:

a. Open the 'SIP General Parameters' page (Configurationtab VoIPmenuSIP Definitionssubmenu General Parameters).

b. From the 'Use user=phone in SIP URL' drop-down list, select 'No'. This instructsthe Gateway application to not use user=phonein SIP URL and therefore,REGISTER and INVITE messages use SIP URI. (By default, REGISTERmessages are sent with sip uriand INVITE messages with tel uri.)

Figure 4-11: Disabling user=phone in SIP URL in SIP General Parameters Page

c. Click Submit.

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1.g

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4.5 Advanced SAS Settings

This section describes the configuration of advanced SAS features that can be optionallyimplemented in your SAS deployment:

Manipulating incoming SAS Request-URI user part of REGISTER message (seeSection4.5.1 on page30)

Manipulating destination number of incoming SAS INVITE messages (see Section4.5.2 on page32)

Defining SAS routing rules based on the SAS Routing table (see Section4.5.3 onpage33)

Blocking unregistered SAS UA's (see Section4.5.3 on page33)

Defining SAS emergency calls (see Section4.5.5 on page37)

Adding SIP Record-Route header to INVITE messages (see Section4.5.6 on page38)

Replacing SIP Contact header (see Section4.5.7 on page38)

4.5.1 Manipulating URI user part of Incoming REGISTER

There are scenarios in which the UAs register to the proxy server with their full phonenumber (for example, "976653434"), but can receive two types of INVITE messages (calls):

INVITEs whose destination is the UAs' full number (when the call arrives from outsidethe enterprise)

INVITES whose destination is the last four digits of the UAs' phone number ("3434" inour example) when it is an internal call within the enterprise

Therefore, it is important that the device registers the UAs in the SAS registered databasewith their extension numbers (for example, "3434") in addition to their full numbers. To dothis, you can define a manipulation rule to manipulate the SIP Request-URI user part of the

AOR (in the To header) in incoming REGISTER requests. Once manipulated, it is saved inthis manipulated format in the SAS registered users database in addition to the original(un-manipulated) AOR.

For example: Assume the following incoming REGISTER message is received and thatyou want to register in the SAS database the UA's full number as well as the last four digitsfrom the right of the SIP URI user part:

REGI STER si p: 10. 33. 38. 2 SI P/ 2. 0

Vi a: SI P/ 2. 0/ UDP 10. 33. 4. 226: 5050; branch=z9hG4bKac10827

Max- For wards: 70

Fr om: ; t ag=1c30219

To: Cal l - I D: 16844@10. 33. 4. 226

CSeq: 1 REGI STER

Cont act : ; expi r es=180

Al l ow:REGI STER, OPTI ONS, I NVI TE, ACK, CANCEL, BYE, NOTI FY, PRACK, REFER, I NFO, SUBSCRI BE, UPDATE

Expi r es: 180

User- Agent : Audi ocodes- Si p- Gat eway- / v.

Cont ent - Lengt h: 0


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After manipulation, the SAS registers the user in its database as follows:

AOR: [email protected]

Associated AOR: [email protected] (after manipulation, in which only the four digitsfrom the right of the URI user part are retained)

Contact:[email protected]

The procedure below describes how to configure the manipulation example scenario above(relevant iniparameter is SASRegistrationManipulation):

To manipulate incoming Request-URI user part of REGISTER message:


2. In the SAS Registration Manipulationtable, in the 'Leave From Right' field, enter thenumber of digits (e.g., 4) to leave from the right side of the user part. (The 'LeaveFrom Right' field defines the number of digits to retain from the right side of the userpart; all other digits in the user part are removed.)

Figure 4-12: Manipulating User Part in Incoming REGISTER in SAS Configuration Page

3. Click Submit.

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4.5.3 SAS Routing Based on SAS Routing Table Rules

SAS routing based on the SAS Routing table is applicable for:

SAS in normal state, if the SASSurvivabilityMode parameter is set to 4

SAS in emergency state, if the SASSurvivabilityMode parameter is notset to 4The SAS routing rule destination can be an IP Group, IP address, Request-URI, or ENUMquery.

To configure SAS routing rules in the SAS Routing table:


2. In the 'Redundant SAS Proxy Set' field, enter the Proxy Set ID of the redundant SAS.

3. Click the SAS Routing Table button to define SAS IP-to-IP routing rules.

Figure 4-14: Defining SAS Routing Rules in IP2IP Routing Page

4. Add an entry and then configure it according to the table below.

5. Click theApplybutton to save your changes.

6. To save the changes to flash memory.

Note: The following fields are not applicable to SAS: Source IP Group ID, RequestType, Destination SRD ID, and Alternative Route Options.

Table 4-1: SAS IP2IP Routing Table Parameters

Parameter Description

Matching Characteristics

Source Username Prefix[IP2IPRouting_SrcUsernamePrefix]

The prefix of the user part of the incoming INVITE's sourceURI (usually the From URI).The default is "*".

Source Host[IP2IPRouting_SrcHost]

The host part of the incoming SIP INVITE's source URI(usually the From URI). If this rule is not required, leave thefield empty. To denote any host name, use the asterisk (*)symbol.The default is "*".

Destination Username Prefix[IP2IPRouting_DestUsernamePrefix]

The prefix of the incoming SIP INVITE's destination URI(usually the Request URI) user part. If this rule is notrequired, leave the field empty. To denote any prefix, use

the asterisk (*) symbol.The default is "*".


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Parameter Description

Destination Host[IP2IPRouting_DestHost]

The host part of the incoming SIP INVITE's destination URI(usually the Request URI). If this rule is not required, leavethe field empty. The asterisk (*) symbol can be used todepict any destination host.

The default is "*".

Operation Routing Rule (performed when match found in above characteristics)

Destination Type[IP2IPRouting_DestType]

Determines the destination type to which the outgoingINVITE is sent.

[0] IP Group (default) = The INVITE is sent to the IPGroup's Proxy Set (if the IP Group is of SERVER type) \registered contact from the database (if USER type).

[1] Dest Address = The INVITE is sent to the addressconfigured in the following fields: 'Destination Address','Destination Port', and 'Destination Transport Type'.

[2] Request URI = The INVITE is sent to the address

indicated in the incoming Request-URI. If the fields'Destination Port' and 'Destination Transport Type' areconfigured, the incoming Request-URI parameters areoverridden and these fields take precedence.

[3] ENUM = An ENUM query is sent to conclude thedestination address. If the fields 'Destination Port' and'Destination Transport Type' are configured, theincoming Request URI parameters are overridden andthese fields take precedence.

Destination IP Group ID[IP2IPRouting_DestIPGroupID]

The IP Group ID to where you want to route the call. TheINVITE messages are sent to the IP address(es) definedfor the Proxy Set associated with this IP Group. If you

select an IP Group, it is unnecessary to configure adestination IP address (in the 'Destination Address' field).However, if both parameters are configured, the IP Grouptakes precedence.

If the destination IP Group is of USER type, the devicesearches for a match between the Request-URI (of thereceived INVITE) to an AOR registration record in thedevice's database. The INVITE is then sent to the IPaddress of the registered contact.

The default is -1.

Note:This parameter is only relevant if the parameter'Destination Type' is set to 'IP Group'. However, regardless

of the settings of the parameter 'Destination Type', the IPGroup is still used - only for determining the IP Profile


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4.5.4 Blocking Calls from Unregistered SAS Users

To prevent malicious calls (for example, Service Theft), it is recommended to configure thefeature for blocking SIP INVITE messages received from SAS users that are not registeredin the SAS database. This applies to SAS in normal and emergency states.

To block calls from unregistered SAS users:


2. From the 'SAS Block Unregistered Users' drop-down list, select 'Block'.

Figure 4-15: Blocking Unregistered SAS Users in SAS Configuration Page

3. Click Submit.

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4.5.5 Configuring SAS Emergency Calls

You can configure SAS to route emergency calls (such as 911 in North America) directly tothe PSTN (through its FXO interface or E1/T1 trunk interface). Therefore, even during acommunication failure with the external proxy, enterprise UAs can still make emergency

calls.You can define up to four emergency numbers, where each number can include up to fourdigits. When SAS receives a SIP INVITE (from a UA) that includes one of the user-definedemergency numbers in the SIP user part, it forwards the INVITE directly to the defaultgateway (seeFigure 3-3on page17). The default gateway is defined in the 'SAS DefaultGateway IP' field, and this is the device itself. The device then sends the call directly to thePSTN.

This feature is applicable to SAS in normal and emergency states.

To configure SAS emergency numbers:


2. In the 'SAS Default Gateway IP' field, define the IP address and port (in the formatx.x.x.x:port) of the device (Gateway application).

Note: The port of the device is defined in the 'SIP UDP/TCP/TLS Local Port' field inthe 'SIP General Parameters' page (Configurationtab VoIPmenu SIPDefinitions General Parameters).

3. In the 'SAS Emergency Numbers' fields, enter an emergency number in each fieldbox.

Figure 4-16: Defin ing SAS Emergency Numbers in SAS Configuration Page

4. Click Submit.

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4.5.6 Adding SIP Record-Route Header to SIP INVITE

You can configure SAS to add the SIP Record-Route header to SIP requests (e.g. INVITE)received from the enterprise UAs. SAS then sends the request with this header to theproxy. The Record-Route header includes the IP address of the SAS application. This

ensures that future requests in the SIP dialog session from the proxy to the UAs are routedthrough the SAS application. If not configured, future request within the dialog from theproxy are sent directly to the UAs (and do not traverse SAS).

This feature is configured using the SASEnableRecordRoute ini file parameter.

Note: This feature is applicable only to SAS outbound mode.

When this feature is enabled, the SIP Record-Route header includes the URI "lr"

parameter, indicating loose routing, for example:Recor d- Rout e:

4.5.7 Replacing Contact Header for SIP Messages

You can configure SAS to change the SIP Contact header so that it points to the SAS host.Therefore, this ensures that the top-most SIP Via header and the Contact header point tothe same host.

Note: This feature is applicable only to SAS outbound mode.

This feature is configured using the SASEnableContactReplaceini file parameter.

[0] (default): Disable - when relaying requests, SAS adds a new Via header (with theIP address of the SAS application) as the top-most Via header and retains the originalContact header. Thus, the top-most Via header and the Contact header point todifferent hosts.

[1]:Enable - SAS changes the Contact header so that it points to the SAS host andtherefore, the top-most Via header and the Contact header point to the same host.

Note: The device may become overloaded if this feature is enabled as all incomingSIP dialog requests will traverse the SAS application.


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Technical Note 5. Viewing Registered SAS Users


5 Viewing Registered SAS UsersYou can view users that are currently registered in the SAS registration database, asdescribed in the procedure below:

To view SAS registered users:

Open the 'SAS/SBC Registered Users' page (Status & Diagnostics tab VoIPStatusmenu SAS/SBC Registered Users).

Figure 5-1: Viewing Registered SAS Users in SAS Registered Users Page

The table displays the following:

Address of Record : An address-of-record (AOR) is a SIP or SIPS URI that points toa domain with a location service that can map the URI to another URI (Contact) wherethe user might be available.

Contact : SIP URI that can be used to contact that specific instance of the UA forsubsequent requests.


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Reader's Notes


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Technical Note 6. Maximum SAS Registered Users


6 Maximum SAS Registered UsersThe table below lists the maximum number of SAS users that can be registered in the SASregistration database per product:

Table 6-1: Max. SAS Registered Users per Device

Product Maximum SAS Registered Users

MP-11x 25

Mediant 800 MSBG 200

Mediant 1000 MSBG 600

Mediant 1000 600

Mediant 2000 250

Mediant 3000 2000

Note: Despite the maximum number of SAS users, you can increase this capacityby implementing the SAS Cascading feature, as described in Section6.1.

6.1 SAS Cascading

The SAS Cascading feature allows you to increase the number of SAS users above the

maximum supported by the SAS gateway. This is achieved by deploying multiple SASgateways in the network. For example, if the SAS gateway supports up to 600 users, butyour enterprise has 1,500 users, you can deploy three SAS gateways to accommodate allusers: the first SAS gateway can service 600 registered users, the second SAS gatewaythe next 600 registered users, and the third SAS gateway the rest (i.e., 300 registeredusers).

In SAS Cascading, the SAS gateway first attempts to locate the called user in its SASregistration database. Only if the user is not located, does the SAS gateway send it on tothe next SAS gateway according to the SAS Cascading configuration.

There are two methods for configuring SAS Cascading. This depends on whether the userscan be identified according to their phone extension numbers:

SAS Routing Table: If users can be identified with unique phone extension numbers,

then the SAS Routing table is used to configure SAS Cascading. This SAS Cascadingmethod routes calls directly to the SAS Gateway (defined by IP address) to which thecalled SAS user is registered.

The following is an example of a SAS Cascading deployment of users with uniquephone extension numbers:

users registered to the first SAS gateway start with extension number 40

users registered to the second SAS gateway start with extension number 20

users registered to the third SAS gateway start with extension number 30


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The SAS Routing table rules for SAS Cascading are created using the destination(called) extension number prefix (e.g., 30) and the destination IP address of the SASgateway to which the called user is registered. Such SAS routing rules must beconfigured at each SAS gateway to allow routing between the SAS users. The routinglogic for SAS Cascading is similar to SAS routing in Emergency state (see theflowchart inFigure 3-3 on page17). For a description on the SAS Routing table, see

Section4.5.3 on page33.The figure below illustrates an example of a SAS Cascading call flow configured usingthe SAS Routing table. In this example, a call is routed from SAS Gateway (A) user toa user on SAS Gateway (B).

Figure 6-1: SAS Cascading Using SAS Routing Table - Example

SAS Redundancy mode:If users cannot be distinguished (i.e., associated to aspecific SAS gateway), then the SAS Redundancy feature is used to configure SASCascading. This mode routes the call in a loop fashion, from one SAS gateway to thenext, until the user is located. Each SAS gateway serves as the redundant SASgateway (redundant SAS proxy server) for the previous SAS gateway (in a one-waydirection). For example, if a user calls a user that is not registered on the same SASgateway, the call is routed to the second SAS gateway, and if not located, it is sent tothe third SAS gateway. If the called user is not located on the third (or last) SASgateway, it is then routed back to the initial SAS gateway, which then routes the call tothe default gateway (i.e., to the PSTN).

SAS Gateway (A)

User 600User 0 User 1201User 601 User 1502User 1202

SAS Gateway (B) SAS Gateway (C)

Call Routed Directly to SAS GatewayAccording to SAS Routing Table Rules

LAN

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Technical Note 6. Maximum SAS Registered Users


Each SAS gateway adds its IP address to the SIP via header in the INVITE messagebefore sending it to the next (redundant) SAS gateway. If the SAS gateway receivesan INVITE and its IP address appears in the SIP via header, it sends it to the defaultgateway (and not to the next SAS gateway), as defined by the SASDefaultGatewayIPparameter. Therefore, this mode of operation prevents looping between SASgateways when a user is not located on any of the SAS gateways.

The figure below illustrates an example of a SAS Cascading call flow when configuredusing the SAS Redundancy feature. In this example, a call is initiated from a SASGateway (A) user to a user that is not located on any SAS gateway. The call issubsequently routed to the PSTN.

Figure 6-2: SAS Cascading Using SAS Redundancy Mode - Example

SAS Gateway (A)

PSTN

User 600User 0 User 1201User 601 User 1502User 1202

SAS Gateway (B) SAS Gateway (C)

Locating User on

Redundant SAS Proxy

Locating User on

Redundant SAS Proxy

User Not FoundSent Back to Initial SAS Gateway

User Not FoundSent to PSTN(If Configured)

LAN

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Technical Note

Date post:	02-Jun-2018
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SAS Technical Note Ver. 6.2

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