What is ICB?

3GPP defines Communication Barring in TS 24.611, including Incoming Communication Barring (ICB), Anonymous Communication Rejection as a special case of ICB, and Outgoing Communication Barring (OCB):

The incoming communication barring (ICB) is a service that rejects incoming communications that fulfil certain provisioned or configured conditions on behalf of the terminating user.

The anonymous communication rejection (ACR) is a particular case of the ICB service, that allows barring of incoming communications from an anonymous originator on behalf of the terminating user.

The incoming communication barring (ICB) service makes it possible for a user to have barring of certain categories of incoming communications according to a provisioned or user configured barring program and is valid for all incoming communications. A barring program is expressed as a set of rules in which the rules have a conditional part and an action part. Examples of conditions are whether the asserted originating public user identity matches a specific public user identity or whether the originating public user identity is restricted (anonymous). The action part could specify for a rule that contains a matching condition that the specific incoming communication is barred.

The inhibition of incoming forwarded calls is a special case of the ICB and allows the served user to reject incoming communications from users or subscribers who have diverted the communication towards the served user. The communication history information will be used to trigger the service.

The anonymous communication rejection (ACR) service allows the served user to reject incoming communications on which the asserted public user identity of the originating user is restricted. In case the asserted public user identity of the originating user is not provided then the communication is allowed by the ACR service. It is highlighted here because it is a regulatory service in many countries.

Feature Cheat Sheet

B2BUA Instance Originating / Terminating Point(s) in Session Plan Network Operator Data Subscriber Data Stateful or Stateless POJO Feature or SBB Feature

MMTEL

Terminating

SipAccess_SubscriberPreCreditCheck

Yes

Yes, comes from the HSS

Stateless

POJO

Prerequisite Features

Note For announcements, SIPPlayAnnouncement is a dependent feature; but it is not a prerequisite.

Source Code

This feature’s source code is available in the Sentinel VoLTE SDK in the mmtel-communication-barring module pack. It can be viewed by using the create-module command in the SDK with that module pack, for example:

> create-module new-cb-module opencloud#mmtel-communication-barring#volte/2.7.0;2.7.0.0

This command will prompt you for information needed to create the new modules, once completed the original source for the feature can be found in the new modules.

The module-pack includes the following modules relevant to this feature:

Module Name Description

mmtel-communication-barring

Group module for the feature that includes all of the modules listed below.

mmtel-communication-barring-library

Contains code shared by both communication barring features.

mmtel-icb-profile

Contains the profile specification for the feature configuration profile table.

mmtel-icb

Contains the feature itself.

Interaction with OIP

According to section 4.6.4 of 3GPP TS 24.611, MMTelICB must run before MMTelOIP.

Network Operator Data

This data is stored in a JSLEE Configuration Profile Table, called MMTelICBConfigProfileTable.

Operator data is scoped according to a Sentinel selection key. There is one profile in the ProfileTable for each network operator.

Attribute Name Type Default Value Description 
PlayAnnouncement

Boolean

 
false

If true, ICB will request an announcement is played in the case that it bars the session setup.

 
ACRAnnouncementID

int

 
0

The ID for the announcement to be played in the case of Anonymous Call Rejection. If set to zero there is no announcement.

 
AnnouncementID

int

 
0

The ID for the announcement to be played in all other ICB cases. If set to zero there is no announcement.

 
InternationalRulesActive

Boolean

 
false

If false, ICB will ignore International and International-exHC rules.

Session Input Variables

Variable name Type Comments 
MMTelICBServiceData

Complex

 
RoamingIndicator

Boolean

 
International

Boolean

 
InternationalExHC

Boolean

Session Output Variables

Variable name Type Comments 
ICBBarred

Boolean

Set to true if the ICB feature bars the call. It exists so that feature execution scripts can read the variable and take action

 
ICBBarredWithAnnouncement

Boolean

Set to true if the ICB feature bars the call, and the feature is configured to request an announcement as part of barring

 
AnnouncementID

int

The announcement ID to be used if an announcement is configured as part of barring

 
EndSessionAfterAnnouncement

int

The status code used when ending the session — if barring has occurred and announcements are used.

 
RanIcb

Boolean

Signals to other features that ICB ran on this session.

Supported Barring Rule Conditions

Barring rule conditions that are evaluated include:

Anonymous

To comply with the requirements as set for simulation of the ACR service, the anonymous element only evaluates to true when the conditions as set out in subclause 4.5.2.6.2 for asserted originating public user identity apply.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for anonymous calls:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="anonymous">
        <cp:conditions>
            <anonymous/>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Roaming

This condition evaluates to true if the session state variable RoamingIndicator is true. This is set by the MMTel Determine International and Roaming Status feature.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for roaming calls:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="roaming">
        <cp:conditions>
            <roaming/>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Media

This condition evaluates to true when the value of this condition matches the media field in one of the "m=" lines in the SDP message body offered in an INVITE request.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for calls offering specific media:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="no_video">
        <cp:conditions>
            <media>video</media>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Combinations of media types may be expressed as multiple conditions within the same rule. For example:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="no_video_and_text">
        <cp:conditions>
            <media>video</media>
            <media>text</media>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Identity

This condition evaluates to true if the identity of the other party in the communication matches that which is expressed in the condition. Identities within the condition can be expressed in different ways:

  • a single, fully expressed identity (e.g. sip:alice@example.com)

  • a whole domain (e.g. example.com)

  • a whole domain, but with exceptional identities or domains (e.g. example.com except for alice@example.com)

  • all identities (may also have exceptions)

  • any combination of the above

The following XML snippets show how to configure the user’s Subscriber data for each of the above cases.

A single, fully expressed identity (the identity 'sip:alice@example.com' is matched)

This example, without any other rule, blocks any session from 'sip:alice@example.com'.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="bar-alice">
        <cp:conditions>
            <cp:identity>
                <one id="sip:alice@example.com"/>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>
A domain (all identities at 'example.com' are matched)

This example, without any other rule, blocks any session from domain 'example.com'.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="bar-domain">
        <cp:conditions>
            <cp:identity>
                <many domain="example.com"></many>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>
A whole domain with an exceptional identity (all identities at 'example.com' are matched except 'sip:alice@example.com')

This example, without any other rule, blocks any session from domain 'example.com' except if originated from 'sip:alice@example.com'.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="barr-domain-with-exception">
        <cp:conditions>
            <cp:identity>
                <many domain="example.com">
                    <except id="sip:alice@example.com"/>
                </many>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>
A whole domain with an exceptional domain (all identities at 'example.com' are matched except 'sip:alice@example.com')

This example, without any other rule, blocks any session from domain 'example.com' except if originated from the subdomain 'callcentre.example.com'.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="barr-domain-except-callcentre">
        <cp:conditions>
            <cp:identity>
                <many domain="example.com">
                    <except domain="callcentre.example.com"/>
                </many>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>
Important Note the attribute of the 'except' element is now 'domain'.
All identites (all identities are matched)

This example, without any other rule, blocks all sessions from any user.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="barr-all">
        <cp:conditions>
            <cp:identity>
                <many />
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>
A more complex Identity condition expression (all identies at 'example2.com' match except for 'sip:charlie@example2.com'. Also the identities 'sip:alice@example1.com' and 'sip:bob@example1.com' match.)

This example, without any other rule, blocks any session from all users registered in the domain 'example2.com', from the user 'sip:alice@example1.com' and from the user sip:bob@example1.com, except from 'sip:charlie@example2.com.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="barr-some">
        <cp:conditions>
            <cp:identity>
                <one id="sip:alice@example1.com"/>
                <one id="sip:bob@example1.com"/>
                <many domain="example2.com">
                    <except id="sip:charlie@example2.com"/>
                </many>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>
Another more complex Identity condition expression with more than one rule.

This example, always blocks some domains, always allow other domains and a set of sip URIs.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="always-allow-these-domains">
        <cp:conditions>
            <cp:identity>
                <many domain="emergency.org"></many>
                <many domain="police.org"></many>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>true</allow>
        </cp:actions>
    </cp:rule>

    <cp:rule id="always-barr-these-domains">
        <cp:conditions>
            <cp:identity>
                <many domain="fakelotery.org"></many>
                <many domain="dhueb!.org"></many>
                <many domain="fakeprize.com"></many>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>

   <cp:rule id="always-barr-these-identities">
        <cp:conditions>
            <cp:identity>
                <one id="sip:john@example.com"/>
                <one id="sip:marc@example.com"/>
            </cp:identity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>

</cp:ruleset>
Tip Depending on the value of the 'allow' element of the rule, the rule can essentially become a 'whitelist' or a 'blacklist'.

International

This condition evaluates to true if the session state variable International is true and 'InternationalRulesActive' is true. 'International' is set by the MMTel Determine International and Roaming Status feature. 'InternationalRulesActive' is configured in the ICB feature profile and defaults to false. This is because it is not possible to accurately determine whether the calling party is international in all circumstances.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for international calls:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="international">
        <cp:conditions>
            <international/>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

International-exHC

This condition evaluates to true if the session state variable InternationalExHC is true and 'InternationalRulesActive' is true. 'International' is set by the MMTel Determine International and Roaming Status feature. 'InternationalRulesActive' is configured in the ICB feature profile and defaults to false. This is because it is not possible to accurately determine whether the calling party is international in all circumstances.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for international-exHC calls:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="international-exHC">
        <cp:conditions>
            <international-exHC/>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Unconditional

An empty conditions element is used to represent unconditional.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for all calls:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="anonymous">
        <cp:conditions/>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Communication Diverted

This condition evaluates to true when the incoming communication has been previously diverted.

Diverted communication can be recognised by the presence of the History header field, as specified in 3GPP TS 24.604

Use this XML in the REM HSS Subscriber Data Page to configure ICB for diverted calls:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="diverted">
        <cp:conditions>
            <communication-diverted/>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Validity

This condition evaluates to true if the current time is within the times specified by the validity period Time is based on the Home Network time; that is, the time of the MMTel Server.

Use this XML in the REM HSS Subscriber Data Page to configure ICB for a validity period:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="validity">
        <cp:conditions>
            <cp:validity>
                <cp:from>2000-01-01T00:00:00</cp:from>
                <cp:until>2099-12-31T23:59:59</cp:until>
            </cp:validity>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Rule Deactivated

This condition always evaluates to false. Generally used to disable a rule that has other conditions without removing the rule entirely.

The rule is re-enabled by removing this condition.

Use this XML in the REM HSS Subscriber Data Page to configure a deactivated rule:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<cp:ruleset xmlns="http://uri.etsi.org/ngn/params/xml/simservs/xcap" xmlns:cp="urn:ietf:params:xml:ns:common-policy" xmlns:ocp="urn:oma:xml:xdm:common-policy">
    <cp:rule id="deactivated">
        <cp:conditions>
            <rule-deactivated/>
        </cp:conditions>
        <cp:actions>
            <allow>false</allow>
        </cp:actions>
    </cp:rule>
</cp:ruleset>

Barring Rule Actions

Barring rule actions are a string. There could be many actions defined, but the only one that makes any sense is the allow action.

The allow action has a Boolean attribute, with meaning as follows:

  • true — allow session setup to proceed

  • false — deny session setup from proceeding.

Any other rule action (in other words, an action that is not set to allow) will result in us treating the action as the following:

  • allow rule action with value of true.

Statistics

MMTelICB statistics are tracked by the volte.sentinel.sip SBB and can be found under the following parameter set:
SLEE-Usage → volte.sentinel.sip service → volte.sentinel.sip SBB

Statistic Incremented when…​ 
MMTelICBFeatureStarted

the feature runs

 
MMTelICBFeatureFailedToStart

sentinel VoLTE encounters an error while attempting to start the feature

 
MMTelICBFeatureIssuedWarning

a non-fatal problem is encountered and the feature and issues a warning

 
MMTelICBFeatureFailedDuringExecution

a fatal problem is encountered and the feature cannot execute correctly

 
MMTelICBFeatureTimedOut

the feature takes too long to complete and Sentinel VoLTE aborts execution

 
MMTelICBFeatureCallBarred

the feature bars a call (including when barring due to ACR)

 
MMTelOCBFeatureCallBarredByOdb

the feature bars a call by Operator Determined Barring rule

 
MMTelICBFeaturePlayAnnouncementTriggered

the feature requests that an announcement be played to the calling party

 
MMTelICBFeatureACRTriggered

a call is barred by ACR

 
MMTelICBFeatureOdbRulesEvaluatedTrue

a rule was evaluated to be True

Behaviour

If operator data is not present, the ICB feature:

  1. Increments an error statistic.

  2. Logs a message at the Fine level.

  3. Informs the Sentinel core that the feature is not configured appropriately (Invalid Configuration).

  4. Exits.

If MMTelICBServiceData.Active is false, the feature finishes execution without modifying any state.

If the rules do not parse, then the feature:

  • instructs Sentinel core that the feature has failed due to configuration problems

  • finishes execution without modifying any state.

When the feature processes a set of rules:

For each rule, if then

  • the rule has no <conditions> element;

  • the rule has an empty <conditions> element; or

  • conditions are present and they all evaluate to true;

the rule matches.

The actions from all matching rules are combined.

If…​ then the combined result for the rule set is:

any matching rules had the action allow=true

allow=true

all matching rules had the action allow=false

allow=false

no rules matched

allow=true
Tip When a rule contains multiple conditions, they all must match for the whole rule to match. This is essentially a logical 'AND' between the conditions. To express a logical 'OR' of conditions, the conditions must be placed in different rules.

If the combined result is allow=false, then the ICB feature sets the session output variable ICBBarred to true. Otherwise the ICB feature sets the session output variable ICBBarred to false and finishes without modifying any further state.

If network configuration has PlayAnnouncement set to true (MmtelICBConfig.PlayAnnouncement == true), and ICB has decided to bar the communication, then the ICB feature sets session output variable AnnouncementID to MmtelICBConfig.AnnouncementID.

Finally, if the communication is to be barred, ICB rejects the call with the appropriate SIP error response code:

If any matching rule contains the “anonymous” condition, use 433 Anonymity Disallowed. This is to provide ACR functionality. (See section 4.5.2.6.1.)

Otherwise use 603 Decline.

Roaming Determination

The ICB feature does not compute whether or not the served user is roaming; rather it relies on a session input variable (isRoaming). This is set by Sentinel’s DetermineIfRoaming feature.

Example feature execution script fragment:

run DetermineInternationalAndRoamingStatus
run MMTelICB

Playing Announcements

The MMTelICB feature does not play announcements itself; rather it relies on setting of session output variables (AnnouncementID, ICBBarredWithAnnouncement, EndSessionAfterAnnouncement). These are set by the MMTelICB feature if an announcement is to be played. They are used by the out-of-the-box feature execution scripts such that if announcements are desired to be played prior to the barred call being terminated, it is played using the SIPPlayAnnouncement feature.

This is an example feature execution script, taken from a fragment of the out-of-the-box execution scripts.

run MMTelICB
if (session.ICBBarredWithAnnouncement) {
   run SIPPlayAnnouncement
}

The SIPPlayAnnouncement feature checks session state for the AnnouncementID field, and if the value is non-zero will play an announcement. When the announcement is played using the SIPPlayAnnouncement feature, it is played to the calling party.

Finally, when the announcement is complete the SIPPlayAnnouncement feature ends the session with the appropriate SIP error response (provided by MMTelICB during its execution). The SIP error response code is set in the EndSessionAfterAnnouncement session output variable.

Graceful Handling of Originating Access

ICB is a terminating feature. It will finish execution without modifying any state if it is invoked in an originating attempt.

Background Information on Format of Barring Rules

Each rule is expressed as an XCAP cp-rule.

That is, it is an XML fragment:

<cp:rule id="rule66">
        <cp:conditions>
		condition1
		condition2
        </cp:conditions>
        <cp:actions>
          <allow>false</allow>
        </cp:actions>
 </cp:rule>

In case that the allow element is not found, the feature assumes allow = false.

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