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Important: The I-CSCF is incorporated into the S-CSCF.
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Assign an S-CSCF to a User Performing SIP Registration - On a UE registration, the I-CSCF carries out a first step authorization and S-CSCF discovery. For this, the I-CSCF sends a Cx User-Authentication-Request (UAR) to the HSS by transferring the Public and Private User Identities and the visited network identifier (all extracted from the UE REGISTER message). The HSS answers with a Cx User-Authentication-Answer (UAA). The UAA includes the URI of the S-CSCF already allocated to the user. If there is no previously allocated S-CSCF, the HSS returns a set of S-CSCF capabilities that the I-CSCF uses to select the S-CSCF.
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E.164 Address Translation - Translates the E.164 address contained in all Request-URIs having the SIP URI with user=phone parameter format into the Tel: URI format before performing the HSS Location Query. In the event the user does not exist, and if configured by operator policy, the I-CSCF may invoke the portion of the transit functionality that translates the E.164 address contained in the Request-URI of the Tel: URI format to a routable SIP URI.
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Obtain the S-CSCF Address from the HSS - When the I-CSCF receives a SIP request from another network, it has to route the request to the called party. For this it obtains the S-CSCF address associated with the called party from the HSS by querying with a Cx Location-Information-Request (LIR) message. The Public-Identity AVP in the LIR is the Request-URI of the SIP request. The Location-Information-Answer (LIA) message contains the S-CSCF address in the Server-Name AVP. The request is then routed to the S-CSCF.
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Route a SIP Request or Forward Response from Another Network - When the I-CSCF receives a request from another network, it obtains the address of the S-CSCF from the HSS using the procedure detailed above and routes the request to the S-CSCF. Responses are also routed to the S-CSCF.
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Perform Transit Routing Functions - The I-CSCF may need to perform transit routing if, based on the HSS query, the destination of the session is not within the IMS. The IMS Transit Functions perform an analysis of the destination address and determine where to route the session. The session may be routed directly to an MGCF, BGCF, or to another IMS entity in the same network, to another IMS network, or to a CS domain or PSTN.
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Generate CDRs - The I-CSCF generates CDRs for its interactions. Upon completing a Cx query, the I-CSCF sends an Accounting Request with the Accounting-Record-Type set to EVENT. The CDF acknowledges the data received and creates an I-CSCF CDR.
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Apart from base software license, the SCM requires feature licenses for various enhanced features supported on the ASR 5000 platform with SCM service. For more information on supported features, refer to the Features and Functionality sections.
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System Management Cards (SMCs): Provides full system control and management of all cards within the ASR 5000 platform. Up to two SMC can be installed; one active, one redundant.
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Packet Services Cards (PSCs/PSC2s/PSC3s): Within the ASR 5000 platform, PSCs provide high-speed, multi-threaded PDP context processing capabilities for 2.5G SGSN, 3G SGSN, and GGSN services. Up to 14 PSCs can be installed, allowing for multiple active and/or redundant cards.
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Switch Processor Input/Outputs (SPIOs): Installed in the upper-rear chassis slots directly behind the SMCs, SPIOs provide connectivity for local and remote management, Central Office (CO) alarms. Up to two SPIOs can be installed; one active, one redundant.
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Line Cards: Installed directly behind PSC/PSC2/PSC3, these cards provide the physical interfaces to elements in the GPRS/UMTS data network. Up to 26 line cards can be installed for a fully loaded system with 13 active PSCs/PSC2s/PSC3s, 13 in the upper-rear slots and 13 in the lower-rear slots for redundancy. Redundant PSCs/PSC2s/PSC3s do not require line cards.
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Redundancy Crossbar Cards (RCCs): Installed in the lower-rear chassis slots directly behind the SMCs, RCCs utilize 5 Gbps serial links to ensure connectivity between Ethernet 10/100 or Ethernet 1000 line cards/QGLCs and every PSC/PSC2/PSC3 in the system for redundancy. Two RCCs can be installed to provide redundancy for all line cards and PSCs/PSC2s/PSC3s.
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Card: Provides card-level statistics
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Context: Provides context-level statistics
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CSCF: Provides CSCF service statistics
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CSCFINTF: Provides CSCF interface statistics
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Diameter-acct: Provides Diameter Accounting statistics
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Diameter-auth: Provides Diameter Authentication statistics
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Map: Provides Map service statistics
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Nat-realm: Provides NAT realm statistics
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Port: Provides port-level statistics
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System: Provides system-level statistics
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Important: For more information on bulk statistic configuration, refer to the Configuring and Maintaining Bulk Statistics chapter in the System Administration Guide.|
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Directory service, toll-free, long distance, international, and operator-assisted calls - are supported through translation lists.
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Emergency calls - are managed through the addition of an Emergency Call/Session Control Function (E-CSCF) that routes emergency calls to a Public Safety Answering Point (PSAP).
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Mobile-to-Mobile SIP calls - supports SIP-based VoIP calls between mobile data users.
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Public Switched Telephone Network (PSTN) calls - can be routed through a 3GPP/2 compliant BGCF located in the S-CSCF.
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Congestion Condition Thresholds: Thresholds dictate the conditions for which congestion control is enabled and establishes limits for defining the state of the system (congested or clear). These thresholds function in a way similar to operation thresholds that are configured for the system as described in the Thresholding Configuration Guide. The primary difference is that when congestion thresholds are reached, a service congestion policy and an SNMP trap, starCongestion, are generated.
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Port Utilization Thresholds: If you set a port utilization threshold, when the average utilization of all ports in the system reaches the specified threshold, congestion control is enabled.
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Port-specific Thresholds: If you set port-specific thresholds, when any individual port-specific threshold is reached, congestion control is enabled system-wide.
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Service Congestion Policies: Congestion policies are configurable for each service. These policies dictate how services respond when the system detects that a congestion condition threshold has been crossed.
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Level 1: For every new call/event received, the system checks if sessmgr memory-usage is above a threshold value (such as 95 percent). If it is, memory-congestion is triggered and new call messages are rejected with 500 SIP response. Memory congestion is disabled when memory usage drops by a tolerance value (default is 10 percent).
Level 2: If the sessmgr usage reaches 100 percent, all newly received SIP messages are dropped at the socket layer in that sessmgr except for the BYE message. The new SIP messages are not processed until the memory reaches the threshold value (95 percent).
Important: For more information on congestion control, refer to the Congestion Control chapter in the Cisco ASR 5000 System Administration Guide.
Important: For this feature, you may bind a CSCF service to either an IPv4 address or to an IPv6 address, but not both simultaneously.
Important: The policy interface to PCRF will be IPv6 based when DIAMETER supports IPv6.|
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Important: SCM management functionality is enabled by default for console-based access. For GUI-based management support, refer to the Web Element Management System section in this chapter.
Important: For more information on command line interface based management, refer to the Command Line Interface Reference.
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Abbreviated Dialing (AD) - This feature allows the subscriber to call a Directory Number by entering less than the usual ten digits.Usually, the subscriber has four digit dialing to mimic PBX dialing privileges but these must be set up prior to use. When the SCM receives these numbers, it translates them and routes the call.
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Call Forward Busy Line (CFBL) - This feature forwards the call if busy line indication is received from the UE. If CFBL is enabled on both the AS and the S-CSCF, the call is forwarded by the S-CSCF on Busy Line indication. The feature detects and eliminates call forward loops if the History-Info header is present. It also terminates forwarding if forwarding causes the forward attempts to be more than the number specified in the Max-Forwards header.
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Call Forward No Answer (CFNA) - This feature forwards the call if no answer is received from the UE. If CFNA is enabled on both the AS and the S-CSCF, the call is forwarded by the S-CSCF on No Answer indication. The feature detects and eliminates call forward loops if the History-Info header is present. It also terminates forwarding if forwarding causes the forward attempts to be more than the number specified in the Max-Forwards header.
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Call Forward Not Registered (CFNR) - This feature forwards the call if the subscriber is not registered. If CFNR is enabled on both the AS and the S-CSCF, the call is forwarded by the S-CSCF on Not Registered indication. The feature detects and eliminates call forward loops if the History-Info header is present. It also terminates forwarding if forwarding causes the forward attempts to be more than the number specified in the Max-Forwards header.
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Call Forward Unconditional (CFU) - This feature unconditionally forwards the call. The check for local CFU is done prior to the filter criteria and before any AS interaction. Thus CFU is enabled on both the S-CSCF and the destination AS, the local CFU occurs and there is no AS interaction. The feature eliminates basic loop detection (A calls B which is forwarded to A) and if the History-Info header is present, enhanced loop detection is performed based on the contents of this header. It also terminates forwarding if forwarding causes the forward attempts to be more than the number specified in the Max-Forwards header.
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Call Transfer - This feature allows the subscriber to transfer a call.
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Call Waiting - This feature allows the subscriber to receive a second call while on the first call.
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Caller ID Display (CID) - This feature inserts P-Preferred-Identity which communicates the identity of the user within the trust domain. If this header is already present, the feature may not do anything different.
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Caller ID Display Blocked (CIDB) - This feature removes P-Preferred-Identity and P-Preferred-Asserted-Identity headers and inserts a Privacy header with the privacy value set to “id”.
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Feature Code Activation/De-activation - This feature allows for activating and de-activating certain features using a star (*) - number sequence (star code). Registered subscribers have the option of activating or deactivated call features using specified star codes. The SCM translates these codes and routes the call.
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Follow Me/Find Me - This feature invokes the incoming call to several configured destinations in parallel and connects the call to the first destination that responds, “tearing down” all the other calls. There are two possible implementations of this feature; one a sequential implementation in which each destination is attempted in sequence till a successful connection. The other is a parallel approach in which several destinations are tried simultaneously. The advantage of the parallel approach is a faster set up.
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Locally Allowed Abbreviated Dialing - This feature allows the subscriber to dial a local-only, legacy, short code such as *CG or *POL. The SCM translates these codes to a ten-digit directory number and routes the call.
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Outbound Call Restrictions/Dialing Permissions - This feature restricts subscribers from initiating certain outbound calls. For example, if a subscriber attempts to make an international call and is not permitted to, the S-CSCF rejects the call.
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Short Code Dialing - This feature allows the subscriber to dial a short code such as #PAYor #MIN. The SCM translates these codes and routes the call.
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Alert: A value is monitored and an alert condition occurs when the value reaches or exceeds the configured high threshold within the specified polling interval. The alert is generated then generated and/or sent at the end of the polling interval.
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Alarm: Both high and low threshold are defined for a value. An alarm condition occurs when the value reaches or exceeds the configured high threshold within the specified polling interval. The alert is generated then generated and/or sent at the end of the polling interval.
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SNMP traps: SNMP traps have been created that indicate the condition (high threshold crossing and/or clear) of each of the monitored values.
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Logs: The system provides a facility called threshold for which active and event logs can be generated. As with other system facilities, logs are generated Log messages pertaining to the condition of a monitored value are generated with a severity level of WARNING.
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Alarm System: High threshold alarms generated within the specified polling interval are considered “outstanding” until a the condition no longer exists or a condition clear alarm is generated. “Outstanding” alarms are reported to the system's alarm subsystem and are viewable through the Alarm Management menu in the Web Element Manager.
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Important: For more information on threshold crossing alert configuration, refer to the Thresholding Configuration Guide.
Important: For more information on WEM support, refer to the WEM Installation and Administration Guide.
Important: For more information on interchassis session recovery support, refer to the Interchassis Session Recovery chapter in the Cisco ASR 5000 Series System Administration Guide.
Important: IPSec implementation is a mandatory part of IPv6, but it is optional to secure IPv4 traffic.In addition, IPv4-IPv6 interworking helps an IPv4 IMS network transition to an all-IPv6 IMS network.
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Task recovery mode: Wherein one or more session manager failures occur and are recovered without the need to use resources on a standby PSC. In this mode, recovery is performed by using the mirrored “standby-mode” session manager task(s) running on active PSCs. The “standby-mode” task is renamed, made active, and is then populated using information from other tasks such as AAA manager.
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Full PSC/PSC2/PSC3 recovery mode: Used when a PSC hardware failure occurs, or when a PSC migration failure happens. In this mode, the standby PSC is made active and the “standby-mode” session manager and AAA manager tasks on the newly activated PSC perform session recovery.
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Important: Session Recovery is supported for either IPv4 or IPv6 traffic.
Important: For more information on session recovery support, refer to the Session Recovery chapter in the Cisco ASR 5000 Series System Administration Guide.|
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Important: For more information on TLS support, refer to the TLS Support appendix in the Cisco ASR 5000 Series Session Control Manager Administration Guide.
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SigComp Detection - P-CSCF detects if the UE supports SigComp and compresses messages it sends to the UE. The P-CSCF also detects if messages it receives are compressed and decompresses them.
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SigComp Parameter Configuration - P-CSCF allows the configuration of Decompression Memory Size (DMS), State Memory Size (SMS), and Cycles Per Bit (CPB).
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Failure Acknowledgement - P-CSCF replies with NACK on decompression failure.
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SIP/SDP Static Dictionaries - P-CSCF supports the Session Initiation Protocol/Session Description Protocol Static Dictionary for Signaling Compression.
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Important: The SCM currently supports the following Release 8 3GPP specifications. Most 3GPP specifications are also used for 3GPP2 support; any specifications that are unique to 3GPP2 are listed under 3GPP2 References.|
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