Session Control Manager Overview

Session Control Manager Overview
 
 
This chapter contains general overview information about the Session Control Manager (SCM) including:
 
 
Product Description
The Session Control Manager (SCM) delivers and controls a robust multimedia environment today, while preparing for the networks of tomorrow. SCM provides an easy on-ramp to deploying Session Initiation Protocol (SIP)-based services and a future-proof migration path to the IP Multimedia Subsystem/Multimedia Domain (IMS/MMD) architectures.
The SCM performs the following functions:
The SCM consists of multiple IMS components that can be integrated into a single ASR 5000 platform or distributed as standalone network elements:
As standards-based network elements, SCM components can be integrated with each other or with third-party IMS components.
 
IMS Architecture
IP Multimedia Subsystem (IMS) specifies a standard architecture for providing combined IP services (voice, data, multimedia) over the existing public switched domain. IMS is an integral part of the 3GPP, 3GPP2, ETSI, and TISPAN network model standards that define circuit switched, packet switched, and IP multimedia domain environments. IMS also supports multiple access methods such as GSM, WCDMA, CDMA2000, WLAN, and wireless broadband access.
The call signaling protocol used in IMS is the Session Initiation Protocol (SIP). The primary component in the network for resolving and forwarding SIP messages is the Call/Session Control Function (CSCF). The CSCF provides the control and routing function for all IP sessions accessing the network. CSCFs are located in the control plane or layer of the Service Delivery Network as shown in the figure below.
When the SCM acts as an Access Border Gateway (A-BG), it uses the RFC3261/P-CSCF to provide a SIP/IMS control plane access border, as well as a bearer access border control function. Therefore, the A-BG provides all session border control functions for all SIP UEs attempting to access the mobile network from a network outside of the operator's control and operations.
 
IMS Service Delivery Networks Components
Collectively, CSCFs are responsible for managing an IMS session, including generating Call Detail Records (CDRs). Four functional behaviors are defined for the CSCF:
The following figure shows the general interaction between the CSCF components and the supporting servers.
 
 
IMS CSCF Components
In addition, the SCM may act as an Access Border Gateway (A-BG).
The following figure shows the general interaction between the A-BG and the supporting servers.
 
Access Border Gateway
 
Proxy-CSCF
The primary point of entry into the IMS network is the Proxy-CSCF (P-CSCF). The P-CSCF is responsible for:
 
The P-CSCF is the handset’s first point of entry into the IMS and is also the outbound proxy for SIP. Once the P-CSCF has completed all of the functions for which it is responsible, the call setup is handed off to the Interrogating-CSCF (I-CSCF).
 
Interrogating-CSCF
The I-CSCF performs mostly as a load distribution device. The I-CSCF queries the Home Subscriber Server (HSS) to identify the appropriate Serving-CSCF (S-CSCF) to which the call is sent. Since the HSS maintains user profile information (much like the Home Location Register (HLR) in the Public Land Mobile Network (PLMN)), the I-CSCF can identify the proper S-CSCF for the call. The I-CSCF may also query a AAA server to determine subscriber profile information using DIAMETER.
Important: The I-CSCF is incorporated into the S-CSCF.
 
I-CSCF Interfaces
The following diagram shows the interfaces/reference points associated with the I-CSCF:
 
 
Serving-CSCF
The Serving-CSCF (S-CSCF) is the access point to services provided to the subscriber. Service examples include session control services, such as call features.
Other services include:
 
The S-CSCF also interacts with the HSS for:
A Breakout Gateway Control Function is integrated into the SCM’s S-CSCF to support PSTN calls.
 
Telephony Application Server (TAS) Basic Supported
The following describe the local basic call features implemented on the S-CSCF:
 
 
Integrated S/I-CSCF
The following Interrogating-CSCF features are supported for the integrated S/I-CSCF:
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.
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.
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.
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.
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.
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.
 
Emergency-CSCF
The Emergency-CSCF (E-CSCF) is a network element in IMS which is responsible for routing an emergency call to a Public Safety Answering Point (PSAP).
To identify the next hop PSAP, E-CSCF interacts with the Location Retrieval Function (LRF). LRF provides the necessary routing information so that E-CSCF can route the request to the appropriate PSAP.
 
E-CSCF Interfaces
The following diagram shows the interfaces/reference points associated with the E-CSCF:
 
 
A-BG
The A-BG is responsible for:
 
 
Product Specifications
 
Technical Specifications
The following table provides product specifications for the SCM.
Session Control Manager Technical Specifications
 
Licenses
The SCM is a licensed product. A session use license key must be acquired and installed to use the SCM service.
The following licenses are available for this product:
Apart from base software license, SCM requires feature licenses for various enhanced features supported on the ASR 5000 platform in SCM service.
 
Hardware Requirements
Information in this section describes the hardware required to properly enable SCM services.
 
Platforms
The SCM operates on the ASR 5000.
 
System Hardware Components
The following application and line cards are required to support SCM functionality on an ASR 5000 platform:
 
 
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.
Packet Services Cards (PSCs/PSC2s): 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.
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.
Line Cards: Installed directly behind PSC/PSC2, 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, 13 in the upper-rear slots and 13 in the lower-rear slots for redundancy. Redundant PSCs/PSC2s do not require line cards.
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 in the system for redundancy. Two RCCs can be installed to provide redundancy for all line cards and PSCs/PSC2s.
Additional information pertaining to each of the application and line cards required to support GPRS/UMTS wireless data services is located in the Hardware Platform Overview.
 
Operating System Requirements
The SCM is available for the ASR 5000 running StarOS Release 8.1 or later.
 
Network Deployments and Interfaces
 
SCM in a CDMA2000 Data Network Deployment
 
Integrated CSCF / A-BG / HA
The SCM is designed to function within a CDMA2000 PDSN network. By combining the SCM with a carrier-class Home Agent, a number of advantages emerge such as increased performance, distributed architecture, and high availability. As shown in the figure below, the SCM supports a number of interfaces used to communicate with other components in an IMS environment and supports the interface used to bridge the CDMA network.
 
CDMA2000 CSCF/A-BG/HA SCM Deployment Example
 
Logical Network Interfaces (Reference Points)
Interfaces, used to support IMS in a CDMA network, can be defined within two categories: SIP and DIAMETER. The SCM incorporates standards-based interfaces for both SIP and DIAMETER network architectures.
 
SIP Interfaces
The following table provides descriptions of SIP interfaces supported by the SCM in a CDMA2000 network deployment.
SIP Interfaces in a CDMA Network
 
DIAMETER Interfaces
The following table provides descriptions of DIAMETER interfaces supported by the SCM in a CDMA2000 network deployment.
DIAMETER Interfaces in a CDMA Network
 
SCM in a GSM/UMTS Data Network Deployment
 
CSCF / A-BG / GGSN Deployment
The SCM is designed to function within a UMTS GGSN network. As shown in following figure, the SCM supports a number of interfaces used to communicate with other components in an IMS environment and supports the interface used to bridge the GGSN network.
 
GSM/UMTS CSCF/A-BG/GGSN SCM Deployment Example
 
Logical Network Interfaces (Reference Points)
Interfaces, used to support IMS in a UMTS network, can be defined within two categories: SIP and DIAMETER. The SCM incorporates standards-based interfaces for both SIP and DIAMETER network architectures.
 
SIP Interfaces
The following table provides descriptions of SIP interfaces supported by the SCM in a GSM/UMTS network deployment.
SIP Interfaces in a GSM/UMTS Network
 
DIAMETER Interfaces
The following table provides descriptions of DIAMETER interfaces supported by the SCM in a GSM/UMTS network deployment.
DIAMETER Interfaces in a GSM/UMTS Network
 
Features and Functionality - Base Software
The following is a list containing a variety of features found in the SCM and the benefits they provide.
 
Call Abort Handling
Call abort handling provides resource cleanup in error scenarios and makes sure resources that are not being used can be used for new calls. This feature is managed gracefully for a P-CSCF failure and CLI-initiated subscriber and session clean up.
 
Call Forking
Call forking allows subscribers to receive calls wherever they are by enabling multi-location UE registration.
 
Call Types Supported
In the IMS architecture, telephony features are normally provided by an external application server. Providing these features with the S-CSCF:
 
The following call types are supported:
 
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).
Mobile-to-Mobile SIP calls - supports SIP-based VoIP calls between mobile data users.
Public Switched Telephone Network (PSTN) calls - can be routed through a 3GPP/2 compliant BGCF located in the S-CSCF.
 
Early IMS Security
Early IMS security allows authenticating the UE without IMS protocols and clients. Based on the 3GPP TR 33.978 specification, the SCM supports security inter-operation with 2G and non-IPSec user devices.
 
Emergency Call Support
P-CSCF gives priority to emergency calls, especially in a congested network. In addition, P-CSCF rejects new calls to any user who is in an emergency call.
 
Error Handling
The SCM supports consistent management of errors in a framework that considers existing and future standards and specifications.
 
Future-proof Solution
The SCM eliminates the capital and operational barriers associated with deploying traditional, server-based SIP proxies that lack carrier-class characteristics, occupy valuable rack space, and require numerous network interfaces, while also introducing additional control hops in the network that add call setup latency.
When operators deploy IMS/MMD, profitability will improve because a seamless on-ramp will be provided by simultaneously supporting 3GPP/3GPP2-based standards, P-CSCF functionality, and IETF SIP standards.
 
Intelligent Integration
For deployed platforms, no new hardware is necessary to install or manage. Functionality is enabled with a simple software download.
Intelligent integration lowers operational expenditure and reduces the number of network elements, network interfaces, and call setup latency.
 
Interworking Function
The SCM allows non-IMS UEs (pre IMS or RFC3261-compliant UEs) to work with the IMS core. When UEs are not IMS compliant, having this protocol interworking function at the edge allows the IMS core to be IMS compliant. After the interworking function inserts all necessary IMS headers toward the IMs core, the call appears to the IMS core network elements as if it is coming from an IMS-compliant UE.
The feature allows simultaneous support of IETF SIP and 3GPP/3GPP2 IMS/MMD clients.
 
MSRP Support
The SCM supports Message Session Relay Protocol (MSRP) session and page modes.
 
Presence Enabled
With its high transaction setup rate, this is an ideal solution to handle a large number of messages generated by presence signaling. CSCF supports all the presence RFC extensions and signaling and interoperates with several presence servers.
 
Redirection
The SCM supports response to 3xx redirect messages. In addition to supporting redirection as per 3GPP, it supports call redirection to other chassis in the network (based on configuration) in case of system overload.
 
Redundancy and Session Recovery
When enabled, provides automatic failover of existing CSCF sessions due to hardware or software faults.
The system recovers from a single hardware or software fault with minimal interruption to the subscriber’s service and maintains session information to rebuild sessions if multiple faults occur.
 
Registration Event Package
A set of event notifications used to inform SIP node of changes made to a registration.
 
Signaling Compression (SigComp)
SigComp compresses SIP call setup messages and is supported on the P-CSCF component. This reduces bandwidth demands on the RAN and reduces setup times.
 
SIP Denial of Service (DoS) Attack Prevention
The A-BG provides a scalable proxy network and a distributed Network Address Translation (NAT) network which effectively mitigates DoS attacks.
Prevents a variety of DoS attacks specific to CSCF and SIP technology.
 
SIP Intelligence at the Core
The SCM provides operators with an easy on-ramp for deploying SIP-based subscriber services while supporting various network control operations that provide the necessary intelligent control to insure a robust, carrier-class subscriber experience is achieved in this always changing multimedia environment.
When integrated into Cisco's session-aware Home Agent or GGSN platform, the SCM becomes the first SIP hop in the network, allowing operators to monitor and control all SIP-based sessions and execute additional value-added functions.
As the logical anchor point within the packet core, the SCM improves the user experience with device and location independence, and enhances subscriber control and policy enforcement with faster, more intelligent decisions for multimedia services.
Furthermore, as Fixed Mobile Convergence takes hold, it will be especially important to incorporate the SCM in the packet core in order to achieve mobility and voice continuity between multiple access networks (3G, WiFi, WiMAX, etc.).
 
Cisco Integrated Session Control Manager
 
SIP Large Message Support
Large notify contains information about multiple users in one message, which reduces the number of SIP messages in the network. Large SIP messages can be sent on UDP if the endpoint can support fragmentation; otherwise, UDP to TCP switching can be used to transport large messages intact.
If a request is within 200 bytes of the path MTU, or if it is larger than 1300 bytes and the path MTU is unknown, the request MUST be sent using TCP. This prevents fragmentation of messages over UDP and provides congestion control for larger messages. P-CSCF/A-BG is also able to handle messages up to the maximum datagram packet size. For UDP, this size is 65,535 bytes, including IP and UDP headers.
Large message support is needed for handling presence signaling traffic as the size of messages could be as large as 50K.
 
SIP Routing Engine
The SIP routing engine deploys SIP in a secure and controlled fashion.
Provides auto discovery of SIP elements, subscriber privacy, call fraud prevention, network security, and thwarting of network overload conditions.
 
Shared Initial Filter Criteria (SiFC)
If both the HSS and the S-CSCF support this feature, subsets of iFC may be shared by several service profiles. The HSS downloads the unique identifiers of the shared iFC sets to the S-CSCF. The S-CSCF uses a locally administered database to map the downloaded identifiers onto the shared iFC sets.
If the S-CSCF does not support this feature, the HSS will not download identifiers of shared iFC sets.
 
Telephony Application Server (TAS) Basic Supported
The following describe the local basic call features implemented on the S-CSCF:
 
TAS Basic provides basic voice call feature support in the SCM. In the IMS architecture, these telephony features are normally provided by an external application server. Providing these features with the S-CSCF:
 
The following describe the local basic call features implemented on the S-CSCF:
 
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.
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.
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.
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.
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.
Call Transfer - This feature allows the subscriber to transfer a call.
Call Waiting - This feature allows the subscriber to receive a second call while on the first call.
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.
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”.
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.
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.
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.
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.
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.
 
Trust Domain
Enables the identification of trusted network entities. This keeps subscriber information confidential when it is received.
 
Features and Functionality - Licensed Enhanced Feature Support
This section describes optional enhanced features and functions.
Each of the following optional enhanced features require the purchase of an additional license to implement the functionality with the SCM.
Important: For more information about enhanced features in this section, refer to the System Enhanced Feature Configuration Guide.
 
Interchassis Session Recovery
The ASR 5000 provides industry leading carrier class redundancy. The systems protects against all single points of failure (hardware and software) and attempts to recover to an operational state when multiple simultaneous failures occur.
The system provides several levels of system redundancy:
Even though Cisco Systems provides excellent intra-chassis redundancy with these two schemes, certain catastrophic failures which can cause total chassis outages, such as IP routing failures, line-cuts, loss of power, or physical destruction of the chassis, cannot be protected by this scheme. In such cases, the Interchassis Session Recovery feature provides geographic redundancy between sites. This has the benefit of not only providing enhanced subscriber experience even during catastrophic outages, but can also protect other systems such as the RAN from subscriber re-activation storms.
The Interchassis Session Recovery feature allows for continuous call processing without interrupting subscriber services. This is accomplished through the use of redundant chassis. The chassis are configured as primary and backup with one being active and one in recovery mode. A checkpoint duration timer is used to control when subscriber data is sent from the active chassis to the inactive chassis. If the active chassis handling the call traffic goes out of service, the inactive chassis transitions to the active state and continues processing the call traffic without interrupting the subscriber session. The chassis determines which is active through a propriety TCP-based connection called a redundancy link. This link is used to exchange Hello messages between the primary and backup chassis and must be maintained for proper system operation.
 
Chassis configured to support Interchassis Session Recovery communicate using periodic Hello messages. These messages are sent by each chassis to notify the peer of its current state. The Hello message contains information about the chassis such as its configuration and priority. A dead interval is used to set a time limit for a Hello message to be received from the chassis' peer. If the standby chassis does not receive a Hello message from the active chassis within the dead interval, the standby chassis transitions to the active state. In situations where the redundancy link goes out of service, a priority scheme is used to determine which chassis processes the session. The following priority scheme is used:
 
Checkpoint messages are sent from the active chassis to the inactive chassis. Checkpoint messages are sent at specific intervals and contain all the information needed to recreate the sessions on the standby chassis, if that chassis were to become active. Once a session exceeds the checkpoint duration, checkpoint data is collected on the session. The checkpoint parameter determines the amount of time a session must be active before it is included in the checkpoint message.
Important: For more information on interchassis session recovery support, refer to the Interchassis Session Recovery chapter in the System Enhanced Feature Configuration Guide.
 
IPSec Support
Encrypted IPSec tunnels are terminated and decrypted so that traffic coming from untrusted networks are secured before entering the secure operator network. This prevents eavesdropping, hijacking, and other intrusive behavior from occurring.
IP Security (IPSec) is a suite of protocols that interact with one another to provide secure private communications across IP networks. These protocols allow the system to establish and maintain secure tunnels with peer security gateways.
Important: IPSec implementation is a mandatory part of IPv6, but it is optional to secure IPv4 traffic.
Important: For more information on IPSec support, refer to the IP Security chapter in the System Enhanced Feature Configuration Guide.
 
IPv4-IPv6 Interworking
This feature allows the P-CSCF to provide IPv4-IPv6 interworking in the following scenarios:
 
In addition, IPv4-IPv6 interworking helps an IPv4 IMS network transition to an all-IPv6 IMS network.
The following interworking requirements are currently supported:
P-CSCF will provide IPv4-IPv6 interworking functionality between IPv6-only UEs and IPv4-only core network elements (I/S-CSCF) by acting as a dual stack. To achieve the dual-stack behavior, P-CSCF will be configured in two services with the first service (V6-SVC) listening on an IPv6 address and the second service (V4-SVC) listening on an IPv4 address. SIP messages coming from IPv6 UEs will come to V6-SVC and will be forwarded to the IPv4 core network through V4-SVC. Similarly, messages from the IPv4 core network come to V4-SVC and will be forwarded to IPv6 UEs via V6-SVC. P-CSCF also provides interworking functionality between IPV4-only UEs and IPv6-only core network elements.
P-CSCF handling different v4-v6 interworking scenarios is shown below.
 
Interworking Between IPv6 UE and IPv4 IMS Core Network
 
Interworking Between IPv4 UE and IPv6 IMS Core Network
To identify the need for IPv4-IPv6 interworking for a new incoming IPv6 REGISTER arriving at V6-SVC, a route lookup is performed based on the request-uri, first in V4-SVC context and then in V6-SVC context if the first lookup does not return any matching route entry. If a matching IPv4 next-hop route entry is found, then this indicates that interworking needs to be done. If no route entry is found, then a DNS query on request-uri domain is done for both A and AAAA type records. If DNS response yields only an IPv4 address, then this is also the case for performing IPv4-IPv6 interworking.
Headers (such as Via, Path, etc.) are automatically set to IPv4 bind address of P-CSCF V4-SVC. Remaining headers will be not be altered and sent as is toward the S-CSCF. The IPv4 address in a Path header received from S-CSCF in 200Ok of REGISTER will be replaced with V6-SVC’s IPv6 address before forwarding to UE.
 
IPv6 Support
In addition to supporting IPv4, the SCM supports IPv6 addressing. A CSCF service can be configured with v6 addresses to support an all v6 network.
Important: For this feature, you may bind a CSCF service to either an IPv4 address or to an IPv6 address, but not both simultaneously.
The following diagram shows the implementation where CSCF supports only IPv4.
 
IPv4 Configuration
With IPv6 support, the configuration supported would look like the following diagram. The DNS server could be either IPv4 or IPv6.
 
 
IPv6 Configuration
Important: The policy interface to PCRF will be IPv6 based when DIAMETER supports IPv6.
 
Session Recovery Support
The Session Recovery feature provides seamless failover and reconstruction of subscriber session information in the event of a hardware or software fault within the system preventing a fully connected user session from being disconnected.
Session recovery is performed by mirroring key software processes (e.g. session manager and AAA manager) within the system. These mirrored processes remain in an idle state (in standby-mode), wherein they perform no processing, until they may be needed in the case of a software failure (e.g. a session manager task aborts). The system spawns new instances of “standby mode” session and AAA managers for each active Control Processor (CP) being used.
Additionally, other key system-level software tasks, such as VPN manager, are performed on a physically separate Packet Services Card (PSC/PSC2) to ensure that a double software fault (e.g. session manager and VPN manager fails at same time on same card) cannot occur. The PSC/PSC2 used to host the VPN manager process is in active mode and is reserved by the operating system for this sole use when session recovery is enabled.
The additional hardware resources required for session recovery include a standby System Management Card (SMC) and a standby PSC/PSC2.
There are two modes for Session Recovery.
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.
Full PSC/PSC2 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.
Session/Call state information is saved in the peer AAA manager task because each AAA manager and session manager task is paired together. These pairs are started on physically different PSCs/PSC2s to ensure task recovery.
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 System Enhanced Feature Configuration Guide.
 
How the SCM Works
This section provides information on the function of the SCM in a CDMA2000 PDSN or UMTS GGSN network and presents call procedure flows for different stages of session setup.
 
Admission and Routing
Admission and routing of subscriber URIs is performed through a number of configurable lists in the SCM.
The following sections describe the main admission and routing techniques used in the SCM. The following figure presents the method and order for admitting and routing sessions within the SCM.
 
Admission and Routing Method
 
CSCF Access Control Lists
Access Control Lists (ACLs) are a set of rules that are applied during CSCF session establishment. A typical use of these rules is to accept or deny registration or session establishment requests. ACLs may be tied to subscribers and/or the whole service. Subscriber based ACLs can also be imported from an external ACL/policy server. In that event, the external policy server address would be configured with the service.
 
A complete explanation of the ACL configuration method is located in Access Control Lists Appendix of the Session Control Manager Configuration Guide.
 
Translation Lists
Translation lists help modify request-uri (i.e. addressing of a CSCF session). One example is that E.164 numbers could be altered by adding prefixes and suffixes or the request-uri could be modified based on the registration database.
 
Route Lists
Route lists are service level lists that assist in finding the next CSCF/UA hop. These are static routes and will override any dynamic routes (based on DNS queries for FQDNs).
 
Signaling Compression
The Session Initiation Protocol (SIP) is a text-based protocol designed for higher bandwidth networks. As such, it is inherently less suited for lower bandwidth environments such as wireless networks. If a wireless handset uses SIP to set up a call, the setup time is significantly increased due to the high overhead of text-based signaling messages.
Signaling Compression (SigComp) is a solution for compressing/decompressing messages generated by application protocols such as SIP. The P-CSCF component of the SCM uses SigComp to reduce call setup times on the access network, typically between the P-CSCF and the UE. The following features are supported:
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.
SigComp Parameter Configuration - P-CSCF allows the configuration of Decompression Memory Size (DMS), State Memory Size (SMS), and Cycles Per Bit (CPB).
Failure Acknowledgement - P-CSCF replies with NACK on decompression failure.
SIP/SDP Static Dictionaries - P-CSCF supports the Session Initiation Protocol/Session Description Protocol Static Dictionary for Signaling Compression.
 
Supported Standards
The SCM service complies with the following standards for CDMA2000 PDSN and UMTS GGSN network wireless data services.
 
Release 8 3GPP References
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 would be listed under Release 8 3GPP2 References.
 
 
Release 7 3GPP References
 
Important: The SCM currently supports the following Release 7 3GPP specifications. Most 3GPP specifications are also used for 3GPP2 support; any specifications that are unique to 3GPP2 are listed under Release 7 3GPP2 References.
 
 
Release 7 3GPP2 References
 
 
 
IETF References
 
 
 
Other
 

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