> Serving Gateway Overview
> The ASR 5000 Core Platform provides wireless carriers with a flexible solution that functions as a Serving Gateway (S-GW) in Long Term Evolution-System Architecture Evolution (LTE-SAE) wireless data networks.
> This overview provides general information about the S-GW including:

> • | eHRPD Network Summary

> • | SAE Network Summary

> • | Product Description

> • | Product Specifications

> • | Network Deployment(s)

> • | Features and Functionality - Base Software

> • | Features and Functionality - External Application Support

> • | Features and Functionality - Optional Enhanced Feature Software

> • | How the Serving Gateway Works

> • | Supported Standards

> eHRPD Network Summary
> In a High Rate Packet Data (HRPD) network, mobility is performed using client-based mobile IPv6 or Client Mobile IPv6 (CMIPv6). This involves the mobile node with an IPv6 stack maintaining a binding between its home address and its care-of address. The mobile node must also send mobility management signaling messages to a home agent.
> The primary difference in an evolved HRPD (eHRPD) network is the use of network mobility (via proxy) allowing the network to perform mobility management, instead of the mobile node. This form of mobility is known as Proxy Mobile IPv6 (PMIPv6).
> One of the eHRPD network’s functions is to provide interworking of the mobile node with the 3GPP Evolved Packet Core (EPC). The EPC is a high-bandwidth, low-latency packet network also know as System Architecture Evolution (SAE), supporting the Long Term Evolution Radio Access Network (LTE RAN). The following figure shows the relationship of the eHRPD network with the EPC.
> eHRPD Network Components
> The eHRPD network is comprised of the following components:
> Evolved Access Network (eAN)
> The eAN is a logical entity in the radio access network used for radio communications with an access terminal (mobile device). The eAN is equivalent to a base station in 1x systems. The eAN supports operations for EPS – eHRPD RAN in addition to legacy access network capabilities.
> Evolved Packet Control Function (ePCF)
> The ePCF is an entity in the radio access network that manages the relay of packets between the eAN and the HSGW. The ePCF supports operations for the EPS – eHRPD RAN in addition to legacy packet control functions.
> The ePCF supports the following:

> • | Main service connection over SO59

> • | Uses PDN-MUX and allows multiplexing data belonging to multiple PDNs

> • | Signaling over Main A10

> • | LCP messages for PPP link establishment

> • | EAP messages used for authentication

> • | VSNCP messages for establishment of PDNs

> • | VSNP for establishment of EPS bearers and QoS mappings (RSVP)

> HRPD Serving Gateway (HSGW)
> The HSGW is the entity that terminates the HRPD access network interface from the eAN/PCF. The HSGW functionality provides interworking of the AT with the 3GPP EPS architecture and protocols specified in 23.402 (mobility, policy control (PCC), and roaming). The HSGW supports efficient (seamless) inter-technology mobility between LTE and HRPD with the following requirements:

> • | Sub 300ms bearer interruption

> • | Inter-technology handoff between 3GPP E-UTRAN and HRPD

> • | Intra-technology handoff between an HSGW and an existing PDSN

> • | Support for inter-HSGW fast handoff via PMIPv6 Binding Update

> SAE Network Summary
> The System Architecture Evolution was developed to provide a migration path for 3GPP systems and introduce higher data rates and lower latency for a variety of radio access technologies. SAE defines the packet network supporting the high-bandwidth radio network as the Evolved Packet Core (EPC). The EPC provides mobility between 3GPP (GSM, UMTS, and LTE) and non-3GPP radio access technologies, including CDMA, WiMAX, WiFi, High Rate Packet Data (HRPD), evolved HRPD, and ETSI defined TISPAN networks.
> The following figure shows the interworking of the EPC with the different radio access technologies.
> E-UTRAN EPC Network Components
> The E-UTRAN EPC network is comprised of the following components:
> eNodeB
> The eNodeB is the LTE base station and is one of two nodes in the SAE Architecture user plane (the other is the S-GW). The eNodeB communicates with other eNodeBs via the X2 interface. The eNodeB communicates with the EPC via the S1 interface. The user plane interface is the S1-U connection to S-GW. The signaling plane interface is the S1-MME connection to MME.
> Basic functions supported include:

> • | Radio resource management, radio bearer control, and scheduling

> • | IP header compression and encryption of user data stream

> • | Selection of MME at UE attachment (if not determined by information sent from the UE)

> • | Scheduling and transmission of paging messages (originated from the MME)

> • | Scheduling and transmission of broadcast information (originated from the MME or OA&M)

> • | Measurement & measurement reporting configuration for mobility and scheduling

> Mobility Management Entity (MME)
> The MME is the key control-node for the LTE access-network. The MME provides the following basic functions:

> • | NAS

> • | signalling

> • | signalling security

> • | UE access in ECM-IDLE state (including control and execution of paging retransmission)

> • | Tracking Area (TA) list management

> • | PGW and SGW selection

> • | MME selection for handovers with MME change

> • | SGSN selection for handovers to 2G or 3G 3GPP access networks

> • | Terminates interface to HSS (S6a)

> • | Authentication

> • | Bearer management functions including dedicated bearer establishment

> • | HRPD access node (terminating S101 reference point) selection for handovers to HRPD

> • | Transparent transfer of HRPD signalling messages and transfer of status information between E-UTRAN and HRPD access, as specified in the pre-registration and handover flows

> Serving Gateway (S-GW)
> For each UE associated with the EPS, there is a single S-GW at any given time providing the following basic functions:

> • | Terminates the interface towards E-UTRAN (S1-U)

> • | Functions (for both the GTP-based and the PMIP-based S5/S8) include:

> • | local mobility anchor point for inter-eNodeB handover

> • | mobility anchoring for inter-3GPP mobility (terminating S4 and relaying the traffic between 2G/3G system and P-GW)

> • | ECM-IDLE mode downlink packet buffering and initiation of network triggered service request procedure

> • | lawful intercept

> • | packet routing and forwarding

> • | transport level packet marking in the uplink and the downlink (e.g. setting the DiffServ Code Point)

> • | Accounting

> • | Handling of Router Solicitation and Router Advertisement messages if PMIP based S5/S8 is used

> • | MAG for PMIP based S5 and S8

> PDN Gateway (P-GW)
> For each UE associated with the EPS, there is at least one P-GW providing access to the requested PDN. If a UE is accessing multiple PDNs, there may be more than one P-GW for that UE. The P-GW provides the following basic functions:

> • | Terminates the interface towards the PDN (SGi)

> • | P-GW functions (for both the GTP-based and the PMIP-based S5/S8) include:

> • | per-user packet filtering (e.g. deep packet inspection)

> • | lawful intercept

> • | UE IP address allocation

> • | UL and DL service level charging, gating control, and service level rate enforcement

> • | DL rate enforcement based on AMBR (Aggregate Max Bit Rate) and based on the accumulated MBRs of the aggregate of SDFs with the same GBR QCI

> • | DHCPv4 and DHCPv6 functions (client, relay and server)

> • | LMA for PMIP6

> Product Description
> The Serving Gateway routes and forwards data packets from the UE and acts as the mobility anchor during inter-eNodeB handovers. Signals controlling the data traffic are received on the S-GW from the MME which determines the S-GW that will best serve the UE for the session. Every UE accessing the EPC is associated with a single S-GW.
> The S-GW is also involved in mobility by forwarding down link data during a handover from the E-UTRAN to the eHRPD network. An interface from the eAN/ePCF to an MME provides signaling that creates a GRE tunnel between the S-GW and the eHRPD Serving Gateway.
> Basic E-UTRAN/EPC and eHRPD Network Topology
> The functions of the S-GW for both GTP-based and PMIP-based network sessions include:

> • | packet routing and forwarding.

> • | providing the local mobility anchor point for inter-eNodeB handover and assisting the eNodeB reordering function by sending one or more “end marker” packets to the source eNodeB immediately after switching the path.

> • | mobility anchoring for inter-3GPP mobility (terminating the S4 interface from an SGSN and relaying the traffic between 2G/3G system and a PDN gateway.

> • | packet buffering for ECM-IDLE mode downlink and initiation of network triggered service request procedure.

> • | replicating user traffic in the event that Lawful Interception is required.

> • | transport level packet marking.

> • | user accounting and QCI granularity for charging.

> • | uplink and downlink charging per UE, PDN, and QCI.

> Product Specifications
> The following information is located in this section:

> • | Licenses

> • | Hardware Requirements

> • | Operating System Requirements

> Licenses
> The S-GW is a licensed product. A session use license key must be acquired and installed to use the S-GW service.
> The following licenses are available for this product:

> • | S-GW Software License, 10k Sessions - 600-00-7644

> • | S-GW Software License, 1k Sessions - 600-00-7645

> Hardware Requirements
> Information in this section describes the hardware required to enable S-GW services.
> Platforms
> The S-GW service operates on the ASR 5000 Series platforms:
> Components
> The following application and line cards are required to support S-GW 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): Within the ASR 5000 platform, PSCs provide high-speed, multi-threaded PDP context processing capabilities for 4G S-GW 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 PSCs, these cards provide the physical interfaces to elements in the E-UTRAN EPC data network. Up to 26 line cards can be installed for a fully loaded system with 13 active PSCs, 13 in the upper-rear slots and 13 in the lower-rear slots for redundancy. Redundant PSCs do not require line cards.

> • | Ethernet 10/100 and/or Ethernet 1000 line cards for IP connections to other network elements.

> • | Redundancy Crossbar Cards (RCCs): Installed in the lower-rear chassis slots directly behind the SPCs/SMCs, RCCs utilize 5 Gbps serial links to ensure connectivity between Ethernet 10/100 or Ethernet 1000 line cards and every PSC in the system for redundancy. Two RCCs can be installed to provide redundancy for all line cards and PSCs.

> Important: Additional information pertaining to each of the application and line cards required to support LTE-SAE services is located in the Hardware Platform Overview chapter of the Product Overview Guide.
> Operating System Requirements
> The S-GW is available for all Cisco ASR 5000 Platforms running StarOS Release 9.0 or later.
> Network Deployment(s)
> This section describes the supported interfaces and the deployment scenarios of a Serving Gateway.
> Serving Gateway in the E-UTRAN/EPC Network
> The following figure displays a simplified network view of the S-GW and how it interconnects with other 3GPP Evolved-UTRAN/Evolved Packet Core network devices.
> S-GW in the E-UTRAN/EPC Network
> Supported Logical Network Interfaces (Reference Points)
> The following figure displays the specific network interface between a Serving Gateway and other E-UTRAN network devices.
> S-GW Interfaces in the E-UTRAN/EPC Network
> The S-GW provides the following logical network interfaces in support of the E-UTRAN/EPC network:
> S4 Interface
> This reference point (not shown in the figure above) provides tunneling and management between the S-GW and an SGSN.
> S5/S8 Interface
> This reference point provides tunneling (bearer channel) and management (signaling channel) between the S-GW and the P-GW. The S8 interface is used for roaming scenarios. The S5 interface is used for non-roaming.
> Supported protocols:

> • | Transport Layer: UDP, TCP

> • | Tunneling:

> • | GTP: IPv4 or IPv6 GTP-C (signaling channel) and GTP-U (bearer channel)

> • | Network Layer: IPv4, IPv6

> • | Data Link Layer: ARP

> • | Physical Layer: Ethernet

> S1-U Interface
> This reference point provides bearer channel tunneling between the eNodeB and the S-GW. It also supports eNodeB path switching during handovers.
> Supported protocols:

> • | Transport Layer: UDP, TCP

> • | Tunneling: IPv4 or IPv6 GTP-U (bearer channel)

> • | Network Layer: IPv4, IPv6

> • | Data Link Layer: ARP

> • | Physical Layer: Ethernet

> S11 Interface
> This reference point provides GTP-C control signal tunneling between the MME and the S-GW.
> Supported protocols:

> • | Transport Layer: UDP, TCP

> • | Tunneling: IPv4 or IPv6 GTP-C (control channel)

> • | Network Layer: IPv4, IPv6

> • | Data Link Layer: ARP

> • | Physical Layer: Ethernet

> Gxc Interface
> This signaling interface supports the transfer of policy control and charging rules information (QoS) between the Bearer Binding and Event Reporting Function (BBERF) on the S-GW and a Policy and Charging Rules Function (PCRF) server.
> Supported protocols:

> • | Transport Layer: UDP, TCP

> • | Network Layer: IPv4, IPv6

> • | Data Link Layer: ARP

> • | Physical Layer: Ethernet

> Features and Functionality - Base Software
> This section describes the features and functions supported by default in the base software for the S-GW service and do not require any additional licenses to implement the functionality.
> Important: To configure the basic service and functionality on the system for the S-GW service, refer to the configuration examples provided in the Serving Gateway Administration Guide.
> The following features are supported and described in this section:

> • | Subscriber Session Management Features

> • | Quality of Service Management Features

> • | Network Access and Charging Management Features

> • | Network Operation Management Functions

> • | System Management Features

> Subscriber Session Management Features
> This section describes the following features:

> • | IPv6 Capabilities

> • | Lawful Intercept

> • | Subscriber Level Trace

> • | Session Recovery Support

> IPv6 Capabilities
> Enables increased address efficiency and relieves pressures caused by rapidly approaching IPv4 address exhaustion problem.
> The S-GW platform offers the following IPv6 capabilities:
> IPv6 Connections to Attached Elements
> IPv6 transport and interfaces are supported on all of the following connections:

> • | Diameter Gxc policy signaling interface

> • | Diameter Rf offline charging interface

> • | Lawful Intercept (X1, X2 interfaces)

> Routing and Miscellaneous Features

> • | OSPFv3

> • | MP-BGP v6 extensions

> • | IPv6 flows (Supported on all Diameter QoS and Charging interfaces as well as Inline Services (e.g. ECS, P2P detection, Stateful Firewall, etc)

> Lawful Intercept
> Provides a standardized architecture for lawful monitoring and interception of subscriber call content and control events as mandated by a court ordered warrant from a law enforcement agency.
> In accordance with 3GPP TS 33.108 Release 8 requirements the Cisco S-GW supports the Lawful Intercept Access Function for intercepting control and data messages of mobile targets. Law Enforcement Agencies request the network operator to start the interception of a particular mobile user based on court ordered subpoenas.
> The Cisco EPC gateways provide access to the intercepted Content of Communications (CC) and the Intercept Related Information (IRI) of the mobile target and services related to the target on behalf of Law Enforcement Agencies. In this release the S-GW supports the following three interfaces:

> • | X1 provisioning interface from Administrative Function (ADMF) using CLI over SSH: Intercept targets can be provisioned using subscriber information including MSISDN, IMSI and MEI. Interception of only events (IRI) or events and call content (IRI + CC) can be provisioned.

> • | X2 event delivery interface for transferring Intercept Related Information (IRI) to a Delivery Function/Mediation server: Intercepted events include QoS information (if available), bearer activation (Default and Dedicated bearer), start of intercept with bearer active, bearer modification, bearer deactivation, and UE requested bearer resource modification.

> • | X3 content delivery: Includes intercepted call content for all default and dedicated EPS bearers.

> The intercepted call control data is encoded in a Cisco proprietary message header format using an optional TLV field to pack the IRI information. The message header also includes other identifying information including sequence numbers, timestamps and session & correlation numbers to correlate session and bearer related information with interception on other EPC elements. If provisioning is activated while the call is active for the target identity then the intercepted information is immediately forwarded to the mediation server. Otherwise camp-on monitoring is used and the system waits for the call to become active (ECM CONNECTED state) and compares the IMSI, MSISDN and MEI against the LI monitoring list as a trigger to begin the intercept.
> A total of 20,000 simultaneous LI triggers can be provisioned on the Cisco P-GW, S-GW or MME. Our solution is currently interoperable with leading mediation solutions from partners such as SS8 and Utimaco.
> Important: For more information on Lawful Intercept support, refer to the Lawful Intercept Configuration Guide.
> Subscriber Level Trace
> Provides a 3GPP standards-based session level trace function for call debugging and testing new functions and access terminals in an LTE environment.
> As a complement to Cisco's protocol monitoring function, the S-GW supports 3GPP standards based session level trace capabilities to monitor all call control events on the respective monitored interfaces including S1-U, S11, S5/S8, and Gxc. The trace can be initiated using multiple methods:

> • | Management initiation via direct CLI configuration

> • | Management initiation at HSS with trace activation via authentication response messages over S6a reference interface

> • | Signaling based activation through signaling from subscriber access terminal

> Note: Once the trace is provisioned it can be provisioned through the access cloud via various signaling interfaces.
> The session level trace function consists of trace activation followed by triggers. The time between the two events is treated much like Lawful Intercept where the EPC network element buffers the trace activation instructions for the provisioned subscriber in memory using camp-on monitoring. Trace files for active calls are buffered as XML files using non-volatile memory on the local dual redundant hard drives on the ASR 5000 platform. The Trace Depth defines the granularity of data to be traced. Six levels are defined including Maximum, Minimum and Medium with ability to configure additional levels based on vendor extensions.
> All call control activity for active and recorded sessions is sent to an off-line Trace Collection Entity (TCE) using a standards-based XML format over a FTP or secure FTP (SFTP) connection. In the current release the IPv4 interfaces are used to provide connectivity to the TCE. Trace activation is based on IMSI or IMEI. Once a subscriber level trace request is activated it can be propagated via the S5/S8 signaling to provision the corresponding trace for the same subscriber call on the P-GW. The trace configuration will only be propagated if the P-GW is specified in the list of configured Network Element types received by the S-GW. Trace configuration can be specified or transferred in any of the following message types:

> • | S11: Create Session Request

> • | S11: Trace Session Activation

> • | S11: Modify Bearer Request

> Performance Goals:
> As subscriber level trace is a CPU intensive activity the max number of concurrently monitored trace sessions per Cisco P-GW or S-GW is 32. Use in a production network should be restricted to minimize the impact on existing services.
> Session Recovery Support
> 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.
> In the telecommunications industry, over 90 percent of all equipment failures are software-related. With robust hardware failover and redundancy protection, any card-level hardware failures on the system can quickly be corrected. However, software failures can occur for numerous reasons, many times without prior indication. StarOS Release 9.0 adds the ability to support stateful intra-chassis session recovery for S-GW sessions.
> When session recovery occurs, the system reconstructs the following subscriber information:

> • | Data and control state information required to maintain correct call behavior

> • | Subscriber data statistics that are required to ensure that accounting information is maintained

> • | A best-effort attempt to recover various timer values such as call duration, absolute time, and others

> Session recovery is also useful for in-service software patch upgrade activities. If session recovery is enabled during the software patch upgrade, it helps to preserve existing sessions on the active PSC during the upgrade process.
> Important: For more information on session recovery support, refer to the Session Recovery chapter in the System Enhanced Feature Configuration Guide.
> Quality of Service Management Features
> This section describes the following features:

> • | QoS Bearer Management

> QoS Bearer Management
> Provides a foundation for contributing towards improved Quality of User Experience (QoE) by enabling deterministic end-to-end forwarding and scheduling treatments for different services or classes of applications pursuant to their requirements for committed bandwidth resources, jitter and delay. In this way, each application receives the service treatment that users expect.
> An EPS bearer is a logical aggregate of one or more Service Data Flows (SDFs), running between a UE and a P-GW in case of GTP-based S5/S8, and between a UE and HSGW in case of PMIP-based S2a connection. An EPS bearer is the level of granularity for bearer level QoS control in the EPC/E-UTRAN. The Cisco P-GW maintains one or more Traffic Flow Templates (TFTs) in the downlink direction for mapping inbound Service Data Flows (SDFs) to EPS bearers. The P-GW maps the traffic based on the downlink TFT to the S5/S8 bearer. The Cisco P-GW offers all of the following bearer-level aggregate constructs:
> QoS Class Identifier (QCI): An operator provisioned value that controls bearer level packet forwarding treatments (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc). The Cisco EPC gateways also support the ability to map the QCI values to DiffServ codepoints in the outer GTP tunnel header of the S5/S8 connection. Additionally, the platform also provides configurable parameters to copy the DSCP marking from the encapsulated payload to the outer GTP tunnel header.
> Guaranteed Bit Rate (GBR): A GBR bearer is associated with a dedicated EPS bearer and provides a guaranteed minimum transmission rate in order to offer constant bit rate services for applications such as interactive voice that require deterministic low delay service treatment.
> Maximum Bit Rate (MBR): The MBR attribute provides a configurable burst rate that limits the bit rate that can be expected to be provided by a GBR bearer (e.g. excess traffic may get discarded by a rate shaping function). The MBR may be greater than or equal to the GBR for a given dedicated EPS bearer.
> Aggregate Maximum Bit Rate (AMBR): AMBR denotes a bit rate of traffic for a group of bearers destined for a particular PDN. The Aggregate Maximum Bit Rate is typically assigned to a group of Best Effort service data flows over the Default EPS bearer. That is, each of those EPS bearers could potentially utilize the entire AMBR, e.g. when the other EPS bearers do not carry any traffic. The AMBR limits the aggregate bit rate that can be expected to be provided by the EPS bearers sharing the AMBR (e.g. excess traffic may get discarded by a rate shaping function). AMBR applies to all Non-GBR bearers belonging to the same PDN connection. GBR bearers are outside the scope of AMBR.
> Policing & Shaping: The Cisco P-GW offers a variety of traffic conditioning and bandwidth management capabilities. These tools enable usage controls to be applied on a per-subscriber, per-EPS bearer or per-PDN/APN basis. It is also possible to apply bandwidth controls on a per-APN AMBR capacity. These applications provide the ability to inspect and maintain state for user sessions or Service Data Flows (SDF's) within them using shallow L3/L4 analysis or high touch deep packet inspection at L7. Metering of out-of-profile flows or sessions can result in packet discards or reducing the DSCP marking to Best Effort priority. When traffic shaping is enabled the P-GW enqueues the non-conforming session to the provisioned memory limit for the user session. When the allocated memory is exhausted, the inbound/outbound traffic for the user can be transmitted or policed in accordance with operator provisioned policy.
> Network Access and Charging Management Features
> This section describes the following features:

> • | OnlineOffline Charging

> Online/Offline Charging
> The Cisco EPC platforms offer support for offline charging interactions with external OCS and CGF/CDF servers.
> Ga/Gz Reference Interfaces
> The Cisco P-GW supports 3GPP Release 8 compliant offline charging as defined in TS 32.251,TS 32.297 and 32.298. Whereas the S-GW generates SGW-CDRs to record subscriber level access to PLMN resources, the P-GW creates PGW-CDRs to record user access to external networks. Additionally when Gn/Gp interworking with pre-release SGSNs is enabled, the GGSN service on the P-GW records G-CDRs to record user access to external networks.
> To provide subscriber level accounting, the Cisco S-GW supports integrated Charging Transfer Functions (CTF) and Charging Data Functions (CDF). Each gateway uses Charging-ID's to distinguish between default and dedicated bearers within subscriber sessions. The Ga/Gz reference interface between the CDF and CGF is used to transfer charging records via the GTPP protocol. In a standards based implementation, the CGF consolidates the charging records and transfers them via an FTP/S-FTP connection over the Bm reference interface to a back-end billing mediation server. The Cisco EPC gateways also offer the ability to FTP/S-FTP charging records between the CDF and CGF server. CDR records include information such as Record Type, Served IMSI, ChargingID, APN Name, TimeStamp, Call Duration, Served MSISDN, PLMN-ID, etc. The ASR 5000 platform offers a local directory to enable temporary file storage and buffer charging records in persistent memory located on a pair of dual redundant RAID hard disks. Each drive includes 147GB of storage and up to 100GB of capacity is dedicated to storing charging records. For increased efficiency it also possible to enable file compression using protocols such as GZIP. The Offline Charging implementation offers built-in heart beat monitoring of adjacent CGFs. If the Cisco P-GW have not heard from the neighbor CGF within the configurable polling interval, they will automatically buffer the charging records on the local drives until the CGF reactivates itself and is able to begin pulling the cached charging records.
> The P-GW supports a Policy Charging Enforcement Function (PCEF) to enable Flow Based Bearer Charging (FBC) via the Gy reference interface to adjunct OCS servers (See Online Charging description above).
> Network Operation Management Functions
> This section describes the following features:

> • | Support Interfaces (Reference Points)

> • | Multiple PDN Support

> • | Congestion Control

> • | IP Access Control Lists

> Support Interfaces (Reference Points)
> S1-U (E-UTRAN EPC)
> In an E-UTRAN network S1-U is the per-bearer user plane tunneling reference interface between the S-GW and eNodeB. The S-GW provides the local mobility anchor point for inter-eNodeB hand-overs. It provides inter-eNodeB path switching during hand-overs when the X2 handover interface between base stations cannot be used. The S1-U interface uses GPRS tunneling protocol for user plane (GTP-Uv1). GTP encapsulates all end user IP packets and it relies on UDP/IP transport.
> In order to support S1-U hand-overs the source eNodeB initiates the hand-over by sending the hand-over required message over the S1-MME interface to the MME. The MME then determines if the S-GW needs to be relocated. The eNodeB decides which EPS bearers are subject to forwarding to the target base station. In the S1-U hand-over, the hand-off occurs indirectly from the source eNodeB to the target via the source and target S-GWs.
> S11 (E-UTRAN EPC)
> S11 is the reference interface that provides the control plane protocol (GTP-Cv2) between the MME and S-GW. As with all GTP-based interfaces S11 relies on UDP/IP transport. A GTP tunnel is identified in each node with a Tunnel Endpoint ID (TEID), IP address and UDP port number. The TEID values are exchanged between the tunnel endpoints using GTP-C. There is one GTP-C tunnel between the MME and S-GW for each mobile terminal. The GTP protocol provides the following functions:

> • | Bearer management function: This functionality is responsible for bearer management; setting up, modifying and releasing EPS bearers, which are triggered by the MME. The release of EPS bearers may be triggered by the P-GW or HSS as well. The messages include Create Session request, Create Bearer request, Create bearer response etc. Additionally GTP tunnel management messages may be sent for any of the following reasons:

> • | Initial UE attachment

> • | UE requests connection to an additional PDN

> • | Tracking Area Update with S-GW change

> • | S1/X2 handover with S-GW change

> • | GERAN or UTRAN to E-UTRAN Inter-RAT handover with SGW change.

> • | Path management function: This functionality is responsible for managing the path between the tunnel endpoints. It includes messages like ECHO request, ECHO response and version not supported indication.

> • | Mobility management functions: This functionality consists of messages that are exchanged between GTP end points to manage UE mobility. Messages such as Forward Relocation request/response are sent between end points. These messages are not sent on the S11 interface.

> S5/S8 GTP (E-UTRAN EPC)
> In accordance with 3GPP TS 23.401 the Cisco S-GW platform supports GTPv2-C and GTPv1-U call control and user plane tunnelling. A GTP tunnel is identified in each node with a Tunnel Endpoint ID (TEID), an IP address and a UDP port number. The S-GW and P-GW nodes provision separate GTP tunnels for each attached subscriber and for the individual PDN connections initiated by the UE. The StarOS distributed software architecture enables each function to run as independent stand-alone services on separate chassis or as simultaneous combination services running on the same platform.
> The S5 reference interface provides user plane tunnelling and tunnel management between an S-GW and P-GW located within the same administrative domain. It is used for S-GW relocation due to UE mobility and if the S-GW needs to connect to a non-collocated P-GW for the required PDN connectivity.
> The S8 reference interface is an inter-PLMN reference point providing user and control plane between the S-GW in the VPLMN and the P-GW in the HPLMN. It is based on the Gp reference point as defined between SGSN and GGSN. S8a is the inter PLMN variant of S5.
> Multiple PDN Support
> Enables an APN-based user experience that enables separate connections to be allocated for different services including IMS, Internet, walled garden services, or offdeck content services.
> The MAG function on the S-GW can maintain multiple PDN or APN connections for the same user session. The MAG runs a single node level Proxy Mobile IPv6 tunnel for all user sessions toward the LMA function of the P-GW. When a user wants to establish multiple PDN connections, the MAG brings up the multiple PDN connections over the same PMIPv6 session to one or more P-GW LMAs. The P-GW in turn allocates separate IP addresses (Home Network Prefixes) for each PDN connection and each one can run one or multiple EPC default & dedicated bearers. To request the various PDN connections, the MAG includes a common MN-ID and separate Home Network Prefixes, APNs and a Handover Indication Value equal to one in the PMIPv6 Binding Updates.
> Congestion Control
> The congestion control feature allows you to set policies and thresholds and specify how the system reacts when faced with a heavy load condition.
> Congestion control monitors the system for conditions that could potentially degrade performance when the system is under heavy load. Typically, these conditions are temporary (for example, high CPU or memory utilization) and are quickly resolved. However, continuous or large numbers of these conditions within a specific time interval may have an impact the system’s ability to service subscriber sessions. Congestion control helps identify such conditions and invokes policies for addressing the situation.
> Congestion control operation is based on configuring the following:

> • | 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.

> A threshold tolerance dictates the percentage under the configured threshold that must be reached in order for the condition to be cleared. An SNMP trap, starCongestionClear, is then triggered.

> • | 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.

> • | Port-specific Thresholds: If you set port-specific thresholds, when any individual port-specific threshold is reached, congestion control is enabled system-wide.

> • | 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.

> Important: For more information on congestion control, refer to the Congestion Control chapter in the System Enhanced Feature Configuration Guide.
> IP Access Control Lists
> IP access control lists allow you to set up rules that control the flow of packets into and out of the system based on a variety of IP packet parameters.
> IP access lists, or Access Control Lists (ACLs) as they are commonly referred to, are used to control the flow of packets into and out of the system. They are configured on a per-context basis and consist of “rules” (ACL rules) or filters that control the action taken on packets that match the filter criteria. Once configured, an ACL can be applied to any of the following:

> • | An individual interface

> • | All traffic facilitated by a context (known as a policy ACL)

> • | An individual subscriber

> • | All subscriber sessions facilitated by a specific context

> Important: For more information on IP access control lists, refer to the IP Access Control Lists chapter in the System Enhanced Feature Configuration Guide.
> System Management Features
> This section describes following features:

> • | Management System Overview

> • | Bulk Statistics Support

> • | Threshold Crossing Alerts (TCA) Support

> • | ANSI T1.276 Compliance

> Management System Overview
> The system's management capabilities are designed around the Telecommunications Management Network (TMN) model for management - focusing on providing superior quality Network Element (NE) and element management system (Web Element Manager) functions. The system provides element management applications that can easily be integrated, using standards-based protocols (CORBA and SNMPv1, v2), into higher-level management systems - giving wireless operators the ability to integrate the system into their overall network, service, and business management systems. In addition, all management is performed out-of-band for security and to maintain system performance.
> Cisco's O&M module offers comprehensive management capabilities to the operators and enables them to operate the system more efficiently. There are multiple ways to manage the system either locally or remotely using its out-of-band management interfaces.
> These include:

> • | Using the Command Line Interface (CLI)

> • | Remote login using Telnet, and Secure Shell (SSH) access to CLI through SPIO card's Ethernet management interfaces

> • | Local login through the console port on SPIO card using an RS-232 serial connection

> • | Using the Web Element Manager application

> • | Supports communications through 10 Base-T, 100 Base-TX, 1000 Base-TX, or 1000

> • | Base-SX (optical gigabit Ethernet) Ethernet management interfaces on the SPIO

> • | Client-Server model supports any browser (i.e. Microsoft Internet Explorer v5.0 and above or Netscape v4.7 or above, and others)

> • | Supports Common Object Request Broker Architecture (CORBA) protocol and Simple Network Management Protocol version 1 (SNMPv1) for fault management

> • | Provides complete Fault, Configuration, Accounting, Performance, and Security (FCAPS) capabilities

> • | Can be easily integrated with higher-level network, service, and business layer applications using the Object Management Group's (OMG’s) Interface Definition Language (IDL)

> The following figure demonstrates these various element management options and how they can be utilized within the wireless carrier network.
> Element Management Methods
> Important: P-GW 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 and P-GW Administration Guide.
> Bulk Statistics Support
> The system's support for bulk statistics allows operators to choose to view not only statistics that are of importance to them, but also to configure the format in which it is presented. This simplifies the post-processing of statistical data since it can be formatted to be parsed by external, back-end processors.
> When used in conjunction with the Web Element Manager, the data can be parsed, archived, and graphed.
> The system can be configured to collect bulk statistics (performance data) and send them to a collection server (called a receiver). Bulk statistics are statistics that are collected in a group. The individual statistics are grouped by schema. Following is a partial list of supported schemas:

> • | System: Provides system-level statistics

> • | Card: Provides card-level statistics

> • | Port: Provides port-level statistics

> • | MAG: Provides MAG service statistics

> • | S-GW: Provides S-GW node-level service statistics

> • | IP Pool: Provides IP pool statistics

> • | APN: Provides Access Point Name statistics

> The system supports the configuration of up to 4 sets (primary/secondary) of receivers. Each set can be configured with to collect specific sets of statistics from the various schemas. Statistics can be pulled manually from the system or sent at configured intervals. The bulk statistics are stored on the receiver(s) in files.
> The format of the bulk statistic data files can be configured by the user. Users can specify the format of the file name, file headers, and/or footers to include information such as the date, system host name, system uptime, the IP address of the system generating the statistics (available for only for headers and footers), and/or the time that the file was generated.
> When the Web Element Manager is used as the receiver, it is capable of further processing the statistics data through XML parsing, archiving, and graphing.
> The Bulk Statistics Server component of the Web Element Manager parses collected statistics and stores the information in the PostgreSQL database. If XML file generation and transfer is required, this element generates the XML output and can send it to a Northbound NMS or an alternate bulk statistics server for further processing.
> Additionally, if archiving of the collected statistics is desired, the Bulk Statistics server writes the files to an alternative directory on the server. A specific directory can be configured by the administrative user or the default directory can be used. Regardless, the directory can be on a local file system or on an NFS-mounted file system on the Web Element Manager server.
> Important: For more information on bulk statistic configuration, refer to the Configuring and Maintaining Bulk Statistics chapter in the System Administration Guide.
> Threshold Crossing Alerts (TCA) Support
> Thresholding on the system is used to monitor the system for conditions that could potentially cause errors or outage. Typically, these conditions are temporary (i.e high CPU utilization, or packet collisions on a network) and are quickly resolved. However, continuous or large numbers of these error conditions within a specific time interval may be indicative of larger, more severe issues. The purpose of thresholding is to help identify potentially severe conditions so that immediate action can be taken to minimize and/or avoid system downtime.
> The system supports Threshold Crossing Alerts for certain key resources such as CPU, memory, IP pool addresses, etc. With this capability, the operator can configure threshold on these resources whereby, should the resource depletion cross the configured threshold, a SNMP Trap would be sent.
> The following thresholding models are supported by the system:

> • | 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.

> • | 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.

> Thresholding reports conditions using one of the following mechanisms:

> • | SNMP traps: SNMP traps have been created that indicate the condition (high threshold crossing and/or clear) of each of the monitored values.

> Generation of specific traps can be enabled or disabled on the chassis. Ensuring that only important faults get displayed. SNMP traps are supported in both Alert and Alarm modes.

> • | 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.

> Logs are supported in both the Alert and the Alarm models.

> • | 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.

> The Alarm System is used only in conjunction with the Alarm model.
> Important: For more information on threshold crossing alert configuration, refer to the Thresholding Configuration Guide.
> ANSI T1.276 Compliance
> ANSI T1.276 specifies security measures for Network Elements (NE). In particular it specifies guidelines for password strength, storage, and maintenance security measures.
> ANSI T1.276 specifies several measures for password security. These measures include:

> • | Password strength guidelines

> • | Password storage guidelines for network elements

> • | Password maintenance, e.g. periodic forced password changes

> These measures are applicable to the ASR 5000 Platform and the Web Element Manager since both require password authentication. A subset of these guidelines where applicable to each platform will be implemented. A known subset of guidelines, such as certificate authentication, are not applicable to either product. Furthermore, the platforms support a variety of authentication methods such as RADIUS and SSH which are dependent on external elements. ANSI T1.276 compliance in such cases will be the domain of the external element. ANSI T1.276 guidelines will only be implemented for locally configured operators.
> Features and Functionality - External Application Support
> This section describes the features and functions of external applications supported on the S-GW. These services require additional licenses to implement the functionality.

> • | Web Element Management System

> Web Element Management System
> The Web Element Manager (WEM) provides a graphical user interface (GUI) for performing fault, configuration, accounting, performance, and security (FCAPS) management of the ASR 5000 Platform.
> The Web Element Manager is a Common Object Request Broker Architecture (CORBA)-based application that provides complete fault, configuration, accounting, performance, and security (FCAPS) management capability for the system.
> For maximum flexibility and scalability, the Web Element Manager application implements a client-server architecture. This architecture allows remote clients with Java-enabled web browsers to manage one or more systems via the server component which implements the CORBA interfaces. The server component is fully compatible with the fault-tolerant Sun® Solaris® operating system.
> The following figure demonstrates various interfaces between the Cisco Web Element Manager and other network components.
> Web Element Manager Network Interfaces
> Important: For more information on WEM support, refer to the WEM Installation and Administration Guide.
> Features and Functionality - Optional Enhanced Feature Software
> This section describes the optional enhanced features and functions for the S-GW service.
> Each of the following features require the purchase of an additional license to implement the functionality with the S-GW service.
> This section describes following features:

> • | IP Security (IPSec) Encryption

> • | Traffic Policing and Shaping

> • | Layer 2 Traffic Management (VLANs)

> IP Security (IPSec) Encryption
> Enables network domain security for all IP packet switched LTE-EPC networks in order to provide confidentiality, integrity, authentication, and anti-replay protection. These capabilities are insured through use of cryptographic techniques.
> The Cisco S-GW supports IKEv1 and IPSec encryption using IPv4 addressing. IPSec enables the following two use cases:

> • | Encryption of S8 sessions and EPS bearers in roaming applications where the P-GW is located in a separate administrative domain from the S-GW

> • | IPSec ESP security in accordance with 3GPP TS 33.210 is provided for S1 control plane, S1 bearer plane and S1 management plane traffic. Encryption of traffic over the S1 reference interface is desirable in cases where the EPC core operator leases radio capacity from a roaming partner's network.

> Important: For more information on IPSec support, refer to the IP Security chapter in the System Enhanced Feature Configuration Guide.
> Traffic Policing and Shaping
> Traffic policing and shaping allows you to manage bandwidth usage on the network and limit bandwidth allowances to subscribers. Shaping allows you to buffer excesses to be delivered at a later time.
> Traffic Policing
> Traffic policing enables the configuring and enforcing of bandwidth limitations on individual subscribers and/or APNs of a particular traffic class in 3GPP/3GPP2 service.
> Bandwidth enforcement is configured and enforced independently on the downlink and the uplink directions.
> A Token Bucket Algorithm (a modified trTCM) [RFC2698] is used to implement the Traffic-Policing feature. The algorithm used measures the following criteria when determining how to mark a packet:

> • | Committed Data Rate (CDR): The guaranteed rate (in bits per second) at which packets can be transmitted/received for the subscriber during the sampling interval.

> • | Peak Data Rate (PDR): The maximum rate (in bits per second) that subscriber packets can be transmitted/received for the subscriber during the sampling interval.

> • | Burst-size: The maximum number of bytes that can be transmitted/received for the subscriber during the sampling interval for both committed (CBS) and peak (PBS) rate conditions. This represents the maximum number of tokens that can be placed in the subscriber’s “bucket”. Note that the committed burst size (CBS) equals the peak burst size (PBS) for each subscriber.

> The system can be configured to take any of the following actions on packets that are determined to be in excess or in violation:

> • | Drop: The offending packet is discarded.

> • | Transmit: The offending packet is passed.

> • | Lower the IP Precedence: The packet’s ToS bit is set to “0”, thus downgrading it to Best Effort, prior to passing the packet. Note that if the packet’s ToS bit was already set to “0”, this action is equivalent to “Transmit”.

> Traffic Shaping
> Traffic Shaping is a rate limiting method similar to the Traffic Policing, but provides a buffer facility for packets exceeded the configured limit. Once the packet exceeds the data-rate, the packet queued inside the buffer to be delivered at a later time.
> The bandwidth enforcement can be done in the downlink and the uplink direction independently. If there is no more buffer space available for subscriber data system can be configured to either drop the packets or kept for the next scheduled traffic session.
> Important: For more information on traffic policing and shaping, refer to the Traffic Policing and Shaping chapter in the System Enhanced Feature Configuration Guide.
> Layer 2 Traffic Management (VLANs)
> Virtual LANs (VLANs) provide greater flexibility in the configuration and use of contexts and services.
> VLANs are configured as “tags” on a per-port basis and allow more complex configurations to be implemented. The VLAN tag allows a single physical port to be bound to multiple logical interfaces that can be configured in different contexts. Therefore, each Ethernet port can be viewed as containing many logical ports when VLAN tags are employed.
> Important: For more information on VLAN support, refer to the VLANs chapter in the System Enhanced Feature Configuration Guide.
> How the Serving Gateway Works
> This section provides information on the function of the S-GW in an EPC E-UTRAN network and presents call procedure flows for different stages of session setup and disconnect.
> The S-GW supports the following network flows:

> • | GTP Serving Gateway CallSession Procedures in an LTE-SAE Network

> GTP Serving Gateway Call/Session Procedures in an LTE-SAE Network
> The following topics and procedure flows are included:

> • | Subscriber-initiated Attach (initial)

> • | Subscriber-initiated Detach

> Subscriber-initiated Attach (initial)
> This section describes the procedure of an initial attach to the EPC network by a subscriber.
> Subscriber-initiated Attach (initial) Call Flow
> Subscriber-initiated Attach (initial) Call Flow Description

> Step | Description
> 1 | The UE initiates the Attach procedure by the transmission of an Attach Request (IMSI or old GUTI, last visited TAI (if available), UE Network Capability, PDN Address Allocation, Protocol Configuration Options, Attach Type) message together with an indication of the Selected Network to the eNodeB. IMSI is included if the UE does not have a valid GUTI available. If the UE has a valid GUTI, it is included.
> 2 | The eNodeB derives the MME from the GUTI and from the indicated Selected Network. If that MME is not associated with the eNodeB, the eNodeB selects an MME using an “MME selection function”. The eNodeB forwards the Attach Request message to the new MME contained in a S1-MME control message (Initial UE message) together with the Selected Network and an indication of the E-UTRAN Area identity, a globally unique E-UTRAN ID of the cell from where it received the message to the new MME.
> 3 | If the UE is unknown in the MME, the MME sends an Identity Request to the UE to request the IMSI.
> 4 | The UE responds with Identity Response (IMSI).
> 5 | If no UE context for the UE exists anywhere in the network, authentication is mandatory. Otherwise this step is optional. However, at least integrity checking is started and the ME Identity is retrieved from the UE at Initial Attach. The authentication functions, if performed this step, involves AKA authentication and establishment of a NAS level security association with the UE in order to protect further NAS protocol messages.
> 6 | The MME sends an Update Location (MME Identity, IMSI, ME Identity) to the HSS.
> 7 | The HSS sends Insert Subscriber Data (IMSI, Subscription Data) message to the MME. The Subscription Data contains the list of all APNs that the UE is permitted to access, an indication about which of those APNs is the Default APN, and the 'EPS subscribed QoS profile' for each permitted APN.
> 8 | The MME validates the UE's presence in the (new) TA. If due to regional subscription restrictions or access restrictions the UE is not allowed to attach in the TA, the MME rejects the Attach Request with an appropriate cause, and may return an Insert Subscriber Data Ack message to the HSS. If subscription checking fails for other reasons, the MME rejects the Attach Request with an appropriate cause and returns an Insert Subscriber Data Ack message to the HSS including an error cause. If all checks are successful then the MME constructs a context for the UE and returns an Insert Subscriber Data Ack message to the HSS. The Default APN shall be used for the remainder of this procedure.
> 9 | The HSS acknowledges the Update Location message by sending an Update Location Ack to the MME. If the Update Location is rejected by the HSS; the MME rejects the Attach Request from the UE with an appropriate cause.
> 10 | The MME selects an S-GW using “Serving GW selection function” and allocates an EPS Bearer Identity for the Default Bearer associated with the UE. If the PDN subscription context contains no P-GW address the MME selects a P-GW as described in clause “PDN GW selection function”. Then it sends a Create Default Bearer Request (IMSI, MME Context ID, APN, RAT type, Default Bearer QoS, PDN Address Allocation, AMBR, EPS Bearer Identity, Protocol Configuration Options, ME Identity, User Location Information) message to the selected S-GW.
> 11 | The S-GW creates a new entry in its EPS Bearer table and sends a Create Default Bearer Request (IMSI, APN, S-GW Address for the user plane, S-GW TEID of the user plane, S-GW TEID of the control plane, RAT type, Default Bearer QoS, PDN Address Allocation, AMBR, EPS Bearer Identity, Protocol Configuration Options, ME Identity, User Location Information) message to the P-GW.
> 12 | If dynamic PCC is deployed, the P-GW interacts with the PCRF to get the default PCC rules for the UE. The IMSI, UE IP address, User Location Information, RAT type, AMBR are provided to the PCRF by the P-GW if received by the previous message.
> 13 | The P-GW returns a Create Default Bearer Response (P-GW Address for the user plane, P-GW TEID of the user plane, P-GW TEID of the control plane, PDN Address Information, EPS Bearer Identity, Protocol Configuration Options) message to the S-GW. PDN Address Information is included if the P-GW allocated a PDN address Based on PDN Address Allocation received in the Create Default Bearer Request. PDN Address Information contains an IPv4 address for IPv4 and/or an IPv6 prefix and an Interface Identifier for IPv6. The P-GW takes into account the UE IP version capability indicated in the PDN Address Allocation and the policies of operator when the P-GW allocates the PDN Address Information. Whether the IP address is negotiated by the UE after completion of the Attach procedure, this is indicated in the Create Default Bearer Response.
> 14 | The Downlink (DL) Data can start flowing towards S-GW. The S-GW buffers the data.
> 15 | The S-GW returns a Create Default Bearer Response (PDN Address Information, S-GW address for User Plane, S-GW TEID for User Plane, S-GW Context ID, EPS Bearer Identity, Protocol Configuration Options) message to the new MME. PDN Address Information is included if it was provided by the P-GW.
> 16 | The new MME sends an Attach Accept (APN, GUTI, PDN Address Information, TAI List, EPS Bearer Identity, Session Management Configuration IE, Protocol Configuration Options) message to the eNodeB.
> 17 | The eNodeB sends Radio Bearer Establishment Request including the EPS Radio Bearer Identity to the UE. The Attach Accept message is also sent along to the UE.
> 18 | The UE sends the Radio Bearer Establishment Response to the eNodeB. In this message, the Attach Complete message (EPS Bearer Identity) is included.
> 19 | The eNodeB forwards the Attach Complete (EPS Bearer Identity) message to the MME.
> 20 | The Attach is complete and UE sends data over the default bearer. At this time the UE can send uplink packets towards the eNodeB which are then tunnelled to the S-GW and P-GW.
> 21 | The MME sends an Update Bearer Request (eNodeB address, eNodeB TEID) message to the S-GW.
> 22 | The S-GW acknowledges by sending Update Bearer Response (EPS Bearer Identity) message to the MME.
> 23 | The S-GW sends its buffered downlink packets.
> 24 | After the MME receives Update Bearer Response (EPS Bearer Identity) message, if an EPS bearer was established and the subscription data indicates that the user is allowed to perform handover to non-3GPP accesses, and if the MME selected a P-GW that is different from the P-GW address which was indicated by the HSS in the PDN subscription context, the MME sends an Update Location Request including the APN and P-GW address to the HSS for mobility with non-3GPP accesses.
> 25 | The HSS stores the APN and P-GW address pair and sends an Update Location Response to the MME.
> 26 | Bidirectional data is passed between the UE and PDN.

> ‌
> Subscriber-initiated Detach
> This section describes the procedure of detachment from the EPC network by a subscriber.
> Subscriber-initiated Detach Call Flow
> Subscriber-initiated Detach Call Flow Description

> Step | Description
> 1 | The UE sends NAS message Detach Request (GUTI, Switch Off) to the MME. Switch Off indicates whether detach is due to a switch off situation or not.
> 2 | The active EPS Bearers in the S-GW regarding this particular UE are deactivated by the MME sending a Delete Bearer Request (TEID) message to the S-GW.
> 3 | The S-GW sends a Delete Bearer Request (TEID) message to the P-GW.
> 4 | The P-GW acknowledges with a Delete Bearer Response (TEID) message.
> 5 | The P-GW may interact with the PCRF to indicate to the PCRF that EPS Bearer is released if PCRF is applied in the network.
> 6 | The S-GW acknowledges with a Delete Bearer Response (TEID) message.
> 7 | If Switch Off indicates that the detach is not due to a switch off situation, the MME sends a Detach Accept message to the UE.
> 8 | The MME releases the S1-MME signalling connection for the UE by sending an S1 Release command to the eNodeB with Cause = Detach.

> ‌
> Supported Standards
> The S-GW service complies with the following standards.

> • | 3GPP References

> • | 3GPP2 References

> • | IETF References

> • | Object Management Group (OMG) Standards

> 3GPP References

> • | 3GPP TR 21.905: Vocabulary for 3GPP Specifications

> • | 3GPP TS 23.003: Numbering, addressing and identification

> • | 3GPP TS 23.007: Restoration procedures

> • | 3GPP TS 23.107: Quality of Service (QoS) concept and architecture

> • | 3GPP TS 23.203: Policy and charging control architecture

> • | 3GPP TS 23.401: General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) access

> • | 3GPP TS 23.402: Architecture Enhancements for non-3GPP accesses

> • | 3GPP TS 23.060. General Packet Radio Service (GPRS); Service description; Stage 2

> • | 3GPP TS 24.008: Mobile radio interface Layer 3 specification; Core network protocols

> • | 3GPP TS 24.229: IP Multimedia Call Control Protocol based on SIP and SDP; Stage 3

> • | 3GPP TS 29.210. Gx application

> • | 3GPP TS 29.212: Policy and Charging Control over Gx reference point

> • | 3GPP TS 29.213: Policy and Charging Control signaling flows and QoS

> • | 3GPP TS 29.214: Policy and Charging Control over Rx reference point

> • | 3GPP TS 29.274: Evolved GPRS Tunnelling Protocol for Control plane (GTPv2-C), version 8.1.1

> • | 3GPP TS 29.274: Evolved GPRS Tunnelling Protocol for Control plane (GTPv2-C), version 8.2.0 (both versions are intentional)

> • | 3GPP TS 29.275: Proxy Mobile IPv6 (PMIPv6) based Mobility and Tunnelling protocols, version 8.1.0

> • | 3GPP TS 29.281: GPRS Tunnelling Protocol User Plane (GTPv1-U)

> • | 3GPP TS 32.251: Telecommunication management; Charging management; Packet Switched (PS) domain charging

> • | 3GPP TS 32.295: Charging management; Charging Data Record (CDR) transfer

> • | 3GPP TS 32.298: Telecommunication management; Charging management; Charging Data Record (CDR) encoding rules description

> • | 3GPP TS 32.299: Charging management; Diameter charging applications

> • | 3GPP TS 33.106: 3G Security; Lawful Interception Requirements

> • | 3GPP TS 36.107: 3G security; Lawful interception architecture and functions

> • | 3GPP TS 36.300: Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description

> • | 3GPP TS 36.412. EUTRAN S1 signaling transport

> • | 3GPP TS 36.413: Evolved Universal Terrestrial Radio Access (E-UTRA); S1 Application Protocol (S1AP)

> • | 3GPP TS 36.414: Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 data transport

> 3GPP2 References

> • | X.P0057-0 v0.11.0 E-UTRAN - eHRPD Connectivity and Interworking: Core Network Aspects

> IETF References

> • | RFC 768: User Datagram Protocol (STD 6).

> • | RFC 791: Internet Protocol (STD 5).

> • | RFC 2131: Dynamic Host Configuration Protocol

> • | RFC 2460: Internet Protocol, Version 6 (IPv6) Specification

> • | RFC 2698: A Two Rate Three Color Marker

> • | RFC 2784: Generic Routing Encapsulation (GRE)

> • | RFC 2890: Key and Sequence Number Extensions to GRE

> • | RFC 3319: Dynamic Host Configuration Protocol (DHCPv6) Options for Session Initiation Protocol (SIP) Servers

> • | RFC 3588: Diameter Base Protocol

> • | RFC 3775: Mobility Support in IPv6

> • | RFC 3646: DNS Configuration options for Dynamic Host Configuration Protocol for IPv6 (DHCPv6)

> • | RFC 4006: Diameter Credit-Control Application

> • | RFC 4282: The Network Access Identifier

> • | RFC 4283: Mobile Node Identifier Option for Mobile IPv6 (MIPv6)

> • | RFC 4861: Neighbor Discovery for IP Version 6 (IPv6)

> • | RFC 4862: IPv6 Stateless Address Autoconfiguration

> • | RFC 5094: Mobile IPv6 Vendor Specific Option

> • | RFC 5213: Proxy Mobile IPv6

> • | Internet-Draft (draft-ietf-netlmm-proxymip6-07.txt): Proxy Mobile IPv6

> • | Internet-Draft (draft-ietf-netlmm-grekey-option-01.txt): GRE Key Option for Proxy Mobile IPv6, work in progress

> • | Internet-Draft (draft-ietf-mext-binding-revocation-02.txt): Binding Revocation for IPv6 Mobility, work in progress

> Object Management Group (OMG) Standards

> • | CORBA 2.6 Specification 01-09-35, Object Management Group

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