> Direct Tunnel
> This chapter briefly describes the 3G/4G UMTS direct tunnel (DT) feature, indicates how it is implemented on various systems on a per call basis, and provides feature configuration procedures.
> Products supporting direct tunnel include:

> • | 3G devices (per 3GPP TS 23.919 v8.0.0):

> • | the Serving GPRS Support Node (SGSN)

> • | the Gateway GPRS Support Node (GGSN)

> • | LTE devices (per 3GPP TS 23.401 v8.3.0):

> • | Serving Gateway (S-GW)

> • | PDN Gateway (P-GW)

> Important: Direct tunnel is an enhanced feature and some products may require a feature implementation license. Refer to your product’s administration guide for feature licensing information.
> The SGSN determines if setup of a direct tunnel is allowed or disallowed. Currently, the SGSN and S-GW are the only products that provide configuration commands for this feature. All other products that support direct tunnel, do so by default.
> This chapter provides the following information:

> • | Direct Tunnel Feature Overview

> • | Direct Tunnel Configuration

> Direct Tunnel Feature Overview
> The direct tunnel architecture allows the establishment of a direct user plane (GTP-U) tunnel between the radio access network equipment (RNC) and the GGSN/P-GW.
> Once a direct tunnel is established, the SGSN/S-GW continues to handle the control plane (RANAP/GTP-C) signaling and retains the responsibility of making the decision to establish direct tunnel at PDN context activation.
> GTP-U Direct Tunneling
> A direct tunnel improves the user experience (for example, expedites web page delivery, reduces round trip delay for conversational services) by eliminating switching latency from the user plane. An additional advantage, direct tunnel functionality implements optimization to improve the usage of user plane resources (and hardware) by removing the requirement from the SGSN/S-GW to handle the user plane processing.
> A direct tunnel is achieved upon PDN context activation in the following ways:

> • | 3G network: The SGSN establishes a user plane (GTP-U) tunnel directly between the RNC and the GGSN, using an Updated PDN Context Request toward the GGSN.

> Direct Tunneling - 3G Network

> • | LTE network: When Gn/Gp interworking with pre-release 8 (3GPP) SGSNs is enabled, the GGSN service on the P-GW supports direct tunnel functionality. The SGSN establishes a user plane (GTP-U) tunnel directly between the RNC and the GGSN/P-GW, using an Update PDN Context Request toward the GGSN/P-GW.

> Direct Tunneling - LTE Network, GTP-U Tunnel

> • | LTE network: The SGSN establishes a user plane tunnel (GTP-U tunnel over an S12 interface) directly between the RNC and the S-GW, using an Update PDN Context Request toward the S-GW.

> Direct Tunneling - LTE Network, S12 Interface
> A major consequence of deploying a direct tunnel is that it produces a significant increase in control plane load on both the SGSN/S-GW and GGSN/P-GW components of the packet core. Hence, deployment requires highly scalable GGSNs/P-GWs since the volume and frequency of Update PDP Context messages to the GGSN/P-GW will increase substantially. The SGSN/S-GW platform capabilities ensure control plane capacity will not be a limiting factor with direct tunnel deployment.
> The following figure illustrates the logic used within the SGSN/S-GW to determine if a direct tunnel will be setup.
> Direct Tunneling - Establishment Logic
> Direct Tunnel Configuration
> The following configurations are provided in this section:

> • | Configuring Direct Tunnel Support on the SGSN

> • | Configuring S12 Direct Tunnel Support on the S-GW

> Configuring Direct Tunnel Support on the SGSN
> By default, direct tunnel support is

> • | disallowed on the SGSN/S-GW

> • | allowed on the GGSN/P-GW.

> The SGSN/S-GW direct tunnel functionality is enabled within an operator policy configuration. One aspect of an operator policy is to allow or disallow the setup of direct GTP-U tunnels. If no operator policies are configured, the system looks at the settings in the system operator policy named default.
> For more information about operator policies and configuration details, refer to the Operator Policy chapter also in this guide.
> Important: If direct tunnel is allowed in the default operator policy, then any incoming call that does not have an applicable operator policy configured will have direct tunnel allowed.
> The following is a high-level view of the steps, and the associated configuration examples, to configure the SGSN to setup a direct tunnel.
> Before beginning any of the following procedures, you must have completed (1) the basic service configuration for the SGSN, as described in the Cisco ASR 5000 Series Serving GPRS Support Node Administration Guide, and (2) the creation and configuration of a valid operator policy, as described in the Operator Policy chapter in this guide.

> 1. | Configure the SGSN to setup GTP-U direct tunnel between an RNC and an access gateway by applying the example configuration presented in the Enabling Setup of GTP-U Direct Tunnels section below.

> 2. | Configure the SGSN to allow GTP-U direct tunnels to an access gateway, for a call filtered on the basis of the APN, by applying the example configuration presented in the Enabling Direct Tunnel per APN section below.

> Important: It is only necessary to complete either step 2 or step 3 as a direct tunnel can not be setup on the basis of call filtering matched with both an APN profile and an IIMEI profile.

> 3. | Configure the SGSN to allow GTP-U direct tunnels to a GGSN, for a call filtered on the basis of the IMEI, by applying the example configuration presented in the Enabling Direct Tunnel per IMEI section below.

> 4. | Configure the SGSN to allow GTP-U direct tunnel setup from a specific RNC by applying the example configuration presented in the Enabling Direct Tunnel to Specific RNCs section below.

> 5. | (Optional) Configure the SGSN to disallow direct tunnel setup to a single GGSN that has been configured to allow it in the APN profile. This command allows the operator to restrict use of a GGSN for any reason, such as load balancing. Refer to the direct-tunnel-disabled-ggsn command in the SGTP Service Configuration Mode chapter of the Cisco ASR 5000 Series Command Line Interface Reference.

> 6. | Save the changes to the system configuration by applying the sample configuration found in the Saving the Configuration section of the Verifying and Saving Your Configuration chapter in this guide.

> 7. | Check that your configuration changes have been saved by using the sample configuration found in the Verifying the SGSN Direct Tunnel Configuration section in this chapter.

> Enabling Setup of GTP-U Direct Tunnels
> The SGSN determines whether a direct tunnel can be setup and by default the SGSN doesn’t support direct tunnel.
> Example Configuration
> Enabling direct tunnel setup on an SGSN is done by configuring direct tunnel support in a call-control profile.
> config
> call-control-profile <policy_name>
> direct-tunnel attempt-when-permitted
> end
> Notes:

> • | A call-control profile must have been previously created, configured, and associated with a previously created, configured, and valid operator policy. For information about operator policy creation/configuration, refer to the Operator Policy chapter in this guide.

> • | Direct tunnel is now allowed on the SGSN but will only setup if allowed on both the destination node and the RNC.

> Enabling Direct Tunnel per APN
> In each operator policy, APN profiles are configured to connect to one or more GGSNs and to control the direct tunnel access to that GGSN based on call filtering by APN. Multiple APN profiles can be configured per operator policy.
> By default, APN-based direct tunnel functionality is allowed so any existing direct tunnel configuration must be removed to return to default and to ensure that the setup has not been restricted.
> Example Configuration
> The following is an example of the commands used to ensure that direct tunneling, to a GGSN(s) identified in the APN profile, is enabled:
> config
> apn-profile <profile_name>
> remove direct tunnel
> end
> Notes:

> • | An APN profile must have been previously created, configured, and associated with a previously created, configured, and valid operator policy. For information about operator policy creation/configuration, refer to the Operator Policy chapter in this guide.

> • | Direct tunnel is now allowed for the APN but will only setup if also allowed on the RNC.

> Enabling Direct Tunnel per IMEI
> Some operator policy filtering of calls is done on the basis of international mobile equipment identity (IMEI) so the direct tunnel setup may rely upon the feature configuration in the IMEI profile.
> The IMEI profile basis its permissions for direct tunnel on the RNC configuration associated with the IuPS service.
> By default, direct tunnel functionality is enabled for all RNCs.
> Example Configuration
> The following is an example of the commands used to enable direct tunneling in the IMEI profile:
> config
> imei-profile <profile_name>
> direct-tunnel check-iups-service
> end
> Notes:

> • | An IMEI profile must have been previously created, configured, and associated with a previously created, configured, and valid operator policy. For information about operator policy creation/configuration, refer to the Operator Policy chapter in this guide.

> • | Direct tunnel is now allowed for calls within the IMEI range associated with the IMEI profile but a direct tunnel will only setup if also allowed on the RNC.

> Enabling Direct Tunnel to Specific RNCs
> SGSN access to radio access controllers (RNCs) is configured in the IuPS service.
> Each IuPS service can include multiple RNC configurations that determine communications and features depending on the RNC.
> By default, direct tunnel functionality is enabled for all RNCs.
> Example Configuration
> The following is an example of the commands used to ensure that restrictive configuration is removed and direct tunnel for the RNC is enabled:
> config
> context <ctx_name>
> iups-service <service_name>
> rnc id <rnc_id>
> default direct-tunnel
> end
> Notes:

> • | An IuPS service must have been previously created, and configured.

> • | An RNC configuration must have been previously created within an IuPS service configuration.

> • | Command details for configuration can be found in the Cisco ASR 5000 Series Command Line Interface Reference.

> Verifying the SGSN Direct Tunnel Configuration
> Enabling the setup of a GTP-U direct tunnel on the SGSN is not a straight forward task. It is controlled by an operator policy with related configuration in multiple components. Each of these component configurations must be checked to ensure that the direct tunnel configuration has been completed. You need to begin with the operator policy itself.
> Verifying the Operator Policy Configuration
> For the feature to be enabled, it must be allowed in the call-control profile and the call-control profile must be associated with an operator policy. As well, either an APN profile or an IMEI profile must have been created/configured and associated with the same operator policy. Use the following command to display and verify the operator policy and the association of the required profiles:
> show operator-policy full name <policy_name>
> The output of this command displays profiles associated with the operator policy.
> [local]asr5000# show operator-policy full name oppolicy1
> Operator Policy Name = oppolicy1
> Call Control Profile Name : ccprofile1
> Validity : Valid
> IMEI Range 99999999999990 to 99999999999995
> IMEI Profile Name : imeiprofile1
> Validity : Invalid
> APN NI homers1
> APN Profile Name : apnprofile1
> Validity : Valid
> APN NI visitors2
> APN Profile Name : apnprofile2
> Validity : Invalid
> Notes:

> • | Validity refers to the status of the profile. Valid indicates that profile has been created and associated with the policy. Invalid means only the name of the profile has been associated with the policy.

> • | The operator policy itself will only be valid if one or more IMSI ranges have been associated with it - refer to the Operator Policy chapter, in this guide, for details.

> Verifying the Call-Control Profile Configuration
> Use the following command to display and verify the direct tunnel configuration for the call-control profiles:
> show call-control-profile full name <profile_name>
> The output of this command displays all of the configuration, including direct tunnel for the specified call-control profile.
> Call Control Profile Name = ccprofile1
> ...
> Re-Authentication : Disabled
> Direct Tunnel : Not Restricted
> GTPU Fast Path : Disabled
> ..
> Verifying the APN Profile Configuration
> Use the following command to display and verify the direct tunnel configuration in the APN profile:
> show apn-profile full name <profile_name>
> The output of this command displays all of the configuration, including direct tunnel for the specified APN profile.
> Call Control Profile Name = apnprofile1
> ...
> IP Source Validation : Disabled
> Direct Tunnel : Not Restricted
> Service Restriction for Access Type > UMTS : Disabled
> ..
> Verifying the IMEI Profile Configuration
> Use the following command to display and verify the direct tunnel configuration in the IMEI profile:
> show imei-profile full name <profile_name>
> The output of this command displays all of the configuration, including direct tunnel for the specified IMEI profile.
> IMEI Profile Name = imeiprofile1
> Black List : Disabled
> GGSN Selection : Disabled
> Direct Tunnel : Enabled
> Verifying the RNC Configuration
> Use the following command to display and verify the direct tunnel configuration in the RNC configuration:
> show iups-service name <service_name>
> The output of this command displays all of the configuration, including direct tunnel for the specified IuPS service.
> IService name : iups1
> ...
> Available RNC:
> Rnc-Id : 1
> Direct Tunnel : Not Restricted
> Configuring S12 Direct Tunnel Support on the S-GW
> The example in this section configures an S12 interface supporting direct tunnel bypass of the release 8 SGSN for inter-RAT handovers.
> The direct tunnel capability on the S-GW is enabled by configuring an S12 interface. The R8 SGSN is then responsible for creating the direct tunnel by sending an FTEID in a control message to the MME over the S3 interface. The MME forwards the FTEID to the S-GW over the S11 interfaces. The S-GW responds with it’s own U-FTEID providing the SGSN with the identification information required to set up the direct tunnel over the S12 interface.
> Use the following example to configure this feature:
> configure
> context <egress_context_name> -noconfirm
> interface <s12_interface_name>
> ip address <s12_ipv4_address_primary>
> ip address <s12_ipv4_address_secondary>
> exit
> exit
> port ethernet <slot_number/port_number>
> no shutdown
> bind interface <s12_interface_name> <egress_context_name>
> exit
> context <egress_context_name> -noconfirm
> gtpu-service <s12_gtpu_egress_service_name>
> bind ipv4-address <s12_interface_ip_address>
> exit
> egtp-service <s12_egtp_egress_service_name>
> interface-type interface-sgw-egress
> validation-mode default
> associate gtpu-service <s12_gtpu_egress_service_name>
> gtpc bind address <s12_interface_ip_address>
> exit
> sgw-service <sgw_service_name> -noconfirm
> associate egress-proto gtp egress-context <egress_context_name> egtp-service <s12_egtp_egress_service_name>
> end
> Notes:

> • | The S12 interface IP address(es) can also be specified as IPv6 addresses using the ipv6 address command.

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