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Chapter 1 Overview of GPRS and UMTS Features Introduced in Prior Releases

The username and password in the Create PDP Context request takes higher precedence than the anonymous user configuration.

For information about configuring anonymous user access under an APN, see the “Configuring Additional Real Access Point Options” section on page 8-20.

• Downloadable Pool Name Support

When the ip-address-pool radius-client access-point configuration command is configured under an APN, if an address pool name is received as a part of the Access-Accept message while authenticating the user, the address pool is used to assign the IP address to the mobile station. If the Access-Accept message also includes an IP address, the IP address takes precedent over the address pool name, and the IP address in the Access-Accept message is used instead of being allocated from the pool.

To configure downloadable pool names, ensure that the ip-address pool access-point configuration command with the radius-client keyword option is configured under the APN:

gprs access-point-list gprsaccess-point 3access-point-name qos1.comip-address-pool radius-client

...

ip local pool pool1500 ipaddress ipaddress

For more information about the ip-address-pool access-point configuration command, see “Configuring Additional Real Access Point Options” section on page 8-20. For more information about configuring RADIUS, see the Cisco IOS Security Configuration Guide.

• Direct Tunnel Support

The direct tunnel feature enables an SGSN to establish a direct user plane tunnel between the radio network controller (RNC) and a GGSN.

The SGSN functions as the gateway between the RNC and the core network. It handles both signaling traffic (to keep track of the location of mobile devices), and the actual data packets being exchanged between a mobile device and the Internet.

Before Cisco GGSN Release 8.0, a tunnel could only exist between the GGSN and SGSN, and between the SGSN and RNC. With this tunnel configuration, all data packets must pass through the SGSN. The SGSN has to terminate one tunnel, extract the packet, and put it into another tunnel. This process takes time and processing power.

With direct tunnel support, the SGSN can initiate a direct tunnel between the RNC and GGSN, and no longer have to process data packets. The SGSN will continue to manage location issues by modifying the tunnel if a mobile device moves to an area served by another RNC.

Specifically, direct tunnel processing is as follows:

a. The SGSN initiates the direct tunnel with an Update PDP Context Request that contains the following elements:

- Direct Tunnel Flags IE with the DTI bit set to 1. (DTI: Direct Tunnel Indicator)

- The RNC user traffic address

- Data TEID (Tunnel End-point IDentifier)

- GGSN updates the RNC user traffic address and Data TEID. The GGSN uses the updated information when sending G-PDUs for the MS.

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b. If the GGSN receives an Error Indication message from the RNC user traffic address, it initiates an Update PDP Context request. The Update PDP Context request includes the Direct Tunnel Flags IE with the Error Indication bit set.

c. Until the Update PDP Context response is received from the SGSN, the GGSN drops subsequent packets to the MS address.

d. The Update PDP Context response is received from the SGSN. If the cause is “Request Accepted,” the PDP is preserved. If the cause is “Not Request Accepted,” the PDP is deleted locally.

Note Direct tunnel support does not apply to international roaming. In addition, direct tunnel support does not apply to when the SGSN is asked by a prepaid system to count the traffic flow.

WirelessMoves: Direct Tunnel - GPRS Core Network Streamlining

WirelessMoves

Thoughts on the evolution of wireless networks and mobile web 2.0

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Direct Tunnel - GPRS Core Network Streamlining

While work is ongoing on 3GPP LTE (Long Term Evolution) and SAE (System Architecture Evolution), current 3G networks continue to be enhanced as well. Since the 3G air interface is in the process continues to evolve with HSPA (High Speed Packet Access) it was felt in the standards groups that the 3G core network should be streamlined to handle the increasing network traffic more efficiently.

One part of the network in particular has been waiting for optimization for quite some time. In today's 3G packet core architecture the SGSN (Serving GPRS Support Node) which is the gateway between the radio network and the core network handles both signaling traffic (e.g. to keep track of a users location) and the actual data packets exchanged between the user and the Internet. Since the users location can change at any time, data packets are tunneled (encapsulated) from the gateway to the Internet (The Gateway GPRS Support Node, GGSN) via the SGSN over the radio network to the mobile device. The current architecture uses a tunnel between the GGSN and the SGSN and another one between the SGSN and the Radio Network Controller (RNC). All data packets thus have to pass the SGSN which has to terminate one tunnel, extract the packet and put it into another tunnel. This requires both time and processing power.

Since both the RNC and the GGSN are IP routers this process is not really required in most circumstances. The one tunnel approach now standardized in 3GPP thus foresees that the SGSN can create a direct tunnel between the RNC and the GGSN and thus remove itself from the chain. Mobility Management remains on the SGSN, however, which means for example that it continues to be responsible to modify the tunnel in case the mobile device is moved to an area served by another RNC.

The approach does not work for international roaming since the SGSN has to be in the loop in order to count the traffic for inter-operator billing purposes. Another case where the one tunnel option can not be used is in case the SGSN is asked for example by a prepaid system to count the traffic flow. A small limitation since in practice it's also possible to connect such a system to the GGSN (via Diameter).

For the details have a look at the following documents:

http://mobilesociety.typepad.com/mobile_life/2007/09/one-tunnel---gp.html (1 of 5)2011/6/1 下午 05:15:44

WirelessMoves: Direct Tunnel - GPRS Core Network Streamlining

● Direct Tunnel 3GPP Work Item Description SP-060142_S2-060545● The TR (Technical Recommendation) describing the overall design and impact on existing

functionalities: TR 23.809● The Change Request (CR) for 3GPP TS 23.060 ● And the latest version of the 'GPRS Service Description; Stage 2' which contains the

enhancements. TS 23.060 7.4.0

September 29, 2007 in GPRS, HSDPA | Permalink

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