May 14, 2007 Violeta Cakulev, Mike Dolan, Frank Alfano, Nancy Lee - Alcatel-Lucent ABSTRACT: This contribution discusses the benefits on several features of idle mode buffering in the RAN. It shows that idle mode buffering in the RAN can be a necessary option available to operators. RECOMMENDATION: Discuss. Notice Contributors grant a free, irrevocable license to 3GPP2 and its Organization Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner’s name any Organizational Partner’s standards publication even though it may include portions of the contribution; and at the Organization Partner’s sole discretion to permit others to reproduce in whole or in part such contributions or the resulting Organizational Partner’s standards publication. Contributors are also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution. This document has been prepared by the contributors to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on the contributors. Contributors specifically reserve the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of the contributors other than provided in the copyright statement above. Benefits of Idle Mode Buffering in the RAN 3GPP2 TSG-A.4 3GPP2 A xxx

2 Outline  Push-to-talk benefits form idle mode buffering in the RAN  Alignment with other standards  Race conditions  Network architecture  Scalability  Intelligent paging strategies  Impact of future changes to the air interface

3 Push-to-Talk Half duplex voice service in cellular network environment that allows one-to-one or one-to-many group communication within a service area  PTT requires instantaneous set up times  PTT is based on SIP signaling which is already delay intensive  PTT supports one-to-many group communication  PTT server sends multiple copies of each packet – one to every group member  Contributes to congestion  Buffering at AGW increases delay  Extra delay: 2 x delay AN-AGW For PTT it is essential to buffer at the RAN  Keep set up times and amount of signaling over the backhaul low

4 Alignment with Other Standards Align with HRPD  Buffering in the RAN is an approach used and tested in HRPD  The PDSN is not aware if AT active/dormant –Idle mode buffering is done in the RAN  The incoming data is always sent via A10 connection  If decision is made to develop a paging strategy that works over different technologies alignment on idle mode buffering is important  Align with 2G (GPRS) and 3G (UMTS) 3GPP networks Align with WiMAX and LTE  Buffering in the ASN-GW (SAE-GW) is an approach accepted in WiMax (LTE)

5 Race Conditions Buffering at AGW introduces numerous race conditions Example: AGW believes AT is active while instead AT is idle  Two options  Sender needs to retransmit –Increases delay – for some applications can be unacceptable  RAN does buffering and paging –Greatly improved delay and efficiency

6 Network Architecture For certain deployments buffering in the RAN significantly reduces paging delay and signaling overhead Example: Home femtocells  If a user is last registered in a particular femtocell it is highly likely that it remains in the coverage of that femtocell  Idle mode buffering in the RAN  Significantly reduces delay  Significantly reduces amount of signaling

7 Scalability Scalability imposes a severe problem for AGW  AGW need to support possibly millions of users  Number of users is not likely to grow rapidly  Amount of user’s data is expected to grow rapidly  Devise solutions that keep AGW as simple as possible Handling idle mode buffering and paging in the RAN allows for better scalability

8 Intelligent Paging Strategies QoS Paging  Adds capability to specify different paging strategies for different QoS flows  “Best Effort” vs. VoIP vs. PTT  Allows trade-off of paging effectiveness, efficiency, and latency for different applications  Enables priority paging  Ability to order the paging messages within the control channel queue based on an assigned priority  Relies on the knowledge of subscription information (QoS profile) of the incoming page If idle mode buffering is done at the AGW, AGW needs to ‘learn’ about QoS paging

9 Intelligent Paging Strategies – Examples PTT  Aggressively page a large area on the initial page to increase likelihood of finding the AT on the 1 st attempt  Inefficient use of control channel resources is a tradeoff to provide high QoS  Make 2 nd Page attempt after a relatively short interval  Abandon paging after a few seconds, since the application server waits for a response only a short interval Best Effort  Initial page can only cover the area where the likelihood of finding the AT is largest  Subsequent page attempts can cover an expanded area to increase effectiveness

10 Future Changes to the Air-Interface What if AT modes defined in air-interface spec change in future?  If only AGW is doing buffering  Change in the air-interface spec will affect AGW  If option to do buffering in both RAN and AGW  Opens a possibility to make changes to the air-interface spec without any effect on AGW

11 Recommendation Discuss and adopt buffering in the RAN as an option necessary to support various features efficiently, and offering observable benefits.