Defining Layer 2.5

1
Defining Layer 2.5

• Alan Carlton
• Interdigital Communications
• alan.carlton_at_interdigital.com

2
Objectives

• To stimulate a discussion on the preferred 802.21
  Mobility Architecture
• To stimulate a discussion on the scope of 802.21
• To review Typical Mobile System architecture
  approaches as they may pertain to the broad
  objectives of 802.21

3
Mobile System Terminology Used in this
Presentation

• Two key modes exist for typical mobile systems -
  IDLE mode and CONNECTED mode
• IDLE mode (STA) characteristics
• No User service, monitoring of paging channels,
  available service request channels
• 100 of Receiver available for Downlink
  Measurements
• Background coordination, unscheduled
  AP/technology reselection
• CONNECTED mode (STA) characteristics
• Active User service (e.g. a call), Handover
  possible
• Limited Receiver availability for measurements
  (User service takes priority)
• Fully Coordinated, scheduled AP/technology
  handover
• Selection
• Prior to entering IDLE mode (e.g. at Power up)
  the STA must perform selection in order to
  determine the best AP and technology available
  for service
• Reselection
• While in IDLE mode (i.e. No User service) the STA
  must continuously examine neighbor AP (and
  different technology AP). Upon determination of a
  better AP the STA will transition over to the
  new AP
• Handover
• While in CONNECTED mode (i.e. Active User
  Service) a handover occurs upon transition from
  one AP to another AP (possibly using a different
  technology) offering significantly better
  service. In the ideal case this transition will
  occur without noticeable interruption of the
  Active User Service.

4
The Cellular Mobility Model
e.g. Switch, Server
Network
Handover Policy Function
e.g. 2G BSC, 3G RNC
Full Mobility Support
Radio Network
Semi-Static Frequency Assignments
AP
GSM900
AP
FDD
e.g. GSM Base Station
e.g. FDD Node B
Cellular STA
e.g. 2G MS, 3G UE
Centralized Radio Resource Management Approach
5
The Cellular Mobility Model (Continued)

• Radio Network Characterization
• Centralized RRM approach (Semi-Static Frequency
  assignments in each AP)
• Some Radio Planning Required
• IDLE Mode Operation
• Intra-technology (e.g. GSM to GSM)
• AP Selection/Reselection decision made in STA
  supported by System information broadcast by the
  Handover Policy function (Policy defined in the
  Handover Policy function)
• Inter-technology (e.g. GSM to FDD/WCDMA)
• AP Selection/Reselection decision made in STA
  supported by System information broadcast at the
  Handover Policy function (Policy defined in the
  Handover Policy function)
• CONNECTED Mode Operation
• Intra-technology
• AP handover decision made in the Handover
  Controller function supported by measurements
  made by the STA and sent to the Handover Policy
  function via L3 signaling (Policy defined in the
  Handover Policy function)
• Inter-technology
• AP handover decision made in the Handover Policy
  function supported by measurements made by the
  STA and sent to the Handover Policy function via
  L3 signaling (Policy defined in the Handover
  Policy function)

6
The WLAN Mobility Model - Current
e.g. Gateway, Router
Network
Limited Mobility Support
Radio Network
Dynamic Frequency Assignments
802.11a
802.11
AP
AP
IEEE 802.X STA
Distributed Radio Resource Management Approach
7
The WLAN Mobility Model (Continued)

• Radio Network Characterization
• Distributed RRM approach (Dynamic Frequency
  assignments in each AP)
• Radio Planning Not Required
• IDLE Mode Operation
• Intra-technology (e.g. 802.11a to 802.11a)
• AP Selection/Reselection decision made
  autonomously in STA (Policy defined in the STA)
• Inter-technology (e.g. 802.11 to 802.16)
• SELECTION/RESELECTION NOT STANDARDIZED SCOPE OF
  802.21
• CONNECTED Mode Operation
• Intra-technology
• HANDOVER NOT STANDARDIZED SCOPE OF 802.21
• Inter-technology
• HANDOVER NOT STANDARDIZED SCOPE OF 802.21

General Scope of 802.21
8
The WLAN Mobility Model Enhanced (802.21)
e.g. Gateway, Router
CENTRALIZED Handover Policy Function
DISTRIBUTED Handover Policy Function
STA ONLY
SYSTEM
Option A
Option B
Enhanced Mobility Support (802.21)
Radio Network
Dynamic Frequency Assignments
802.11b
802.11a
802.11a
802.11
AP
AP
AP
802.11
AP
AP
AP
AP
802.16
802.11n
IEEE 802.X STA
Two Basic Options Are Considered
9
Option A Option B Definition

• IDLE Mode Operation
• Intra-technology (e.g. 802.11a to 802.11a)
• AP Selection/Reselection decision made
  autonomously in STA (Policy defined in the STA)
• Inter-technology (e.g. 802.11 to 802.16) SCOPE
  OF 802.21
• Option A AP Selection/Reselection decision made
  autonomously in STA (Policy defined in the STA)
• Option B AP Selection/Reselection decision made
  in STA supported by System information broadcast
  at the Handover Policy function level (Policy
  defined in the Handover Policy Function)
• CONNECTED Mode Operation
• Intra-technology SCOPE OF 802.21
• Option A AP handover decision made autonomously
  in STA (Policy defined in the STA)
• Option B AP handover decision made in the
  Handover Policy function supported by
  measurements made by the STA and sent to the
  Handover Policy function via new signaling
  mechanisms (Policy defined in the Handover Policy
  Function)
• Inter-technology SCOPE OF 802.21
• Option A AP handover decision made autonomously
  in the STA (Policy defined in the STA)
• Option B AP handover decision made in the
  Handover Policy function supported by
  measurements made by the STA and sent to the
  Handover Policy function via new signaling
  mechanisms (Policy defined in the Handover Policy
  Function)

10
Option A DISTRIBUTED Handover Policy Function

• Intra/Inter Technology Reselection decision made
  autonomously by the STA
• Adequate but sub-optimal solution
• Intra/Inter Technology Handover decision made
  autonomously by the STA
• Slow Handover Solution /Really just an extension
  of Reselection and would be characterized as such
  in a typical Mobile system
• Break and then Make strategy (Resource
  availability not guaranteed)
• Adequate solution for non real-time services
• Unacceptable solution for real time services
  (such as voice)
• Poorly scaleable solution

Local MIB
802.11 Model
MAC Sublayer ME
MAC Sublayer
Handover Policy Function
PLCP Sublayer
Physical Sublayer ME
PMD Sublayer
STA Functional Architecture Concept
Option A Provides a Very Limited Mobility Solution
11
Option B CENTRALIZED Handover Policy Function
Handover

• Intra/Inter Technology Reselection decision
  supported by System Information
• Optimal solution
• Intra/Inter Technology Handover decision
  coordinated by RPF and supported by measurement
  reports and System signaling
• Fast Handover Solution
• Make and then Break strategy (Resource
  availability is guaranteed)
• Adequate solution for non real-time services
• Acceptable solution for real time services (such
  as voice)
• Easily scaleable solution

System Info
Measurements
802.11 Model
System HPF
MAC Sublayer ME
MAC Sublayer
Layer 2.5 Signaling/Control Function
PLCP Sublayer
Physical Sublayer ME
PMD Sublayer
STA Functional Architecture Concept
Option B Provides a Full Mobility Solution
Typical Mobile System Architecture Approach
12
Typical Mobile System Architecture compared to
802.X
GPRS (2G) STA
3GPP (3G) STA
IP
IP
Mobility Protocol (MM)
Mobility Protocol (MM)
Convergence
Convergence
Network
GSM 04.18
3GPP 25.331
RLC
RLC
Transparent Mode Option
Transparent Mode Option
Data Link
MAC
MAC
Physical
Physical
Physical
User Plane
User Plane
Control Plane
Control Plane
In a Full Mobility Solution Layer 2.5 is a key
enabler
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Key Protocol Functions
Mobility Protocol
Resource Control Protocol
(e.g. GSM-MM/MAP, Mobile IP)
(e.g. GSM-RR, 3GPP RRC, L2.5?)

• System Information
• Termination (or Paging)
• Cell Selection/Reselection
• Establishment
• Release
• Measurement Reporting
• Power Control
• Handover at Radio Level

• Discovery
• Registration
• Tunneling
• Termination (or Paging)
• Handover at Network Level
• Security

14
Example End to End Functional Configuration
CENTRALIZED Handover Policy Function
802.11
802.11a
AP
IEEE 802.X STA
802.11a
AP
e.g. Gateway, Router
AP
Station Function
Network/Radio Network Functions
Higher Layers
Higher Layers
Mobility Protocol
Mobility Protocol
U-Plane
U-Plane
Layer 2.5
Layer 2.5
Handover Policy Function
LLC
Link Layer
MAC
MAC
Lower Layers
Lower Layers
Physical
Physical
The RHF may be defined as logical functional
entity
15
Conclusions

• The Option B architecture with a centralized
  Handover Policy Function would seem to be the
  most promising approach and is recommended.
• In order to provide a full mobility solution both
  Radio Mobility (e.g. GSM RR) and Network Mobility
  (e.g. Mobile IP) protocol functionality is
  required in the system.
• Layer 2.5 is a key enabler in a full mobility
  solution.
• In order to support the Option B Architecture
  802.21 should define a Layer 2.5 Signaling and
  Control Protocol with some similar properties to
  RR style protocols currently used in typical
  Mobile systems.
• The Handover Policy Function may be defined as a
  logical entity. It is not necessary to define any
  restrictions in the Standard on its location in a
  physical implementation though some
  recommendations may be made if valuable.
• The Option B architecture closely maps to well
  proved typical Mobility System architectures and
  will simplify future advanced interworking
  scenarios unanticipated at this time (e.g.
  tightly coupled handover).
• The Centralized Handover Policy Functional
  architecture may be easily extended to support
  Wireless to Wired interworking scenarios e.g. the
  Handover policy upon connecting a Wireless device
  to a Wireline system may be automatic handover.