2004-05-12
Project
21-04-00xx-01-0021-Overview_stack_text.doc
IEEE 802.21
<http://www.ieee802.org/21/>
Title
Overview of 802.21 Stack Model
Date
Submitted
July 12th 2004
Source(s)
David Johnston (Intel Corp)
Re:
IEEE 802.21 Session #3 in Portland, OR
Abstract
This document provides overview text for the 802.21 Media Independent Handover Services draft document,
describing the 802.21 stack layering model and theory of operation
Purpose
To provide overview text and stack model for the 802.21 draft
Notice
Release
Patent Policy
This document has been prepared to assist the IEEE 802.21 Working Group. It is offered as a basis for
discussion and is not binding on the contributing individual(s) or organization(s). The material in this
document is subject to change in form and content after further study. The contributor(s) reserve(s) the right
to add, amend or withdraw material contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this
contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in
the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution;
and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE
Standards publication. The contributor also acknowledges and accepts that this contribution may be made
public by IEEE 802.21.
The contributor is familiar with IEEE patent policy, as outlined in Section 6.3 of the IEEE-SA Standards
Board Operations Manual <http://standards.ieee.org/guides/opman/sect6.html#6.3> and in Understanding
Patent Issues During IEEE Standards Development <http://standards.ieee.org/board/pat/guide.html>.
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Include in the definitions sections, the following definitions:
1 Definitions
L3MP
HMC
SME
NME
ARID
Layer 3 Mobility Protocol. Any layer, immediately above the 802 defined protocol stack,
that provides layer 3 mobility, E.G. Mobile IP.
Heterogeneous Media Convergence. The function of the HCS layer
Sublayer Management Entity. A management function defined in 802.11
Network Management Entity. Defined in 802.16, synonymous with SME
Access Router Identifier. An identifier for a mobile IP first hop router
Include in the appropriate section of the draft, and renumber as required, the text given the section
below
2 Overview
802.21 defines services in 802 systems that enable and enhance handover between heterogeneous systems.
This is achieved through:
 Service interfaces providing access to state and event information within the MAC and PHY.
These are described in clause <x>
 An information model and database, defining information useful to handover processes and
network entry processes. This is described in clause <y>
 A layer 2 protocol operating over 802 style MSDUs, enabling the transport of events, handover
related information and network detection between pairs of attached 802 systems.
 A Heterogeneous Media Convergence (HMC) layer above the LLC that crosses heterogeneous
interface types, enabling policy enforcement, network selection, QoS parameter mapping and
handover signaling between heterogeneous interfaces in multi interfaced systems.
A standard IEEE communication stack includes MAC and PHY layers. Depending on the media type, there
may also be a management plane with MLME and PLME layers. An unspecified management function, the
SME (in 802.11) or NME (in 802.16) provides coordinated management of the layers.
Figure x,y,z describes the 802.21 layering structure for an 802 interface
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L3MP
LSAP
LSAP
LSAP
LSAP
HMC_SAP
HMCME_SAP
802.21 Scope
HMC
HMCIB
HMCIB
HP_SAP
HM_SAP
LSAP
HMC_MLME_SAP
MAC_SAP
MLME
MAC
HP_SAP
PHY_SAP
PHY
SME
or
NME
MLME_PLME_SAP
PLME
PLME_SAP
HM_SAP
MLME_SAP
LLC
802.21 HMC Layering for a Single 802 Interface
802.21 defines the HMC layer. The HMC layer includes interfaces to the MAC (HM_SAP) and PHY
(PM_SAP). In addition, the HMC layer includes one or two instances of the HMC Information Base
(HMCIB) service that attaches to standard 802.2 LLC LSAPs. The HMC layer is a convergence layer in
which interworking and policy functions relating to handover and network entry reside.
LSAPs other than the LSAPs to which the HMCIB entities attach, are transparently passed through to the
layer above.
The HMCIB entities contain a database of information pertinent to network detection, network entry and
handover. In the case of a system supporting 802.1X, there are two HMCIB entities, one on the controlled
port side of the 802.1X fork and the other on the uncontrolled port side. Data in the HMCIB on the
uncontrolled port side may be accessed both before and after 802.1X mediated authentication. Data in the
HMCIB on the controlled port side may be accessed only after 802.1X mediated authentication. Access to
the data is via the LSAP, using LLC class 1 frames. Each HMCIB entity has a distinct ethertype.
It is assumed that for a system that implements layer-3 mobility, such as mobile IP, there will be such a
protocol attached to a transparent LSAP on the HMC. This protocol is termed the Layer-3 Mobility
Protocol (L3MP) and it may be any layer 3 protocol capable of handovers. The HMC provides an
additional interface to any L3MP, the HMC_SAP. The HMC_SAP enables the L3MP to determine state
changes in the layers below that may influence its mobility behavior, through the 802.21 event service.
Also it provides access to the 802.21 information service.
The HM_SAP interfaces the 802.21 event service to the MAC.
The HP_SAP interfaces the 802.21 event service to the PHY. This is similar to the HM_SAP, but operates
with the PHY and communicates PHY related information.
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The HMC_MLME_SAP provides a path for management primitives to pass between the HMC and the
MLME of the stack below. At this time, there are no primitives defined for this interface.
The HMCME_SAP is an interface through which the SMC, NME or equivalent may manage the HMC. At
this time, there are no primitives defined for this interface.
2.1 Theory of Operation
2.1.1 Event Service Theory of Operation
The event service allows event information to be propagated upwards from the MAC to the L3MP and for
events to be propagates downwards from the L3MP to a L3MP in another stack connected directly through
the medium to which the local stack attaches. Events either indicate changes of state, or predict changes of
state to the HMC_SAP.
The event service will typically be used to enable optimized handover signaling within the L3MP. E.G. an
indication that the link will cease to carry MSDUs at some point in the near future may be used by the
L3MP to prepare a new point of attachment ahead of the current point of attachment ceasing to carry
frames. This has the potential to reduce the time taken to hand over between attachment points.
In an asymmetric link, such as a STA-AP link in 802.11 or an SS-BS link in 802.16, the AP or BS might
make a management decision to require an attached node to handoff elsewhere at some point in the future,
allowing the node to prepare a layer 3 handover. For this reason, events may originate not only within the
MACs or PHYs of the 802 link, but also from the L3MP.
Events defined include Link Available, Link Up, Link Going Up, Link Down, Link Going Down and Event
Rollback.
Events can originate from the MAC, the PHY or the HM_SAP. The destination of any event may be the
HM_SAP within the local stack, the HM_SAP of the remote stack at the other end of the link, or both. The
destination of events is established dynamically with a registration mechanism that enables an endpoint to
register its interest in particular event types.
Events may carry additional context data. E.G. A link_up event may carry an ARID. This enables a mobile
station to determine whether or not a handover has necessitated a layer 3 handover immediate at the time of
attachment. This can serve to improve the performance of layer 3 handovers.
2.1.2 Information Service Theory of Operation
The information service provides a pull model of information transfer. This contrasts with the push model
of the event service. The requesting endpoint seeks particular information from the event service at the
other end of the link at a time of the requesting endpoint’s own choosing.
The information is stored within the HMCIB. The access protocol for the HMCIB is carried over normal
data frames with the HMCIB ethertype encoded in the SNAP header.
The information that is held within the HMCIB conforms to structure and semantics specified within
802.21.
Examples of information that may be made available through the HMCIB include neighborhood lists that
enable efficient detection of nearby access points or base stations and service provider identifiers that
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enable a mobile station to determine whether it is authorized to access particular access points or base
stations.
2.1.3 Heterogeneous Interface Coordination
In the case of a system with multiple 802 interfaces, of arbitrary type, the HMC or L3MP is able to use the
event service to determine the state of the underlying interfaces and select between them appropriately. It is
also able to use the information service to understand.
In a system containing both 802 and non 802 interfaces, this layer may contain procedures to couple
services across both 802 and non 802 interface types. This functionality is not defined in 802.21 since
definition of not 802 systems is out of scope for 802.21.
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