Inter Access Point Protocol
Prepared by: 
Aironet & Lucent Technologies
Agenda
•	Introduction
•	Goals
•	History
•	Requirements
•	Architecture
•	Specifications
•	Conclusion
Introduction
•	Wireless Networks introduce new concepts
–	Medium is unbounded, but range is limited.
–	End nodes can be mobile.
•	IEEE 802.11 is developing a Wireless LAN standard.
–	Standard is in final stage, expected to go to Sponsor Ballot.
–	802.11 defines MAC and PHY specifications, “Air Interface” only.
–	Provides basic primitives to support mobility.
•	IEEE 802.11 extends its coverage beyond the range of its PHY through a Distribution System.
–	Distribution System connects multiple AP to form an ESS. 
–	However, the Distribution System  is not specified.
–	This represents an interoperability issue at the system level.
IEEE 802.11 architecture
•	IEEE 802.11 defines the “over the air” protocol.
IEEE 802.11 architecture
•	IEEE 802.11 defines the “over the air” protocol.
•	Range extension through use of a Distribution System.
IEEE 802.11 architecture
•	IEEE 802.11 defines the “over the air” protocol.
•	Range extension through use of Distribution System.
•	AP to AP protocol is not defined by 802.11.
The Missing Link
•	A standard protocol for Access Point communication.
The Missing Link
•	A standard protocol for Access Point communication.
•	A particular Distribution System Medium.
–	based on existing LAN standards
Goals of this initiative
•	Specify the “missing link” for Wireless LAN systems interoperability.
–	to support mobility of end nodes
•	Enable multivendor Distribution Systems.
–	based on existing network standards
–	by specifying IAPP, the protocol between Access Points
•	Aironet , Digital Ocean and Lucent Technologies have developed an initial specification.
–	It is published as an “open voluntary standard”.
–	To solicit feedback by interested parties
History
•	IEEE 802.11 started work in 1990.
–	Its PAR specifies support for range extension and mobility.
–	802.11 decided early on not to specify the Distribution System.
»	it is beyond IEEE 802 MAC level authority
»	Distribution System requires Network and Transport layer functionality
–	802.11 specifies the services the Distribution System must provide
•	There were a number of attempts to specify interoperability functions on the Distribution System.
–	The term IAPP was introduced in IEEE P802.11-94/17.
–	IEEE P802.11-95/188 by Michael Fischer proposed a limited Distribution System by introduction of the MESS.
•	Aironet, Digital Ocean and Lucent Technologies provide an initial specification of the IAPP.
General IAPP requirements
•	Build upon specified 802.11 functionality.
•	Use existing networks to serve as the Distribution System Medium.
–	Existing 802 wired Networks
–	802.11 Wireless LANs
•	Support a wide range of Network transfer protocols.
–	Support MAC level Bridge based Data Link level implementations
–	Support Router based Network layer implementations
»	Allow multi-segment IAPP
»	Not intended to solve addressing issues for Network layer mobility.
•	Allow for different network Management topologies.
•	Provide mechanisms to allow APs to communicate with each other.
•	The IAPP should be flexible and extendable.
–	allow proprietary extensions
Architecture background
•	The 802.11 architecture is designed to allow diverse Distribution System implementations:
–	The DS may be created from different technologies including but not limited to current 802.x wired LANs.
–	It is not constrained to either Data Link or Network layer.
–	Its addressing space can be separate from the addressing space used in the DS or integrated wired LAN.
•	This IAPP initiative focuses on a set of solutions representing a typical case.
–	Distribution Systems based on existing 802.x wired LANs.
»	The Distribution Medium (DM) can be an existing LAN with stations connected.
»	With 802.11 and DM using the same MAC level address space.
IAPP Architecture
•	IAPP defines a communication mechanism between APs.
–	to allow for coordination between APs
–	to exchange channel or hop sequence information
•	IAPP allows AP MAC Management entities to communicate.
–	to enable a station to disassociate from the “Old AP”
–	to redirect the Distribution System  filtering functions
•	Two transfer protocols will be implemented.
–	UDP/IP
»	used whenever an IP address is present in the AP
–	802.2 Sub-Network Access Protocol (SNAP)
»	for simpler systems when no IP Address is present
IAPP Architecture
•	Distribution System Medium can be built from existing networks
–	including 802.11 wireless LANs
General IAPP Message Format
•	Protocol Header:	SNAP or UDP/IP protocol Header.
•	Ver#:		IAPP Version number.
•	PDU-Type:		Identifies Specific PDU.
•	n * PDU element:	PDU data element fields.
 				Following 802.11 element format
–	Element-ID:	Element identification
–	Length:		Length of element data field in octets.
–	Data:		Data of the element.

•	Messages can be specifically addressed to one AP, or group addressed to all APs.
Basic IAPP protocol functions
•	IAPP Announce Protocol
–	to facilitate AP awareness and coordination
–	to support the formation of Wireless Distribution Systems

•	IAPP Handover Protocol
–	to extend the 802.11 Re-Association MAC management function across the distribution system
IAPP Announce Protocol
•	IAPP Announce protocol:
–	Inform other APs and/or network management functions that a new AP has become active.
–	Inform other APs and/or network management functions of the continued operation of that AP.
–	Allow APs to communicate their configuration.
–	Allow for network Management function to provide AP coordination.
•	Associated PDU Types:
»	Announce.Request
»	Announce.Response
•	Supports centralized or distributed AP coordination, and allows autonomous operation in uncoordinated environments.
•	Provides a means for Wireless APs to “Register” with other APs.
–	enables creation of a Wireless Distribution System
AP management topologies
•	Topologies supported:
–	Uncoordinated APs
–	Centralized AP Management
–	Distributed AP Management
•	Provides for “Management level AP awareness”
–	Needed to configure wireless Distribution Systems.
–	This is not covered by 802.11.
Uncoordinated APs
•	New AP generates Announce.response.
–	sent as a general Broadcast
•	Allows AP to identify itself and its operational status.
Centralized AP Management
•	Announce.request generated by new AP.
–	AP manager will respond (with Master bit set).
•	AP manager can query AP’s by sending Announce.requests.
–	with “Response desired” enabled
Distributed Control
•	New AP generates Announce.request
–	with “Response desired” enabled.
•	Other APs send Announce.response
•	New AP generates Announce.response
–	Indicating its operational status.
•	APs can generate Announce.response messages periodically as an “Alive indication”.
IAPP Handover Protocol
•	IAPP Handover Protocol:
–	Inform the “old AP” that a station has associated with a new AP.
»	To release resources assigned to that station by the old AP.
»	To allow optional frame forwarding of buffered frames,
»	or discard them.
–	Update filter tables of intermediate MAC layer Bridges.
»	By using the “Mobile Station Source address” as the SA of the handover request message.
•	Associated PDU Types:
»	Handover.Request
»	Handover.Response.
Handover procedure
•	Relationship between 802.11 reassociation and IAPP handover.
PDU Elements
•	ESSID			as in 802.11
•	BSSID			as in 802.11
•	Old BSSID			as in 802.11
•	MS-Address			Mobile Station address
•	IAPP capability/Status	
•	Announce interval		in Kusec
•	Handover Timeout		in Kusec
•	PHY type			identify 802.11 PHY
•	Regulatory Domain		as in 802.11 MIB
•	Channel			PHY dependent
•	Beacon Interval		as in 802.11
•	OUI Company identifier	Precedes block of proprietary elements.
–	Proprietary elements	Following OUI Company ID only.
Element Usage
•	Element use per PDU type:
–	fixed elements are specified
–	other elements are optional
•	Proprietary elements are allowed.
–	receivers ignore elements they don’t understand
•	OUI Company ID precedes block of proprietary elements.
–	This prevents Element ID conflicts.
»	(OUI, Element ID) tuple will be unique
Conclusion
•	IAPP provides the “missing link” in Wireless networking.
–	interoperability between multiple vendor AP implementations
•	IAPP is compatible with IEEE 802.11.
–	it builds upon the 802.11 functionality
•	IAPP enables a multitude of AP management schemes. 
–	with support across Bridges and Routers
•	IAPP is scalable for the future.
–	element structure allows for migratable extensions
–	proprietary extensions are allowed 
How to continue
•	Short term
–	Comments on the IAPP are solicited from all interested parties.
–	Specification is maintained by Aironet and Lucent Technologies.
–	New versions are distributed via:
»	IEEE Email reflector
»	Web sites
–	Aironet, Digital Ocean and Lucent Technologies agree to implement IAPP in their 802.11 products
•	Long term:  Consensus of the meeting:
–	A lot of interest to move forward with this proposal.
–	Proposal to present it to 802.1 Technical plenary to see where it should belong.
»	Do this in November, to prevent impact on 802.11 Sponsor ballot
»	Would be very useful as informative annex to 802.11, but not now.