`
`
`
`Abstract
`The core Internet technolegics were in the hands of the research community 10 or more years befare the World Wide Web happened and popu-
`larized the Internet as a place lo find information, access service, and teade. The Infrared Data Association has been in existence for oversix
`years. Products cmbedding the communication lechnology IrDA defines have been around for overfive years, starting with printers and portable
`PC's. TDA is cheap to embed, uses uncegulaied spectrum, andis dicreasingly pervasive ina wide tange of devices. Vront its roots in portable PCs
`andprinters, IrDA technology is presentin virtually all new PDAs,it is emerging in mobile phones, pagers, digital cameras, and image capture
`devices. We are silling on the cusp of the information appliance ape, aud WDA is playing a significant role in enabling the interaction between
`information appliances, between information appliances ancthe information infrastructure, and between appliances communicating across the
`information infrastructure, This article discusses T1A’s communications model. It charts the evolution of the 1DA-Data (Lx) platform architce-
`ture, andthe carly applications aud application services now in common use. [t consicters the present day and the explosion in device calegorics
`embedding the WDA platform. Lt broadens its horizons to consider other emerging appliances lechnologics and Lo consider communications
`models that might arise from a blend of WDA short-range wircless communications and mobile object technologies. Finally, it briefly considers
`future directions fer the TrDA platformitself,
`
`IrDA: Past, Present and Future
`
`
`
`STUART WILLIAMS, HP LABORATORIES
`
`a md
`L
`
`!
`:
`W he Infrared Data Association
`(WDA) was formed in June 1993 and has worked steadily to
`establish specifications for a low-cost, interoperable, and casy-
`to-use wireless communications technology. Today, the
`infrared data communication technologies detined by the
`IrDA ship in over 40 million new devices cach year ranging
`{from personal camputers, personal digital assistants (PDAs),
`digital cameras, mobile phones, pagers, portable information
`gathering appliances, and printers.
`{t is a remarkable achicvement for a new communications
`technology to establish such widespread deployment in such a
`wide range of devices in such a relatively short time. ‘Me core
`Internet platform technologies existed for a full 10 years prior
`to the explosive growth brought about by the introduction of
`the Web.
`IrDA is a communication technology for the appliance era.
`This is an era that, while not excluding the PC, liberates
`devices that have long bcen viewed as peripherals. It cnables
`themto engage in useful interactions with each other without
`having to mediate their communications through some com-
`mon control point.
`ind users have remarkably high expectations of wirclcss
`communications. In the wired world there is general acccp-
`tance of the mechanic] constraints imposed by the various
`plugs and sockets that, at least in part, avoid mismatched con-
`nections. There is acceptance of the cognitive load required to
`sort oul the connectivity and clutter of cabling at the rear ofa
`hi-fi setup or the back of a PC, Llowever, in the wireless
`world, there is an expectation that communications and con-
`nectivity will just work, and work simply. In the wired world
`short-range connectivity between devices is established by
`explicit actions on the part of the end user, In the wireless
`world there is an expectation that conncctivity between
`devices will be established as required without explicit inter-
`vention by the end user. The expectationis that if the user
`allempts to print, the “system” will scek out and establish
`connectivity to a nearby printer,
`The author regularly finds it remarkable that he cat use
`the same infrared pertto:
`* Simply “squirt” files bctweon devices
`
`* Connecel to the local LAN
`* Dial in froma portable PC or PDA via an WDA-cnabled
`ecll phone
`* Print to an WDA-enabled printer
`All ofthis is achieved without reconfiguring betweenactions
`and in most cases merely by placing the appropriate devices in
`proximily to ouc anothier.
`The work of IrDA has sought to go far beyond mere cable
`replacement, and provide a communications platlorm and
`application serviccs fit for the era of information appliances
`and which excel in the arca of case ofuse.
`
`A Brief History of IrDA-Data
`The IrDA was formed in June 1993 to develop an intcropera-
`ble, low-cost and easy-to-use, short-range, infrared, wircless
`communications technology. The inaugural mecting was
`attended by 70+ companics which recognized the consider-
`able value of defining a single family of specifications for the
`communication of data ever infrared.
`Prior to June 1993, a number of noninteroperable single-
`vendorpreprictary schemes tor infrared data communications
`existed. There was considerable risk that the marketplace for
`short-range wireless infrared communications would fragment
`around a numberof proprictary schemes, all of which would
`individually fail to achieve critical mass. Vor system and periph-
`eral vendors cager to deploy short-range witcless solutions in
`their information appliances, the absence of a dominant, com-
`mon conncctivity technology represented a void. Withoul a
`dominant technology, the risk of choosing the wrong propri-
`etary technology was significant. Thus, there was considerable
`sharedinterest in the generation of commonspecifications, and
`this set the tone for the carly years of the IrDA,
`The original requirements can be summarizedas:
`* Marginal cost to addinfrared to a product , under $5
`Data rates of up to 115 kb/s
`Range [rem contact (0 m) through at least 1m
`* Angular coverage delined by a 15-30 degree half-angle cone
`By the end of September, 1rDA had selected ane of 3 pro-
`posed approaches for defining its physical layer[1] defined by
`
`TEIPersonal Communications * Febrrary 2000
`
`1070-991 6/00/$ (0,00 © 2000 TREE
`
`if
`
`1
`
`Exhibit 1040
`Apple, et al. v. Uniloc
`IPR2019-00251
`
`1
`
`Exhibit 1040
`Apple, et al. v. Uniloc
`IPR2019-00251
`
`

`

`
`
`
`
`comm apps
`
`Application and communication services
`
`
`
`
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`'
`
`Ll m cones, cach with a 15-30
`degree half-angle.
`TU soon became apparent that
`the definition of LAP would not
`be sufficient to meet IrDA’s case-
`of-use goals, Certainly, TrlAP
`would provide a reliable connec-
`tion- oriented communication ser-
`vice between two devices, but it
`provided ne means to identify
`prospective clicnts of the TrLAP
`communication services. The yoar
`1993 was a “hot” period with the
`
` Legacy
` inally the union of two overlapping
`1i'FFt17''
`1'1’1
` emergence of numcrous PDAs,
`i''
`'aa'
`1‘1'4
`
`
`
`
`
`
`
`1
`
`Platform
`
`IrLMIP LMAAS
`services
`
`.
`Tiny TP services
`
`irLMIP LM-MUX services
`
`IrLLAP services
`
`Physical
`
`
`
`notebook, and sub-noteboak PCs, It
`was apparent that a model which
`turned overthe infrared communi-
`cation facilities to a single applica-
`tion would be inadequate. The
`emerging multithreaded consumer
`computing platforms required a
`multiplexing communications model
`that cnabled several applications to
`son
`share acecss to the infrared commu-
`hications resources within a device.
`In this way, multiple applications
`could passively listen for appropri-
`ate peer application entities to con-
`neet. Thus, in December 1993 the
`activity to define the Infrared [ink
`Management Protocol (rlMP) [5] was born.
`IrLMPprovides a connection-oricnted multiplexer, LM-
`MUX, and a lookup service, LM-TAS, that cnahles multiple
`IrLMPclients to claim a “port” above (he multiplexer and
`advertise their availability by placing critical contact infor-
`mation into the lookup service. The namespace for the
`lookup service is designed to be self-administering in order
`to avoid the burcaucracy of maintaining administrative
`records about namespace registrations and to ensure “fair
`access” to make use of the namespacc.
`By June 1994, just 12 months after the inaugural IrDA
`mecting, version 1.0 of the core IrDA platform specifications,
`IrPHY, IrLAP, and WIMP, was released [4-6].
`Work continued to define a per-connection flaw contro}
`scheme to operate within IVLMP connections. When multi-
`plexing above a reliable connection, untess there is a means of
`independent flow control for cach derived channel, the deliv-
`ery property of the derived channel is reduced to “best-
`effort.” Per-channel flow control restores a “reliable” delivery
`property. This work led to the definition of the Tiny Trans-
`port Protocol (Tiny TP or ‘VLP) [7].
`TtPHY, IVLAP, IrLMP, and TinyTP are the currently
`acceptedspecifications that define the core of the DA plat-
`form, often referred to as the 1rDA-Data or 1.x platform.
`The platform has been extended three times to accommo-
`date:
`* The addition of (.152 Mb/s and 4 Mb/s data rates
`* ‘The inclusion of a short-range, low-power option primarily
`for use in devices such as mobile phones where battery life
`is paramount
`* The addition of a 16 Mb/s data rate
`Tt was not cnough merely to define a communications plat-
`form, In order to promote interoperability betwecn applica-
`tions, it was essential to devclop specifications for the
`application services aad the application protocols that suppert
`them. Hence, work has also progressed to define application
`
`BM Figure 1. TheDA protocol architecture.
`
`Hewlett-Packard. All three approaches assumed the presence
`of a UARTthat could be used to modulate the infraredtrans-
`missions. The silicon cost of UART devices was well undet-
`stood, and in many cases the system design of many products
`included redundant UAR's; thus, the marginal cost of adding
`(DA could amount to just the components ofthe infrared
`transceiver,
`So far, these requirements havelittle to say about the fune-
`tional model of communication. There was an implicit requirc-
`ment that the infrared medium serve as a cable replacement,
`but, as we shall see later, the question of which cable
`remained.
`The natural abstraction of a half-duplex, asynchronous
`character-oriented transmission was too poor an abstraction
`for building interactions that were self-organizing and casy lo
`use. In addition, there were frequent discussions of how to
`select data rate, how media access control was to function,
`and how, in the context of a 115 kb/s link, reasonably cfficient
`use could be made of the available bandwidth.
`By November 1993 IrDA had settled on a token-passing
`approach, originated by TBM [2] and derived from high-
`leyel data link control (HDLC) (3] operating in normal
`response mode (NRM), As with other proposals, this was a
`packelized scheme, However, in contrast to contention-
`based schemes that were also considered, the HDLC-SIR
`(fater renamed Infrared Link Access Protocol, LAP [3])
`approachyielded contention-free access ta the medium
`once initial communication had been established. IrLAP
`defines a fixed-rate slotted contention-made device discov-
`ery scheme that enables initial contact to be established.
`Critical communication parameters such as connection data
`rate, maximum packet sizes, and certain minimum and max-
`imum gap timings are negotiated during connection estab-
`lishment. Following LAP connection establishment, the
`two devices engaged in communication are deemed to
`“own” the spatial region which they both ilhumimate — nom-
`
`12
`
`TREE Personal Communications * February 2000
`
`2
`
`

`

`LSAP connection Connectionless XID discovery
`LSAP connection
`
`
`AP‘ -
`endpaints
`endpoints
`service access point
`LM-MUx sevice|(@ @ @ 7 (8 8 @; ee
`protocols and services that reside above
`boundary
`‘
`a
`tee” LSAP nll” LSAP
`the IrDA 1.x platform, most notably:
`1rCOMM [8], which provides for serial
`IrLAP cannecticn
`and parallel port emulation over the
`endpoints
`(DA platform, This allows legacy com-
`InLAP sorvice
`ee
`munications applications to operate
`,
`°
`me ISAP
`unchangedover [rDA andalso provides
`boundary
`for wircless access to cxternal modems.
`Station
`The most novel example ofthe latteris
`N1T’s deployment of IrDA-cnabled
`integrated services digital network
`(ISDN) payphones.
`TrLAN [9|, which provides wireless access to TAEL 802 style
`LANs.
`TrOBEX [10], which provides for the exchange of simple
`data objects and could be considered the IrDA analog of
`HTTP. WORBEX delivers on the notion of “squirting” infor-
`mation objects such as business cards, phone lists, calendar
`entrics, and binaryfiles between devices.
`IrvTRAN-P [11]: which provides for the exchange of images
`between digital still image cameras, photo printers, and PCs.
`IrMC [12], which defines a profile of relevant IDA specifi-
`cations for inelusion in cell phones. Much of this work is
`being leveraged by the Bluetooth community. IrMCpre-
`vides for vendor independent interactions with commoncell
`phone features such as phone list synchronization, calendar
`synchronization, and wircless modemaccess. Tt also pro-
`vides for third-generation smart phones.
`* IrjetSend [13, 14]: which describes how to bind Llewlett-
`Packards JetSend protocol for networked appliance interac-
`tion to the WDA platform.
`Figure | below summarizes the TrDA-Data platform and
`application services defined to date.
`The discussion so far has focused on the history of the
`standards development process. ‘Table 1 below shows key
`milestones in terms of the introduction of classes of products
`implementing various mixes of applications services.
`
`|
`
`Figure 2. Service access pointsand connection endpoints.
`
`IrDA Lx Platform Architecture
`
`|u
`
`l
`
`
`
`
`
`In this section we describe the layered protocol architecture of
`the 1DA-Data 1.x platform, the services providedat ils layer
`boundaries, its connection model, and the information model
`and philosophy ofits device andservice discovery processes.
`Figure | shows the layering of the IrDA protocol architecture
`and many ofthe application services mentionedin the previous
`section, ‘The upper boundary of cach of the boxes represents an
`interface where the services of that layer are abstracted.
`The segmented physical layer provides packet transmission
`and reception service for individual packets, aud the means to
`determine when the infrared mediumis busy.
`The TrLAPlayer provides for the discovery of devices with-
`in range and the establishment of reliable connections
`belweenclevices.
`‘Phe wLMPlayer provides connection-oricnted multiplexing
`services with both sequenced and unsequenced delivery prop-
`erties (LM-MUX services) and the service information access
`service (LM-TAS). ILM-MUX provides for multiple logically
`independent channels between application entities within the
`communicating devices. Note that the absence of per-channel
`flow control in LM-MUX channacls means that they may only
`satcly be regarded as best-effort delivery channels.
`Tiny ‘IP mirrors the LM-MUX services; however, it aug-
`ments them with the inclusion of per-connection
`flow control. This restores the reliable delivery
`properties for sequenced data. Tiny ‘TP provides
`a null pass-through for unsequeneed data whose
`delivery properties remain best-effort.
`LM-IAS provides query/response services on
`an information base that contains essential con-
`tact information that cnables prospective service
`users (clients) to identify and bind to service pro-
`viders (servers).
`These four protocel layers, IrPHY, LAP,
`IrMP, and Tiny TP, form the core of the WDA
`platform,
`
`PaseoLe
`Malate Toit (elam Srctns
`
`Davice Catagory
`
`
`
`
`
`ftDA Connection Medel
`The IrDA 1.x connection model is established
`primarily by the IrLAP andIrl.MPlayers. ‘There
`isa l:l correspondence between LrT.MP I.M-
`MUX service access points (LSAPs) and‘liny ‘1’?
`setvice access points (TSAPs), Thus, the ‘Viny ‘TP
`layer docs not contribute to the connection
`model, it merely alters the delivery propertics of
`the channel from best-cffort to reliable.
`Within cach IrDA device (orstation) (Mig. 2),
`IrlLAP serviecs are accessed via a single LAP
`setvice access point (ISAP). The architecture
`allows multiple IrLAP connection endpoints to
`exist within the [ISAP; however, in practice the
`IWLAP protocol defines only single point-to-pomt
`connectivity. There are no known research or
`
`IFFE Personal Communications * February 2000
`
`13
`
`3
`
`

`

`
`
`Station A
`multipoint
`
`primary
`
`Key
`
`
`~——_—_>{rLAP-connection
`
`~~ LSAP-connection
`
`
`
`
`
`
`
`
`
`
`Station B
`secondary
`
`IrLAP service
`access point (LSAP)
`
`Link service access
`point (LSAP)
`
`Connection endpoint
`
`
`
`
`
`LSAP-SEKEP "TeMUx ESAP-SEL
`lients
`
`
`
` LSAP-SEL=J_
`“LSAP-SEL=I1
`"Station ¢
`LM-MUX
`7’
`secondary
`~..__ clients
`cee
`
`Figure 3. Conacetion model.
`
`commercial TrDA stacks that support point-to-multipoint
`connectivily, Tlowever, one commercially available implemen-
`tation supports multiple [rLAP interfaces and gives the
`impression of multipoint operation through multiple indepen-
`dent instances of IrLAP and IrPHY.
`Likewise, Ir.MP LM-MUX services are accessible via mul-
`tiple LSAPs, Typically, an application entity will bind to an
`iTSAPand, in general, will support multiple WLMP LM-MUX
`connections (or Tiny TP connections). ‘Thus, cach LSAP may
`contain multiple LM-MUX connection cndpoints. LSAP
`addresses are formedby the concatenation of an 8-bit LSAP
`sclector and the device address of the device where the LSAP
`resides,
`Figure 3 illustrates the IrDA 1,x connection model in the
`case of point-to-multipoint connectivity.
`IrLAP connections are labeled by the (unordered) pair of
`32-bit device addresses of the devices involved in the connec-
`(ion. Following connection establishment, a temporary 7-bit
`connection address is used in the packets as an alias for this
`concatenated device address.
`Likewise, IrLMP [.M-MUX connections are labeled by the
`(unordered) pair of PSAP addresses at cach end of the LM-
`MUX connection. A corollary of this is that at most only a
`single LM-MUX connection may be established between any
`two LSAPs,
`This connection model is identical to that offered by
`FCPAIP where, semantically, IP addresses may be substituted
`for IrDA device addresses and TCP/IP port numbers are sub-
`stituted for Ir. MP LSAP selectors.
`
`Device and Service Discovery
`IrLAP provides a basic device discavery mechanism. lunc-
`tionally, the result of invoking the LAPdiscovery process is
`a list of records that encode:
`* Device Address: A 32-bit semi-permanent device identifier
`of the discovereddevice.
`* Nickname: A short multilingual name for the discovered
`device that may be presented in user interfaces to aid in
`sclection.
`* Hints: A bit mask giving nonauthoritative hints as to the
`services that may be available on the discovered device.
`
`This may be used to order “decper” queries into the IAS to
`authoritatively establish the presence or absence of a partic-
`ular service.
`The device discovery process ts further abstracted through
`Ir_LMP by defining procedures for the resolution of contlicting
`device addresses, and “hiding” such issucs from the LM-MUX
`user.
`
`Device discovery enables entilics within one device to
`establish the presence of other devices. Llowever, for a system
`to be largely autoconfiguring and to operate with minimum
`unnecessary intervention from the enduser, it is essential that
`application entities within one device be capable of identilying
`and establishing contact with peer catities, These peer entities
`share a commoninterface (or application protocol) that
`enables them to interact. Contrast this with the situation
`where an end usecis faced with the problem of ensuring that
`the right applications are boundto the right serial ports, or
`that the correct scrial ports are connected together and the
`appropriate pin-pin mappings have beeninstalled in the cable
`depending on whetherthe connection is DTE-DCT! or DTH-
`DLE and on particular idiosyncrasies in the device’s serial
`port implementation.
`LM-IAS defines:
`° Asct of operations that an IAS client may invoke on an
`IAS server
`* ‘The behavior of an LAS server
`* An information model for representing the application ser-
`vices accessible at a given clevice
`Starling with the information model, cach application ser-
`vice is represented by a named [AS object class, The name of
`the object class reflects the name of the service and may be
`up to 40 octets in length. A hicrarchical naming convention is
`used to avoid name space clashes and to minimize the admin-
`istrative burden on the IrDA office. Tt also in effect provides
`open and equitable acecss to the class namespace, Thus, class-
`
`names that start “DA: are defined by IrDA, while class-
`names that start “Hewlett-Packard:” are defined bythe
`Hewlett-Packard Company, andso forth,
`list of
`An object class acts as a container for a
`attribute/value pairs. Attributes are named, and in general the
`attribule namespace is scoped by the enclosing class. Hawev-
`
`14
`
`NE Personal Communications * February 2000
`
`4
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`

`

`cr, by convention some attributes are of such global utility’
`thal they are deemed to have the same semantics in all scopes.
`Such attributes carry hicrarchically structured names that tol-
`low the same syntactic conventions as the [AS classname.
`Thus, (DAT LMP.sapSel and WDA:TinyTP: LsapSel are the
`names of globally scoped attributes that carry the LSAPselec-
`tor portion of the address of the entity represented by an
`inslanee of the object. WDA: LMP:InstanceName is a plobal-
`ly scoped attribute used to carry a distinguishing name that
`may be used in user interfaces to aid in selection when multi-
`ple instances of a given service are found on asingle device.
`‘There are three attribute value types:
`*Inleger: A 32-bit signedinteger.
`«Userstrings: Intendedfor presentation via a user interfacc;
`up ta 255 octets in length with multilingual support.
`* Octet sequence: An opaque sequence of up to 1024 actcts
`of information, The attribute may impose further structure
`on the contents ef the sequence, This is a soad way to clus-
`ter a body of formation vader one attribute.
`WLMP defines a number of operations for traversing aud
`retrieving information from an TAS information base; howev-
`er, only the GetValucByClass operation is mandatory, A pos-
`sible C function prototype for the client operation would be:
`AttributeValuchist
`GetValuchyClass (ClassName class,
`AtbLributeName altribute) ;
`where the result type, AttributeList, encapsulates a possibly
`empty list of object instance ids and attribute valucs from
`objects that match given object and attribute names, Thus, a
`single invocation may resull in responses for multiple object
`instances, and further attributes, such as instance names, may
`need to be sought in order for an appropriate choice to be
`made,
`The IrDA platform provides a space for the definition of
`new applications and application services above the platform.
`In defining new services it places three obligations on the ser-
`vice designer:
`* The definition of an IAS object class
`* ‘The definition of a hints mask that indicates the strong like-
`lihood that an instance of that service exists on the discov-
`cred device
`° The definition of the semantics of the application Icvel
`interaction and the communication stack profile(s) that
`provides the channel tor the interaction
`IrDA-Data, Lx Platform Summary
`Before moving on to cousider some of the application services
`defined above the IrDA platform, a bricf recap of what we
`have described so far is whorthwhile.
`The IrDA platform provides a connection model identical to
`that provided by TCP/IP. The semantics of the Tiny ‘TP trans-
`port service are sufficiently close to those of PCP that in practi-
`cal implementations they can be provided through an application
`programming interface (APY) based on Berkeley sockets.
`Naming and addressing in reDA differs from TCP/IP nam-
`ing and addressing, Device addresses are flat and dynamically
`assigned. While device addresses change infrequently, auio-
`mited processes do force change when conflicts arise. Both
`the names and addresses of devices are explicitly discovered.
`Neither are assumed to be known apriori. Services in the
`(DA environment are named using IAS classnames. These
`names are dynamically mapped to WhMP LSAPs and/or Tiny
`TP TSAPs through LAS querics. This dynamic mapping
`reduces the administrative burden imposed on the WDA
`olfice. With the limited 7-bit “port” address space of the LM-
`MUX, it also removes the problem of organizations making
`unfair claims on address space real estate.
`
`TEER, Personal Communications + February 2000
`
`Device discovery and LL.M-IAS provide the pivotal case-of
`use features in the platform that cuable application entities to
`locate andestablish contact with peer entitics which support a
`given interaction protocol (i.c,, the semantics of the message
`set exchanged between application entities via the channel
`established through the IrDA platform).
`
`Advanced Infrared
`
`The WDA-Data 1.x architecture has some obvious limitations.
`Kirst, although the architecture can accommodate a point-
`to-multipoint mode of operation, the LAP specification has
`never been extended to deline the protocol machinery to
`enable that functionality. From an end-user point of view it is
`also questionable whether such extension of the 1.x platform is
`even desirable, Viewed as a single point-to-point link, the
`behavior of an WLAP connection is largely symmetric, and the
`differences in behavior between an WLAP primary station and
`an IrLAP secondary station are larpely moot. TTowever, the
`introduction of point-to-multipoint operation would signiti-
`cantly disturb this symmetry in ways that would become imcon-
`venient for the end user, Consider a portable computer that
`needs to access both a LAN access point and a desktop print-
`er. [t would be natural for the portable computer to become
`the IWLAP primary and establish IrLAP connections with the
`LAN access point and the printer, cach of which acts as an
`IrLAPsecondary station. However, it is also reasonable that
`the LAN access point (or the printer for that matter) is capa-
`ble of “serving” multiple “clients,” bat in order for it to do that
`it woulditself have to take on the TrLAP primary role. [f the
`connection to the LAN access point were established first anc
`the access point were to cease the primary role (possibly
`through role reversal), the portable computer would be unable
`to establish a sccond LAP connection to the printer. If the
`portable computer retained the primary role, it could establish
`that second connection, but the LAN access point (and the
`printer) would be prevented from establishing connections to
`other potential “clicats.” What the user could achieve would
`not only depend on the set of concurrent interactions they
`were attempting to initiate, but also en the order in which
`those interactions were initiated, This would lead to inconsis-
`tent behavior which would become frustrating for end users,
`Thus, WDA so far has chosen not fo expand the (rlLAP defini-
`tion te encompass point-to-multipoint aperation.
`Second, within some given field of view, the establishment
`of an IrLAP connection between a siugle pair of devices
`inhibits the establishment of connections between other inde-
`pendent devices whose fields of view intersect that of the
`established connection. ‘hus, use of the medium becomes
`dedicated to a single pair of devices. An important subclass af
`general multipoint communication in a shared mediumis to
`enable multiple independent pairs of devices to establish inde-
`pendent communication relationships. [ff two devices are in
`view of cach other, it is reasonable that they should be able to
`establish communications and share access to the medium
`with other users of the space.
`Thus, members of the TDA community sought to extend
`the WDA-Data architecture to cnable true multipoint connec-
`tivity while af the same time preserving the investment in
`upper layer applications and services by cnsuring that the
`semantics of the service definitions al the upper layers ot the
`platform are maintained.
`It is important to be aware of a few differences between
`the goats of the WDA community and the goals of those
`defining wireless LAN specifications. The TENE 802 medium
`access control (MAC) service defines a best-effort ordered
`delivery service with at mest once delivery semantics. [t also
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`5
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`COM "Appliance
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`Legacy
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`Physical
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`IrDA1.x
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`AIR
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`protocol architecture adds an WLCpro-
`tocol entily, which provides multipoint
`link Layer connectivity alongside an
`IrLAP protocol entity, which provides
`logacy connectivity to IrDA 1.x devices.
`‘The link manager (Irl.M) layer [17] is a
`“thin” layer that multiplexes the use of
`IrLAP and LCover their respective
`physical layers. At the upper bound of
`the link control layer, WIC and IrLAP
`provide identical services to the Ir1.MP
`layer. Thus, within an AIR device, the
`inLAP, IvlC, and Irl.M protocol entities
`may be regarded as a single logical entity,
`with a single device address which sup-
`ports an integrated discovery process,
`and both LAP and IrLCconnections.
`The particular use of IrDA 1.x IrLAP or
`AIR ILprocedures for establishing
`device-lo-device connections becomes
`transparent to LMP entitics and abeave.
`IrMAC defines a burst reservation
`carricr sonse multipte access with colli-
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`Figure 4, 16DAAdata advancelR protocol architecture.
`
`assumes a transitive communications relationship. At the
`MAClayer:
`If A can communicate with B
`AND RB can communicate with C
`THEN A can communicate with C.
`In the world ofshort-range infrared wircless communication
`this is not the case. It may even be the case that the communi-
`cation relationship is asymmetric: A may be “heard” by B, but
`B cannot be “heard” by A. With the wired LAN imedium the
`notion of “belonging” to a particular LAN seginent is strongly
`associated with a physical attachment to that segment. Arrivals
`and departures, Infrequent in most wired cases, can be noted
`by both the arriving/departing node, and potentially the wired
`infrastructure and the other devices attachedto that infra-
`structure. In the wireless case, the bounds of a given LAN
`segment are less well defined, and arrival and departure are
`much more the norm.
`Thus, the primary geals in extending TrDA-Data’s connec-
`tion model were:
`* To cnable devices in view of one another to establish cam-
`munication relationships uninhibited by the connection
`state of nearby devices.
`* To enable an advancedinfrared (ATR) device to establish
`communications with at most oue WDA Lx deviec. This
`enables ATR devices to intereperate with legacy 1.x devices
`in a way that is well understoedby users of legacy 1.x
`devices.
`¢ For AIR devices to respect established WDA 1.x connee-
`ions with which they could interfere. This is a coexistence
`requirement intended to ensure that ATR devices do not
`disrupt active T1rDA 1.x connections
`From an architectural point of viewit is relatively simple to
`introduce multi-access communication. It requires that LAP
`be partitioned into a MAC layer (IMAC) [14] and a link con-
`trol layer (Irl.C) [16]. In fact, as illustrated in Fig. 4, the ATR
`
`16
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`TERR Personal Communications * February 2000
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`i
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`tocol. Such MAC protocols rely on the
`exchange of Request-l'o-Send, Clear-to-
`Send MACprotocol data units (PDUs).
`Vor such a mechanism to function prop-
`erly, it is important that the reservation
`MAC PDUs be decoded, not only by
`devices capable of engaging in commu-
`nications, but also by devices capable of
`interfering with communications. In some radio frequency
`(RF) systems using this style of MAC protocol, the range of
`the reservation messages is extended by boosting the trans-
`mission power for the rclated MAC PDUs. ATR makes use
`of a variable rate (VR} coding technique known as repetition
`coding to robustly cade the headers of all ATR MAC PDUs.
`The use of this technique was pioneered by [BM Research
`in Zurich [18], and fuil details are given in the ATR physical
`layer specification [19]. Repetition coding trades signal-to-
`noise ratio (SNR) (range) for transmission rate by repcti-
`tion of physical
`layer symbols. Repetition decoders
`“average” the repeated symbols reccived prior to making a
`decision on what symbol was encoded. In theory, successive
`halving of the data cate by successively doubling the number
`of symbol repelilions yiclds approximately a 19 percent
`range increase al cach reduction step. Cumulatively, the
`effect of a L6-fold rate reduction (four doublings of the rep-
`etition rate) yiclds a doubling of the effective range of
`transmission, Key ficlds of the AIR TYMAC [17] PDUs are
`coded with 16x repetition.
`This VR physical layer delivers two benefits. First, it pro-
`vides a means of robustly coding the media reservation mes-
`sages defined by the CSMA/CA burst reservation MAC
`protocol defined in the IrMAC specification so that they
`reach more potential sources ofinterference,
`Second, by actively mon