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IEEE 802.11s terms and definitions

IEEE 802.11s terms and definitions. Authors:. Date: 2008-07-16. Abstract.

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IEEE 802.11s terms and definitions

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  1. IEEE 802.11s terms and definitions Authors: Date: 2008-07-16 Guido R. Hiertz et al., Philips

  2. Abstract IEEE 802.11s faces many new problems that require interaction with other 802 groups. From the initial PAR until the most recent draft, TGs has significantly changed its terms and definitions several times. Often the terms chosen did not base on solid research. Thus, imprecise definitions were mistaken and members developed contradicting understandings. This document resolves the issue and provides a framework of terms that fits into the 802 family of standards. Guido R. Hiertz et al., Philips

  3. IEEE 802 definitions Guido R. Hiertz et al., Philips

  4. Definitions according to 802-2001 • We refer to [1] • On two pages with column notation • Left hand column has original text • Highlighted text provides key definitions • Right hand column holds explanatory notes Guido R. Hiertz et al., Philips

  5. 3.1.1 Access Domain • A set of LAN or MAN stations together with interconnecting data transmission mediaand related equipment (e.g., connectors, repeaters), in which the LAN or MAN stations use the same MAC protocol to establish the sequence of stations that are in temporary control of the shared transmission media. • The definition comes close to what a BSS in 802.11 is • A can connect with B-F • Inside A’s access domain • A cannot connect with G-J • Outside A’s access domain Guido R. Hiertz et al., Philips

  6. 3.1.5 End station • A device attached to a LAN or MAN, which acts as a source of, and/or destination for, data traffic carried on the LAN or MAN. • The definition of an end station is clear and simple • Use it in 802.11s whenever traffic will not be relayed • Path selection information • Security related messages • Traffic forwarded to final destination • Etc. • We do not need to invent another term for 802.11s Guido R. Hiertz et al., Philips

  7. 3.1.3 Bridge • MAC bridge: A functional unit that interconnects two or more LANs or MANs that use the same Data Link layer protocols above the MAC sublayer, but can use different MAC protocols. • A bridge connects similar and dissimilar 802 networks • A bridge is a superior term to the 802.11 definition of a portal • The portal connects dissimilar 802 networks • 802.11 and 802.XY • When several Meshes interconnect, a bridge relays traffic between the different LANs • Even between two 802.11 Meshes • Definition is simple and clear • Use it in 802.11s! Guido R. Hiertz et al., Philips

  8. 3.1.23 Station • An end station or bridge. • The 802-2001 standard provides a superset of terms to all other 802 standards • The station definition is broad • The 802.11 definition of a station is more specific than the 802-2001 standard • However, 802.11 has no definition for a bridge between 802.11 networks • This might be covered the Distribution System concept Guido R. Hiertz et al., Philips

  9. 3.1.14 Interconnection • The provision of data communication paths between LAN or MAN stations. • This is truly what 802.11s does Guido R. Hiertz et al., Philips

  10. 6.3 Interconnection and interworking • In some cases, the end systems on a LAN or MAN have no need to communicate with end systems on other networks (other LANs, WANs, etc.). However, this is not expected to be the norm; there are many cases in which end stations on a LAN or MAN will need to communicate with end systems on other networks and so devices that interconnect the LAN or MAN with other kinds of networks are required. In addition, several standard methods have been developed that permit a variety of interconnection devices to operate transparently to end stations on a LAN or MAN in order to extend the LAN/MAN capabilities available to end stations, particularly in terms of the geographical extent and/or total number of end stations that can be supported. [to be continued on next page] • This is exactly the use case for Wireless Mesh Networks • A solution within the technology to achieve interconnection Guido R. Hiertz et al., Philips

  11. 6.3 Interconnection and interworking • [continued from previous page] See also Clause 11 of this standard, for an outline of the optional methods by which ISLANs and MANs may support isochronous interworking with WANs and with remote ISLANs and MANs. Standard methods of interworking fall into the following three general categories, depending on the layer at which the corresponding interconnection devices operate: • Physical-layer interconnection, using devices usually termed repeaters or hubs (6.3.1) • MAC-sublayer interconnection, using devices termed bridges (6.3.2) • Network-layer interconnection, using devices usually termed routers (6.3.3) • 802.11s provides wireless multi-hop connectivity at MAC layer level • Mesh devices mutually forward frames  Mesh devices mutually serve as bridge Guido R. Hiertz et al., Philips

  12. 6.3.2.4 Transparent bridging and source routing • ISO/IEC 15802-3 specifies transparent bridging operation, so called because the MAC bridging function does not require the MAC user frames transmitted and received to carry any additional information relating to the operation of the bridging functions; end-station operation is unchanged by the presence of bridges. […] • This description describes the desired behavior of an 802.11 network from an 802.11 station’s point of view •  Mesh devices shall be transparent to outside Guido R. Hiertz et al., Philips

  13. 6.3.1 Physical-layer interconnection: repeaters and hubs • The original IEEE 802 LAN specifications were for end stations attached to a shared communication medium. This basic LAN configuration is referred to as a single access domain; the domain consists of the set of LAN stations such that at most one can be transmitting at a given time, with all other stations acting as (potential) receivers. to be continued on next page] • With 802.11, the access domain would relate to the set of 802.11 stations that an 802.11 station has an 802.11 link with • For 802.11s, the access domain is the Mesh neighborhood Guido R. Hiertz et al., Philips

  14. 6.3.1 Physical-layer interconnection: repeaters and hubs • [continued from previous page] A repeater is a device usedtointerconnectsegmentsof the physical communications media, for example, to extend the range of a LAN when the physical specifications of the technology would otherwise be exceeded, while providing a single access domain for the attached LAN stations. Repeaters used in support of multiple end stations attached by star-wired network topologies are frequently referred to as hubs. • Although 802.11s extends the range of the wireless network, it does not rely on simple repeaters • 802.11s uses MAC based relaying Guido R. Hiertz et al., Philips

  15. 6.3.2.1 Bridges and bridged LANs • Bridges (see 3.1.3) are devices that interconnect multiple access domains. ISO/IEC 15802-3 provides the basic specification for bridge interworking among IEEE 802 networks. A bridged LAN (see 3.1 of ISO/IEC 15802-3) consists of one or more bridges together with the complete set of access domains that they interconnect. A bridged LAN provides end stations belonging to any of its access domains with the appearance of a LAN that contains the whole set of attached end stations. A bridged LAN can provide for the following: • Communication between stations attached to LANs of different MAC types • An increase in the total throughput of a LAN • An increase in the physical extent of, or number of permissible attachments to, a LAN • Partitioning of the physical LAN for administrative or maintenance reasons • If “access domain” is the generic 802 term for the 802.11s “radio neighborhood” “bridged LAN” is the 802 generic term for an 802.11s network Guido R. Hiertz et al., Philips

  16. 6.3.2.2 Relaying and filtering by bridges • A bridge processes protocols in the MAC sublayer and is functionally transparent to LLC and higher layer protocols. MAC frames are forwarded between access domains, or filtered (i.e., not forwarded to certain access domains), on the basis primarily of MAC addressing information. [to be continued on next page] • In 802.11s, the path selection protocol provides filtering, the Mesh devices provide forwarding between different radio neighborhoods (=“access domain”) Guido R. Hiertz et al., Philips

  17. 6.3.2.2 Relaying and filtering by bridges • [continued from previous page] Figure 4 shows the position of the bridging functions within the MAC sublayer; note particularly that the relaying and filtering functions are considered to belong entirely within the MAC sublayer. Filtering by bridges tends to confine traffic to only those parts of the bridged LAN that lie between transmitting end stations and the intended receivers. This permits a bridged LAN to support several transmitting end stations at any given time (up to the total number of access domains present). • The wireless is a broadcast medium • 802.11s cannot achieve this degree of filtering • However, 802.11s does not apply pure flooding • The directed forwarding of 802.11s provides similar functionality Guido R. Hiertz et al., Philips

  18. Internal organization of the MAC sublayer with bridging • From 802-2001 point of view, an 802.11 portal is “just another” bridge • Another example for bridging in 802.11 is a Mesh device that is collocated with an AP • Due to minor implementation details, 802.11 chose not to use the bridge term in 802.11 • See Backup – B slides Guido R. Hiertz et al., Philips

  19. Conclusions on IEEE 802 definitions • 802-2001 describes the general framework • 802.11 concepts fit into the framework • However, some terms are different • The radio environment is different than a wired network • There are legacies on both sides that sometimes lead to confusion • AP, PC, HC and Portal are relaying entities • They operate as filtering bridges • Often, the 802.11 term “station” is understood as 802 “end station” • Important to consider the difference Guido R. Hiertz et al., Philips

  20. IEEE 802.11 definitions Guido R. Hiertz et al., Philips

  21. Definitions according to 802.11-2007 • We refer to [2] • On two pages with column notation • Left hand column has original text • Highlighted text provides key definitions • Right hand column holds explanatory notes Guido R. Hiertz et al., Philips

  22. 3.40 Distribution System • A system used to interconnect a set of basic service sets (BSSs) and integrated local area networks (LANs) to create an extended service set (ESS). • A system is a set of entities, devices & services • It’s more than a single entity/device • Here • The term is specific to 802.11 • The term LAN is broad • Any 802 network • To integrate a non-802.11 LAN, however, a portal is mandatory • The portal unifies the DS & non-802.11 LANs Guido R. Hiertz et al., Philips

  23. 3.8 Association • The service used to establish access point/station (AP/STA) mapping and enable STA invocation of the distribution system services (DSSs). • To “associate” in 802.11 is a process similar to connecting a station with a wired 802 network • In an 802.3 network, the bridge learns about the station and forwards frames on the according port • 802.1X (Port-Based Network Access Control) provides security related features in the wired network Guido R. Hiertz et al., Philips

  24. 3.39 Distribution Service • The service that, by using association information, delivers medium access control (MAC) service data units (MSDUs) within the distribution system (DS). • The 802.11 association process is used as similar information as an 802.3 bridge would learn addresses of its attached stations • 802.11s uses the information of membership in a Mesh to forward frames Guido R. Hiertz et al., Philips

  25. 3.42 Distribution System Service (DSS) • The set of services provided by the distribution system (DS) that enable the medium access control (MAC) to transport MAC service data units (MSDUs) between stations that are not in direct communication with each other over a single instance of the wireless medium (WM). These services include transport of MSDUs between the access points (APs) of basic service sets (BSSs) within an extended service set (ESS), transport of MSDUs between portals and BSSs within an ESS, and transport of MSDUs between stations in the same BSS in cases where the MSDU has a multicast or broadcast destination address or where the destination is an individual address and the station is associated with an AP. DSSs are provided between pairs of IEEE 802.11 MACs. • An 802.11s Mesh could be seen as one implementation of a DS as it transports MSDUs between stations that are not in direct communication range Guido R. Hiertz et al., Philips

  26. 3.41 Distribution System Medium (DSM) • The medium or set of mediaused by a distribution system (DS) for communications between access points (APs) and portals of an extended service set (ESS). • The DSM can use a wireless or wired medium Guido R. Hiertz et al., Philips

  27. Access Point (AP) • Any entity that has station functionality and provides access to the distributionservices, via the wireless medium (WM) for associated stations. • In 802.11 it is not mandatory for an AP to be collocated with a portal! • Huge difference to what Wi-Fi Alliance & “ordinary users” think about an AP • The distribution service delivers MSDUs within the distribution system • The distribution system can be a logical “thing” inside the AP Guido R. Hiertz et al., Philips

  28. 3.71 Infrastructure • The infrastructure includes the distribution system medium (DSM), access point (AP), and portal entities. It is also the logical location of distribution and integration service functions of an extended service set (ESS). An infrastructure contains one or more APs and zero or more portals in addition to the distribution system (DS). • In 802.3, the infrastructure consists of wires, patch panels, outlets, bridges, hubs etc. • The Mesh could be one element of the infrastructure Guido R. Hiertz et al., Philips

  29. 3.72 Integration Service • The servicethat enables delivery of medium access control (MAC) service data units (MSDUs) between the distribution system (DS) and a non-IEEE 802.11 local area network (LAN) (via a portal). • The 802.11s Mesh is not part of the integration service • 802.11s delivers MSDUs within the 802.11 network Guido R. Hiertz et al., Philips

  30. 3.110 Portal • The logical point at which the integration service is provided. • The term portal is specific for 802.11 • A portal is a non-802.11-to-802.11 bridge Guido R. Hiertz et al., Philips

  31. 3.16 Basic Service Set (BSS) • A set of stations that have successfully synchronized using the JOIN service primitives and one station that has used the START primitive. Membership in a BSS does not imply that wireless communication with all other members of the BSS is possible. • The BSS definition is broad • BSS = A bunch of stations • In a BSS, stations may be able to communicate with each other • Via AP • Directly • BSS description in accordance with 802.11s • “Wireless communication” is possible  A link exist between two stations • “Wireless communication” is not possible  No link between two stations • In 802.11s, Multi-hop enables communication if no link exists Guido R. Hiertz et al., Philips

  32. 3.69 Independent Basic Service Set (IBSS) • A basis service set (BSS) that forms a self-contained network, and in which no access to a distribution system (DS) is available. • Has a common identifier • Stations join an IBSS based on the SSID Guido R. Hiertz et al., Philips

  33. Infrastructure BSS • In 802.11-2007, the term does not exist • It’s the combination of the definitions for • Infrastructure • BSS • Has unique identifier • SSID = AP’s MAC address • A BSS where all frames are exchanged via the AP • AP operates as relay for all associated stations Guido R. Hiertz et al., Philips

  34. 3.54 Extended Service Set (ESS) • A set of one or more interconnected basic service sets (BSSs) that appears as a single BSS to the logical link control (LLC) layer at any station associated with one of those BSSs. • An ESS is the union of the BSSs connected by a DS. The ESS does not include the DS. • ESS = {BSS0 BSS1 …  BSSn} Guido R. Hiertz et al., Philips

  35. 3.53 Extended Service Area (ESA) • The area within which members of an extended service set (ESS) may communicate. An ESA is larger than or equal to a basic service area (BSA) and may involve several basic service sets (BSSs) in overlapping, disjointed, or both configurations. • In an ESA, connectivity to a specific 802.11 is available Guido R. Hiertz et al., Philips

  36. Annex M.4, Integration service versus bridging • There are a number of differences between the 802.11 Integration Service and the service provided by an 802.1 bridge. In the 802.11 architecture, a Portal provides the minimum connectivity between an 802.11 WLAN system and a non-802.11 LAN. Requiring an 802.1D bridge in order to be compliant with 802.11 would unnecessarily render some implementations non-compliant. The most important distinction is that a Portal has only one "port" (in the sense of 802.1D, for example) through which it accesses the DS. This renders it unnecessary to update bridging tables inside a Portal each time a STA changes its association-status. That is, the details of distributing MSDUs inside the 802.11 WLAN need not be exposed to the Portal. • The decision to distinguish between an 802 bridge and an 802.11 portal is due to historic reasons • “… unnecessarily render some implementations non-compliant” • The portal does not know about the DS • Details about DS are hidden to portal • DS works transparently to portal Guido R. Hiertz et al., Philips

  37. Annex M.4, Integration service versus bridging • Another difference is that the DS is not an IEEE 802 LAN (although it carries IEEE 802 LLC SDUs). Requiring that the DS implements all behaviors of an 802 LAN places an undue burden on the architecture. Finally, it is an explicit intent of this standard to permit transparent integration of an 802.11 WLAN into another non-802.11 LAN, including passing Bridge Protocol Data Units through a Portal. While an implementer may wish to attach an 802.1D bridge to the Portal (note that the non-802.11 LAN interface on the bridge need not be any particular type of LAN), it is not an architectural requirement of this standard to do so. • The DS remains unspecific • A logical concept • May be filled by 802.11s? Guido R. Hiertz et al., Philips

  38. Conclusions on IEEE 802.11 definitions Guido R. Hiertz et al., Philips

  39. Generic terms • In 802.11, everything is an STA • “Any device that contains an IEEE 802.11-conformant MAC and PHY interface to the WM.”  Way too broad for 802.11s • Fun in 802.11, fun for 802.11s? • non-AP STA • non-HC STA • non-MP STA • non-Portal STA • non-Portal MP • non-AP MP • non-QoS STA • … • Do we really want to define all these categories? Guido R. Hiertz et al., Philips

  40. Transparent operation • 5.1.1.4 Interaction with other IEEE 802 layers • IEEE 802.11 is required to appear to higher layers [logical link control (LLC)] as a wired IEEE 802 LAN. • Ok … No problem for 802.11 • How about 802.11s? • Tough goal • In accordance: • IEEE 802.11s is required to appear to higher layers (LLC) as a wired IEEE 802 LAN Guido R. Hiertz et al., Philips

  41. Basic building block • 5.2 Components of the IEEE 802.11 architecture • […] The basic service set (BSS) is the basic building block of an IEEE 802.11 LAN. • 802.11 knows different types of BSSs • IBSS, infrastructure BSS, QBSS etc. • We can extend the BSS concept • Introduce the Mesh BSS Guido R. Hiertz et al., Philips

  42. Implications for 802.11s Guido R. Hiertz et al., Philips

  43. Issues with current definitions • What is a WLAN? • 802.11 defines the WLAN system • Broad term, includes almost anything • Too generic • What is a Mesh? • Not a well defined term • What’s a WLAN Mesh? Guido R. Hiertz et al., Philips

  44. One example … • The default values used by non-AP STAs and MPs for the parameters in the EDCA Parameter Set element are defined in Table 7-37. • The text indicates that two categories exist: • non-AP STAs • non-AP MPs • Here, both categorizes shall have the same behavior. • However, one might ask if that is a general assumption? • Is any description for the non-AP STA mandatory for the non-AP MP too? • Is it necessary to explicitly state “non-AP STA and MP”? • If not, what applies to the MP? • Do we need to check all occurences of non-AP STA in 802.11-2007? • Do we need to add non-AP MP in this places too? Guido R. Hiertz et al., Philips

  45. Where do we fit in? • Notice the terms! • Relay • Intra BSS • Figure taken from 802.11-2007 Guido R. Hiertz et al., Philips

  46. Simple modifications for 802.11s Guido R. Hiertz et al., Philips

  47. Mesh STA & Mesh BSS • Replace the term “Mesh Point” with “Mesh Station” • Derive definition for a set of Mesh STAs Mesh BSS • The term “station” is well defined  802.11s should build on it • A set of Mesh stations communicates in a Mesh BSS Guido R. Hiertz et al., Philips

  48. Mesh Point or Mesh Station? • Mesh Point • Defines its own device category class • Unique and new • In mathematics, an n-tuple defines a point • No two points are equal • In a BSS, the AP is unique • STAs are not unique • A BSS may have multiple STAs but only one AP • Mesh STA • In accordance with other STA definitions • Mesh devices do not provide access service • Prevent confusion with AP definition • Mesh has no unique devices • All devices are equal • No “singularity”  Mesh device closer to station than to access point specification Guido R. Hiertz et al., Philips

  49. Mesh BSS • Introduce a new term • Mesh BSS • Either you are in the Mesh BSS or you’re not • Only mesh devices can be in the Mesh BSS • No need to hassle with non-MP, non-AP, non-XYZ terminology • Can be easily extended • HT mesh station (802.11n & 802.11s compliant entity) • Consistent with 802.11n definitions • 802.11y & 802.11s • Dependent mesh STA • Etc. Guido R. Hiertz et al., Philips

  50. Why Mesh BSS? • In an Independent BSS there are Stations only • See 802.11 definitions • In an Infrastructure BSS there is only one AP & one or more Stations • See 802.11 definitions • In an ESS there are APs & Portals only • See 802.11 definitions • In an 802.11s network there are MPs only • No integration of non-Mesh STAs into Mesh BSS • Consistent terminology: Mesh BSS Guido R. Hiertz et al., Philips

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