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Interpretations of the Distribution System Service Based on the 802.11 Specification

This article describes the logical representation and functionality of the 802.11 Distribution System Service (DSS) and explores the impact of existing definitions on new task groups. It also discusses the role of portals and provides examples of message delivery within a DS.

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Interpretations of the Distribution System Service Based on the 802.11 Specification

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  1. Interpretations of theDistribution System Service Based on the 802.11 Specification W. Steven Conner, Intel Corp. Tricci So, Nortel Networks Tyan-Shu Jou, Janusys Networks July 13, 2004 W.S. Conner, T. So, T.-S. Jou

  2. Objectives • Describe the logical representation of 802.11 Distribution System (DS) and Distribution System Service (DSS) • According to the 802.11 spec • Clarify the functionality of the Distribution Service and the Integration Service and the role of the portal • Provide logical data path examples for 802.11 message delivery • Discuss the impact of the existing logical definitions on new task groups such as TGr and TGs W.S. Conner, T. So, T.-S. Jou

  3. Distribution System (DS) • “A system used to interconnect a set of BSSs and integrated LANs to create an ESS” (3.20) • The “output” point of a DS can be a portal or an AP (5.4.1.2) • “IEEE 802.11 explicitly does not specify details of DS implementations. Instead, IEEE 802.11 specifies services” (5.3) • Interpretation: the DS is defined by the services, not by the physical network(s) used to implement the DS W.S. Conner, T. So, T.-S. Jou

  4. Distribution System Service (DSS) • “The set of services provided by the DS that enable the MAC to transport MSDUs between stations that are not in direct communication with each other over a single instance of the wireless medium (WM).” (3.22) • 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, but the station sending the MSDU chooses to involve DSS. • DSS services: • Association • Disassociation • Reassociation • Distribution • Integration Distribution of messages within a DS W.S. Conner, T. So, T.-S. Jou

  5. Distribution of Messages within a DS • Distribution Service: • “It is the job of the distribution service to deliver the message within the DS in such a way that it arrives at the appropriate DS destination for the intended recipient” (5.4.1.1) • Integration Service: • “The service that enables delivery of MSDUs between the DS and an existing, non-IEEE 802.11 local area network (via a portal).” (3.29) • “If the distribution service determines that the intended recipient of a message is a member of an integrated LAN, the “output” point of the DS would be a portal instead of an AP” (5.4.1.2) • “Messages that are distributed to a portal cause the DS to invoke the Integration function (conceptually after the distribution service). The integration function is responsible for accomplishing whatever is needed to deliver a message from the DSM to the integrated LAN media” (5.4.1.2) W.S. Conner, T. So, T.-S. Jou

  6. 802.11 Access Point (AP) Portal • “The logical point at which MSDUs from a non-IEEE 802.11 LAN enter the DS of an ESS.” (3.39) • “A Bridge to an 802-11 LAN shall connect to an 802-11 Portal, which in turn connects to an 802-11 Distribution System (DS). For the purpose of bridging, the service interface presented at the Portal is identical to the service interface presented at the 802-11 MAC SAP. An instance of an 802-11 Distribution System can be implemented from 802 LAN components. 802-11 STAs attach to the Distribution System via an 802-11 Access Point (AP). A bridge shall not connect to an 802-11 Independent BSS.” (802.1D-1998: MAC Bridges, 6.5.6: Support by IEEE Std 802.11) 802.x Bridge 802.11 Portal MSDU STA 802.11 Distribution System (DS) Logical 802.11 LAN Non-802.11 LAN W.S. Conner, T. So, T.-S. Jou

  7. Interpretations on Portal and Integration Service • Portal: • Interpretation: There can be zero or more portals in a DS and portals can be part of any device that provides integration between 802.11 MSDUs and a non-802.11 LAN (including AP devices that provide such an interface) • Integration Service: • Interpretation: Whether or not the Integration Service is required to be invoked for a particular message depends on the source and destination of the message. • If both endpoints are within the DS, integration through a portal is not required (even though the Distribution Service may transport the message across a non-802.11 LAN). • If one endpoint is within the DS and one outside of the DS, integration through a portal is required. W.S. Conner, T. So, T.-S. Jou

  8. Complete 802.11 Architecture Figure 7 of IEEE 802.11-2003 W.S. Conner, T. So, T.-S. Jou

  9. Reassociation Reassociation STA-Y STA-X STA STA Logical View of Portal, DSS, BSS and ESS Non-802.11 LAN 802.11 Portal Integration Service Distribution System Services (DSS) Distribution Service Dissociation Association Dissociation Association 802.11 AP-2 802.11 AP-1 BSS-1 BSS-2 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  10. Dissociation Dissociation Association Association Reassociation Reassociation STA-Y STA-X STA STA Inter-BSS Communication within the ESS Non-802.11 LAN 802.11 Portal Integration Service Distribution System Services (DSS) Distribution Service 802.11 AP-1 802.11 AP-2 BSS-2 BSS-1 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  11. Dissociation Dissociation Association Association Reassociation Reassociation STA-Y STA-Z STA-X STA STA Intra-BSS STA-to-STA Communicationwithin an ESS Non-802.11 LAN 802.11 Portal Integration Service Distribution System Services (DSS) Distribution Service 802.11 AP-1 802.11 AP-2 BSS-2 BSS-1 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  12. Dissociation Dissociation Association Association Reassociation Reassociation STA-Y STA-X STA STA Communication between an 802.11 LAN and Non-802.11 LAN Non-802.11 LAN 802.11 Portal Integration Service Distribution System Services (DSS) Distribution Service 802.11 AP-1 802.11 AP-2 BSS-1 BSS-2 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  13. 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY STA-Y STA-X STA-Z STA STA Integrated DSS AP-Devices IEEE 802.11-1999, 5.2.4: . . . It is possible for one device to offer both the functions of an AP and a portal; this could be the case when a DS is implemented from IEEE 802 LAN components. Non-802.11 LAN (e.g. 802.x LAN) 802.x MAC/PHY 802.x MAC/PHY 802.11 Portal 802.11 Portal Integration Service Integration Service Distribution System Distribution Service Distribution Service Association Dissociation Reassociation Reassociation Dissociation Association 802.11 AP- Device-1 802.11 AP- Device-2 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY BSS-1 BSS-2 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  14. 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY STA-X STA-Y STA-Z STA STA Logical AP Devices:Inter-BSS Communication within the ESS Non-802.11 LAN (e.g. 802.3 LAN) 802.3 MAC/PHY 802.3 MAC/PHY 802.11 Portal 802.11 Portal Integration Service Integration Service Distribution System Services (DSS) Distribution System Distribution Service Distribution Service Association Dissociation Reassociation Reassociation Dissociation Association 802.11 AP- Device-1 802.11 AP- Device-2 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY BSS-1 BSS-2 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  15. 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY STA-X STA-Y STA-Z STA STA Logical AP Devices: Intra-BSS STA-to-STA Communication Non-802.11 LAN (e.g. 802.3 LAN) 802.3 MAC/PHY 802.3 MAC/PHY 802.11 Portal 802.11 Portal Integration Service Integration Service Distribution System Services (DSS) Distribution System Distribution Service Distribution Service Association Dissociation Reassociation Reassociation Dissociation Association 802.11 AP- Device-1 802.11 AP- Device-2 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY BSS-1 BSS-2 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  16. 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY STA-Y STA-X STA-Z STA STA Logical AP Devices:Communication between an 802.11 and Non-802.11 LAN Non-802.11 LAN (e.g. 802.3 LAN) 802.3 MAC/PHY 802.3 MAC/PHY 802.11 Portal 802.11 Portal Integration Service Integration Service Distribution System Services (DSS) Distribution System Distribution Service Distribution Service Association Dissociation Reassociation Reassociation Dissociation Association 802.11 AP- Device-1 802.11 AP- Device-2 802.11 MAC/PHY 802.11 MAC/PHY 802.11 MAC/PHY BSS-1 BSS-2 Extended Service Set (ESS) W.S. Conner, T. So, T.-S. Jou

  17. Discussion • The 802.11 DS and DSS are defined logically to maximize implementation flexibility • Distribution System (DS) is logically defined by Distribution System Service (DSS) and not by the physical network used to implemented the DS. • The Distribution Service is responsible for delivering a message within the DS and the Integration Service enables delivery of a message between the DS and a non-802.11 LAN through the portal. • But… existing implementations do not always cleanly separate the different services of DSS • Possible impact on new task groups such as TGr and TGs: • Before creating new functionality, may need to clarify assumptions about DS and DSS beyond what is currently specified by 802.11 (e.g. define a particular instance of DS or DSS) • To maintain compatibility, how can TGr and TGs avoid conflicting assumptions? W.S. Conner, T. So, T.-S. Jou

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