From: fbauchot@vnet.ibm.com at -WIN-connection Date: 5/27/93 9:00 AM Priority: Normal TO: Vic Hayes at WCND-Utrecht TO: vic.hayes@Utrecht.NCR.COM at -WIN-connection Subject: Submission P802.11/93-62 ------------------------------- Message Contents ------------------------------- Bonjour Vic, Please find hereunder the source file of the submission 93-62. I would appreciate if you can acknowledge correct reception of this file. Best regards, Frederic Bauchot =============================================================================== .*------------------------------------------------------------------------------ --------------------------------------------------- - :userdoc. .*********************************************************************** :prolog. :docprof style = IEEE duplex = SB layout = 1 justify = YES headnum = NO toc = 123456 rhrfrule = BOTH ldrdots = YES ptoc = '*6' . .*---------------------------------------------------------------------* .* The following symbols will ease name changing T (page 378) .*---------------------------------------------------------------------* .se bs='Access Point' .se rs='Mobile Station' .*---------------------------------------------------------------------* .* Common title for all documents .*---------------------------------------------------------------------* :title stitle='' .*---------------------------------------------------------------------* .* The following is the title of this document .*---------------------------------------------------------------------* :topic. Medium Access Control Protocol for Wireless LAN: 2nd Update :etitle. :docnum.DOC: IEEE P802.11/93-62 :author.FJB/KSN - IBM :date.May 1993 :eprolog. .*********************************************************************** :frontm. :tipage. :body. .ce on .* *************** .*********************** TITLE ********************************* .* *************** .sk 4 :h1 num=none. Wireless LAN Medium Access Control Protocol: 2nd Update .sk 3 .* *************** .*********************** AUTHORS ********************************* .* *************** Fr&ea.d&ea.ric J. Bauchot .sk CER IBM La Gaude 06610 La Gaude, France .sk K. S. Natarajan .sk IBM Thomas J. Watson Research Center P.O. Box 704, Yorktown Heights, NY 10598 .ce off .sk 2 .* *************** .*********************** ABSTRACT ********************************* .* *************** :h2.ABSTRACT This contribution provides a 2nd updated description of a medium access control protocol for wireless LANs that can be characterized as follows. :ul. :li.It is based on the MAC protocol framework proposed in :f.&lbrk NAT91a &rbrk:ef. and revised in :f.&lbrk NAT92 &rbrk:ef. and retains its key characteristics. :li.This update introduces a natural way to utilize :hp2.Listen-Before-Talk:ehp2. capability in the MAC when required by different PHY layers available for wireless LANs. :li.This updated-MAC is intended to speed convergence to a consensus WLAN MAC protocol within the 802.11 committee. :eul. :p. The medium access control protocol used is a hybrid of reservation and random access based protocols. Channel time is structured as a sequence of frames of equal duration. The protocol relies on the use of broadcast messages from a central controller that demarcates three intervals in a frame. In the first two intervals (known as the :hp2.Reservation:ehp2. intervals: Period A and Period B), transmission is scheduled by the controller and is used for transfer all isochronous traffics as well as some asynchronous data traffic and control traffic. A distributed contention-based protocol is used in the third interval. This third interval (known as the :hp2.Contention:ehp2. interval: Period C), is used for transfer of some asynchronous traffic as well as control traffic. An adaptively movable boundary separates the contention-free and contention-based intervals in each frame. This provides for flexibility of bandwidth allocation to meet a variety of asynchronous and isochronous services that are required in wireless applications. The MAC protocol is applicable to all the 5 PHY layers (SS FH, SS DS, IR, User-PCS, Single Channel PHY) that require support by a 802.11 MAC. Different PHYs will deploy different cell isolation techniques. :p. The communication architecture is flexible and permits several modes of operation. In particular, wireless communication is supported: :ul. :li.When an infrastructure backbone network (i.e., a Distribution System) that facilitates extended coverage and mobility is available, and :li.When there is no preexisting infrastructure to enable communication between mobile stations. :eul. :h2.Introduction The demand for wireless data communications is expected to grow in the coming years as a wide variety of user applications are developed and used in a number of operating environments. The following usage scenarios are expected to become increasingly common in the future. :p. :hp2.Infrastructure-based LANs: :ehp2. The network architecture will consist of a finite number of :hp1. Access Points:ehp1. that are attached to a :hp1.Distribution System:ehp1.. The Distribution System, typically an IEEE 802 network, would enable: :ul. :li.Communication between mobile stations and fixed destinations ( ex, servers, applications, data etc) that are attached to the Distribution System. Mobile stations communicate to an Access Point (a fixed station) that acts as a :q.bridge:eq. between the radio environment and the Distribution System. The Access Point relays messages from/to stations that request its services. :li.Communication between mobile stations :ul. :li.If communication is between two mobile stations that are not within range of each other, this will occur utilizing the store-and-forward capability of one or more Access Points attached to a Distribution System. :li.If communication is between two mobile stations that are within range of each other, this can occur with direct or indirect support of an Access Point that can serve both of them. :eul. :eul. :hp2.Adhoc LANs::ehp2. A primary requirement for a segment of user applications would be the capability to accomplish wireless communication without any dependence on a preexisting infrastructure. An adhoc LAN consisting of a set of mobile stations and shared resources like servers may be created, used for wireless communication and :q.dismantled:eq. when the needs have been satisfied. :p. In this contribution we propose a communication architecture that is flexible and encompasses the several modes of usage scenarios outlined above. In particular, wireless communication among participating stations is supported: :ul. :li.When an infrastructure backbone network (i.e., a Distribution System) that facilitates extended coverage and mobility is present and available for the mobile station to use, and :li.When there is no preexisting infrastructure available to enable communication between mobile stations that wish to communicate. :eul. :p The Revised-MAC scheme will allow the implementation of non-isochronous and isochronous applications. :h2.Revised Scheme The proposed MAC scheme is first described in the context of Infrastructure-based LANs. The same scheme is used in Adhoc LANs as described in a later section. :p. A half-duplex wireless link is assumed. The link is used in one of the following modes: :ul. :li.Inbound traffic (Mobile stations to Access Point) :li.Outbound traffic (Access Point to mobile stations) :li.Peer-to-peer traffic (direct any-to-any station transfer) :eul. Channel time is structured as a sequence of frames of equal duration. The duration of a frame is subdivided into three intervals as shown in :figref refid=frame.. :ul. :li.Conflict-free access (:hp2.Reservation-based:ehp2.) is used in the first two intervals, and :li.Random-access (:hp2.Slotted Aloha-based:ehp2.) protocol is used in the third interval. :eul. :p. In the first two intervals (Period A and Period B), the link is used for transfer of all :hp1.isochronous:ehp1. data, some reservation-based :hp1.asynchronous:ehp1. data and of outbound control data (such as AH/BH). This includes outbound data transfer from the Access Point to mobile stations and inbound data transfer in the reverse direction as well as peer-to-peer traffic. In this interval, bandwidth is shared according to a reservation-based bandwidth allocation function performed by a SCHEDULER resident in the Access Point wireless adapter. Bandwidth is allocated in each frame for inbound/outbound/peer-to-peer isochronous and asynchronous transfers. :p. The third interval (Period C), is used for :hp1.asynchronous:ehp1. data transmission from any &rs. to any other station (both mobile stations and Access Point) in a random-access (i.e., unscheduled) mode of operation. A Slotted Aloha protocol, optionally enhanced by a :hp2.Listen-Before-Talk:ehp2. phase when required by the PHY layer constraints, is used in this interval. Control as well as data packets (or frames) will use this interval. :p. The control information for Periods A, B and C are AH, BH and CH respectively. The medium access control protocol is now briefly described with respect to :figref refid=frame. below. :fig place=inline frame=box id=frame. :figcap.Frame Structure of Revised-MAC Scheme :cgraphic. &Et.G&Et.AH&Et. A &Et.BH&Et. B &Et.CH&Et. C &Et.G&Et. ....... ... .   Reservat- Reservat-  Slotted Aloha (+ LBT)     ion based ion based  Contention based     From AP  From MS   From MS to AP/MS     to MS  to AP/MS     &Eb. &Eb. &Eb.&Al.