The invention is based on a priority application EP 05290415.8 which is hereby incorporated by reference
The invention relates to a method for providing admission control for the admission of a mobile terminal to a mobile network according to the preamble of claim 1, an admission controller according to the preamble of claim 6 and a communication system according to the preamble of claim 8.
The IEEE 802.11e standard provides Quality of Service (QoS) capabilities to Wireless Local Area Network (WLAN) systems by supporting traffic differentiation by means of Enhanced Distributed Channel Access (EDCA) mechanism, time-division multiplexing by means of Hybrid coordination function Controlled Channel Access (HCCA) mechanism, and means to request, release or modify network resources. The set of IEEE 802.11e tools promises to allow or ease the deployment of QoS-sensitive realtime and interactive services like Voice over Internet Protocol (VoIP) telephony and video streaming.
On the other hand, also admission control is a key building piece for QoS support. It is used to control network resources for QoS-constrained traffic. The admission control function accepts or rejects resource reservation requests based on network resource availability.
Unfortunately, while defining the messages to request, release or modify network resources, the IEEE 802.11e standard does not define a complete admission control mechanism, comprehensive of decision algorithm and means to estimate channel utilization.
Currently there are only either best effort solutions, which provide no QoS support, like in legacy IEEE 802.11a/b/g WLAN systems, or non-controlled solutions based on traffic differentiation using e.g. EDCA mechanisms, for the access to the network resources available.
In case of solutions based on traffic differentiation like e.g. EDCA mechanisms, the network resources are used by the terminals without control. The use of priorities brings effective traffic differentiation (e.g. voice with higher priority than web traffic), but the lack of resource control does not protect such solutions from network, i.e. radio channel, saturation. The main problem is, that a newly activated traffic flow, e.g. a voice call, can impact all already existing (active) streams like e.g. voice calls by degrading the overall satisfaction of the full set of users/customers of the WLAN system.
The object of the invention is to propose a solution for providing admission control for the admission of a mobile terminal to a mobile network.
This object is achieved by a method according to the teaching of claim 1, an admission controller according to the teaching of claim 6 and a communication system according to the teaching of claim 8.
The main idea of the invention is to use a measurement-based admission control that can be applied e.g. to IEEE 802.11e EDCA-enhanced WLAN systems. The proposed solution can be combined with the QoS capabilities introduced by the IEEE 802.11e standard, that provide to mobile terminals the means to reserve and release radio resources as well as to modify them. The solution is based on the measurement of some important metrics characterizing the radio channel, as specified e.g. by the IEEE 802.11k/D1.2 draft standard.
The resource reservation request, i.e. the so-called ADDTS request message (ADDTS=Add Traffic Stream) sent from a mobile terminal to an access point, contains traffic specifications like e.g. the nominal MSDU size (MSDU=MAC Service Data Unit), the mean data rate or the minimum PHY rate (PHY=Physical Layer).
The admission control decision is concentrated into a functional admission controller, responsible to execute the Channel Admission Control (CAC) algorithm. The admission controller can reside e.g. in a so-called fat access point or in a Wireless Network Controller (WNC). In the following the admission controller will be described as external to the access point, in order to explicitly detail the communication between the access point and the admission controller. In case of colocated access points and admission controller, such communication is internal.
The CAC algorithm takes as input the traffic specifications (TSPEC) describing the to-be-admitted flow, i.e. the so-called TSPEC element, combines it with the measured network load information, i.e. the current channel utilization, and decides whether or not the flow can be admitted without impacting the performance of already admitted flows.
Briefly, the channel admission control process can be described in the following way:
The access point measures the channel utilization Umeas during the time period of a so-called measurement window (MW). Then, it provides this information to the admission controller, as input for the CAC algorithm.
The admission controller uses the channel utilization and has initial values to build its own internal view of the channel utilization that is called current channel utilization Ucurr:
UmeasUcurr
When the admission controller receives a resource reservation request, i.e. an ADDTS request message, from a mobile terminal, it computes the increase in utilization of the channel requested by the new flow Uadd as the synthesis of the flow characteristics specified in the TSPEC element:
TSPECUadd
The admission controller combines the current channel utilization Ucurr with the calculated increment of the channel utilization that is called additional channel utilization Uadd to get the (theoretical) new channel utilization Unew, as if the new flow was already admitted:
Unew=Ucurr+Uadd
The admission controller takes the admission decision by checking if Unew does not exceed a given target channel utilization Utarget, i.e. the maximum acceptable channel utilization. If Unew is smaller than Utarget , the new flow is admitted, otherwise it is rejected:
Unew<Utarget ?Decision
When a flow is admitted, the admission controller updates its internal view of the channel utilization, i.e. the current channel utilization Ucurr, in order to account for the increase in the channel utilization due to the newly admitted flow:
Ucurr=Unew
Further developments of the invention can be gathered from the dependent claims and the following description.
In the following the invention will be explained further making reference to the attached drawings.
A communication system according to the invention is depicted in
The access points AP1 and AP2 are connected to each other e.g. via a backbone system and at least the mobile terminal STA1 is connected to the access point AP1 via a wireless connection. Additionally, the access points AP1 and AP2 are both connected to the access controller AC via a fixed or wireless connection. The mobile terminal STA1 that is connected via a wireless connection to the access point AP1 can by means of the backbone system be further connected via the further access point AP2 to one of the mobile terminals STA3 or STA4 within the same mobile network. Furthermore, this mobile terminal STA1 can also be connected by means of the backbone system and via gateways to devices like e.g. terminals or servers located in a further network NW like e.g. the Internet or another mobile network.
The access points AP1 and AP2 comprise the functionality of an access point of a mobile network, i.e. they provide the possibility for mobile terminals to get connected to a mobile network. Furthermore, the access points AP1 and AP2 comprise means for sending admission requests that are originated by a mobile terminal STA1-STA4 to the admission controller AC and means for receiving admission responses from the admission controller AC.
The mobile terminals STA1-STA4 comprise the functionality of a mobile terminal for a mobile network, i.e. they can be connected to a mobile network by means of an access point AP1 or AP2. Particularly, the mobile terminals STA1-STA4 comprise means for sending admission requests to the access points AP1 or AP2 and for receiving admission responses from the access points AP1 or AP2.
The admission controller AC according to the invention comprises means for receiving admission requests for the admission of a mobile terminal STA1-STA4 to the mobile network, for receiving parameters that characterize the radio channel that shall be used for a connection of the mobile terminal STA1-STA4 to the mobile network, for receiving parameters that characterize the traffic flow of said connection, for controlling the admission based on at least one of said parameters that characterize the radio channel that shall be used for a connection of the mobile terminal STA1-STA4 to the mobile network and on at least one of said parameters that characterize the traffic flow of said connection and for sending a response concerning the admission request towards the mobile terminal STA1-STA4.
In the following, by way of example the method according to the invention is described in detail making reference to
The proposed method for providing channel admission control (CAC) is implemented in a WLAN system according to the IEEE 802.11e standard and is based on the following assumptions and initial considerations:
In a basic embodiment of the invention, only one class of service, i.e. only one so-called EDCA access category, is defined in the so-called QoS basic service set (QBSS) of the system. Despite such simplification, the description details precisely and completely the chosen approach. The useful parameters will be presented, as well as the metrics measured by the access point AP1 and the ones computed by the admission controller AC. Finally the admission control algorithm itself is detailed.
The following definitions of useful static parameters are introduced to the CAC algorithm proposal:
In
In the following, the measurements performed by the access point AP1 that lead to the parameters APP that are provided to the admission controller AC as input for the CAC algorithm CALG are described. As already mentioned, the measured metrics of interest are computed over the time period TW of a measurement window (MW) that is depending on traffic load and throughput and expressed in number of observed successful accesses WA, i.e. successful transmitted packets, instead of in seconds.
To perform admission control, the admission controller AC computes a number of metrics. The input data used for this computation are provided by both the access point AP1 and the mobile terminal STA2 involved in the process. The access point AP1 provides to the admission controller AC the parameters APP that characterize the radio channel that shall be used for the connection like e.g. the measured channel utilization Umeas, the packet loss probability p1 and the duration of the measurement window denoted TW. The mobile terminal STA2 provides to the admission controller AC by means of the ADDTS request message the parameters STAP that characterize the traffic flow of the connection from the mobile terminal STA2 to the mobile network, i.e. the description of the to be admitted flow comprised e.g. in the TSPEC element.
The metrics computed by the admission controller AC are listed and described below:
The IEEE 802.11e specification just mentioned also provides full detailed indications about the computation of the medium time parameter TM. The medium time parameter TM is computed by the admission controller AC and used in the CAC algorithm as estimation of the increase in utilization of the channel requested by the new flow Uadd:
TmUadd
The next section details the proposed CAC algorithm CALG. It massively uses the metrics defined in the previous sections.
The basic principle of the CAC algorithm CALG is the following: The admission controller AC builds and maintains the estimation of the current channel utilization Ucurr and uses it to check whether the resources needed for the increase in utilization of the channel by the new flow Uadd are available or not.
The CAC algorithm CALG is executed by the admission controller whenever an ADDTS request message is received, i.e. the reception of such an ADDTS request message acts as a triggering event. The CAC algorithm CALG takes the following metrics as input:
Given these input data, the admission controller AC computes the new (theoretical) channel utilization Unew that it would have if the new flow was admitted:
Unew=Ucurr+Uadd
Once the new channel utilization Unew is calculated, the admission controller AC can take its admission decision by checking if the new channel utilization Unew does not exceed a given threshold, the target channel utilization Utarget. The target channel utilization Utarget represents the target value of utilization that the admission controller AC wants to achieve within its controlled QBSS set.
The admission controller AC can take three possible decision: Accept the new flow and reserve the resources requested, reject it or initiate a renegotiation by proposing a less resource consuming TSPEC element for the flow.
The admission controller AC will accept the admission of the new flow if:
Unew<Utarget
In that case, the admission controller AC updates the current channel utilization Ucurr in order to take into account the newly accepted flow:
Ucurr=Unew
In the ADDTS response message, the admission controller AC indicates as medium time parameter TM in the TSPEC element the increase in utilization of the channel requested by the new flow Uadd computed for the flow.
The admission controller AC will try to renegotiate the admission of the new flow with the mobile terminal STA2 if:
Unew>Utarget
If there is a value of data rate R′r greater than or equal to the required minimum data rate Rmin of the new flow specified by the mobile terminal STA2, this value of data rate R′r can replace the mean data rate Rr in the computation of the increase in utilization of the channel requested by the new flow Uadd, i.e. in the computation of the medium time parameter TM, if the following inequation is true:
U′new<Utarget
In this formula, U′new denotes the new channel utilization that has been derived by means of using the value of data rate R′r instead of the mean data rate Rr in the computation of the increase in utilization of the channel requested by the new flow Uadd. During the renegotiation process, the current channel utilization Ucurr is not updated with the parameters of the requested flow, and the resources are not reserved.
The admission controller AC will reject the admission of the new flow for any mean data rate Rr greater than or equal to the minimum data rate Rmin specified by the by the mobile terminal STA2, if:
Unew>Utarget
Clearly, in case of rejection, the current channel utilization Ucurr is not updated with the parameters of the requested flow.
In a preferred embodiment, the described admission control mechanism is extended to a more realistic case, where multiple classes of traffic/service, i.e. multiple EDCA access categories are defined like e.g. Voice, Video, and Data. The main difference is that now the most important metrics must be measured/computed taking into account the different access categories.
In the following, the modifications requested in the definition of the useful parameters, as well as in the metrics measured by the access point AP1 and the ones computed by the admission controller AC are described. Also, the admission control decision must take into account the existence of the different EDCA access categories.
In the case of multiple classes of service, the static parameters evolve as follows:
The measurements performed by the access point AP1 are also impacted by the presence of multiple classes of service:
Some of the metrics computed by the admission controller AC are impacted by the effect of prioritization among the different classes of service:
To extend the proposed solution for the CAC algorithm CALG to the case where several EDCA access categories are defined, the CAC algorithm CALG must take into account the traffic differentiation. To do so, the following redefined metrics must be used: The measured channel utilization UmeasACi per access category from the access point AP1, the target channel utilization UtargetACi per access category, the medium time parameter TMACi per access category and the current channel utilization UcurrACi per access category.
The CAC algorithm CALG can be easily derived from the basic case described above using the redefined metrics for the case of multiple access categories. The main idea is that now the admission controller AC performs admission control per EDCA access category, keeping an indication of the current channel utilization UcurrACi for each access category ACi.
At the end of each measurement window, the access point AP1 provides to the admission controller AC the measured channel utilization UmeasACi for each access category ACi.
When an ADDTS request message is received by the admission controller AC, the admission controller AC identifies to which access category ACi the new flow maps by means of the so-called TS Info field of the TSPEC element, and perform exactly the same process as described for the CAC algorithm CALG in case of only one access category ACi, now using the metrics for multiple access categories, i.e. the admission controller AC computes the new (theoretical) channel utilization UnewACi that it would have if the new flow were admitted in the requested access category ACi according to the following formula:
UnewACi=UcurrACi+UaddACi
The admission controller AC can now take its decision by checking if the new (theoretical) channel utilization UnewACi does not exceed the target channel utilization UtargetACi of the considered access category ACi. Similar to the basic case with only one access category ACi, the admission controller can accept, reject or renegotiate the flow.
The admission controller AC will accept the admission of the new flow if the following inequation is true:
UnewACi<UtargetACi
In that case, the admission controller AC updates the corresponding current channel utilization UcurrACi in the following way in order to take into account the newly accepted flow:
UcurrACi=UnewACi
In the ADDTS response message sent to the mobile terminal STA2, the admission controller AC indicates as medium time parameter TMAci in the TSPEC element the increase in utilization of the channel requested by the new flow UaddACi computed for the flow.
The admission controller AC will try to renegotiate the admission of the new flow with the mobile terminal STA2 if:
UnewACi>UtargetACi
If there is a value of data rate R′r greater than or equal to the required minimum data rate Rmin of the new flow specified by the mobile terminal STA2, this value of data rate R′r can replace the mean data rate Rr in the computation of the increase in utilization of the channel requested by the new flow UaddACi, i.e. in the computation of the medium time parameter TMACi, if the following inequation is true:
U′newACi<UtargetACi
In this formula, U′newACi denotes the new channel utilization that has been derived by means of using the value of data rate R′r instead of the mean data rate Rr in the computation of the increase in utilization of the channel requested by the new flow UaddACi. During the renegotiation process, the current channel utilization UcurrACi is not updated with the parameters of the requested flow, and the resources are not reserved.
The admission controller AC will reject the admission of the new flow for any mean data rate Rr greater than or equal to the minimum data rate Rmin specified by the by the mobile terminal STA2, if:
UnewACi>UtargetACi
Clearly, in case of rejection, the current channel utilization UcurrACi is not updated with the parameters of the requested flow.
Number | Date | Country | Kind |
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05290415.8 | Feb 2005 | EP | regional |