Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
2000-09-19
2004-04-27
Maung, Nay (Department: 2684)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S338000, C370S352000, C370S395400, C370S395210, C370S395420, C370S395520, C370S401000, C370S469000
Reexamination Certificate
active
06728208
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to controlling the Quality of Service (QoS) in mobile communications systems having a packet data transmission capability.
BACKGROUND OF THE INVENTION
Mobile communications system refers generally to any telecommunications system which enable a wireless communication when users are moving within the service area of the system. A typical mobile communications system is a Public Land Mobile Network (PLMN).
Often the mobile communications network is an access network providing a user with a wireless access to external networks, hosts, or services offered by specific service providers.
The general packet radio service GPRS is a new service in the GSM system (Global system for mobile communications), and is one of the objects of the standardization work of the GSM phase 2+ at the ETSI (European Telecommunications Standards Institute). The GPRS operational environment comprises one or more subnetwork service areas, which are interconnected by a GPRS backbone network. A subnetwork comprises a number of packet data service nodes SN, which in this application will be referred to as serving GPRS support nodes SGSN, each of which is connected to the GSM mobile communication network (typically to base station systems) in such a way that it can provide a packet service for mobile data terminals via several base stations, i.e. cells. The intermediate mobile communication network provides packet-switched data transmission between a support node and mobile data terminals. Different subnetworks are in turn connected to an external data network, e.g. to a public switched data network PSPDN, via GPRS gateway support nodes GGSN. The GPRS service thus allows to provide packet data transmission between mobile data terminals and external data networks when the GSM network functions as an access network.
In order to access the GPRS services, a MS shall first make its presence known to the network by performing a GPRS attach. This operation establishes a logical link between the MS and the SGSN, and makes the MS available for SMS over GPRS, paging via SGSN, and notification of incoming GPRS data. More particularly, when the MS attaches to the GPRS network, i.e. in a GPRS attach procedure, the SGSN creates a mobility management context (MM context). Also the authentication of the user is carried out by the SGSN in the GPRS attach procedure. In order to send and receive GPRS data, the MS shall activate the packet data address that it wants to use, by requesting a PDP activation procedure contexts (PDP, Packet Data Protocol). This operation makes the MS known in the corresponding GGSN, and interworking with external data networks can commence. More, particularly a PDP context is created in the MS and the GGSN and the SGSN. The PDP context defines different data transmission parameters, such as the PDP type (e.g. X.25 or IP), PDP address (e.g. X.121 address), quality of service QoS and NSAPI (Network Service Access Point Identifier). The MS activates the PDP context with a specific message, Activate PDP Context Request, in which it gives information on the TLLI, PDP type, PDP address, required QoS and NSAPI, and optionally the access point name APN.
The quality of service QoS defines how the packet data units (PDUs) are handled during the transmission through the GPRS network. For example, the quality of service levels (QoS) defined for the PDP addresses control the order of transmission, buffering (the PDU queues) and discarding of the PDUs in the SGSN and the GGSN, especially in the congestion situation. Therefore, different quality of service levels will present different end-to-end delays, bit rates and numbers of lost PDUs, for example, for the end users.
For each PDP Address a different quality of service (QoS) may be requested. For example, some PDP addresses may be associated with E-mail that can tolerate lengthy response times. Other applications cannot tolerate delay and demand a very high level of throughput, interactive applications being one example. These different requirements are reflected in the QoS. If a QoS requirement is beyond the capabilities of a PLMN, the PLMN negotiates the QoS as close as possible to the requested QoS. The MS either accepts the negotiated QoS, or deactivates the PDP context.
Current GPRS QoS profile contains five parameters: service precedence, delay class, reliability, and mean and peak bit rates. Service precedence defines some kind of priority for the packets belonging to a certain PDP context. Delay class defines mean and maximum delays for the transfer of each data packet belonging to that context. Reliability in turn specifies whether acknowledged or unacknowledged services will be used at LLC and RLC (Radio Link Control) layers. In addition, it specifies whether protected mode should be used in case of unacknowledged service, and whether the GPRS backbone should use TCP or UDP to transfer data packets belonging to the PDP context. Furthermore, these varying QoS parameters are mapped to four QoS levels available at LLC layer.
There are various problems, drawbacks, undefined issues and open questions involved with the quality of service in the GPRS.
Firstly, the above mentioned mapping of GPRS QoS parameters to four QoS levels available at LLC layer is not well defined either. In addition, relationships between delay class and service precedence are not defined in the standard.
Secondly, the scheduling and policing based on current QoS Profile is rather difficult to implement (and unspecified in the standard). For example, how the network elements can guarantee the delay requirements? It is too expensive to employ timers to guarantee the required delay requirements. Moreover, the delay requirements are end-to-end requirements: How this end-to-end delay information can be used by GPRS network elements is not obvious either. In practice they cannot because information about the delay occurred in the previous network element is not conveyed to the next element (i.e. GSN). Also policing the negotiated mean and peak bit rates is rather difficult and would consume a lot of time and processing power. In addition, if we wanted to make sure that a certain bit rate could always be provided, we would have to reserve fixed capacity for that. This would however lead to inefficient link capacity usage.
Interpretation of mean bit rate is questionable. GPRS network cannot guarantee a certain mean bit for a user if he or she is not transmitting at fixed speed, ie. at the mean bit rate. Otherwise, the user could have an one hour connection in which he or she has not transmitted any data for the first 55 minutes. The user cannot assume that he or she could transmit data at much higher speed during the last 5 minutes in order to meet the mean bit rate requirement. Instead, the mean bit rate can only be guaranteed for the rest of the connection, i.e. for the last 5 minutes.
The GPRS network is not capable of meeting various QoS requirements of Internet applications. The IP (Internet Protocol) traffic goes between the mobile host and the fixed host located in an external network, e.g. in the Internet. Different Internet applications require different kind of service, i.e. QoS, from the underlying network. Thus, when the mobile host is using GPRS to access the Internet, GPRS network should be capable of meeting various QoS requirements of Internet applications. There are actually at least two IP traffic types that should be taken into account: real-time and non-real-time traffic. One example of real-time traffic is voice transmission. Email and file transfer in turn are examples of non-real-time applications.
Currently, QoS parameters can only be associated with a certain PDP context (i.e. a certain IP address). Setting different QoS values for different applications that use the same IP address is not therefore possible. This is a very severe drawback of the current scheme. The current GPRS specifications also define only very static QoS behaviour: QoS negotiation can only be initiated by the MS when activating the PDP cont
Maung Nay
Nokia Networks Oy
Pillsbury & Winthrop LLP
Sharma Sujatha
LandOfFree
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