Multiplex communications – Data flow congestion prevention or control
Reexamination Certificate
2000-03-29
2004-07-06
Pezzlo, John (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
C370S431000, C370S437000
Reexamination Certificate
active
06760303
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data packet communications, and in particular, to controlling switching between communication channels of different types in a Wideband Code Division Multiple Access (W-CDMA) cellular communications network.
BACKGROUND OF THE INVENTION
In current and future mobile radio communications systems, a variety of different services either are or will be provided. While mobile radio systems have traditionally provided circuit-switched services, e.g., to support voice calls, packet-switched data services are becoming increasingly utilized. Exemplary packet data services include e-mail, file transfers, and information retrieval using the Internet. Because packet data services often utilize system resources in a manner that varies over the course of a data packet session, the flow of packets is often characterized as “bursty.” Transmitted packet bursts are interspersed with periods where no packets are transmitted so that the “density” of packets is high for short time periods and often very low for long periods.
It is often desired that mobile communications systems be capable of accommodating both circuit-switched and packet-switched services. It is also typically desired that the limited radio bandwidth be efficiently used. Consequently, different types of radio channels may be employed to more efficiently accommodate different types of traffic to be transported across the radio interface (e.g., the radio interface between cell phones/pagers and corresponding base station(s)).
The Global System for Mobile communications (GSM) is one example of a mobile communications system that offers circuit-switched services via a Mobile Switching Center (MSC) node and packet-switched services via a General Packet Radio Service (GPRS) node. For circuit-switched guaranteed service, dedicated traffic channels are typically employed. A radio channel is dedicated to a particular mobile user and delivers frames of information as received without substantial delay, and typically provides high data throughput. For packet-switched, best effort service, common channels may be employed where plural mobile users share a common channel at the same time. Typically, a common channel delivers packets of information at a relatively low data throughput as compared to a dedicated channel. Thus, when the Quality of Service (QoS) parameter(s) requested is/are relatively high (e.g., for speech or synchronized communication, soft handover, etc.), a dedicated circuit-switched channel may be well suited to handle this kind of traffic. When the quality of service requested is relatively low (e.g., for an e-mail message, or if the user only has a small amount of data to transmit), a common, packet-switched channel may be well suited to handle this kind of traffic. Unfortunately, there is no “switching” between different types of channels in GSM/GPRS. All dedicated traffic is GSM circuit-switched, and all common traffic is GPRS packet-switched.
The selection of the appropriate channel type and channel type switching are desirable features to be included in third generation mobile systems that employ Wideband Code Division Multiple Access (W-CDMA). W-CDMA systems may support a variety of circuit-switched and packet-switched services over a wide range of bit rates, e.g., kilobits per second to megabits per second. Two radio resources in wideband CDMA used to support such services are channelization codes and transmission power. Channelization codes are used to reduce interference and to separate information between different users. The more channel capacity required, the more channelization codes to be allocated. As for transmission power, dedicated channels employ closed loop transmit power control which provides more accurate power assignments resulting in less interference and lower bit error rate. Common channels typically employ open loop power control which is less accurate and not as well suited for transmitting large amounts of data.
Because of the bursty nature of packet data transmissions, congestion-sensitive transmission protocols, QoS parameters, and other dynamic factors of packet data transmissions, the channel-type best suited to efficiently support a user connection often changes during the life of the user connection. At one point, it might be better for the user connection to be supported by a dedicated channel, while at another point it might be better for the user connection to be supported by a common channel. A problem addressed by the present invention is determining if and when to make a channel-type switch during the course of a particular user connection.
One way of determining when to switch a user connection from a dedicated channel to a common channel is to monitor the amount of data currently being stored in a transmission buffer associated with that user connection. When the amount of data stored in the buffer is less than a certain threshold, that smaller amount of data may not justify the use of a dedicated channel. Thus, the connection may be switched to a common channel. On the other hand, the decrease in the amount of data to be transmitted for that user may only be temporary, given the dynamic aspects of data transmission, i.e., the amount of data in the buffer may quickly accumulate because of the load on the common channel or increased capacity needs for the connection. As a result, the connection may need to be switched right back to a dedicated channel.
Consider the situation where a user connection is currently assigned a dedicated radio channel having a higher data transmission rate/capacity than the current incoming rate of the user data to be transmitted over that channel. This situation might arise if there is congestion at some part of the Internet, e.g., Internet congestion causes TCP to dramatically reduce its transmission rate as described above. A slower incoming rate may also be the result of a “weak link” in the connection external to the radio network, e.g., a low speed modem. In such situations, the radio transmit buffer is emptied faster than the data to be transmitted arrives. As a result of the slow incoming data rate, which may only be temporary, the user connection may be switched from the dedicated channel to a common channel, even though soon thereafter the user will have a large amount of data to transmit. Shortly after the user connection is switched to the common channel, the buffer fills up rapidly due to lower throughput on the common channel, and the user connection is switched back to a dedicated channel. These conditions may ultimately result in rapid, prolonged or cyclical switching back and forth between a common channel and a dedicated channel as long as such conditions persist. Such back-and-forth effects are undesirable because each channel type switch consumes power of the battery-operated terminal, loses packets during the switch, and requires additional control signaling overhead. Such back-and-forth switching is especially undesirable in environments where cell load (i.e., the amount of traffic in a particular cell) is low and channel resources are not in high demand.
FIGS. 1-2
illustrate a scenario where, for a given user, undesirable switching back-and-forth between dedicated and common channels is realized.
FIG. 1
is a graph simulating a constant 32 kbit/sec incoming data stream to the transmission buffer where the user connection is assigned a dedicated channel with a capacity of 64 kbit/sec. The common channel capacity was simulated at 16 kbit/sec but is illustrated as 0 kbit/sec in FIG.
1
. The buffer's channel switch threshold which triggers a switch from dedicated-to-common channel and from common-to-dedicated channel is set at 1,000 bytes (i.e., when it is determined that less than 1,000 bytes are being stored in the buffer, this threshold triggers initiation of a timer whose expiration results in a switch from the dedicated channel to a common channel). An expiration timer may be set, e.g., to one second.
FIG. 1
shows the allocated achieved channel capacity (in kbit/sec)
Pezzlo John
Telefonaktiebolaget LM Ericsson (publ)
Tsejaye Saba
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