High QOS with Traffic Control for Effective Bandwidth Management | Solutions and Recommendations

Overloading of a wireless network could occur because of the heavy data traffic. Traffic flow control for effective management of transmission resources, particularly the bandwidth, facilitates high quality of service (QOS). For example, by shaping (that is, spacing) the data traffic which usually comes in bursts unlike the voice traffic, the network bandwidth could be utilized more effectively. On the other hand, overloading of the wireless network even for short durations of time could result in degradation of QOS due to increased bit error rates.

Figure 1 depicts the different feedback controls used in our system for traffic flow adjustment for effective data transmission. Signal power of the mobile device or any other direct indicator of power for the RF link constitutes the inner power control just as in the traditional wireless systems. This feedback is provided every 1 -2 milliseconds. Similarly, outer power comprises a link error rate and/or interference indicator for the wireless link and may account for soft handoff power. This feedback may be provided every 50-100 milliseconds. The inner and outer power control loops conjointly provide feedback based on the signal strength of the RF link. The packet level control is provided every several hundred milliseconds by the queuing system in the WR based on the congestion status of the queues. Finally, our repertoire of traffic control mechanisms included the well known and well studied TCP flow control, which is provided through the acknowledgment messages between the two end points of the TCP flow. Based on the acknowledgment messages received, the source (WR) adjusts its transmission rate. Thus, with this mechanism, traffic flow is controlled by the congestion and/or interference state of the wireless links.


Figure 1: Feedback mechanism for traffic flow control
 
In our WR, there is also a provision for the traditional end-to-end rate control with a queue mechanism to shape up bursty traffic from a source into a smooth traffic flow of radio frames into the sink (mobile). The ACKs from the sink are also similarly queued up, and used as feedback for the source so that it can control its egress traffic flow.

An innovative flow control mechanism in the present work is Gang (or Group) flow control which seeks to shape the TCP flows from various sectors of the wireless network simultaneously, shown as Figure 2 with N acknowledge shapers corresponding to N sectors of the WR. Each shaper accepts the packets from wireless network and stores the packets in the acknowledge queues inside the WR. The acknowledge shaper can transmit acknowledge message over time to change the traffic flow for the sector based on the flow's power indicator of the RF link from wireless network.


Figure 2: Gang flow control for sectors of a wireless
 
Figure 2 illustrates two kinds of shaped acknowledge messages. In the first type shown for flows 1 and 2, the acknowledge messages are arranged in small groups and the groups are dispatched periodically. In the second type depicted for Flow N, on the other hand, the ACKS are evenly distributed overtime and transmitted. The difference of these two arrangements is that they have different transmit time. The first type of ACK shaping will affect the offsetting bursts for the traffic flow whereas the second type will affect the steady flow rate for the traffic flow.

The flows with unused bandwidth or lack of bandwidth will be identified for each TCP group for the interval related to retransmission time out for the TCP flow. The fair share of each TCP flow within the group will be calculated and used in adjusting the speed of acknowledge messages for the flows inside the gang. The fair share of each TCP flow may be used together with the RTT and arrival time for each traffic flow.

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