Ruixi Yuan

Data link control protocols for wireless ATM access channels

Describes data link control procedures for wireless ATM access channels based on a dynamic TDMA/TDD frame-work. The system provides integrated ATM services including available bit-rate (ABR) data and constant/variable bit-rate (CBR/VBR) voice or video through the addition of wireless-specific medium access control (MAC) and data link control (DLC) protocol layers between the physical and ATM network layers. The purpose of the DLC protocol layer is to insulate the ATM network layer from wireless channel impairments by selective retransmission of erroneous or lost cells before they are released to the ATM layer. The DLC methods described exploit the on-demand ABR burst transmission capability of the dynamic TDMA channel to retransmit unacknowledged cells in available slots not allocated to service data. Specific error recovery procedures are outlined for both (asynchronous) ABR and (isochronous) CBR services. For ABR, the DLC operation follows a group ACK/NACK based selective reject (SREJ) procedure on a burst-burst basis, without time limits for completion. For CBR, the retransmission procedure is constrained to complete within a specified time interval, so that isochronous delivery of cells to the ATM layer can be maintained. The proposed protocols have been validated using a software emulator which incorporates a choice of radio channel models, dynamic TDMA/TDD MAC, and ABR or CBR DLC. Numerical results show that the data link control protocols under consideration can significantly improve wireless ATM service quality over impaired radio channels for both packer data ABR and stream type CBR virtual circuits.

An SVM-based machine learning method for accurate internet traffic classification

Accurate and timely traffic classification is critical in network security monitoring and traffic engineering. Traditional methods based on port numbers and protocols have proven to be ineffective in terms of dynamic port allocation and packet encapsulation. The signature matching methods, on the other hand, require a known signature set and processing of packet payload, can only handle the signatures of a limited number of IP packets in real-time. A machine learning method based on SVM (supporting vector machine) is proposed in this paper for accurate Internet traffic classification. The method classifies the Internet traffic into broad application categories according to the network flow parameters obtained from the packet headers. An optimized feature set is obtained via multiple classifier selection methods. Experimental results using traffic from campus backbone show that an accuracy of 99.42% is achieved with the regular biased training and testing samples. An accuracy of 97.17% is achieved when un-biased training and testing samples are used with the same feature set. Furthermore, as all the feature parameters are computable from the packet headers, the proposed method is also applicable to encrypted network traffic.

Accurate Classification of the Internet Traffic Based on the SVM Method

The need to quickly and accurately classify Internet traffic for security and QoS control has been increasing significantly with the growing Internet traffic and applications over the past decade. Pattern recognition by learning the features in the training samples to classify the unknown flows is one of the main methods. However, many methods developed in the previous works are too complicated to be applied in real-time, and the prior probabilities based on the training samples are severely biased. This paper uses the SVM (support vector machine) method to train 7 classes of applications of different characteristics, captured from a campus network backbone. A discriminator selection algorithm is developed to obtain the best combination of the features for classification. Our optimized method yields approximately 96.9% accuracy for un-biased training and testing samples. For regular biased samples, the accuracy is about 99.4%. Furthermore, all the feature parameters are computable in real time from captured packet headers, suggesting real time network traffic classification with high accuracy is achievable.

Semi-random backoff: towards resource reservation for channel access in wireless LANs

This paper proposes a semi-random backoff (SRB) method that enables resource reservation in contention-based wireless LANs. The proposed SRB is fundamentally different from traditional random backoff methods because it provides an easy migration path from random backoffs to deterministic slot assignments. The central idea of the SRB is for the wireless station to set its backoff counter to a deterministic value upon a successful packet transmission. This deterministic value will allow the station to reuse the time-slot in consecutive backoff cycles. When multiple stations with successful packet transmissions reuse their respective time-slots, the collision probability is reduced, and the channel achieves the equivalence of resource reservation. In case of a failed packet transmission, a station will revert to the standard random backoff method and probe for a new available time-slot. The proposed SRB method can be readily applied to both 802.11 DCF and 802.11e EDCA networks with minimum modification to the existing DCF/EDCA implementations. Theoretical analysis and simulation results validate the superior performance of the SRB for small-scale and heavily loaded wireless LANs. When combined with an adaptive mechanism and a persistent backoff process, SRB can also be effective for large-scale and lightly loaded wireless networks.

A Novel Scheduled Power Saving Mechanism for 802.11 Wireless LANs

Power conservation is a general concern for mobile computing and communication. In this paper, we investigate the performance of the current 802.11 power saving mechanism (unscheduled PSM) and identify that background network traffic can have a significant impact on the power consumption of mobile stations. To improve power efficiency, a novel scheduled PSM protocol based on time slicing is proposed in this paper. The protocol adopts the mechanism of time division, schedules the access point to deliver pending data at designated time slices, and adaptively adjusts the power state of the mobile stations. The proposed scheme is near theoretical optimal for power saving. It greatly reduces the effect of background traffic, minimizes the station idle time, and maximizes its energy utilization. Comprehensive analysis and simulations are conducted to evaluate the new protocol. The results show that the new protocol provides significant energy saving over the unscheduled PSM, particularly in circumstances where multiple traffic streams coexist in a network. Moreover, it achieves the saving at the cost of only a slight degradation of the one-way-delay performance.

The IEEE 802.11 Power Saving Mechanism: An Experimental Study

This paper presents an experimental study of the IEEE 802.11 power saving mechanism on PDA in a wireless local area network (WLAN). The power consumptions of the PDA in both continuous active mode (CAM) and power saving mode (PSM) are measured under various traffic scenarios, and the impact of both internal and external factors on power performance, such as beacon/DTIM period and background multicast traffic, are examined. Our findings are: 1) The impact of beacon/DTIM period is only significant when their values are small and the imposed traffic rate is high. 2) The presence of background traffic can significantly reduce the effectiveness of the PSM. Analysis of these findings may provide important guidance to the design of future power saving mechanisms.

Mobility Support in a Wireless ATM Network

This paper presents an architecture for mobility support in a wireless ATM network scenario. We first introduce a TDMA based wireless ATM system where a datalink control protocol is used to convert the wireless channel into an ATM like multi-service transport. Afterwards, a mobility support architecture is proposed to facilitate terminal mobility in an ATM network environment. We separate the end-to-end VC into static segments and dynamic segments. In the process of mobile migration, the dynamic segment is reconfigured by the mobility support network switches and base stations. We also present a method for smooth handoff and cell resequencing by transferring the wireless datalink state information between base stations. For signaling support in a mobile ATM network, enhancements of current Q.2931 protocol are proposed.

Scheduled PSM for Minimizing Energy in Wireless LANs

Power conservation is a general concern for mobile computing and communication. In this paper, we investigate the performance of the current 802.11 power saving mechanism (unscheduled PSM) and demonstrate that background network traffic can have a significant impact on the power consumption of mobile stations. To improve power efficiency, a scheduled PSM protocol based on time slicing is proposed in this paper. The protocol adopts the mechanism of time division, schedules the access point to deliver pending data at designated time slices, and adaptively adjusts the power state of the mobile stations. The proposed scheme is near theoretical optimal for power saving in the sense that it greatly reduces the effect of background traffic, minimizes the station idle time, and maximizes its energy utilization. Comprehensive analysis and simulations are conducted to evaluate the new protocol. Our results show that it provides significant energy saving over the unscheduled PSM, particularly in circumstances where multiple traffic streams coexist in a network. Moreover, it achieves the saving at the cost of only a slight degradation of the one-way delay performance.

Semi-Random Backoff: Towards resource reservation for channel access in wireless LANs

In this paper, we propose a Semi-Random Backoff (SRB) mechanism to combat network collisions for 802.11 DCF/EDCA in wireless LANs. SRB is fundamentally different from traditional random backoff methods because it provides a form of resource reservation at no extra cost. The key idea of SRB is to set the backoff counter to a deterministic value upon a successful transmission. This allows a station to reuse a time slot in consecutive backoff cycles without colliding with other stations, thus achieving resource reservations. In cases of failed transmissions due to network collisions or channel errors, SRB automatically reverts to the standard random backoff method. SRB can be readily applied to both 802.11 DCF and 802.11e EDCA networks with minimum modification to the existing DCF/EDCA implementations. Theoretical analysis and simulations are conducted to evaluate this new method and our results validate its good performance in small to middle-sized 802.11 wireless LANs.

A reservation based backoff method for video streaming in 802.11 home networks

QoS provisioning for video streaming over 802.11 home networks is challenging due to the tight bandwidth and delay constraints. Currently, both 802.11e HCCA and EDCA have their disadvantages when delivering video over 802.11 networks. EDCA exhibits degraded QoS performance for increased number of stations, while HCCA has high complexity, and also suffers from the impact of inter-cell interference. In this paper, we propose a new backoff mechanism which is fundamentally different from traditional random backoff methods in 802.11. The mechanism achieves resource reservation by reusing one or multiple time slots for transmission in consecutive backoff cycles. The basic idea is borrowed from R-ALOHA, but several modifications are made to allow it to work in the context of CSMA network. An additive increase multiplicative decrease based algorithm is proposed to control resource allocation for video streaming in the 802.11 network. Theoretical analysis and numerical simulations are conducted to validate the effectiveness of the method and the algorithm.