Changqing An

Research papers: A study of traffic from the perspective of a large pure IPv6 ISP

Our understanding of IPv6 traffic cannot keep up with the growth of IPv6 traffic. Unraveling the characteristics of traffic is essential for network scale expansion, network technology selection, network management and security enhancement. In this paper, we conduct a comprehensive study of IPv6 traffic based on the packet-level traces of a nation-wide pure IPv6 network - CERNET2, and track user behaviors in 6TUNET, one of the largest campus network in CERNET2, by binding IP address with user name. We first analyze the usage and development of IPv6 network, especially user behaviors and new technologies, e.g. the efficiency of fine-grained source address validation technology which is widely deployed in CERNET2. Then we investigate the distribution of the aggregate traffic and the results reveal that traffic distribution is highly skewed among protocols, ports, applications and hosts. We pay particular attention to dominating protocols, ports, applications and hosts, as well as special protocols of IPv6 network, e.g. the usage of extension headers, which supplement the simplified basic header of IPv6. At last, we model the skewness in traffic distribution and present the dynamics of the traffic from the aspects of traffic prediction and inference. Based on the analysis, we obtain a comprehensive knowledge of IPv6 traffic which, we believe, can provide an experimental basis for IPv6 network operators and researchers.

A study on key strategies in P2P file sharing systems and ISPs’ P2P traffic management

The flourish of P2P systems draws a lot of attention of networking researchers. Some research efforts focus on P2P systems, trying to understand the mechanism of various implementations and the behavior pattern of P2P users, and then improve the systems’ performance. Others look at the issue from the angle of ISPs, trying to help ISPs solve various issues brought by P2P applications. In this article, we conduct a review study on recent research efforts in these two areas. The first part of this article focuses on several key strategies that have significant influence on the performance of P2P systems. In the second part, we review some important techniques for ISPs to manage P2P traffic, i.e., blocking, caching and localization, and compare their advantages and disadvantages.

BPR: a bit-level packet recovery in wireless sensor networks

In Wireless Sensor Networks (WSNs), the Bit-Error-Rate (BER) is so high that the receiver requests retransmission frequently. Packet recovery is an important technology to improve transmission performance. In this paper, we propose BPR, a Bit-level Packet Recovery scheme in WSNs. In BPR, if a packet is corrupted for two times, instead of request the whole packet, the receiver compares these two corrupted copies of the packets and determines which bit(s) should be retransmitted. BPR sits between MAC sub-layer and Logical Link Control (LLC) sub-layer and can be compatible with most of current packet recovery schemes and is very easy to implement. The analysis shows that BPR can yield a gain of 364% compared with Seda[1] and even more with 802.11 in high BER environments.

Transmission power selection for ad hoc networks

In wireless ad hoc networks, as an important technology, power control is widely used to increase energy efficiency and improve network throughput. Power control is composed of two components: one component handles the problems caused by asymmetric channel; the other component is responsible for selecting transmission power. In this paper, we focus on transmission power selection for ad hoc networks using 802.11 DCF MAC protocol. In this paper, we model the network with power control in joint with PHY layer and MAC layer. Then we prove that in considering the noise, interference from other nodes and packet length, it is NP-hard to obtain the optimal transmission power for every node even if it knows the complete knowledge of the network. After that, we propose two heuristic transmission power selection algorithms, one for energy-oriented power control and the other for throughput-oriented power control, which are time efficiency and able to improve the network performance largely. Finally, we evaluate our algorithms under different topologies and in different packet size. The results show that our algorithms can improve the network performance largely when compared with 802.11 and traditional power control algorithms.

Finding hierarchical heavy hitters in network measurement system

Focused on identifying hierarchical heavy hitters (HHH) in multiple dimensions from network management perspective, this paper presents a framework of finding HHHs in network measurement systems and proposes a heuristic algorithm on finding static and dynamic HHH in two dimensions. Our algorithm dramatically reduces the space and time complexity comparing with other previous algorithms. We implement and test it in a typical local network and the experimental results verify the effectiveness and efficiency of the algorithm.

Unravel the characteristics and development of current IPv6 network

In this paper, many aspects related to characteristics and development of IPv6 network are investigated. Additionally, in order to gain a deep view of IPv6 network, we correlate our system with a user authentication system, so we explore some meaningful user behaviors. According to the analysis, we obtain a comprehensive knowledge of current operating situation of IPv6 network which, we believe, can provide an experimental basis for IPv6 network operators and researchers.

MIB design and application for source address validation improvement protocol

In this paper, we present SAVI-MIB, a management information base (MIB) designed to support configuration and monitoring of SAVI protocol which can provide fine granularity source address validation. Objects are defined to meet the detailed management requirement of local networks and accommodate different scenarios. SAVI-MIB is implemented in switches and deployed in some campus networks. Objects of SAVI-MIB are retrieved and used to help find configuration errors in SAVI deployment and profile behavior of end hosts. SAVI-MIB can also be used in parameter optimization, auto configuration, anomaly detection, etc.

Towards Next Generation Internet Management: CNGI-CERNET2 Experiences

Manageability is an important feature of next generation Internet; management and monitoring of IPv6-based networks are proving a big challenge. While leveraging current IPv4-based SNMP management scheme to IPv6 networks’ management need is necessary, it is more urgent to coin a new network management architecture to accommodate the scalability and extensibility requirements of next generation Internet management. The paper proposes a novel network management architecture, IMN (Internet Management Network), which creates an overlay network of management nodes. While each management node can perform management tasks autonomously and independently, it can finish more sophisticated management tasks by collaboratively invoking management operations or sharing information provided by other management nodes. P2P-based communication services are introduced in IMN to enable such collaboration. The paper presents a prototyping implementation based on the Web service related technology, as well as some of the key technologies, especially solutions to those issues arising from the management practice of CERNET2. Experiences of deployment of CERNET2 operation and lessons learned from the management practice are discussed.

Analysis on MAC layer retransmission scheme in wireless networks

Due to poor Signal to Noise and Interference Ratio (SNIR) in wireless networks, retransmission schemes are proposed to improve the transmission performance. These retransmission schemes can be classified into three levels-frame level, block level and bit level according to their retransmission granularity. Analysis on these schemes is significant for applying suitable retransmission scheme, evaluating transmission performance, optimizing retransmission schemes or protocols, etc. In this paper, we modified the implementation of retransmission strategy algorithm used in PPR because our algorithm is more computation efficient and more easy to analysis. And according to the metric FDDR we introduced, we analyze the retransmission performance of three level retransmission schemes. For performance analysis of different levels, we use 802.11, Seda and PPR as typical schemes, respectively. We obtain the optimal frame size and the best FDDR of theses schemes and discuss their changes in different Bit Error Rate (BER) scenarios.

Characteristics analysis at prefix granularity

As IPv6 has much larger address space than IPv4, investigating the characteristics of IPv6 prefixes is of great benefit to understand and manage IPv6 networks. In this paper, (1) we conduct a case study on prefix-level characteristics in IPv6 world. We find that the number of assigned prefixes and the coverage areas are increasing and expanding. Traffic and packet distribution across prefixes are highly skewed. The sizes of active prefixes are relatively stable over time. These results provide experimental basis for routing cache design in IPv6 world. If we update the routing cache once an hour, we only need to reserve 5184 bytes memory for the worst-case burst changes. (2) In addition, we find that 61% destination prefixes have more than two paths to reach, which shows that multihoming path diversity of the studied IPv6 network is obvious. Therefore, we propose an experimental framework with the ability of measuring the performance of each destination prefix, tuning the path for each destination prefix with the best performance, and evaluating the effect during and after the performance tuning. IPv6 has been experiencing fast development as the next generation network. Hence understanding prefix-level characteristics and enhancing performance management are essential for IPv6 networks.