Se Gi Hong

7DS - Node Cooperation and Information Exchange in Mostly Disconnected Networks

When the node density in a network decreases below the level necessary to sustain ad-hoc and mesh networks, communication can succeed only by leveraging node mobility and transitioning to message-based communications. In the 7DS (Seven Degrees of Separation) project, we have been investigating how to emulate two core Internet services, namely Web access for information retrieval and email for delivering messages from mobile nodes to the Internet. We have implemented and evaluated a 7DS prototype system that leverages search, feedback and propagation limits to build a scalable system that can deliver data to and from mobile nodes. 7DS makes data exchange in disconnected networks possible by providing an application-level set of protocol services that will enable exchange of information between peer devices. It enables dynamic information exchange by using a proxy server, a multicast query system, a search engine, and a transport entity. With these entities, 7DS can perform efficient and transparent data exchange among peers in the absence of a network connection. Data exchange with the larger Internet occurs when peers enter or exit the peer network.

Accelerating Service Discovery in Ad-Hoc Zero Configuration Networking

Zero Configuration Networking (Zeroconf) assigns IP addresses and host names, and discovers service without a central server. Zeroconf can be used in wireless mobile ad-hoc networks which are based on IEEE 802.11 and IP. However, Zeroconf has problems in mobile ad-hoc networks as it cannot detect changes in the network topology. In highly mobile networks, Zeroconf causes network overhead while discovering new services. In this paper, we propose an algorithm to accelerate service discovery for mobile ad-hoc networks. Our algorithm involves the monitoring of network interface changes that occur when a device with IEEE 802.11 enabled joins a new network area. This algorithm allows users to discover network topology changes and new services in real-time while minimizing network overhead.

Measurements of Multicast Service Discovery in a Campus Wireless Network

Applications using multicast service discovery protocols, such as iTunes, have become increasingly popular. However, multicast service discovery protocols generate significant network traffic overhead, especially in a wireless network. We measure and analyze the traffic of one of the most widely deployed multicast service discovery protocols, DNS-SD/mDNS, in a campus wireless network where a single multicast domain serves a large number of users. We define three service discovery models which correspond to different service discovery behaviors. We compare these three models in terms of packet overhead and service discovery delay for different network sizes and service lifetime assumptions. The measurement shows that mDNS traffic consumes about 13 percent of the total bandwidth of the network.

ICOW: internet access in public transit systems

When public transportation stations have access points to provide Internet access to passengers, public transportation becomes a more attractive travel and commute option. However, the Internet connectivity is intermittent because passengers can access the Internet only when a transit vehicle is within the networking coverage of an access point at a stop. We propose ICOW, a system that provides a low-cost way for public transit operators to enhance quality of experience for passengers who access the Internet. Each public transit vehicle is equipped with a smart cache that serves popular content to passengers. The cache updates its content based on passenger requests when it is within range of Internet access points placed at stops, stations, or depots. We have developed a system architecture and built a prototype of the ICOW system. Our evaluation shows that ICOW is significantly more efficient than having passengers contact Internet access points individually and ensures continuous availability of content throughout the journey.

PBS: Signaling architecture for network traffic authorization

We propose a signaling architecture for network traffic authorization, called Permission-Based Sending (PBS), aiming to prevent DoS attacks and other forms of unauthorized traffic. Toward this goal, PBS takes a hybrid approach: a proactive approach of explicit permissions and a reactive approach of monitoring and countering attacks. PBS uses a concept similar to existing capability-based systems in the manner in which the sender should get authorization (permission) from a receiver for flows. However, PBS introduces new and practical approaches to overcome the deficiencies (the difficulty of obtaining permission and incompatibility with current network architecture) of those systems. On-path signaling enables easy installation and management of the permission state. Working on current network protocols supports compatibility and allows PBS to be deployed in existing networks. In addition, a monitoring mechanism provides a second line of defense against attacks. Our analysis and performance evaluation show that PBS is an effective and scalable solution to prevent several kinds of attacks, and improves the resilience of the system against network failure by using soft-state mechanisms.

Signaling Architecture for Network Traffic Authorization

Capability-based systems that use explicit authorization (permission) for flows have been proposed in order to prevent Denial-of-Service (DoS) attacks. Even though the performance analyses of these systems show that they are efficient in preventing the attacks, they suffer from the difficulty of obtaining permission, incompatibility with current network architecture, and attacks that circumvent the permission rules. We propose a signaling architecture for network traffic authorization, called Permission-Based-Sending (PBS), aiming to prevent DoS attacks. PBS uses the concept similar to existing capability-based systems in the manner that the sender should get authorization (permission) from a receiver for flows. However, PBS introduces new and practical approaches to overcome the deficiencies of those systems. On-path signaling enables easy installation and management of the permission state. Working on current network protocols supports compatibility and allows PBS to be deployed in existing networks. In addition, a monitoring mechanism provides a second line of defense against attacks. Our analysis and performance evaluation show that PBS is an effective and scalable solution to prevent several kinds of attacks, and improves the resilience of the system against network failure by using soft-state mechanisms.

ASAP: Fast, Controllable, and Deployable Multiple Networking System for Satellite Networks

Satellite networks, which provide high bandwidth but have high latency, suffer from performance degradation for secure web access (HTTPS). The use of multiple networks, which combines a satellite network with a low latency network, becomes an attractive method for a satellite Internet Service Provider (ISP) to provide better network services. We propose a novel and practical multiple networking system, called Accelerating Network Services by Adding a Short Path (ASAP). ASAP accelerates secure web page loading with a little help from a low latency network while exploiting the high bandwidth of a satellite network. By using a middlebox approach with a multipath tunneling mechanism, ASAP is deployable to the current Internet architecture without modifying core networks and protocols. Phase-based classification mechanism of ASAP enhances network services while minimizing and controlling the data usage of the auxiliary, low latency network to reduce the operation cost for a satellite ISP, which leases the auxiliary network. Our performance evaluation shows that ASAP is an effective solution to reduce secure web page load time while reducing and controlling the data usage of networks. Our real-world testbed shows that ASAP works with the current Internet infrastructure.

Mitigating network service disruptions in high-bandwidth, intermittently connected, and peer-to-peer networks

Users demand high-bandwidth, ubiquitous and low-cost network services. This demand has pushed ISPs and application providers to offer more bandwidth, allow users to access the Internet almost everywhere, and provide cheap or free network services using peer-to-peer networks. These three trends underlie the growing success of todays Internet. However, (1) high-bandwidth can empower more effective denial-of-service attacks; (2) Internet access is widespread, but still not ubiquitous; and (3) peer-to-peer network services need to solve the service discovery problem. This thesis addresses these three challenges. First, we tackle denial-of-service attacks. The high bandwidth available in many parts of the Internet allows denial-of-service attacks to be effective, and the large scale of the Internet makes detecting and preventing these attacks difficult. Anonymity and openness of the Internet worsens this problem because anyone can send anything to anybody. To prevent these denial-of-service attacks, we propose Permission-Based-Sending (PBS), a signaling architecture for network traffic authorization. PBS uses the explicit permission to give legitimate users the authority to send packets. Signaling is used to configure this permission in the data path. This signaling approach enables easy installation for granting authorization to flows, and allows PBS to be deployed in existing networks. In addition, a monitoring mechanism provides a second line of defense against attacks. Next, we strive to make Internet access more ubiquitous. When public transportation stations have access points to provide Internet access to passengers, public transportation becomes a more attractive travel and commute option. However, the Internet connectivity is intermittent because passengers can access the Internet only when a bus or train is within the networking coverage of an AP at a stop. To efficiently handle this intermittent network for the public transit system, we develop Internet Cache on Wheels (ICOW), a system that provides a low-cost way for bus and train operators to offer access to Internet content. Each bus and train car is equipped with a smart cache that serves popular content to passengers. The cache updates its content based on passenger requests when it is within range of Internet access points placed at bus stops, train stations or depots. This aggregated Internet access is significantly more efficient than having passengers contact Internet access points individually and ensures continuous availability of content throughout the journey. Finally, we consider peer-to-peer services. Typical service discovery mechanisms in peer-to-peer networks cause significant overhead, consuming energy and bandwidth: (1) in highly mobile networks, service discovery consumes the energy of mobile devices to discover services that newly joined members provide; and (2) peer-to-peer network systems consumes bandwidth during service discovery. To resolve and analyze these service discovery problems, (1) we design an efficient service discovery mechanism that reduces energy consumption of mobile devices; and (2) we evaluate the bandwidth consumption caused by service discovery in real-world peer-to-peer networks.