Kyoung-Min Yoo

Design of AWG-based WDM-PON architecture with multicast capability

Recently, the triple play service (TPS) has been considered to be a promising business model or application. Thus, the capability for multicast transmission has become a very important requirement for access networks. However, unlike existing passive optical networks (PONs), the arrayed-waveguide grating (AWG) based wavelength-division multiplexing (WDM)-PON does not have multicast capability because it is a P2P network for the downstream direction, from optical line terminal (OLT) to optical network units (ONUs). In this paper, AWG- based WDM-PON architecture with multicast capability is proposed. It provides high scalability and single copy broadcast (SCB) capability by employing multi-stage AWGs at a remote node (RN) and a multi-wavelength converter (MWC) at OLT. The performance of the proposed architecture is evaluated in terms of cost, scalability, link capacity and bandwidth per user, in both upstream and downstream directions, by comparison with other multicasting architectures.

Design and performance comparison of multiple-token based MAC protocols for optical burst switched ring networks

Optical burst switching (OBS) has been proposed as a new optical switching paradigm for the next generation Internet due to its flexibility and feasibility compared to OCS and OPS. Moreover, serving as a backbone that interconnects a number of access networks, OBS ring topologies have been a good choice for solving the current metro gap problem between core network and access network owning to its simplicity and scalability. In this paper, we provide an insight into the OBS ring network that consists of nodes using TT–TR (Tunable Transmitter–Tunable Receiver). The node architectures with TT–TR may make efficient use of network resources even though traffic pattern, such as IP traffic with self-similarity dynamically change, and can support good expandability. However, all nodes share the limited network resources. This may result in contention such as wavelength contention and transceiver contention leading to burst loss. In order to use the shared network resources fairly and efficiently as well as reducing the resource contention, we focus on the design of medium access control (MAC) protocols based on multiple tokens. Each token is allocated to one wavelength to denote the accessibility of that wavelength, i.e., once the token is captured, the corresponding wavelength can be used to transmit a burst. As tokens hold the key for using wavelengths to transmit bursts, token management including the token release time is crucial in the proposed MAC protocols. Thus, two kinds of multiple-token based MAC protocols with different token release times are proposed: token release after transmitting burst (TRTB) and token release after transmitting control header (TRTC). Each of them is classified into two schemes called TRTB/TRR and TRTB/RCA and correspondingly TRTC/TRR and TRTC/ RCA. RCA stands for receive collision avoidance. The target is to increase the performance while reducing the processing overhead at each node. The performance of the TRTB and TRTC protocols are evaluated and compared in terms of queuing delay, burst loss rate, and channel utilization by OPNET simulation. The effects of various design parameters are also investigated through simulation in order to evaluate their scalability. In all the proposed schemes, tokens are just used to denote the accessibility of each wavelength. Finally, as an alternative, we also propose a new scheme based on the TRTC protocol called TRTC/CAT (collision avoidance by tokens) to avoid contention by using tokens.

Design and performance evaluation of token-based MAC protocols in WDM burst switched ring networks

Token-based MAC(Medium Access Control) Protocols are proposed for WDM Burst-Switched Ring Network which consists of nodes using TT-TR(Tunable Transmitter-Tunable Receiver). The node architectures with TT-TR may make an efficient use of network resources, even though traffic pattern such as IP traffic with high self-similarity are dynamically changed, and can also support good expandability. However, MAC protocols suitable for TT-TR node architecture must be designed with consideration for various factors in order to use the limited resources of network efficiently. A variety of Token-based MAC protocols are suggested to increase the performance while reducing the processing overhead at each node. The performance of the MAC protocols are evaluated and compared in terms of average packet delay, channel utilization and burst loss rate through OPNET simulation. Finally, we provide insight into the design of MAC protocols by investigating the effect of various parameters.

1+X: A Novel Protection Scheme for Optical Burst Switched Networks

As a link failure may lead to severe burst loss in optical burst switched networks, survivability has emerged as one of the most important issues in the design of the optical networks. In this paper, we propose the 1+X protection scheme, which is a novel protection scheme that not only reduces the loss of burst caused by a link failure but also improves the efficiency of resources in OBS networks. Through numerical analysis, we confirm that the proposed 1+X protection scheme has better performance than conventional schemes in terms of reservation redundancy, end-to-end delay and resource efficiency.

ST-FL and HTU: Tunnel Allocation and Routing Algorithm in MG-OXC Networks

The advance of WDM technologies has increased the number of available wavelengths of a fiber and requires many ports at intermediate switching nodes. Multi-granularity optical cross-connect (MG-OXC) has been proposed to handle efficiently the growing bandwidth and decrease the number of required ports and multiplexes at the nodes by switching in waveband or fiber. In this paper, we propose an efficient tunnel allocation algorithm based on link-weight and traffic flow for MG-OXC networks: static tunnel-fixed length (ST-FL). In order to use the tunnels efficiently, high tunnel utilization (HTU) routing algorithm is proposed. This algorithm increases tunnel utilization and decreases blocking probability through cost function. The performance is evaluated through simulation.

Cooperative Scenario based Centralized Defense Mechanisms for Low-Rate TCP Attacks

The low-rate TCP attack has been reported recently. That is essentially a periodic short burst which exploits the homogeneity of the minimum retransmission timeout (RTO) of TCP flows. It is difficult to identify this sort of attack in BcN (broadband convergence network) due to no cooperative defense mechanisms among different networks. In this paper, NCP (network control platform) based centralized defense mechanisms are proposed. Firstly, low-rate TCP attack and the previous defense mechanisms are reviewed. It helps us to find and select reasonable features of them for supporting the proposed mechanism. Secondly, we propose a cooperative defending scenario between NCP as centralized controller and MDRs (monitoring and defending routers). Without adopting defense mechanism to all routers in network, it is possible to effectively protect network resource from low-rate TCP. That is because the attack flows can be filtered at both victim-side and attack side MDRs with cooperative scenario. The performance id evaluated by using ns-2 simulator