ASON is new type of optical network which can offer the flexibility for bandwidth allocation and fast provision of the new service. However, until now there still are many non-ASON optical networks. It is a challenging issue to reconstruct them into ASON smoothly. In this paper, we propose a new reconstructing technology. This technology performs the function of the control plane such as link management, path management and interface management by an embedded top-set-box (ETSB). The ETSB is located between EMS and the traditional NE such as DWDM, WDM, SDH, etc. By this technology the hardware module of the existing optical network element (NE) need not modification. Thus, compared with other reconstructing technologies, the cost and the risk of this reconstructing technology are smaller.
Nowadays IEEE 802.11 Wireless Local Area Networks (WLANs) become pervasive driven by huge demands for portable access to the Internet. Meanwhile, Voice over Internet Protocol (VoIP) is one of the fastest growing Internet applications because of its high resource utilization and low cost. This paper focuses on the combination of these two technologies. Aiming to support more voice calls in IEEE 802.11 infrastructure networks, voice capacity in IEEE 802.11 WLAN is studied. Through simulation, it is found that Access Point (AP) is a bottleneck that limits the number of concurrent voice calls. This is because in infrastructure networks, all frames must go through the AP so that the AP has much more traffic, but the AP has no advantage on accessing the medium. In this paper an enhanced DCF protocol is proposed to give AP higher priority to access wireless medium and mitigate AP bottleneck effect. In proposed scheme, AP's priority is adjusted dynamically by changing some Distributed Coordination Function (DCF) parameters according to the length of the AP queue. Simulations in various scenarios well verify the improvement achieved with increased voice capacity and decreased access delay.
Specification and description language (SDL) is an object-oriented formal language defined as a standard by ITU-T. Though SDL is mainly used in describing communication protocols, it is an efficient way to simulate the network performance with SDL tools according to our experience. This paper presents our methodology of SDL-based network performance simulation in such aspects as the simulation platform, the simulation modes and the integrated simulation environment. Note that Telelogic Tau 4.3 SDL suite is used here as the simulation environment though our methodology isn't limited to the software. Finally the SDL-based open shortest path first (OSPF) performance simulation in the wireless private network is illustrated as an example of our methodology, which indicates that SDL is indeed an efficient language in the area of the network performance simulation.
The private network serves as an information exchange platform to support the integrated services via microwave channels and accordingly selects the open shortest path first (OSPF) as the IP routing protocol. But the existing OSPF can't fit the private network very well for its special characteristics. This paper presents our modifications to the standard protocol in such aspects as the single-area scheme, link state advertisement (LSA) types and formats, OSPF packet formats, important state machines, setting of protocol parameters and link flap damping. Finally simulations are performed in various scenarios and the results indicate that our modifications can enhance the OSPF performance in the private network effectively.
A pure silica microstructured optical fiber(MOF) with seven dual cores is designed for chromatic dispersion compensation by a finite difference frequency domain(FDFD) method with a perfect matched layer(PML) boundary condition. The multi-core structure fiber is presented for the first time. The negative chromatic dispersion peak value of the designed microstructured fiber is -4500ps/nm.km and the full width at half maximum (FWHM) is evaluated at 12nm. Furthermore the effective area of the inner core fundamental mode can reach 65mm2 at 1550nm wavelength, which is three times that of a conventional dispersion compensating fiber (DCF).
Nowadays multi-protocol label switching (MPLS) technology has achieved great popularity in the world. Because MPLS adopts the scheme of “route once and switch many”, routing is the key element to ensure packets are transmitted to destinations. Though there are many designs of MPLS routing protocol for public networks, they can hardly fit the private network very well for its special characteristics. This paper presents the design of MPLS routing protocol in the private network using the specification and description language (SDL), which is an object-oriented formal language and mainly used in communications area. In our design the whole autonomous system (AS) is regarded as a single area to reduce the number of protocol packets. The SDL module of MPLS routing protocol consists of four kinds of processes, namely Management, Checking, NeigSession and LSADbase. Simulations of the SDL design are run in many scenarios, the results of which indicate that the SDL module is manageable and the overall performance is satisfying. From our design and simulation experience, we find that the software development cycle can be drastically reduced by the use of SDL, and the code is easy to maintain and reuse.