Sharif Digital Repository

In the internet telephony, loss of IP packets causes instantaneous discontinuities in the received speech. In this paper, we have focused on finding an error resilient method for this problem. Our proposed method creates artificial correlation between speech samples that pre-distorts the speech signal. The receiver uses this correlation to reconstruct the lost speech packets. An appropriate speech enhancement technique is designed for the reduction of the processing error in the recovered speech caused by the speech codecs. The SegSNR results show the superiority of our proposed speech enhancement method over a recently proposed one. © 2007 IEEE  

Mobile Ad-hoc Networks (MANETs) are forming dynamically by joining or leaving the nodes into/from the network without any fix infrastructure. It is also possible that each mobile node act as a host or router. This kind of wireless network is prone to various security threats or attacks due to its unique characteristics like dynamic topology, open medium, lack of central monitoring, etc. So security is a vital scope in MANET to protect communication between mobile nodes. Ad-hoc On-demand Distance Vector (AODV) is one of the on-demand reactive routing protocols in MANET that initially was improved without considering security protection. Significant attempts have been done to secure AODV... 

Over the past few years, rapid advances in wireless broadband networks have been driving the evolution of communication and network technologies towards new mobile services for users. Handover management is still one of the most challenging issues to be solved for seamless mobility in wireless networks. To support mobility on terminal stations mobile WiMAX has been standardized. Moreover to provide seamless communications for such network Fast Mobile IPv6 (FMIPv6) has been proposed by IETF. But for seamless handover, collaboration of layer 2 and layer 3 is required. Thus, there is a requirement for cross-layering design to support proper behavior of the MIPv6 nodes in WiMAX networks. In this... 

In this paper, a new effective and computationally reduced method for congestion control in high speed dynamic computer networks is introduced. The controller is designed using the well-known predictive functional control (PFC) scheme and an ARMarkov model representation that considers the system delay explicitly. Use of the multi-step-ahead predictive ARMarkov model structure within the PFC results in a simple algebraic control law that does not require recursive model output computation in the so-called prediction horizon performed in the other Model Predictive Controllers (MPC). This combination not only reduces the required computational load, but the accumulative error due to the model... 

This paper presents a performability estimation approach which measures the ability of a network to deliver its services in the presence of component failures. The measurement is based on two important network service parameters, the endto- end delay and the packet loss. To evaluate the approach, different network topologies are studied using the OPNET Modeler. The results of simulations for four random topologies and two routing protocols, the RIP and the OSPF are presented and compared. The OSPF protocol with different delay timer values is also evaluated. © 2007 Springer  

A realistic and practicable modeling of unbalanced distribution networks (DNs) is the missing link in most studies undertaken in these networks, e.g., optimal power flow (OPF), energy markets, etc. To address the issue, this letter proposes an unbalanced linear three-phase four-wire power flow (PF) model based on current injection equations at nodes. Also, the ZIP representation is considered for loads. The model can be easily generalized for unbalanced three-wire networks with minor changes and assumptions. Hence, the scope of the proposed method can be extended to cover both low-voltage and medium-voltage DNs. The performance of the proposed model is verified through simulations on two... 

A web attack is an attack against a web server through the HTTP Protocol. By analyzing known web attacks, we find out that each one has its own behavior. Vestiges of their behavior could be detected in non-body parts of the HTTP Protocol. Such information can be used to verify web alerts generated by Web Application Firewalls (WAFs) and Web Intrusion Detection Systems (Web IDSs). In this paper, we propose a method to verify web alerts generated by mentioned sensors. The goal of the alert verification component is to eliminate or tag alerts that do not represent successful attacks. Our approach is based on analyzing HTTP Transaction metadata, including Request method, Request Headers, Status... 

This paper presents a new group key management protocol, CKC (Code for Key Calculation) for secure IP multicast. In this protocol which is based on logical key hierarchy, only the group key needs to be sent to new member at join. Then, using the group key current members and the new member calculate the necessary keys by node codes and one-way hash function. A node code is a random number assigned to each node to help users calculate necessary keys. Again, at leave server just sends the new group key to the remaining members. By this key, members calculate necessary keys using node codes and one-way hash function. The security of the keys is based on one-wayness of hash function. The results... 

The 3rd Generation Partnership Project (3GPP) defined a new architecture, called Home eNode B (HeNB). HeNB is able to provide new services with higher data rate in a low cost. Security is a critical aspect of HeNB. In order to have HeNB secure access to core network, 3GPP defines an authentication protocol based on IKEv2. A number of security vulnerabilities such as HeNB masquerading have not been addressed and solved by 3GPP technical specification yet. In this paper an improved HeNB authentication protocol is introduced which does not allow an attacker to connect unauthorized network users using a mask. Finally, we evaluate our protocol performance and verify it by Automated Validation of... 

This paper presents a new group key management protocol, CKC (Code for Key Calculation). This protocol is based on logical key hierarchy. When a new member joins the group, server sends only the group key for that member. Then, current members and the new member calculate the necessary keys using node codes and one-way hash function. Node code is a code which is assigned to each node of the key tree. Again at leave, server just sends the new group key to remaining members. By this key, members calculate necessary keys using node codes and one-way hash function. The security of the keys is based on one-wayness of hash function. The results show that CKC reduces computational and communication... 

The Session Initiation Protocol (SIP), which is becoming the de facto standard for the next-generation VoIP networks, is currently receiving much attention in many aspects. One aspect that was not deeply addressed in the original SIP is its authentication procedure. Apart from its security, an SIP authentication procedure should be efficient. This paper proposes a robust and efficient three-party SIP authentication protocol. In this protocol, the. end users are. authenticated with the proxy server in their domain using the. registrar server. Compared to previous works, our proposed protocol is more efficient and secure. To support our protocol with a formal security proof, its model is... 

Named Data Networking (NDN) is a new information-centric networking architecture in which data or content is identified by a unique name and saved pieces of the content are used in the cache of routers. Certainly, routing is one of the major challenges in these networks. In NDN, to achieve the required data for users, interest messages containing the names of data are sent. Because the source and destination addresses are not included in this package, routers forward them using the names that carried in packages. This forward will continue until the interest package is served. In this paper, we propose a routing algorithm for NDN. The purpose of this protocol is to choose a path with the... 

To ameliorate high collision, a nefarious side effect of route discovery stage of reactive routing protocols in wireless networks, jitter mechanisms are proposed which enforce wireless nodes to postpone their transmission for a random amount of time so as to reduce probability of simultaneous transmission. Although it has been shown that jitter mechanisms can dramatically improve reactive routing protocols, it was not until recently that jitter mechanisms have been subjected to study. In this paper, different random distributions are proposed for jittering mechanisms and also shaping function, with the aim of which a simple routing protocol like AODV becomes sensitive to any arbitrary...