Wook Hyun

An application level gateway for traversal of SIP transaction through NATs

SIP has been used to develop many kinds of SIP service, such as instant messaging, conference and presence, and these various services are being bundled to one application. NAT traversal has long been identified as a large problem when considered in the context of the session initiation protocol (SIP). The problem is further confused by the variety of NATs that are available in the market place today and the large number of potential deployment scenarios. In this paper, we suggest an ALG which operates inside NAT for traversal of SIP transactions

Call management mechanism for internet phone services based on SIP

Absnuct VOW (Voice over IP) Technology is highlighted because of easy adopting the value added services related voice. In this paper, we described the architecture and its internal processing procedure of user agent system for Internet telephony services based on SIP (Session Initiation Protocol). Especially, we focused the call management mechanism for establishing the dialog within user agent system.

Basic call flow for interoperability test in the presence services based on SIP

Presence service is emerged to meet the needs of integrated service and presence service will be a core function within integrated service. IETF SIMPLE WG generates standard SIP extensions for presence service. In this paper, we described the presence service systems including internal logical function modules. We classified functions of presence service systems with itemized functions, conditions to be occurred related SIP request messages and response message for each request message. And, we also described the basic call flows for interoperability test among presence service systems based on SIP

An implementation of SIP servers for internet telephony

Abstruct- This paper addresses the design and implementation of Session Initiation Protocol (SIP) server components required for providing Internet telephony services. We first describe a family of SIP servers necessary for Internet telephony, and discuss overall functionality for each SIP server, Then we present our implementations of SIP servers including proxy server and registrar server, along with details of processing routines. We also discuss possible organization of SIP server components for providing Internet telephony services. We will also mention about our experiences on interoperability tests with other products.

Design considerations for user authorization in the presence services based on SIP

SIP plays an important role in VoIP service infrastructure. Presence service is emerged to meet the needs of integrated service and presence service is a core function within integrated service. IETF SIMPLE WG generates standard SIP extensions for presence service. In this paper, we described the service scenarios of presence services based on SIMPLE. We also described the construction of presence system. Especially, we described the design considerations of presence agent supporting for multiple presence packages and those of presence agent supporting for user authorization function

Study on Architectural Model and Design of P2P-Based Streaming Client

P2P technology is widely used for distributing contents. The P2P applications increase the load of ISP on handling massive and unpredictable P2P traffic. By the way, P2P itself provides very good performance on receiver-side when it receive large-sized files from multi-points. Furthermore, the usage of P2P technology is enhanced its area on multimedia streaming. Nowadays, the volume of multimedia is tends to be massive and need high performance of network. In the case of server-client model, there are definitely limitations on accommodating a number of users. In this paper, we present architecture for providing P2P-based streaming services and framework model for client agent.

A Study on Keepalive Mechanism between SIP UA and Proxy server for Internet Telephony Service

When Internet telephony service is provided using SIP protocol, The session initiation protocol (SIP) does not define a keepalive mechanism for the sessions it establishes. Although the user agents may be able to determine whether the session has timed out by using session specific mechanisms, proxies will not be able to do so. The result is that call stateful proxies will not always be able to determine whether a session is still active.

A study on design and implement of XCAP server

A XCAP (XML configuration access protocol) proposed by IETF SIMPLE WG is based on both XML and HTTP protocol. XCAP server maintains users configuration information of specific application described by XML. This protocol can be applied to many application servers for adapting users preferences. There are many way to interwork with other applications. In this paper, we will describe the experience of designing and implement of XCAP server and the way of interworking with application servers

A study on buddy list control in XCAP server system for SIP-based IMPP services

XCAP (XML configuration access protocol) is protocol for communication between XCAP client and XCAP server. XCAP allows a client to read, write and modify application configuration data, stored in XML format on a server. XCAP maps XML document subtrees and element attributes to HTTP URIs, so that these components can be directly accessed by HTTP. In this paper, we study on XCAP server behaviors SIP-based IMPP services in order to buddy list control

Implementations of automated testing environment for distributed multimedia streaming applications

Nowadays, multimedia streaming service is one of the widely used application over Internet. However, it costs much and needs infrastructures to accommodate massive concurrent users in server-client model. Hence, there several solutions and standards are under development based on peer-to-peer networking, and we are implementing prototype based on ITU-T Recommendation. On testing application in distributed systems, operator has to control whole client one-by-one manually on every test scenario, and it was not easy to test time critical scenarios. Hence, we have constructed our own testing environment by using several open source solutions. In this paper, we share our experiences on constructing automated testing environment for distributed multimedia streaming application.