Jae Cheon Han

A Study on SIP-based Instant Message and Presence

There are many instant message and presence services in the world. The services are not inter-operable since they take their own way to implement services. To solve this problem, IETF IMPP WG defined service models for presence and instant message without concern with any other protocols. In IETF SIMPLE working group, many SIP-based standards on the IMPP have been developed or are being developed. This paper describes standards technologies which have been developed or being developed in the IETF IMPP WG and SIMPLEWG.

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

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 XCAP client system for SIP-based IMPP services

Internet users are rapidly increased and various services which use Internet are invented. IM (instant messaging) and presence service is one of them. IM and presence is looked upon as a major killer application in the field of IP telephony. In this paper, we describe about the standard technologies for SIP-based IMPP service and about XCAP (XML configuration access protocol) technologies. And then we describe service scenarios and models for SIP-based IMPP services. And finally, we suggest authorization policy and resource list manipulation mechanism using XCAP. And suggests XCAP client system. IMPP service is expecting to contribute in new service creation being integrated with various service such as conference and instant messaging services

Mechanism of Audio-Text Mode Assignment on SIP-based Internet Telephony System

Next to the binary-based H.323 signaling protocol for Internet telephony service developed by the Telecommunication World (ITU-T), a more lightweight text-based protocol was deemed necessary to address the specific needs of the Internet World. The session initiation protocol (SIP) was introduced in the IETF and has meanwhile gained maturity and support. The SIP-based Internet telephony service guarantees the user mobility. If SIP user is the place where the Internet connection is possible, it anytime can use a Internet telephony service in a where. Internet telephony communication with the user who is connected Internet softphone without headset or deaf people or speech-impaired people is difficult. Therefore, in this paper, we suggest mechanism of audio-text mode assignment on SIP Internet telephony system.

SIP based VoIP System for E911 Service

Today the world is undergoing a massive shift from the traditional PSTN to All-IP-based Internet telephony, implying an eventual replacement of the PSTN with VoIP sooner or later. Internet telephony users have an expectation to be able to initiate a request for help in case of an emergency. The problem arises for originating calls made to emergency services, where VoIP devices move while identifiers remain the same and the callers location cannot be provided. So, unfortunately the existing mechanisms to support emergency calls that have evolved within the PSTN, are not appropriate to handle evolving IP-based telephony service. In this paper, we suggest the mechanisms that solve the problem of E911 calling on SIP-based VoIP system using traditional E911 network.

Design of sip transaction distributor to support multiple applications

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. To make an application which supports various services may be not easy since the behavior of transaction user of the application is obviously become very complicated. In this paper, we describe a design of SIP transaction distributor which can support various transaction users such as VoIP, instant messaging, and presence at the same time

A study on ACK message processing mechanism in SIP transaction layer

According to the RFC3161, ACKs corresponding to 2xx responses to INVITE is handled in the transaction user as separate messages without any transactions. And the transaction user receives all retransmitted ACKs without any filtering. In this paper, ACK transactions and the finite state machines for those are defined. And the rules for matching messages to transactions are also redefined so that the retransmission of ACKs and the filtering of the retransmitted ACKs are treated in the transaction layer.