Technologie-Zentrum Informatik Digital Media
and Networks
Department for
Mathematics and
Computer Science
Universität Bremen

Research Interests Research Projects Teaching Selected Publications Some Useful Links Contact


Jörg Ott

Jörg Ott

Jörg Ott holds a Diploma in Computer Science and in Economics. He received his Doctor in Engineering (Dr.-Ing.) in 1997 from Technische Universität Berlin. Since 1997, he is Assistant Professor in the Digital Media and Networks Group in the Center for Computing Technology (TZI) at the Universität Bremen. His research interests are in protocol and system architectures for multipoint communications, content distribution, and multimedia conferencing, including Internet Telephony as special interest area. His current research focus is on communication in challenged networks, particularly on networking with intermittent connectivity. In the IETF, he is co-chair of the MMUSIC working group since 1997 and has been co-chairing the SIP working group from its foundation in 1999 to October 2002. In the ITU-T, he was one of the core designers of H.323 from the very beginning in 1995 and editor of two of its Annexes. Jörg is co-founder of Tellique Kommunikationstechnik GmbH, a TZI spin-off which provides solutions for IP multicast-based content distribution.

This page is no longer maintained. As of 2005-03-01, my new home is at Helsinki University of Technology, Networking Laboratory.


Research Interests
Networking with
Intermittent Connectivity
Diverging from today's usual approaches towards supporting mobile users by providing ubiquitous and seamless connectivity across several networks, the goal of this research area is to accept the non-permanent nature of connectivity experienced and achievable today. My primary interest is to investigate architectures, protocols, and applications to maximize the gain a user a draw even from rare and short-lived connectivity as one aspect and to minimize the impact of connectivity interruption when commuting or traveling. One key example is the introduction of Drive-thru Internet &mdash an application scenario where we provide WLAN-based short range connectivity islands to users traveling at potentially high speeds on the road.
Interactive Interpersonal
Multimedia Communications
Design and implementation of control protocols for interpersonal (multiparty) (multimedia) communications such as teleconferences, support for face-to-face meetings, etc. This particularly includes system architectures for multimedia communication systems — endpoints as well as infrastructure components. I am also interested in transport aspects of real-time (RTP, RTCP) and/or multiparty communications (reliable multicast).
IP Telephony Research and development in the area of signaling protocols for IP telephony as well as architectures for and implementation of endpoints and infrastructure components and endpoint integration with personal/desk area environment. Of particular interest are also concepts and architectures architectures for intra- and inter-domain IP telephony deployments, including scalable, decentralized call routing and addressing infrastructures.
IP Multicast-based
Content Distribution
and Media Streaming
Publication of the availability of content (related but not restricted to) Electronic Program/Service Guides (EPGs/ESGs) and distribution of media via IP-based networks. My particular interests include (reliable) multicast transport protocols and service architectures for content dissemination (real-time streaming, reliable data delivery) for unidirectional and bidirectional network infrastructures: multicast-enabled IP networks, satellite (DVB-S), digital terrestrial broadcast (DVB-T), and cable (DVB-C) as well as hybrid networks using wireline and wireless networks as back channels. I am also working on specific enhancement protocols and middleboxes (performance enhancing proxies) for accelerated on-demand access to content and/or receiver-specific content delivery. Finally, I am working on a framework for disseminating Internet Media Guides (IMGs), a generalization of EPGs/ESGs.
Physical Networks
Research for IP-based multimedia communications and content distribution tailored to deal with specific aspects of access and distribution networks: my primary interests are in satellite (DVB-S) and terrestrial broadcast (DVB-T) networks as well as wireless LANs (802.11) and, to some degree, 3G networks.
IETF Standardization I have been participating in the IETF since 1993 focussing on the areas outlined above, particularly control and transport protocols for multimedia conferencing. I am co-chair of the MMUSIC WG since 1997 and maintain the informal MMUSIC web page as well as of the SIP WG since 1999 (informal page). I am also interested in closely related areas such as security, QoS, mobility, mapping IP to various link layers, satellite communications and dealing with middleboxes.
ITU-T Standardization In a former life, from 1994 through 2000, I have been active in the Telecommunication Sector of the International Telecommunication Union (ITU-T, formerly known as CCITT). Particular interests included the infrastructure for data conferencing (T.120) which was developed by Study Groups 8 and later 16 and the design of the H.323 series of Recommendations for IP-based multimedia conferencing (in local area networks) and IP telephony which I accompanied from the the very beginning in early 1995, first in SG15 and later in SG16.
Research Projects
GEOCOOP Oct 2004 –
   Sep 2005
An industry project on investigating location techniques and concepts for providing location-based services with the aim of enabling interpersonal communications based upon proximity. Particular consideration of privacy aspects and decentralized operation.
IPTEL-via-Sat Oct 2004 –
   Jan 2005
Protocol analysis, simulations, and measurements for deploying IP telephony via bi-directional satellite links for selected scenarios. Consideration of satellite channel characteristics, different IP telephony protocols (SIP, H.323, Skinny), network topology, and server placement with the aim of deriving a set of operational recommendations for (satellite) service providers.
PASST Nov 2003 –
   Sep 2004
Presence Aggregation System: An industry project investigating the automated (but ultimately end-user-controlled) aggregation of personal presence information from a number of sources. The project focuses on defining rule sets for presence aggregation and validating the concepts in a complete SIP-based presence infrastructure.
Mar 2003 – Exploiting short-lived Internet connectivity for mobile users on the road by means of connectivity islands provided by 802.11 wireless LANs as inexpensive yet powerful communications infrastructure. The research project has shown that vehicles traveling at speed of 180km/h and more can be supported with off-the-shelf equipment today — provided that appropriate Drive-thru Services are available to the mobile users that conceal the intermittent nature of connectivity from the user's general purpose applications.
FETA Jan 2003 –
   Sep 2003
Functional Enhancement for Telephony Applications: An industry project (following up on DTI) to augment stand-alone IP phones by external software components with a focus on secure multiparty peering in ad-hoc networks, conferencing, and video communications.
DTI Feb 2002 –
   Oct 2002
Desktop-Telephony Integration: An industry project on the integration of various personal computing appliances (PC, laptop, PDA) and stand-alone IP phones, focusing on peerwise ad-hoc networking, autoconfiguration, and distributed phone control.
6WINIT Jan 2001 –
   Dec 2002
A European project that deals with the integration of IPv6 and various wireless technologies (in particular, GRPS and UMTS) as a platform to provide mobile interactive conferencing applications in a clinical environment.
SIPHON June 2000 –
   Nov 2001
SIP for telePHONy: A research project addressing script-based testing of SIP-based IP telephony endpoints (IP phones) in phase I and dealing with aspects of IP telephony to the home user in phase II.
MDiS June 2000 –
   Oct 2000
Multicast Distribtion Service: Multicast distribution of large volumes of weather data (12 GB per hour) in the network of the Deutsche Wetterdienst. Development of a file distribution application based upon the multicast transport protocol MTP/SO.
WINSPECT Oct 1999 –
   Sep 2002
Wireless Inspection: Using wearable computers to support inspection and maintenance tasks in production environments, focusing on multimedia conferencing as always available communication link to (off-site) personnel. Development of dedicated conferencing policies and error resilient transmission schemes for wireless LAN as mobile communication infrastructure.
IP Telephony Lab Since 1998 University-internal project: The IP telephony lab deals with research and development of a protocol-agnostic infrastructure for IP telephony specifically in research institutions. Work in the lab combines developing protocol and component implementations (endpoints, telephony servers, etc. for both SIP and H.323) with testing commercial products and freely available components. Core points are setting up and running a heterogenous (multi-vender, multi-protocol) infrastructure within the computer science department; designing naming and numbering infrastructures; developing address resolution facilities using TRIP and ENUM, among others. The following "projects" are part of this activity, numerous diploma thesises contribute to this effort.
WIPTEL May 1999 –
   Nov 2000
Piloting an infrastructure for IP telephony in the German Research Network (WiN): definition of a reference architecture for intra- and inter-site IP telephone and establishment of an IP telephony lab.
MUSIG May 1999 –
   May 2000
An industry project on gatewaying between different (multimedia) communications technologies and IP telephony (H.323, SIP) and integration of conventional telephony (analogue, ISDN, GSM). Development of an Mbus-based architecture for multi-way signaling (and media) gateway.
MECCANO Jun 1998 –
   May 2000
A European project that deals Internet multimedia group conferencing based. Care and feeding of parts of the European Mbone as communication infrastructure and pilot use of the European ATM infrastructure. Design of an architecture for multimedia conferencing endpoints and development of the Message Bus (Mbus) as local coordination infrastructure.

  Lectures and Seminars
Control Protocols for IP-based Multimedia Winter 2004/05 Starting with a review of the basics of IP-based multimedia communications, we will explore the details of media annoucements (SAP, SDP), Internet Media Guides (IMG), media streaming (RTSP), and as the focus of the Session Initiation Protocol (SIP) as defined in RFC 3261. We will discuss concepts, protocol details, numerous extensions, and SIP's service creation architecture. Specific application scenarios to be discussed include telephony as well as instant messaging and personal presence. We will also address security and NAT/firewalls traversal. Finally, system design aspects (for endpoints as well as for infrastructures) will be investigated.
Extreme Networking Summer 2004 This seminar starts from networking environments with unusual characteristics, i.e. properties that traditional design of communication protocols has not taken into account. Those characteristics are partly inherent to certain link layer technologies (e.g. transmission error rate in wireless networks), partly arise from communication settings (e.g. geostationary satellite orbits), or stem from specific networking architectures (e.g. mobile ad-hoc networking or sensor nets). We investigate numerous extreme networking environments, analyse their communication characteristics, and assess the impact on networking, transport, and application layer protocols. We discuss approaches to deal with such specific environments and also look into potential consequences for applications and user interaction paradigms.
3,4,7-Multicast Winter 2003/04 We will take a very close glance at IP multicast, addressing aspects from the IP (3), transport (4), and application (7) layers. An introduction to IP multicast in general and a comparably short review of various IP multicast routing protocols developed so far will provide the basis for a sound discussion of our focus: multicast transport. We will discuss general principles for multicast transport protocols and review the recent IETF activities for Reliable Multicast Transport (RMT) as well as multicast-aspects of the Real-time Transport Protocol (RTP). We will also discuss issues of multicast congestion control and touch on group security. Finally, we will address various types past, current, and emerging multicast applications as well as (issues with) real-world deployment of multicast deployment today.
Control Protocols for IP-based Multimedia Winter 2002/03 Starting with a review of the basics of IP-based multimedia communications, we will explore the details of the Session Initiation Protocol (SIP) as defined in RFC 3261 and move on to present the details of the various extensions to SIP that have been are still are being developed. Specific application scenarios to be discussed include telephony as well as instant messaging and personal presence. Finally, system design aspects (for endpoints as well as for infrastructures) will be investigated.
Rechnernetze 1 every winter Lecture on the basics of computer networks. Part 1: basics of protocol hierarchies, protocols and services, link layer technologies. Primarily held by Prof Dr Ute Bormann.
Rechnernetze 2 every summer Lecture on the basics of computer networks. Part 2: advanced topics on real-time communications, QoS, multimedia applications, mobility, and security. Primarily held by Prof Dr Ute Bormann.
Student projects
  The Department of Mathematics and Computer Sciences at Universität Bremen supports the concept of student projects that constitute a significant part (two years!) of the diploma. For the project duration, some ten to twenty-five students will work jointly in small groups towards a common project goal. Each semester a new project management team is chosen from the project itself — so that management skills are also gained during those two years. Projects start yearly and are offered by the various research groups. They are typically closely tied to a each group's research activities so that a project will offer a good entry point in a particular field of research and may pave the way towards a diploma thesis and/or student jobs at the university.
CLIP Starting Winter 2004/05 The CLIP project aims at providing an environment for personalized media access and management at home as well as on the road. The goals include dynamically locating devices (e.g. media sources and sinks), evaluating their capabilities, and combining selected ones as needed to fulfill a certain task (e.g. synchronized rendering of music in several rooms, remotely controlled from heldheld devices). The project focus will be the design of a system and protocol architecture for secure decentralized coordination of and access to a variety of components, building on standardized (IETF) protocols where possible.
MATRIX Winter 2002/03 –
Summer 2004
The MATRIX project is about providing content distribution services in heterogenous distribution and access networks with a focus on streaming media delivery. Access to content can be interactive on-demand with unicast and multicast media as well as receiver-based filtering with multicast media. Rendering content should be supported on a variety of device ranging from powerful workstations to palmtop computers.
HAUSGEIST Winter 2000/01 –
Summer 2002
The HAUSGEIST project deals with the development of an Mbus-based home networking environment in which IP-enabled appliances interact (sensors, actors, controllers, etc.) with each other to provide a ubiquitous computing infrastructure.
UniTel Winter 1998/99 –
Summer 2000
The UniTel project has focused on developing an IP telephony infrastructure for students at the Bremen university. The work particularly included the development of a user database, policy decision modules, infrastructure and endpoint components as well as a usage policy for such an infrastructure.
Selected publications
A few useful links
IETF Communications Services (mostly in German)

Universität Bremen
Department for Mathematics and Computer Sciences
Research Group for Computer Networks
Bibliothekstr. 1
D-28359 Bremen
tel: +49 421 201-7028
tel: +49 421 218-2085 (secr.)
fax: +49 421 218-7000

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