© 2004 Jörg Ott · Dirk Kutscher Why Seamless? Towards Exploiting WLAN-based Intermittent Connectivity on the Road Jörg Ott Dirk Kutscher TNC 2004 · Rhodes · 9 June 2004

© 2004 Jörg Ott · Dirk Kutscher Approaches to Seamless Connectivity  Link Layer Mobility Cellular Networks (GSM, GPRS): Intended for ubiquitous coverage Fundamental Service: low-bandwidth bit-pipe with transparent mobility Cell range rather large Disruptions are a every-day phenomenon  IP Layer Mobility Maintain communication relationships despite network layer mobility Handover delays  Dependent on many factors (RTT to HA etc)  Vertical handovers likely to cause disruptions  Hybrid Networks Always-Best-Connected approach Utilise multiple network interfaces concurrently, select most appropriate dynamically Still no guarantee for non-disrupted service

© 2004 Jörg Ott · Dirk Kutscher Seamless Connectivity  100% coverage not achievable Service disruptions, battery life, occasional obstacles, network saturation Economics of service provisioning (mountains, tunnels, valleys, deserts, …)  Where available, not necessarily suitable (particularly cellular) Limited data rate Cost structure  Does not address all use cases Nomadic users: Switching locations with computer turned off Legal enforcement: e.g. on aircrafts  Finally: not needed for many applications!

© 2004 Jörg Ott · Dirk Kutscher Seamless Connectivity  100% coverage not achievable Service disruptions, battery life, occasional obstacles, network saturation Economics of service provisioning (mountains, tunnels, valleys, deserts, …)  Where available, not necessarily suitable (particularly cellular) Limited data rate Cost structure  Does not address all use cases Nomadic users: Switching locations with computer turned off Legal enforcement: e.g. on aircrafts  Finally: not needed for many applications! Little point in striving for ubiquitous connectivity – service disruptions may occur anyway...  Disconnection Tolerant Networking

© 2004 Jörg Ott · Dirk Kutscher Disconnection Tolerant Networking  Successive periods with and without connectivity Well known: moving between office, home, hotels, Internet cafés, etc. Controlled long periods of connectivity, manually managed by user  Rather cumbersome to handle  Extreme case Drive-thru Internet: network access from vehicles Initially: rare and short connectivity periods, long periods without network  Ultimately: may potentially transition to approximate permanent connectivity Limited influence by the mobile user, manual control not possible  Goal: conceal intermittent nature of connectivity from users Automate connectivity establishment, support applications In vehicles, on trains, …  but also for commuting between home and office

© 2004 Jörg Ott · Dirk Kutscher Extreme Networking Scenario: Autobahn 1 km 6 km 4 km 2 min3 min 0,5 min

© 2004 Jörg Ott · Dirk Kutscher System Architecture ISP B ISP A Internet Connectivity Islands Server

© 2004 Jörg Ott · Dirk Kutscher Data Rate (TCP, b, plain AP) Entry phase Production phase Exit phase

© 2004 Jörg Ott · Dirk Kutscher b vs g (High Gain Antenna) TCP transmission, 120 km/h, fixed  mobile

© 2004 Jörg Ott · Dirk Kutscher g Data Volume (120km/h) 25 – 30 MB over ~1000m in about 30 seconds

© 2004 Jörg Ott · Dirk Kutscher Architectural Implications  Concentrate data exchange on the production phase Minimize activities during entry and exit phases: Lower transmission rates and packet loss hurt overall performance  Perform autoconfiguration + authentication during the entry phase Workable with minimal effort Allows to make most of the production phase  Make short-lived connectivity useful for applications E.g. persistent transport across connectivity islands To exchange larger data volumes independent of the application  Application-specific support where necessary

© 2004 Jörg Ott · Dirk Kutscher Types of Applications  Asynchronous Applications Examples: Mail (SMTP, POP3), NetNews Bidirectional push and pull, usually initiated by mobile node Session-oriented communications, identifiable transactions Individual transactions may complete within one cloud Transactions can only be recovered as a whole  Access to information resources (WWW)  Audio/Video Communication  Distributed Object Synchronisation  New Applications

© 2004 Jörg Ott · Dirk Kutscher System Architecture ISP B ISP A Internet Server Drive-thru-Proxies Drive-thru Client

© 2004 Jörg Ott · Dirk Kutscher Different Levels of Support No Support Sessions must complete within connectivity windows No Support Sessions must complete within connectivity windows Persistent Connections Concealing intermittent nature of connectivity Persistent Connections Concealing intermittent nature of connectivity ALG services Drive-thru clients proxy and manage application transactions ALG services Drive-thru clients proxy and manage application transactions Advanced ALG services ALG performs message prefetching and provides local message store Advanced ALG services ALG performs message prefetching and provides local message store

© 2004 Jörg Ott · Dirk Kutscher Application Example:  well suited to Drive-thru environment  Sending straightforward Drive-thru client as local SMTP relay server  Retrieving requires more thought Offline mode preferable  Allows for short session and automated message retrieval Online mode more difficult  Requires persistent connections  Using POP3 as protocol Commonly supported by servers

© 2004 Jörg Ott · Dirk Kutscher Sample POP3 Operation ClientServer +OK USER foo PASS bar +OK UIDL +OK … RETR 1 +OK 400 octets QUIT

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Drive-thru POP3 Operation with ALG Support ClientServerDrive-thru-ClientDrive-thru-Proxy Origin POP3 server Message store (optional)

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server  Network Attachement IEEE association IP auto-configuration Authentication  Must be automatic  Dependent on hot-spot architecture  Network Attachement IEEE association IP auto-configuration Authentication  Must be automatic  Dependent on hot-spot architecture

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server  Application interaction Initiate sessions through local Drive- thru client  Access to with POP3 Drive-thru client provides application layer support for POP3  Careful transaction completion  Monitors current connectivity status  Forwards requests to actual POP3 server via Drive-thru proxy  Application interaction Initiate sessions through local Drive- thru client  Access to with POP3 Drive-thru client provides application layer support for POP3  Careful transaction completion  Monitors current connectivity status  Forwards requests to actual POP3 server via Drive-thru proxy

© 2004 Jörg Ott · Dirk Kutscher POP3 Operation: Client Initiates Retrieval ClientServerDrive-thru-ClientDrive-thru-Proxy +OK +OK

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Drive-thru POP3 Operation ClientServerDrive-thru-ClientDrive-thru-Proxy +OK UIDL +OK … RETR 1 UIDL +OK … RETR 2

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server  Resuming interrupted sessions Repeating outstanding and interrupted POP3 requests Answering local POP3 requests  Resuming interrupted sessions Repeating outstanding and interrupted POP3 requests Answering local POP3 requests

© 2004 Jörg Ott · Dirk Kutscher Drive-thru POP3 Operation ClientServerDrive-thru-ClientDrive-thru-Proxy RETR 1 +OK … UIDL +OK … RETR 1 +OK … RETR 2 +OK …

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server  Terminating application sessions  Removing ALG state  Terminate Drive-thru session  Terminating application sessions  Removing ALG state  Terminate Drive-thru session

© 2004 Jörg Ott · Dirk Kutscher Application Example ISP B ISP A Internet Drive-thru Proxy Server

© 2004 Jörg Ott · Dirk Kutscher Conclusion  Questioning seamless connectivity Rarely available, not always required  Disconnection Tolerant Networking Take intermittent connectivity into account Viable for many, but not for all application classes Approach: Provide different levels of infrastructure support  Drive-thru Internet approach Testbed for Disconnection Tolerant Networking with extreme characteristics Drive-thru entities maintain persistent connections during disruptions Application-specific functions as optional enhancements

© 2004 Jörg Ott · Dirk Kutscher