ConnectionMigration 818L Network Centric Computing Spring 2002 Ishan Banerjee

Connection Migration Hosts Mobility Network ANetwork B Wireless Network A mobile device is attached to a different network A mobile device migrates to another cell

Connection Migration Service Availability Client may or may not be aware of redundant servers

I-TCP Host Mobility Rutgers DCS

TCP – Mobile Hosts Traditional fixed hosts TCP was developed keeping in mind the fixed nature of hosts. Physical link assumed was wired network Mobile Hosts - Weak wireless link - Cell crossover causes dropped TCP segments and longer restoration time

I-TCP – Mobile Hosts MH MSR-2 MSR-1 FH Handoff Architecture Split transport layer

I-TCP – Mobile Hosts Issues + Concept is simple and direct + Fixed TCP backbone unchanged + No new transport protocol is required  Implemented over Mobile IP ? Fixed host is unaware of mobility ? Application is unaware of mobility ? End-to-end semantics violated ? Split transport layer

Migrate Host Mobility MIT LCS

Internet Mobility – Issues Disconnected state is a fundamental property of any network connection End points must not have static addressing Application must be aware of network disconnection and treat it as natural, not an error Application must handle disconnection and resume upon network reconnection Upper layers should not depend on lower layer naming system Reconsidering Internet mobility – Snoeren, Balakrishnan, Kaashoek – MIT LCS

Mobile IP – Host Mobility Mobile Host Home Agent Care of address / foreign agent Fixed Host Architecture

Issues Pure network layer solution. Upper layers unchanged Triangle routing consumes more resources Mobile IP – Host Mobility

Migrate – Host Mobility Addressing Mobile host location Connection migration DNS Updates IP TCP Modification

Migrate – Host Mobility Addressing IP address is used to identify the host. The policy of obtaining a new IP in a foreign domain is separated from the location mechanism. + Implies no change to the network layer infrastructure

Migrate – Host Mobility Mobile host location Uses DNS updates to broadcast new location Mobile Clients – require no DNS updates Mobile Servers – update DNS DNS entry for mobile hosts made non cacheable ? Are there any dropped packets ? How scalable is DNS update

Migrate – Host Mobility Connection migration Traditional TCP connection - Modification - Mobile host can re-establish a connection using the connection token - Implies modifying the TCP stack

Issues Applications are unaware of mobility of hosts - TCP stack needs modification Migrate – Host Mobility

Migrate Service Availability MIT LCS

Migrate – Service Availability Health monitoring Server selection Connection migration External Application Independent

Migrate – Service Availability Connection migration Support group Client Information advertised Application dependent Transport layer IP, Port, Seq # URL

Migrate – Service Availability Issues What about transaction servers Transport state migrated Application-unaware X Specific application (HTTP) aware Transport module

Comments  Internet has changed from a collection of fixed nodes to a combination of fixed and mobile nodes  Provide temporary patches  Search for permanent solutions  Content/ service naming- consider mobility  Should give up trying to protect one layer or the other from disconnection or mobility transparency. Accept the fact that short/ long disconnections are natural. Each layer should be prepared.