Transcript I-TCP – For Mobile Hosts

Connection
Migration
818L Network Centric Computing
Spring 2002
Ishan Banerjee
Connection Migration
Hosts Mobility
Network A
A mobile device is attached to
a different network
A mobile device migrates to
another cell
Wireless Network
Network B
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
Architecture
MSR-2
MH
FH
Handoff
MH
MSR-1
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
Architecture
Care of address / foreign agent
Fixed Host
Mobile Host
Home Agent
Mobile IP – Host Mobility
Issues
 Pure network layer solution. Upper layers unchanged
 Triangle routing consumes more resources
Migrate – Host Mobility
IP
DNS Updates
 Addressing
 Mobile host location
 Connection migration
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
- <source IP, source port, dest IP, dest port>
 Modification
- <source IP, source port, token>
 Mobile host can re-establish a connection
using the connection token
- Implies modifying the TCP stack
Migrate – Host Mobility
Issues
 Applications are unaware of mobility of hosts
- TCP stack needs modification
Migrate
Service Availability
MIT LCS
Migrate – Service Availability
External
 Health monitoring
 Server selection
 Connection migration
Application Independent
Migrate – Service Availability
Connection migration
Information advertised
 Application dependent
 Transport layer
URL
IP, Port, Seq #
Support group
Client
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.