ITCP For Mobile Hosts

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Connection Migration
818L Network Centric Computing Spring 2002
Ishan Banerjee
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Connection Migration

• Hosts Mobility

Network A
Network B
A mobile device is attached to a different network
A mobile device migrates to another cell
Wireless Network
3
Connection Migration

• Service Availability

Client may or may not be aware of redundant
servers
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I-TCP Host Mobility
Rutgers DCS
5
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

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

8
Migrate Host Mobility
MIT LCS
9
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
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Mobile IP Host Mobility
Architecture
Care of address / foreign agent
Fixed Host
Mobile Host
Home Agent
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Mobile IP Host Mobility

• Issues
• Pure network layer solution. Upper layers
  unchanged
• Triangle routing consumes more resources

12
Migrate Host Mobility
IP
DNS Updates

• Addressing
• Mobile host location
• Connection migration

TCP Modification
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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
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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

15
Migrate Host Mobility

• Connection migration
• Traditional TCP connection
• - ltsource IP, source port, dest IP, dest
  portgt
• Modification
• - ltsource IP, source port, tokengt
• Mobile host can re-establish a connection using
  the connection token
• - Implies modifying the TCP stack

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Migrate Host Mobility

• Issues
• Applications are unaware of mobility of hosts
• - TCP stack needs modification

17
Migrate Service Availability
MIT LCS
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Migrate Service Availability
External

• Health monitoring
• Server selection
• Connection migration

Application Independent
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Migrate Service Availability
Connection migration

• Information advertised
• Application dependent
• Transport layer

URL
IP, Port, Seq
Support group
Client
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Migrate Service Availability

• Issues
• What about transaction servers
• Transport state migrated
• Application-unaware
• X Specific application (HTTP) aware Transport
  module

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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.