Cellular IP:A new Paradigm in Internet Host Mobility

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Cellular IP A new Paradigm in Internet Host
Mobility

• P R E S E N T E D B Y
• Venu Pragada
• Abhinav Anand

2
Overview

• Introduction
• Cellular IP Mobile IP
• Paging
• Routing
• Handoff
• Performance
• Summary

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• What is Cellular IP ??

4

• Cellular IP
• new robust, simple, and flexible protocol for
  highly mobile hosts
• CIP supports local mobility efficiently
  interworks with Mobile IP
• can accommodate large no. of users by separating
  idle from active hosts
• requires no new packet formats, encapsulations,
  or address space allocations

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Why bother for Cellular IP?When we have Mobile
IP...

• because..
• Mobile IP is optimized only for
• macro level mobility and
• relatively slow moving hosts

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Mobile IP and Cellular IP

Cell sizes smaller Migration freq faster User
population greater
Hierarchical Mobility Management
Faster smooth handoff Less load on
Internet Cheap-passive connectivity
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Wireless Access network Model
D
B
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What if MH moves from one Access Network to
another
Handoff sequence between two Access Networks
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5 key Features of CIP

• Easy Global Migration
• Cheap Passive Connectivity
• Efficient Location Management
• Flexible Handoff
• Simple Memory less Mobile hosts

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Easy Global Migration

• Migration should be transparent to the user
• This is achieved by
• allowing the BS to emit beacon signals
• when MH connects the access network it must
  inform its HA as required by MIP
• for global reachability, the MH uses a local C/O
  address, but within the access network its
  identified by its home IP

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Cheap Passive connectivity

• mechanism of keeping track of idle MHs.
• allows max. no users connected to a network
• reduces the network load

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How Mappings are created?

• Simplicity and Scalability
• Optimization of control packets
• Problems using timers
• Differentiated time scales

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Efficient Location Management
PAGING ROUTING

• Two parallel structures of mappings (PC RC)
• 1 - idle MH keeps PC upto-date
• 2 - PC mappings used to find the loc of idle MH
• 3 - maintains RC mappings until actively
  connected
• 4 - routing of data packets to MH

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PROTOCOL DETAILS

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Protocol Parameters
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Different Packet Formats used

• Data packets
• Route up-date packets
• paging up-date packets
• paging tear-down packets
• All the control packets have the same format

Control Packets
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Control Packet(s) Format

• Is an ICMP packet
• - source address IP of sending MH
• - destination addr gateway
• - type cellular IP
• - code control (eg route up-date)
• Timestamp determines order of pkts
• CU currently unused
• S flag( 1) indicates semi-soft handoff
• A Type denotes auth. method used
• Auth. Length length of authentication
• Type type of control information
• Length length of following data
• Data determined by Type Length

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Beacon Signal Structure

• Transmitted by each BS periodically
• Info carried
• CIP network identifier
• IP address of the GW
• ID of the paging area

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Paging

• What is paging how is it done?
• process of keeping track of MHs in idle state
  and promoting to active state upon receiving data
• idle MHs periodically generate paging-update
  messages
• paging-update messages travel up the GW
• Nodes with PC updates PC mappings
• finally GW discards the paging-update packets

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Illustration of Paging
I dont have a PC
Paging-update packets create mappings in PCs
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PCs updated for a moving host
No change in PC at A
X from F
X from F,G
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Paging packets are routed to the mobile host by
PCs
X
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Paging Routing caches

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• Routing
• Basic operation Same as that of paging
• Routing Paging are separated by two intrinsic
  time scales
• Routing deals with active hosts only
• MHs actively receiving data must send
  route-update packets periodically
• PCs do not stop tracking active MHs

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CIP Routing

• CIP nodes need to implement the Up-link and
  Dn-link routing algorithms (only)
• Packets routed on a hop-by-hop basis
• How are uplinks configured?
• by using a simple shortest path algorithm
• Gateway beacon packet are sent

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Uplink Routing

• Packet arriving from a Dn-link first updates RC
  and PC mappings and is then forwarded on Up-link
• 5-tuples (mappings)
• IP-address, interface, MAC address, exp.time,
  timestamp
• DATA packets only refresh the caches(RC PC) but
  do not change them
• A mapping is refreshed only when one exists and
  the exp.timer is reset else pkt dropped
• exp.time current time route-timeout

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Uplink Routing (contd..)

• Route-update packets, both refresh and create new
  mappings in RCs
• PCs are updated the same way but uses
  paging-timeout instead of route-timeout
• If its a paging-teardown packet, then the
  mappings from both RC and PC are purged
• Finally after the cache modifications the control
  packet is forwarded on the Uplink

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Downlink Routing

• Packet arriving from the Uplink is assumed to be
  destined to the MH

Check for valid mapping in RC
Check for PC
Broadcast on all links, except the one it came on
Check for valid mapping in PC
Forward it to the Dnlink neighbor
Packet dropped
Downlink routing Mechanism
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Handoff in Cellular IP

• Defn a change of access point during active data
  transmission or reception .
• Types
• Hard Handoff
• Semi Soft Handoff

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Hard handoff

• Initiated by the mobile host (MH).
• Based on signal strength measurements of Beacon
  Signal from the BS.
• MH has capability to listen to only one BS at a
  time.
• During the Handoff Latency the downlink packets
  are lost.
• Not suitable for applications where loss of
  packets are not tolerated.

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Handoff
X from D
X from D, E
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Semi soft Handoff

• Improvement over Hard Handoff NO packet loss
  smooth handoff.
• Trade off Packets are received in duplication.
• Mechanism
• Hosts radio device is capable of listening to
  two logical channels.
• Reduces handoff latency by sending semisoft
  packet to the new BS while listening to the old
  BS.
• The regular handoff occurs after a semisoft delay
  which is arbitrary value between mobile -GW round
  trip time and route -timeout.

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Semi soft handoff contd...
For smooth handoff

• Need for buffering at the cross over point

6 5 4
Crossover point
BS
GW
BS
GW
Crossover pt
3
NBS
2
OBS
1
NBS
OBS
Case I
Case II
Depending on the network topology the time to
transmit packets
From the cross over point to the new BS and old
BS will differ
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Soft handoff mechanism Contd....

• To ensure smooth handoff, a constant delay is
  introduced temporarily to compensate, with high
  probability, the time difference between two
  streams.
• Mapping created by the semisoft packet has a flag
  to indicate that downlink packets must pass
  through a delay device.
• After handoff the flag is cleared and all the
  packets in delay device is delivered with no
  further delaying of packets.
• Goals accomplished
• no packet loss
• smooth handoff

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Implementation

• CIP comprises of two protocol modules
• the Node module Mobile host modules.
• NODE module(important functions)
• paging update fn maintains the paging cache
• classifier parses uplink packets and select
  those which update the routing cache.
• route update fn updates the routing cache
• routing cache look up fn parses downlink packets
  and searches the cache for mappings.
• Paging cache look up fn

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Implementation contd.

• forwarding engine forwards downlink packets to
  the interface selected by RC or PC.
• Delay device temporarily inserted in the
  downlink route if a semisoft handoff is in
  progress.
• Beacon generator for each wireless interface.
• MH module
• handoff controller statistics of measured beacon
  strengths and deciding and performing handoff.
• Protocol state machine active and idle state.
• Control packet generator periodically
  transmitting route update packets or paging
  update packets as required by state machine.

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MH implementation contd.

• Mobile host state machine

Paging packet arrives
idle
active
Sending route update packets
Sending paging update
All connections closed
Assigning Active state timer required to
return to idle state.
Timer setting depends on the nature of traffic.
Trade off

• Higher active state timeout results in more route
  update packets.
• Lesser active state timeout results in more
  paging packets.

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Gateway Schematic

IP network
GW controller
GW packet filter
CIP node

• Three building blocks
• CIP node
• GW packet filter
• GW controller

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GW implementation

• CIP node block the RC and PC are updated by the
  uplink packets
• GW filter reads the destination IP address.
• Case 1 If GWs address, then forwarded to the
  GW controller.
• Case II. If not GWs address, then look up in RC
  and PC and if an entry is found, then treat the
  packet as downlink packet. Otherwise send the
  packet to Internet.
• GW controller control information is processed
  and the packet is dropped.
• Recommended that GW has both RC and PC to avoid
  loading the CIP n/w when no mapping in RC or PC.

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Performance of CIP

• Three major issues
• performance of Hard and semi soft handoff. Impact
  of handoff in TCP performance
• the cost of setting active state timeout at the
  MH.
• Scalability limits of a BS based on Multi homed
  PC hardware.

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Performance contd...

• Test configuration

host
router
GW
BS2
BS1
MH
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Performance contd...

• In the testbed the BS are statically assigned
  frequencies.
• The MH dynamically changes frequency to perform a
  handoff.
• MH is a 300 MHz pentium PC notebook.
• All the three nodes in the CIP are multi homed
  300 MHz pentium PCs.
• 100 Mbps full duplex links interconnects CIP
  nodes.

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Handoff performance

• MH receives 100 bytes UDP packets at rates of 25
  and 50 pps
• MH continually make handoffs between BS every 5
  seconds.
• Packet loss per handoff
• Mobile-GW
• round trip time
• (ms)

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Handoff performance contd...

• Inferences
• hard handoff causes packet loss proportional to
  the round trip time and to the downlink packet
  rate.
• Semi soft handoff eliminates packet loss
  completely.

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Handoff performance on tcp throughput

• downlink TCP throughput kbps)
• Number of
• handoffs
• per minute

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Handoff performance contd.

• Inferences
• as the handoff frequency increases, the
  performance of TCP degrades due to packet loss.
• Semi-soft handoff reduced packet loss and
  significantly improved the throughput in relation
  to hard handoff.
• Unlike the UDP traffic experiment, packet loss is
  not entirely eliminated which is reflected in in
  the decline of throughput.

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Active state timeout

• This parameter determines the time a mobile host
  maintains a routing cache mappings after
  receiving a packet.
• It reflects the expectation that one downlink
  packet may with high probability be soon followed
  by another and that it is worth keeping
  up-to-date routing information for sometime.
• The trade off involved is the cost associated
  with transmitting route update packets for
  maintaining a higher value of timer and reducing
  paging traffic.

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Rate of paging traffic to mobile bps
Active state timeout
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Active state timeout contd.

• Inferences
• paging traffic is reduced drastically by
  increasing the value of active state timeout
  timer.
• Reducing the paging traffic saves the paging time
  and buffering requirement at the GW.

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Scalability

• Main concern of scalability is the use of per
  host routes which is required for semi soft
  handoff.
• In CIP scalability is achieved by separating the
  location management of idle host from active MH.
• Thus CIP can accommodate large number of users.

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Scalability contd.

• throughput Mbps
• Number
• of entries
• in routing
• cache

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Scalability contd..

• Inference
• throughput curve is hardly decreasing with
  increasing routing cache size and it suggest that
  in the studied scenario the performance
  bottleneck is not the routing cache entries.

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Summary

• Limitations imposed by MIP for highly mobile
  hosts Improvements offered by CIP
• Separation of local mobility and wide area
  mobility
• Cheap passive connectivity using PC and RC
• Flexible handoff
• Scalability of CIP
• Authentication and security issues

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Ongoing work...

• Authentication information in the control ICMP
  packets.(dealing security issues)
• Providing QOS.(in terms of differentiated
  services)

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References

• A. G. Valko, A. T. Campbell, J.
  Gomez, "Cellular IP - A Local Mobility Protocol,"
  IEEE 13th Annual Computer Communications
  Workshop, Oxford, Mississippi, October 1998.
• A. G. Valko, "Cellular IP - A New Approach
  to Internet Host Mobility," ACM Computer
  Communication Review, January 1999
  
• A. G. Valko, A. T. Campbell, J.
  Gomez, "Cellular IP," Internet Draft,
  draft-valko-cellularip-00.txt, November 1998.
  Slides of the presentation at 43rd IETF, Mobile
  IP WG, Orlando, December 1998.
• A. G. Valko, J. Gomez, S. Kim,
  A. T. Campbell, "On the Analysis of Cellular IP
  Access Networks", IFIP Sixth International
  Workshop on Protocols for High Speed Networks
  (PfHSN'99), Salem Massachusetts, August 1999.
• Andrew T. Campbell, Javier
  Gomez, Andras G. Valko, "An Overview of
  Cellular IP" IEEE Wireless Communications and
  Networking Conference (WCNC'99), New Orleans,
  September 1999.

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References contd..

• S. Kim, C-Y. Wan, W. B. Paul, T. Sawada, A. T.
  Campbell, J. Gomez, A. G. Valko, "A Cellular
  IPDemostrator", Sixth IEEE International Workshop
  on Mobile Multimedia Communications (MOMUC'99),
  San Diego, California, November 1999.
• A. T. Cambell, S. Kim, J.
  Gomez, C-Y. Wan, Z. Turanyi, A. Valko,
  "draft-ietf-mobileip-cellularip-00.tx", IETF
  mobile IP Working Group Document, December 1999.
  
• A. G. Valko, A. T. Campbell, J.
  Gomez, "Cellular IP (old version)," Internet
  Draft, draft-valko-cellularip-00.txt, November
  1998.
• A. Campbell, J. Gomez, C-Y.
  Wan, Z. Turanyi, A. Valko, "Cellular IP,"
  Internet Draft, draft-valko-cellularip-01.txt,
  October 1999.
• A. T. Campbell, S. Kim, J.
  Gomez, C-Y. Wan, Z. Turanyi, A. Valko, "Cellular
  IP Performance", draft-gomez-cellularip-perf-00.t
  xt, October 1999.
• A. T. Campbell, J. Gomez, S.
  Kim, C-Y. Wan, Z. Turanyi, A. Valko, "Cellular IP
  Performance" Slides of the presentation at IETF,
  Mobile IP WG, Washington, November 1999.