Cellular IP

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					Cellular IP: A new Paradigm in
    Internet Host Mobility

         Venu Pragada
         Abhinav Anand

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

                 Cellular IP
What is Cellular IP ??

        Cellular IP
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

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

• Mobile IP is optimized only for:
  – macro level mobility and
  – relatively slow moving hosts

                    Cellular IP
Mobile IP and Cellular IP

                         Hierarchical Mobility *Cell sizes smaller
                                               *Migration freq faster
                             Management        *User population greater

                                                *Faster & smooth handoff
                                                *Less load on Internet
                                                *Cheap-passive connectivity

           Cellular IP
   Wireless Access network Model
                                                E          G
  Internet with                    C
    Mobile IP                                          D
                  Gateway A                                    F
                     R                      B

                                       Beacon signal

Home agent of MH              MH

                         Cellular IP
       What if MH moves from one Access
               Network to another
                         Current                         Previous
Mobile Node            Foreign Agent                   Foreign Agent            Home Agent       Correspondent node

       New c/o address






                                                                                Binding Update


                *Handoff sequence between two Access Networks
                                                      Cellular IP
         5 key Features of CIP
•   Easy Global Migration
•   Cheap Passive Connectivity
•   Efficient Location Management &
•   Flexible Handoff
•   Simple Memory less Mobile hosts

                   Cellular IP
         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

                         Cellular IP
    Cheap Passive connectivity
• mechanism of keeping track of idle MHs.
• allows max. no users connected to a network
• reduces the network load

                     Cellular IP
  Efficient Location Management
ROUTING            PC                     RC

              1         2          3               4
                                                       Mobile Host
               X               X               X
                        Service Area

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
                            Cellular IP

      Cellular IP
                 Protocol Parameters

      Name                      Meaning                   Typical Value
Route-update-     Maximal inter-arrival time of packets       3 sec
time              updating the Route cache

Route-timeout     Validity of Route cache mappings            9 sec

Paging-update-    Maximal inter-arrival time of packets      3 min
time              updating the Paging cache

Paging-timeout    Validity of Paging cache mappings          9 min

                                Cellular IP
    Different Packet Formats used
•   Data packets
•   Route up-date packets
•   paging up-date packets                      Control Packets

•   paging tear-down packets

*All the control packets have the same format

                              Cellular IP
                Control Packet(s) Format
Is an ICMP packet
                                                        IP header               ICMP message

- source address     : IP of sending MH
- destination addr   : gateway                        8 bit TYPE     8 bit CODE        16 bit CHECKSUM

- type               : cellular IP
- code               : control (eg: route up-date)

                                                     0                 1                2              3
Timestamp            : determines order of pkts      01234567890123456789012345678901
CU                   : currently unused              |                                                   |
                                                     |          Timestamp (64 bits long)                   |
S flag( =1)          : indicates semi-soft handoff   |                                                   |
A Type               : denotes auth. method used     | CU |S| AType | Auth. Length |         CU          |
Auth. Length         : length of authentication      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                     |                                                   |
                                                     |         Authentication (variable length)          |
                                                     |                                                   |
Type                 : type of control information   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                                     |                                                   |
Length               : length of following data      |       Control information (variable length)        |
                                                     |                                                   |
Data                 : determined by Type & Length   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                          Cellular IP
      Beacon Signal Structure
• Transmitted by each BS periodically
• Info carried:
  – CIP network identifier
  – IP address of the GW
  – ID of the paging area

                    Cellular IP
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
  – paging-update messages travel up the GW
  – Nodes with PC updates PC mappings
  – finally GW discards the paging-update packets
                       Cellular IP
      Illustration of Paging
                                            I don’t
                                           have a PC

                          X : from C              X : from G

                                            E                  G
                               C                                        Paging-update
Internet with
  Mobile IP                                   D
                GW   A                                             MH    X
                 R                     B

       Paging-update packets create mappings in PCs

                         Cellular IP
PCs updated for a moving host
                 No change
                 in PC at A

                                                                X : from F
                              X : from C           X : from G   X : from F,G
                                               E                 G       G times out
 Internet with
   Mobile IP                                   D
                 GW       A                                                    X
                  R                        B


                          Cellular IP
Paging packets are routed to the
     mobile host by PCs

                              X : from C           X : from F

                                               E                G
    Internet with
      Mobile IP                                D
                    GW    A                                                  X
                     R                     B

                                                                    MH   X

                         Cellular IP
 Paging & Routing caches
               Paging Caches (PC)              Route Cache (RC)
Refreshed by   All uplink packets              Data and route-update
Updated by     All update packets              Route-update packets

Updated        Moving to a new paging area,    Moving to a new cell,
when           or after paging-update-time     or after route-update-
Scope          Both idle and active MHs        Active MHs

Purpose        Route down-link packets if      Route down-link
               there is no route cache entry   packets

                           Cellular IP
• 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
                     Cellular IP
                 CIP Routing
CIP nodes: need to implement the Up-link
  and Dn-link routing algorithms (only)
Packets routed on a hop-by-hop basis
                                    N O D E

                 Up-link                 Dn-links

How are uplinks configured?
  – by using a simple shortest path algorithm
• Gateway beacon packet are sent

                           Cellular IP
                Uplink Routing
• Packet arriving from a Dn-link first updates RC
  and PC mappings and is then forwarded on Up-
• 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
                        Cellular IP
      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 it’s 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
                    Cellular IP
                         Downlink Routing
 • Packet arriving from the Uplink is assumed to be
   destined to the MH

Pkt from Uplink     Check for valid      no                        no    Broadcast on all links,
                                                  Check for PC
                    mapping in RC                                       except the one it came on

                  Forward it to the
                  Dnlink neighbor                Check for valid   no
                                                                            Packet dropped
                                                 mapping in PC

                                      Downlink routing Mechanism

                                           Cellular IP
          Handoff in Cellular IP

Defn: a change of access point during active data
  transmission or reception .

• Hard Handoff
• Semi Soft Handoff

                         Cellular IP
                      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

                          Cellular IP

                         X : from C           X : from D

                                      X : from D, E

                                 X : from E

                                                  X : from F

                                              E                G
Internet with
  Mobile IP                                   D
                GW   A                                             X
                 R                    B

                     Cellular IP
                  Semi soft Handoff
• Improvement over Hard Handoff ; NO packet loss &
  smooth handoff.
• Trade off: Packets are received in duplication.

• Host’s radio device is capable of listening to two logical
• 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.

                         Cellular IP
             Semi soft handoff contd...
Need for buffering at the cross over point : For smooth handoff
    GW        BS  Crossover pt  GW           BS Crossover point
             OBS                                      2

        Case I                                       OBS
                                        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

                          Cellular IP
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
• After handoff the flag is cleared and all the packets in
  delay device is delivered with no further delaying of

Goals accomplished:
• no packet loss
• smooth handoff
                          Cellular IP
• 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

                          Cellular IP
                 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
                           Cellular IP
                MH implementation contd.
• Mobile host state machine
                              Paging packet arrives

                      idle                             active
      Sending paging update                                Sending route update packets
                              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.
                                     Cellular IP
                  Gateway Schematic
                        IP network

        GW controller          GW packet filter

                                 CIP node

    Three building blocks:
    •CIP node
    •GW packet filter
    •GW controller
                          Cellular IP
                 GW implementation
• CIP node block: the RC and PC are updated by the uplink
• GW filter: reads the destination IP address.
  Case 1: If GW’s address, then forwarded to the GW
  Case II. If not GW’s 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.

                         Cellular IP
                 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

                        Cellular IP
                 Performance contd...
• Test configuration

          host                        router


         BS1                             BS2


                        Cellular IP
                 Performance contd...

• In the testbed the BS are statically assigned frequencies.
• The MH dynamically changes frequency to perform a
• 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.

                          Cellular IP
                       Handoff performance
• MH receives 100 bytes UDP packets at rates of 25 and 50
• MH continually make handoffs between BS every 5 seconds.
                          Packet loss per handoff
                           Hard          Hard       Semi
                           (25pps)       (50pps)    soft(25 &
                                                    50 pps)
                  3        0.2           0.68       0
round trip time
                  43       1.22          2.64       0

                  83       2.21          4.50       0

                               Cellular IP
           Handoff performance contd...

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

                         Cellular IP
    Handoff performance on tcp throughput
                  downlink TCP throughput [kbps)
                                  Hard             Semi soft(1
Number of    0                  1500                1510
per minute   2                  1423                1426
             5                  1120                1350
             20                  966                1300
             60                  519                1036

                             Cellular IP
              Handoff performance contd.
• 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

                          Cellular IP
                  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

• The trade off involved is the cost associated with
  transmitting route update packets for maintaining a higher
  value of timer and reducing paging traffic.

                          Cellular IP
                    Rate of paging traffic to mobile [bps]
                         telnet      telnet      WWW         WWW
                         local       remote      local       remote

Active state   100ms 79              391         118         1507

               1s        2           94          47          438

                                   Cellular IP
             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.

                          Cellular IP

• 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.

                          Cellular IP
                    Scalability contd.

                      throughput [Mbps]
                                  Binary search

             1                         63
of entries   11                        62
in routing   301                       62
             6001                      61
             100001                    60
                         Cellular IP
                   Scalability contd..

• 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.

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

                  Cellular IP
              Ongoing work...

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

                  Cellular IP

•              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.

                                     Cellular IP
                         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.txt, 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.
                                     Cellular IP

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