Cellular IP: A new Paradigm in
Internet Host Mobility
PRESENTED BY
Venu Pragada
Abhinav Anand
Cellular IP
Overview
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•
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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...
because..
• 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
Internet with
Mobile IP
G
C
D
Gateway A
R
F
B
R
Beacon signal
Home agent of MH
MH
Cellular IP
What if MH moves from one Access
Network to another
Current
Foreign Agent
Mobile Node
Previous
Foreign Agent
Home Agent
New c/o address
Registration
Registration
Notification
Packet
Packet
Binding Update
Packet
Packet
Packet
*Handoff sequence between two Access Networks
Cellular IP
Correspondent node
5 key Features of CIP
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•
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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
PAGING &
ROUTING
PC
1
RC
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
PROTOCOL DETAILS
Cellular IP
Protocol Parameters
Name
Route-updatetime
Meaning
Maximal inter-arrival time of packets
updating the Route cache
Route-timeout
Validity of Route cache mappings
9 sec
Paging-updatetime
Maximal inter-arrival time of packets
updating the Paging cache
3 min
Paging-timeout
Validity of Paging cache mappings
9 min
Cellular IP
Typical Value
3 sec
Different Packet Formats used
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•
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Data packets
Route up-date packets
paging up-date packets
paging tear-down packets
*All the control packets have the same format
Cellular IP
Control Packets
Control Packet(s) Format
Is an ICMP packet
IP header
- source address
- destination addr
- type
- code
: IP of sending MH
: gateway
: cellular IP
: control (eg: route up-date)
Timestamp
CU
S flag( =1)
A Type
Auth. Length
: determines order of pkts
: currently unused
: indicates semi-soft handoff
: denotes auth. method used
: length of authentication
Type
Length
Data
: type of control information
: length of following data
: determined by Type & Length
8 bit TYPE
ICMP message
8 bit CODE
16 bit CHECKSUM
Contents
0
1
2
3
01234567890123456789012345678901
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Timestamp (64 bits long)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CU |S| AType | Auth. Length |
CU
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Authentication (variable length)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Control information (variable length)
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
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
Cellular IP
Illustration of Paging
I don’t
have a PC
X : from C
X : from G
E
Internet with
Mobile IP
G
C
GW
R
Paging-update
D
A
F
B
Paging-update packets create mappings in PCs
Cellular IP
MH
X
PCs updated for a moving host
No change
in PC at A
X : from F
X : from C
X : from G
E
Internet with
Mobile IP
X : from F,G
G
G times out
C
GW
R
D
A
X
F
B
MH
Cellular IP
Paging packets are routed to the
mobile host by PCs
X : from C
X : from F
E
Internet with
Mobile IP
G
C
GW
R
D
A
X
F
B
MH
Cellular IP
X
Paging & Routing caches
Paging Caches (PC)
Route Cache (RC)
Refreshed by
All uplink packets
Data and route-update
packets
Updated by
All update packets
Route-update packets
Updated
when
Moving to a new paging area,
or after paging-update-time
Scope
Both idle and active MHs
Moving to a new cell,
or after route-updatetime
Active MHs
Purpose
Route down-link packets if
there is no route cache entry
Route down-link
packets
Cellular IP
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
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
GW
Dn-links
Up-link
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 Uplink
• 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
mapping in RC
Check for PC
no
Broadcast on all links,
except the one it came on
yes
yes
Forward it to the
Dnlink neighbor
no
Check for valid
mapping in PC
Downlink routing Mechanism
Cellular IP
no
Packet dropped
Handoff in Cellular IP
Defn: a change of access point during active data
transmission or reception .
Types:
• 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
tolerated.
Cellular IP
Handoff
X : from D
X : from C
X : from D, E
X : from E
X : from F
E
Internet with
Mobile IP
G
C
GW
R
D
A
F
B
Cellular IP
X
Semi soft Handoff
• Improvement over Hard Handoff ; NO packet loss &
smooth handoff.
• Trade off: Packets are received in duplication.
Mechanism:
• Host’s 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.
Cellular IP
Semi soft handoff contd...
Need for buffering at the cross over point : For smooth handoff
654
Crossover point
BS
Crossover
pt
GW
BS
GW
3
NBS
2
OBS
1
NBS
Case I
Case II
OBS
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
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
Cellular IP
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
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
machine.
Cellular IP
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.
Cellular IP
Gateway Schematic
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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
packets
• GW filter: reads the destination IP address.
Case 1: If GW’s address, then forwarded to the GW
controller.
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
hardware.
Cellular IP
Performance contd...
• Test configuration
host
router
GW
BS1
BS2
MH
Cellular IP
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.
Cellular IP
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)
Hard
(25pps)
Hard
(50pps)
Semi
soft(25 &
50 pps)
3
0.2
0.68
0
43
1.22
2.64
0
83
2.21
4.50
0
Cellular IP
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.
Cellular IP
Handoff performance on tcp throughput
downlink TCP throughput [kbps)
Hard
Number of
handoffs
per minute
Semi soft(1
buffer)
0
1500
1510
2
1423
1426
5
1120
1350
20
966
1300
60
519
1036
Cellular IP
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.
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
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.
Cellular IP
Rate of paging traffic to mobile [bps]
telnet
local
Active state
timeout
telnet
remote
WWW
local
WWW
remote
100ms 79
391
118
1507
1s
94
47
438
2
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
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.
Cellular IP
Scalability contd.
throughput [Mbps]
Binary search
Number
of entries
in routing
cache
1
63
11
62
301
62
6001
61
100001
60
Cellular IP
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.
Cellular IP
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
Cellular IP
Ongoing work...
• Authentication information in the control
ICMP packets.(dealing security issues)
• Providing QOS.(in terms of differentiated
services)
Cellular IP
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, draftvalko-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-ietfmobileip-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