C e l l u l a r I P

Cellular IP: A new Paradigm in Internet Host Mobility

P R E S E N T E D B Y

Venu Pragada

Abhinav Anand

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Overview

• Introduction

• Cellular IP & Mobile IP

• Paging

• Routing

• Handoff

• Performance

• Summary

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What is Cellular IP ??

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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

Hierarchical Mobility Management

*Cell sizes smaller*Migration freq faster*User population greater

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

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Wireless Access network Model

MH

B

DInternet with

Mobile IP

R

R

A

CE

F

G

Home agent of MH

Gateway

Beacon signal

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What if MH moves from one Access Network to another

Mobile NodeCurrent

Foreign AgentPrevious

Foreign Agent Home Agent Correspondent node

New c/o address

Registration

Notification

Registration

Packet

Packet

Packet Binding Update

Packet

Packet

*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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Efficient Location Management

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

X XX

PC RC

Service Area

Mobile Host1 2 3 4

PAGING &ROUTING

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PROTOCOL DETAILS

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Protocol Parameters

Name Meaning Typical ValueRoute-update-time

Maximal inter-arrival time of packetsupdating the Route cache

3 sec

Route-timeout Validity of Route cache mappings 9 sec

Paging-update-time

Maximal inter-arrival time of packetsupdating the Paging cache

3 min

Paging-timeout Validity of Paging cache mappings 9 min

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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) FormatIs 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

IP header ICMP message

Contents

8 bit CODE8 bit TYPE 16 bit CHECKSUM

0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Timestamp (64 bits long) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CU |S| AType | Auth. Length | CU | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Authentication (variable length) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Control information (variable 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

MHB

D

R

A

C

E

F

G

Internet withMobile IP

GW X

Paging-update packets create mappings in PCs

X : from GX : from C

Paging-update

I don’thave a PC

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PCs updated for a moving host

X : from GX : from C

B

D

R

A

C

E

F

G

Internet withMobile IP

GW X

X : from F

X : from F,G

G times out

MH

No change in PC at A

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X : from FX : from C

B

D

R

A

C

E

F

G

Internet withMobile IP

GW

MH X

Paging packets are routed to the mobile host by PCs

X

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Paging & Routing caches

Paging Caches (PC) Route Cache (RC)

Refreshed by All uplink packets Data and route-updatepackets

Updated by All update packets Route-update packets

Updatedwhen

Moving to a new paging area,or after paging-update-time

Moving to a new cell,or after route-update-time

Scope Both idle and active MHs Active MHs

Purpose Route down-link packets ifthere is no route cache entry

Route down-linkpackets

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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 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

CIP Routing

Up-link Dn-links

N O D E

GW

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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 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

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Downlink Routing• Packet arriving from the Uplink is assumed to be

destined to the MH

Broadcast on all links, except the one it came on

Check for valid mapping in RC

Check for PC

yes

Check for valid mapping in PC

Packet dropped

Forward it to the Dnlink neighbor noyes

no no

yes

Pkt from Uplink

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

X : from E

X : from C

E

B

D

R

A

C

F

G

Internet withMobile IP

GW X

X : from F

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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.

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Semi soft handoff contd...Need for buffering at the cross over point :

GW BS

NBS

OBS

GW BS

OBS

NBS

Case I Case II

6 5 4

3

2

1

For smooth handoff

Depending on the network topology the time to transmit packets From the cross over point to the new BS and old BS will differ

Crossover point Crossover pt

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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

idle active

Sending paging update

Paging packet arrives

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.

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Gateway Schematic

GW controller

CIP node

GW packet filter

IP network

•

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 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.

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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

GW

BS2BS1

host router

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)

Hard(25pps)

Hard(50pps)

Semisoft(25 &50 pps)

3 0.2 0.68 0

43 1.22 2.64 0

83 2.21 4.50 0

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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

Hard Semi soft(1buffer)

0 1500 1510

2 1423 1426

5 1120 1350

20 966 1300

60 519 1036

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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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telnetlocal

telnetremote

WWWlocal

WWWremote

100ms 79 391 118 1507

1s 2 94 47 438

Rate of paging traffic to mobile [bps]

Active statetimeout

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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

Binary search

1 63

11 62

301 62

6001 61

100001 60

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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.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.