Transcript Sample

Mobile Computing
Gihwan Cho
[email protected]
Distributed Computing Lab.
1
2001 Fall
Mobile Computing
Content

Getting start



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
distributed computing, what means for MC?
Internet protocol, and its considerations for MC
Next generation Internet
Cellular technology overview
Internet host mobility

INTERNET
routing optimization
Distributed Computing Lab.
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2001 Fall
Mobile Computing
Distributed Computing (I)

What’s distributed computing? by Donovan
A computing paradigm which is provided by a collection of
computers connected by a communications subnet and logically
integrated in varying degrees by a distributed operating system
and/or distributed database system on purpose to resolve a task
co-operatively


Each node has autonomous mechanisms which also
coordinate their operations through a global mechanism
Background


price vs. performance revolution in computer hardware
cost effective and efficient communication subnets
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Mobile Computing
Distributed Computing (II)

Why distributed computing? by Donovan


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
Technical Aims

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
distributed nature of real world
equipment cost
user know-how and control
flexibility and configurability
etc.
resource sharing
location transparency
Models

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system : client-server
programming : RPC (Remote Procedure Call), CORBA
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Mobile Computing
Distributed Computing (III)

Transparencies

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Advantages

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good performance, reliability, resource sharing and
extensibility...
Application Spectrum
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location, execution, device, program code ...
e-mail ... command & control ... resource sharing ...
Using Fields
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banking, university computing, factory, office automation ...
Distributed Computing Lab.
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2001 Fall
Mobile Computing
OS Perspectives

NOS (Network OS) vs. DOS (Distributed OS)
Host 1
Host 2
Host 3
Host 4
NOS
NOS
NOS
NOS
Unix
Ultrix
VMS
OS/2
Host 1
Host 2
Host 3
Host 4
Mach
Mach
Distributed Computing Lab.
Mach
Mach
6
DOS Examples :
V system, Eden, Amoeba
Locus, Mach, Spring...
2001 Fall
Mobile Computing
Multiprocessor System vs.
Distributed System

Tightly-coupled vs. Loosely-coupled
A Computer
Processor
Shared I/O
Devices
Memory &
I/O Device
Processor
Shared Memory
Computer
Computer
Memory &
I/O Device
Network
Memory &
I/O Device
Computer
Distributed Computing Lab.
Computer
7
2001 Fall
Memory &
I/O Device
Mobile Computing
Why should be Distributed
Algorithms changed?

Underlying network structure changes with host’s
moving

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Mobile hosts may disconnect or doze off!

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no more logical structure of infrastructure can be utilized
whenever an algorithm tries to refer overall structure, a physical
structure which reflects current situation should be repeatedly
reconstructed, and then convert it to a logical structure
communication costs are no longer the same for all hosts in a
logical subnet (source host would be still keep moving)
offload and/or download
Broadcast communication is available for a group of
hosts using only one transmission
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Mobile Computing
Ex) Distributed Mutual Exclusion

Lamports Algorithm
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each host maintains a logical clock
each host maintains a request queue that contains
messages in increasing order of timestamps
host hj requires a resource by sending a timestamped
request message to all others and inserts it into its queue.
Each host which gets this send a timestamped reply
message, and inserts this request into its queue
hj can access the resource when its request is at the head of
the queue, and it has received replies from all other hosts
with higher timestamps
when it is done with the resource, it sends a release
message to all others. The recipients delete the request from
their queues
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Ex) Distributed Mutual Exclusion
(Suppl. -1)
Enters
critical
region
8
{0, 8}
0
8
1
8
12
12
{0, 8}
0
OK
2
1
12
{0, 8}
{2,12}
{2,12}
OK
OK
OK
{2,12}
0
2
1
2
{0, 8}
{2,12}
{2,12}
{2,12}
Make a
Decision
Enters
critical
region
{host id, timestamp}
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Mobile Computing
What problems and what should be
changed?
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Problems

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high search costs for all MH - MH messages
all hosts required to participate with running the algorithm, so
no doze or disconnect can be allowed
data structures need to be maintained at the MHs (with lots of
messages exchanged), so higher power usage
The algorithm be possibly changed as:

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only MA participates in the coordination (Indirect model). An MA
treats all requests from MHs within its cell as if they were its
own requests
an MH simply initiates the process by sending a init_req()
message to the MA. The MA then processes, waits and
maintains the request on behalf of the MH
when this virtual request is ready for execution, the MA sends a
grant_req() message to the MH
the MH sends a rel_req() when it is done, the MA then sends a
release message to all others
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Mobile Computing
The Internet (I)

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The collection of networks and gateways that use the
TCP/IP protocol suite and function as a single,
cooperative virtual network
Virtual Circuit
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connection set up at the beginning
connection remains throughout
reliable Communications
ex) TCP
Datagram
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each datagram routed separately
each contains an address
no guarantee of delivery
ex) IP and UDP
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Mobile Computing
The Internet (II)


The TCP/IP Stack
Host A
Host B
Application
Application
Uses TCP/IP
Services
Virtual Circuit
TCP
Gateway G
TCP
IP
IP
IP
Network
Interface
Network
Interface
Network
Interface
Hardware
Hardware
Hardware
Routes
Datagrams
Well-known TCP/IP services

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mail (SMTP), ftp, rlogin, telnet, rcp, X window clients ...
rpc, rfs, nfs, rwho ...
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Mobile Computing
Internetworking with TCP/IP
Distributed Computing Lab.
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Mobile Computing
IP(Internet Protocol)

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A user thinks of an internet as a single virtual network
that interconnects all hosts, and through which
communication is possible; its underlying hardware is
both hidden and irrelevant
IP provides three important definitions

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defines the basic unit of data transfer
performs the routing function
includes a set of rules that embody the idea of unreliable
packet delivery, such as packet processing, error control
Connectionless delivery service
:= unreliable, best-effort, connectionless
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Mobile Computing
Internet Addresses (I)
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Universal communication service requires a globally
accepted method of identifying each computer that
attaches to it
Three host identifiers
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names : what object is (a location independent characteristic of
a network entity)
addresses : where it is (a function of the location of the
destination)
routes : how to get there (something that depends on both the
source and destination)
Internet address was made to standardize on compact,
binary addresses that make computations such as the
selection of a route efficient
Distributed Computing Lab.
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Mobile Computing
Internet Addresses (II)
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Each host on a TCP/IP internet is assigned a unique
32-bit internet address that is used in all communication
with that host
IP address is a pair (netid, hostid), where netid
identifies a network, and hostid identifies a host on that
network
Because IP addresses encode both a network and a
host on that network, they do not specify an individual
computer, but a connection to a network
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Mobile Computing
Internet Address (III)

consists of four “Octets” (8 bit chunks)
0
8
16
24
31
Class A
0 networkid
hostid
Class B
10
Class C
110
networkid
Class D
1110
multicast address
224-239.*.*.*
Class E
11110
reserved for future use
240-254.*.*.*
networkid
0-127.*.*.*
hostid
128-191.*.*.*
hostid
192-223.*.*.*
** hostid (or all bits) set to 1 : broadcast
** networkid (or hostid) set to 0 : means “this”
Distributed Computing Lab.
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Mobile Computing
IP Address (Considerations)
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With current IP address,
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IP datagrams clearly are routed based on the networkid (and
subnetid) in the IP address
networkid (and subnetid) do not specify an individual machine,
but a connection to a network
all hosts having addresses with the same networkid (and
subnetid) are connected to the same physical network
When we consider host mobility,

“If a host moves from one network to another, its IP address
must change.” - D. E. Comer, Internetworking with TCP/IP, pp 65
4.8 weaknesses in Internet Addressing


how it can be resolved?
in addition, It may need another facility to trace the physical
location of moving host in order to find out the host’s current
location
Distributed Computing Lab.
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Mobile Computing
Internet Routing

Note : the hierarchical structure of the IP address aims to
scale internetworking well by providing the abstraction of
address clustering. This implies to the routing domain as:

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allows routers to keep minimal routing information, so a gateway
needs to maintain networkid, not full IP address only specifies
one step along the path to a destination network
make their routing decisions efficiently by allowing a gateway to
use default routes to possible distant destinations
permits some degree of autonomy to organizations to do their
own internal routing structure (with subnetting)
Table-driven IP routing
Basic principles

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each router announces which networks it can reach
each router remembers the other’s announcements
remembered routes time out to delete stale routes
Distributed Computing Lab.
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Mobile Computing
Routing Algorithm
Route_IP_Datagram(datagram, routing_table)
Extract destination IP address, ID, from datagram Compute IP address
of destination network, IN
if IN matches any directly connected network address
send datagram to destination over that network;
else if ID appears as a host-specific route
route datagram as specified in the table;
else if IN appears in routing table
route datagram as specified in the table;
else if a default route has been specified
route datagram to the default gateway;
else declare a routing error;
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Mobile Computing
Internet Routing (Considerations)
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The Internet topology is rapidly growing or changing
In this situation, in order to provide an Internet-wide
routing service, the Internet uses an architectural
approach that allows groups to manage local gateway
autonomously, adding new network interconnections
and routes without changing distant gateways
In the mobile computing model, a packet routing path
bound for a mobile host is mainly decided on the fixed
network
Current IP routing mechanisms cannot decouple the
host tracing function from an IP address
The Internet protocol needs another facility to trace a
moving host, and then to deliver the packets following
the host based on the location information
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Mobile Computing
Which the Internet layer should take
charge of host mobility? (I)

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If applications do this, each time an application wants to
communicate with another, it must obtain the current
address of its peer. Moreover, it is impossible to provide
on-line moving without modifying the application
program itself, so as to re-establish the existing session
with the new location
If the transport layer do this, it does not see the notion of
host with the same reason as above. Thus, host mobility
causes increased delays and packet losses. TCP
interprets these as signs of network congestion - so, it
throttle its transmissions, further degrading performance
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Mobile Computing
Which the Internet layer should take
charge of host mobility? (II)


The internet layer hides the different hardware address,
and resolves the exact location of a host on an
internetworking its own addressing and routing facilities.
Therefore, it could give to higher level protocols the
abstraction that the network address remains
unchanged
If the network interface layer do this, there is no way to
maintain host location in the network (with physical
address). Also, a bridge-based routing scheme is not
enough (too restricted). However, it could have some
useful features, such as monitoring
connection/disconnection to/from communication
medium, then reporting it to higher layer
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The Internet Protocol (Considerations, I)

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When the source host specifies the destination host's
address, a binding between the address and its route is
established, and thereafter no re-evaluation of the
binding takes place : in a static network, there is little
re-evaluation of the binding
In a mobile computing environment, mobile hosts are
expected to move from time to time, and in a way that
necessitates changing their address - moves to other
locations in different parts of the hierarchy
In order to re-evaluate of the binding at times, the IPbased approach for supporting host mobility can be
formalized as a location problem
Distributed Computing Lab.
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Mobile Computing
The Internet Protocol (Considerations, II)

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The location domain includes an addressing
convention for identifying mobile hosts, and
acquisition and/or preservation of locale information
In addition, it is inevitable that the routing scheme must
be re-structured as well, according to the address
convention adopted
The location issue seems similar with the mapping
elaboration between name and address, that is, the
mapping what to where is changed to the one knownwhere to current-where
Distributed Computing Lab.
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Mobile Computing
Three Addressing Schemes for host
mobility

PAS (Permanent IP-Address Scheme)

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each MH has a permanent IP address from the initial (home)
administration address space
whenever an MH moves, some hosts or routers (at least the
home MA) are informed of the current MA’s address
the hosts or routers forward packets, which are passing through
them, to the current MA using the location information recorded
Internet
Packets
from the
Internet
MA a
{MH a, *}
MA k
{MH k, MA s}
MH a
Distributed Computing Lab.
MA p
MA s
{MH k, #}
MH k
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Host Moving
2001 Fall
Mobile Computing
Three Addressing Schemes (Cont.)

TAS (Temporary IP-Address Scheme)

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a temporary address is assigned dynamically every time a host
connects with an MA
the location information is managed by supporting a directory or
the source host broadcasts a query to find the current location
the source host directly routes packets using the location
information obtained
Who serves
MH k at a
moment?
MA a
Internet
MA k
That’s me!
MA p
{MH k, -}
MH a
Distributed Computing Lab.
MA s
{MH k, MH t}
MH k
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Host Moving
2001 Fall
Mobile Computing
Three Addressing Schemes (Cont.)
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ENS (Embedded Network Scheme)
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each host has a permanent IP-add. and an embedded network
add. which consists of the current MA’s add. and a temp. add.
the gateways maintain a mapping between IP-addresses and the
embedded network address
the gateways use the mapping to forward any on-going packets
Internet
{MH k,
(MA s,MH t)}
MA a
{MH k,
(MA s,MH t)}
MH a
Distributed Computing Lab.
MA k
Notify MH k’s
address to the
Internet
MA p
MA s
{MH k,
(MA s,MH t)}
MH k
29
Host Moving
2001 Fall
Mobile Computing
Location Considerations
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A routing decision must be made based on the location
information that is available - packet routing efficiency
depends critically on how effectively a packet comes
across its current address
The packet routing paths that go with host mobility
depend decisively on the somewhere which holds the
information for a mobile host's physical locator
A trade-off in devising a location scheme : excessive
location preservation can be wasteful of network
resource, whilst insufficient location propagation leads
to inefficient routing
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Common Approach
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Addressing : uses two IP addresses, that is, a
separation the dual nature of an IP address into a
logical identifier which is the permanent (home) IP
address of the host, and a physical locator which is a
forwarding (current) IP address
Routing : uses tunneling technique, that is, a forwarding
mechanism in association with location caches held
around the network
The arguments that host mobility support system now
faces are


how to distribute location information,
and then how to utilize the information effectively, in order
efficiently to deliver packets to moving destinations whilst still
limiting costly location updates as much as possible
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Content

Getting start





distributed computing, what means for MC?
Internet protocol, and its considerations for MC
Next generation Internet
Cellular technology overview
Internet host mobility

routing optimization
Distributed Computing Lab.
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2001 Fall
Mobile Computing
The Internet Protocol



Internet is not a physical network, but it is a method
of internetworking physical networks and a set of
conventions for using networks that allow the
computers they reach to Internet
The collection of networks and gateways that use the
TCP/IP protocol suite and that function as a single,
cooperative virtual network
Network level interconnection scheme
(as opposed to application level interconnection)


connectionless packet delivery service
reliable stream transport service
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Mobile Computing
National Information Infrastructure
"The NII will provide all Americans with the information
they need, when they need it and where they need it,
at an affordable cost."
Dr. Jack Gibbons, Presidential Science Advisor
ARPA HPCC Symposium, 15 March 1994
"Hundreds of different networks, run by different
companies and using different technologies, all
connected together in a giant 'network of networks,'
providing telephone and interactive digital video to
almost every American."
Vice President Al Gore, Jr.
Address to the ITU, 21 March 1994
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Next Generation Internet (NGI) (I)

The NGI initiative is a multi-agency federal research
and development program, that aims to:
http://www.ngi.gov
 new technologies and services : sponsor research and
development in new networking technologies and services in
support of the high performance applications requirements
 testbed(s) : build a high performance network infrastructure
(100 to 1,000 times faster end-to-end than today's Internet)
in support of both network research and science applications
research
 applications: support demonstration of next generation
applications requiring advanced networking technologies

It began October 1, 1997, with the following
participating agencies: DARPA, NASA, NIH, NIST,
NSF, (DE)
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Internet 2

UCAID (University Corporation for Advanced Internet
Development) is supported by over 175 member
organizations. universities, corporations have joined to
advance networking in higher education
http://www.ucaid.edu

Internet 2 is a collaborative project by over 120 U.S.
research universities engaged in the major challenges
facing the next generation of university networks
http://www.internet2.edu

Abilene is a project to develop a nationwide advanced
network to serve as backbone network for the Internet2
http://www.ucaid.edu/html/abilene.html
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Distributed Computing Lab.
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Mobile Computing
IP Next Generation (IPng)

IPng is an IETF WG intended to provide IPv6 which is
designed to be an evolutionary step from IPv4
http://www.ietf.org/html.charters/ipngwg-charter.html
http://playground.sun.com/pub/ipng/html/ipng-main.html

It’s motivations are:




limited number of available addresses
difficulty in managing routing tables
need to support high performance network (e.g. ATM), at the
same time, low bandwidth network (e.g. wireless)
6Bone is the IPv6 backbone that was set up to assist
in the evolution of IPv6 in the Internet
http://www.6bone.net/
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6Bone
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IP version 6 (I)

IPv6 is the formal name of the protocol recommended by
the IETF’ IPng group, its objectives are:
The Recommendation for the IP Next Generation Protocol, RFC 1752, Jan.,
1995
Internet Protocol, Version 6 (IPv6) Specification, Internet Draft, Nov., 1997




support large global internetwork
support new low-end Internet devices
(PDAs, mobile computers, consumers, devices)
support the networked multimedia services
Implementations

Apple, BSDI,Bull, Dassault, Digital, Epilogue, FTP Software, IBM,
INRIA, Linux, Mentat, Microsoft, Novell, NRL, NTHU, Pacific
Softworks, Process Software, SICS, SCO, Siemens Nixdorf,
Silicon Graphics, Sun, UNH and WIDE
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The Challenges from IPv4


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Plenty of addresses
Reduced administrative overhead
Opportunity for better routing
Support for address renumbering
Improved header processing
Reasonable security
Support for host mobility
QoS control capability
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IPv6 Design (I) : Addressing


Two-level structure of the IPv4 address, what?
Address paces are:
340,282,366,920,938,463,463,374,607,431,768,211,456 (2^^96 times that of IPv4)

An address is represented as x:x:x:x:x:x:x:x (x is 16 bit
long) (ex, fedc:ba45:00d4:4354:f345:ad23:546d:232c)




compression 0’s (ex, ff01:0:0:0:0:0:0:43 => ff01::43)
combination between the IPv4 address and IPv6’s one
 IPv4 compatible address => ::IPv4 address
(eg. x:x:x:x:x:x:d.d.d.d)
 IPv4 mapped address => ::ffff:IPv4 address
IPv6 addresses are identifiers for interfaces, not nodes
A single interface may be assigned multiple IPv6
addresses of any type, that is, unicast, anycast, multicast
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IPv6 Addressing (Cont’)

Unicast :

provider based address :1/8 fraction of address space
010

REGISTRY PROVIDER SUBSCRIBER SUBNET INTERFACE
link (or site) local use address 1/1024 fraction
1111111010
0
INTERFACE
1111111011
0
SUBNET INTERFACE


anycast : use unicast address format
multicast
(4)
(4)
Usually ID
IEEE802 48 bit address
GROUP
11111111 FLGS SCOP
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What’s in an IPv6 Datagram
0
15
Vers
Prior
31
Flow Level
Payload Length
Next Header
Hop Limit
Source Address (128)
10 X 32 bit
= 40 octets
Destination Address (128)
Next Header Header Length
Hop-by-hop option (variable)
Next Header Header Length
Other option headers …
IP payload : TCP header (variable)
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IPv6 Design (II) : Performance

To meet performance requirement on the NGI



reduce the number of fields in the datagram : options are
placed in separate optional headers, and most of these
optional header are not examined on in-between routers
fix the length of header : IPv6 extension headers act as a
separated extension headers with arbitrary length
packet fragmentation is not performed by IPv6 routers,
but by the source host only
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IPv6 Header Extensions

Currently defined extension headers (in sequence)






hop-by-hop : hop by hop processing on the router
routing : similar to the source record route for IPv4
fragment : fragmentation / reassembly
authentication : packet integrity and authentication
encapsulating : privacy
destination : processed at the final destination only
- jumbo payload option : 2**32 octets
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IPv6 Design (III) : QoS Capabilities


QoS is controlled by the flow label and the priority
field
Priority (4bit)


congestion controlled traffic (0 ~ 7), such as back-off
internet control traffic; snmp
interactive traffic; on-line user-to-host
attended bulk traffic; ftp, http
unattended data transfer; email
filler traffic; USENET
uncharacterized : no priority
non-congestion controlled traffic (8 ~ 15) : constant (at least
smooth) data rate and delivery delay from most willing to
discard(8) to least willing to discard(15)
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IPv6 QoS Capabilities (Cont’)


Flow is a sequence of packets sent from a source
to a destination: a flow is uniquely identified by the
combination of a source address and a 24-bit flow
level
Flow label is used by a source to label a flow for
which it requests special handling by the
intervening IPv6 routers, such as real-time service



the nature of special handling might be conveyed to the
routers by a control protocol, such as a resource
reservation protocol, before the source start to send
a router can decide how to route and process these packet
by simply looking up the flow label in a table, without
examining the rest of the header
the flow level is chosen randomly and uniformly
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IPv6 Design (IV) : Routing

Almost identical to IPv4, but new routing
functionality:




provider selection (based on policy, performance, cost)
host mobility (route to current location)
auto-readdressing (route to new address)
These functionalities are achieved by creating
sequences of IPv6 addresses using ipng routing
option, which is very similar to IPv4’s LSRR option
(cf. home-based tunneling)
P1
H1
P2
H2
P3
Distributed Computing Lab.
50
2001 Fall
Mobile Computing
IPv6 Design (V) : Security

Application specific security mechanism on IPv4, such
as privacy enhanced mail, secure http, what
problems?
An Overview of a security architecture, RFC 1825, Aug., 1995
Description of a packet authentication extension to IP, RFC 1826,
Aug., 1995

IP level security could ensure the interoperability
between the secured packet and unsecured packet


it has two functional areas : authentication and privacy
Support for security features could be implemented
both, but mandatory for IPv6 and optional for IPv4
Distributed Computing Lab.
51
2001 Fall
Mobile Computing
IPv6 Transition

ngtrans is an IETF WG which is responsible for the
transition of the Internet from IPv4 to IPv6
http://www.ietf.org/html.charters/ngtrans-charter.html

Aims to allow IPv6 and IPv4 hosts to interoperate



incremental upgrade and deployment (one by one
installation)
minimal upgrade dependencies (DNS only for IPv6
address record)
easy addressing (inter-use two types addresses)
Distributed Computing Lab.
52
2001 Fall
Mobile Computing
IPv6 Transition (Cont’)

Step 1 : IPv4 >> IPv6 (number of hosts)

dual stack model
Application
TCP, UDP
IPv6
IPv4
Ethernet, FDDI, etc.

Step 2 : IPv4 ::~ IPv6


tunneling IPv6 packet within IPv4 header
Step 3 : IPv4 << IPv6

header translation
Distributed Computing Lab.
53
2001 Fall
Mobile Computing
21 Century Applications

Enabling applications:






collaboration technologies
digital libraries
distributed computing
privacy and security
remote operation and simulation
Disciplinary applications:







basic science
crisis management
education
the environment
federal information services
health care
manufacturing
Distributed Computing Lab.
54
2001 Fall
Mobile Computing
21 Century Applications (Cont’)
Network Uses
Application Examples
Rqmts
Teleoperation
Telemedicine, Distance Learning,
Telescience
Battlefield awareness, Virtual
Aerospace environment,
Engineering
Chesapeake Bay virtual
environment, Material collaboratory
Intelligent Assistants, Optical Nets,
Systems of systems
Genome Database, Patient records,
Earth and Space science
Aerodynamics, astrophysics, Global
Change, Stockpile Stewardship
1Gbps
Virtual Reality,
Visualization
Collaboratories
Network Research
Distributed Data and
Digital Libraries
Computation
Distributed Computing Lab.
55
2001 Fall
155Mbps1Gbps
155Mbps/l
ink
10Gbps
1Gbps
2.4Gbps
Mobile Computing
Content

Getting start





distributed computing, what means for MC?
Internet protocol, and its considerations for MC
Next generation Internet
Cellular technology overview
Internet host mobility

routing optimization
Distributed Computing Lab.
56
2001 Fall
Mobile Computing
The Vision
The Vision Revisited
"It is dangerous to put limits on
wireless."
Guglielmo Marconi (1932)
The Vision
People and their machines should be able to access information and
communicate with each other easily and securely, in any medium or
combination of media-voice, data, image, video, or multimedia-any time,
anywhere, in a timely, cost-effective way
Dr. George H. Heilmeier
IEEE Communication Mag.
October 1992
Distributed Computing Lab.
57
2001 Fall
Mobile Computing
Wireless Overlays
(borrowed from Kerz’s talk)
Distributed Computing Lab.
58
2001 Fall
Mobile Computing
Overview of Cellular Systems


The wireless communication of the future will utilize
cellular techniques
Why use cellular technology?




limited spectrum available
demand-assigned channel
allows frequency reuse
Three basic methods by which cellular carriers could
make use of the bandwidth that they are allowed



FDMA (Frequency Division Multiple Access)
TDMA (Time Division Multiple Access)
CDMA (Code Division Multiple Access)
Distributed Computing Lab.
59
2001 Fall
Mobile Computing
Three Multiple Access Methods
Amplitude
FDMA
Time
1
2
1
2
F1
F2
F’1
F’2
Amplitude
Frequency
Amplitude
TDMA
CDMA
Time
1
F1
2
3
1
1
F2
2
3
Time
1
1
2
3
F’1
Distributed Computing Lab.
1
1
F’2
2
3
1
1
Frequency
60
2
1
3
4
F1
2001 Fall
2
3
4
F’1
Frequency
Mobile Computing
Cellular Principle




The cellular technology increases the network
capacity. It relies on the concept of concurrency
Concurrency is created by reusing channels in
different cells; i.e., channel/reuse. This is allows
increase in total capacity of the system (i.e., the
number of supported users)
The total coverage area is divided into cells. In each
cell, only a subset of all the channels is available
All the channels are partitioned into sets, which are
assigned to cells. The same set if assigned to two
cells that are geographically distant “enough,” so that
the interference between the co-channel cells is very
small.
Distributed Computing Lab.
61
2001 Fall
Mobile Computing
Cellular Principle (Cont’)
Distributed Computing Lab.
62
2001 Fall
Mobile Computing
Cellular Principle (Cont’)
Distributed Computing Lab.
63
2001 Fall
Mobile Computing
Cellular Network Structure
System
Database
Mobile Terminal
Base
Station
MTSO
Radio Link
Distributed Computing Lab.
Switching&
Control
64
Network
Intelligence
2001 Fall
PSTN
Local
Exchange
Mobile Computing
Cellular Architecture
Distributed Computing Lab.
65
2001 Fall
Mobile Computing
FDMA : AMPS (Advanced Mobile
Phone System)



AMPS provides the basement of cellular technology
The total spectrum is divided into channels; channels
are assigned to users for the duration of a call
Cellular phones use a full-duplex channel


Forward (downlink) channel from BS to MT: 869 to 894 MHz
 FCC (Forward Control Channel) : broadcast channel, used
for subscriber paging and voice channel assignment
 FVC (Forward Voice Channel) : dedicated channel for a
single call
Reverse (Uplink) channel from MT to BS: 824 to 849 MHz
 RCC (Reverse Control Channel) : random access with
sensing provided by FCC
 RVC (Reverse Voice Channel) : dedicated channel for a
single call and paired with the FVC
Distributed Computing Lab.
66
2001 Fall
Mobile Computing
Frequency Allocation ( in Korea)
AM Radio
526.5kHz
851
FM
88MHz 108
Cellular
869MHz
TV
894
Distributed Computing Lab.
470MHz
CT-2
910MHz
914
PCS
Cellular
752
824MHz
TRS
849
851
866
PCS
1750MHz
1840MHz
1780
1870
67
2001 Fall
Mobile Computing
AMPS (Cont.)

25 MHz is split into channels that are 30 kHz wide
(24 kHz of which is used exclusively for voice)
 channels 800-900 are not used
 832 total number of full-duplex channels includes 21 control
channels and 395 voice channels
824 - 849 MHz
991
...
1023 1
2
869 - 894 MHz
...
799
991
...
Reverse channels

1023 1
2
...
799
Forward channels
416 channels each between RCC (Radio Common Carrier)
and WCC (Wireless Common Carrier)
Distributed Computing Lab.
68
2001 Fall
Mobile Computing
AMPS (Cont.)
824
825
835
991-1023
1-333
A’’
A
845
846.5
849
334-666 667-716 717-799
B
A’
B’
Reverse channels



869
870
880
991-1023
1-333
A’’
A
890
891.5
894
334-666 667-716 717-799
A’
B
B’
Forward channels
416 channels are divided among a number of cells that
are designed so that adjoining cells overlap slightly (59
or 60 channels for each cell)
The number of cells among which all of the channels
are assigned, but none is repeated, is called a group
The configuration would be repeated, reusing the
frequencies, how?
Distributed Computing Lab.
69
2001 Fall
Mobile Computing
Reuse Pattern of 7
{f5}
{f7}
{f6}
{f4}
{f2}
Maximum number of
simultaneous calls =
total number of channels
(e.g., 416)
{f6}
{f3}
{f4}
{f2}
{f1}
{f5}
{f5}
{f7}
{f7}
{f6}
{f3}
{f3}
{f4}
{f2}
3 x 7 x (416 % 7) = 3 x 416
Distributed Computing Lab.
70
2001 Fall
Mobile Computing
Propagation Characteristics

Two different antennas



RSA (Rural Service Area) uses omnidirectional antennas to
cover the maximum amount of area per cell
MSA (Metropolitan Service Area) face with meeting the
demands imposed by a concentrated customer base (120
degrees of a circle)
Capacity : the number of subscribers that may be used





the number of calls placed by the system’s subscribers
the way the calls placed are distributed in time
the average time per call
the amount of frequency reuse utilized
the size of cells
Distributed Computing Lab.
71
2001 Fall
Mobile Computing
Cell Splitting


More capacity vs. more handoff (infrastructure)
Wireless characteristics

partial loss, fading, doppler effect
{f2}
{f2}
{f1}
{f1}
{f3}
{f7}
{f6}
{f7}
{f7}
{f2}
{f6}
{f4}
{f5}
{f2}
{f1}
{f6}
{f3}
{f2}
{f4}
{f5}
{f5}
{f6}
{f3}
{f4}
{f6}
Example:
Cell Radius = 1 mile
number of cells = 32 (48 ch. / cell)
=> 1536 concurrent calls
Distributed Computing Lab.
72
Cell Radius = 0.5 mile
number of cells = 128 (48 ch. /cell)
=> 6144 concurrent calls
2001 Fall
Mobile Computing
Cellular Technology has

Advantages





more capacity
less transmission power
more predictable propagation environment
more robust system
Disadvantages





need more infrastructure (more base-stations)
need network (to interconnect the base-stations)
residual interference
handoffs
“hot sport” in user concentration
Distributed Computing Lab.
73
2001 Fall
Mobile Computing
Handoff

Handoff (U.S. cellular standards) is a procedure of
changing the MT to BS binding from one BS to
another BS, according to the MT’s move
cf) handover(CCITT/CCIR), ALT(Automatic Link Transfer, ANSI)



It procedure provides means for improving the quality
(e.g., RF signal strength) of the received signal, while
the MT moves or when reception conditions change
The trigger for handoff is the RF signal strength falling
below some threshold, and when there is another BS
that can serve the MT with a stronger signal
Soft handoff is a handoff in which the new binding is
completed before the old binding is torn down
Distributed Computing Lab.
74
2001 Fall
Mobile Computing
Handoff (Cont.)

A cell has three distinct regions with different hand-off
circumstances




central region (1) : the area in which a need for hand-off would
be caused by a deep fade
twofold region (2) : two cell overlap
threefold region (3)
Cell 2
Cell 7
When handoffs are
not possible?
3
2
3
3
Cell 6
1
Cell 3
3
2
Cell 5
75
2
Cell 1
2
3
Distributed Computing Lab.
2
2001 Fall
3
2
Cell 4
Mobile Computing
AMPS Hand-off Routine
MR
Cell A (old)
Cell B (new)
MTSO
Talking
Talking
Degradation of corner level (V-Ch, M-wire)
Carrier level check order
To another
cell sites
Carrier level
Check order
Carrier level
Carrier level
Check with RLR
Check with RLR
Level response
Level response
Hand-off message
V-Ch
Audio mute
Carrier off
change to
new V-Ch
Carrier on
at new V-Ch
Hand-off message
10 Kb/s (v-Ch)
Select the
best Cell and
an idle Ch.in the
selected cell
TX-on
SAT-on
Audio mute
ST on (old V-Ch)
ST off
TX off
TX-on (Ch skip)
Old Ch on Hosk
(V-Ch Ch. Completion
E-wire)
TX off
Talking
Distributed Computing Lab.
Change to
new V-Ch
Talking
76
2001 Fall
Mobile Computing
Complexity and Cost of Cellular System

The cost that the consumer sees first



The cost of the network components is an important
consideration for the system operator : the cost of the
system must be justified by increase in capacity


the user likes the idea of getting something for nothing
the provider will more than recoup its expenditure in its service
charges
if the antennas are designed to handle only a sector of a cell,
the cost of the switching equipment becomes higher
The quality of service for cellular system is usually the
percentage of blocked and dropped calls
Distributed Computing Lab.
77
2001 Fall
Mobile Computing
TDMA Techniques



With the proliferation of computers, digital
communication technologies (i.e., DSP) have advanced
rapidly
Allows multiple users to share bandwidth by giving a
slice of time to each user for transmitting and receiving
data
One of the inherent complexities is synchronization


accurate distance and time delay measurements are required in
order to compute the correct transmission time or time advance
But several advantages of using TDMA



burst mode transmission results in lower battery power
consumption
increased number of concurrent users
quality of the voice channel
Distributed Computing Lab.
78
2001 Fall
Mobile Computing
NADC (North American Digital
Cellular )

VSELP (Vector Sum Excited Linear Predictive) CODEC


Dividing channels of the AMPS system into time slots




8kbps
the same 30 kHz channels of AMPS are used, but each
channel is divided into three time slots
Handoff could occur between time slots within the
same channel, in addition to the handoff between
channels
Both the transmitters and receivers become more
complex, as timing circuits are needed to ensure that a
transmitter does not infringe upon another time slot
within the channel
As a result, adding capacity becomes more expensive
for both the cellular carrier and for the user
Distributed Computing Lab.
79
2001 Fall
Mobile Computing
GSM (Group Special Mobile)



Aims to unify the EC by offering a single standard so
that users can use one phone throughout Europe
Designed with the OSI model in mind
125 full-duplex channels for eight users on each
channel




the channel bandwidth is 200 kHz
the data throughput is 270.833 kbps per a channel
in each time slot, 33 kbps are allocated (13 for speech coding
(RELP), and 20 for overhead signaling)
TDMA employs advanced measurement techniques
for determining the link quality and the best cell for
handoff

more expensive equipment and computers for processing
Distributed Computing Lab.
80
2001 Fall
Mobile Computing
CDMA



CDMA allows multiple users to share the same
frequency by multiplexing their transmissions in the
code space
It was envisioned by Qualcomm as a cellular system
to replace the current AMPS, using the same
frequency
Spectrum is divided into a number of 1.25 MHz
channels



for each channel, there are 64 orthogonal codes
CELP (Code Excited Linear Predictive) for speech coding with
variable rate, 8.55 kbps max, 3.9 kbps avrage
Each channel is potentially shared by a number of
users that all use a different code to modulate data in
a spread spectrum transmission
Distributed Computing Lab.
81
2001 Fall
Mobile Computing
CDMA (Cont.)

CDMA paradigm shift




multiple users on one frequency
channel is defined by code
capacity limit is soft
Three primary techniques



vocoder (voice compression / decompression)
interleaving (variable data rate)
spectrum spread
Distributed Computing Lab.
82
2001 Fall
Mobile Computing
Comparison of FDMA, TDMA and CDMA




AMPS is by far the cheapest system to construct, build,
operate and use, but it is limited by the number of
users
CDMA is the most complex and costly, but advances in
computer technology will make it more attractive in the
future for the increased capacity and service quality
Intermediated shifting : CDMA is inserted into a portion
of the spectrum and used side-by-side with the AMPS
For 15MHz spectrum allocation
Parameter
Channel BW (MHz)
No. of CHs
Effective CHs
Distributed Computing Lab.
Voice calls/CH
83
AMPS
GSM
CDMA
0.03
0.20
1.25
500
75
11
500/7
75/3
11/1
1
2001 Fall
7.25
25~40+
Mobile Computing
PCS (Personal Communications Systems)


In the narrow sense “a mobile telephone service that is
associated with a person instead of a place or a
vehicle”
Basic requirements




users must be allowed to make calls wherever they are
the service must be reliable and of good quality
it must offer a range of service that the users need, such as
voice, data, fax, paging and even video
In the operational sense “ the type of wireless
communication that implements new digital
microcellular and provides personal services”
Distributed Computing Lab.
84
2001 Fall
Mobile Computing
PCS (Personal Communications Systems)

The principal idea behind PCS



each individual user have a unique identification number
using the number, a person can be reached at any time and at
any place, even if a caller does not know the location of the
called one
PCS essentially replicates that of a cellular network
with one major difference, that is, microcellular
architecture



smaller size of cells and large number of base stations
numerous handoffs between cells for moving callers
large investment to setting up a PCS service
Distributed Computing Lab.
85
2001 Fall
Mobile Computing
Wireless Roaming Environment


Heterogeneous (different technology)
Unified by Internet Protocol
Satellite
Wireless WAN (GPRS, CDMA 1x, IMT2000…)
Wired or Wireless LAN
Internet
Picocell MAN
(Cellular + LAN)
(Bluetooth, IEEE802.11…)
Distributed Computing Lab.
86
2001 Fall
Mobile Computing
Wireless Roaming Dimension
(IMT2000, IMT2000)
(WLAN, WLAN)
(LAN, IMT2000)
Internet
IMT2000
(WLAN, IMT2000)
LAN
WLAN
(LAN, WLAN)
Distributed Computing Lab.
87
2001 Fall
Mobile Computing
Content

Getting start





distributed computing, what means for MC?
Internet protocol, and its considerations for MC
Next generation Internet
Cellular technology overview
Internet host mobility

routing optimization
Distributed Computing Lab.
88
2001 Fall
Mobile Computing
Internet Host Mobility Support

Five major proposals






Mobile*IP (Columbia University)
Virtual Internet Protocol (Sony)
Multiple Address Approach (Matsushita)
IP Option Approach (IBM, CMU)
IP Mobility Support (IETF)
Main points of view in this lecture



addressing conventions
location details
routing effectiveness
Distributed Computing Lab.
89
2001 Fall
Mobile Computing
Proposal 1: Mobile*IP


Designed and implemented by John Ioannidis
(Columbia Univ.)
Aims



The setup




allows mobile hosts to keep their address even if it moves
decouples mobile host’s routing scheme from the normal IP
routing
mobile Hosts (MHs)
mobile Support Routers (MSRs)
campus : defined by fully-connected MSRs
IP protocols defined


IPIP (IP inside IP)
MICP (Mobile Internetworking Control Protocol)
Distributed Computing Lab.
90
2001 Fall
Mobile Computing
Model

System model
Embedded Network (Campus)
subnet a
Host A
subnet s
subnet k
MSR a
MSR k
MH a
MH k
Distributed Computing Lab.
91
MSR p
MSR s
MH s
2001 Fall
Mobile Computing
Addressing (I)

Based on the embedded network concept





logical ID : embedded address (home address)
physical locator : IP address of the MSR which currently
serves a MH
Embedded network consists of its own hosts and
gateways, and has its own addressing and network
protocol, but uses parts of another existing networks
as its infrastructure (it is called as “local network”)
An embedded address is a two-level construct (m,h),
where m is the network’s identifier and h is the host’s
identifier
Virtual network : a set of subnets which consists of
MSRs and their MHs under an admin. control, and
which therefore share the same m
Distributed Computing Lab.
92
2001 Fall
Mobile Computing
Addressing (II)



For the MHs controlled by a virtual network, only the
home addresses are used - the addresses are
immutable even if the MH moves around
Each MSR maintains the home addresses of MHs
under its control and the IP addresses of MSRs
within the virtual network, and is responsible for lasthop delivery to MHs within its service area
How the home address can be mapped into the
current MSR?
Distributed Computing Lab.
93
2001 Fall
Mobile Computing
Location






Uses a proxy-ARP between MSRs
A source host sends a datagram to its current MSR
If the current MSR does not know which MSR is
currently responsible for a destination, it broadcasts
location search queries, using control message
MICP_WHOHAS (with the destination’s home
address), to all other MSRs of the virtual network
The current MSR of the destination responds a
control message MICP_IHAVE, including its IP
address
The current MSR of the source uses the IP address
to tunnel the datagram to the destination
Imagine the location cost, and scalability as well!
Distributed Computing Lab.
94
2001 Fall
Mobile Computing
Encapsulation

IPIP encapsulation
New IP Header
IP Header
IP Payload
Distributed Computing Lab.
Source Add := Source’s
Current MSR
Dest. Add := Dest.’s
Current MSR
Old IP Header
IP Payload
95
2001 Fall
Mobile Computing
Routing




MHs in the same cell : direct routing using ARP
MHs in different cells : tunneling using proxy-ARP
MH to fixed host : routed through MSR
Fixed host (or host outside of the virtual network) to
MH :





datagrams routed to one of MSR
the MSR locate the destination MH
the MSR tunnels the datagrams to the current MSR
the current MSR delivers them locally, using ARP
Always pass through an optimal route


at the expense of heavy network traffic
also, with taking much time delay
Distributed Computing Lab.
96
2001 Fall
Mobile Computing
Routing : Example

In order to deliver a datagram from MH s to MH k
Data from outside
of the virtual
network
Virtual Network
MICP_WHOHAS
MICP_IHAVE
subnet a
Host a
subnet k
MSR a
MSR k
subnet s
MSR p
MH k
MSR s
MH s
Control
Data
Data tunneling
Distributed Computing Lab.
97
2001 Fall
Mobile Computing
Popup Operation

How it will manage in the cases of inter-campus
mobility?





MH gets an embedded address from the current campus when
it newly connect to the current campus
MH notifies the embedded address to an MSR in its campus the MSR is called a designated MSR for the MH
the designated MSR acts as a member of the current campus,
and it treats the MH as if it serves locally
datagrams for the MH firstly arrive its campus, and the
receiving MSR tunnels to the designated MSR, after identifying
the designated MSR
the designated MSR again tunnels the datagrams to the current
MSR, after identifying the current MSR, using a proxy ARP at
the current campus
Distributed Computing Lab.
98
2001 Fall
Mobile Computing
Proposal 2 : Virtual Internet Protocol
(VIP)



Designed and implemented by Fumio Teraoka (Sony)
Main subject in the WIDE project
Key Ideas

virtual internet protocol
TCP
TCP
UDP
VIP
IP
IP


UDP
propagating cache method
The setup


migrating host
gateways
Distributed Computing Lab.
99
2001 Fall
Mobile Computing
Addressing (I)

Based on the virtual network concept




logical ID : virtual network address (immutable) - usually its
own add.
physical locator : physical network address (which is a
temporary one assigned by the subnetwork which a host is
currently visiting)
Virtual networks are logically constructed above the
physical network by assigning two different IP address
to each host
The IP layer then is split into two sublayer


virtual IP sublayer : address mapping between the two
addresses
physical IP sublayer : conventional IP layer
Distributed Computing Lab.
100
2001 Fall
Mobile Computing
Addressing (II)



The transport layer specifies the target host by its virtual
IP address
A packet sent by a mobile host that is away from its
home subnetwork carries both addresses
The Physical IP source and destination addresses are
conveyed in the conventional IP header, whilst the
virtual ones are carried either as an encapsulated
format or as an IP option
Distributed Computing Lab.
101
2001 Fall
Mobile Computing
Datagram Header Format

When VIP is implemented as an IP option
0
16
Vers
Len
Service Type
IP Identification
Time to Live
31
Total Length
Flags
Fragment Offset
Header Checksum
Protocol Num.
Source IP Address
Destination IP Address
Option Type
Option length
Type
Hold Time
Source VIP Address
Destination VIP Address
Source Address Timestamp
Destination Address Timestamp
Option Type = 140
Timestamps := acts as a version number
Distributed Computing Lab.
102
2001 Fall
Mobile Computing
Location

Uses a propagating cache method





each host and gateway has a cache for address resolution
the cache is called the AMT(Address Mapping Table)
AMT entries are updated/created by two control packets,
connection/disconnection notification
AMT entries propagate across the network as data
communication progresses, i.e. with precisely finding out the
VIP header
VIP packet types






VipData : normal data packet
VipConn : connection notification
VipConnAck : ack. of VipConn
VipDisc : disconnection notification
VipDelAmt : AMT entry deletion request
VipErrObs : error notification
Distributed Computing Lab.
103
2001 Fall
Mobile Computing
Connection / Disconnection

Connection to a subnetwork





a temporary address is assigned to connecting host
the MH sends a VipConn packet to its home gateway
intermediate gateway create an AMT entry for the MH
the home gateway broadcasts the VipConn packet in the
home network and returns a VipConnAck to the MH
Disconnection from a subnetwork




the MH sends a VipDisc packet to its home gateway
the home gateway broadcasts a VipDelAmt packet
if a gateway, which received the VipDelAmt, has an AMT
entry for the MH, it deletes the corresponding entry and
broadcasts the packet
the migrating host releases the IP address
Distributed Computing Lab.
104
2001 Fall
Mobile Computing
Model / Location

Connection to a subnetwork
Net-E
Gw-EF
Net-G
Net-F
Host-X
Net-A
Gw-CG
Gw-BF
Host-X
Gw-AB
Gw-CD
Gw-BC
Net-B
Net-D
Net-C
Gw-AH
Host-Y
Net-H
Host-Z
Connection Notification Packet
Ack
Distributed Computing Lab.
105
2001 Fall
Mobile Computing
Disconnection

Disconnection from a subnetwork
Net-E
Gw-EF
Net-G
Net-F
Host-X
Net-A
Gw-CG
Gw-BF
Host-X
Gw-AB
Gw-CD
Gw-BC
Net-B
Net-D
Net-C
Gw-AH
Host-Y
Net-H
Host-Z
Disconnection Notification Packet
AMT Deletion Request Packet
Distributed Computing Lab.
106
2001 Fall
Mobile Computing
Routing (I)

When a host communicates with a migrating host,
each host or gateway acts as:


upon reception
create/update the AMT entry for the source if necessary
before transmission
if destination’s ATM entry exists,
destination’s IP address is resolved
else assume the IP = VIP
Distributed Computing Lab.
107
2001 Fall
Mobile Computing
Routing (II)

Packet forwarding
Net-E
Gw-EF
Net-G
Net-F
Host-X
Net-A
Gw-CG
Gw-BF
Host-X
Gw-AB
Gw-CD
Gw-BC
Net-B
Net-D
Net-C
Gw-AH
Net-H
Newly build
a cache entry
for Host-X
Host-Z
Host-Y
Packet with incorrect PN-address
Packet with correct PN-address
Response packet from Host-X
Distributed Computing Lab.
108
2001 Fall
Mobile Computing
Proposal 3 : Multiple Addresses Scheme


Designed and implemented by Hiromi Wada et al.
(Matsushita)
Key Ideas



Addressing



Packet Forwarding Server (PFS)
autonomous forwarding mode
logical ID : home IP address (immutable)
physical locator : temporary IP address (which is assigned
by the subnetwork which a host is currently visiting)
Location



each subnetwork has at least one special router, PFS
the PFS is responsible for tracking the temporary IP address
the new temporary address for a mobile host should be
notified from the host itself to its home PFS and the
previous PFSs which have been just left by the host
Distributed Computing Lab.
109
2001 Fall
Mobile Computing
Model / Location

MH k’s move from subnet m to subnet k, then to
subnet a
To Previous PFS
To Home PFS
subnet a
Internet
PFS a
PFS k
PFS m
SH m
MH k
Get a temp.
address from
subnet a
subnet s
subnet m
subnet k
host moving
PFS s
SH s
host moving
Location notification
Distributed Computing Lab.
110
2001 Fall
Mobile Computing
Datagram Header Format)

IPTP (Internet Packet Transmission Protocol)
encapsulation
0
16
31
Vers
Len
Service Type
IP Identification
Time to Live
Total Length
Flags
Protocol Num.
Fragment Offset
Header Checksum
Source IP Address
Destination IP Address
Type
Autonomous
Counter
Aim
Sequence
Status
(not used)
Home Address of MH
Temporary Address of MH
Address of PFS
Distributed Computing Lab.
Type
0 : Packet transmission message
1 : MH Location information message
2 : Ping autonomous supporter message
3 : MH visiting message
4 : Echo message
2001 Fall
Mobile Computing
111
Routing (I)

Forwarding (tunneling) based on the mobile host’s
home PFS





the PFS is promiscuously listening on the subnetwork
it intercepts any packets for the host, encapsulates them
It then forwards them using the host’s current temporary
address that it maintains
This forwarding scheme is very inefficient in a large
network like the Internet due to long chains of
forwarding routes
Autonomous mode



whenever a PFS forwards packets to the other subnetwork, the
PFS returns a location notification packet to the source host
the source host caches the mobile host’s current temporary
address
packet encapsulation then is done by the sender itself
Distributed Computing Lab.
112
2001 Fall
Mobile Computing
Routing (II)

Forwarding mode
Internet
subnet a
subnet s
subnet m
subnet k
PFS a
PFS k
PFS m
SH m
MH k
host moving
PFS s
SH s
host moving
Data
Data tunneling
Distributed Computing Lab.
113
2001 Fall
Mobile Computing
Autonomous mode

Autonomous mode
Internet
subnet a
subnet s
subnet m
subnet k
PFS a
PFS k
PFS m
SH m
MH k
PFS s
SH s
host moving
Location notification
Data
Data tunneling
Distributed Computing Lab.
114
2001 Fall
Mobile Computing
Proposal 4 : IP Option Scheme


Designed and implemented by Charles Perkins
(IBM), also by David Johnson (CMU)
Key Ideas


The setup




IP’s LSRR (loose Source and Record Route) option
Mobile Hosts (MHs)
Mobile Access Stations (MASs)
Mobility Routers (MRs)
Addressing

home IP address (immutable)
Distributed Computing Lab.
115
2001 Fall
Mobile Computing
IP Option Scheme (LSRR)

LSRR concept
Src: Host-x
Dst: Host-a
LSRR: GW-n
Src: Host-x
Dst: Host-a
LSRR: GW-k
LSRR: GW-n
Host-a
GW-k
Src: Host-x
Dst: Host-a
GW-n
Host-x
Src: Host-a
Dst: GW-k
Src: Host-a
Dst: GW-n
Src: Host-a
Dst: Host-x
LSRR: GW-n
LSRR: GW-k
LSRR: GW-k
LSRR: Host-x
LSRR: Host-x
LSRR: GW-n
Distributed Computing Lab.
116
2001 Fall
Mobile Computing
LSRR Optioned Datagram Header
Format

Source route options
0
16
Vers
Len
Service Type
IP Identification
Time to Live
31
Total Length
Flags
Fragment Offset
Header Checksum
Protocol Num.
Source IP Address
Destination IP Address
Option Type
Option length
Pointer
Not Used
IP Address of First Hop
IP Address of Second Hop
...
IP Address of Seventh Hop
Option Type = 03
Distributed Computing Lab.
117
2001 Fall
Mobile Computing
Model / Location

MH k’s move from subnet k to subnet a
To home MR
subnet a
MAS a
Internet
subnet m
subnet k
MR a
MR k
MAS k
subnet s
MR m
MAS m
SH s
MH k
host moving
Location notification
Distributed Computing Lab.
118
2001 Fall
Mobile Computing
Location & Routing

Location




each subnetwork has at least one special router, MR
the MR is responsible for keeping track of the current location of
each MH that has been assigned an address on that subnet.
the IP address of the current MAS for an MH should be notified
from the host itself to its home MR
Routing




when an MH is away from its home subnetwork, a datagram
sent to the host initially ends up at its home MR
the MR tries to forward them to the host’s current MAS, and it
then adds an LSRR option to the datagram
when the MH replies to the source, it also inserts a LSRR option
in the outgoing datagram that specifies the address of its current
MAS as transit router
the source reverses the recorded route on the datagram and
inserts it as a LSRR option in future datagrams sent to the MH
Distributed Computing Lab.
119
2001 Fall
Mobile Computing
Routing (II)

Packet transmission from an SH to an MH
Internet
subnet a
subnet m
subnet k
MR a
MAS a
MR k
MAS k
subnet s
MR m
MAS m
SH s
MH k
host moving
Src: SH s
Dst: MH k
LSRR: MAS a
Distributed Computing Lab.
Src: SH s
Dst: MAS a
Src: SH s
Dst: MH k
LSRR: MH k
120
2001 Fall
Mobile Computing
Routing (III)

Packet transmission from an MH to an SH
Internet
subnet a
subnet m
subnet k
MR a
MAS a
MR k
MAS k
subnet s
MR m
MAS m
SH s
MH k
host moving
Src: MH k
Dst: MAS a
Src: MH k
Dst: SH s
LSRR: SH s
Distributed Computing Lab.
Caches the
source route
of MH m
I.e. {MH k
MAS a}
LSRR: MAS a
121
2001 Fall
Mobile Computing
IETF mobileip Group


http://www.ietf.org/html.charters/mobileip-charter.html
Mailing lists



Aims




general discussion : [email protected]
to subscribe : [email protected]
develop or adopt architecture and protocols to support mobility
within the Internet
in the future, will develop protocols for supporting transparent
host roaming among different subnetworks and different media
consist of new and/or revised protocols at the network layer
Requirement

the proposed solutions allow mobile hosts to interoperate with
existing Internet systems
Distributed Computing Lab.
122
2001 Fall
Mobile Computing
IETF mobileip Group (Cont.)

Internet drafts






route optimization in mobile IP
mobility support in IPv6
firewall traversal for mobile IP: goals and requirements
reverse tunneling for mobile IP
firewall traversal for mobile IP: guidelines for firewalls and
mobile IP entities
Request for Comments





IP in IP tunneling (rfc 1853)
applicability statement for IP mobility support (rfc 2005)
minimal encapsulation within IP (rfc 2004)
IP encapsulation within IP (rfc 2003)
IP mobility support (rfc 2002)
Distributed Computing Lab.
123
2001 Fall
Mobile Computing
IP Mobility Support

History




Aims



start the work from 1993
has mainly referenced with Mobile*IP
registered by C. Perkins as a RFC 2002 at Oct. 1996
provides a recommendation with minimal functionalities
works as an input of IPv6’s mobility support part
Implementations







CMU
FTP Software
IBM
Motorola
Nokia
SUN
Telxon
Distributed Computing Lab.
Dave Johnson
Frank Kastenholz
Charlie Perkins
Jim Solomon
Gunyho Gabor
Gabriel Montenegro
Frank Ciotti
124
2001 Fall
Mobile Computing
Introduction

To begin with,




Two possible mechanisms can be considered as:



IPv4 assumes that a host’s IP address uniquely identifies the
host’s point of attachment
a host MUST be located on the network indicated by its IP
address in order to receive datagrams destined to it
how can a host change its point of attachment without losing
its ability to communicate?
the host must change its IP address whenever it moves, but it
brings the backward compatibility problem
host-specific routes must be propagated throughout the
Internet, but it suffers severe scaling problem
It has been defining a new scalable mechanism, which
enables nodes to change their point of attachment to
the Internet without changing their IP address
Distributed Computing Lab.
125
2001 Fall
Mobile Computing
Set UP

Protocol requirements





a mobile host MUST be able to communicate with other hosts
- that do not implement these mobility functions
- without changing its IP address
the number (size) of administrative messages sent over the
wireless link by which a mobile host should be minimized
An MH is given a permanent IP add. on a home network
When away from its home, it is associated with a care-of
add. which reflects the MH’s current point of attachment
Two types of the care-of address



foreign agent care-of address: an address of a foreign agent with
which the mobile host is currently registered
co-located care-of address: an externally obtained local address
which the mobile host has associated with
what are differences on these?
Distributed Computing Lab.
126
2001 Fall
Mobile Computing
Protocol Overview
Three steps with the protocol
1. agent discovery: mobility agents may advertise their
availability for they provide service, or a newly arrived
mobile host may send a solicitation to learn if any
prospective agents are present
- ICMP router discovery (rfc 1256)
2. registration: when a mobile host is away from home, it
registers its care-of address with its home agent
- UDP control messages
3. tunneling: when a mobile host is away from home,
datagrams sent to it must be tunneled to hide its home
address from intervening routers
- encapsulation protocol (rfc 2003, 2004, 1701)

Distributed Computing Lab.
127
2001 Fall
Mobile Computing
Message Type

Control message format
0
7
Type

Length
Data ...
ICMP discovery message
0
16
19

15
one-byte padding
mobility agent advertisement
prefix-lengths
Registration control message (UDP, port number 434)
1
3
32
33
34
registration request
registration reply
mobile-home authentication
mobile-foreign authentication
foreign-home authentication
Distributed Computing Lab.
128
2001 Fall
Mobile Computing
Agent Discovery

Agent discovery provides the method by which a
mobile host:




determines whether it is currently connected to its home
network or to a foreign network
can detect when it has moved from one network to another
determine the care-of address if it is connected to a foreign
agent
Agent advertisement


an agent advertisement is formed by including a mobility
agent advertisement extension in an ICMP router
advertisement message
the normal interval at which agent advertisement are sent
should be 1/3 of the advertisement lifetime given in ICMP
header, a recommended maximum rate is once per second
Distributed Computing Lab.
129
2001 Fall
Mobile Computing
ICMP Router Discovery Messages
(rfc1256) (I)

When a host sends IP datagram beyond its directlyattached subnet, it must discover the address of at least
one operational router by:



reading the address from a configuration file at startup time, but
it could bring a significant burden to track dynamic router’s
changes
listening to routing protocol traffic, but router discovery would be
dependent of any specific routing protocol
Two ICMP messages with use on multicast links


router advertisements : each router periodically multicasts to
announce its IP address of that interface, hosts then find it by
listening them
router solicitations : when a host attached to a multicast link, it
multicasts to ask for immediate advertisement
Distributed Computing Lab.
130
2001 Fall
Mobile Computing
ICMP Router Discovery Messages
(rfc1256) (II)


The message only enable hosts to discover the
prospected router, but not which router is best (this is
constituted with the ICMP redirection)
the default advertising rate is once every 7 to 10
minutes, and the default lifetime is 30 minutes
Distributed Computing Lab.
131
2001 Fall
Mobile Computing
Mobility Agent Advertisement
Extension
0
15
Vers
Len
Service Type
IP Identification
TTL(1)
31
Total Length
Flags
Protocol # (1)
Fragment Offset
Header Checksum
IP
Source IP Address
Dest. Add, (224.0.0.1 or 255.255.255.255)
Type (9)
Code (0 or 16)
Checksum
Num Addrs
Addr Entry Size
Lifetime
ICMP
router
discovery
message
Router Address [1]
Preference Level [1]
Router Address [2]
...
Type
Length
Registration Lifetime
Sequence Number
RBHFMGV
reserved
Zero or more Care-of Addresses
R: registration required, B: busy, H: home agent, F: Foreign agent
M: minimal encap. G: GRE encap. V: Van Jacobson header comp.
Distributed Computing Lab.
2001 Fall
132
Mobility
Agent
Advertisement
Extension
Mobile Computing
Mobility Router Solicitation


An agent solicitation message is identical to an ICMP
router solicitation, except that its IP TTL must be set to 1
a mobile node may solicit more often than once every
three seconds
0
15
Vers
Len
Service Type
IP Identification
1
31
Total Length
Flags
Fragment Offset
Header Checksum
Protocol # (1)
IP
Source IP Address
224.0.0.1 or 255.255.255.255
10
Checksum
0
Reserved
Distributed Computing Lab.
133
2001 Fall
ICMP router
solicitation
message
Mobile Computing
Move Detection (I)

Prefix-lengths extension : used to indicate the number of
bits of network prefix that applies to each router address
listed in the ICMP router advertisement portion of the
agent advertisement
0
7
Type (19)

15
Length
23
Prefix Lth ...
One-byte padding extension, with type field (0) only
Distributed Computing Lab.
134
2001 Fall
Mobile Computing
Move Detection (II)

Move detection


based on the lifetime field within the ICMP router advertisement
portion of the agent advertisement, if a mobile host fails to
receive another advertisement from the same agent within the
previously received lifetime, it should assume that it has lost
contact with that agent
based on the prefix lengths extension, a mobile node may
determine whether or not a newly received agent advertisement
was received on the same subnet as the mobile mode’s current
care-of address, if the prefixes differ, the mobile node may
assume that it has moved
Distributed Computing Lab.
135
2001 Fall
Mobile Computing
Registration (I)

Mobile IP registration provides a mechanism for mobile
nodes to communicate their current reachability
information to their home agent

request forwarding services when visiting a foreign network
inform their home agent of their current care-of address
renew a registration which is due to expire, and/or

deregister when they return home



Mobile IP defines two different registrations, one via a
foreign agent, and one directly with the mobile node’s
home agent
Distributed Computing Lab.
136
2001 Fall
Mobile Computing
Registration (II)

When registering via a foreign agent, the registration
procedure is:




the mobile node sends a registration request to the prospective
foreign agent to begin the registration process
the foreign agent processes the registration request and then
relays it to the home agent
the home agent sends a registration reply to the foreign agent
to grant or deny the request
the foreign agent processes the registration reply and then
replays it to the mobile node to inform it of the disposition of its
request
Distributed Computing Lab.
137
2001 Fall
Mobile Computing
Registration Request
S: simultaneous bindings
B: broadcast datagrams
D: decapsulation by mobile node M: Minimal encapsulation
G: GRE encapsulation
V: Van Jacobson header comp.
0
15
31
434
UDP Source Port
UDP Message Length
Type (1)
S B D M G V rev
UDP Checksum
UDP
Lifetime
Home Address
UDP
Registration
Request
Message
Home Agent
Care-of Address
Identification
Authentication
Extension
Authentication
Distributed Computing Lab.
138
2001 Fall
Mobile Computing
Registration Reply

Code field



registration successful: 0, 1
registration denied by the foreign agent: 64 ~ 88
registration denied by the home agent: 128 ~ 136
0
15
31
434
UDP Source Port
UDP Message Length
Type (3)
Code
UDP Checksum
UDP
Lifetime
Home Address
UDP
Registration
Reply
Message
Home Agent
Identification
Authentication
Extension
Authentication
Distributed Computing Lab.
139
2001 Fall
Mobile Computing
Location / Routing

Location



Routing


HA is responsible for keeping track of the current location of
each MH that has been assigned an address on that subnet
when an MH away from the HA, the IP address of the current
MA should be notified from the host itself to its home MA
HA takes charge of intercepting datagrams addressed to the
host’s home address and forwarding them to the associated
care-of address
Three tunneling types




IP encapsulation within IP (rfc 2003)
Minimal encapsulation within IP (rfc 2004)
IP in IP tunneling (rfc 1853)
Generic Routing Encapsulation (rfc 1701)
Distributed Computing Lab.
140
2001 Fall
Mobile Computing
Location (Suppl.)

MH a’s move from subnet a to subnet k
Internet
subnet a
subnet s
subnet k
MA a
Caches the
current MA’s
address of
MH a
I.e. {MH a
MA k}
MA k
host moving
MA n
MH a
MA s
MH s
Location notification
Distributed Computing Lab.
141
2001 Fall
Mobile Computing
Encapsulation Methords
Outer IP Header
IP Header
IP Payload
Delivery Header
Tunnel Header
GRE Header
Inner IP Header
Payload Packet
IP Payload
GRE
Outer IP Header
Modified IP Header
IP Header
Minimal IP Header
IP Packet
IP Packet
IP encap. within IP
Distributed Computing Lab.
IP in IP tunneling
142
Minimal encap. for IP
2001 Fall
Mobile Computing
Routing (Suppl.)

Packet transmission from MH s to MH a
Internet
subnet a
subnet s
subnet k
HA
FA
HA
MH a
host moving
MH s
Data
Data tunneling
HA : Home Agent
FA : Foreign Agent
Distributed Computing Lab.
FA
143
2001 Fall
Mobile Computing
Internet Host Mobility Support (Summary)

Addressing, Location and Routing
Mobile*IP
VIP
Multiple
Address
Addressing
Embedded
Temporary
Temporary
(Physical
Locator)
Current MA
Add.
Temp. Add.
Temp. Add.
Location
Broadcast
Location
Cache
Forwarding
Pointer
(Somewhere)
Current MA
Gateways
Home Server
Tunneling
Mobile Host Intermediate
Gateways
Criteria
Distributed Computing Lab.
144
IP Option
Permanent
IP Mobility
Support
Permanent
Home Add.
Current MA
Add.
IP Option
Forwarding
Pointer
Home Server
Home MA
Forwarding
Server
Mobility
Router
Home MA
(Mobile Host)
(Mobile Host)
2001 Fall
Mobile Computing
Tip 1 (Smooth Hand-offs)

MH simply asks the new FA to relay its mobility binding
update to the CA that the host wants to let them know
its new location. The FA tries to do this and needs to
pass the result, which indicates success or not, to the
host
Internet
subnet a
subnet s
subnet k
MA a
MA k
MA n
host
moving
Distributed Computing Lab.
145
MH a
2001 Fall
MA s
MH s
Mobile Computing
Tip 2 (Orphan Packets)

After the destination mobile host disconnected with the
previous agent, packets bound for the host would be
delivered to the previous agent until the sender stops
forwarding to this agent
Possible time zone to
occur orphan packets
Start tunneling
to new location
MA j
Leave
Connection
hand-off
Address
propagation
MA k
Detect Check
authorization

Buffering vs. Special tunneling
Distributed Computing Lab.
146
2001 Fall
Mobile Computing
Location and Routing Optimization




The key service for providing seamless connectivity
to MH is the creation and maintenance of a packet
forwarding tunnel between a known location and the
host's current agent
Clearly, packet routing paths going with host mobility
depend critically on where and/or how much location
information is preserved on the network as a whole
In considering the current IP address's role, the most
common (simple) placing method is to hold the
current location for moving hosts on the host's HA
In this case, an IP packet must be sent to the mobile
host's home agent where it is tunneled to the mobile
host's current location, resulting in triangle routing
Distributed Computing Lab.
147
2001 Fall
Mobile Computing
Triangle Routing

A triangular round-trip route
Internet
Host
Home-based
Location
Home
Agent
Reply Path
Tunneling
Foreign
Agent
MH k
Host Moving

Triangle routing is undesirable :

increased network utilization (sensitivity to network partition)

irregularity of performance variance
Distributed Computing Lab.
148
2001 Fall
Mobile Computing
Location and Routing Optimization
Schemes (I)



In the host mobility environment, there is a tradeoff
between the two key issues, locating hosts' physical
locale and routing datagrams to and from them
If the system initially puts effort into location, routing
overheads caused by host mobility should be reduced
However, in practice, it is very important to try to
optimize this situation in order to reduce the total
network cost; that is, providing higher performance to
the system as a whole, so eventually the mobile user's
satisfaction. How this condition can be resolved?
Distributed Computing Lab.
149
2001 Fall
Mobile Computing
Location and Routing Optimization
Schemes (II)



Two seemingly conflicting aims :

limiting costly location distribution as far as possible

achieving optimal routing for most communication traffic
How much of the location overhead should be
incorporated to achieve the prospective routing
efficiency?
Object function
location overhead << routing effect
Distributed Computing Lab.
150
2001 Fall
Mobile Computing
IMHP Approach


Based on the lazy location notification
If a network entity receives a packet that it must
tunnel to a MH



it is likely that the source node of the packet has an incorrect
binding (so the packet has been tunneled to this node)
no binding for the destination host (in the case of a normal
packet)
In either case, if this entity determines that a new
binding might improve packet routing, that is, the
tunneling on this entity makes for an unnecessarily
long route for the packet, it then may send a binding
notification to the source node of the packet

the notification is issued not only by the HA, FA, and its
correspondent host acts as a cache agent
Distributed Computing Lab.
151
2001 Fall
Mobile Computing
IMHP (Location Notification)

Packet transmission from MH s to MH a
Internet
subnet a
subnet s
subnet k
HA
FA
host moving
HA
MH a
MH s
Location Notification
Data
Data tunneling
Distributed Computing Lab.
152
FA
2001 Fall
Caches the
current MA’s
address of
MH a
I.e. {MH a
MA k}
Mobile Computing
IMHP (Routing)

Packet transmission from MH s to MH a (thereafter)
Internet
subnet a
subnet s
subnet k
HA
FA
host moving
Distributed Computing Lab.
HA
MH a
153
FA
MH s
2001 Fall
Mobile Computing
IMHP Approach (Cont.)




Because an MH continues to move around, cache
agents easily end up with out-of-date cache entries
for the host
Each notification message indicates the maximum
lifetime for any location cache entry created from it
An old cache entry, especially on the previous
agent(s), is eventually deleted after the expiration of
the lifetime period established
A mobility entity wanting to provide continued service
with a particular location cache entry may attempt to
reconfirm that mobility binding before the expiration
of this lifetime period
Distributed Computing Lab.
154
2001 Fall
Mobile Computing
IMHP (Operational Example)
{MH 212, MA 21}
{MH 211, MA 21}
{MH 212, MA 18}
MA 18
MA 11
{MH 211, -}
{MH 212, -}
MA 28
MA 24
MA 21
{MH 212, MA 18}
{MH 212, MA 24}
{MH 212, MA 21}
{MH 212, MA 24}
{MH 211, MA 28}
MH 211
MH 212
Location notification
Data tunneling
Distributed Computing Lab.
155
2001 Fall
Mobile Computing