CCM 4300 Lecture 8
Computer Networks: Wireless
and Mobile Communication
Systems
Dr E. Ever
School of Computing Science
1
Mobility and IP …… more information
Mobile Wireless Internet Forum
• http://www.ipv6forum.com/
http://playground.sun.com/pub/ipng/html/ipng-main.html
IPv6 work including mobility support
•"The 3G IP Multimedia Subsystem" by Gonzalo Camarillo and
Miguel A. Garcia Martin (available in google books)
2
Facts about Mobile IP
• More than 2 billion subscribers
•More than 70% of all digital mobile phones use GSM
•7.3 million people accesses the net via their mobile phones, during the second
and third quarters of 2008. (BBC news channel)
•An increase of 25% compared to growth of juts 3% for the PC based net
audience-(BBC news channel)
• IPv4 can do it all, it will be at a tremendous (unimaginable) cost and
complexity
•Only IPv6 offers enough addresses
•IPv6 offers features needed for mobile networking
•IPv6 utilises features to offer seamless roaming
•Network layer roaming enables cost reduction and improve deploy ability
3
Lesson objectives
 To acquire a basic understanding of the basics of Mobile
IPv4 and IPv6, you will:
- Understand principles of network MIP and HMIP:
HA, CN, MN, FN, HN, FA, binding updates, CoA, RCoA.
Triangular rule
Route optimisation
Home Agent (HA)
Availability and access control.
-Security in MIP
Key
distribution
Correspondent Node (CN)
Mobile Node (MN)
Foreign Network(FN)
Home Network(HN)
Foreign Agent (FA)
Care-of Address (COA)
4
Mobile Network layer
• Mobile phone
• Mobile IP (Internet Protocol)
• Hand-off effects:
• addressing and routing
• operation of upper layer protocols
• Mobile IPv6
5
Why Mobile IP
• Routing
– Both ends of TCP (connection) need to keep the same IP
address for the life of the session (home address, end-end)
– change of physical subnet implies change of IP address to
have a topological correct address (standard IP) or needs
special entries in the routing tables (care-of-address,
routing
• Specific routes to end-systems?
– change of all routing table entries to forward packets to the
right destination
– does not scale with the number of mobile hosts and
frequent changes in the location, security problems
• Changing the IP-address?
– adjust the host IP address depending on the current
location (managing a binding)
– almost impossible to find a mobile system, DNS updates
take a long time (dynamic tunnel between CoA & HA)
6
– TCP connections break, security problems!!!!
Requirements for Mobile IP
• Transparency
– mobile end-systems keep their IP address
– continuation of communication after interruption of link possible
– point of connection to the fixed network can be changed
• Compatibility
– support of the same layer 2 protocols as IP
– no changes to current end-systems and routers required
– mobile end-systems can communicate with fixed systems
• Security
– authentication of all registration messages
• Efficiency and scalability
– only little additional messages to the mobile system required
(connection typically via a low bandwidth radio link)
– world-wide support of a large number of mobile systems in the whole
Internet
7
Mobile IP: Terminology
Mobile Node (MN)
system
(node) that can change the point of connection to the network without changing
its IP address
Home Agent (HA)
system
in the home network of the MN, typically a router
registers
the location of the MN, tunnels IP datagrams to the COA
Foreign Agent (FA)
system in the current foreign network of the MN, typically a router
forwards
the tunneled datagrams to the MN, typically the default router for the MN
Care-of Address (COA)
address of the current tunnel end-point for the MN (at FA or MN)
temporary IP address for a mobile device
allows a home agent to forward messages to the mobile device.
separate address is required because the IP address of the device that is used as host
identification is topologically incorrect
actual
location of the MN from an IP point of view, can be chosen, e.g., via DHCP
Correspondent Node (CN)
communication partner
8
Key Question
How do mobile hosts maintain IP connectivity
when mobility is supported at layer 3?
Here we investigate two extensions to IPv4.
•As mobile computing devices increase in capability
mobile communication becomes increasingly widespread.
THE BIG QUESTION IS:
How can IP support mobile connectivity?
9
Mobile IP: An Overview
COA
home
network
router
FA
router
HA
MN
foreign
network
Internet
CN
router
home
network
router
HA
router
FA
2.
Internet
1.
CN
router
3.
MN
4.
foreign
network
Mobile Phone network routing
Call set-up
During call
• MS emits beacon:
• Hand-off:
• IMSI/IMEI unique ID
• beacon heard by BTS
• BTS  BSC  MSC
• MSC:
• within area: BTS  BTS
• between areas: BSC  BSC,
MSC informed of move to
different area
• HLR
• MSC  MSC: updates to
• VLR
• updates HLR/VLR
• if VLR updated, sends info
HLR/VLR
to home network for MS
• Network always knows location of
MS
• Call maintained during hand-off:
• only last-hop link
• Transparent to user:
• momentary signal loss(?)
IMSI: international mobile subscriber identity
IMEI: international mobile equipment identity
11
Data transfer to the mobile system
Triangular
HA
2
MN
home network
Internet
receiver
3
FA
1
CN
sender
foreign
network
1. Sender sends to the IP address of MN,
HA intercepts packet
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet to the MN
12
Data transfer from the mobile system
HA
1
home network
MN
sender
Internet
FA
foreign
network
1. Sender sends to the IP address
of the receiver as usual,
FA works as default router
CN
receiver
13
Mobile phone network routing
HA
2
MN
home network
Internet
receiver
3
FA
1
CN
foreign
network
1. Sender sends to the IP address of MN,
HA intercepts packet (proxy ARP)
2. HA tunnels packet to COA, here FA,
by encapsulation
3. FA forwards the packet to the MN
sender
14
Mobile IP (1)
• Need to support mobile
users:
• Transparency:
• to upper layers
• to remote end-systems
• IPv4: IP address indicates
point of attachment to
Network
• Movement of host means:
• Mobile host (MH):
• home network (HN), home agent (HA)
• foreign network (FN),
foreign agent (FA)
• care-of-address (CoA)
• Communication:
• HA sends packets to CoA:
IP-in-IP encapsulation
• must reply to ARP for MH
• CoA:
• new IPv4 address?
• may be new IP address
• update routing
information?
• foreign agent
15
Mobile IP (2)
1) MH arrives at FN, and locates FA (using agent
advertisements from FA or by solicitation).
2) MH completes registration procedure with FA.
3) MH updates HA with its new CoA (i.e. the FA).
4) Host A now tries to contact MH. Packets for MH are
intercepted by HA
5) HA tunnels the packets from Host A to the CoA for MH
(i.e. the FA)
6) The FA de-encapsulates the inner IP packet and transmits
the packet locally to MH.
7) The packets from MH to Host A are sent directly from the FN.
16
Mobile IP (2)
Host A
HA
home network
4
5
remote network
IP-in-IP encapsulation
Data
Internet
src = Host A
dst = MH
Data
Host A
MN
src = Host A
7
src =
dst = MH
dst =
2
MH
6
1
FA3
foreign network
17
Encapsulation
original IP header
original data
new IP header
new data
outer header
inner header original data
Mobile IP (3)
 Transparent to non-mobile hosts
X Security:
 Does not break/change existing IP
addressing and routing
• firewalls have to be
(dynamically) configured
 Can be introduced into the network
• authentication:
as required
 Normal (unicast) routers do not
need to be modified
X Asymmetric routing:
Packets flowing in i.e. TCP connections flow
through different routes to different directions.
• could be inefficient
MH  FN(?), FA  HA(?)
MH  HA
• end-to-end security?
X Hand-off between FAs or FA/HA:
• lost packets(?)
• QoS
• higher layer protocol operation
(e.g. TCP)
19
Registration
MN
FA
HA
MN
HA
t
t
20
Handoffs: layer 2 versus Layer 3
Layer 2
• No global changes:
• only local last hop
Register a
new IP
Register an
FA only
Layer 3
• Global, end-system to end-system
connectivity
• No routing at layer 2
• Addresses have global significance
• No global addressing
• Change in layer 3 address is change
to network
significance at layer 2
• Need to have same layer 2
technology across network
• Mobility within network:
• Layer 3 address valid across
different layer 2 technologies
• Mobility across networks:
• internetworking!
• no hand-off between network
technologies
21
TCP behaviour (1)
Problems
• Layer 2 cell hand-off:
• data loss /corruption (also due to high BER in general)
• no ACK for data
• TCP:
• no ACK  slow start
• TCP has degraded performance
• High BER on wireless link (~10-3 - ~10-4 common):
• corrupt data requires end-to-end re-tx (use layer 2 FEC)
• Affects other transport-layer or application-layer protocols:
• real-time applications – errors and packet loss are harmful
22
TCP behaviour (2)
Possible solutions
• TCP SACK option:
(selective acknowledgment)
• retransmission of missing “holes” in byte stream
• not always implemented
• Use ECN in IP:
(explicit congestion notification)
• need to modify TCP interface and applications
• Link-local re-tx:
• on wireless hop
• need to hold TCP, e.g. at base station
• need re-tx protocol
• Soft hand-off at layer 2: (a cell phone is simultaneously connected to
two or more cells during a call.)
• need to use CDMA, which has its own problems
23
Network integration

Agent Advertisement




Registration (always limited lifetime!)



HA and FA periodically send advertisement messages into their physical
subnets
MN listens to these messages and detects, if it is in the home or a
foreign network (standard case for home network)
MN reads a COA from the FA advertisement messages
MN signals COA to the HA via the FA, HA acknowledges via FA to MN
these actions have to be secured by authentication
Advertisement




HA advertises the IP address of the MN (as for fixed systems), i.e.
standard routing information
routers adjust their entries, these are stable for a longer time (HA
responsible for a MN over a longer period of time)
packets to the MN are sent to the HA,
independent of changes in COA/FA
Encapsulation I

Encapsulation of one packet into another as
payload



e.g. IPv6 in IPv4 (6Bone), Multicast in Unicast
(Mbone)
here: e.g. IP-in-IP-encapsulation, minimal
encapsulation or GRE (Generic Record
Encapsulation)
IP-in-IP-encapsulation (mandatory, RFC
2003)

tunnel between HA and COA
Encapsulation II

Minimal encapsulation (optional)



avoids repetition of identical fields
e.g. TTL, IHL, version, DS (RFC 2474, old: TOS)
only applicable for unfragmented packets, no
space left for fragment identification
Generic Routing Encapsulation
An example:
outer header
RFC 1701
IHL
DS (TOS)
length
IP identification
flags
fragment offset
TTL
GRE
IP checksum
IP address of HA
Care-of address COA
C R K S s rec.
rsv.
ver.
protocol
checksum (optional)
offset (optional)
key (optional)
sequence number (optional)
routing (optional)
ver.
IHL
DS (TOS)
length
IP identification
flags
fragment offset
TTL
lay. 4 prot.
IP checksum
IP address of CN
IP address of MN
GRE
header
new header
original
header
original data
original
header
original data
new data
ver.
TCP/UDP/ ... payload
RFC 2784
C
reserved0
ver.
checksum (optional)
protocol
reserved1 (=0)
Optimisation of packet forwarding

Triangular Routing



“Solutions”





sender sends all packets via HA to MN
higher latency and network load (for each RTT)
sender learns the current location of MN (give away your position!)
direct tunneling to this location
HA informs a sender about the location of MN
big security problems!
Change of FA


packets on-the-fly during the change can be lost
new FA informs old FA to avoid packet loss (chaining), old FA now
forwards remaining packets to new FA

this information also enables the old FA to release resources for the MN
Change of the foreign agent with the optimized mobile IP
Direct tunneling is used. HA only provides information about FA
CN
request
update
ACK
HA
FAold
FAnew
data
MN
data
MN changes
location
registration
registration
update
data
ACK
warning
data
data
update
ACK
data
data
t
29
Change of foreign agent
CN
HA
Data
Update
ACK
FAold
Data
Data
Data
Warning
Request
Update
ACK
FAnew
Data
Data
Update
ACK
Data
Data
MN
MN changes
Registrationlocation
Data
Data
t
Reverse Tunneling (RFC 2344)
•Mobile Internet Protocol (IP) uses tunneling from the
home agent to the mobile node's care-of address, but
rarely in the reverse direction.
•Usually, a mobile node sends its packets through a
router on the foreign network, and assumes that
routing is independent of source address.
•When this assumption is not true (it is not feasible
or desired to have the mobile node send datagrams
directly to the internetwork using FA), it is convenient
to establish a topologically correct reverse tunnel
from the care-of address to the home agent.
Reverse tunneling:
HA
2
MN
home network
Internet
sender
1
FA
foreign
network
1. MN sends to FA
3
CN
receiver
2. FA tunnels packets to HA
by encapsulation
3. HA forwards the packet to the
receiver (standard case)
32
Reverse tunneling (RFC 3024, was: 2344)
HA
2
home network
MN
Internet
1
sender
FA foreign
network
CN
3
receiver
1. MN sends to FA
2. FA tunnels packets to HA
by encapsulation
3. HA forwards the packet to the
receiver (standard case)
Mobile IP with reverse tunneling

Router accept often only “topological correct“ addresses
(firewall!)



Reverse tunneling does not solve



a packet from the MN encapsulated by the FA is now topological
correct
furthermore multicast and TTL problems solved (TTL in the home
network correct, but MN is to far away from the receiver)
problems with firewalls, the reverse tunnel can be abused to
circumvent security mechanisms (tunnel hijacking)
optimization of data paths, i.e. packets will be forwarded through the
tunnel via the HA to a sender (double triangular routing)
The standard is backwards compatible


the extensions can be implemented easily and cooperate with
current implementations without these extensions
Agent Advertisements can carry requests for reverse tunneling
Mobile IP and IPv6

Mobile IP was developed for IPv4, but IPv6 simplifies the
protocols





security is integrated and not an add-on, authentication of registration
is included
COA can be assigned via auto-configuration (DHCPv6 is one
candidate), every node has address auto configuration
no need for a separate FA, all routers perform router advertisement
which can be used instead of the special agent advertisement;
addresses are always co-located (any router can act like an FA)
MN can signal a sender directly the COA, sending via HA not needed
in this case (automatic path optimsation)
“soft“ hand-over, i.e. without packet loss, between two subnets is
supported



MN sends the new COA to its old router
the old router encapsulates all incoming packets for the MN and forwards
them to the new COA
authentication is always granted
Mobile IP and IPv6 (2)



Once a MN moves into a foreign
network, acquiring a new IP address (CoA)
The MN is required to register this
address with its HA via a binding
update.
This binding update is issued over an
IPSec tunnel, using an IPv6 security
association, to protect its integrity and
authenticity.
Mobile IPv6 Protocol: an overview
Home agent
Correspondent node
lasebae@mdx.ac.uk
Local router
Correspondent node
with binding
Advertisement from local router contains routing
prefix
•Seamless Roaming: MN always uses home address
•Address configuration for care-of-address
•Binding Updates sent to home agent & correspondent
nodes (home address, care-of address, binding life
time)
•Mobile node ALWAYS ON by way of Home agent

Mobile IPv6 Design Points (why?)
• Enough address (340 undecillion 1036 addresses)
Addresses in IPv6 are 128 bits long, compared to 32-bit addresses in IPv4.
The very large IPv6 address space supports a total of 2128 (about 3.4×1038)
addresses
340,282,366,920,938,463,463,374,607,431,768,211,456
In China alone, there are 8 million IPv4 addresses and 70+ million handsets
•Enough security (almost, not quite!)
•
KDC, symmetric key, managing 10 million security associates,
authentication header, security payload
•Address Autoconfiguration
•
Movement detection, Monitoring advertisement
•Route Optimisation (binding updates part of IPv6)
•Destination Options (binding updates and acks) no reg and reg reply
•
Other relevant issues with IP
Seamless Mobility
•
•
Paging, context transfer, micro-mobility (localised binding
management)
Robust Header Compression
•
•
Reducing 40/60 bytes of header overhead to 2-3 byte
Authentication, Authorisation, and Accounting (AAA)
•Smooth handover == low loss
•Fast handover == low delay (approx 30 ms)
•Seamless handover == smooth and fast
•
Mobile-controlled seamless handover
RS
RA
HI
HAck
Scenario I: mobile sends special Router Solicitation (RS)
•
•
•
•
Previous Access Router replies with proxy Router Advert
(RA)
Previous Access Router sends Handover Initiate (HI)
New Access Router sends Handover Acknowledge (HACK)
Network Controlled Handover
HI
Proxy router adv
HAck
Previous access router sends Proxy Router
Advertisement on behalf of the new access router –
contains prefix and lifetime information …
•Previous access router sends Handover Initiate
message to new access router
•Mobile node May finalise context transfer at new
access router
•
Problems with mobile IP




Security
 authentication with FA problematic, for the FA typically belongs to
another organisation
 no protocol for key management and key distribution has been
standardised in the Internet
 patent and export restrictions
Firewalls
 typically mobile IP cannot be used together with firewalls, special setups are needed (such as reverse tunneling)
QoS
 many new reservations in case of RSVP
 tunneling makes it hard to give a flow of packets a special treatment
needed for the QoS
Security, firewalls, QoS etc. are topics of current research and
discussions!
RSVP (Resource reSerVation Protocol)
Security in Mobile IP

Security requirements (Security Architecture for the Internet
Protocol, RFC 1825)
 Integrity: any changes to data between sender and receiver
can be detected by the receiver
 Authentication: sender address is really the address of the
sender and all data received is really data sent by this
sender
 Confidentiality: only sender and receiver can read the data
 Non-Repudiation: sender cannot deny sending of data
 Traffic Analysis: creation of traffic and user profiles should
not be possible
 Replay Protection: receivers can detect replay of messages
IP security architecture I

Two or more partners have to negotiate security
mechanisms to setup a security association


typically, all partners choose the same parameters
and mechanisms
Two headers have been defined for securing IP
IP headerAuthentification-Header
authentication header
UDP/TCP data
packets: IP-Header
UDP/TCP-Paket

Authentication-Header



guarantees integrity and authenticity of IP packets
if asymmetric encryption schemes (Public, Private Keys) are
used, non-repudiation can also be guaranteed
Encapsulation Security Payload

protects confidentiality between communication partners
not encrypted
IP header
encrypted
ESP header
encrypted data
IP security architecture II

Mobile Security Association for registrations


parameters for the mobile host (MH), home agent (HA),
and foreign agent (FA)
Extensions of the IP security architecture

extended authentication of registration
MH-FA authentication
FA-HA authentication
MH-HA authentication
registration request
MH

registration reply
registration request
FA
registration reply
HA
prevention of replays of registrations


time stamps: 32 bit time stamps + 32 bit random number
Nonces (number for once pseudo random number): 32 bit random
number (MH) + 32 bit random number (HA)
Key distribution

Home agent distributes session keys
FA



MH
response:
EHA-FA {session key}
HA
EHA-MH {session key}
foreign agent has a security association with the home
agent
mobile host registers a new binding at the home agent
home agent answers with a new session key for foreign
agent and mobile node
IP Micro-mobility support

Micro-mobility support (Change FA):




Example approaches:




Efficient local handover inside a foreign domain
without involving a home agent
Reduces control traffic on backbone
Especially needed in case of route optimisation
Cellular IP
HAWAII
Hierarchical Mobile IP (HMIP)
Important criteria:
Security Efficiency, Scalability, Transparency, Manageability
Support for Mobility in IPv6
• Stateless address autoconfiguration:
• find an address (CoA) for use
at the FN
• Neighbour discovery:
• find default router
• No FA required to support
mobility:
• Route optimisation:
• send CoA to remote endsystem
• Security:
• authentication and
privacy
• MH takes care of home
address and foreign address
• Need dynamic DNS update
support
48
Cellular IP (CIP)

Operation:




CIP Gateway:



“CIP Nodes“ maintain routing
entries (soft state) for MNs
Multiple entries possible
Routing entries updated based on
data/control
packets sent by MN
Mobile IP tunnel endpoint
Initial registration processing
Security provisions:



all CIP Nodes share
„network key“
MN key: MD5(net key, IP addr)
MN gets key upon registration
Internet
Mobile IP
CIP Gateway
packets
from MN 1
BS
MN1
BS
BS
MN2
packets from
MN2 to MN 1
Cellular IP: Security

Advantages:




Initial registration involves authentication of MNs
and is processed centrally by CIP Gateway
All control messages by MNs are authenticated
Replay-protection (using timestamps)
Potential problems:

MNs can directly influence routing entries
Network key known to many entities
(increases risk of compromise)
No re-keying mechanisms for network key
No choice of algorithm (always MD5, prefix+suffix mode)

Message-Digest algorithm 5 is a widely used cryptographic hash function



Cellular IP: Other issues


Advantages:

Simple and elegant architecture

Mostly self-configuring (little management needed)

Integration with firewalls / private address support possible
Potential problems:



Not transparent to MNs (additional control messages)
Public-key encryption of MN keys may be a problem
for resource-constrained MNs
Multiple-path forwarding may cause inefficient use of
available bandwidth
HAWAII

Operation:




MN obtains co-located COA 1
and registers with HA 2
Handover: MN keeps COA,
new BS answers Reg. Request
and updates routers 4
MN views BS as foreign agent
Internet
HA
Backbone
Router
3
Crossover
Router
2
Mobile IP
Security provisions:


MN-FA authentication
mandatory
Challenge/Response Extensions
mandatory
BS
BS
BS
Mobile IP
MN
MN
DHCP
Server
1
DHCP
HAWAII: Security


Advantages:
 Mutual authentication and Challenge/Response extensions mandatory
 Only infrastructure components can influence routing entries
Potential problems:
 Co-located COA raises DHCP security issues
(DHCP has no strong authentication)
 Decentralised security-critical functionality
(Mobile IP registration processing during handover)
in base stations (BS)
 Authentication of HAWAII protocol messages unspecified
(potential attackers: stationary nodes in foreign network)
 MN authentication requires PKI or AAA infrastructure
PKI: Public Key Infrastructure
AAA: authentication, authorization and accounting
HAWAII: Other issues

Advantages:



Mostly transparent to MNs
(MN sends/receives standard Mobile IP messages)
Explicit support for dynamically assigned home addresses
Potential problems:


Mixture of co-located COA and FA concepts may not be
supported by some MN implementations
No private address support possible
because of co-located COA
Hierarchical Mobile IPv6 (HMIPv6)

Operation:




Network contains mobility anchor point
(MAP)
 mapping of regional COA (RCOA) to
link COA (LCOA)
Upon handover, MN informs
binding
MAP only
update
 gets new LCOA, keeps RCOA
HA is only contacted if MAP
changes
Security provisions:


no Hierarchical Mobile IPv6 -specific
security provisions
binding updates should be authenticated
Internet
HA
RCOA
MAP
AR
AR
LCOAnew
MN
LCOAold
MN
Hierarchical Mobility Agents



Problem: how to
reduce latency due
to signalling Agent
Solution: localise
signalling to visited
Domain
How, "method":
Regional
Registration/Regional Binding
Update
Hierarchical Mobile IP: Security
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Advantages:
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Local COAs can be hidden,
which provides some location privacy
Direct routing between CNs sharing the same link is
possible (but might be dangerous)
Potential problems:
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Decentralised security-critical functionality
(handover processing) in mobility anchor points
MNs can (must!) directly influence routing entries via
binding updates (authentication necessary)
Hierarchical Mobile IP: Other issues
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Advantages:
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Handover requires minimum number of overall changes to
routing tables
Integration with firewalls / private address support
possible
Potential problems:
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Not transparent to MNs
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Handover efficiency in wireless mobile scenarios:
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Complex MN operations
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All routing reconfiguration messages sent over wireless link
Other features (for IPv6 or seamless h/o)
• integration of Regional Registration with GPRS
•Header compression
•Buffer management
•UDP Lite
•AAA
HLR adaptation layer
•Challenge generation (optionally from HLR)
•Privacy considerations
•QoS handover
•Smooth handover mechanisms for keys