Mobile Data Networking

1
Mobile Data Networking

• Prof. Ian W Marshall
• Ian.w.marshall_at_bt.com

2
Mobile Data Services

• Enhanced SMS e-mail
• Location Services
• Find restaurant/garage/me
• Tourist info
• Who is that over there
• Link to GIS
• Operations management
• WWW on the move
• MP3
• Video??

3
GSM Overview
Fixed-mobile Interface
AUC
HLR
VLR
MS
MSC
PSTN
BSS
AUC authentication centre BSS Base station
system EIR equipment identity register HLR
Home location register ME mobile equipment MS
Mobile station MSC Mobile switching centre OMC
Ops Maintenance centre VLR Visited location
register
EIR
ME
SIM
Radio Interface
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GSM security

• Charging, fraud prevention, confidentiality
• Cryptographic authentication
• Ciphering of traffic control data on air
  interface only (A5 algorithm)
• Assumes fixed network is secure (not Internet)
• Subscriber identity module (SIM) is security
  module for keys etc
• International mobile subscribers identity
• 128 bit secret key, K (also kept at AUC on subs
  HLR)
• Performs all calculations using K

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GSM binding

• MS sends IMSI to AUC
• AUC chooses a random 128 bit challenge RAND,
  and computes a 64 bit session key KS
• AUC computes a 32 bit expected response
  XRESA8(K, RAND)
• RAND is sent back to MS by HLR/BSS
• SIM computes KS RESA3(K, RAND), sends RES to
  BS
• If RESXRES at BS then MS is authenticated and
  session proceeds
• KS is used as key by A5 wired into ME

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GSM roaming

• Use a VLR
• VLR caches RAND, KS, XRES
• Calculated and sent by HLR on registration using
  the K for the mobile IMSI
• KS A8(K, RAND)
• XRES A3(K, RAND)

7
Wireless data?

• Users want access to data while on the move
• BUT MS is not a PC
• WAP attempts a bridging capability

Gateway (coders Decoders)
Web server
MS
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Evolution

• GSM
• slow to connect
• Requires dispatch cache (only on for calls)
• GPRS
• Always on
• More bandwidth?
• More services
• 3G mobile
• Client is a true PDA
• More bandwidth (is it enough?)
• Still need internet gateways (inefficient
  routing)
• Probably expensive

9
Other options

• IEEE 802.11 (Wavelan)
• 10 Mbit/s
• Link layer only
• Bluetooth
• Small range (10m) bandwidth (620K)
• Infrared
• Line of sight only, proprietary interfaces

10
Mobile IP

• A protocol that enables hosts to move from one IP
  subnet to another and yet
• Always be reachable
• maintain existing connections (but update is too
  slow for real time handover).
• Layer 3 technology that can be used with any
  link-layer device, whether wired or wireless.

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Salient features of Mobile IPv4

• Mobile nodes (MN) can move from one IP subnet to
  another.
• Mobility support provided using home agents (HA)
  and foreign agents (FA).
• Employs protocol tunneling for data forwarding.
• Uses soft- state (time-outs and refreshes).
• Authentication using keyed MD5 (default).
• Changes required only at HA, FA, MN.

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Components

• Mobile node
• A node that changes its point of attachment
• Home Agent
• A router with an interface on the mobile nodes
  home link, and an enhanced datastore
• Advertises
• Registers
• Holds Care of Address
• Tunnels
• Foreign Agent
• A router on the mobile nodes foreign link
• Advertises
• Forwards registrations
• Detunnels
• Correspondent node a remote host

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Agent Discovery

• Provides current location and move detection
  information for mobile nodes.
• HA and FA transmit Agent Advertisements (1 hop
  ICMP messages - AAs) to advertise their services
  on a link.
• MN deduces its current location based on the
  presence/content of AAs.
• If no AA received an agent solicitation message
  (ICMP router solicitation with TTL1) can be sent
  by MN
• Discovery also possible using link layer
  mechanisms where available

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Agent Discovery
IP Header
IP(src)agents address
IP(dst)broadcast
IP(protocol)ICMP
Mobility Agent extension
Registration lifetime
RBHF etc.
Care of address(es)
CN
Public network
Routers
MN
HA
FA
Foreign Network
Home network
MN examines adverts and decides whether home or
away
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Registration

• Used to set up mobility states at HA, FA, MN.
• MN chooses CoA and sends Registration Request
  message to FA (UDP).
• FA relays the message to HA.
• HA sets up mobility state and sends Registration
  Reply message (UDP)to FA.
• FA then sets up mobility state and relays message
  to MN.
• Mobility states have finite lifetime and require
  periodic refresh of registration messages.
• If at home registration goes to HA. HA adjusts
  state and replies to MN

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Registration Messages
Registration request
Registration reply
IP header (src, dst)
UDP header (src MN choice, dstport 434)
Type/bits/lifetime(secs)
Home address
Home agent
Care of Address
Registration ID (64 bit)
Extensions (e.g. authent)
IP header (src, dst)
UDP header (srcvar, dstportrqstsrc)
Type/code/lifetime(secs)
Home address
Home agent
Registration ID
Extensions
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Registration
CN
Public network
Routers
Request
Reply
MN
HA
FA
Foreign Network
Home network
18
Data Forwarding (at home)
CN
Public network
Routers
HA
FA
MN
Foreign Network
Home network
19
Data Forwarding (Away)
CN
Public network
Routers
IP/IP Tunnel
MN
HA
FA
Foreign Network
Home network
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Tunnelling

• Tunnel is a path followed by a packet while
  encapsulated in the payload of a second packet
• Encapsulating packet is a standard packet
  addressed to FA

Outer Header
Header
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Security

• Registration message authentication (keyed-MD5 is
  default).
• Based on mobile security association
• MN- HA key is compulsory.
• MN- FA, FA- HA keys are optional.

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DHCP and security

• Dynamic host configuration
• No permanent IP address
• MD5 key cannot be calculated
• Still need to authenticate mobile host
• NAI
• Originally just for PPP hosts
• Now generalised
• Extension to registration request

23
IPv6

• 32 bit -gt 128 bit address space
• Enables big increase in no. of mobile hosts
• Enables permanent address allocation
• Extension headers
• Authentication header
• Neighbour discovery
• Address autoconfiguration
• Discovery agent

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Outline of operation (IPv6)

• Mobile node determines location (neighbour
  discovery, anycast)
• Behaves like fixed node when at home
• Uses autoconfiguration to obtain care of address
  (stateful or stateless)
• Reports COA to selected correspondents including
  home agent
• New correspondents get update from home agent (or
  use IPv4 mechanisms)

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Example of route optimisation
2-Binding ack
1-Update CoA
Mobile node
Home agent
3-send 1st packet
5-send more packets
4-update binding cache
Correspondent node
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Wireless IP?

• Cellular IP www.ctr.columbia.edu/andras/cellula
  rip/
• Ad-Hoc networks - www.ietf.cnri.reston.va.us/html.
  charters/manet-charter.html
• Programmable hardware Soft radio
  klamath.stanford.edu/NetFPGA/ www.cis.upenn.edu/b
  oosters/
• Or something over the horizon?

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References

• Mobile IP WG http//www.ietf.org/
  html.charters/mobileip-charter.html links to
  drafts on
• Route optimisation
• Mobile IPv6
• Mobile IPv4
• Generalised NAI
• Other IETF drafts/RFCs are referenced
• Mobile IP at NUS - http//mip.ee.nus.edu.sg
• Charles E. Perkins Mobile IP Design Principles
  and Practices, Addison-Wesley, 1998
• James D. Solomon Mobile IP The Internet
  Unplugged, Prentice Hall, 1997