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Mobile Data Networking
Prof. Ian W Marshall
[email protected]
Mobile Data Services
• Enhanced SMS & e-mail
• Location Services
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Find restaurant/garage/me
Tourist info
Who is that over there
Link to GIS
Operations management
• WWW on the move
• MP3
• Voice over IP (VOIP)
GSM Overview
Fixed-mobile
Interface
AUC
HLR
MS
MSC
BSS
EIR
ME
SIM
Radio
Interface
VLR
PSTN
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
Wireless data?
• Users want access to data while on the
move
• BUT MS is not a PC
• WAP attempts a bridging capability
MS
Gateway
(coders &
Decoders)
Web
server
Evolution
• GSM –
• slow to connect
• Requires dispatch cache (only on for calls)
• GPRS
• Always on
• More bandwidth?
• More services
• 3G mobile
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Client is a true PDA
More bandwidth (is it enough?)
Still need internet gateways (inefficient routing)
Probably expensive
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
DHCP
• Dynamic host configuration protocol
• IETF RFC 2131 (and more recent extensions)
• Automatic allocation of reusable network
addresses
• Additional configuration options
• Allows network layer mobility
• Clients can use network from anywhere (if
authorised)
• Sessions (e.g. TCP not mobile – no handover)
• Servers do not have permanent addresses
Basic operation of DHCP
• Client broadcasts DHCP discover message
• Relay possible via BOOTP relay
• Contacted servers respond with DHCP Offer
messages
• Client picks a server and sends ( via broadcast)
DHCP request to identified server
• Servers get message and identified server
responds with DHCP ack containing IP config
details (or DHCP nack if request fails), and
lease period
• Client configures itself
• Client either renews using DHCP request or
terminates using DHCP release
DHCP Schematic
Server A (not selected)
Client
DHCPDISCOVER
Begins
Server B (selected)
DHCPDISCOVER
Determines Config
DHCPOFFER
Determines Config
DHCPOFFER
Collects replies
Selects config (& server)
DHCPREQUEST
Commits Config
Initialises IP stack
Shutdown
DHCPACK
DHCPRELEASE
Discards Lease
DHCP Messages
• Always broadcast
• Always contain
• Message opcode
• Client hardware address
• May contain
• Server address and fully qualified DNS name
• Offered IP address
• Important options
• Get specified address
• Address lease time
• MTU size
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 to enable transport layer
mobility.
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.
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 node’s foreign link
» Advertises
» Forwards registrations
» Detunnels
• Correspondent node – a remote host
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 TTL=1) can be
sent by MN
• Discovery also possible using link layer
mechanisms where available
Agent Discovery
IP Header:
IP(src)=agent’s address
CN
IP(dst)=broadcast
Public network
IP(protocol)=ICMP
Mobility Agent extension:
Routers
Registration lifetime
RBHF etc.
Care of address(es)
HA
Home network
FA
MN
Foreign Network
MN examines adverts and decides whether home or away
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
Registration Messages
Registration request
Registration reply
IP header (src, dst)
IP header (src, dst)
UDP header (src = MN
choice, dst=port 434)
UDP header (src=var,
dstport=rqstsrc)
Type/bits/lifetime(secs)
Type/code/lifetime(secs)
Home address
Home address
Home agent
Home agent
Care of Address
Registration ID
Registration ID (64 bit)
Extensions
Extensions (e.g. authent)
Registration
CN
Public network
Routers
Request
Reply
HA
Home network
FA
MN
Foreign Network
Data Forwarding (at home)
CN
Public network
Routers
MN
HA
Home network
FA
Foreign Network
Data Forwarding (Away)
CN
Public network
Routers
HA
Home network
IP/IP
Tunnel
FA
MN
Foreign Network
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
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.
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
IPv6
• 32 bit -> 128 bit address space
• Enables big increase in no. of mobile hosts
• Enables permanent address allocation
•
•
•
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Extension headers
Authentication header
Neighbour discovery
Address autoconfiguration
Discovery agent
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)
Example of route optimisation
2-Binding ack
1-Update CoA
Mobile node
Home agent
5-send more
packets
3-send 1st
packet
4-update binding cache
Correspondent node
Wireless IP?
• Cellular IP –
www.ctr.columbia.edu/~andras/cellularip/
• 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/~boosters/
Or something over the horizon?
References
• Mobile IP WG – http://www.ietf.org/
html.charters/mobileip-charter.html links to
drafts on:
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•
•
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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