mobile data networking prof. ian w marshall [email protected]
Post on 19-Dec-2015
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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• Voice over IP (VOIP)
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GSM Overview
AUC – authentication centreBSS – Base station systemEIR – equipment identity registerHLR – Home location registerME – mobile equipmentMS – Mobile stationMSC – Mobile switching centreOMC – Ops & Maintenance centreVLR – Visited location register
SIM
ME
MS
BSSMSC
EIR
PSTN
RadioInterface
Fixed-mobileInterfaceAUC
HLR VLR
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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
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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
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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
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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
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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
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DHCP SchematicServer A (not selected) Client Server B (selected)
Begins
Determines Config Determines Config
Collects replies
Selects config (& server)
Commits Config
Initialises IP stack
Shutdown
Discards Lease
DHCPDISCOVER
DHCPOFFER
DHCPDISCOVER
DHCPOFFER
DHCPREQUEST
DHCPACK
DHCPRELEASE
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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
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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.
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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 node’s 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 TTL=1) can be sent by MN
• Discovery also possible using link layer mechanisms where available
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Agent Discovery
HAMN
FA
CN
Home network Foreign Network
Public network
Routers
IP Header:
IP(src)=agent’s address
IP(dst)=broadcast
IP(protocol)=ICMP
Mobility Agent extension:
Registration lifetime
RBHF etc.
Care of address(es)
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
IP header (src, dst)
UDP header (src = MN choice, dst=port 434)
Type/bits/lifetime(secs)
Home address
Home agent
Care of Address
Registration ID (64 bit)
Extensions (e.g. authent)
Registration request Registration reply
IP header (src, dst)
UDP header (src=var, dstport=rqstsrc)
Type/code/lifetime(secs)
Home address
Home agent
Registration ID
Extensions
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Registration
HAMN
FA
CN
Home network Foreign Network
Public network
Routers
Request
Reply
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Data Forwarding (at home)
HAMN FA
CN
Home network Foreign Network
Public network
Routers
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Data Forwarding (Away)
HAMN
FA
CN
Home network Foreign Network
Public network
Routers
IP/IP Tunnel
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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
OuterHeader 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
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IPv6
• 32 bit -> 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
Correspondent node
Mobile nodeHome agent
2-Binding ack
1-Update CoA
4-update binding cache
3-send 1st packet5-send more
packets
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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?
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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