Mobile Data Networking

Prof. Ian W Marshall [email protected]

Mobile Data Services

• Enhanced SMS & e-mail • Location Services • MP3 – Find restaurant/garage/me – Tourist info – Who is that over there – Link to GIS – Operations management • WWW on the move • Voice over IP (VOIP)

MS ME SIM Radio Interface BSS

GSM Overview

AUC HLR VLR Fixed-mobile Interface EIR MSC 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 • 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 Begins Server B (selected) DHCPDISCOVER DHCPDISCOVER Determines Config DHCPOFFER Determines Config Collects replies Selects config (& server) DHCPOFFER DHCPREQUEST Commits Config DHCPACK Initialises IP stack Shutdown 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

IP Header: IP(src)=agent’s address IP(dst)=broadcast IP(protocol)=ICMP Mobility Agent extension: Registration lifetime RBHF etc.

Care of address(es)

Agent Discovery

Public network Routers HA Home network CN MN FA 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 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 reply IP header (src, dst) UDP header (src=var, dstport=rqstsrc) Type/code/lifetime(secs) Home address Home agent Registration ID Extensions

Registration

CN HA Home network Public network Routers Reply Request MN FA 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 MN FA 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 • 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 5-send more packets 3-send 1 st packet Home agent 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:

• 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