Mobile Data Networking

Prof. Ian W MarshallIan.w.marshall@bt.com

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)

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

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 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

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

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

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

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

Registration

HAMN

FA

CN

Home network Foreign Network

Public network

Routers

Request

Reply

Data Forwarding (at home)

HAMN FA

CN

Home network Foreign Network

Public network

Routers

Data Forwarding (Away)

HAMN

FA

CN

Home network Foreign Network

Public network

Routers

IP/IP Tunnel

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

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

Correspondent node

Mobile nodeHome agent

2-Binding ack

1-Update CoA

4-update binding cache

3-send 1st packet5-send more

packets

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