Mobile Data Networking Prof. Ian W Marshall

Mobile Data Services Enhanced SMS & Location Services –Find restaurant/garage/me –Tourist info –Who is that over there –Link to GIS –Operations management WWW on the move MP3 Video??

GSM Overview 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 SIM ME MS BSS MSC EIR PSTN Radio Interface Fixed-mobile Interface AUC HLRVLR

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

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 XRES=A8(K, RAND) RAND is sent back to MS by HLR/BSS SIM computes KS & RES=A3(K, RAND), sends RES to BS If RES=XRES at BS then MS is authenticated and session proceeds KS is used as key by A5 wired into ME

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)

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

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.

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

Registration HA MN FA CN Home network Foreign Network Public network Routers Request Reply

Data Forwarding (at home) HA MN FA CN Home network Foreign Network Public network Routers

Data Forwarding (Away) HA MN 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 Outer 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 node Home agent 2-Binding ack 1-Update CoA 4-update binding cache 3-send 1 st packet 5-send more packets

Wireless IP? Cellular IP – Ad-Hoc networks - -charter.html Programmable hardware & Soft radio – klamath.stanford.edu/NetFPGA/ Or something over the horizon?

References Mobile IP WG – 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 - Charles E. Perkins – Mobile IP: Design Principles and Practices, Addison-Wesley, 1998 James D. Solomon – Mobile IP: The Internet Unplugged, Prentice Hall, 1997