Mobile Data Networking Prof. Ian W Marshall Ian.firstname.lastname@example.org
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 Fixed-mobile Interface AUC HLR VLR MS MSC PSTN BSS 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 EIR ME SIM Radio Interface
Wireless data? • Users want access to data while on the move • BUT MS is not a PC • WAP attempts a bridging capability Gateway (coders & Decoders) Web server MS
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 DHCPDISCOVER DHCPDISCOVER DHCPOFFER 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 oneIP 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 anylink-layer device, whether wired or wireless to enable transport layer mobility.
Salient features of Mobile IPv4 • Mobile nodes (MN) can move from one IP subnetto 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 detectioninformation 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 thepresence/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 CN Public network Routers MN HA FA Foreign Network Home 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 RegistrationReply message (UDP)to FA. • FA then sets up mobilitystate and relays message to MN. • Mobility states have finite lifetime and requireperiodic refresh of registration messages. • If at home registration goes to HA. HA adjusts state and replies to MN
Registration Messages Registration request Registration reply
Registration CN Public network Routers Request Reply MN HA FA Foreign Network Home network
Data Forwarding (at home) CN Public network Routers HA FA MN Foreign Network Home network
Data Forwarding (Away) CN Public network Routers IP/IP Tunnel MN HA FA Foreign Network Home 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 Home agent 3-send 1st packet 5-send more packets 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