Mobility: vocabulary

Transcription

1 What is mobility? spectrum of mobility, from the perspective: no mobility high mobility mobile wireless user, using same access point mobile user, connecting/ disconnecting from using DHCP. mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) Wireless, Mobile Networks 6-1 Mobility: vocabulary home : permanent home of mobile (e.g., /24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote permanent address: address in home, can always be used to reach mobile e.g., wide area Wireless, Mobile Networks 6-2 1

2 Mobility: more vocabulary permanent address: remains constant (e.g., ) visited : in which mobile currently resides (e.g., /24) care-of-address: address in visited. (e.g., 79, ) wide area : wants to communicate with mobile foreign agent: entity in visited that performs mobility functions on behalf of mobile. Wireless, Mobile Networks 6-3 IP addresses: how to get one? Q: how does get subnet part of IP addr? A: gets allocated portion of its provider ISP s address space ISP's block /20 Organization /23 Organization /23 Organization / Organization /23 Network Layer 4-4 2

3 Hierarchical addressing: route aggregation hierarchical addressing allows efficient advertisement of routing information: Organization /23 Organization /23 Organization /23 Organization /23. Fly-By-Night-ISP Send me anything with addresses beginning /20 Internet ISPs-R-Us Send me anything with addresses beginning /16 Network Layer 4-5 Hierarchical addressing: more specific routes ISPs-R-Us has a more specific route to Organization 1 Organization /23 Organization /23 Organization /23. Fly-By-Night-ISP Send me anything with addresses beginning /20 Internet Organization /23 ISPs-R-Us Send me anything with addresses beginning /16 or /23 Network Layer 4-6 3

4 How do you contact a mobile friend: Consider friend frequently changing addresses, how do you find her? I wonder where Alice moved to? search all phone books? call her parents? expect her to let you know where he/she is? Wireless, Mobile Networks 6-7 Mobility: approaches let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile located no changes to end-systems let end-systems handle it: indirect routing: communication from to mobile goes through home agent, then forwarded to remote direct routing: gets foreign address of mobile, sends directly to mobile Wireless, Mobile Networks 6-8 4

5 Mobility: approaches let routing handle it: routers advertise permanent address of mobile-nodes-in-residence not via usual routing table exchange. scalable routing tables indicate where each mobile located to millions of no changes to end-systems mobiles let end-systems handle it: indirect routing: communication from to mobile goes through home agent, then forwarded to remote direct routing: gets foreign address of mobile, sends directly to mobile Wireless, Mobile Networks 6-9 Mobility: registration home visited wide 2 area foreign agent contacts home agent home: this mobile is resident in my 1 mobile contacts foreign agent on entering visited end result: foreign agent knows about mobile home agent knows location of mobile Wireless, Mobile Networks

6 Mobility via indirect routing home home agent intercepts packets, forwards to foreign agent foreign agent receives packets, forwards to mobile 3 visited addresses packets using home address of mobile 1 wide area 2 4 mobile replies directly to Wireless, Mobile Networks 6-11 Indirect Routing: comments mobile uses two addresses: permanent address: used by (hence mobile location is transparent to ) care-of-address: used by home agent to forward datagrams to mobile foreign agent functions may be done by mobile itself triangle routing: -home- -mobile inefficient when, mobile are in same Wireless, Mobile Networks

7 Indirect routing: moving between s suppose mobile user moves to another registers with new foreign agent new foreign agent registers with home agent home agent update care-of-address for mobile packets continue to be forwarded to mobile (but with new care-of-address) mobility, changing foreign s transparent: on going connections can be maintained! Wireless, Mobile Networks 6-13 Mobility via direct routing forwards to foreign agent foreign agent receives packets, forwards to mobile visited home requests, receives foreign address of mobile mobile replies directly to Wireless, Mobile Networks

8 Mobility via direct routing: comments overcome triangle routing problem non-transparent to : must get care-of-address from home agent what if mobile changes visited? Wireless, Mobile Networks 6-15 Accommodating mobility with direct routing anchor foreign agent: FA in first visited data always routed first to anchor FA when mobile moves: new FA arranges to have data forwarded from old FA (chaining) wide area 1 agent anchor foreign agent new foreign agent foreign net visited at session start 2 new foreign Wireless, Mobile Networks

9 Mobile IP RFC 3344 has many features we ve seen: home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a -packet) three components to standard: indirect routing of datagrams agent discovery registration with home agent Wireless, Mobile Networks 6-17 Mobile IP: indirect routing foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet dest: dest: dest: Permanent address: dest: packet sent by Care-of address: Wireless, Mobile Networks

10 Mobile IP: agent discovery agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) H,F bits: home and/or foreign agent R bit: registration required Wireless, Mobile Networks 6-19 Mobile IP: registration example Wireless, Mobile Networks

11 Components of cellular architecture cell covers geographical region base station (BS) analogous to AP mobile users attach to through BS air-interface: physical and link layer protocol between mobile and BS connects cells to wired tel. net. manages call setup (more later!) handles mobility (more later!) Mobile Switching Center Mobile Switching Center Public telephone wired Wireless, Mobile Networks 6-21 Cellular s: the first hop Two techniques for sharing mobile-to-bs radio spectrum combined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slots CDMA: code division multiple access frequency bands OFDM: orthogonal frequency division multiplexing time slots Wireless, Mobile Networks

12 2G (voice) architecture Base station system (BSS) BTS BSC G Gateway Public telephone Legend Base transceiver station (BTS) Base station controller (BSC) Mobile Switching Center () Mobile subscribers Wireless, Mobile Networks G (voice+data) architecture radio controller G Gateway Public telephone Key insight: new cellular data operates in parallel (except at edge) with existing cellular voice voice unchanged in core data operates in parallel SGSN G GGSN Public Internet Serving GPRS Support Node (SGSN) Gateway GPRS Support Node (GGSN) Wireless, Mobile Networks

13 3G (voice+data) architecture radio controller G Gateway Public telephone SGSN G GGSN Public Internet radio interface (WCDMA, HSDPA) radio access Universal Terrestrial Radio Access Network (UTRAN) core General Packet Radio Service (GPRS) Core Network public Internet Wireless, Mobile Networks 6-25 Handling mobility in cellular s home : of cellular provider you subscribe to (e.g., Sprint PCS, Verizon) home location register (HLR): database in home containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another ) visited : in which mobile currently resides visitor location register (VLR): database with entry for each user currently in could be home Wireless, Mobile Networks

14 GSM: indirect routing to mobile home consults HLR, gets roaming number of mobile in visited mobile user HLR 2 home home Mobile Switching Center VLR Mobile Switching Center 4 visited 3 1 call routed to home Public switched telephone home sets up 2 nd leg of call to in visited in visited completes call through base station to mobile Wireless, Mobile Networks 6-27 GSM: handoff with common old BSS VLR Mobile Switching Center old routing new routing new BSS handoff goal: route call via new base station (without interruption) reasons for handoff: stronger signal to/from new BSS (continuing connectivity, less battery drain) load balance: free up channel in current BSS GSM doesn t mandate why to perform handoff (policy), only how (mechanism) handoff initiated by old BSS Wireless, Mobile Networks

15 GSM: handoff with common old BSS VLR Mobile Switching Center new BSS 1. old BSS informs of impending handoff, provides list of 1 + new BSSs 2. sets up path (allocates resources) to new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS 6. mobile, new BSS signal to activate new channel 7. mobile signals via new BSS to : handoff complete. reroutes call 8 -old-bss resources released Wireless, Mobile Networks 6-29 GSM: handoff between s home Home anchor PSTN (a) before handoff anchor : first visited during call call remains routed through anchor new s add on to end of chain as mobile moves to new optional path minimization step to shorten multi- chain Wireless, Mobile Networks

16 GSM: handoff between s home Home anchor PSTN (b) after handoff anchor : first visited during call call remains routed through anchor new s add on to end of chain as mobile moves to new optional path minimization step to shorten multi- chain Wireless, Mobile Networks 6-31 Mobility: GSM versus Mobile IP GSM element Comment on GSM element Mobile IP element Home system Gateway Mobile Switching Center, or home. Home Location Register (HLR) Visited System Visited Mobile services Switching Center. Visitor Location Record (VLR) Mobile Station Roaming Number (MSRN), or roaming number Network to which mobile user s permanent phone number belongs Home : point of contact to obtain routable address of mobile user. HLR: database in home system containing permanent phone number, profile information, current location of mobile user, subscription information Network other than home system where mobile user is currently residing Visited : responsible for setting up calls to/from mobile nodes in cells associated with. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user Routable address for telephone call segment between home and visited, visible to neither the mobile nor the. Home Home agent Visited Foreign agent Care-of -address Wireless, Mobile Networks