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Special Topics in Computer Engineering Wireless and Mobile Networks II Some of these Slides are Based on Slides by Kurose and Ross Prepared for Sections 6.4 – 6.8 of the Book Computer Networking: A Top Down Approach Featuring the Internet Spring 2006 CPE 0907532:Wireless and Mobile Networks II 1 Chapter 6 outline 6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4 Cellular Internet Access architecture standards (e.g., GSM) Spring 2006 Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higherlayer protocols 6.9 Summary CPE 0907532:Wireless and Mobile Networks II 2 A wireless network : 802.11 network infrastructure Wi-Fi Hotspot Spring 2006 CPE 0907532:Wireless and Mobile Networks II 3 Components of cellular network architecture MSC cell connects cells to wide area net manages call setup (more later!) handles mobility (more later!) covers geographical region base station (BS) analogous to 802.11 AP mobile users attach to network through BS air-interface: physical and link layer protocol between mobile and BS Spring 2006 Mobile Switching Center Public telephone network, and Internet Mobile Switching Center wired network : Public Switched Telephone Network (PSTN) OR the Internet 4 Components of cellular network architecture Coverage area of cell depends on factors, including : Transmitting power of base station Transmitting power of mobile station Obstructing buildings in cell Height of base station antennae Many systems place base stations at corners where three cells intersect A single base station with directional antennas can service three cells Spring 2006 Mobile Switching Center Public telephone network, and Internet Mobile Switching Center CPE 0907532:Wireless and Mobile Networks II 5 Cellular networks: the first hop Many simultaneous calls take place in a cell Calls share the portion of the radio spectrum allocated to the cellular service provider 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 Spring 2006 CPE 0907532:Wireless and Mobile Networks II 6 Pure FDM and TDM FDMA Channel is partitioned into a number of frequency bands, with each band devoted to a call TDMA Time is partitioned into frames • Each frame is further partitioned into slots • Each call being assigned the use of a particular slot in the frame Spring 2006 CPE 0907532:Wireless and Mobile Networks II 7 Cellular networks: Combined FDM/TDM Channel is partitioned into a number ( F ) of frequency sub-bands For each sub-band, time is partitioned into frames and each frame into a number of slots , T Channel will be able to time slots frequency bands support F * T simultaneous calls Spring 2006 CPE 0907532:Wireless and Mobile Networks II 8 Cellular networks: Code division multiple access (CDMA) Users share same radio frequency Each user is allocated a distinct chipping sequence Sender and receiver use the same chipping sequence Receiver recovers sender’s transmission from among simultaneous transmissions from other senders Spring 2006 CPE 0907532:Wireless and Mobile Networks II 9 Cellular standards: brief survey I 2G systems: voice channels IS-136 TDMA: combined FDMA/TDMA (north america) GSM (global system for mobile communications): combined FDMA/TDMA most widely deployed IS-95 CDMA: code division multiple access GSM Spring 2006 Don’t drown in a bowl of alphabet soup: use this for reference only CPE 0907532:Wireless and Mobile Networks II 10 Cellular standards: brief survey II 2.5 G systems: voice and data channels for those who can’t wait for 3G service: 2G extensions general packet radio service (GPRS) evolved from GSM data sent on multiple channels (if available) enhanced data rates for global evolution (EDGE) also evolved from GSM, using enhanced modulation Date rates up to 384K CDMA-2000 (phase 1) data rates up to 144K evolved from IS-95 Spring 2006 CPE 0907532:Wireless and Mobile Networks II 11 Cellular standards: brief survey III 3G systems: voice/data Universal Mobile Telecommunications Service (UMTS) GSM next step, but using CDMA CDMA-2000 Spring 2006 CPE 0907532:Wireless and Mobile Networks II 12 Chapter 6 outline 6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4 Cellular Internet Access architecture standards (e.g., GSM) Spring 2006 Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higherlayer protocols 6.9 Summary CPE 0907532:Wireless and Mobile Networks II 13 What is mobility? spectrum of mobility, from the network perspective: no mobility high mobility mobile wireless user, mobile user, using same access connecting/ point disconnecting from network using DHCP. Spring 2006 mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) CPE 0907532:Wireless and Mobile Networks II 14 Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 Spring 2006 home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network correspondent CPE 0907532:Wireless and Mobile Networks II 15 Mobility: more vocabulary Permanent address: remains constant (e.g., 128.119.40.186) visited network: network in which mobile currently resides (e.g., 79.129.13/24) Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile CPE 0907532:Wireless and Mobile Networks II 16 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? Spring 2006 CPE 0907532:Wireless and Mobile Networks II 17 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 correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Spring 2006 CPE 0907532:Wireless and Mobile Networks II 18 Mobility: approaches Let routing handle it: routers advertise permanent not address of mobile-nodes-in-residence via usual scalable routing table exchange. to millions of routing tables indicate mobiles where each mobile located no changes to end-systems let end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote direct routing: correspondent gets foreign address of mobile, sends directly to mobile Spring 2006 CPE 0907532:Wireless and Mobile Networks II 19 Mobility: registration visited network home network 2 1 wide area network foreign agent contacts home agent home: “this mobile is resident in my network” mobile contacts foreign agent on entering visited network End result: Foreign agent knows about mobile Home agent knows location of mobile Spring 2006 CPE 0907532:Wireless and Mobile Networks II 20 Mobility via Indirect Routing foreign agent receives packets, forwards to mobile home agent intercepts packets, forwards to foreign agent home network visited network 3 wide area network correspondent addresses packets using home address of mobile Spring 2006 1 2 4 mobile replies directly to correspondent CPE 0907532:Wireless and Mobile Networks II 21 Indirect Routing: comments Mobile uses two addresses: permanent address: used by correspondent (hence mobile location is transparent to correspondent) care-of-address: used by home agent to forward datagrams to mobile foreign agent functions may be done by mobile itself triangle routing: correspondent-home-networkmobile inefficient when correspondent, mobile are in same network Spring 2006 CPE 0907532:Wireless and Mobile Networks II 22 Indirect Routing: moving between networks suppose mobile user moves to another network 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 networks transparent: on going connections can be maintained! Spring 2006 CPE 0907532:Wireless and Mobile Networks II 23 Mobility via Direct Routing correspondent forwards to foreign agent foreign agent receives packets, forwards to mobile home network 4 wide area network 2 correspondent requests, receives foreign address of mobile Spring 2006 visited network 1 3 4 mobile replies directly to correspondent CPE 0907532:Wireless and Mobile Networks II 24 Mobility via Direct Routing: comments overcome triangle routing problem non-transparent to correspondent: correspondent must get care-of-address from home agent what if mobile changes visited network? Spring 2006 CPE 0907532:Wireless and Mobile Networks II 25 Accommodating mobility with direct routing anchor foreign agent: FA in first visited network data always routed first to anchor FA when mobile moves: new FA arranges to have data forwarded from old FA (chaining) foreign net visited at session start wide area network anchor foreign agent 1 2 4 5 correspondent agent correspondent Spring 2006 3 new foreign agent new foreign network CPE 0907532:Wireless and Mobile Networks II 26 mobility with direct routing Details Step I: data forwarded to mobile in foreign network where mobile was located when session first started Step 2: mobile moves to a new foreign network Step 3: mobile registers with new foreign agent Step 4: new foreign agent provides anchor foreign agent with mobile new COA Step 5: anchor foreign agent receives an encapsulated datagram for a departed mobile it re-encapsulate datagram and forward it to mobile using new COA If mobile node moves again to a new foreign network, foreign agent in new network contacts anchor foreign agent to set up forwarding to new foreign network foreign net visited at session start wide area network anchor foreign agent 1 2 4 5 correspondent agent correspondent Spring 2006 3 new foreign agent new foreign network CPE 0907532:Wireless and Mobile Networks II 27 Chapter 6 outline 6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4 Cellular Internet Access architecture standards (e.g., GSM) Spring 2006 Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higherlayer protocols 6.9 Summary CPE 0907532:Wireless and Mobile Networks II 28 Mobile IP Internet architecture and protocols for supporting mobility collectively known as Mobile IP Defined in RFC 3220 has many features we’ve seen: home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) Spring 2006 CPE 0907532:Wireless and Mobile Networks II 29 Mobile IP Three Components Indirect routing of datagrams The manner in which datagrams are forwarded to mobile nodes by a home agent including • Rules for forwarding datagrams • Rules for handling error conditions • Several forms of encapsulation [RFC 2003, RFC 2004] Agent discovery Protocols used by agents to advertise services Protocols for mobile nodes to solicit services Registration with home agent Protocols used by mobile node and/or foreign agent to register and deregister COAs with home agent Security: discussed in chapter 8 Spring 2006 CPE 0907532:Wireless and Mobile Networks II 30 Mobile IP: indirect routing foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet dest: 79.129.13.2 dest: 128.119.40.186 dest: 128.119.40.186 Permanent address: 128.119.40.186 dest: 128.119.40.186 Care-of address: 79.129.13.2 packet sent by correspondent Spring 2006 CPE 0907532:Wireless and Mobile Networks II 31 Mobile IP: agent discovery agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) IP of Agent 0 16 8 type = 9 24 checksum =9 code = 0 =9 H : a home agent F : a foreign agent standard ICMP fields router address R: registration required •A mobile user in this network must type = 16 register with a foreign agent length registration lifetime •Cannot obtain a care-of address in foreign network and assume functionality of foreign agent Spring 2006 sequence # RBHFMGV bits reserved 0 or more care-ofaddresses CPE 0907532:Wireless and Mobile Networks II mobility agent advertisement extension 32 Mobile IP: registration example home agent HA: 128.119.40.7 foreign agent COA: 79.129.13.2 visited network: 79.129.13/24 ICMP agent adv. COA: 79.129.13.2 …. registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format …. Mobile agent MA: 128.119.40.186 registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 …. registration reply time Spring 2006 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format …. registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 …. CPE 0907532:Wireless and Mobile Networks II 33 Components of cellular network architecture recall: correspondent wired public telephone network MSC MSC MSC MSC MSC different cellular networks, operated by different providers Spring 2006 CPE 0907532:Wireless and Mobile Networks II 34 Handling mobility in cellular networks home network: network of cellular provider you subscribe to (e.g., Fastlink, Jo Mobilecom) home location register (HLR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network) visited network: network in which mobile currently resides visitor location register (VLR): database with entry for each user currently in network Spring 2006 CPE 0907532:Wireless and Mobile Networks II 35 GSM: indirect routing to mobile home network HLR 2 home MSC consults HLR, gets roaming number of mobile in visited network correspondent home Mobile Switching Center 1 3 VLR 4 mobile user Spring 2006 Mobile Switching Center Public switched telephone network call routed to home network home MSC sets up 2nd leg of call to MSC in visited network MSC in visited network completes call through base station to mobile visited network CPE 0907532:Wireless and Mobile Networks II 36 GSM: handoff with common MSC Handoff goal: route call via new base station (without interruption) reasons for handoff: VLR Mobile Switching Center old routing old BSS new routing new BSS stronger signal to/from new BSS (continuing connectivity, less battery drain) load balance: free up channel in current BSS (cell overloaded with a large # of calls) GSM doesn’t mandate why to perform handoff (algorithms used to determine whether or not to perform handoff) • only how (mechanism) handoff initiated by old BSS Spring 2006 CPE 0907532:Wireless and Mobile Networks II 37 GSM: handoff with common MSC VLR Mobile Switching Center 2 4 1 8 old BSS 5 Spring 2006 7 3 6 new BSS 1. old BSS informs MSC of impending handoff, provides list of 1+ new BSSs 2. MSC sets up path (allocates resources) to new BSS 3. new BSS allocates radio channel for use by mobile 4. new BSS signals MSC, 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 MSC: handoff complete. MSC reroutes call 8 MSC-old-BSS resources released CPE 0907532:Wireless and Mobile Networks II 38 GSM: handoff between MSCs anchor MSC: first MSC visited during call home network correspondent Home MSC anchor MSC PSTN call remains routed through anchor MSC Two alternatives Maintaining a single MSC-hop from anchor MSC to current MSC (illustrated in figure) MSC MSC MSC (a) before handoff Spring 2006 CPE 0907532:Wireless and Mobile Networks II 39 GSM: handoff between MSCs anchor MSC: first MSC visited during call home network correspondent Home MSC anchor MSC PSTN MSC MSC MSC (b) after handoff Spring 2006 call remains routed through anchor MSC Two alternatives Maintaining a single MSC-hop from anchor MSC to current MSC (illustrated in figure) Chain the MSCs visited by mobile • An old MSC forward ongoing call to new MSC each time mobile moves to new MSC • IS-41 allows optional path minimization step to shorten multi-MSC chain CPE 0907532:Wireless and Mobile Networks II 40 Mobility: GSM versus Mobile IP GSM element Comment on GSM element Mobile IP element Home system Network to which the mobile user’s permanent phone number belongs Home network Gateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR) Home MSC: 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 Home agent Visited System Network other than home system where mobile user is currently residing Visited network Visited Mobile Services Switching Center. Visitor Location Record (VLR) Visited MSC: responsible for setting up calls to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user Foreign agent Mobile Station Roaming Number (MSRN), or “roaming number” Routable address for telephone call segment between home MSC and visited MSC, visible to neither the mobile nor the correspondent. Care-ofaddress Spring 2006 CPE 0907532:Wireless and Mobile Networks II 41 Wireless, mobility: impact on transport protocols logically, impact should be minimal … best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobile … but performance-wise: packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff TCP interprets loss as congestion, will decrease congestion window un-necessarily TCP’s congestion control could be problematic in wireless networks Spring 2006 CPE 0907532:Wireless and Mobile Networks II 42 Wireless, mobility: impact on application protocols limited bandwidth of wireless links Applications must treat bandwidth as a scare commodity Serving content to a browser on 3G phone same image-rich content is not possible like serving a browser operating over a wired connection mobility makes possible a rich set of location-aware and context-aware applications we’ve only seen tip of iceberg impact of wireless and mobile networks on networked applications and their protocols! Spring 2006 CPE 0907532:Wireless and Mobile Networks II 43