Wireless and Mobile Management
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JFK/KWR Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition Jim Kurose, Keith Ross Addison-Wesley, July 2004 All material copyright 1996-2006 J.F Kurose and K.W Ross, All Rights Reserved 6: Wireless and Mobile Networks 6-1 Chapter 6: Wireless and Mobile Networks Background: Ì # wireless (mobile) phone subscribers now exceeds # wired phone subscribers! Ì computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet access Ì two important (but different) challenges r r communication over wireless link handling mobile user who changes point of attachment to network 6: Wireless and Mobile Networks 6-2 Chapter outline 6.1 Introduction Wireless Ì 6.2 Wireless links, characteristics r CDMA Ì 6.3 IEEE 802.11 wireless LANs (“wi-fi”) Ì 6.4 Cellular Internet Access r r architecture standards (e.g., GSM) Mobility Ì 6.5 Principles: addressing and routing to mobile users Ì 6.6 Mobile IP Ì 6.7 Handling mobility in cellular networks Ì 6.8 Mobility and higherlayer protocols 6.9 Summary 6: Wireless and Mobile Networks 6-3 Elements of a wireless network network infrastructure wireless hosts Ì laptop, PDA, IP phone Ì run applications Ì may be stationary (nonmobile) or mobile r wireless does not always mean mobility 6: Wireless and Mobile Networks 6-4 Elements of a wireless network network infrastructure base station Ì typically connected to wired network Ì relay - responsible for sending packets between wired network and wireless host(s) in its “area” r e.g., cell towers 802.11 access points 6: Wireless and Mobile Networks 6-5 Elements of a wireless network network infrastructure wireless link Ì typically used to connect mobile(s) to base station Ì also used as backbone link Ì multiple access protocol coordinates link access Ì various data rates, transmission distance 6: Wireless and Mobile Networks 6-6 Characteristics of selected wireless link standards 54 Mbps 5-11 Mbps Mbps 802.11{a,g} 802.11b 11 p-to-p link 802.15 3G UMTS/WCDMA, CDMA2000 384 Kbps 2G IS-95 CDMA, GSM 56 Kbps Indoor Outdoor Mid range outdoor Long range outdoor 10 – 30m 50 – 200m 200m – 4Km 5Km – 20Km 6: Wireless and Mobile Networks 6-7 Elements of a wireless network network infrastructure infrastructure mode Ì base station connects mobiles into wired network Ì handoff: mobile changes base station providing connection into wired network 6: Wireless and Mobile Networks 6-8 Elements of a wireless network Ad hoc mode Ì no base stations Ì nodes can only transmit to other nodes within link coverage Ì nodes organize themselves into a network: route among themselves 6: Wireless and Mobile Networks 6-9 Wireless Link Characteristics Differences from wired link … decreased signal strength: radio signal attenuates as it propagates through matter (path loss) r interference from other sources: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as well r multipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times r … make communication across (even a point to point) wireless link much more “difficult” 6: Wireless and Mobile Networks 6-10 Chapter outline 6.1 Introduction Wireless Ì 6.2 Wireless links, characteristics r CDMA Ì 6.3 IEEE 802.11 wireless LANs (“wi-fi”) Ì 6.4 Cellular Internet Access r r architecture standards (e.g., GSM) Mobility Ì 6.5 Principles: addressing and routing to mobile users Ì 6.6 Mobile IP Ì 6.7 Handling mobility in cellular networks Ì 6.8 Mobility and higherlayer protocols 6.9 Summary 6: Wireless and Mobile Networks 6-48 Mobile IP Ì RFC 3220 Ì has many features we’ve seen: r home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) Ì three components to standard: r indirect routing of datagrams r agent discovery r registration with home agent 6: Wireless and Mobile Networks 6-49 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 6: Wireless and Mobile Networks 6-50 Mobile IP: agent discovery Ì agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) type = 24 checksum =9 code = =9 H,F bits: home and/or foreign agent R bit: registration required 16 standard ICMP fields router address type = 16 length registration lifetime sequence # RBHFMGV reserved bits or more care-ofaddresses mobility agent advertisement extension 6: Wireless and Mobile Networks 6-51 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 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 … 6: Wireless and Mobile Networks 6-52 Components of cellular network architecture recall: correspondent wired public telephone network MSC MSC MSC MSC MSC different cellular networks, operated by different providers 6: Wireless and Mobile Networks 6-53 Handling mobility in cellular networks home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon) r 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) Ì visited network: network in which mobile currently resides r visitor location register (VLR): database with entry for each user currently in network r could be home network Ì 6: Wireless and Mobile Networks 6-54 GSM: indirect routing to mobile home network HLR home MSC consults HLR, gets roaming number of mobile in visited network correspondent home Mobile Switching Center VLR 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 mobile user visited network MSC in visited network completes call through base station to mobile 6: Wireless and Mobile Networks 6-55 GSM: handoff with common MSC Ì Handoff goal: route call via new base station (without interruption) Ì reasons for handoff: VLR Mobile Switching Center old routing old BSS r new routing r new BSS r 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) Ì handoff initiated by old BSS 6: Wireless and Mobile Networks 6-56 GSM: handoff with common MSC VLR Mobile Switching Center old BSS new BSS old BSS informs MSC of impending handoff, provides list of 1+ new BSSs MSC sets up path (allocates resources) to new BSS new BSS allocates radio channel for use by mobile new BSS signals MSC, old BSS: ready old BSS tells mobile: perform handoff to new BSS mobile, new BSS signal to activate new channel mobile signals via new BSS to MSC: handoff complete MSC reroutes call MSC-old-BSS resources released 6: Wireless and Mobile Networks 6-57 GSM: handoff between MSCs Ì home network correspondent Home MSC anchor MSC MSC anchor MSC: first MSC visited during cal r call remains routed through anchor MSC Ì new MSCs add on to end PSTN MSC MSC (a) before handoff of MSC chain as mobile moves to new MSC Ì IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks 6-58 GSM: handoff between MSCs Ì home network correspondent Home MSC anchor MSC MSC anchor MSC: first MSC visited during cal r call remains routed through anchor MSC Ì new MSCs add on to end PSTN MSC MSC (b) after handoff of MSC chain as mobile moves to new MSC Ì IS-41 allows optional path minimization step to shorten multi-MSC chain 6: Wireless and Mobile Networks 6-59 Mobility: GSM versus Mobile IP GSM element Home system Comment on GSM element Mobile IP element Network to which the mobile user’s permanent phone number belongs Home network Gateway Mobile Home MSC: point of contact to obtain routable Home agent Switching Center, or address of mobile user HLR: database in home “home MSC” Home system containing permanent phone number, Location Register (HLR) profile information, current location of mobile user, subscription information Visited System Network other than home system where mobile Visited network user is currently residing Visited Mobile services Switching Center Visitor Location Record (VLR) Visited MSC: responsible for setting up calls Foreign agent to/from mobile nodes in cells associated with MSC VLR: temporary database entry in visited system, containing subscription information for each visiting mobile user Mobile Station Roaming Routable address for telephone call segment Care-of-address Number (MSRN), or between home MSC and visited MSC, visible to “roaming number” neither the mobile nor the correspondent 6: Wireless and Mobile Networks 6-60 Wireless, mobility: impact on higher layer protocols should be minimal … r best effort service model remains unchanged r TCP and UDP can (and do) run over wireless, mobile Ì … but performance-wise: r packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff r TCP interprets loss as congestion, will decrease congestion window un-necessarily r delay impairments for real-time traffic r limited bandwidth of wireless links Ì logically, impact 6: Wireless and Mobile Networks 6-61 Chapter Summary Wireless Ì wireless links: r r r capacity, distance channel impairments CDMA Ì IEEE 802.11 (“wi-fi”) r CSMA/CA reflects wireless channel characteristics Ì cellular access r architecture r standards (e.g., GSM, CDMA-2000, UMTS) Mobility Ì principles: addressing, routing to mobile users r r r home, visited networks direct, indirect routing care-of-addresses Ì case studies r mobile IP r mobility in GSM Ì impact on higher-layer protocols 6: Wireless and Mobile Networks 6-62 ... communication over wireless link handling mobile user who changes point of attachment to network 6: Wireless and Mobile Networks 6-2 Chapter outline 6.1 Introduction Wireless Ì 6.2 Wireless links,... slot channel output 6: Wireless and Mobile Networks 6-13 CDMA: two-sender interference 6: Wireless and Mobile Networks 6-14 Chapter outline 6.1 Introduction Wireless Ì 6.2 Wireless links, characteristics... and link layer protocol between mobile and BS Mobile Switching Center Public telephone network, and Internet Mobile Switching Center wired network 6: Wireless and Mobile Networks 6-29 Cellular