©1996-2016, J.F Kurose and K.W Ross Chapter Wireless and Mobile Networks Computer Networking: A Top Down Approach 7th Edition, Global Edition Jim Kurose, Keith Ross Pearson April 2016 Wireless and Mobile Networks 7-1 Ch 7: Wireless and Mobile Networks Background: § # wireless (mobile) phone subscribers now exceeds # wired phone subscribers (5-to-1)! § # wireless Internet-connected devices equals # wireline Internet-connected devices ©1996-2016, J.F Kurose and K.W Ross • laptops, Internet-enabled phones promise anytime untethered Internet access § two important (but different) challenges • wireless: communication over wireless link • mobility: handling the mobile user who changes point of attachment to network Wireless and Mobile Networks 7-2 Chapter outline 7.1 Introduction Mobility Wireless 7.5 Principles: addressing and routing to mobile users 7.6 Mobile IP 7.7 Handling mobility in cellular networks 7.8 Mobility and higher-layer protocols 7.2 Wireless links, characteristics â1996-2016, J.F Kurose and K.W Ross ã CDMA 7.3 IEEE 802.11 wireless LANs (“Wi-Fi”) 7.4 Cellular Internet Access • architecture • standards (e.g., 3G, LTE) Wireless and Mobile Networks 7-3 Elements of a wireless network ©1996-2016, J.F Kurose and K.W Ross network infrastructure Wireless and Mobile Networks 7-4 Elements of a wireless network wireless hosts ©1996-2016, J.F Kurose and K.W Ross network infrastructure § laptop, smartphone § run applications Đ may be stationary (nonmobile) or mobile ã wireless does not always mean mobility Wireless and Mobile Networks 7-5 Elements of a wireless network base station ©1996-2016, J.F Kurose and K.W Ross network infrastructure § typically connected to wired network § relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e.g., cell towers, 802.11 access points Wireless and Mobile Networks 7-6 Elements of a wireless network wireless link ©1996-2016, J.F Kurose and K.W Ross network infrastructure § typically used to connect mobile(s) to base station § also used as backbone link § multiple access protocol coordinates link access § various data rates, transmission distance Wireless and Mobile Networks 7-7 Characteristics of selected wireless links 1300 Data rate (Mbps) ©1996-2016, J.F Kurose and K.W Ross 450 54 5-11 802.11ac 802.11n 802.11a,g 802.11b 802.11a,g point-to-point 4G: LTWE, WIMAX 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 802.15 384 2.5G: UMTS/WCDMA, CDMA2000 056 2G: IS-95, CDMA, GSM Indoor Outdoor 10-30m 50-200m Mid-range outdoor Long-range outdoor 200m – Km 5Km – 20 Km Wireless and Mobile Networks 7-8 Elements of a wireless network infrastructure mode ©1996-2016, J.F Kurose and K.W Ross network infrastructure § base station connects mobiles into wired network § handoff: mobile changes base station providing connection into wired network Wireless and Mobile Networks 7-9 ©1996-2016, J.F Kurose and K.W Ross Elements of a wireless network ad hoc mode § no base stations § nodes can only transmit to other nodes within link coverage § nodes organize themselves into a network: route among themselves Wireless and Mobile Networks 7-10 Mobile IP § RFC 3344 § has many features we’ve seen: • home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-apacket) ©1996-2016, J.F Kurose and K.W Ross § three components to standard: • indirect routing of datagrams • agent discovery • registration with home agent Wireless and Mobile Networks 7-61 Mobile IP: indirect routing foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet ©1996-2016, J.F Kurose and K.W Ross 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 Wireless and Mobile Networks 7-62 Mobile IP: agent discovery § agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) type = ©1996-2016, J.F Kurose and K.W Ross 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 bits reserved or more care-ofaddresses mobility agent advertisement extension Wireless and Mobile Networks 7-63 Mobile IP: registration example home agent HA: 128.119.40.7 visited network: 79.129.13/24 foreign agent COA: 79.129.13.2 ICMP agent adv mobile agent MA: 128.119.40.186 COA: 79.129.13.2 … ©1996-2016, J.F Kurose and K.W Ross registration req COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format … registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format … registration req COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 … registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 … time Wireless and Mobile Networks 7-64 Components of cellular network architecture recall: correspondent wired public telephone network MSC MSC ©1996-2016, J.F Kurose and K.W Ross MSC MSC MSC different cellular networks, operated by different providers Wireless and Mobile Networks 7-65 Handling mobility in cellular networks § home network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon) ©1996-2016, J.F Kurose and K.W Ross • 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 • could be home network Wireless and Mobile Networks 7-66 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 ©1996-2016, J.F Kurose and K.W Ross 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 Wireless and Mobile Networks 7-67 GSM: handoff with common MSC ©1996-2016, J.F Kurose and K.W Ross VLR Mobile Switching Center old routing old BSS § handoff goal: route call via new base station (without interruption) § reasons for handoff: new routing new BSS • 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 and Mobile Networks 7-68 GSM: handoff with common MSC VLR ©1996-2016, J.F Kurose and K.W Ross old BSS Mobile Switching Center 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 Wireless and Mobile Networks 7-69 GSM: handoff between MSCs home network correspondent Home MSC anchor MSC ©1996-2016, J.F Kurose and K.W Ross MSC PSTN MSC MSC § anchor MSC: first MSC visited during call • call remains routed through anchor MSC § new MSCs add on to end of MSC chain as mobile moves to new MSC § optional path minimization step to shorten multi-MSC chain (a) before handoff Wireless and Mobile Networks 7-70 GSM: handoff between MSCs home network correspondent Home MSC anchor MSC ©1996-2016, J.F Kurose and K.W Ross MSC PSTN MSC MSC § anchor MSC: first MSC visited during call • call remains routed through anchor MSC § new MSCs add on to end of MSC chain as mobile moves to new MSC § optional path minimization step to shorten multi-MSC chain (b) after handoff Wireless and Mobile Networks 7-71 Handling Mobility in LTE § Paging: idle UE may move from cell to cell: network does not know where the idle UE is resident ©1996-2016, J.F Kurose and K.W Ross • paging message from MME broadcast by all eNodeB to locate UE § handoff: similar to 3G: P-GW source MME target MME § preparation phase § execution phase § completion phase old eNodeB old routing new routing new eNodeB Wireless and Mobile Networks 7-72 Mobility: cellular versus Mobile IP ©1996-2016, J.F Kurose and K.W Ross cellular element Comment on cellular element Mobile IP element Home system Network to which 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 Wireless and Mobile Networks 7-73 Wireless, mobility: impact on higher layer protocols Đ logically, impact should be minimal ã best effort service model remains unchanged • TCP and UDP can (and do) run over wireless, mobile ©1996-2016, J.F Kurose and K.W Ross Đ but performance-wise: ã 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 • delay impairments for real-time traffic • limited bandwidth of wireless links Wireless and Mobile Networks 7-74 Chapter summary Wireless Mobility § wireless links: § principles: addressing, routing to mobile users • capacity, distance • channel impairments ã CDMA â1996-2016, J.F Kurose and K.W Ross Đ IEEE 802.11 (Wi-Fi) ã CSMA/CA reflects wireless channel characteristics Đ cellular access • architecture • standards (e.g., 3G, 4G LTE) • home, visited networks ã direct, indirect routing ã care-of-addresses Đ case studies • mobile IP • mobility in GSM, LTE § impact on higher-layer protocols Wireless and Mobile Networks 7-75