Administrivia Channel Partitioning Random Access and Scheduling No lecture on Thurs Channel partitioning GSM CDMA etc is Last homework will be out this week not inflexible in accomdating bursty traffic Random access allows on demand allocation but has significant overhead due to collision or RTS CTS 4th generation cellular systems are shifting to explicit centralized scheduling of resources by the BS due covers wireless Extra office hours for next week and the week after 1 4 CSMA CA Recap Sensing in wireless medium is limited by hidden terminal problem Mobility Management Collision detection is limited by half duplex nature of radios cannot talk and listen at the same time Collision avoidance is the key Random backoff after sensing busy slot reservation protocol RTS CTS 2 Collision Avoidance RTS CTS exchange A 5 Mobility Management B AP General principles RTS B RTS A Cellular network examples reservation collision RTS A CTS A CTS A DATA A defer time ACK A ACK A 3 6 1 What is mobility Mobility Vocabulary home network permanent spectrum of mobility from the network perspective home of mobile e g 128 119 40 24 Verizon no mobility home agent entity that will perform mobility functions on behalf of mobile when mobile is remote high mobility mobile wireless user mobile user using same access connecting point disconnecting from network using DHCP wide area network mobile user passing through multiple access point while maintaining ongoing connections like cell Permanent address address in home network can always be used to reach mobile correspondent e g 128 119 40 186 510 642 5807 phone 7 Example simple mobility within same 802 11 subnet 10 Mobility more vocabulary visited network network H1 remains in same IP subnet IP address can remain same switch which AP is associated with H1 self learning Ch 5 switch will see frame from H1 and remember which switch port can be used to reach H1 Permanent address remains router constant e g 128 119 40 186 hub or switch in which mobile currently resides e g 79 129 13 24 Care of address address in visited network e g 79 129 13 2 BBS 1 AP 1 wide area network AP 2 H1 BBS 2 8 Wide Area Mobility Managment correspondent wants to communicate with mobile foreign agent entity in visited network that performs mobility functions on behalf of mobile 11 Mobility approaches In the 802 11 example mobility is handled at the link layer For wide area roaming it must be handled at the network layer Issues 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 How to find the destination How to route stuff to the destination How to update and keep track of its location correspondent to mobile goes through home agent then forwarded to remote direct routing correspondent gets foreign address of mobile sends directly to mobile 9 12 2 Mobility approaches Indirect Routing comments Let routing handle it routers advertise permanent let end systems handle it indirect routing communication from 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 triangle routing correspondent home networkmobile inefficient when correspondent mobile are in same network address of mobile nodes in residence via usual not routing table exchange scalable millions of routing tables to indicate where each mobile located mobiles no changes to end systems correspondent to mobile goes through home agent then forwarded to remote direct routing correspondent gets foreign address of mobile from home agent sends directly to mobile 13 Mobility registration 16 Indirect Routing moving between networks visited network home network suppose mobile user moves to another network registers 1 2 with new foreign agent 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 new wide area network mobile contacts foreign agent on entering visited network foreign agent contacts home agent home this mobile is resident in my network mobility changing foreign networks transparent on going connections can be End result Foreign agent knows about mobile Home agent knows location of mobile maintained 14 Mobility via Indirect Routing 17 Mobility via Direct Routing foreign agent receives packets forwards to mobile home agent intercepts packets forwards to foreign agent correspondent forwards to foreign agent visited network home network wide area network correspondent addresses packets using home address of mobile visited network home network 3 1 foreign agent receives packets forwards to mobile 4 wide area network 2 2 4 correspondent requests receives foreign address of mobile mobile replies directly to correspondent 15 1 3 4 mobile replies directly to correspondent 18 3 Mobility via Direct Routing comments Components of cellular network architecture overcome triangle routing problem recall non transparent to correspondent correspondent wired public telephone network correspondent must get care of address from home agent what if mobile changes visited network MSC MSC MSC MSC MSC different cellular networks operated by different providers 19 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 22 Handling mobility in cellular networks subscribe to e g Sprint Verizon 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 foreign net visited at session start wide area network anchor foreign agent 1 2 4 5 correspondent agent correspondent 3 new foreign agent home network network of cellular provider you new foreign network 20 Examples 23 GSM indirect routing to mobile home network HLR Mobile IP 2 Cellular networks home MSC consults HLR gets roaming number of mobile in visited network correspondent home Mobile Switching Center Will focus on latter 1 3
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