Mobility Management 嚴 力 行 高 雄 大 學 資 工 系

Transcription

1 Mobility Management 嚴 力 行 高 雄 大 學 資 工 系

2 Mobility Management in Cellular Systems

3 Cellular System HLR PSTN MSC MSC VLR BSC BSC BSC cell BTS BTS BTS BTS MT BTS BTS BTS BTS

4 HLR and VLR HLR (Home Location Register) aa database to store and management permanent data of subscribers VLR (Visitor Location Register) aa database to store temporary information about subscribers needed by MSC in order to service visiting subscribers

5 Mobility Management Mobility management enables telecommunications networks to locate roaming mobile terminals (MTs( MTs) ) for call delivery (location management) maintain connections with MTs that change their point of attachment (handoff/handover management)

6 Location Management When not connected, MT periodically performs location registration (i.e., location update) explicitly notify the network of its new access point and store changes to its user location profile (VLR/HLR) when incoming calls arrive, the network performs call delivery querying the user profile to deliver the calls to the current cell location of the MT

7 GSM Registration Procedure 1: old TMSI + old VLR id 2: TMSI IMSI IMSI 3: location update 4: new TMSI 5: registration cancellation VLR 5 HLR VLR

8 Call Delivery for Mobile Terminated Call request roaming number dial MSISDN 1 1 other switches GMSC (INTX) 3 routing 1 2 other switches HLR allocate MSRN VLR MSC 3 paging MS

9 Registration Area Beside periodic registrations, MT will perform a location update whenever it crosses the boundary of a registration/location area Registration/Location Area (RA/LA) consists of one or more cells the basic unit of registration/paging registration paging

10 Registration Area Planning Tradeoff between location update cost and paging cost Big RA means high paging cost but low location update cost Small RA means low location update cost but high paging cost Cost cell RA VLR PLMN GSM Total Paging Location update Size of RA

11 Hand-off (Hand-over) Switches and Processor Hand-off (Hand-over): switches cells Cell #1 Cell #2

12 Handoff Management Ongoing calls are modified under two conditions: signal strength deterioration and user mobility intra-cell and inter-cell handoffs within and between cells soft handoff and hard handoff without and with interruptions in radio links

13 Who Initiates the Handoff? NCHO (Network-controlled handoff) or MAHO (Mobile-assisted Handoff) the networks generates a new connection, finding new resources for the handoff and performing any additional routing operations MCHO (Mobile-controlled handoff) the MT finds the new resources and the network approves

14 Three Classes of Handoffs in GSM MSC MSC BSC BSC BSC BTS BTS BTS BTS MS MS 1. different BTS, same BSC MS MS 2. different BSC, same MSC MS MS 3. different MSC, same PLMN (old MSC=anchor MSC new MSC=relay MSC)

15 Call drop rate Technical Terms The probability that an ongoing call is dropped due to handoff Call blocking rate The probability that a new call is denied due to lack of available channel call drop rate is usually more important than call blocking rate

16 Handoff Management: Channel Reservation Scheme Reserve some channels in BTS for handoff calls Trade call blocking rate for call drop rate A new call in this BTS will be denied if all non-reserved channels are in use However, a handoff call can still use a reserved channel In use In use for both new calls and handoff calls Reserved for handoff calls Channels in a BTS

17 Mobility Management in IP over WLAN Environment

18 DHCP Server 1 L2H and L3H Subnet1 Internet/Intranet Subnet2 DHCP Server 2 AP 1 AP 2 or Router association WS L2H: change of WS s association from one AP to another L3H: change of WS s network-layer setting

19 General Handoff Phases L2H L2H Execution L2H Detection Probing Authentication Association L3H L3H Execution L3H Detection DHCP DAD IP Config.

20 L2H Execution WS AP Active or Passive Scanning Authentication Request Authentication Response Association Request Association Response Probing Authentication Association 802.1X (Optional) i (Optional)

21 L2H Detection Detect the need to start an L2H (probing) Various methods RSSI Bit error rate Frame error rate should differentiate intermittent bad communication state from persistent one that necessitates an L2H Detection time can t t be too short!

22 Inter-ESS L2H? L2Hs within an ESS are intrinsically supported does not specify how to perform an inter-ess L2H (ESS transition) ncnu ncnu hinet ESSID Intra-ESS L2H Inter-ESS L2H

23 Enabling ESS Transition By default, only APs belonging to the current ESS are considered in the probing phase By specifying the designated ESSID in Probe Request If no such AP can be found, the probing will fail and link-down eventually arises When ZeroConfig, a Windows XP module, receives link-down event, it will instruct L2 module to switch to another ESS (enabling ESS transition)

24 Layer-3 3 Handoff (L3H) Needed when the new and previous APs belong to different network domains Should renew network-layer settings (IP address, default gateway, etc.) subnet * Router * subnet2 No L3H is needed L3H is needed

25 L3H Execution Typical L3H execution Dynamic Host Configuration Protocol (DHCP) Duplicated Address Detection (DAD) IP Configuration Station s s IP address changes after an L3H Ok for most application If want to retain IP address, Mobile IP should be used

26 CISCOSYSTEMS CISCOSYSTEMS Hierarchical Addressing in the Internet Address implies location Subnet A * * Subnet B

27 IP Routing Router uses routing table to direct packets to the appropriate interface Target Interface /24 a /24 b /24 c a b Dest = Router c

28 CISCOSYSTEMS CISCOSYSTEMS When a Node Roams to Another Subnet How to retain its connections? Subnet A * * Subnet B

29 Traditional Routing for a Mobile Host Host moving to another network is unreachable Target Interface /24 a /24 b /24 c a b X Dest = Router c Mobile Host

30 Potential Strategies for Mobile Nodes if a node roaming in another subnet wishes to retain its connections, it can use a new IP address (e.g., using DHCP) not transparent to transport layer (TCP/UDP) exploit host-specific specific route poor scalability use Mobile IP

31 CISCOSYSTEMS CISCOSYSTEMS Use A New IP Address Current TCP protocol stack must be modified Subnet A * * Subnet B

32 Change the Node s s IP Address A TCP connection within a node is uniquely identified by the following four values IP Source Address IP Destination Address TCP Source Port TCP Destination Port TCP checksum is computed using these four fields in addition to the data in the payload of the segment.

33 Host-Specific Routes Target Interface /24 a /32 c /24 b /24 c a not scaleable since updates and unique entries would be needed for every mobile host b Dest = Router c Mobile Host

34 Host-Specific Routes (Cont.)

35 Mobile IP Overview published by IETF as a Proposed Standard in Nov The Mobile IP standards documents include the following Request For Comments (RFCs( RFCs): RFC2002, 2003, 2004, 1701, 2005, 2006.

36 Requirements of Mobile IP A mobile node must be able to communicate with other nodes after changing its link-layer layer point-of of-attachment to the Internet be able to communicate using only its home IP address,, regardless of its current link-layer layer point-of of- attachment to the Internet be able to communicate with other computers that do not implement the Mobile IP mobility functions not be exposed to any new security threats over and above those to which any fixed node on the Internet is exposed

37 Mobile IP Architecture Mobile Node (MN):: a node which can change its point-of of-attachment to the Internet Home Agent (HA):: a router with an interface on the MN s s home link Foreign Agent (FA):: a router on an MN s s foreign link

38 Mobility Binding Home address: : permanent address of MN care-of-address: : MN s s new address used in foreign area, can be foreign agent care-of address assigned by FA, usually the same address as the FA co-located care-of address obtained by MN itself through some means (e.g., DHCP)

39 Operations of Mobile IP

40 An Analogy of Mobile IP Mobile Node (MN): 你 Home Agent (HA): 你 母 親 或 其 他 家 人 Foreign Agent (FA): 系 上 的 助 理 小 姐 當 你 在 家 時, 寄 給 你 的 信 由 自 己 處 理 當 你 出 外 唸 書 時, 你 的 筆 友 還 是 將 信 寄 至 你 的 Home Address,, 而 由 你 的 母 親 替 你 轉 寄 信 件 要 讓 你 的 母 親 轉 信, 你 必 須 告 訴 她 你 的 Care-of Address

41 An Analogy of Mobile IP (cont.) 如 果 是 Foreign Agent Care-of Address,, 則 你 母 親 將 信 寄 至 系 上, 由 系 助 理 轉 交 給 你 如 果 是 Co-located Care-of Address,, 則 你 母 親 將 信 寄 至 你 目 前 通 訊 處, 由 你 自 己 收 信 無 論 是 哪 一 種 情 形, 你 的 筆 友 是 不 知 道 你 的 Care-of Address 的 你 的 Care-of Address 只 用 於 讓 你 的 HA 轉 信 用 你 的 對 外 通 信 仍 使 用 Home Address

42 Tunneling A tunnel is the path followed by a first packet while it is encapsulated within the payload portion of a second packet. Tunnel HA

43 IP-in in-ip Encapsulation CN Original IP Packet Outer Header Encapsulated IP Packet Tunnel Header Payload Header HA Payload

44 Agent Discovery Agent advertisement Agent solicitation advertisement solicitation Agent advertisement Agent MN MN

45 Registration and Deregistration Inform HA MN s care-of-address performed when MN detects that it has moved to another subnet current registration expires FA restarts aa lot of retransmissions in transport layer deregistration when MN moves back home

46 Registration in Mobile IP MN sends registration message to foreign agent foreign agent stores MN s s link-layer layer address in visitor list foreign agent sends back registration reply register MN nn Agent register reply visitor list node link-layer address n xxxxxxxxxx

47 Packet Delivery with Foreign Agent Care-of of-address CN sends packet to MN CN MN s s Home Agent FA captures it and Internet tunnels it to MN Foreign Agent FA decapsulates the packet and forwards it to MN using MN s s link-layer layer address HA

48 Packet Delivery with Co-located Care-of of-address CN sends packet to MN MN s s Home Agent MN captures it and tunnels it to MN MN decapsulates the packet by itself Internet CN HA

49 Proxy ARP and Gratuitous ARP Proxy ARP replies ARP requests on behalf of other nodes Gratuitous ARP spontaneously causes other nodes to update an entry in their ARP cache

50 When an MN registers with an FA MN disables its own future processing of ARP requests HA performs a gratuitous ARP on behalf of the MN HA use proxy ARP to reply ARP requests for the MN

51 When an MN registers at home MN enables its own future processing of ARP requests MN performs a gratuitous ARP for itself HA stops using proxy ARP for the MN HA performs a gratuitous ARP on behalf of the MN

52 Triangle Routing MN FA HA Triangle Routing CN

53 Route Optimization (Optional) MN FA Other packets HA First packet Binding Cache Home IP CoA CN

54 Route Optimization Issues Security CN 收 到 關 於 MN CoA 的 訊 息 可 能 是 假 的 CN 的 封 包 被 非 MN 的 第 三 者 攔 截 Mobility 當 MN CoA 變 動 時, 需 通 知 所 有 CN Compatibility CN 需 實 作 封 包 Encapsulation 與 Binding Cache 與 Mobile IP 當 初 設 計 的 requirement 不 符

55 Conclusions Mobility management in cellular systemss consists of location management and handoff management Mobile IP is a network-layer solution to address mobility