IP-Layer Handover Transport Layer Mobility

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1 IP-Layer Handover Transport Layer Mobility h"p:// Mobile Systems Prof. Marco Di Felice Department of Computer Science and Engineering University of Bologna

2 q IP-Layer handover can be managed at network layer (just seen), transport layer or applica?on layer. ² BENEFITS of NETWORK-LAYER MOBILITY MOBILE IP and extensions Ø Core component of IPv6 networks (Mobile IPv6) Ø Guarantee node s reachability (i.e. a node is always reachable even when crossing different IP domains) Ø Support all possible applica?ons/transport protocols Ø No change to network core (only edge routers affected) 2

3 q IP-Layer handover can be managed at network layer (just seen), transport layer or applica?on layer. ² DRAWBACKS of NETWORK-LAYER MOBILITY Ø Performance, handover latency (triangular rou?ng) Ø Privacy concerns (route op?miza?on) Ø Need for infrastructure support Ø Upper layers are not aware of mobility events MOBILE IP and extensions 3

4 q IP-Layer handover can be managed at network layer (just seen), transport layer or applica?on layer. ² BENEFITS of TRANSPORT-LAYER MOBILITY Ø No need for infrastructure support Ø Reduced latency for handover management, low network overhead (i.e. no triangular rou?ng) Ø Make congeshon control aware of mobility events TCP VARIANTS 4

5 q IP-Layer handover can be managed at network layer (just seen), transport layer or applica?on layer. ² DRAWBACKS of TRANSPORT-LAYER MOBILITY TCP VARIANTS Ø Reachability might not always be guaranteed (must rely on lower layers or on applica?on layer). Ø Suppor?ng mobility of both end-points (source and des?na?on) can be highly challenging. Ø Need to change users device protocol stack. 5

q IP-Layer handover can be managed at network layer (just seen), transport layer or applica?on layer. W. M. Eddy, At what layer does mobility belong? IEEE Communica?

6 q IP-Layer handover can be managed at network layer (just seen), transport layer or applica?on layer. W. M. Eddy, At what layer does mobility belong? IEEE Communica?ons Magazine, 2004 Most of Mobile IP s problem can be tackled by a higher transport or session layer approach. Due to a cultural unacceptance of a session layer, the transport layer approaches to mobility are likely the strongest, despite requiring modifica?ons to the TCP protocol. 6

7 q Transmission Control Protocol (TCP) ² Core protocol of the Internet TCP/IP stack ² First version released in 1974, several variants available ² Reliable transmission (ACK + retransmissions) ² In-order data delivery ² Three-way handshake mechanism ² Receiver congeshon control ² Network congeshon control 7

8 q Conges?on control is implemented at the sender side through a CongesHon Window (CW) à equal to the number of sender packets in flight (i.e. not yet acknowledged). ² Reduce the CW at the sender side à less packets in the network. ² Increase the CW at the sender side à more packets in the network ² Hence, window is smaller when conges?on is larger, and vice-versa. DATA ACK 8

q Conges?on control is implemented at the sender side through a CongesHon Window (CW) à equal to number of sender packets in flight (i.e. not yet acknowledged).

9 q Conges?on control is implemented at the sender side through a CongesHon Window (CW) à equal to number of sender packets in flight (i.e. not yet acknowledged). AIMD Algorithm ² Increment the CW of one packet (or less) for each received ACK packet. ² Divide the CW by two for each?meout event (i.e. data without ack). ² Timout is adjusted as a weighted mean of the Round Trip Time (RTT). Source: h"p://orm-chimera-prod.s3.amazonaws.com/ 9

10 q Conges?on control is implemented at the sender side through a CongesHon Window (CW) à equal to number of sender packets in flight (i.e. not yet acknowledged). TCP Slow start ² ExponenHal increase of the CW up to the conges?on threshold, then linear increase. ² A missing acknowledgement causes the reduc?on of the conges?on threshold to one half of the current conges?on window. 10

11 q Conges?on control is implemented at the sender side through a CongesHon Window (CW) à equal to number of sender packets in flight (i.e. not yet acknowledged). TCP Fast recovery & Fast retransmit ² Each TCP ACK packet contains the seq. no. of the last in-order TCP data. ² If mul?ple ACKs are received with the same sequence number à a packet loss has occurred, there is a gap in received packets. ² Sender concludes that packet loss is not due to congeshon, con?nue with current conges?on window (no slow-start), just retransmit missing packets. 11

12 q Simple model of TCP performance ² B n à TCP throughput (B/s) ² RTT à Round Trip Time,?me to send DATA and receive the ACK ² p à probability of end-to-end packet loss 12

13 q Stream Control Transmission Protocol (SCTP) ² Message-oriented (instead of flow-oriented), like UDP ² (Op?onal) Reliable communica?on, like TCP ² CongesHon and flow control, like TCP ² Ordered or unordered message delivery ² Support mulhple streams for each end-to-end associa?on ² Na?vely support mulh-homing scenarios, i.e.: (i) each node can have mul?ple IP addresses; (ii) fault-tolerance in case one path becomes unavailable. 13

14 q Stream Control Transmission Protocol (SCTP) ² A transport-layer connec?on between end-points is called associahon and iden?fied by a unique id for each node. ² Two SCTP endpoints cannot have more than one associa?on between them at any?me. ² An ac?ve associa?on can include mul?ple streams: Ø User messages of a stream must be delivered in order Ø But messages of different streams might not be in order (head of line blocking problem in TCP) 14

MN q Stream Control Transmission Protocol (SCTP) ² Each end-point can have mul?ple IP addresses ² A primary path (i.e. the best path) is selected for data transmission, while a secondary path is used for sending retransmission data.

15 MN q Stream Control Transmission Protocol (SCTP) ² Each end-point can have mul?ple IP addresses ² A primary path (i.e. the best path) is selected for data transmission, while a secondary path is used for sending retransmission data. ² Dynamic path selechon based on actual network condi?ons. ASSOCIATION STREAM 1 STREAM 2 STREAM 3 IP1 IP2 PRIMARY PATH INTERNET IP1 IP2 ASSOCIATION 15

16 TSN:SSN Data Chunk Application SCTP s1 s2 s3 7:3 8:3 9:3 4:2 5:2 6:2 1:1 2:1 3:1 Association Application SCTP s1 s2 s3 buffer buffer :999 IP2 IP IP :999 Primary Path :888 IP1 IP IP :888 Retransmission Path

q According to the TCP, packet loss means network conges?on Is it really true in a wireless scenario? MulHple packet losses can be mis-interpretated as a conges?

17 q According to the TCP, packet loss means network conges?on Is it really true in a wireless scenario? MulHple packet losses can be mis-interpretated as a conges?on symptom, leading to the decrease of the CW. T. Tian, K. Xu, N. Ansari, TCP in Wireless Environments: Problems and Solu?ons, IEEE Communica?ons Magazine, 43 (3), pp ,

18 q According to the TCP, packet loss means network conges?on Is it really true in a wireless scenario? Similarly, short disconnechons might cause ACK losses, that in turn translate into?meouts and CW decrease. T. Tian, K. Xu, N. Ansari, TCP in Wireless Environments: Problems and Solu?ons, IEEE Communica?ons Magazine, 43 (3), pp ,

19 q According to the TCP, packet loss means network conges?on Is it really true in a wireless scenario? TCP is not able to track the available network bandwidth in a fast and responsive way (e.g. when changing channel or current wireless access technology) K. Chowdhury, M. Di Felice, I. F. Akyildiz, TCP CRAHN: A Transport Control Protocol for Cogni?ve Radio Ad Hoc Networks, in IEEE Transac?ons on Mobile Compu?ng (TMC), Vo. 12, No. 4, pp ,

20 q Possible solu?on: Cross-layer protocol design ² Make informa?on gathered/produced by one layer available to the whole protocol stack. ² Protocols can be ophmized based on feedbacks coming from the upper/lower layers. ² Triggers and no?fica?ons can be sent to other protocols based on a push-andsubscribe paradigm. E. Borgia, M. Con? and F. Delmastro, MobileMAN: Design, integra?on and experimenta?on of cross-layer mobile mul?hop ad hoc networks, IEEE Communica?ons Magazine,

sent by intermediate routers to iden?fy packet losses due to conges?on condi?

fy packet losses due to mobility of the corresponding node.

fy packet losses which might be caused by temporary disconnec?ons.

21 q An example of cross-layer solu?on: the ATCP protocol ² Use Explicit CongesHon NoHficaHon (ECN) messages sent by intermediate routers to iden?fy packet losses due to conges?on condi?ons. ² Use ICMP (Des?na?on Unreachable) messages to iden?fy packet losses due to mobility of the corresponding node. ² Use Explicit Link Failure NoHficaHon (ELFN) messages to iden?fy packet losses which might be caused by temporary disconnec?ons. FEEDBACKS SETTINGS TCP VARIABLES ATCP NETWORK LAYER MAC LAYER J. Liu and S. Singh, ATCP: TCP for Mobile Ad Hoc Networks, IEEE Journal on Selected Area of Communica?ons, 19(7),

22 q An example of cross-layer solu?on: the ATCP protocol J. Liu and S. Singh, ATCP: TCP for Mobile Ad Hoc Networks, IEEE Journal on Selected Area of Communica?ons, 19(7),

23 q Tradi?onal TCP protocol does not offer any specific support to IP handover management. ServerSocket MyService; Socket clientsocket=null; try { MyServerice = new ServerSocket(PortNumber); servicesocket = MyService.accept(); } catch (IOException e) { System.out.println(e); } TCP uses a 4-field tuple to iden?fy a Network ConnecHon: <Source IP, Source Port, Dest IP, Dest Port> Port 80 Port

24 q Tradi?onal TCP protocol does not offer any specific support to IP handover management. ServerSocket MyService; Socket clientsocket=null; try { MyServerice = new ServerSocket(PortNumber); servicesocket = MyService.accept(); } catch (IOException e) { System.out.println(e); } As soon as the Mobile Node changes IP address, current TCP connec?ons become unreachable, and new end-toend connec?ons must be enstablished. Port 1200 ACK

25 q TCP connec?on migra?on (e.g. TCP Migrate protocol) ² Enable dynamic binding of IP addresses into a TCP network connec?on. ² HOW? A mobile node can nohfy its IP address change to the corresponding node. ² The corresponding node simply modifies the network connec?on iden?fier. No further changes to the TCP current state. <Source IP, Source Port, Des?na?on IP, Des?na?on Port> <Source IP, Source Port, New Dest IP, Des?na?on Port> 25

q TCP connec?on migra?on (e.g. TCP Migrate protocol) ² Migra?on op?on is enabled by the SYN packet, which is sent before opening a TCP connec?on. The token iden?

26 q TCP connec?on migra?on (e.g. TCP Migrate protocol) ² Migra?on op?on is enabled by the SYN packet, which is sent before opening a TCP connec?on. The token iden?fies a TCP connec?on, instead of the tradi?onal tuple. The request contains the new IP address (e.g. IPv4) of the mobile node. 26

27 q TCP connec?on migra?on (e.g. TCP Migrate protocol) ² Migra?on op?on is enabled by the SYN packet, which is sent before opening a TCP connec?on. SYN + migrahon op?on SYN ACK + token ACK ENSTABLISH THE TCP CONNECTION (first?me) SYN ACK + token SYN + migrahon op?on ACK DATA EXCHANGE RE-ENSTABLISH THE TCP CONNECTION (ater IP handover); replace IP address 27

28 q How to modify the TCP protocol for IP handover ² Several proposals: Indirect TCP, Snooping TCP, M-TCP, transmission/?me-out freezing, MP-TCP, ² Three main approaches: Ø Ø Ø ConnecHon spli\ng à Different versions of TCP protocol on the wired link and on the wireless link. Link-layer solu?ons à Retransmissions occur at the Link Layer, no changes to the TCP layer. End-to-end soluhons à Modified conges?on control and reliability control mechanisms on TCP end-points. 28

$q ConnecHon-spli\ng example: Indirect TCP (I-TCP) ² Two TCP for each end-to-end connec?on: wired TCP and wireless TCP.$

29 q ConnecHon-spli\ng example: Indirect TCP (I-TCP) ² Two TCP for each end-to-end connec?on: wired TCP and wireless TCP. ² Wired TCP is classical TCP ; no changes for the Corresponding Node (CN). ² Wireless TCP can be ophmized for the wireless scenario. ² The Corresponding Node (CN) is not aware of the connec?on spliung process. WIRED TCP INTERNET WIRELESS TCP 29

$q ConnecHon-spli\ng example: Indirect TCP (I-TCP) MOBILITY event MN SOCKET Socket1 Socket2 TCP$

30 q ConnecHon-spli\ng example: Indirect TCP (I-TCP) MOBILITY event MN SOCKET Socket1 Socket2 TCP migrate + state migrate TCP migrate + state migrate INTERNET CN SOCKET MN SOCKET Socket1 Socket2 30

$q ConnecHon-spli\ng example: Indirect TCP (I-TCP) ² PRO: q No changes to the fixed network and to the CN.$

31 q ConnecHon-spli\ng example: Indirect TCP (I-TCP) ² PRO: q No changes to the fixed network and to the CN. q Transmissions errors do not propagate from wireless to wired links; retransmissions can be faster. ² CONS: q No more end-to-end semanhcs. q Higher overhead due to the packet buffering at the Mobile Node, and to the indirect forwarding. 31

32 q Link-layer approach example: Snooping TCP FA MN SPOOF ACK BUFFER DATA CN END-TO-END CONNECTION ² Transparent extension of the legacy TCP protocol. ² The Foreign Agent (FA) buffers the packet sent to the Mobile Node (MN), and filters the ACK messages in both direc?ons. ² Local retransmissions à lost packets are immediately retransmi"ed by the Foreign Agent or by the Mobile Node. 32

33 q Link-layer approach example: Snooping TCP FA MN SPOOF ACK BUFFER DATA CN END-TO-END CONNECTION q Data transfer TO the Mobile Node ² FA buffers packets un?l an ACK is received from the MH ² Packet loss is detected when?me-outs or duplicated ACKs are detected; in these cases, the FA retransmits the packet. 33

buffers packets un?l an ACK is received from the MH ² Packet loss is detected when?

34 q Link-layer approach example: Snooping TCP MN LOSS SPOOF ACK FA BUFFER DATA CN END-TO-END CONNECTION RETRANSMIT DATA q Data transfer TO the Mobile Node ² FA buffers packets un?l an ACK is received from the MH ² Packet loss is detected when?me-outs or duplicated ACKs are detected; in these cases, the FA retransmits the packet. 34

35 q Link-layer approach example: Snooping TCP MN SPOOF DATA FA CN END-TO-END CONNECTION SEND NACK MESSAGE q Data transfer FROM the Mobile Node ² FA detects packet losses on the wireless link by using sequence numbers; if a packet loss is detected, a NACK is sent, and a retransmission occurs by the MN. 35

36 q Link-layer approach example: Snooping TCP ² PRO: q End-to-end semanhcs is preserved. q Seamless implementahon for the end-points (CN and MN). ² CONS: q Does not work in case of encypted traffic. q Resource uhlizahon at FH (e.g. memory, CPU processing)? q Wireless link is not isolated as in the case of I-TCP. 36

37 q Link-layer approach example: Snooping TCP C. H. Ng, J. Chow, L- Trajkovic Performance Evalua?on of TCP over WLAN with Snoop performance enhancing proxy 37

38 q End-to-end approach example: Time-out freezing ² The MAC layer detects mobility events and disconnec?on from the current FH (how? For example, monitoring the current signal strength). ² If mobilty is detected, a no?fica?on is sent to the TCP. ² TCP enters into a frozen state (no data transmissions, same CW size) ² When the link-layer handover is completed, TCP is nohfied and the previous TCP state is restored. 38

39 q End-to-end example: Fast retransmit/fast recovery ² If the MH is receiving data: Ø The MH sends duplicated acknowledgements when it registers to a new FA, so that it can force the fast retransmit mode at the CN. ² If the MH is sending data: Ø CP of the MH does not go into slow-start mode, same CW size than before handover is used. 39

40 q MulHpath TCP ² OpHon (1): Single TCP connechon, mul?ple rou?ng paths toward a des?na?on MAIN RESULT: Simultaneous uhlizahon of mulhple paths on a single TCP performance might not lead to a performance increase! M. Di Felice, L. Bononi, A. Molinaro, S.Pizzi, Cross- Layered Joint Channel Assignment and Mul?-Path Rou?ng for Mul?- Radio Wireless Mesh Networks, IJCS,

41 q MulHpath TCP (MP-TCP) h"p:// ² OpHon (2): Single data stream spli"ed across mul?ple paths; each path can use different IP addresses, and different access technologies (mul?-homing). 41

Chapter 13 TRANSPORT. Mobile Computing Winter 2005 / Overview. TCP Overview. TCP slow-start. Motivation Simple analysis Various TCP mechanisms

Chapter 13 TRANSPORT. Mobile Computing Winter 2005 / Overview. TCP Overview. TCP slow-start. Motivation Simple analysis Various TCP mechanisms Overview Chapter 13 TRANSPORT Motivation Simple analysis Various TCP mechanisms Distributed Computing Group Mobile Computing Winter 2005 / 2006 Distributed Computing Group MOBILE COMPUTING R. Wattenhofer