ITTC Mobile Wireless Networking The University of Kansas EECS 882 Wireless and Mobile Internet

Transcription

1 Mobile Wireless Networking The University of Kansas EECS 882 Wireless and Mobile Internet James P.G. Sterbenz Department of Electrical Engineering & Computer Science Information Technology & Telecommunications Research Center The University of Kansas 11 April 2016 rev James P.G. Sterbenz

2 Mobile Wireless Networking Wireless and Mobile Internet WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-2

3 Wireless and Mobile Internet WI.1: Untethered Internet Operation WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-3

4 Internet History Link Types ARPANET ~1970 considered variety of links leased PSTN lines packet radio satellite Internet evolved into primarily wired infrastructure TCP/ protocol suite developed under these assumptions problems? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-4

5 Internet History Link Evolution ARPANET ~1970 considered variety of links leased PSTN lines packet radio satellite Internet evolved into primarily wired infrastructure TCP/ protocol suite developed under these assumptions no direct support for lossy wireless links no support for mobility 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-5

6 Internet History Link Evolution ARPANET ~1970 considered variety of links leased PSTN lines packet radio satellite Internet evolved into primarily wired infrastructure TCP/ protocol suite developed under these assumptions no direct support for lossy wireless links no support for mobility: static binding of addresses Solution? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-6

7 Internet History Mobility Support ARPANET ~1970 considered variety of links leased PSTN lines packet radio satellite Internet evolved into primarily wired infrastructure TCP/ protocol suite developed under these assumptions no direct support for lossy wireless links no support for mobility: static binding of addresses Solution attempts mobile to support end-system movement TCP modifications to support wireless links 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-7

8 Wireless and Mobile Internet WI.2: Mobile WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-8

9 Mobility Overview Problem: node mobility between subnets need to revisit -address/node bindings 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-9

10 DHCP Overview DHCP: dynamic host configuration protocol [RFC 2131] Allows node to dynamically obtain address as well as other configuration parameters, e.g. DNS server Benefits reduces manual configuration allows mobile nodes to easily move attachment point Limitations? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-10

11 DHCP Overview DHCP: dynamic host configuration protocol [RFC 2131] Allows node to dynamically obtain address as well as other configuration parameters, e.g. DNS server Benefits reduces manual configuration allows mobile nodes to easily move attachment point Problems no handoff capabilities flows and sessions interrupted during move 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-11

12 Mobile Overview Mobile [RFC 3220] (designed by C.E. Perkins) designed to enable untethered Internet access with limited mobility without disrupting higher level protocol flows 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-12

13 Mobile Overview Mobile [RFC 3220] (designed by C.E. Perkins) designed to enable untethered Internet access with limited mobility without disrupting higher level protocol flows Simple way of forwarding packets to mobile nodes 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-13

14 Home Net Mobile Architecture Home Network MN AP AP /24 Home network: permanent (normal) home of MN MN: mobile node permanent address assigned from home network block e.g assigned from /24 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-14

15 Mobile Architecture Visited Network Home Net Visited Net AP AP MN / /24 Home network permanent (normal) home of MN Visited Network: temporary location of MN e.g /24 CN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-15

16 Mobile Architecture Visited Network Home Net Visited Net AP AP MN MN / /24 Home network permanent (normal) home of MN Visited Network: temporary location of MN e.g /24 problem? CN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-16

17 Home Net Mobile Architecture Visited Network Visited Net MN AP AP MN / /24 CN Home network permanent (normal) home of MN Visited Network: temporary location of MN home addr not in visited block: packets fwd to wrong net e.g /24 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-17

18 Home Net Mobile Architecture Visited Network Visited Net MN AP AP MN / /24 CN Home network permanent (normal) home of MN Visited Network: temporary location of MN home addr not in visited block: packets fwd to wrong net solution? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-18

19 Home Net Mobile Architecture Visited Network Visited Net MN AP AP MN / /24 CN Home network permanent (normal) home of MN Visited Network: temporary location of MN home addr not in visited block: packets fwd to wrong net use DHCP to get address in visiting net: all flows interrupted 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-19

20 Home Net Mobile Architecture Visited Network Visited Net MN AP AP MN / /24 CN Home network permanent (normal) home of MN Visited Network: temporary location of MN home addr not in visited block: packets fwd to wrong net solution? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-20

21 Home Net Mobile Architecture Visited Network Visited Net MN AP AP MN / /24 CN Home network permanent (normal) home of MN Visited Network: temporary location of MN home addr not in visited block: packets fwd to wrong net mobile agents forward on behalf of MN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-21

22 Home Net Mobile Architecture Home Agent Visited Net MN HA AP AP MN / /24 CN Home network receives traffic destined for MN home agent (HA) receives traffic destined for MN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-22

23 Home Net Mobile Architecture Foreign Agent Visited Net MN HA AP AP FA MN / /24 CN Home agent (HA) forwards on behalf of MN to visited Foreign agent (FA) intercepts and relays to MN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-23

24 Home Net Mobile Architecture Foreign Agent Visited Net MN HA AP AP FA MN / /24 CN Home agent (HA) forwards on behalf of MN to visited Foreign agent (FA) intercepts and relays to MN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-24

25 Home Net Mobile Architecture Reverse Path Visited Net MN HA AP AP FA MN / /24 CN Home agent (HA) forwards on behalf of MN to visited Foreign agent (FA) intercepts and relays to MN Does MN need to use agents to send to CN? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-25

26 Home Net Mobile Architecture Reverse Path Visited Net MN HA AP AP FA MN / /24 Home agent (HA) forwards on behalf of MN to visited Foreign agent (FA) intercepts and relays to MN MN can address datagrams directly to CN issues? CN 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-26

27 Home Net Mobile Architecture Triangle Routing Visited Net MN HA AP AP FA MN / /24 CN Home agent (HA) forwards on behalf of MN to visited Foreign agent (FA) intercepts and relays to MN MN can address datagrams directly to CN triangle routing : forward path reverse path 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-27

28 Direct routing Mobile Architecture Direct Routing overcomes triangle routing problem Correspondent requests care-of address home agent replies correspondent sends packets directly to COA Problem additional signalling complexity and handoff latency 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-28

29 Mobile Protocol Overview What steps must be taken? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-29

30 Agent discovery Registration Tunneling Handoff Mobile Protocol Overview 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-30

31 Agent discovery process Mobile Protocol Agent Discovery home and foreign agents advertise their service mobile nodes solicit the existence of an agent ICMP message router advertisement: type = 9 mobility agent advertisement extension: code = April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-31

32 Mobile Protocol Registration Registration process for mobile nodes request forwarding services from foreign agent registers care-of address with home agent directly via foreign agent renew binding about to expire deregister from foreign agent UDP messages mobile message header 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-32

33 Tunneling Mobile Protocol Tunneling home agent tunnels datagrams to care-of address Methods -in- encapsulation minimal encapsulation [RFC 2004] eliminates redundant fields from -in- GRE (generic routing encapsulation) [RFC 1701, 1702] 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-33

34 Mobile Protocol Handoff Handoff: mobile node moves to new visited network Procedure mobile node deregisters with old foreign agent mobile node registers with new foreign agent new foreign agent registers with home agent home agent updates care-of-address for mobile packets continue to be forwarded to mobile new care-of-address 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-34

35 Mobile Protocol Handoff Handoff: mobile node moves to new visited network Procedure mobile node deregisters with old foreign agent mobile node registers with new foreign agent new foreign agent registers with home agent home agent updates care-of-address for mobile packets continue to be forwarded to mobile new care-of-address Problem? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-35

36 Mobile Protocol Handoff Handoff: mobile node moves to new visited network Procedure mobile node deregisters with old foreign agent mobile node registers with new foreign agent new foreign agent registers with home agent home agent updates care-of-address for mobile packets continue to be forwarded to mobile Problem new care-of-address hand-off delay packet loss during handoff 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-36

37 Advantages? Mobile Protocol Advantages and Disadvantages 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-37

38 Advantages Mobile Protocol Advantages and Disadvantages very simple mechanism 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-38

39 Mobile Advantages and Disadvantages Advantages very simple mechanism Disadvantages hand-off latency may be seconds registration authentication many optimisations proposed triangle routing different forward and reverse paths security issues ingress and firewall address filtering of address mismatches no support for policy 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-39

40 routers Mobile Reality most supported mobile for a long time Service providers some deployment within cellular telephony service providers Users very little actual use why? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-40

41 Users very little actual use Mobile Reality: Users DHCP reattachment sufficient for many applications and Web transactions not yet much continuous wireless coverage very few users roam among hot spots users using mobile telephony to roam LAN to mobile telephony would be more useful 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-41

42 Wireless and Mobile Internet WI.3: TCP over Wireless Links WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.3.1 TCP error and congestion control WI.3.2 TCP loss discrimination WI.3.3 TCP modifications for wireless WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-42

43 Wireless and Mobile Internet WI.3.1: TCP Error and Congestion Control WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.3.1 TCP error and congestion control WI.3.2 TCP loss discrimination WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-43

44 TCP Error Control Overview TCP uses end-to-end ARQ (automatic repeat request) go-back-n by default numbers bytes in stream rather than packets 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-44

45 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions 0 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-45 1

46 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight A0 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-46 2

47 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged t ack A A1 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-47 3

48 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged how is packet loss detected? t ack A0 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-48 4

49 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet t ack A0 A1 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-49 5

50 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet t ack A0 A1 A o sender timer fires if ACK not received A1 implication? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-50 6

51 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet t ack A0 A1 A1 A1 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-51 7

52 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet t ack A0 A1 4 5 A1 2 A1 3 2 A1 A2 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-52 8

53 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet t ack A0 A1 4 5 A1 2 A1 3 2 A1 4 3 A2 A3 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-53 9

54 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet t ack A0 A1 4 5 A1 2 A1 3 2 A A2 A3 A4 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-54 10

55 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet t ack A0 A1 4 5 A1 2 A1 3 2 A A2 5 A3 6 A4 A5 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-55 11

56 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet disadvantages? t ack A0 A1 4 5 A1 2 A1 3 2 A A2 5 A3 6 A4 6 A5 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-56 12

57 E2E Error Control Closed Loop Retransmission: Go-Back-n Go-back-n : pipeline transmissions + multiple packets simultaneously in flight Packets are sequentially acknowledged o previous ACK retransmitted for subsequent packets after loss out of sequence packet o sender timer fires if ACK not received reset transmission beginning at lost packet significant loss penalty for high bw- -delay go back and retransmit all since loss many unneeded retransmissions significant additional delay 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-57 t ack A0 A1 A1 A1 A1 A2 A3 A4 A

58 E2E Error Control Closed Loop Retransmission: Go-Back-n Optimisation possible for go-back-n? t ack A0 A1 A1 A1 A1 A2 A3 A4 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-58

59 E2E Error Control Closed Loop Retransmission: Go-Back-n Optimisation go-back-n timer the only way to detect loss? t ack A0 3 A1 4 A1 5 2 A1 3 2 A1 4 3 A2 A3 A4 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-59

60 ITTC E2E Error Control Closed Loop Retransmission: Selective Repeat Go-back-n fast retransmit and delayed ACK help slightly significant delay penalty for losses Alternative don t go back: selective repeat 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-60

61 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged 0 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-61 1

62 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged A0 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-62 2

63 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged 1 0 t ack A0 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-63 3

64 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged 1 0 t ack A0 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-64 4

65 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o acknowledged and held at receiver t ack A0 A A3 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-65 5

66 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o packets held and reordered at receiver increases receiver complexity t ack A0 A1 A A4 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-66 6

67 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o packets held and reordered at receiver increases receiver complexity Lost packets o selectively retransmitted t ack A0 A1 A3 A4 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-67 7

68 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o packets held and reordered at receiver increases receiver complexity Lost packets o selectively retransmitted t ack A0 A1 A3 A4 A no go-back-n latency penalty requires more receiver buffer space A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-68

69 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o packets held and reordered at receiver increases receiver complexity Lost packets o selectively retransmitted + no go-back-n latency penalty requires more receiver buffer space t ack A0 A1 A3 A4 A5 A2 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-69

70 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o packets held and reordered at receiver increases receiver complexity Lost packets o selectively retransmitted + no go-back-n latency penalty requires more receiver buffer space t ack A0 A1 A3 A4 A5 A2 A A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-70

71 E2E Error Control Closed Loop Retransmission: Selective Repeat Selective repeat o all packets acknowledged Missequenced packets o packets held and reordered at receiver increases receiver complexity Lost packets o selectively retransmitted + no go-back-n latency penalty requires more receiver buffer space Latency and Bandwidth reduced t ack A0 A1 A3 A4 A5 A2 A6 A7 A April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-71

72 Transmission Control Protocol Error Control TCP uses end-to-end ARQ (automatic repeat request) go-back-n by default numbers bytes in stream rather than packets SACK (selective acknowledgement) is option implements selective repeat over three blocks within segment TCP uses byte-sequence numbers not TPDU numbers as in the previous selective repeat example 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-72

73 Transmission Control Protocol Congestion Control Slow start to probe capacity Implicit congestion control lack of expected ACK assumed to be congestion-based loss sender halves congestion window (AIMD) Recovery then retransmits (go-back n or SACK block) begins increase of congestion window (AIMD) 1 MSS (max. segment size) every RTT 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-73

74 Transmission Control Protocol Congestion Control initialisation steady state phase AI congestion detection sending rate slow start MD Initialisation phase: slow start Steady-state phase: AIMD time 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-74

75 TCP Congestion and Error Control Assumptions TCP assumes all losses are due to congestion why? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-75

76 TCP Congestion and Error Control Assumptions TCP assumes all losses are due to congestion buffer overflow (tail drop) under congestion AQM (active queue management) for congestion avoidance sender throttles to reduce congestions Problem? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-76

77 TCP Congestion and Error Control Assumptions TCP assumes all losses are due to congestion buffer overflow (tail drop) under congestion AQM (active queue management) for congestion avoidance sender throttles to reduce congestion Problem: what if loss is due to bit error in wireless channel what should the response be? 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-77

78 TCP Congestion and Error Control Assumptions TCP assumes all losses are due to congestion buffer overflow (tail drop) under congestion AQM (active queue management) for congestion avoidance sender throttles to reduce congestions Problem: what if loss is due to bit error in wireless channel sender should retransmit, not throttle! 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-78

79 TCP Congestion and Error Control Assumptions TCP assumes all losses are due to congestion buffer overflow (tail drop) under congestion AQM (active queue management) for congestion avoidance sender throttles to reduce congestions Problem: what if loss is due to bit error in wireless channel sender should retransmit, not throttle! Note: selective repeat can help but TCP SACK only covers only 3 independent loss events due to implementation as TCP option then reverts to go-back-n behaviour 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-79

80 Wireless and Mobile Internet WI.3.2: TCP Loss Discrimination WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.3.1 TCP error and congestion control WI.3.2 TCP loss discrimination WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-80

81 TCP Loss or Delayed Arrivals Causes Absence of expected packet or ACK arrival three distinct and unrelated causes: 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-81

82 TCP Loss or Delayed Arrivals Causes Absence of expected packet or ACK arrival three distinct and unrelated causes: 1. Congestion: packet dropped in network congestion control: queue overflow (tail drop) congestion avoidance: intentional packet drop 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-82

83 TCP Loss or Delayed Arrivals Causes Absence of expected packet or ACK arrival three distinct and unrelated causes: 1. Congestion: packet dropped in network 2. Corruption: packet lost or delivered corrupted channel error causing bit errors 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-83

84 TCP Loss or Delayed Arrivals Causes Absence of expected packet or ACK arrival three distinct and unrelated causes: 1. Congestion: packet dropped in network 2. Corruption: packet lost or delivered corrupted 3. Delay: packet arrival later than expected store-and-forward delays in disruption tolerant network long path speed-of-light delay in delay-tolerant network very long path around disruption Lecture SR and EECS April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-84

85 Loss Discrimination Proper Response to Loss Discrimination and proper response essential: congestion back off corruption retransmit delay wait or retransmit via lower delay path Lecture RS and EECS April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-85

86 Loss Discrimination Explicit Notification Discrimination and proper response essential: congestion back off corruption retransmit delay wait or retransmit via lower delay path Explicit notification ECN: explicit congestion notification ELN: explicit loss notification (due to corruption) ELN cannot be determined from ECN (& vice versa) packet that first causes congestion may then be corrupted 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-86

87 Mechanisms Explicit Loss Notification Error Control Mechanisms observation that error has occurred (detection) notification of error decision on what response to take action to correct error Taxonomy of mechanisms each mechanism may have different implementations (e.g. E2E vs. HBH) but they are frequently related ETEN: explicit transport error notification [KSE+20004] 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-87

88 Determinism ETEN Taxonomy Determinism and Granularity deterministic (take action based on specific corruptions) probabilistic (e.g. throttle source x% of the time) Granularity Control feedback Control locus Control band Control direction 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-88

89 Determinism Granularity ETEN Taxonomy Determinism and Granularity PETEN: per packet response CETEN: cumulative error rate response Control feedback Control locus Control band Control direction 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-89

90 sender ETEN Taxonomy Control Feedback n ACK N Closed loop feedback from notifier nodes {n,n} (N)ACK from end system or switch (e.g. congestion drop) sender FEC Open loop Unreliable or FEC for statistical reliability, rate control sender n N Hybrid open + closed loop FEC for statistical reliability + (N)ACKs as needed 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-90

91 sender ETEN Taxonomy Control Locus ETEN N End-to-end no changes to network infrastructure Some hop-by-hop ETEN sender n n n n N deployed as needed (e.g. optional n at wireless access links) ETEN sender N N N N N All hop-by-hop (N indicates required notifier functionality) deployment challenges: impractical for Internet as a whole 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-91

92 ETEN Taxonomy Control Band sender n ETEN N Out-of-band ETEN signalling messages may be forward or backward sender n In-band ACK/ETEN ETEN ETEN information carried by packets; options: corrupted packets not dropped but marked (violates RFC 1812) carried by subsequent packets in flow (header field or option) 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-92 N

93 sender ETEN Taxonomy Control Direction ETEN n N Backward ETEN messages returned by switches out-of-band unless inserted in reverse flow requires HBH ETEN sender n N Forward ETEN ETEN forwarded to receiver; turned back to sender may be in- or out-of band longer delay in response for interactive over high bw- -delay 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-93

94 Wireless and Mobile Internet WI.3.3: TCP Modifications for Wireless WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.3.1 TCP error and congestion control WI.3.2 TCP loss discrimination WI.3.3 TCP modifications for wireless WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-94

95 TCP Modifications for Wireless Proper Response to Loss TCP Westwood TCP Peach 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-95

96 TCP Westwood based on TCP Reno Operation TCP Westwood Overview monitors ACK receipt rate at source computes congestion window and ssthresh Eliminates performance penalty from halving cwind No explicit cross-layering 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-96

97 TCP Westwood TCP Westwood Operation [WYSG2005, GNUS2013] sender side modification to TCP Reno eligible rate estimation (ERE) based on ACK reception rate calculates amount of ACKed data between ACK intervals based on number of DUPACKs and new ACKs Slow start ERE resets ssthresh for faster convergance to proper value Congestion avoidance: agile probing persistent noncongestion detection excess capacity suddenly becomes available random loss during slow start causing premature exit 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-97

98 TCP Westwood+ modification of Westwood TCP Westwood+ Operation Reduces overestimation of bandwidth in presence of ACK compression Samples bandwidth every RTT instead of every ACK results in enhanced fairness in presence of multiple flows 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-98

99 TCP Peach based on TCP Reno Sends dummy segments low priority TCP Peach Overview receive rate indicates available bandwidth Peach foils based on Justin P. Rohrer ResiliNets journal club presentation 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-99

100 Starts with TCP Peach Sudden Start 1 data segment and rwind 1 dummy segments cwind incremented for real and dummy segments cwind = rwind after 2 RTTs 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-100

101 TCP Peach Rapid Recovery Halves congestion window after loss as in Reno Transmits cwind dummy segments before loss Ignores first half of dummy ACKs cwind incremented for second half of dummy ACKs 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-101

102 Wireless and Mobile Internet WI.4: Internet Applications WI.1 Impact of untethered operation in the Internet WI.2 Mobile WI.3 TCP over wireless links WI.3.1 TCP error and congestion control WI.3.2 TCP loss discrimination WI.4 Internet applications 11 April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-102

103 Wireless and Mobile Internet Further Reading Charles E. Perkins, Mobile : Design Principles and Practices, Addison Wesley, 1998 Michael Welzel Network Congestion Control: Managing Internet Traffic, Wiley, 2005 Rajesh Krishnan, James P.G. Sterbenz, et al., Explicit Transport Error Notification (ETEN) for Error-Prone Wireless and Satellite Networks, Computer Networks, Elsevier, vol.46 iss.3, October 2004, pp April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-103

104 Wireless and Mobile Internet Acknowledgements Some material in these foils is based on the textbook Murthy and Manoj, Ad Hoc Wireless Networks: Architectures and Protocols Significant material in these foils is derived from EECS 780 and James P.G. Sterbenz and Joseph D. Touch, High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication, John Wiley, 2001 James F. Kurose and Keith F. Ross, Computer Networking: A Top-Down Approach Featuring the Internet, 4th ed, Pearson Addison Wesley, November 2011 KU EECS 882 Mobile Wireless Nets Internet MWN-WI April 2016 KU EECS 882 Mobile Wireless Nets Internet MWN-WI-104