Research Issues in Satellite and Wireless Networks: Experiences and Lessons at the University of Catania

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1 Research Issues in Satellite and Wireless Networks: Experiences and Lessons at the University of Catania Sergio Palazzo (University of Catania)

2 Wireless Networking Lab (WiNe-Lab) People Full Professors: Sergio Palazzo and Alfio Lombardo Associate Professor: Giovanni Schembra Assistant Professor: Giacomo Morabito Ph.D. Students: Laura Galluccio, Alessandro Leonardi, Mario Barbera and Francesco Licandro. Research Engineers: Antonio Pantò, Renato Narcisi, Sergio Armenia, Salvatore Gallo, Dario Marchese.

3 Research Projects European Union: NEWCOM SATNEX DISCREET (under construction ) Italian Government: PATTERN VICOM TANGO RAMON PLANET IP Marconi Selenia Packet Radio TTSAT

4 Research Activities (1/2) Heterogeneous Wireless Networks Reconfigurable Platforms Transport Protocols Mobility Management Ad-Hoc and Sensor Networks Satellite Networks Multicast Protocols Adaptive Low Bit Rate Video Transmission Transport Protocols.

5 Research Activities (2/2) Real-time Multimedia over the Internet Adaptive Video over IP Adaptive Voice over IP (AVoIP) Perceived QoS TCP-Friendly Rate Control Cross-layer protocols IP Quality of Service IP Network Planning Active Queueing Management (AQM) Traffic Modeling (Video, Audio, Multimedia, TCP)

6 Outline Satellite Networks Unicast Transport Protocol TCP-Peach TCP-Peach and FACK/SACK Options Multicast Transport Protocol Reliable Delivery Multimedia Streaming Heterogeneous Wireless Networks Ad-Hoc and Sensor Networks Neighbor discovery MACRO

7 Satellite Networks Unicast Transport Protocol

8 General Transport Architecture

9 TCP Problems in Satellite Networks TCP throughput is low in satellite networks because: BER is high: packet losses are interpreted as the signal of network congestion Unnecessary transmission rate decrease Low performance. Propagation delay is long: the transmission rate increase is reciprocal to RTT The above problem is amplified. Also, long duration of Slow Start!

10 TCP-Peach and RCS Support: Protocol design in collaboration with Georgia Institute of Technology, supported by NASA Prototype implementations supported by ASI: ACE: ASI CNIT Emulator Selected Publications: J. Tang, G. Morabito, I. Akyildiz and M. Johnson. RCS: A Rate Control Scheme for Real-Time Traffic in Networks with High Bandwidth-Delay Products and High Bit Error Rates, IEEE Infocom May I. F. Akyildiz, G. Morabito, S. Palazzo, TCP-Peach: A New Congestion Control Scheme for Satellite IP Networks,. IEEE/ACM Transactions on Networking. June G. Morabito, R. Narcisi, S. Palazzo, and A. Pantò, TCP-Peach and FACK/SACK Options: Putting Pieces Together,. IEEE Globecom Satellite Communication Symposium. November 2002.

11 TCP-Peach and RCS Unicast transport layer solutions: TCP-Peach: for reliable, non real-time communucations Rate Control Scheme (RCS): for unreliable, real-time communications Based on the concept of dummy segments/packets: Carried by low priority IP packets (TOS can be used) Used to probe the availability of unused resources in the end-to-end path Dummy segments (for TCP-Peach) do not contain new information

12 Basic Idea When the sender detects a packet loss: 1. Conservative behavior: Decreases the transmission rate. 2. Transmits a certain number of dummy segments/packets to probe the end-to-end path: If the network is congested, dummy segments/packets are dropped as first If there are unused resources the dummy segments/packets arrive to the destination which sends ACKs back. 3. The sender sets the transmission window/rate according to the number of ACKs received for dummy segments/packets In the beginning of a new connection several dummy segments/packets are transmitted

13 TCP-Peach Behavior cwnd (packets) cwnd (packets) Time (sec) Initial Time (sec) Loss Recovery

14 Advantages: End-to-end solution Higher throughput Fairness Disadvantages: Characteristics Some priority scheme must be supported by all network elements.

15 SACK and FACK Options Well known TCP options. Currently implemented in several TCP implementation (e.g., Linux kernel implementations). Selective Acknowledgement: Recover several packet losses in the same congestion window. Forward Acknowledgement: Better estimation of the number of outstanding segments.

16 Impairments TCP-Peach as it is cannot be applied with FACK/SACK options. Problem 1: FACK provides different computation of not acknowledged segments Less dummy segments are transmitted Benefits of TCP-Peach are not achieved. Problem 2: Multiple losses cause duration of Rapid Recovery longer than RTT Most of the ACKs for dummy segments arrive during Rapid Recovery (not during Congestion Avoidance). This ACKs do not increment the cwnd value as expected.

17 as a consequence (a) cwnd nackseg (b) cwnd nackseg segments segments t (RTT) Expected t (RTT) Actual

18 Modifications The variables wdsn and adsn are initially set to half of the value given in original TCP-Peach: wdns = cwnd 0 /4 adsn = cwnd 0 /2 Problem 1 is solved!!! A new variable called num_dummy is defined. It represents the number of dummy segments actually sent. If num_dummy ACKs arrive for dummy segments cwnd is set to its previous value. Problem 2 is solved!

19 Implementation We implemented TCP-Peach in the Linux kernel (Ver ) Modified files: /usr/src/linux/include/net/sock.h /usr/src/linux/include/net/tcp.h /usr/src/linux/include/linux/tcp.h /usr/src/linux/net/ipv4/tcp_ipv4.c /usr/src/linux/net/ipv4/tcp_output.c /usr/src/linux/net/ipv4/tcp_input.c /usr/src/linux/net/ipv4/tcp_timer.c /usr/src/linux/net/ipv4/tcp.c

20 Emulation Testbed GNU/Linux with NIST Net ACE Emulator Satellite Network Emulator FTP Sender S FTP Receiver S

21 Congestion Window cwnd Time (sec)

22 Performance Comparison (a) (b) Tcp Reno Tcp Peach Tcp Reno Tcp Peach throughput (bytes/sec) average delivery time (sec) Packet Error Rate (x10e-2) File size: 2 Mbytes Packet Error Rate (x10e-2)

23 Conclusions We introduced some modifications to TCP-Peach to make it work with FACK and SACK options. We implemented the protocol in the Linux protocol stack. You can download it at We are currently testing fairness in more complex scenarios: Intra-protocol fairness Inter-protocol fairness

24 Satellite Networks Multicast Transport Protocol

25 Multicast Transport Protocols: Applications Reliable Multicast Tranport Protocol File Delivery News Dissemination Unreliable Multicast Trasnport Protocol Multimedia Streaming

26 Reliable Multicast Issues Different multicast applications have different requirements in terms of reliability delivery ordering delay delay jitter one or many senders level of scalability A TCP-friendly behavior need for congestion control frequent feedback from receivers feedback implosion at the sender. Involved network entities: senders, receivers and network routers.

27 Reliable Multicast Proposals NACK (Negative ACKnowledgement) based feedback scheme (PGM and SRM). Use of FEC (Forward Error Correction) to reduce the number and the frequency of feedback messages. Implementation of transport functionality in the network elements (PGM). Election of a group s representative (the acker) to implement a TCP-like congestion control scheme (PGMCC).

28 Why Focus on PGMCC Well knonw solution End-to-end solution Easy implementation No need of multilevel encoding schemes (single rate solution)

29 PGMCC Problems in Satellite IP Networks PGMCC congestion control scheme interprets packet losses as the signal of network congestion. This assumption is not realistic in satellite communications (packet losses occur due to link errors). The long propagation delays amplify the previous problem. In fact, the time interval required to recover from packet losses is proportional to the round trip time.

30 RMT: a New Reliable Multicast Transport Protocol Election of a group's representative to implement a TCP- Peach like congestion control scheme. The feedback scheme uses adaptive pacing for the transmission of NACK packets. Receivers importance in the acker switching algorithm. Advantages: The network elements are not involved The throughput performance increases

31 Protocols Implementation Linux operating system Open source Support of NISNET and networking facilities Documentation Multithreaded structure User space application over UDP sockets. Multisocket implementation Data Packet over UDP multicast Dummy packet over UDP unicast Active NACK over UDP unicast Passive NACK over UDP multicast

32 Emulated Network Topology

33 Testbed Scheme Sole Terra Mercurio Plutone

34 Testbed Description Sole is the multicast router. The packet loss rate, the delay and the bandwidth of every link is emulated using NISTNet emulator running on the end node of each link.

35 Delivery Time Analysis

36 UMT: a New Unreliable Multicast Transport Protocol The UMT protocol implements the same algorithms as the RMT protocol, but the packet retransmission scheme. Being the UMT suited for multimedia streaming transmission, a new problem arises: if the slowest receiver lead the sender rate under the streaming transmission rate, the other receivers cannot enjoy the service, even if they have adequate bandwidth. The UMT protocol solves this problem introducing an appropriate threshold, and classifying receivers into two lists: a white list, including the receivers that have an evaluated throughput higher than the threshold; a black list, including the receiver that have an evaluated throughput lower than the threshold. Depending on the persistence in the black list, the worst receivers are invited to leave the UMT session, and the IP multicast group.

37 UMT Inter-protocol Fairness 6 x bandwidth (byte/s) TCP 1 TCP 2 UMT time(s)

38 UMT Intra-protocol Fairness 6 x bandwidth (byte/s) UMT 1 UMT time (s)

39 Ad Hoc and Sensor Networks Energy efficiency and Timeliness of Neighbor Discovery in Self-Organizing Networks

40 The problem Ad hoc and sensor networks: nodes mobility and failures lead to very dynamic topology If nodes are able to discover very rapidly Self-organization can be achieved Higher responsiveness is paid in terms of energy consumption!

41 Scenario

42 Scenario

43 Neighborhood Time Neighborhood time (Ω): time interval during which a pair of nodes are neighbors. Discovery time (T): time interval necessary for the discovery between two nodes. Transmit time (T T ): time interval necessary for the exchange of the data required by the application. In case of correct functioning: T T Ω -T Probability of discovery success (PDS): probability that the above relationship holds

44 The Approach A Trade-off is needed between increasing the PDS and decreasing the energy cost associated to this process. We derived a Markov analytical framework for evaluating the energy cost of the hunting process which is the process of searching for other nodes in the proximity. This framework allows the developer to design the hunting process so as to meet the requirements in terms of the energy consumption

45 2 1 1 ' N N N v v v r r r = cosφ 2 ' N N N N N v v v v v + = If remains constant in direction and magnitude for a sufficient amount of time: and v' N1 1 1 ' / ' / 2 N N y v S v P = Ω = ) ( 4 1 ) ( s R s R s f s R R R s F S S = =

46 The Hunting Process To discover neighbors, a node periodically runs a set of procedures which we call hunting process. The states of this process could be: Inquiry: a beacon message is transmitted (I) Inquiry Scan: a node listens for beacon messages (S) Doze: no TX or RX of beacons are executed (D) If M channels are used for discovery, the hunting process can be described as: (H ) state space F S ( H) ( t) = F( H) I1, I2,... S1, S2,... D Q (H) = state of the hunting process transition rate matrix π (H) steady state array

47 QoS Parameters Energy Cost M ( H ) c = [ PW INQ [ π ][ I m ] + PWSCAN [ m= 1 π ( H ) ][ S m ] Pdf of the discovery time T A( t) F ( t) = 1 k e M ( P) ( P) ( [ π ](, ) + [ ](, ) ) k = 1 S m I m π m= 1 A( t) = t 0 ρ T t ( τ ) dτ = π ( P) di eigenvalues of (0) Γ 1 I m S m 1 e diag d (P) NODISC d1t 1 1,... e d dl Rt L R T, t... t ΓΛ ( DISC)* (P) Q NODISC Q Γ eigenvectors of which is the matrix of the transition rates, given that the mobile nodes do not discover each other

48 PDS in data transfer = T T v s T R S S ds d d f f s f P ) '( / ) ( ) ( ) ( ϕ π φ ϕ τ τ ϕ

49 Cycle Time T = T + T + T Cycle IDLE SCAN INQ The cycle time can be related to the scan, inquiry and idle probabilities. It can be demonstrated that, once the probabilities are set, does not depend on or or T. v T Cycle T

50 P S vs. T with T v = Cycle Cycle 5 T T T Cycle = 0 T T T Cycle = 5

51 Case Study We applied the proposed methodology to a relevant case study: -A single channel system We derived some design implications on neighbor discovery algorithms and verified that P S increases as the cost TT constraint increases and the ratio decreases. Moreover, TCycle increases as T Cycle v increases. P S

52 Case Study

53 Case Study

54 Case Study

55 Ad Hoc and Sensor Networks MACRO: An Integrated MAC/Routing Protocol for Geographical Forwarding in Wireless Sensor Networks

56 The Problem In commercial sensor devices different TX power levels are available This feature can be exploited for reducing energy consumption We propose a MAC/ROuting protocol which uses this capability This protocol works with a cross-layer approach, is simple and does not require any location information knowledge Uses competition to select the most efficient next relay

57 Prerequisites G d ( R', D) d ( R' ', D P ) R ', R '' = Weighted progress factor (WPF) P1 < P2 <... PM S1( R') S2( R')... SM ( R') Set of power levels and coverage range R R D S 1( R ')

58 G Protocol Functioning Routing functionalities d ( R', D) d ( R' ', D P ) R ', R '' = P1 < P2 <... PM S1( R') S2( R')... SM ( R') 1. To select the next relay node R triggers a competition 2. Be R the winner of the competition in the set S 1 (R ) and G R R1 its WPF 3. If R estimates that a higher WPF can be obtained increasing P, a new competition is triggered in the set S 2 (R ). 4. The procedure is repeated until no better relay nodes can be found 5. When the best relay is identified the information is transmitted Weighted progress factor (WPF) Set of power levels and coverage range R R D S 1( R ')

59 G Protocol Functioning MAC functionalities d ( R', D) d ( R' ', D P ) R ', R '' = P1 < P2 <... PM S1( R') S2( R')... SM ( R') 1. Nodes periodically switch ON and OFF to reduce energy consumption 2. Synchronization is not needed 3. A wake up phase is requires for R identifying the best relay node in S i (R ) 4. To this purpose R transmits several short WAKE-UP messages for a T Cycle 5. Then R sends a Go MESSAGE which triggers competition among nodes in S i (R ) 6. A node in Si(R ) hearing the WAKE_UP messages calculates its WPF and stays awake waiting for the GO MESSAGE 7. Then upon hearing the GO MESSAGE a node sends randomly back to R its WPF so that R performs the choice of the best relay in S i (R ) Weighted progress factor (WPF) Set of power levels and coverage range T Cycle T ON T T 2T In WU Tx T WU ON In T WU Tx WU

60 Select Next Relay Node

61 Select the Winner of the Competition

62 Questions Analytical Framework What is the probability that outside the coverage area obtained using, exists at least one node whose WPF is higher than g, provided that G = G ( M ) i i? P i Once the probability is known, when it is worth enlarging the coverage area? If we stop the competition at time t, what is the probability to choose not the best available relay node in the considered coverage area?

63 Answer to Question 1 Pr{ G ( M ) ( M ) i+ 1 g Gi = Gi} = 1 e ς a ( g G i ) Where ζ is the nodes density and a ( g Gi ) is the area where a node B must be located in order to belong to S ( R i+1 ') and have a WPF higher than g. R P i i+1 g R P i > i+1 g

64 Answer to Question = = ) ( ) ( 1 / / ) ( ) ( 1 ) ( } { i i i i i M i M i P R P P G i G G i M i M i dg G g f g G G G E Where is the probability density function which can be evaluated using the previous results as ) ( ) ( ) ( 1 i G G G g f M i M i+ ) ( ) ( ) ( ) ( ) ( 1 i g G a i G G G g a dg d e G g f i M i M i = ς ς +

65 Pr{ A S + i Answer to Question 3 > > = Ri / Pi 1 ( R') : GR', A Gi, τ A t} 1 G Pr{ τ = i A t GR', A g} f ( M ) ( g) G i This represents the probability that a node having a WPF higher than the best available one exists out of S i (R') and its CONTROL ACK message arrives later than other nodes messages. dg Pr{ τ t G, = g} = 1 e A R' A kt g f G i d ( M ) ( M ) = Pr{ Gi g} dg

66 Performance evaluation Policy for the TX power level choice Policy 1: TX power levels increase linearly Policy 2: TX power levels give a linear increase in Policy 3: TX power levels give a linear increase in (R') S i R i

67 Performance evaluation Policy for the TX power level choice Average power consumption Average TX power Average range

68 Performance evaluation Comparison with other protocols Average power consumption Average number of hops

69 Performance evaluation Impact of node density Average power consumption vs. nodes nominal radio area Ninra=NπR 2 /Ξ 2

70 Performance evaluation Number of packets delivered at destination

71 Conclusions 1. MACRO is an integrated MAC/Routing geocast protocol 2. Convenient in case of strict requirements in terms of energy efficiency 3. The increase in end-to-end delay can turn into an advantage in terms of data aggregation 4. MACRO greately extends node s lifetime

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