<Emphasis Type="BoldItalic">LAMA/CA</Emphasis>: A Load-Adaptive MAC Protocol for Short Packets

An efficient Media Access Control (MAC) protocol for wireless Internet access is developed in this study. The proposed access protocol exploits the fact that very often the Internet access messages, such as HTTP download requests, are based on short packets. In addition, whenever the user is able to access to multiple overlapping base stations (e.g., in WiMAX access networks, or in 3GPP cellular networks), the proposed protocol enables the user to select the least loaded base station. Consequently, the user gets a better quality of service, while load balancing is achieved by preferring links that are less loaded over congested links. The key idea is to adjust the access probability to the load on the local link, and to use a different access protocol for short messages. Delay insensitive and long messages are transmitted using a Request To Send (RTS) and Clear To Send (CTS) mechanism, in a similar way to IEEE 802.11, over hops that are able to support this protocol type, while short and delay-sensitive messages are transmitted using another method, that offers a reduced call delivery delay, as well as better channel utilization. Whenever the message length drops below a certain threshold (evaluated in this study), the overhead of transmitting an RTS and CTS messages becomes too large. The analysis in this study shows that this threshold is load-dependent. Whenever the message length drops below this load-dependent threshold, this study proposes to use a protocol which is more efficient for short messages transmissions, such as HTTP download requests, Short Message Service (SMS) messages, and signaling messages. The proposed MAC protocol is especially suitable for 3G and beyond cellular networks. Whenever there are number of channels that can be possibly used to deliver a message, it enables to select the least loaded channel among several channels.     

Performance analysis of DS/SSMA unslotted ALOHA system withvariable length data traffic

We analyze the throughput of a direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system with variable length data traffic. The system is analyzed for two cases: (1) systems without a channel load sensing protocol (CLSP) and (2) systems with a CLSP. The bit-error probability and the throughput are obtained as a function of the signal-to-noise ratio (SNR) during message transmission, considering the number of overlapped messages and the amount of time overlap. We assume that the generation of data messages is Poisson distributed and that the messages are divided into packets before transmission. The system is modeled as a Markov chain under the assumption that the number of packets in a message is geometrically distributed with a constant packet length. The throughput variance of the DS/SSMA unslotted ALOHA system with variable length data traffic is obtained as the Reed-Solomon code rate varies. Results show that a significant throughput improvement can be obtained by using an error-correcting code     

Performance of token schemes supporting delay-constrained prioritytraffic streams

A symmetric priority-based token network is considered. Messages are divided into two priority classes. High-priority messages are assumed to require tight delay constraints. As a result, each station is allowed to establish, at any time, at most a single real-time high-priority access concentration. High-priority messages are guaranteed access onto the channel within a prescribed limited period. In turn, regular priority messages are only served when the system determines, through the repetitive use of circulating tokens (as used by the IEEE 802.5 token-ring-type protocol), that no high-priority messages are currently waiting in the system. Two token schemes employing different service disciplines are used to provide network access. Exact and approximate mean delay formulas for both message classes are derived. Numerical results are then exhibited to illustrate the network performance under various traffic conditions     

Prioritized-virtual-time CSMA: head-of-the-line priority classeswithout added overhead

The prioritized-virtual-time carrier sense multiple access (PVT-CSMA) protocol is a media access algorithm for cable- and radio-based local area networks that incorporates message-based priority classes. PVT-CSMA implements the head-of-the-line (HOL) priority queuing discipline, in which higher priority messages are always transmitted in preference to lower priority messages, and messages are transmitted first-come-first-served within each priority class. Expressions are obtained for both throughput as a function of offered load and mean delay as a function of throughput for asynchronous (unslotted) PVT-CSMA, which are easily solvable for any number of priority classes and for class-dependent message lengths, arrival rates, retransmission rates, etc. Specialization of the delay analysis to the single class case yields a substantial improvement over previous results for asynchronous virtual-time CSMA. Comparisons are made between this analysis and simulations of PVT-CSMA, and with simulations of Tobagi's P-CSMA (1982) protocol     

Selective parsing to enhance SIP performance

The session initiation protocol (SIP) is used as the signaling protocol in the IP multimedia subsystem (IMS) and the signaling is becoming computing intensive comparing to the current telecommunication network. The SIP is a text-based protocol with characteristics of unordered and verbose headers, variable-size message, and case-insensitive keyword. It imposes challenges for an efficient message processing. The property of SIP elements being able to process SIP messages quickly is critical for the performance of IMS networks. This article investigates the performance of SIP message processed in SIP servers, mainly focusing on improving message parsing by introducing a method named selective parsing for SIP message (SP4SIP). By modeling and analyzing a SIP server with a tandem Jackson network, it is concluded that parsing messages is the bottleneck of a SIP server performance, i.e., it is the most processing intensive activity in the system. To validate the approach, it has been implemented in a high-performance SIP server in the authors' lab. The results show that selective parsing for SIP message can indeed reduce processing time.     

Performance measurement of data transfer services in MAP

The emergence of the enhanced performance architecture, which provides the application process with direct access to a fast datalink datagram service provided by the full MAP (manufacturing automation protocol), is discussed. An explanation is given of the functional differences between the two service types and why both are useful in the manufacturing environment. It is shown that message segmentation makes a substantial contribution to overall message latency. The effect of retransmission timer setting and the maximum credit window size is illustrated. Throughput and end-to-end delay for one implementation of MAP are reported, and conclusions are drawn about the expected performance cost of messages sent as datagrams versus messages sent over virtual circuits     

Meeting real-time constraints in CAN

This paper deals with the problem of information flow scheduling in a communication system based on CAN ISO IS-11898 physical medium access mechanism. It mainly features a bus access arbitration protocol based on a priority assigned to each message to be transmitted; if two or more messages are transmitted at the same time by different communication nodes, only the message with the highest priority continues to be transmitted, the other being stopped. In real-time applications, messages are relevant to process variables which must be transmitted within strict time constraints; according to the CAN ISO IS-11898 bus arbitration protocol, respect of real-time constraints depends on the priority assigned to each variable. The aim of the paper is to propose a procedure for dynamic assignment of priorities to variables to be transmitted, in such a way the relevant real-time requirements are fulfilled. Although many other approaches can be found in literature, the proposal is original as it is based on standard full CAN communication stacks.     

Enhanced EDCA with Deterministic Transmission Collision Resolution for Real-Time Communication in Vehicular Ad Hoc Networks

The collision prevention system is one of most important research issues on vehicle safety technology. Sending worming messages within the right time and reliable transmission will get prevention of a possible vehicle accident. The communication standards of vehicular networks (VANET) are unable to guarantee the delivery of critical messages within tight deadlines. Indeed, the transmission collisions are handled with probabilistic manner that can reduce the transmission latency; however, it is inept to predict an upper bound value of this delay to verify the deadline. In this paper, we propose a medium access protocol that ensures the delivery of critical messages within a deadline. It is a hard real-time system with delay constant guarantee. We are focusing on improving the EDCA medium access protocol to prioritize critical messages and to get access to the transmission channel within a predictable communication delay. We create a new enhanced access protocol that is compatible with the IEEE 802.11p VANET standards and adapted to real-time communication requirements related to the vehicle collision avoidance problem.     

Queuing disciplines and passive congestion control in byte-streamnetworks

The mean delay and throughput characteristics of various trunk queuing disciplines of the FIFO (first in, first out) and round-robin types for byte-stream data networks are investigated. It is shown that, under normal traffic, high-speed trunks substantially reduce queuing delays. Almost any queuing discipline will give acceptable delay if the backbone network is sufficiently faster than the access lines. In the absence of high-speed trunks, both the packet FIFO and the round-robin discipline can be augmented with a priority queue that expedites single-packet messages, which may carry network control signals or echoplex characters. In FIFO-type disciplines, the mean delays of messages that do not go through the priority queue depend on the overall message length distribution. A sprinkling of very long messages can significantly increase the mean delays of other messages. In disciplines of round-robin type, the mean delay of each message type is not affected by the presence of very long messages of other types     

A simulation study of delay in multichannel CSMA/CD protocols

Simulation is used to estimate the performance of media access control (MAC) protocols derived from carrier-sense multiple access with collision detection (CSMA/CD), and operating in local area networks comprising several parallel broadcast channels. The influence of possible protocol and system alternatives on the network performance is discussed, based on results of the packet delay average, variance, mean square, coefficient of variation, and histogram, as well as the packet rejection probability due to lack of buffer space. The delay incurred by multipacket messages is estimated, comparing the single channel to the multichannel option. Numerical results indicate that the multichannel option provides reductions in both the packet delay average and variance, even when stations are only able to simultaneously receive from a subset of channels     

Evolved broadcast scheduling mechanism supporting energy conserving e-MBMS transmission

This study designed a data broadcasting method called evolved broadcast scheduling algorithm (eBSA) to further support LTE evolved multimedia broadcast/multicast services (e-MBMS). This eBSA provides new scheduling technology for e-MBMS and a new information searching method for user equipments that simultaneously conserves user equipment energy and maintains favorable access latency of broadcast messages. The eBSA constructs index and message channels based on the message popularities, using the index channel to guide user equipments to rapidly locate the position of the desired message in the message channel. Consequently, a short mean access time and mean turning time can be attained. The results of numerical analysis verify that when access messages possess skewed access characteristics, the proposed eBSA method performs exceptionally. Additionally, by adequately adjusting the parameter provided by the eBSA method, the optimal tradeoff between energy conservation and access latency performance can be attained.     

Medium Access Control Protocol Design for Vehicle–Vehicle Safety Messages

We propose a medium access control protocol design for a vehicle to send safety messages to other vehicles. We develop a Quality-of-Service (QoS) model for safety messages that are consistent with the active vehicle safety systems literature. Each message has a range and useful lifetime. The QoS target has each message received with high probability within its specified lifetime by each vehicle within its specified range. The protocol design is based on rapidly rebroadcasting each message multiple times within its lifetime in combination with the 802.11 Distributed Coordination Function. This makes the design compatible with emerging standards for Dedicated Short-Range Communication. Six different design variations are proposed. We derive equations and develop a simulation tool to assess the performance of the designs. Using these, we identify the best and most easily implemented designs. Design performance depends on the number of rebroadcasts, power, modulation, coding, and vehicular traffic volumes. We show that under certain assumptions on the loss probability tolerated by safety applications, the design is able to transport safety messages in vehicular ad hoc networks     

Latency analysis of the Totem single-ring protocol

The Totem single-ring protocol provides reliable totally ordered multicasting of messages to processes in process groups over a single local-area network (LAN) using a logical token-passing ring. The protocol provides two levels of message delivery: delivery in agreed order and delivery in safe order. This paper presents the probability density functions (PDFs) for the latency to message delivery for the Totem single-ring protocol for these two levels of service in the presence of both message loss and token loss. These PDFs are calculated by repeated convolutions of the PDFs for the various components of the latency. The analysis shows that the mean latency to safe delivery is greater than the mean latency to agreed delivery and that the tail of the latency distribution for safe delivery is longer. It also shows that a deterministic arrival process for message generation exhibits lower mean latencies and shorter tails of the latency distribution than a Poisson arrival process     

Enhanced fuzzy logic‐based spray and wait routing protocol for delay tolerant networks

Delay tolerant networks are a class of ad hoc networks that enable data delivery even in the absence of end‐to‐end connectivity between nodes, which is the basic assumption for routing in ad hoc networks. Nodes in these networks work on store‐carry and forward paradigm. In addition, such networks make use of message replication as a strategy to increase the possibility of messages reaching their destination. As contact opportunities are usually of short duration, it is important to prioritize scheduling of messages. Message replication may also lead to buffer congestion. Hence, buffer management is an important issue that greatly affects the performance of routing protocols in delay tolerant networks. In this paper, Spray and Wait routing protocol, which is a popular controlled replication‐based protocol for delay tolerant networks, has been enhanced using a new fuzzy‐based buffer management strategy Enhanced Fuzzy Spray and Wait Routing, with the aim to achieve increased delivery ratio and reduced overhead ratio. It aggregates three important message properties namely number of replicas of a message, its size, and remaining time‐to‐live, using fuzzy logic to determine the message priority, which denotes its importance with respect to other messages stored in a node's buffer. It then intelligently selects messages to schedule when a contact opportunity occurs. Because determination of number of replicas of a message in the network is a difficult task, a new method for estimation of the same has been proposed. Simulation results show improved performance of enhanced fuzzy spray and wait routing in terms of delivery ratio and resource consumption. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimal MAC packet size in networks without cut-through routing

This paper presents an analytical method of optimal breaking of a transmission control protocol (TCP)/Internet protocol (IP) message into medium access control (MAC) packets in networks without cut-through routing (such as networks compliant with the IEEE 802.11 wireless local area network standard). The method accounts for the transmission delay of acknowledgement frames, the sliding window flow control in TCP/IP protocol, error control via retransmissions, and heterogeneity of transport parameters (link-to-link and upstream-downstream) along a multihop network path. Mathematically, the problem consists in minimizing the TCP/IP message transaction time, a nonlinear function of the MAC packet size, in the presence of a set of linear restrictions. Throughput calculations illustrating this method are performed using IEEE 802.11 data.     

无线传感器网络中带消息恢复机制的PBC广播认证协议

为了在无线传感器网络(WSN)中保证安全等级的情况下最小化通信和计算成本,提出了一种带消息恢复机制的基于配对密码学的广播认证协议。该机制不需要同时传输原始签名信息和新生成的签名信息,认证/消息恢复过程能自动恢复原始签名信息。首先初始化系统,基站产生系统参数;然后用户从基站获取密钥,访问WSN;最后当用户需要广播消息给WSN时,用户使用包含消息恢复机制的身份签名(IBS)协议写下签名消息,生成签名后进行消息广播。实验性能分析表明,与IMBAS和IDBAS相比,本文协议的广播消息大小分别减少了30%和22.3%,在112比特位安全等级,总能耗至少减少30%左右,在80比特位安全等级至少可降低15%的总能耗。     

Block acknowledgment: redesigning the window protocol

A window protocol based on the block acknowledgment method, in which acknowledgment message has two numbers, m and n, to acknowledge the reception of all data messages with sequence numbers ranging from m to n, is discussed. In the window protocol, message sequence numbers are taken from a finite domain and both message disorder and loss can be tolerated. An initial version of the protocol that uses a simplified timeout action and unbounded sequence numbers is presented, the simplified timeout action in the protocol is replaced by a sophisticated one without disturbing the protocol's correctness, and the unbounded sequence numbers are replaced by bounded ones while preserving the protocol's correctness. Remarks concerning other variations of the protocol are also presented     

Self-stabilizing sliding window ARQ protocols

It is shown that implementing a practical self-stabilizing sliding window protocol requires a bound on the maximum delay or maximum memory of the communication channel involved. This motivates using communication channel models that incorporate a delay or memory bound. For such models, two new ARQ protocols are presented that self-stabilize by using 1 bit of overhead in each transmitted message. The protocols operate like selective repeat ARQ, except that when a fault places them in an incorrect (unsafe) state, the additional bit in the protocol messages allows automatic recovery. Following a transient fault, the bounded delay protocol stabilizes within four round-trip times. The bounded memory protocol stabilizes after sending at most 2(K+n) messages, where K the is maximum number of messages that can be stored in one direction on the channel, and n is the window size of the sender     

A Secure Ambulance Communication Protocol for VANET

Vehicular ad hoc networks (VANETs) have been a research focus in recent years. VANET’s main applications are enhancing road safety and reducing traffic accidents. Moreover, the VANET system can also reduce the time it takes for emergency vehicles to arrive at the accident location. The security of the transmission messages is of utmost importance, and to protect the transmission messages we propose a secure ambulance communication protocol for VANET to ensure that messages will not be revealed or stolen. The proposed scheme combines symmetric encryption, message authentication codes and digital signature mechanisms, and thereby achieves non-repudiation, availability, integrity, confidentiality, mutual authentication, session key security, known-key security and the ability to prevent known attacks. Finally, with NS2 simulation results that are based on realistic vehicle density statistics and the Taipei city road map, we argue that our secure ambulance communication protocol is effective in real VANET scenarios.     

Spread‐spectrum CDMA packet radio MAC protocol using channel overload detection and blocking

An analytical and simulation performance evaluation is presented for a multi‐access protocol for a data packet radio network with a limited user capacity. The network employs direct‐sequence code division multiple access (DS‐CDMA) in a centralised channel load‐sensing scheme with channel overload (collision) detection and blocking via a separate ancillary channel state information broadcast system. Traffic models that incorporate both a finite population and an infinite population and variable length data messages are considered. Results show that an improved throughput/delay performance can be obtained by implementing a channel overload detection (message dropping) scheme as well as a channel overload avoidance (message blocking) scheme. The channel overload threshold β is fixed at the system's maximum user capacity whereas it is shown that the overload avoidance blocking threshold α should be variable and dependent on the mean message arrival rate. This revised version was published online in July 2006 with corrections to the Cover Date.