A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> Stream Control Transmission Protocol (SCTP) currently uses an Adler- 32 checksum. For small packets Adler-32 provides weak detection of errors. This document changes that checksum and updates SCTP to use a 32 bit CRC checksum. <s> BIB001 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> The stream control transmission protocol (SCTP) is being standardized by IETF as a reliable transport protocol to address a number of limitations of TCP. Due to its attractive features, such as multi-streaming and multi-homing, SCTP has received much attention from the research community and industry. The paper serves as a tutorial by introducing the main features of SCTP, and discussing the state of the art in SCTP research activities. We also provide a survey on the available products which implement SCTP. Finally, the challenges faced by SCTP research community are identified with a view to stimulating further research. <s> BIB002 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> PR-SCTP (partial reliability stream control transport protocol) is the new unreliable extension to SCTP. This paper first introduces SCTP and PR-SCTP. Then it describes the mechanism of transmitting MPEG-4 over PRSCTP. Next we compare the performance of PR-SCTP, TCP and UDP for MPEG-4 video traffic over mobile networks. <s> BIB003 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> In this paper, we explore end-to-end loss differentiation algorithms (LDAs) for use with congestion-sensitive video transport protocols for networks with either backbone or last-hop wireless links. As our basic video transport protocol, we use UDP in conjunction with a congestion control mechanism extended with an LDA. For congestion control, we use the TCP-Friendly Rate Control (TFRC) algorithm. We extend TFRC to use an LDA when a connection uses at least one wireless link in the path between the sender and receiver. We then evaluate various LDAs under different wireless network topologies, competing traffic, and fairness scenarios to determine their effectiveness. In addition to evaluating LDAs derived from previous work, we also propose and evaluate a new LDA, ZigZag, and a hybrid LDA, ZBS, that selects among base LDAs depending upon observed network conditions. We evaluate these LDAs via simulation, and find that no single base algorithm performs well across all topologies and competition. However, the hybrid algorithm performs well across topologies and competition, and in some cases exceeds the performance of the best base LDA for a given scenario. All of the LDAs are reasonably fair when competing with TCP, and their fairness among flows using the same LDA depends on the network topology. In general, ZigZag and the hybrid algorithm are the fairest among all LDAs. <s> BIB004 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> In the field of personal mobile communications, it has been suggested that SCTP could provide a solution to the problems encountered by the currently implemented TCP/Mobile IP scheme. By exploiting SCTP's multihoming feature to connect to several separate wireless networks concurrently, allows a Mobile Node to choose which wireless path suits the particular needs of the user application it is running. However, there is one drawback to this scenario - the current handover scheme implemented in SCTP is failure-centric in nature. This paper proposes an improved handover scheme for SCTP. This proposed scheme offers the benefit of performing handover based on measured path delays, thus it does not require a path failure for handover to occur. In some cases it can actually pre-empt the path failure, and handover before it occurs. <s> BIB005 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> Concurrent multipath transfer (CMT) uses the Stream Control Transmission Protocol's (SCTP) multihoming feature to distribute data across multiple end-to-end paths in a multihomed SCTP association. We identify three negative side-effects of reordering introduced by CMT that must be managed before efficient parallel transfer can be achieved: (1) unnecessary fast retransmissions by a sender; (2) overly conservative congestion window (cwnd) growth at a sender; and (3) increased ack traffic due to fewer delayed acks by a receiver. We propose three algorithms which augment and/or modify current SCTP to counter these side-effects. Presented with several choices as to where a sender should direct retransmissions of lost data, we propose five retransmission policies for CMT. We demonstrate spurious retransmissions in CMT with all five policies and propose changes to CMT to allow the different policies. CMT is evaluated against AppStripe, which is an idealized application that stripes data over multiple paths using multiple SCTP associations. The different CMT retransmission policies are then evaluated with varied constrained receive buffer sizes. In this foundation work, we operate under the strong assumption that the bottleneck queues on the end-to-end paths used in CMT are independent. <s> BIB006 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> This document describes the Stream Control Transmission Protocol (SCTP). SCTP is designed to transport PSTN signaling messages over IP networks, but is capable of broader applications. <s> BIB007 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> In this paper, we evaluate via real experiments the performance of the Stream Control Transmission Protocol (SCTP) and the Partial Reliability extension (PR-SCTP) for transmitting real-time H.264 video streaming over the Internet. This work looks into ways to apply the partial reliability services of PR-SCTP to exploit the implicit temporal scalability of P and B pictures in H.264/AVC video streams. We develop a simple probabilistic model that allow us to assign a limited number of retransmissions, using PR-SCTP, to each H.264/AVC frame type (e.g. I, P or B) before transmission. With our model we achieve a high probability of frame arrival at the receiver while at the same time keeping a low delay and bandwidth. <s> BIB008 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> The IETF is developing a new transport layer solution, MultiPath TCP (MPTCP), which allows to efficiently exploit several Internet paths between a pair of hosts, while presenting a single TCP connection to the application layer. From an implementation viewpoint, multiplexing flows at the transport layer raises several challenges. We first explain how this major TCP extension affects the Linux TCP/IP stack when considering the establishment of TCP connections and the transmission and reception of data over multiple paths. Then, based on our implementation of MultiPath TCP in the Linux kernel, we explain how such an implementation can be optimized to achieve high performance and report measurements showing the performance of receive buffer tuning and coupled congestion control. <s> BIB009 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> Mobile devices equipped with multiple network interfaces can increase their throughput by making use of parallel transmissions over multiple paths and bandwidth aggregation, enabled by the stream control transport protocol (SCTP). However, the different bandwidth and delay of the multiple paths will determine data to be received out of order and in the absence of related mechanisms to correct this, serious application-level performance degradations will occur. This paper proposes a novel quality-aware adaptive concurrent multipath transfer solution (CMT-QA) that utilizes SCTP for FTP-like data transmission and real-time video delivery in wireless heterogeneous networks. CMT-QA monitors and analyses regularly each path's data handling capability and makes data delivery adaptation decisions to select the qualified paths for concurrent data transfer. CMT-QA includes a series of mechanisms to distribute data chunks over multiple paths intelligently and control the data traffic rate of each path independently. CMT-QA's goal is to mitigate the out-of-order data reception by reducing the reordering delay and unnecessary fast retransmissions. CMT-QA can effectively differentiate between different types of packet loss to avoid unreasonable congestion window adjustments for retransmissions. Simulations show how CMT-QA outperforms existing solutions in terms of performance and quality of service. <s> BIB010 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> In recent years, with proliferation of smart phones and tablet PCs, speedup of wireless LAN communication is required for dealing with increase of traffic in wireless networks. However, transmission speed through a wireless network often slows down in comparison with that through a wired network since packets of wireless networks frequently drop due to the influence of surrounding environment such as electromagnetic noise. In this paper, we propose a method to mitigate the impacts caused by packet loss by virtue of SCTP bicasting in lossy multihoming environment with two or more wireless networks. This method bicasts not all packets but only important packets concerning retransmission for efficiency since bicasting all packets would cause congestion. We also implemented a prototype system based on the proposed method. According to the result of performance evaluation experiment, we confirmed the effectiveness of the proposed method by the fact that the prototype system performed faster transmission than normal SCTP transmission even in high packet loss rate environment. <s> BIB011 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> The massive proliferation of wireless infrastructures with complementary characteristics prompts the bandwidth aggregation for Concurrent Multipath Transfer (CMT) over heterogeneous access networks. Stream Control Transmission Protocol (SCTP) is the standard transport-layer solution to enable CMT in multihomed communication environments. However, delivering high-quality streaming video with the existing CMT solutions still remains problematic due to the stringent quality of service (QoS) requirements and path asymmetry in heterogeneous wireless networks. In this paper, we advance the state of the art by introducing video distortion into the decision process of multipath data transfer. The proposed distortion-aware concurrent multipath transfer (CMT-DA) solution includes three phases: 1) per-path status estimation and congestion control; 2) quality-optimal video flow rate allocation; 3) delay and loss controlled data retransmission. The term ‘flow rate allocation’ indicates dynamically picking appropriate access networks and assigning the transmission rates. We analytically formulate the data distribution over multiple communication paths to minimize the end-to-end video distortion and derive the solution based on the utility maximization theory. The performance of the proposed CMT-DA is evaluated through extensive semi-physical emulations in Exata involving H.264 video streaming. Experimental results show that CMT-DA outperforms the reference schemes in terms of video peak signal-to-noise ratio (PSNR), goodput, and inter-packet delay. <s> BIB012 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> This document defines two additional policies for the Partially ::: Reliable Stream Control Transmission Protocol (PR-SCTP) extension. ::: These policies allow limitation of the number of retransmissions and ::: prioritization of user messages for more efficient usage of the send ::: buffer. <s> BIB013 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> The growing availability of various wireless access technologies promotes increasing demand for mobile video applications. Stream control transmission protocol (SCTP)-based concurrent multipath transfer (CMT) improves the wireless video delivery performance with its parallel transmission and bandwidth (BW) aggregation features. However, the existing CMT solutions deployed at the transport layer only are not accurate enough due to lower layer uncertainties, such as variations of the wireless channel. In addition, CMT-based video transmission may use excessive BW in comparison with the popular Transmission Control Protocol (TCP)-based flows, which results in unfair sharing of network resources. This paper proposes a novel cross-layer fairness-driven (CL/FD) SCTP-based CMT solution (CMT-CL/FD) to improve video delivery performance, while remaining fair to the competing TCP flows. CMT-CL/FD utilizes a cross-layer approach to monitor and analyze path quality, which includes wireless channel measurements at the data-link layer and rate/BW estimations at the transport layer. Furthermore, an innovative window-based mechanism is applied for flow control to balance delivery fairness and efficiency. Finally, CMT-CL/FD intelligently distributes video data over different paths depending on their estimated quality to mitigate packet reordering and loss, under the constraint of TCP-friendly flow control. Simulation results show how CMT-CL/FD outperforms existing solutions in terms of both video delivery performance and TCP-friendliness. <s> BIB014 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> Video streaming has already become the main portion of data traffic over the Internet. However, it is hard to guarantee the user-perceived video quality in single access networks due to the limitation in available bandwidth. Multihomed systems enable concurrent multipath data transfer over multiple network paths. Path control can be implemented at the transport layer such as in Stream Control Transport Protocol (SCTP). SCTP has built-in support for multihoming, but offers only a limited standard path selection mechanism. In this paper a new method for video streaming over SCTP is proposed. Secondary paths are used to send redundant information to prevent degradation of viewer's perceived quality. The efficiency of the proposed method is demonstrated by computer simulations using video coded with H.264/MPEG-4 AVC (Advanced Video Coding). The results show that the proposed method can prevent degradation of video quality at the cost of small extra bandwidth usage. <s> BIB015 </s> A Holistic Survey of Wireless Multipath Video Streaming <s> 5) SCTP and CMT (extension of SCTP): <s> Delivering high-definition (HD) wireless video under stringent delay constraint is challenging with regard to the limited network resources and high transmission rate. Concurrent multipath transfer (CMT) using stream control transmission protocol (SCTP) exploits the multihoming feature of mobile devices to establish associations with different access networks. In this paper, we study the multihomed HD video communication with SCTP over heterogeneous wireless networks. The existing CMT schemes mainly treat the traffic data in a content-agnostic fashion, and thus cannot effectively leverage the scarce wireless resources to maximize the perceived video quality. To address this critical issue, we propose a content-aware CMT (CMT-CA) solution that featured by the unequal frame-level scheduling based on estimated video parameters and feedback channel status. First, we develop an analytical framework to model the total distortion of parallel video transmission over multiple wireless access networks. Second, we introduce a joint congestion control and data distribution scheme to minimize the total distortion based on online quality evaluation and Markov decision process (MDP). The performance of CMT-CA is evaluated through extensive semi-physical emulations in Exata involving HD video encoded with H.264 codec. Experimental results show that CMT-CA outperforms the reference schemes in terms of video peak signal-to-noise ratio (PSNR), end-to-end delay, and goodput. Or conversely, CMT-CA achieves the same video quality with $20$ percent bandwidth conservation. <s> BIB016
The first SCTP specification was published in the now obsolete RFC 2960 [189] in 2000 and then it was updated in RFC 3309 BIB001 and RFC 4460  . The current protocol specification is in RFC 4960 BIB007 containing updates and standardized by IETF in 2007. SCTP provides multihoming, multistreaming, and there is support for SCTP by different operating systems and platforms (e.g., FreeBSD, Linux and Android). Here, firstly, we have an overview of SCTP, such as data transmission process, and SCTP properties. Then, we indicate performance limitations. Finally, we discuss the surveyed works that are based on this protocol. SCTP overview. SCTP is a message-oriented protocol like UDP and supports reliability by using congestion control and retransmission like TCP BIB007 . Default SCTP uses one path as a primary path for transferring data packets, and other paths are used for redundancy transferring (retransmission and backup packets). Redundant paths are used to have more resilience and reliable data transferring than using only a single path. In particular, SCTP sets up an association with different IP addresses for each end host BIB002 . Association, in SCTP, refers to the connection between SCTP end hosts. SCTP provides multistreaming capabilities that reduce the HOL blocking problem. In SCTP, each stream is a subflow within the overall data flow, where multistreaming refers to the simultaneous transmission of several independent streams of data in an SCTP association. SCTP multistreaming works by adding stream sequence numbers to the chunks of each stream. Sequence numbering guarantees the in-order packet delivery inside a stream while unordered delivery can happen across streams. Therefore, arrived data of a stream can be delivered to the application layer even if other streams are blocked because of losses. Default SCTP also uses another sequence space called Transmission Sequence Number (TSN) for each chunk -the unit of information within an SCTP packet BIB007 . TSN is global for all streams with the goal of lost detection and reconstructing the original data at the receiver. Besides, SACK/Cumulative TSN ACK are leveraged as acknowledgment methods. Cumulative TSN ACK is a field of SACK to acknowledge the TSN of the last successfully received DATA chunk to the sender. For data transmission protection, SCTP uses a retransmission mechanism upon two types or events. First, whenever RTO expires. Second, after four SACK chunks have reported gaps with the same data chunk missing. Besides, SCTP uses uncoupled congestion control, and a shared buffer is used for all paths on the receiver side. SCTP performance limitations. SCTP presents performance limitations in heterogeneous paths and it is challenging to adopt it for video streaming: • Applications modification requirement: SCTP requires distinct socket API and applications modifications BIB009 . • Lack of support in middleboxes: SCTP suffers from lack of support in middleboxes BIB009 . • Frequent primary path exchange: SCTP is slow due to frequent primary path exchanges in case of failure. In SCTP, the process of path primary exchange takes a long time BIB015 by, for example, detecting 6 lost packets. In SCTP, a packet is recognized as lost if the sender does not receive ACK at a specific time of RTO. RTO is set to 1 second at the start and after each lost detection, it doubles. Finally, the minimum time to change the path is 63 seconds. Therefore, the process of path primary exchange takes a long time and causes a high delay. This issue is considered in the works, BIB005 , BIB011 , and SRMT BIB015 . • Lack of load balancing support: Default SCTP is not load balancing over multiple paths. Load balancing is an important factor in multipath transmission. Several efforts have been done to add capability of bandwidth aggregation to SCTP, and also adapting this protocol for video streaming. This issue is considered in the surveyed works, CMT-DA BIB012 , CMT-CA BIB016 and CMT-QA BIB010 . • Unnecessary fast retransmission: Out-of-order packet delivery and wireless losses could trigger unnecessary fast retransmissions, decrease goodput sharply, and consequently mitigate transmission efficiency BIB010 . This issue is considered in the surveyed works, CMT-DA BIB012 , CMT-CA BIB016 and CMT-QA BIB010 . • Content-agnostic traffic scheduling: While considering video content features in scheduling strategy could improve the QoE and network utilization, default SCTP scheduling treats in a content-agnostic fashion. This issue is considered in the surveyed work, CMT-CA BIB016 . • Fully reliable and ordered service: SCTP is a fully reliable and in order protocol, which is not required by video streaming. In our surveyed works, PR-SCTP BIB008 applied the concept of partial reliability in SCTP for realtime video delivery. Improved scheduling mechanisms. There are several approaches to improve SCTP to solve the above mentioned problems and provide video streaming over this transport protocol. We briefly mentioned them and next, we provide more details. To reduce the explained problem of longtime primary path exchanging in SCTP, Kelly et al. BIB005 proposed a delaycentric strategy to set the primary path based on the lowest End-to-End delay and RTT. The solution improves quality, but using this adaptive primary path selection in the lossy wireless environment makes the SCTP slow due to frequent path exchanges. This approach does not use the full ability of all paths and uses the primary path for data transmission and secondary paths as backup. A more stable solution based on SCTP is in BIB011 . The authors defeated with packet loss by proposing a selective bicasting method. Therefore, instead of sending the same data through two different paths (bicasting), which would lead to significant congestion and reduce the throughput, the selective bicasting method duplicates only important packets. These important packets are retransmissions. However, this approach has not defined sensitive data, like I-frames, as important packets. Da Silva et al. BIB015 proposed a Selective-Redundancy Multipath Transfer (SRMT) scheme. In this approach, the primary path is used to transfer data and secondary paths are used to send redundant packets, which have more priority and stronger delay limitation. These redundancies mitigate degradation QoE. There are two key factors for packet selection over secondary paths. The first one is the amount of redundant packets to be transferred, which is calculated based on smooth Round Trip Time (sRTT) of the primary path and the maximum delay tolerated by the application. The second one is the selection of packets, which have to be sent redundantly based on the importance of packets for reconstructing the video (a content-aware approach). For example, I-frames have the highest priority and among the Iframe packets, the initially ordered ones have more priority than others. P-frames are the next and the lowest priority is for B-frames. Duplicated packets on the receiver side would be discarded. SRMT uses the default SCTP handover scheme to avoid HOL problem. In order to make reliable SCTP protocol flexible for video streaming, the Partially Reliable SCTP (PR-SCTP) extension was firstly defined in  , and later additional policies were specified in BIB013 . Similar to the explained concept of partial reliability for MPTCP in Section IV-B4, PR-SCTP introduced some policies for choosing reliability level. PR-SCTP supports choosing the retransmission policy by using either a maximum number or a time for retransmissions, and after that, the packet will not be retransmitted anymore. PR-SCTP shows benefits for time-sensitive applications involving video and audio streaming BIB003 . In our surveyed works, the proposed approach in BIB008 utilized the partial reliability services of PR-SCTP for real-time H.264/AVC video streaming. H.264/AVC has a Network Adaptation Layer (NAL) feature, which is a layer of abstraction over the actual encoded data. NAL header contains decoding parameters and its level of importance for decoding. This information is used by PR-SCTP to decide the number of retransmissions for each I, P and B-frames. A probabilistic model is developed to find optimum values for the maximum number of retransmissions for different types of frames in order to provide a trade-off between reliability and delay. Retransmissions are over the secondary paths. The result shows that the proposed solution outperforms UDP and TCP. Another extension solution of SCTP is Concurrent Multipath Transfer (CMT) BIB006 . Most CMT solutions use all the available paths simultaneously for data transferring to increase the throughput and network resiliency. There are many schemes developed based on CMT, such as CMT-DA BIB012 , CMT-CA BIB016 and CMT-QA BIB010 . Among these works, CMT does not use any path selection method and uses Round Robin for data distribution. Using Round Robin for CMT not only increases out-of-order delivery, and HOL blocking at receiver, but also increases SACK overhead and additional unnecessary retransmission. CMT evolved to perform better estimation of the network situation and choosing qualified paths for data transmission in CMT-QA BIB010 , CMT-DA BIB012 and CMT-CA BIB016 . CMT-CA BIB016 is also fed with video content properties besides the network situation. These works are also different in designing of congestion control and retransmission mechanism. More details will be presented in Section VI-A. Xu et al. BIB010 proposed a path and quality-aware adaptive concurrent multipath transfer (CMT-QA) approach for packet scheduling over network channels. The goal of this scheme is decreasing out-of-order problem by reducing the unnecessary fast retransmissions and reordering delay. To achieve this target, a path quality estimation model (PQEM), an Optimal Retransmission Policy (ORP) and Data Distribution Scheduler (DDS) are introduced. PQEM calculates each path quality by estimating the rate of the distributed data, which is a function of sending buffer size and transmission delay. In PQEM, the shared sender buffer is divided into subbuffers. Each path has its own subbuffer and management independently and the allocation of buffer space size is dynamical. ORP handles packet loss differentiation and retransmits the lost packets over faster paths. DDS predicts the arrival time of data distributed over each path, and determines the amount of data to be transferred based on the congestion control parameters including cwnd, rwnd and sender buffer size. Therefore, DDS distributes data per path in the way that they arrive to the receiver in order. SACK is used for acknowledgment method. However, the approach does not concern TCP fairness toward other traffic flows BIB014 and it is not appropriate for video due to the lack of use of video content parameters. Wu et al. BIB012 proposed a distortion-aware concurrent multipath transfer (CMT-DA) scheme and claimed that this approach was the first work to introduce the video distortion into SCTP for enhancing HD video quality in heterogeneous wireless environments. The goal of this approach is decreasing video distortion by mitigating the effective loss rate for variable bit rate video streaming. To achieve this goal, three main methods are proposed: path status estimation and congestion control, flow rate allocation, and data retransmission control. CMT-DA estimates path situations (e.g., RTT and available bandwidth) by processing ACK feedbacks, and applies a distortion-aware model at the flow level to schedule the packets. Aggregated feedback packets are sent after each packet delivery. The used SACK/Cumulative ACK feedback packets return to the sender through the most reliable paths to avoid losing or dropping during the network transmission. In addition, the congestion control is designed per path and defined parameters are RTT, cwnd and RTO. ECN detects path congestion and changes the congestion window size. The rate controller is proposed to choose a subset of paths dynamically and assign data transmission rates. The data retransmission control is defined to retransmit the packets which are estimated to arrive at the destination within the deadline. However, only flow level distortion consideration without analyzing frame priority and decoding dependency of frames is not adequate for video streaming. In another surveyed work, Wu et al. BIB016 proposed a content-aware CMT (CMT-CA) scheme and claimed this approach was the first SCTP to incorporate the video content analysis into the scheduling for enhancing HD video quality in heterogeneous wireless environments. The goal of CMT-CA is to accurately estimate the video content parameters and appropriately schedule the video frames to achieve the optimal quality. To achieve this goal, three main methods are proposed: quality evaluation based decision making, congestion control, and data distribution. Quality evaluation based decision making estimates network situation and frame level distortion. Further, these pieces of information are used for packet scheduling. Similar to what explained for CMT-DA, SACK/Cumulative ACK feedbacks are used for path situation estimation and they are sent after each packet delivery through the most reliable paths. The congestion control for CMT-CA is designed per path, Markov model-based (MDP), and is TCP-Friendliness. Congestion control parameters are RTT, cwnd, RTO and ssthresh. ZigZag scheme BIB004 detects path congestion and MDP changes the congestion window size. Data distribution is responsible for packet scheduling and different transmission is applied for I and P frames. Therefore, high priority frames can be transmitted first, which helps to decrease video distortion. Besides that, the proposed algorithm drops the video frame if its parent frame cannot be delivered due to bandwidth restriction. Therefore, this algorithm conserves network resources. Besides the proposed methods, CMT-CA also utilizes similar data retransmissions methods designed in CMT-DA. For example, SACK  , which provides a list of correctly/incorrectly received packets to the sender, and cumulative ACK, which informs the last successfully received packet to the sender.