• International Journal of Computer Science & Network Security
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• v.22 no.10
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• pp.191-200
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• 2022

Constrained Application Protocol (CoAP) is a standardized protocol by the Internet Engineering Task Force (IETF) for the Internet of things (IoT). IoT devices have limited computation power, memory, and connectivity capabilities. One of the significant problems in IoT networks is congestion control. The CoAP standard has an exponential backoff congestion control mechanism, which may not be adequate for all IoT applications. Each IoT application would have different characteristics, requiring a novel algorithm to handle congestion in the IoT network. Unnecessary retransmissions, and packet collisions, caused due to lossy links and higher packet error rates, lead to congestion in the IoT network. This paper presents an adaptive congestion control protocol for CoAP, Adaptive Congestion Control with a Backoff algorithm (ACCB). AACB is an extension to our earlier protocol AdCoCoA. The proposed algorithm estimates RTT, RTTVAR, and RTO using dynamic factors instead of fixed values. Also, the backoff mechanism has dynamic factors to estimate the RTO value on retransmissions. This dynamic adaptation helps to improve CoAP performance and reduce retransmissions. The results show ACCB has significantly higher goodput (49.5%, 436.5%, 312.7%), packet delivery ratio (10.1%, 56%, 23.3%), and transmission rate (37.7%, 265%, 175.3%); compare to CoAP, CoCoA+ and AdCoCoA respectively in linear scenario. The results show ACCB has significantly higher goodput (60.5%, 482%,202.1%), packet delivery ratio (7.6%, 60.6%, 26%), and transmission rate (40.9%, 284%, 146.45%); compare to CoAP, CoCoA+ and AdCoCoA respectively in random walk scenario. ACCB has similar retransmission index compare to CoAp, CoCoA+ and AdCoCoA respectively in both the scenarios.

• Korean Journal of Veterinary Service
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• v.32 no.1
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• pp.61-76
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• 2009

At the present study, it was aimed to explore the molecular genetic characterization of multiple antimicrobial resistant Salmonella spp. isolates from pigs and cattle. A total of 138 Salmonella Typhimurium (S. Typhimurium) isolates were typed with phage, among them, 83.3% of S. Typhimurium tested could divide into a 10 phage types. Definitive type 193 (DT193) (25.4%) and DT195 (24.6%) were exhibited as the dominant types. DT104 and U302 were found from pigs and cattle. On the other hand, S. Enteritidis had 6 phage types, of them, phage type 21 (PT21) and PT11b were the popular types. In the plasmid profiles, 135 of S. Typhimurium isolates were exhibited 1 to 6 plasmid bands which molecular weight ranged from 90 to 2kb. 35 isolates (25.4%) harbored a 90kb plasmid which is thought to be the serotype specific virulence plasmid. Two of twenty five S. Enteritidis had common plasmids at 2 and 1.5kb. With multiplex polymerase chain reaction, virulence genes (invA and spvC) were detected from all Salmonella spp. from 167 of S. Typhimurium, S. Enteritidis and chloramphenicol resistant S. Schwarzengrund, but some drug resistant genes, such as PSE-1, cml/tetR and flo were not determined but other drug resistant genes, for example TEM and int were found. The detection rates of spvC, TEM and int gene was 35.3%, 29.3% and 72.5%, respectively. The TEM gene was highly popular in S. Typhimurium, which was detected from ampicillin and amoxicillin resistant strains as 95.9%. int gene was able to detect from all the isolates identified as multidrug resistsnt (MDR), particularly DT193 was thought as the most prevalent virulence and multidrug resistance isolate. The major plasmid profile and drug resistance pattern of DT193 were 90, 40, 10.5, 6.3, 3.0kb and ACCbDNaPSSuT, respectively. MDR was commonly found in other phage types, particularly DT104, U302 and DT203.

• Korean Journal of Veterinary Service
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• v.32 no.1
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• pp.49-59
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• 2009

At the present study, it was aimed to explore the states of antimicrobial resistant Salmonella spp. isolates from 3,850 pigs (2,732 ileocecocolic lymphnodes and 1,118 cecal contents) and 1,764 cattle (965 cecal lymphnodes and 799 cecal contents) slaughtered in Busan province from December 2000 to November 2001. Among 5,614 samples, 457 of Salmonella spp. were isolated from pig lymphnodes (13.5%), pig cecal contents (4.4%), cattle lymphnodes (3.5%) and cattle cecal contents (0.5%). Salmonella spp. were showed different isolation ratio, that was 10.8% in summer, 9.0% in autumn, 8.4% in spring and 5.0% in winter. As a result of serotyping, B group (65.4%) were identified as the most common in pigs and cattle, in order of $C_1$ (14.0%), $D_1$ (5.5%), $C_2$ (4.2%), $E_1$ (4.2%) and L (3.5%). 34 serotypes were found, among them, Salmonella Typhimurium (S. Typhimurium) (21.0%) was the most common serotype from pigs and cattle. The major serotypes were in order of S. Derby (15.3%), S. Schwarzengrund (14.7%), S. Typhimurium var Copenhagen (9.2%), S. Mbandaka (5.7%), S. Enteritidis (5.5%) and S. Ruiru (3.5%). The most common serotype was S. Typhimurium in pigs, and S. Ruiru in cattle. S. Ruiru was firstly isolated from pigs and cattle in Korea. In antimicrobial susceptibility test, all the isolates were demonstrated susceptibility to norfloxacin and ofloxacin. But the isolates were showed resistance other antibiotics in order of doxycycline (68.3%), tetracycline (67.8%), penicillin (54.5%) and streptomycin (52.5%). S. Typhimurium were exhibited resistance to ampicillin (34.8%), chloramphenicol (36.2%), streptomycin (94.9%), sulfamethoxazole/trimethoprim (34.8%) and tetracycline (97.8%). There were 53 strains (38.4%) which had multi drug resistant (MDR) isolates, resistant to more than 6 antimicrobial agents. The most common resistance patterns of MDR isolates were ampicillin, chloramphenicol, carbenicillin, doxycycline, nalidixic acid, penicillin, streptomycin, sulfamethoxazole/trimethoprim and tetracycline (ACCbDNaPSSuT).