George Philokyprou

Efficient design of totally self-checking checkers for all low-cost arithmetic codes

A method is proposed that is based on the partitioning of the input code variables into two sections, each section representing the binary form of a number Z/sub 1/ and Z/sub 2/, respectively. For a code with check base A=2/sup m/-1, two m-bit end-around carry adder trees calculate the modulo m residue of Z/sub 1/ and Z/sub 2/, while a totally self-checking (TSC) translator maps the output of the pair of trees onto m-variable two-rail code. A TSC two-rail checker maps the m-variable two-rail code onto one-out-of-two code. The checkers present significant improvement in the implementation cost, number of gate levels, and reliability over TSC checkers previously proposed in the literature. >

Research: Congestion control protocols for interconnected LANs supporting voice and data traffic

Congestion control schemes in LANs interconnected by bridges are presented. The networks are assumed to support voice and data traffic through the use of prioritized media access control protocols. The proposed congestion control protocols throttle the data input traffic to the network using special feedback messages called choke packets, thereby dynamically allocating bandwidth to voice and data traffic in case of bridge overload. A simulation study has been carried out to demonstrate the feasibility and effectiveness of the proposed protocols. Simulation results have shown that the protocols yield higher bridge throughput efficiency for both voice and data traffic with minimum protocol overhead.

FBC-Net: a reverse round robin LAN for voice and data traffic

Abstract A local area network (LAN) that provides a reverse order service discipline from round to round is presented. The network, Folded Bus with Control channel Network (FBC-Net), consists of two buses: a folded unidirectional data bus, and an auxiliary bus that coordinates access to the data bus. The FBC-Net provides bounded delay, a feature that makes it particularly suitable for voice transmission. An access protocol for integrating voice and data traffic is also described. This protocol meets the delay constraint for voice transmission, while at the same time guaranteeing sufficient bandwidth for data traffic transmission. The performance of the FBC-Net under various traffic conditions is evaluated via simulation.

VIBDaST: a virtual interactive book as a data structures teaching aid

Internet based teaching is well established under various contexts. WWW based virtual interactive books are used for this purpose. Using WWW browsers students can study such books locally or remotely. Enhanced by JavaTM applets, such books provide an interactive as well as a traditional approach to learning. Examples and exercises implemented as applets cater for both observation and exploration. Such a book, addressing the topic of data structures, is being developed as a teaching aid for a first year Computer Science students. Theory is presented in a hyperlinked textual form thus realising cross references, while examples and exercises are visualised as interactive JavaTM applets.

Research: SBP-Net: an integrated voice/data token ring LAN

This paper presents a modified token ring LAN, called the Scheduling Bypass Periods Network (SBP-Net). SBP-Net uses the ring to implement the IEEE 802.5 standard token ring functions and an auxiliary bus for control purposes. In our proposal idle stations are bypassed, therefore the relevant delay produced in the standard token ring is minimized. This improvement is particularly significant at light and medium loads, and makes the proposed LAN suitable for voice applications. An access protocol for integration of voice and data is also described which meets the delay constraints of voice traffic while guaranteeing a minimum bandwidth requirement for data traffic. The performance of the SBP-Net is evaluated via simulation tools. Results obtained show significant improvement of delay-throughput characteristics compared with those of the token ring.

Voice and data integration on a unidirectional bus LAN

Abstract Two combined voice and data transmission protocols implemented on a folded unidirectional bus LAN are proposed. The first is a round-robin service protocol, while the second is a reverse round-robin service protocol. Data transmissions on both protocols and voice transmissions on the first protocol are based on a mechanism according to which a station starts transmitting when it detects an end of carrier on the outbound channel, and it aborts its transmission when it detects a transmission from upstream. In the second protocol, voice is transmitted in the reverse round exploiting the periodicity of voice. According to this mechanism, each station computes its transmission time by relying on the preceding transmissions. Separation of the two traffic types is achieved by the requirement for sharing the channel alternately in voice and data rounds. The transmission of data packets and voice call packets for setting up calls is assigned to the data round, while the transmission of voice packets is assigned to the voice round. In these protocols, access delay for voice packets can be bounded to a desirable upper limit by not allowing the transmission of data. The performance of the proposed protocols under various traffic conditions was studied via simulation tools.

Bridge protocol for creating a loop-free topology in an extended LAN

Abstract This paper presents a bridge protocol that creates a loop-free topology from an arbitrary mesh topology consisting of a collection of LANs and bridges. The protocol is transparent to stations, thus no modifications are required to existing end stations. The protocol provides reconfiguration mechanisms under bridge failure or insertion of additional bridges without management intervention. The operation of the protocol has been tested via simulation tools and has been shown to behave well for mesh topology configurations and bridge failures.

Family of protocols for ring LANs with an auxiliary bus and parallel reservations

Abstract A family of local area network protocols is presented. The LAN we consider consists of a ring and a bidirectional bus to which stations are connected via adapters and passive taps respectively. The data frames in these protocols can avoid several stations resulting in less delays. The main feature of these protocols is that reservation procedures for the bypassed stations take place in parallel with the data frame transmission. Another interesting feature is that all the standard token ring functions do operate under the proposed topology. The last member of this family is a protocol with the ability to change its behaviour according to the offered load at each station. The performance of the protocols is evaluated by simulation models. Also performance comparisons of the new protocols are presented.

Skipnet: a two channel token access scheme

Abstract A modified token ring Local Area Network called Skipnet is presented, which uses the ring channel for all normal functions of the standard token ring, and an extra bus channel for control messages. In the model idle stations are bypassed, therefore the relevant delay produced in the standard token ring is minimized. Using simulation models, a standard token ring Medium Access Control protocol is compared with the modified network. The results show significant improvement in delay-throughput characteristics when the offered load is light. As the load increases performance is close to (but still better than) that of the standard token ring network.