Jussi Ruutu

Simple integrated media access-a comprehensive service for future internet

The basic objectives of future Internet are to increase the network capacity, to offer a practical real-time service, and to develop a feasible charging scheme. These objectives introduce very strict requirements for the traffic control system. This paper presents a new simple approach for traffic management: Simple Integrated Media Access (SIMA). The strength of SIMA lies in its wide area of applications. There is no need to build complex systems with several service classes each appropriate to only certain applications.

Performance measurements and analysis of TCP flows in a differentiated services WAN

This paper presents results from performance measurements carried out in a differentiated services WAN connecting three major cities in southern Finland. The target of the measurements was to collect precise information about the level of service experienced by a user transmitting files with FTP in a network that implements service differentiation by using drop precedence levels and separate classes for real time and non-real time traffic. Special attention was paid to the behaviour of competing TCP flows produced by users with different service level specifications. Background traffic from ISPs network was injected into our test network in order to create traffic profiles which are typical in a core network. The results show clearly that the SIMA model used for the implementation of the DS mechanisms in the network nodes can provide service differentiation in a useful and fair manner in traffic conditions varying from light load to severe overload.

An enhanced TCP mechanism—fast-TCP in IP networks with wireless links

This paper presents the results of the first study on performance of Fast‐TCP over wireless links with transmission errors. We have studied a case in which a TCP source is connected with a TCP receiver over two routers. The link between the routers is wireless and has bit errors. We compare the performance of Fast‐TCP with plain TCP in the wireless environment. We evaluate Fast‐TCP using the OPNET Radio ModelerTM discrete event simulation tool. Simulation results show that even without any adaptations of other wireless protocols Fast‐TCP still has more advantages over plain TCP.

Energy Efficiency of Recharging a Mobile Device

Because of losses in electricity conversion and storage only part of the energy taken from the power grid produces useful work in a battery-operated mobile device, the rest evaporates as heat. We analyze the recharging activity of a mobile phone to understand the efficiency of the different units involved (charger, EPM chipset, battery). Our measurements show that the efficiency is quite low, only about 15 % of the electricity from the power grid ends up being used for the actual computing and communication elements of the mobile phone. It seems that there is room for improvement in the recharging efficiency. However, as the consumption of electricity of a single phone is small the incentive for improvements has been weak.

Packet discarding inside a SIMA network: a waste of network resources?

Simple Integrated Media Access (SIMA) is a network service based on drop preference bits in every packet. A key characteristic of SIMA is that the packet discarding decision are made locally without any knowledge about the load condition in other parts of the network. A possible problem of SIMA is that some packets could be lost in the last node after they have gone through the whole network. This seems to be a waste of network resource,s as some other packets could be transmitted in the network instead of the packets discarded in the last node. The question addressed in the paper is how much a network may profit by using perfect information about the network load condition in a way that the goodput in maximized by discarding packets only in the first node. A network with 5 nodes has been evaluated with a large number of different load conditions. The results show that the average benefit is less than 2 percent of the network capacity if the overall packet loss ratio is at most 20 percent. Only if the average packet los ratio is very high, could the benefit be significant.

Energy Efficiency of Mobile Device Recharging

Because of losses in electricity conversion and storage only part of the energy taken from the power grid produces useful work in a battery-operated mobile device; the rest evaporates as heat. The authors analyze the recharging activity of a mobile phone to understand the efficiency of the different units involved (charger, EPM chipset, battery). Their measurements show that the efficiency is quite low; only about 15% of the electricity from the power grid ends up being used for the actual computing and communication elements of the mobile phone. It seems that there is room for improvement in the recharging efficiency. However, as the consumption of electricity of a single phone is small the incentive for improvements has been weak.

Effect of Battery Charge on Energy Consumption

The power consumption of a mobile device has been measured with a continuously repeated multimedia use case starting with a full battery charge until the battery empties. We have discovered a clear dependency between the charge level of the battery and the power consumption of the device. The origin of this finding is associated with the DC-DC conversion made between the battery and the components inside the mobile device. The practical consequence is that e.g. software developers optimizing the energy consumption of their code must be aware of this phenomenon since minor changes in the code may be easily shadowed by the found effect. We provide some advice how to avoid or alleviate the error caused by the battery charge level.

Performance of simple integrated media access (SIMA)

Simple integrated media access (SIMA) is a new service category for packet based communications systems, such as ATM or IP. SIMA offers a simple way to introduce easy charging, real time support and increase in the capacity of networks. According to the SIMA concept each customer shall define only two issues before a connection establishment: a nominal bit rate (NBR) and the selection between real-time and non-real- time classes. NBR forms the basis of charging and defines how the network capacity is divided among different connections during overload situations. The ratio of momentary bit rate of the source and NBR defines for each individual cell a priority level that is used to select the cells to be discarded under congestion. Simulation results are described about the cell loss as a function of priority level of a cell. SIMA can be also be equipped with a priority feedback system that informs traffic sources about the condition of the network. Results on the performance of sources using this information are published. This paper also presents some simulations on a SIMA network that uses packet discarding. Simulations presented in this paper show that SIMA is capable of fulfilling requirements for the future broadband Internet networks.

Comparison of energy consumption between a mobile device and a collection of dedicated devices

It is often considered that general purpose mobile devices, such as smartphones, consume more energy than dedicated devices, e.g. MP3 players. This is typically associated with the application specific hardware that is optimized for its particular function. While this assumption might be true for a single function, there exists the fact that a modern smartphone combines multiple functions which traditionally only could be provided by a large collection of dedicated devices. The energy consumption of a multi-functional mobile device could be less than the augmentation of the dedicated devices. In addition, there can be benefits related to convenience and agility. To get better understanding, a study was made to compare the power consumption of some typical use cases between a mobile device and dedicated devices (each with a dedicated function). Our findings indicate that in the tested cases the mobile device can be significantly more energy efficient and more environmental friendly than combining the dedicated devices for the same set of functionalities. It should be understood that the results are not statistically significant over a wide range of markets and should not be considered as a generic claim. However, the findings will provide a starting point for discussions and for possible future work.

Transfer delays in a SIMA network

Differentiated Services approach has been recently proposed for providing Quality of Service in Internet. Simple Integrated Media Access is a network service concept that use this approach by utilizing priority bits in packet headers. Three drop preference bits are used for making the decision about packets to be discarded when congestion arises in a core network node. A single delay indication bit marks the packet either as belonging to a realtime or non real time flow. The acceptance of packets is not directly connected with real time properties of a packet. The real time support of SIMA is based on two features. First, real time packets are placed to a short real time buffer inside a core network node. Secondly, the real time buffer is always emptied before the longer, non real time buffer. This means a shorter queuing delay for real time packets. For the successful operation of the network it is crucial to have small enough transfer delay for real time packets. On the other hand, the difference in transfer delay must be significant enough between real time and non real time service in order to justify their existence. Finally, there is also the question, whether real time packets can block non real time flows since the real time packets are always transmitted first in a SIMA node. To answer these questions this paper addresses the issues related with transfer delay of packets over a SIMA network. We present extensive simulation results about the transfer delay distributions in order to provide insight into SIMA and transfer delays.