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Corrected a lot of errors in chapter 1&2

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niklas 2011-05-04 15:37:19 +02:00
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@ -401,7 +401,7 @@ Due to the increasing importance of computer gaming, more focus should be
spent on improving the quality of the gaming service. spent on improving the quality of the gaming service.
As more and more computer games are gaining multi-player capabilities, As more and more computer games are gaining multi-player capabilities,
the demands for multiplayer networking software rises. the demands for multiplayer networking software rises.
This thesis is about techniques for improving the quality if this networking This thesis is about techniques for improving the quality of this networking
software. software.
\end_layout \end_layout
@ -465,14 +465,15 @@ generic
framework for developing network games. framework for developing network games.
The framework is generic in the sense that it is not bound to a specific The framework is generic in the sense that it is not bound to a specific
game. game.
There are many different types of games, some are inheritly more time sensitive There are many different types of games, some are inherently more time
than others, strategy games are examples of games which are not very sensitive sensitive than others, strategy games are examples of games which are not
to time delays, first-person shooters however, can be very sensitive. very sensitive to time delays, first-person shooters however, can be very
sensitive.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The generic nature of the GGS allows the creation of many different types The generic nature of the GGS allows the creation of many different types
of games, the motivation behind this is to remove the neccessity of writing of games, the motivation behind this is to remove the necessity of writing
new game servers when developing new games. new game servers when developing new games.
\end_layout \end_layout
@ -481,9 +482,9 @@ The GGS is in addition to being generic, also
\emph on \emph on
reliable reliable
\emph default \emph default
in the sense that the gaming service provided is consistant and available. in the sense that the gaming service provided is consistent and available.
A consistant and available server is a server that handles hardware failiures A consistent and available server is a server that handles hardware failures
and software failiures gracefully. and software failures gracefully.
In the event of a component breaking within the GGS, the error is handled In the event of a component breaking within the GGS, the error is handled
by fault recovery processes, thereby creating a more reliable system. by fault recovery processes, thereby creating a more reliable system.
\end_layout \end_layout
@ -494,7 +495,7 @@ Background
\begin_layout Standard \begin_layout Standard
The game industry is a quickly growing industry where the need for new technique The game industry is a quickly growing industry where the need for new technique
s is large. s are large.
One specific section where the development has stalled is the game server One specific section where the development has stalled is the game server
section. section.
\begin_inset Note Note \begin_inset Note Note
@ -520,7 +521,7 @@ Citation needed
. .
Users will notice this in low uptime and many crashes. Users will notice this in low uptime and many crashes.
This is a problem that has existed and been resolved in other industries. This is a problem that has existed and been resolved in other industries.
In the telecom industry solutins to similar problems have been found. In the telecom industry solutions to similar problems have been found.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
@ -720,8 +721,8 @@ A database server can also be seen as an application server.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
One of the purposes of this thesis is to investigate how we can make a game One purpose of this thesis is to investigate how we can make a game server
server as generic as possible. as generic as possible.
Some important helpers are discussed, such as abstraction of the network Some important helpers are discussed, such as abstraction of the network
layer, data store and game specific features. layer, data store and game specific features.
@ -815,8 +816,8 @@ The purpose of creating a generic and fault tolerant game server is to provide
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Fault tolerance is important for the GGS in order to create a reliable service. Fault tolerance is important for the GGS to create a reliable service.
The purpose of a reliable game server is to provide a consistant service The purpose of a reliable game server is to provide a consistent service
to people using the server. to people using the server.
Going back to the telecom example, the purpose of creating a reliable telecom Going back to the telecom example, the purpose of creating a reliable telecom
system is to allow calls, possibly emergency calls, at any time. system is to allow calls, possibly emergency calls, at any time.
@ -848,9 +849,9 @@ The word
generic generic
\emph default \emph default
in the name of the GGS implies that the system is able to run a very broad in the name of the GGS implies that the system is able to run a very broad
range of different code, for instance code written in different programming range of different code, for instance code wrote in different programming
languages, in addition to a broad range of different game types. languages, besides a broad range of different game types.
In order to support this, a virtual machine (VM) for each To support this, a virtual machine (VM) for each
\emph on \emph on
game development language game development language
\emph default \emph default
@ -933,9 +934,8 @@ The implementation of the GGS protocol, together with storage possibilities,
\begin_layout Standard \begin_layout Standard
The UDP protocol is not supported for communication between client and server. The UDP protocol is not supported for communication between client and server.
The TCP protocol was chosen in favour of UDP, due to the fact that the The TCP protocol was chosen in favor of UDP, because the implementation
implementation process using TCP was faster than if UDP would have been process using TCP was faster than if UDP would have been used.
used.
UDP is generally considered to be faster than TCP for the transfer of game UDP is generally considered to be faster than TCP for the transfer of game
(and other) related data, this is discussed in more depth in (and other) related data, this is discussed in more depth in
\begin_inset CommandInset ref \begin_inset CommandInset ref
@ -955,7 +955,7 @@ reference "sec:Choice-of-network"
\begin_layout Standard \begin_layout Standard
In real time games all players are playing together at the same time. In real time games all players are playing together at the same time.
Latency is a huge problem in real time games, a typical round trip time Latency is a huge problem in real time games, a typical round trip time
for such games is one of for such games are one of
\begin_inset Formula $50$ \begin_inset Formula $50$
\end_inset \end_inset
@ -991,7 +991,7 @@ World of Warcraft
\begin_layout Standard \begin_layout Standard
In turn based games each player has to wait for their turn. In turn based games each player has to wait for their turn.
Latency is not a problem since the gameplay does not require fast interactions Latency is not a problem since the gameplay does not require fast interactions
between the players, long round trip times will not be noticed. among the players, long round trip times will not be noticed.
Examples of turn based games include board and card games, as well as multiplay Examples of turn based games include board and card games, as well as multiplay
er games like er games like
\emph on \emph on
@ -1012,9 +1012,8 @@ Due to the limited capability of threading in many GDL VM:s, the GGS prototype
The implementation of the GGS described in this thesis is only a small prototype The implementation of the GGS described in this thesis is only a small prototype
and tests will be performed on simple games like pong or chess, thus there and tests will be performed on simple games like pong or chess, thus there
are no need to implement more advanced features in the system. are no need to implement more advanced features in the system.
It is important to note that these limitations only apply for the prototype Note that these limitations only apply for the prototype of the project,
of the project, and that further developments to the GGS could be to implement and that further developments to the GGS could be to implement these features.
these features.
\end_layout \end_layout
\begin_layout Section \begin_layout Section
@ -1026,8 +1025,7 @@ Development process
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
A prototype was developed early on in the project in order to carry out A prototype was developed early on in the project to carry out experiments.
experiments.
Using this prototype, the system was divided into modules. Using this prototype, the system was divided into modules.
A demand specification was created, using this specification, the modules A demand specification was created, using this specification, the modules
were easily identifiable. were easily identifiable.
@ -1035,17 +1033,17 @@ A prototype was developed early on in the project in order to carry out
\begin_layout Standard \begin_layout Standard
The first prototype of the GGS consisted of simple modules, however, due The first prototype of the GGS consisted of simple modules, however, due
to the separation of concerns between the modules, they were easily independant to the separation of concerns among the modules, they were easily independently
ly modified and improved. modified and improved.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Once the basic structure of the GGS had been established, the first prototype Once the basic structure of the GGS had been established, the first prototype
was removed, remaining was the structure of the modules and the internal was removed, remaining was the structure of the modules and the internal
flow of the application. flow of the application.
This could be seen as an interative workflow, with the first prototype This could be seen as an iterative workflow, with the first prototype being
being the first iteration. the first iteration.
The second iteration later became the final result of the GGS The second iteration later became the result of the GGS
\end_layout \end_layout
\begin_layout Subsection \begin_layout Subsection
@ -1059,7 +1057,7 @@ The layout of the GGS is both layered and modular.
GGS. GGS.
The modular structure of the GGS plays an important role in making the The modular structure of the GGS plays an important role in making the
system fault tolerant. system fault tolerant.
The approach to fault tolerance is by replication, and restarting faulting The approach to fault tolerance is by replication, and restarting the faulting
modules with the last known good data. modules with the last known good data.
\end_layout \end_layout
@ -1101,7 +1099,7 @@ In this chapter, the theory behind the techniques used in the GGS are discussed.
Benchmarking techniques are discussed. Benchmarking techniques are discussed.
The options when choosing network protocols are given, along with a discussion The options when choosing network protocols are given, along with a discussion
of each alternative. of each alternative.
Finally, a overview of scalability, fault tolerance and availability is Finally, an overview of scalability, fault tolerance and availability are
presented. presented.
\end_layout \end_layout
@ -1117,7 +1115,7 @@ name "sec:Design-of-the"
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The GGS is modelled after a real world system performing much of the same The GGS is modeled after a real world system performing much of the same
duties as GGS. duties as GGS.
This is common practice This is common practice
\begin_inset CommandInset citation \begin_inset CommandInset citation
@ -1126,12 +1124,11 @@ key "armstrong2011"
\end_inset \end_inset
in the computer software world, in order to understand complex problems in the computer software world, to understand complex problems more easily.
more easily.
While there may not always be a real world example of a system performing While there may not always be a real world example of a system performing
th exact duties of the system being modelled in the computer, it is often the exact duties of the system being modeled in the computer, it is often
easier to create and analyze requirements for real world systems and processes easier to create and analyze requirements for real world systems and processes
than systems existing soley in a computer. than systems existing solely in a computer.
The requirements and limitations imposed on the real-world system can, The requirements and limitations imposed on the real-world system can,
using the proper tools, be transferred in to the software. using the proper tools, be transferred in to the software.
\end_layout \end_layout
@ -1276,7 +1273,7 @@ Räkning
can be kept, ensuring that there are not too many players within the building. can be kept, ensuring that there are not too many players within the building.
In the GGS setting, too many players entering would mean too many connections In the GGS setting, too many players entering would mean too many connections
have been accepted to the GGS system, and that the structure of the system have been accepted by the GGS system, and that the structure of the system
thus must be modified, adding additional servers. thus must be modified, adding additional servers.
\end_layout \end_layout
@ -1302,16 +1299,16 @@ Moves by players are made using the tables present in the chess club.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
This isolation of the games plays an imporant part in many properties of This isolation of the games play an important part in many properties of
the GGS, the isolation means that games can for example be transferred the GGS, the isolation means that games can for example be transferred
between different chess clubs, furthermore, if cheating takes place, corruption among different chess clubs, furthermore, if cheating takes place, corruption
can only occur in the particular table where it was found, and can not can only occur in the particular table where it was found, and can not
spread. spread.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Moving chess players from one location to another is one of the alterations Moving chess players from one location to another is one alteration made
made to the real world chess club system to make the system more appropriate to the real world chess club system to make the system more appropriate
for a software setting. for a software setting.
Allowing games to be transferred is not a property usually desired in a Allowing games to be transferred is not a property usually desired in a
real world chess club, where transferring players would mean moving the real world chess club, where transferring players would mean moving the
@ -1332,10 +1329,10 @@ reference "alg:game-lifecycle"
\end_inset \end_inset
. .
In order to make this life cycle as efficient and useful as possible, the To make this life cycle as efficient and useful as possible, the scalability,
scalability, fault tolerant and generic traits are added to the GGS. fault tolerant and generic traits are added to the GGS.
These are not shown in the algorithm, as these traits are tools in making These are not shown in the algorithm, as these traits are tools in making
the algorithm behave as efficient as possible, and are not the main focus the algorithm behaves as efficient as possible, and are not the main focus
when studying the life cycle of a game. when studying the life cycle of a game.
\end_layout \end_layout
@ -1768,10 +1765,10 @@ There are many ways in which performance could be measured.
\begin_layout Standard \begin_layout Standard
In a first person shooter game, the speed of delivery of messages is essential. In a first person shooter game, the speed of delivery of messages is essential.
Failiure to deliver messages in time results in choppy gameplay for the Failure to deliver messages in time results in choppy gameplay for the
players. players.
In strategy games, the reliability of delivery may be more important than In strategy games, the reliability of delivery may be more important than
the speed, since the game is not percieved as choppy even if the messages the speed, since the game is not perceieved as choppy even if the messages
are delayed. are delayed.
\end_layout \end_layout
@ -1779,7 +1776,7 @@ In a first person shooter game, the speed of delivery of messages is essential.
For someone operating a GGS, it is perhaps more interesting to measure the For someone operating a GGS, it is perhaps more interesting to measure the
system load, memory consumption, energy consumption and network saturation. system load, memory consumption, energy consumption and network saturation.
These topics are discussed in theory in this section. These topics are discussed in theory in this section.
The practical results for the prototype are discussed in chapter The practical results for the prototype is discussed in chapter
\begin_inset CommandInset ref \begin_inset CommandInset ref
LatexCommand vref LatexCommand vref
reference "cha:Implementation-of-a" reference "cha:Implementation-of-a"
@ -1924,12 +1921,12 @@ name "sec:Choice-of-network"
\begin_layout Standard \begin_layout Standard
There are three main ways in which computer communication over the Internet There are three main ways in which computer communication over the Internet
usually takes place; TCP, UDP and HTTP. usually takes place; TCP, UDP and HTTP.
The first two are transport layer protocols, which are commonly used to The first two is transport layer protocols, which are commonly used to
transport application layer protocols, such as HTTP. transport application layer protocols, such as HTTP.
TCP and UDP can not be used on their own, without an application layer TCP and UDP can not be used on their own, without an application layer
protocol on top. protocol on top.
Application layer protocols such as HTTP on the other hand needs a transport Application layer protocols such as HTTP on the other hand needs a transport
layer protocol in order to work. layer protocol to work.
\end_layout \end_layout
@ -1993,7 +1990,7 @@ TCP
\begin_layout Standard \begin_layout Standard
For reliable transfers, TCP is often used on the Internet. For reliable transfers, TCP is often used on the Internet.
Built in to the protocol are the error checking and correction mechanisms Built in to the protocol is the error checking and correction mechanisms
missing in UDP. missing in UDP.
This ensures the consistency of data, but also makes the transfer slower This ensures the consistency of data, but also makes the transfer slower
than if UDP had been used. than if UDP had been used.
@ -2082,13 +2079,12 @@ Fault tolerance is an important factor in all servers, a server that is
safe and guaranteed to be available. safe and guaranteed to be available.
It should be noted that it is not possible to achieve complete fault tolerance, It should be noted that it is not possible to achieve complete fault tolerance,
a system will always have a certain risk of failure. a system will always have a certain risk of failure.
With this in mind the goal is to make the GGS prototype as fault tolerant Therefore the goal is to make the GGS prototype as fault tolerant as possible.
as possible.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
In order to make the GGS prototype fault tolerant the programming language To make the GGS prototype fault tolerant the programming language Erlang
Erlang has been used. has been used.
Erlang will not guarantee a fault tolerant system but it has features that Erlang will not guarantee a fault tolerant system but it has features that
support and encourage the development of fault tolerant systems. support and encourage the development of fault tolerant systems.
In the GGS it is important that the system overall is fault tolerant. In the GGS it is important that the system overall is fault tolerant.
@ -2100,12 +2096,12 @@ In order to make the GGS prototype fault tolerant the programming language
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The need for fault tolerance in game servers is not as obvious as it may The need for fault tolerance in game servers are not as obvious as it may
be for other typ of servers. be for other type of servers.
In general all servers strive to be fault tolerant as fault tolerance means In general all servers strive to be fault tolerant as fault tolerance means
more uptime and a safer system. more uptime and a safer system.
This applies to game servers aswell, in brief good fault tolerance is a This applies to game servers as well, in brief good fault tolerance is
way of satisfying customers. a way of satisfying customers.
In general, game servers differ from many other fault tolerant systems In general, game servers differ from many other fault tolerant systems
in that high-availability is more important than the safety of the system. in that high-availability is more important than the safety of the system.
For example a simple calculation error will not be critical for a game For example a simple calculation error will not be critical for a game
@ -2132,14 +2128,14 @@ name "sec:Availability"
\begin_layout Standard \begin_layout Standard
One important factor of any server is the availability. One important factor of any server is the availability.
A server to which you are unable to connect to is a useless server. A server to which you are unable to connect to is an useless server.
Other then within telecomunication, their uptime is of about 99,9999999%, Other then within telecommunication, their uptime is of about 99,9999999%,
the game developer community has not approched this problem very genuinely the game developer community has not approached this problem very genuinely
yet so there is much room for improvement. yet so there is much room for improvement.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
There are several good papers on how to migrate whole virtual machines between There are several good papers on how to migrate whole virtual machines among
nodes to replicate them nodes to replicate them
\begin_inset Note Note \begin_inset Note Note
status open status open
@ -2191,22 +2187,22 @@ Each instance of the GGS contains several tables.
or a poker game. or a poker game.
The way that the GGS scales is to distribute these tables on different The way that the GGS scales is to distribute these tables on different
servers. servers.
In many games it is not necessary for a player to move between tables during In many games it is not necessary for a player to move among tables during
games. games.
This is for example not a common occurrence in chess, where it would be This is for example not a common occurrence in chess, where it would be
represented as a player standing up from her current table and sitting represented as a player standing up from her current table and sitting
down at a new table, all within the same game session. down at a new table, all within the same game session.
With this in mind, the main focus of the GGS is not to move players between Therefore, the main focus of the GGS is not to move players among tables,
tables, but to keep a player in a table, and to start new tables instead. but to keep a player in a table, and to start new tables instead.
When a server has reached a certain amount of players the performance will When a server has reached a certain number of players the performance will
start to decrease. start to decrease.
To avoid this the GGS will start new tables on another server, using this To avoid this the GGS will start new tables on another server, using this
technique the players will be close to evenly distributed between the servers. technique the players will be close to evenly distributed among the servers.
It is important to investigate and find out how many players that are optimal It is important to investigate and find out how many players that are optimal
for each server. for each server.
This approach makes it possible to utilize all resources with moderate This approach makes it possible to use all resources with moderate load,
load, instead of having some resources with heavy load and some with almost instead of having some resources with heavy load and some with almost no
no load. load.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
@ -2228,7 +2224,7 @@ Load balancing
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The need for load balancing varies between different kind of systems. The need for load balancing varies among different kind of systems.
Small systems that only use one or a couple of servers can cope with a Small systems that only use one or a couple of servers can cope with a
simple implementation of it, while in large systems it is critical to have simple implementation of it, while in large systems it is critical to have
extensive and well working load balancing. extensive and well working load balancing.
@ -2241,10 +2237,10 @@ The need for load balancing varies between different kind of systems.
\begin_layout Standard \begin_layout Standard
Load balancing and scaling is difficult in different scenarios. Load balancing and scaling is difficult in different scenarios.
When running in a separate server park, there are a set number of servers When running in a separate server park, there are a set number of servers
available, this means that an even distribution on all servers is preferable. available, this means that an even distribution on all servers are preferable.
When running the GGS in a cloud, such as Amazon EC2, it is possible to When running the GGS in a cloud, such as Amazon EC2, it is possible to
add an almost infinite number of servers as execution goes on. add an almost infinite number of servers as execution goes on.
In this cloud setting, it may be more important to evenly distribute load In this cloud setting, it may be more important to distribute evenly load
on newly added servers. on newly added servers.
\end_layout \end_layout
@ -2253,7 +2249,7 @@ Two methods of balancing load (increasing structure):
\end_layout \end_layout
\begin_layout Itemize \begin_layout Itemize
Fill up the capacity of one server completely, and then move over to the Fill up the capacity for one server completely, and then move over to the
next server next server
\end_layout \end_layout
@ -2284,7 +2280,7 @@ Load balancing is a key component to achieve scalability in network systems.
Load balancing can often be implemented using dedicated software, this means Load balancing can often be implemented using dedicated software, this means
that in many applications load balancing may not be implemented because that in many applications load balancing may not be implemented because
it already exist functional solutions. it already exist functional solutions.
This depends on what specific needs the system have and a minor goal of This depends on what specific needs the system has and a minor goal of
the project is to analyze whether the GGS project can use existing load the project is to analyze whether the GGS project can use existing load
balancing tools or if it is necessary to implement load balancing in the balancing tools or if it is necessary to implement load balancing in the
project. project.
@ -2487,10 +2483,10 @@ A simple (insufficient) generator for identifiers
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Inside the GGS, everything has a unique identifier. Inside the GGS, everything has an unique identifier.
There are identifiers for players, tables and other resources. There are identifiers for players, tables and other resources.
When players communicate amongst each other, or communicate with tables, When players communicate amongst one another, or communicate with tables,
they need to be able to uniquely identify all of these resources. they need to be able to uniquely identify all these resources.
Within one machine, this is mostly not a problem. Within one machine, this is mostly not a problem.
A simple system with a counter can be imagined, where each request for A simple system with a counter can be imagined, where each request for
a new ID increments the previous identifier and returns the new identifier a new ID increments the previous identifier and returns the new identifier
@ -2712,7 +2708,7 @@ We only support languages running in a sandboxed environment.
In the storage each game has its own namespace, much like a table in a In the storage each game has its own namespace, much like a table in a
relational database. relational database.
A game is not allowed to venture outside this namespace, and can because A game is not allowed to venture outside this namespace, and can because
of this not modify the persistent data of other games. this not modify the persistent data of other games.
\end_layout \end_layout
\begin_layout Subsection \begin_layout Subsection