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Even more small changes!

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niklas 2011-05-11 17:42:39 +02:00
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@ -1017,8 +1017,8 @@ The choice of implementation language for the prototype of the GGS was made
highly available and dependable telecom switches. highly available and dependable telecom switches.
One of the most reliable systems ever developed by Ericsson, the AXD301 One of the most reliable systems ever developed by Ericsson, the AXD301
was developed using Erlang. was developed using Erlang.
The AXD301 is also possibly has the largest code base even written in a The AXD301 has possibly the largest code base even written in a functional
functional language language
\begin_inset CommandInset citation \begin_inset CommandInset citation
LatexCommand citep LatexCommand citep
key "Armstrong03" key "Armstrong03"
@ -1613,7 +1613,7 @@ Coordinator
\emph default \emph default
, and is seated by a table. , and is seated by a table.
The coordinator keeps track of all the players in the building, and all The coordinator keeps track of all the players in the building, and all
moved made by the players. moves made by the players.
The information available to the coordinator means that cheating can be The information available to the coordinator means that cheating can be
monitored and book keeping can be performed by this entity. monitored and book keeping can be performed by this entity.
\end_layout \end_layout
@ -1622,23 +1622,24 @@ Coordinator
Moves by players are made using the tables present in the chess club. Moves by players are made using the tables present in the chess club.
Every game is isolated to a table, just as expected. Every game is isolated to a table, just as expected.
This means that communication during a game only has to pass by the players This means that communication during a game only has to pass by the players
of that particular game, and the coordinator, making sure that no cheating of that particular game and the coordinator, making sure that no cheating
takes place. takes place.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
This isolation of the games play an important 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
among different chess clubs, furthermore, if cheating takes place, corruption among different chess clubs.
can only occur in the particular table where it was found, and cannot spread. Furthermore, if cheating takes place, corruption can only occur in the
particular table where it was found and cannot spread.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Moving chess players from one location to another is one alteration made Moving chess players from one location to another is one alteration 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 an attribute usually desired in
real world chess club, where transferring players would mean moving the a real world chess club, where transferring players would mean moving the
players from one building to another. players from one building to another.
In the software setting, moving players means moving the game processes In the software setting, moving players means moving the game processes
from one system to another, perhaps to balance the system load. from one system to another, perhaps to balance the system load.
@ -1647,7 +1648,7 @@ Moving chess players from one location to another is one alteration made
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
The simplified life cycle of a game in GGS can be viewed using algorithm The simplified life cycle of a game in the GGS can be viewed using algorithm
\begin_inset CommandInset ref \begin_inset CommandInset ref
LatexCommand vref LatexCommand vref
@ -1671,8 +1672,8 @@ reference "alg:game-lifecycle"
\end_inset \end_inset
are arbitrary for this example, there are no limits in the GGS on the number are arbitrary for this example, there are for example no limits in the
of players connecting, for example. GGS on the number of players connecting.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
@ -2119,7 +2120,7 @@ Performance measurements
\begin_layout Standard \begin_layout Standard
\begin_inset Note Note \begin_inset Note Note
status open status collapsed
\begin_layout Plain Layout \begin_layout Plain Layout
Tue apr 26, 9:15. Tue apr 26, 9:15.
@ -2141,14 +2142,8 @@ Which games are affected by what, and what does this mean for the number
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
How many players can we have on a server? Performance differences between In the current state game servers are coded for each game that needs it,
games? e.g can one game have thousands players on a server and another only often this seems like a bad solution.
have hundreds? Questions
\end_layout
\begin_layout Standard
In the current state game servers is coded for each game that needs it,
in many cases this seems like a bad solution.
Developers that want to make a network game need to understand network Developers that want to make a network game need to understand network
programming. programming.
A way to change this is a generic game server which give the game developers A way to change this is a generic game server which give the game developers
@ -2159,7 +2154,7 @@ In the current state game servers is coded for each game that needs it,
to be discussed here. to be discussed here.
\begin_inset Note Note \begin_inset Note Note
status open status collapsed
\begin_layout Plain Layout \begin_layout Plain Layout
Create a game with several thousand players, see how our server scales, Create a game with several thousand players, see how our server scales,
@ -2249,7 +2244,7 @@ name "sec:Choice-of-network"
There are two main ways in which computer communication over the Internet There are two main ways in which computer communication over the Internet
usually takes place; TCP, UDP are known network layer protocols and HTTP usually takes place; TCP, UDP are known network layer protocols and HTTP
is the most prominent application layer protocol. is the most prominent application layer protocol.
The transport layer protocols, are commonly used to transport application The transport layer protocols are commonly used to transport application
layer protocols, such as HTTP. layer protocols, such as HTTP.
TCP and UDP cannot be used on their own, without an application layer protocol TCP and UDP cannot be used on their own, without an application layer protocol
on top. on top.
@ -2292,7 +2287,7 @@ Many online games use UDP as the carrier for their application layer protocol.
ruling out UDP as the transport later protocol. ruling out UDP as the transport later protocol.
\begin_inset Note Note \begin_inset Note Note
status open status collapsed
\begin_layout Plain Layout \begin_layout Plain Layout
Perhaps we should only say that we chose TCP just for our GGS prototype Perhaps we should only say that we chose TCP just for our GGS prototype
@ -2319,7 +2314,7 @@ For reliable transfers, TCP is often used on the Internet.
thus TCP is a better alternative than UDP. thus TCP is a better alternative than UDP.
\begin_inset Note Note \begin_inset Note Note
status open status collapsed
\begin_layout Plain Layout \begin_layout Plain Layout
Same here it is simply not true for a generic server to chose one or the Same here it is simply not true for a generic server to chose one or the
@ -2340,20 +2335,19 @@ HTTP
\begin_layout Standard \begin_layout Standard
Since HTTP is so widely used on the Internet today in web servers, it is Since HTTP is so widely used on the Internet today in web servers, it is
available on most Internet connected devices. available on most Internet connected devices.
This means that if HTTP is used in the GGS, firewalls will not pose problems, This means that if HTTP is used in the GGS, firewalls will not be a problem,
which is a great benefit. which is a great benefit.
However, due to the intended usage of HTTP in web servers, the protocol However, due to the intended usage of HTTP in web servers, the protocol
was designed to be stateless and client-initiated. was designed to be stateless and client-initiated.
In order to maintain a state during a game session using HTTP, some sort In order to maintain a state during a game session using HTTP, some sort
of token would have to be passed between client and server at all times, of token would have to be passed between client and server at all times,
much like how a web server works. much like how a web server works.
These facts combined makes HTTP unsuitable for our purposes, since the These facts combined make HTTP inappropriate for use in the GGS, since
GGS requires a state to be maintained throughout a session, and also needs the GGS requires a state to be maintained throughout a session and also
to push data from the server to clients without the clients requesting needs to push data from the server to clients without the clients requesting
data. data.
It should also be mentioned that HTTP uses the TCP protocol for transport, It should also be mentioned that HTTP uses the TCP protocol for transport,
and what is said about TCP also applies to HTTP. and what is said about TCP applies to HTTP.
\end_layout \end_layout
\begin_layout Subsection \begin_layout Subsection
@ -2361,15 +2355,15 @@ The GGS Protocol
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
HTTP was designed to be a stateless protocoll which by adding some overhead HTTP was designed to be a stateless protocol, which by adding some overhead
is able to remove the need of a permanent connection and a state for each is able to remove the need of a permanent connection and a state for each
client. client.
The GGS however already has a permanent connection to each client because The GGS however already has a permanent connection to each client because
it needs to push information to the clients. it needs to push information to the clients.
Therefore is able to use the state to minimize the overhead in the communicatio Therefore it is able to use the state to minimize the overhead in the communica
n between server and client. tion between server and client.
Because of that it has been decided to invent a new protocol which human Therefore it was decided to invent a new protocol which was human readable
readable like HTTP but customized for this special use. like HTTP but customized for this special use.
The GGS protocol is described in more detail in section The GGS protocol is described in more detail in section
\begin_inset CommandInset ref \begin_inset CommandInset ref
LatexCommand ref LatexCommand ref
@ -2402,13 +2396,13 @@ The GGS is a game server.
The GGS can be run as a listen server on the players computer and host The GGS can be run as a listen server on the players computer and host
games locally. games locally.
It could also be a dedicated server running on independent hardware. It could also be a dedicated server running on independent hardware.
It is meant to run any game in any environment in any way desired, therefor It is meant to run any game in any environment in any way desired, therefore
being as generic as possible. being as generic as possible.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Another aspect was the desire to let a client to load up the source code Another aspect was the desire to let a client upload the source code of
to the game it would like to play on the GGS. the game it would like to play on the GGS.
This way every client could connect to the server and install the game This way every client could connect to the server and install the game
through a API without the need of installation through the server provider through a API without the need of installation through the server provider
or maintainer. or maintainer.
@ -2428,14 +2422,13 @@ name "sec:Fault-Tolerance"
\begin_layout Standard \begin_layout Standard
Fault tolerance is an important factor in all servers, a server that is Fault tolerance is an important factor in all servers, a server that is
fault tolerant should be able to follow a given specification when parts fault tolerant should be able to follow a given specification when parts
of the system failures. of the system fails.
This means that fault tolerance is different in each system depending on This means that fault tolerance is different in each system depending on
what specification they have. what specification they have.
A system could be fault tolerant in different aspects, one is where the A system could be fault tolerant in different aspects, one is where the
system is guaranteed to be available but not safe and it could also be system is guaranteed to be available but not safe and it could also be
reversed, that the system is safe but not guaranteed to be available. reversed, that the system is safe but not guaranteed to be available.
Depending on the system one property may be more important(some example Depending on the system one property may be more important.
here).
A system could also have non existent fault tolerance or it could be both A system could also have non existent fault tolerance or it could be both
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,
@ -2449,7 +2442,8 @@ In order to make the GGS prototype fault tolerant the programming language
Erlang has been used. Erlang 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 and
not small parts only.
Crashes of the whole system should be avoided as this would make the system Crashes of the whole system should be avoided as this would make the system
unusable for a time. unusable for a time.
By using supervisor structures it is possible to crash and restart small By using supervisor structures it is possible to crash and restart small