Wiley.Games.on.Symbian.OS.A.Handbook.for.Mobile.Development.Apr.2008 (779888), страница 37
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In either case, the number ofplayers of a multiplayer game is, as the name suggests, more than one.However, it is not limited to two. Depending on the game’s design, anumber of people can play a mobile game together – either as a team (ortwo teams, playing against each other) or as opposing individuals.In a single-player game, the player plays against the game, and ischallenged to either complete an action at a given time – or as quicklyas possible – or solve a mental puzzle, or some combination thereof. Theplayer is challenged by the artificial intelligence (AI) of the game alone.In a multiplayer game, the player is still challenged by the game, but alsointeracts with others, either playing against them or working as a teamagainst other players or the game’s AI.5.1.1 Connection DropsIn a multiplayer game, a player may leave the game before it is finished,perhaps by choice1 (for example, if the player is interrupted and needs to1A game designer should avoid giving players an incentive to leave a game.
If a gamehas a leader board where their rank improves if they win, and declines if they lose, but isunaffected by dropping out of a game, they are likely to leave a game they are pessimisticabout winning.158MULTIPLAYER GAMESdo something else) or because of a dropped connection (for example, ifa train goes into a tunnel).Once a player’s departure is detected, the game must handle it gracefully. If there is only one player left, the game may stop and declare theremaining player the victor. If there are still multiple players remaining,the game designer can opt to keep the game running so the other playersare not inconvenienced. A number of techniques are feasible:• ‘Civil Disorder’: the departed player remains in the game, but doesnothing.
This phrase was originally used in Allan Calhammer’s boardgame Diplomacy, in which the armies and fleets of a player remainin place on the board after they have left.• AI takeover: the game’s AI takes over the leaving player’s position(commonly used in online multiplayer card games). This approachworks even if a single player is left after all other opponentsdrop out.• Replacement player: with some types of games, it may be feasible tofill the position with a new player.
For example, in online multiplayercard games, if a game is full, a player can wait to take over a positionwhen another gamer leaves.When a player decides to stop playing the game and do somethingelse, with a single-player game, it’s simple enough to save the gamestate for next time. However, with multiplayer games, it is more complex,since although one player has left, others may choose to continue playing,and certainly will not want to sit and wait indefinitely for that player torejoin and resume where he or she left off! Some games are designedso that players may drop in and out, and the game continues regardlesswhen they are offline.
Good examples are massively multiplayer onlinerole-playing games (MMORPGs). Other games are played to completionwithout the player who has departed, or are simply abandoned whenthe player leaves. When the player resumes the game in multiplayermode, he or she starts a new game and does not resume the previoussession, since it cannot be predicted that the player’s original opponentsare still online and the game in the same state as when he or shedeparted.5.1.2 LatencyLatency – the time between when a device makes a request and it isreceived – is a big factor in multiplayer mobile games when played overa phone network.
While it can be measured in milliseconds on the wiredInternet and for Bluetooth connections, it can be several magnitudeshigher, measurable in seconds, over the air. High latency currently makesLOCAL MULTIPLAYER GAMES OVER A BLUETOOTH CONNECTION159it almost impossible to develop certain genres of mobile game, like firstperson shooter action games, for online multi-play over GPRS.Although the move to third-generation (3G) technologies does expandthe bandwidth available to over the air networks, it does not necessarilysignificantly change the latency equation.
(That is, you may be able tosend 100 KB in the time it used to take to send 10 KB, but it will still takea second or more for the data to start arriving.)Game design needs to take latency into account to avoid issues oflatency. Suggested approaches include:• Turn-based games: each player takes a turn and, because the playerstake some time to respond, the additional seconds imposed by networklatency are acceptable. However, if there are too many players, theamount of time a player must wait for a turn may be intolerable, sogame designers should limit the number of players of a turn-basedgame accordingly.• Simultaneous-move games: these are games in which each playerdecides what to do during the next turn, and submits the move,which the game sends over the network.
All moves are revealedsimultaneously, the winner is determined and the result sent to eachplayer. One of the advantages of this system is that players don’thave to wait through everyone else’s move. A player who sends in hermove quickly may have to wait until the slowest player has completedhis move, but this is still faster than waiting on every turn separately.A good example of this kind of game is Roshambo – also known asRock, Paper, Scissors.• Solo multiplayer games: even though this sounds like a contradiction!In fact, in a solo multiplayer game, players each face the samechallenge, playing in single-player mode, with scores compared atthe end of the round, and a winner declared.
Because informationis only exchanged with the server at the beginning and end of eachchallenge, latency is less of an issue.5.2 Local Multiplayer Games Over a Bluetooth ConnectionLocal multiplayer games are those that can be played by more thanone player, each using a different phone, communicating by a shortlink connection. Here we will concentrate on multiplayer games over aBluetooth connection because this is the most convenient technology foruse on a Symbian smartphone.Bluetooth is a technology that allows devices to establish a localarea wireless network. Devices must be within about 10 meters ofeach other to establish connections. Bluetooth connections allow for160MULTIPLAYER GAMESfast data transfer rates when compared to transfer over the cellularnetwork.
Over GPRS, you can expect multi-second latency, but over aBluetooth network, latency is of the order of 20 to 50 milliseconds. Therelative throughput (the amount of data flowing through a connection,disregarding protocol overhead) of a Bluetooth connection approximates700 kbps, while comparatively, over GPRS, throughput is approximately50 kbps. Throughput and latency both favour Bluetooth over GPRS forfast, action-based multiplayer games.Multiplayer functionality using a Bluetooth connection can be a niceaddition to a game because it is fun for users to play against friends thatare in the same room without having to pay for a data connection, orhave any other equipment besides their mobile handset.
All S60 and UIQsmartphones support Bluetooth, and most users are familiar with its use,although, for a good multiplayer game experience, it is still important topresent an easy way for players to set up the Bluetooth connection sothere is no barrier to its use.The information and example code required to provide a good multiplayer game using a Bluetooth connection is significant. We have decidedthat the level of detail required is beyond the scope this book. Instead,we have written a paper and created example code to illustrate howto use L2CAP sockets to create multi-point Bluetooth connections for amultiplayer game. Both the example code and paper may be downloadedfrom the Symbian Developer Network at developer.symbian.com – a linkis also provided on the developer wiki page for this book (found at developer.symbian.com/wiki/display/academy/Games+on+Symbian+OS).An alternative way of creating Bluetooth multipoint connections is touse the Bluetooth PAN profile to establish a local ad hoc piconet.
Thispresents the PAN profile as a network interface, or Internet Access Point(IAP).2 However, at the time of writing, the PAN profile is not currentlywidely supported on Symbian OS smartphones, so we currently have nodocumentation on its use in Bluetooth multiplayer games. However, weanticipate this to change, and recommend that you check the SymbianDeveloper Network for papers on using PAN and WLAN connections inmultiplayer games.5.3 Online Multiplayer GamesAt first glance, online multiplayer games (meaning those games wherecommunication from the handset goes over the Internet rather than overa short link technology such as Bluetooth) may seem to differ very little2An IAP is a concept specific to Symbian OS, associated with IP-based applications. Itis a collection of settings that defines how a connection to a particular network is made.
AnIAP can be thought of as representing a single network interface.ONLINE MULTIPLAYER GAMES161from short link gaming. You might initially guess that there will be somedifferences because the network will be slightly less reliable due to greatercomplexity when connecting to the global Internet.Also, there may be differences in game design for a game that canchallenge people anywhere in the world rather than just other playerswithin Bluetooth range. There are design implications for setting up amultiplayer game session over a network with a stranger, compared tosetting up a session to play over Bluetooth with someone who you canprobably see and talk to as the game progresses.However, those differences seem relatively minor.
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