12 Networking and Online Games: Understanding and Engineering Multiplayer Internet Games The high fees for such online game play brought a new group of users who would host individual Bulletin-Board Systems (BBSes) that provided play-by-email or play-bybulletin-board system versions of table-top games such as chess or Dungeons and Dragons. Users connected to these BBSes by modem (usually by making only a local phone call). Some hobbyists provided richer gaming experiences, still charging money for MUDs, but at much lower, flat monthly rates than had previously been charged. Although commercial successes, the early computer games were fundamentally different from today s modern computer games. Players would move a dot or simple geometric shape on the screen, perhaps push a button to shoot and something would happen if one shape hit another. There were no opportunities to control anything near human-like avatars, or have complex interactions with other characters or the game-world environment. The game-world environment did not support a variety of vehicles, weapons or even different levels. It is not just that the early games had poorer graphics, rather the game play itself was fundamentally different. Immersiveness, often cited as very important for the success of modern games, was out of the question a player just controlled abstract shapes on the screen, with any immersiveness coming from the imagination of the player. These early computer games were relatively easy to produce, too, both in terms of cost and time. This is in striking contrast with today s popular computer games, which take 18 to 24 months to produce and often have budgets in millions of dollars. 2.3 Multiplayer Network Games By the early to mid-nineties, computer power was increasing rapidly, allowing computers to produce more realistic graphics and sound. Computer game players were no longer forced to go to great lengths to suspend their disbelief. Instead of controlling a square moving slowly around on a four-colour screen, they were able to move rapidly in a 256-colour environment, heightening the overall experience of a more realistic, lush, virtual world. In addition, it was increasingly common for computers to have network connections, ushering in a new area in multiplayer games, the multiplayer networked game. 2.3.1 DOOM Networked First-Person Shooters Arrive At the end of 1993, id Software produced Doom, a First-Person Shooter (FPS) game. Although there had been other FPS games produced before, Doom took the genre to the next level, providing a powerful engine that enabled a fast-paced and violent shoot- em-up with more realistic levels and creatures than had been seen in previous shooter games (Figure 2.11). For multiplayer players, Doom enabled up to four players to play cooperatively using the IPX protocol (an early internetworking protocol from Novell) on a LAN, (Figure 2.12) or competitively in a mode that was coined death-match . In the death-match mode, players compete against each other in an attempt to earn more frags (kills) than their opponent(s). Note: Novell s Internet Packet Exchange (IPX), was an internetworking protocol primarily for interconnecting LANs (Figure 2.13). It was often combined with Novell s Sequence Packet Exchange (SPX), to form the SPX/IPX stack functionally equivalent to the TCP/IP stack on which today s Internet is based. SPX/IPX could not compete with TCP/IP for wide area performance, and has since all but disappeared.
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Early Online and Multiplayer Games Figure 2.11 Screen shots of Doom, the popular First-Person Shooter that started a surge in online, multiplayer gaming. Reproduced by permission of Id Software, Inc. Doom node IPX driver Device driver Network card Local area network Doom node IPX driver Device driver Network card Software Hardware Figure 2.12 The hardware and software layers required to run multiplayer networked Doom Computer Computer Computer Ethernet Modem Modem Computer Computer (a) (b) Figure 2.13 Network topologies used by Doom. Computers connected to an ethernet LAN acted as peers (a), or computers connected by a modem acted as peers (b) Doom used a peer-to-peer topology for networking. All players in the game were independent peers running their own copy of the game and communicating directly with the other Doom peers. Every 1/35th of a second, each Doom game sampled the input from each player (such as move left, strafe, shoot, etc.) and transmitted them to all other players in the game. When commands for all other players for that time interval had been received, the game timeline advanced. Doom used sequence numbers to determine if a packet was lost. If a Doom node received a packet number that was not expected (i.e. the previous packet was lost), it decided that a packet had been lost and sent a resend request (a negative acknowledgement, or NACK) to the sender [DOOMENGINE].
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Early Online and Multiplayer Games Figure 2.9 Atari Football featured two-or four-player multiplayer play Figure 2.10 Gauntlet, released right about the time of the arcade decline, featured two to four players in cooperative, multiplayer hack-and-slash 2.2.4 Hosted Online Games In the 1980s, the idea of pay for play first emerged, with several game companies hosting online games and charging a monthly fee to play them. Companies such as Dow- Jones (The Source) and Compuserv (H and R Block) made use of the idle compute-cycles on their servers during nonbusiness hours by charging non-premium fees to access their computers to play games. Such systems primarily featured text-based games that were prevalent in academia, but several were multiplayer versions such as Compuserv s Mega Wars I, a space battle that supported up to 100 simultaneous players. Even though such games were limited by today s gaming standards, the prices charged were steep, ranging from $5 per hour up to $22.50 per hour.
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10 Networking and Online Games: Understanding and Engineering Multiplayer Internet Games Network Terminal Terminal Terminal Server Figure 2.7 Basic client server topology used by early MUD games Figure 2.8 Pong, one of the best known of the early multiplayer games. Reproduced by permission of William Hunter. seeing Spacewar as fun, Nolan saw Spacewar as having economic potential. So in 1972, he formed Atari, a company dedicated to producing video arcade games. One of the earliest games Atari produced was known as Pong, an arcade-friendly version of Hinginbotham s Tennis for Two. Pong was the first big commercially successful video game, while also being a multiplayer game (Figure 2.8). The 1970s saw a tremendous growth in computer games, with video arcades gaining widespread popularity, and with them, new styles of multiplayer action. In 1978, Atari developed Football for video arcades, a game based on American football (not to be confused with European football, also known as Soccer in places such as America and Australia), and rendered with simple X s and O s. Atari Football featured addictive multi- player game play, initially for two players and later for four players (Figure 2.9). Despite the crash in computer games in the early 1980s, Atari released Guantlet, an innovative dungeon crawl for up to four players simultaneously (Figure 2.10).
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Early Online and Multiplayer Games Figure 2.6 Screen shot of MUD 1, one of the early Multiuser Dungeons can add more structure to the world by adding more content to the world database. The open source nature of many MUDs spurred them on to become popular in academia. Early MUDs became a source of inspiration for later multiplayer network games, such as Everquest, and many MUDs still support a core group of dedicated players. The game was initially populated primarily by students at Essex, but as time wore on and we got more external lines to the DEC-10, outsiders joined in. Soon, the machine was swamped by games-players, but the University authorities were kind enough to allow people to log in from the outside solely to play MUD, as long as they did so between 2 am and 6 am in the morning (or 10 pm to 10 am weekends). Even at those hours, the game was always full to capacity . Richard Bartle, Early MUD history, 15 Nov 90. MUDs used a client server architecture, where the MUD administrator would run the server and MUD players would connect to the MUD server with a simple Telnet program, initially from a terminal (Figure 2.7). The disadvantage of Telnet was that it did not always do an effective job of wrapping lines text and incoming messages sometimes got printed in the middle of the commands the user was entering. In response to Telnet s shortcomings, there sprang up a range of specialised MUD client applications that addressed some of the interface issues that Telnet had, and also provide extra capabilities such as highlighting certain kinds of information, providing different fonts and other features. 2.2.3 Arcade Games Nolan Bushnell, an electrical engineer, was another person influenced by Spacewar, encountering it during the mid-1960s at a university campus in Utah. Apart from just
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Networking and Online Games: Understanding and Engineering Multiplayer Internet Games Figure 2.5 Galaxy War, early 1970s. Reproduced by permission of Id Software, Inc. 2.2.1 PLATO Perhaps the first online network community was PLATO (which initially was supposedly not an acronym for anything, but later became an acronym for Programming Logic for Automatic Teaching Operations) that had users log into mainframe servers and interact from their terminals [PLATO]. PLATO included various communication mechanisms such as email and split-screen chat and, of course, online games. Two popular PLATO games were Empire, a multiship space simulation game and Airfight, what may have been the precursor to Microsoft flight simulator. There was even a version of Spacewar written for PLATO. These early online games were networked only in the sense that a terminal was connected to a mainframe, much like other interactive applications (such as a remote login shell or an email client) of the day. Thus, the game architecture featured a thin game client (the terminal) with all the computation and communication between avatars taking place on the server. The network performance of early systems was thus determined by the terminal communication with the mainframe server via the protocol used by the Telnet program [RFC854]. A Telnet connection uses the Transmission Control Protocol (TCP) connection to transmit the data users type with control information. Typically, the Telnet client will send characters entered by keystrokes and wait for the acknowledgment (echo) to display them on the screen. From the user perspective, a typical measure of performance is the echo delay, the time it takes for a segment sent by the source to be acknowledged. Having characters echoed across a TCP connection in this manner can sometimes lead to unpredictable response times to user input. 2.2.2 MultiUser Dungeons MultiUser Dungeons (MUDs) rose to popularity shortly after PLATO, providing a virtual environment for users to interact with the world and with each other with some game- play elements. MUDs are effectively online chat sessions with game-play elements and structure; they have multiple places for players to move to and interact in like an adventure game, and may include elements such as combat and traps, as well as puzzles, spells and even simple economics. Early MUDs had text-based interfaces that allowed players to type in basic commands, such as go east or open door (Figure 2.6). Typically, characters
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Networking and Online Games: Understanding and Engineering Multiplayer Internet Games Multiplayer Games Networked Games Figure 2.1 The sets of multiplayer games and network games are overlapping, but not subsets or supersets of each other 1960s 1958 Tennis for Two Era of early multiplayer 1961 Space War games 1970s and 1980s 1970 Galaxy War Era of arcade multiplayer games 1972 Pong 1990s and beyond 1978 Atari Football Era of on-line, multiplayer games 1993 Doom (a) (b) Figure 2.2 Timeline overview of early online and multiplayer games. (a) Lists approximate game eras. (b) Lists the release of milestone games mentioned in this chapter may have each player working one member of opposing teams. The game field could either be entirely seen by both players or the screen would be physically split into the part of the field viewable by each player. Thus, the area of multiplayer games includes some games that are not network games. On the flip side, some network games are not multiplayer games. A game can use a network to connect the player s machine to a remote server that controls various game- play aspects. The game itself, however, can be entirely a single-player game where there is no direct interaction with other players or their avatars. Early games, in particular, were networked because a player logged into a mainframe server and played the game remotely over a network via a terminal. Even with today s modern computer systems, players can run a game locally on a PC and connect to a server for map content or to interact with Artificial Intelligence (AI) units controlled by a server. Thus, multiplayer and network games overlap, as depicted in Figure 2.1, but neither fully contains the other. This sets the stage for discussing the evolution of computer games, starting with early multiplayer games, early networked games and progressing to early, multiplayer networked games (Figure 2.2) 2.2 Early Multiplayer Games In 1958, William A. Hinginbotham, working at the Brookhaven National Laboratory, used an oscilloscope to simulate a virtual game of tennis. This crude creation utilised an overhead view, allowing two players to compete against each other in an attempt to sneak the ball past the paddle of their opponent. Hinginbotham called this game Tennis
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Early Online and Multiplayer Games William A. Hinginbotham Figure 2.3 William Hinginbotham invented the multiplayer game Tennis for Two using an oscilloscope. Reproduced by permission of William Hunter. Steve Russel, J.M. Graetz, and Alan Kotok Figure 2.4 Spacewar was the first real computer game, and featured a multiplayer duel of rocket ships. Reproduced by permission of William Hunter. for Two [PONG] and it was perhaps the first documented multiplayer electronic game (Figure 2.3). However, while definitely a multiplayer game Tennis for Two used hard-wired circuitry and not a computer for the game play. The honour of the first real computer game goes to Spacewar, which was designed in 1961 to demonstrate a new PDP-1 computer that was being installed at MIT (Figure 2.4). In Spacewar, two players duelled with rocket ships, firing torpedos at one another. Spacewar had no sound effects or particle effects, but illustrated just how addictive compelling game play could be even without fancy graphics. It even showed sophisticated AI was not needed since real intelligence, in the form of a human opponent, could enhance game play in both competitive and cooperative modes. Soon after its creation, Spacewar programmers were discovering the tradeoffs between realism and playability, adding gravity, star maps and hyperspace. Although the price of the PDP-1 (then over $100 000) made it impossible for Spacewar to be a commercial success, it had lasting influence on the games that followed, including subsequent multiplayer and networked games. A version of Spacewar that was a commercial success was Galaxy War, appearing on campuses in Stanford in the early 1970s (Figure 2.5). It may have been up and running even before the far more popular Pong by Atari.
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Early Online and Multiplayer Games In this chapter, we cover some of the history of early online and multiplayer games. Like most computer systems and computer applications, online games evolved as the capabilities of hardware changed (and became cheaper) and user expectations from those games grew to demand more from the hardware. Besides being interesting in their own right, examining early online and multiplayer game history can help us understand the context of modern network games. We will deal with the following: Introduce important early multiplayer games that set the tone for the networking multiplayer games that would follow. Describe early network games that often had a centralised architecture, suitable for the mainframe era in which they were developed. Provide details on turn-based games that were popular before low latency network connections were widespread. End with popular network games that made use of widespread Local Area Network (LAN) technology. 2.1 Defining Networked and Multiplayer Games By its very definition, a network game must involve a network, meaning a digital connection between two or more computers. Multiplayer games are often network games in that the game players are physically separated and the machines, whether PCs or consoles or handhelds, are connected via a network. However, many multiplayer games, especially early ones were not network games. Typically, such multiplayer games would have users take turns playing on the same physical machine. For example, one player would take turns fighting alien ships while the second player watched. Once the first player was destroyed or when he/she completed the level, the second player would have a turn. Scores for each player were kept separately. For simultaneous multiplayer play, either cooperatively or head-to-head, each player would see their avatar on the same screen or the screen would be split into separate regions for each player. For example, a multiplayer sports game Networking and Online Games: Understanding and Engineering Multiplayer Internet Games Grenville Armitage, Mark Claypool, Philip Branch . 2006 John Wiley & Sons, Ltd
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Networking and Online Games: Understanding and Engineering Multiplayer Internet Games (IP) networking. We review the concept of best effort service, IP addressing and the role of transport protocols such as TCP (Transmission Control Protocol) and User Datagram Protocol (UDP) as they pertain to game developers. When you complete this chapter, you will have an understanding of the differences between routing and forwarding, addresses and domain names. You will learn why Network Address Translation (NAT) exists and how it impacts on network connectivity between game players. Our next chapter, Network Latency, Jitter and Loss , should be of interest to all readers. Here we look in detail at how modern IP networks fail to provide consistent and reliable packet transport service by losing packets or by taking unpredictable time to transmit packets. We discuss how much of this network behaviour is unavoidable and how much can be controlled with suitable network-level technology and knowledge of game traffic characteristics. This leads naturally to Mark Claypool s next chapter, Latency Compensation Techniques , where we look at the various techniques invented by game developers to cope with, and compensate for, the Internet s latency and packet loss characteristics. A fundamental issue faced by multi-player online games is that the latency experienced by each player is rarely equal or constant. And yet, to maintain a fair and realistic immersive experience, games must adapt to, predict and adjust to these varying latencies. We look at client-side techniques such as client prediction and opponent prediction, and server-side techniques such as time warping. Compression of packets over the network is introduced as a means to reduce network-induced latency. Our next chapter, Playability versus network conditions and cheats , takes a different perspective. We look at how two separate issues of network conditions and cheating influence player satisfaction with their game experience. First, we look at the importance of knowing the tolerance your players have of latency for any particular game genre. Such knowledge helps game hosting companies to estimate which area on the planet their satisfied customers will come from (and where to place new servers to cover new markets). We discuss existing research in this area and issues to consider when trying to establish this knowledge yourself. Next we look at communication models, cheats and cheat mitigation. Cheating is prevalent in online games because such games combine competitiveness with a sense of anonymity and the anonymity leads to a lessened sense of responsibility for one s actions. We look at examples of server-side, client-side and network-based cheating that may be attempted against your game, and discuss techniques of detecting and discouraging cheating. In Broadband Access Networks , Philip Branch takes us through a discussion of the various broadband access technologies likely to influence your game player s experiences in the near future. Access networks are typically the congestion point in a modern ISP service; they come in a variety of technologies allowing fixed and wireless connectivity, and have unique latency and loss characteristics. From a high level, we review the architectures of cable modems, Asymmetrical Digital Subscriber Line (ADSL) links, 802.11 wireless Local Area Networks (LANs), cellular systems and Bluetooth. We then move in an entirely different direction with the chapter Where do players come from and when? . One of the key questions facing game hosting companies is determining where their market exists, who their players are, and where they reside. This has an impact on the time zones over which your help desk needs to operate and the ebb and flow of game-play traffic in and out of your servers. Taking a very practical direction, we first discuss how you can monitor and measure traffic patterns yourself with
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