eScience Lectures Notes : .

Slide 1 : 1 / 26 : Communication Architectures

Communication Architectures


Two Players on a LAN (Local Area Network)


Case study : DIS Protocol and PDU

NPSNET-IV Performance with DIS

Some network parameters

Ethernet Bandwidth

V90. Modem

Players supportable in a DIS-like networked virtual environment

Multi-Player Client Server - Logical Architecture

Multi-Player Client Server - Physical Architecture. On a LAN

Multi-Player Client Server - Physical Architecture - Phone Lines

Multi-Player Client Server with Multiple Servers


Peer-to-Peer on a Lan

Peer to Peer Multicast

VE Software Scalability Statement

AOIM (Aera Of Interest Management)

Simnet Case Study : Michael Zyda team

Blizzard : World of WarCraft (WoW) : FAQ

Blizzard :

Slide 2 : 2 / 26 : Communication Architectures

Communication Architectures

Based on Chapter 4 of "Networked Virtual Environments..." (Singhal and Zyda)

Logical architecture vs Physical architecture

Client/Server vs Peer to Peer

Slide 3 : 3 / 26 : Two Players on a LAN (Local Area Network)

Two Players on a LAN (Local Area Network)

Slide 4 : 4 / 26 : Latency


100 milliseconds ... typical VR feedback loop

200 milliseconds

Or what?

How long before we can’t control or react to the other players across the net? This the THE BIG DEAL, IN FACT THE WHOLE DEAL with Net-VEs.

For Online Game addicts, only one question : "What is your ping ?"

Slide 5 : 5 / 26 : Case study : DIS Protocol and PDU

Case study : DIS Protocol and PDU

The DIS (Distributed Interactive Simulation ) network software architecture is a direct descendent from SIMNET but has packets that are more general than SIMNET’s.

DIS has the same three basic components

Each Event is a packet sent over the network called a Protocol Data Unit : PDU

The form of a PDU is standardised :

144 bytes in length and contains the information necessary to manage entity state for the various players.

Identification of the player, player's location, orientation, velocity acceleration, any articulation information for the player, any dynamic information about the player that need to be communicate.

Other hypothesis : Graphics performance - 30 frames per second.

Thanks to predictive modelling algorithms, there is no need to systematically send a PDU every frames

Slide 6 : 6 / 26 : NPSNET-IV Performance with DIS

NPSNET-IV Performance with DIS

From experience and type of behaviour of these objects

Slide 7 : 7 / 26 : Some network parameters

Some network parameters

Question : How many players / objects can we support with these different bandwidths ?

NB. We forget any other use of the network : no mail, no web browsing, no NFS, no overhead, and assume that only the network is the bottleneck

Slide 8 : 8 / 26 : Ethernet Bandwidth

Ethernet Bandwidth

From official 10 Mbps to 7 Mbps of available bandwidth (above, saturation)

Aside questions to Markus Buchhorn :

Where those that limitation commes from ?

The 70% number came from shared Ethernet, where everybody effectively shared a single cable, and only one machine could talk at a time - statistically you could not run data on it more than 70% of the time, and it is 10Mb/s total across all the connected devices.
Switched Ethernet is different, in that it's only you and the switch on that single cable.
What about 100 Mbps and 1Gbps ethernet ?
Both of these are only run in switched mode, not in shared mode.
Over that, you need to take care of the usual protocol overhead costs

Is there some way (tables...) to easily evaluate these costs or is it necessary to sniff your network each time you want to be sur that you have enough bandwidth available (Of course, you have to do that on a shared network, but on your local ethernet, you should be able to be more in charge ?

You can look at tables or standards documents to identify protocol overheads. In general these are "pretty small", around 10% or so.
In terms of measuring if you have enough bandwidth available - you can't do that deterministically on any frame/packet based network. You cannot predict when another device will send a burst of large packets, which fill up buffers, or a very large number of small packets, which chew up the CPU. This can vary on timescales from milliseconds to mega-minutes. All you can do is look at the path and identify where you might see congestion. Applications running over IP have to be able to deal with congestion, leading to latency and jitter, or leading to packet loss, or routing changes that also impact latency and jitter. A sad fact, but that's also the power of the Internet.
On your local network, the main bandwidth constraint is the switch in the middle, and then any other applications that are talking to your two endpoints. If you have two PCs on their own on a dedicated switch and no other applications, you should be able to get close to 100% throughput. I've seen over 95Mb/s transport rate on a 100Mb/s Ethernet network.
If you have a need to guarantee bandwidth, there are some ways you can do that - Ethernet and IP both allow traffic to be tagged with 'priorities', giving those frames/packets better (or worse) treatment than other traffic. That requires support from the hardware along the way though, and is not a 100% guarantee in all cases. To get guarantees like that requires a more deterministic network like ATM and its virtual circuits.

A PDU is 8 bits/byte times 144 bytes or 1152 bits.

NB. : Mbps = 1000 x 1000 bps, kbps = 1000 bps, Gbps = 1000 Mbps

Meaning we can send about 6,076 PDUs per second on our Ethernet LAN.

If we assume mayhem, all players firing once each second, we can make some statements about the outer bounds of what we can support.

So we can support between 184 to 759 players on our LAN, assuming away all other usage.

NPSNET-IV maxed out at about 300 players.

Slide 9 : 9 / 26 : V90. Modem

V90. Modem

56Kbps implies about 48 PDUs/second.

1 human, 3 aircrafts or 6 ground vehicles.

If we do better than that and make our packets only 22% of that size (32 B instead of 144), we can have 218 PDUs/second.

6 humans, 14 aircrafts or 27 ground vehicles.

Slide 10 : 10 / 26 : How many players can we support with a DIS-like architecture?

Players supportable in a DIS-like networked virtual environment

versus various available network technologies.


1. Infinite compute cycles at each node.





2. Infinite graphics cycles at each node.





3. Network interface with infinite cycles.












Packet size for DIS-like VEs =






Packet size for Game-like VEs =








Just moving




Articulated humans (PDUs/second) =



Mayhem used for Min. Players

Aircraft (PDUs/second) =




Not used but here for completeness.

Ground vehicles (PDUs/second) =



Mayhem used for Max. Players


Min. Speed

Max. Speed

Min. Players

Max. Players

Min. Players

Max. Players








V.90 Modem










































Cable Modems



































Slide 11 : 11 / 26 : Multi-Player Client Server - Logical Architecture

Multi-Player Client Server - Logical Architecture

Servers are bottlenecks!

But useful for compression & admin tasks

Slide 12 : 12 / 26 : Multi-Player Client Server - Physical Arch. on a LAN

Multi-Player Client Server - Physical Architecture. On a LAN

Messages to and from the server from all players travel on the same wire !

For a server to be meaningful in that physical architecture, the server must be performing some added value function

It might really look like this physically!

Slide 13 : 13 / 26 : Multi-Player Client Server - Physical Architecture - Phone Lines

Multi-Player Client Server - Physical Architecture - Phone Lines

This physical architecture matches the logical one

Slide 14 : 14 / 26 : Multi-Player Client Server with Multiple Servers

Multi-Player Client Server with Multiple Servers

Or this, if we are using a multi-player video game service company ...

Need High bandwidth between each server (100 Mbps LAN ... )

Well adjusted to Spatial partitioning of the Virtual Environment


Slide 15 : 15 / 26 : Peer-to-Peer


No Server, because Servers mean that eventually, we cannot scale our Net-VE

Communications go directly from the sending player to the receiving players

When each player speaks directly to the player/players to whom it needs to communicate state.

Could be done using TCP/IP (and a server that keeps a list of the set of players), UDP, Broadcasting or Multicasting !

Slide 16 : 16 / 26 : Peer-to-Peer on a Lan

Peer to Peer ...   ... on a Lan

Again, unicasting (TCP or UDP) is possible but not at all adapted (not scalable).


NB. in WarCraft, we need a server even on a LAN because of Licensing issue (the CD is the key !)

Slide 17 : 17 / 26 : Peer to Peer Multicast

Peer to Peer ...   ... on a Lan or anywhere



Slide 18 : 18 / 26 : VE Software Scalability Statement

VE Software Scalability Statement

Virtual environment software architectures can exploit wide area multicast communications and entity relationships to partition the virtual world and enable the development of scalable VEs.

Areas of interest in the VE

Slide 19 : 19 / 26 : AOIM (Aera Of Interest Management)

AOIM (Aera Of Interest Management)

Partition the simulation into workable chunks to reduce computational load on hosts and minimize communications on tail links.

Distribute partitioning algorithms among hosts.

Different possible partitioning classes


Slide 20 : 20 / 26 : Spatial Partitioning of the VE Using AOIM

Spatial Partitioning of the VE Using AOIM

Slide 21 : 21 / 26 : AIOM Software Layer

AIOM Software Layer :

AOIM (Aera Of Interest Management)


Slide 22 : 22 / 26 : How to set up a Client Server Architecture

How to set up a Client Server Architecture

Slide 23 : 23 / 26 : How to set up a Peer to Peer Architecture

How to set up a Peer to Peer Architecture

Slide 24 : 24 / 26 : Blizzard : World of WarCraft (WoW) : FAQ

Blizzard : World of WarCraft (WoW) : FAQ

What is World of Warcraft?

World of Warcraft is a Massively Multiplayer Online Role Playing Game (MMORPG).

In World of Warcraft, thousands of players will have the opportunity to adventure together in an enormous, persistent game world, forming friendships, slaying monsters, and engaging in epic quests that can span days or weeks.

We have not yet announced a release date for World of Warcraft. MMORPGs are vast and complex; we want to make sure that we take the time necessary to develop a game that will meet the high standards that our developers and fans have come to expect from Blizzard games.

What are the game's system requirements?
We have not yet finalized the system requirements for World of Warcraft. As with our past games, our goal is to ensure that the game will run on a wide variety of 3D cards and at a wide range of processor speeds.

For what platforms will the game be available?
The game will initially be available for PCs.

How will World of Warcraft differ from other MMORPGs?
World of Warcraft will differ from other MMORPGs in many ways. One of our main goals is to ensure that players can enjoy World of Warcraft without having to invest huge amounts of playtime. Players will be able to complete quests and experience the world at their own pace-whether it be a few hours here and there, or week-long adventuring marathons. Additionally, our quest system will provide an enormous variety of captivating quests with story elements, dynamic events, and flexible reward systems. World of Warcraft will also feature a faster style of play, with less downtime and an emphasis on combat and tactics against multiple opponents. We also plan to incorporate several unique features, which we'll disclose throughout the course of development.

Is Blizzard aware of some of the game play problems that have been prevalent in other MMORPGs?
Yes. Blizzard employees are gamers first and foremost, and we have played more than our fair share of existing Massively Multiplayer games. We tend to agree with MMORPG gamers on the strengths and weaknesses of the genre to date. We will strive to advance the genre by both building on its positives and improving its negatives.

Will World of Warcraft mix with Warcraft III? If there are new foes, do they include the Night Elves, Undead or Burning Legion?
World of Warcraft will be set in lands both familiar and new to long-time players of the series. It is difficult to discuss the World of Warcraft story without giving away the plot for Warcraft III. We can say that Azeroth will experience significant changes and be a very different world than Warcraft fans know today. And, while there will be plenty of recognizable characters and places to explore, we think that the balance between discovering what is known and what is different is something that players will really enjoy.

In regard to the inclusion of the Night Elves, Undead or Burning Legion, you will just have to wait and see...

Does the game require a 3D accelerator?
Yes, the game will require a 3D graphics card. Again, we will support a wide range of 3D cards.

Will the game be playable over a modem?

Will there be monthly fee to play the game?
Yes; however, we are still investigating our business model and have not yet determined what the fee will be.

Why isn't World of Warcraft free?
World of Warcraft will require a fee to play. This fee will be used to support the costs associated with the high-quality levels of service, support, and ongoing content creation that we are planning for World of Warcraft.

How will the game be distributed or sold?
Gamers will be able to purchase World of Warcraft at retail outlets, online sites, or directly from Blizzard Entertainment. However, in order to play you will need to sign up for a monthly account.

Will there be Cinematic sequences in the game?
Yes. The Blizzard Film Department will create cinematic sequences for World of Warcraft. We do not anticipate, however, that the game will have as many as our previous games due to the nature of Massively Multiplayer Role Playing Games. You can see the first cinematic for World of Warcraft on the movies page.

Will players have the opportunity to provide feedback about the development of the game?
Yes. Players will always be able to share their input via the forums and beta testing. We also plan to devise additional methods for players to communicate with the developers.

Does Blizzard plan on addressing Kill Stealing and Item Farming?
Yes, and we will reveal more details on our plans at a later date.

Will you be able to randomly find items, and if so, will these items be classified as in Diablo II (Rare, Unique, etc.)?
Monsters will have treasure that characters can loot, but these will be drawn randomly from a specific item class for that monster type. We do not expect to have the same vast amount of random items as in the Diablo series, but we will have items that are rare and even some that could be truly unique by limiting them to only one per server.


Slide 25 : 25 / 26 : Blizzard :

Blizzard :

What changes have been made to since the release of Diablo II?

Blizzard Entertainment continues to make several enhancements to the infrastructure by increasing the number of servers and providing additional bandwidth.

Beginning June 2000 and continuing through August 2001, we have increased the number of game servers in our Asia gateway to 300, increased the number of servers in the US gateways to 200 and raised the number of servers to 100 in the Europe gateway.

We have also added two new Asian Realms to our Diablo II world as well as increased the size of all Realms. The team is extremely committed to providing our users with the best possible game play experience. In order to provide this experience, we have also expanded the number of personnel dedicated to These changes were put into place in order to make your gaming experience enjoyable while maintaining our dedication to keeping a complimentary service.

Why are players from another country on my Diablo II Realm/ Server?

Anyone in any country is free to play on whatever Realm or Gateway they choose. This is not changing. The Diablo II Realms and Gateways are named to give people an idea which one is best to pick based on their location. They are NOT named to suggest ownership of the realms by geographical areas or to suggest who has to play where. Please respect people's right to play on any server they choose.

Why do you allow people from all over the world to connect to any Diablo II Realm or Server?

We want to allow friends from around the world to be able to play together on the same server. To do this, the servers must be open to anyone. We have no intention of restricting access based on location.


Gateways acts as portals through which players get onto The four Gateways that Blizzard maintains are: US West, US East, Asia or Europe. For the best play experience, you should select the Gateways that is closest to your geographic location.
You cannot talk to or play games with players on other Gateways. To play together you must select the same Gateway.

The 19/08/02 :



Slide 26 : 26 / 26 : Simnet Case Study

Simnet Case Study : Michael Zyda team

Does partitioning using the chosen architecture reduce bandwidth and computational requirements for large-scale virtual environments?

Does the architecture scale and if so how well?