132 Networking and Online Games: Understanding and Engineering
134 Networking and Online Games: Understanding and Engineering Multiplayer Internet Games information (the UMTS Subscriber Identity Module or USIM). The UTRAN is made up of a number of RNSs. Each RNS contains a number of radio transceivers, perhaps more commonly referred to as Base Stations, but known in UMTS as Node B, and a number of Radio Network Controllers (RNCs). Each Node B can have associated multiple radio transceivers. The CN contains even more nodes, the key ones being the Mobile Switching Centre (MSC) responsible for call switching, the Gateway Mobile Switching Centre (GMSC) responsible for connecting voice calls to the Public Switched Telephone Network (PSTN), the Home Location Register (HLR) containing subscriber data, the Visitor Location Register (VLR) containing location data about users, the Serving General Packet Radio System Node (SGSN) which terminates data calls and the Gateway GPRS Support Node (GGSN) which acts as a gateway for packet data to the Internet. From this brief description, it should be apparent that broadband cellular networks are complex and expensive systems. UMTS defines different levels of service based on two criteria: Quality of Service type and Service Capability. Quality of Service specifies minimum bit rates, delay and delay variation. Although quality of service across the air interface is inherently difficult to provide, the standard allows for flexible allocation of bandwidth to enable a reasonably consistent quality of service to be maintained. The Service Capability specifies a number of capabilities rather than performance requirements. Such capabilities might include location services, perhaps using the Global Positioning System (GPS), extended capabilities built around data stored in the smart card originally included in Mobile Telephones for identification but now, given advances in flash memory capacity, able to store more and different kinds of data, or the Customised Applications for Mobile Network Enhanced Logic (CAMEL) which provides a full development environment. 3G networks are able to support a range of Quality of Service values [3GPP1999]. Latency within the 3G network across the air interface is able to be controlled to a high level of accuracy. Depending on the application, latencies of 10 ms, 20 ms and 80 ms within the network and across the air interface can be specified. Broadband cellular access networks are reliable, handle mobility well, usually have good coverage and can provide guarantees of quality of service. However, they are also complex, expensive to install and expensive to use. Whether they become a successful and widely used access network is still an open question. 8.7 Bluetooth Networks Bluetooth networks are included in this chapter even though they are not really an access network technology. Bluetooth is more of a short distance cable replacement technology. Typically, Bluetooth networks extend to no more than 10 metres and are used primarily for peripheral device connectivity such as printers, mice and the like [HAAR1998]. Nevertheless, Bluetooth is an increasingly important technology, typically used in conjunction with broadband access networks or used to construct small ad hoc networks. It is perhaps this last characteristic of Bluetooth that is of most interest to game players. Bluetoothenabled devices can be brought together to form a network with minimal configuration and difficulty. Bluetooth bit rates are comparatively low. It provides shared bit rates up to 1 Mbps. However, a substantial amount of this is used in Bluetooth overhead leaving approximately 720 to 760 kbps for user data.
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