The Symbian OS (779886), страница 54
Текст из файла (страница 54)
It isprincipally used by DHCP to determine when and how to performaddress negotiation.• The TCP/IPv4/v6 PRT supplies the core protocol implementationsfor TCP/IP networking including the IPv4 and IPv6 stacks, TCP, UDP,ICMP and ARP protocols, a Hook interface allowing access to packets,IPSec and QOS protocol modules, and an event notifier service.• The IP Hook PRT defines an interface to which modules bind to perform transformations on inbound and outbound packets, respectivelyNetwork Protocol PluginsTCP/IPv4/v6PRTIPHookIP HookExamplesQOSFrmwk.PRTCoreIPSecPRTFigure 9.29 Network Protocol Plug-insIPEventNotifier242THE COMMS SERVICES BLOCKupon receipt from or before delivery to the Network Interface. IPSecis such a Hook, inspecting all incoming and outgoing packets andapplying cryptographic transformations as specified in the Securityassociation database.• The QoS Framework PRT is a Hook module, implementing QoSchannels through which it schedules packets.
Additional plug-insmap the desired QoS characteristics to relevant link technology.• The Core IPSec PRT implements core functionality for IPSec in amulti-homed context, that is multiple active network interfaces, forsimultaneous use by multiple applications, providing tunnel modesand various high-level APIs. It includes a cryptographic library module, policy managers and parsers.Networking Plug-ins CollectionThis collection contains the network interface agents (AGT files).
Twoadditional components are also included, the Bluetooth PAN profile andthe GPRS/UMTS QOS PRT (which is considered a ‘pseudo PRT’). SeeFigure 9.30.Table 9.18 Networking Plug-insComponent NameDevelopment NameConnection Provider Plug-inIPCPRCSD AGTCSDAGTPSD AGTPSDAGTNULL AGTNULLAGTGPRS/UMTS QOS PRTGUQOSBluetooth PAN ProfileBLUETOOTHPANSecondary PDP UMTS DriverSPUDNetworking PluginsControlProv.PluginCSDAGTPSDAGTNullAGTGPRS/UMTSQOSPRTFigure 9.30 Networking Plug-insSecndry PDPUMTSDriverBtoothPANProfileImpl.NETWORKING SERVICES243• The Connection Provider Plug-in provides IP connections to clients,supporting bearer mobility.• The CSD AGT plug-in to the Connection Agent framework negotiatesa circuit-switched data connection, for example to GSM or CDMAnetworks, supporting dial-up networking services.• The PSD AGT plug-in is deprecated and its functionality is replacedby other components. It is an agent plug-in to the Connection Agentframework that negotiates packet-switched connection for example toGPRS networks, supporting ‘always on’ networking services.• The NULL AGT plug-in implements a minimal agent used to passstraight through to an Ethernet connection that is provided by theEthernet packet driver.• The GPRS/UMTS QOS PRT is a plug-in helper module to the QoSFramework that gets and validates QoS parameters from the QoSframework at the request of a loaded NIF and is used to implement3GPP parameters.• The Bluetooth PAN Profile plug-in is an agent-like module that implements the Bluetooth Network Encapsulation Protocol (BNEP), as anEthernet Packet Driver module.
It serves as the network interfaceagent used to create PAN connections, enabling PAN to behave likea regular Internet access provider.• The Secondary PDP context UMTS Driver (also called the PDP NIF)supports multiple primary PDP contexts (multi-homing over GPRS) onthe telephony reference platform. It is not a production component.Link Layer ControlLink-layer components of the networking stack, Network Interface modules (NIF files) are selected by the Network Controller and loaded, startedand stopped by the Network Interface Manager to implement the interface to the physical link layer (which is, in turn, provided by networkingdevice drivers, serial communications CSYs, or telephony TSYs).
SeeFigure 9.31.NIFs implement the polymorphic plug-in interface defined by theNetwork interface manager (NIFMan).Link Layer ControlEthernetNIFEther- EthernetnetOver IRPacket PacketDRVDRVPPPNIFPPPCompressionPluginsSlipNIFTunnelNIFPacketLoggerFigure 9.31 Link Layer Control componentsRaw IPNIFWirelessLAN244THE COMMS SERVICES BLOCKTable 9.19 Link Layer Control ComponentsComponent NameDevelopment NameEthernet NIFETHER802Ethernet Packet DriverETHERDRVEthernet Over IR Packet DriverIRLANPACKETDRIVERSPPP NIFPPPPPP Compression Plug-insPREDCOMP, MSCOMP,STACCOMPSLIP NIFSLIPTunnel NIFTUNNELNIFPacket LoggerPACKETLOGGERRaw IP NIFRAWIPNIFWireless LAN802.11• The Ethernet NIF component provides a generic Ethernet layer networkinterface, that manages Ethernet framed packets.
It is designed to sitbelow any number of supported Protocol modules and on top of morespecialized Ethernet framing interfaces, called packet drivers.• The Ethernet Packet Driver is an Ethernet framing interface, the driverlevel component (DRV files, that is, lower-layer packet drivers) thatsupports the Ethernet NIF.• The Ethernet Over IR Packet Driver is an Ethernet framing interface,the underlying networking interface driver for infrared.• The Serial Line IP (SLIP) NIF component is supplied as a referencecomponent that licensees can choose to remove or replace witha production implementation.
SLIP was the earliest (and simplest)protocol for relaying IP packets over dial-up lines and has largelybeen replaced by PPP.• The Point to Point protocol (PPP) NIF provides TCP/IP over serialcommunications (i.e. over a point-to-point link). It allows a device toconnect to a phone and use it as a gateway to the Internet. Once thelink has been established, optional facilities such as data compressionmay be negotiated.SHORT-LINK SERVICES245• The PPP Compression Plug-ins supplies the implementation of common PPP compression algorithms as dynamically loaded DLLs.
Itincludes Microsoft Compression (MSCOMP), Stac Electronics Compression (STACCOMP) and Predictor Compression (PREDCOMP)implementations.• The Tunnel NIF component implements the IPSec tunnel to enableIPSec to operate in tunnel mode, for example, as used by VPN clients.• Wireless LAN supports IEEE 802.11 wireless networking.9.9 Short-link ServicesShort-link services enable individual devices to communicate directlywith each other (‘peer-to-peer’), either over a physical cable connectionsuch as serial or USB, or using short-range radio, either line-of-sightsuch as infrared, or unseen paired, such as Bluetooth. (Note that, bythis definition, Wi-Fi, which is fast becoming important on phones, isconsidered a network access technology not a short-link connectiontechnology, although Wi-Fi hardware supports a peer-to-peer mode.)Symbian OS supports the principal short-link technologies: RS232serial, USB, infrared/IrDA and Bluetooth, as well as the higher-level OBEXobject transfer protocol, which is supported over both IrDA and Bluetooth.USBManagerOBEXShort LinkShort LinkProtocol PluginsSerial Comms ServerPluginsShort Link ServicesFigure 9.32Short-link services246THE COMMS SERVICES BLOCKThe short-link-services block includes managers, utilities, protocol implementations and serial-hardware-adaptation plug-ins.
Associated devicedrivers are located lower down in the system model, at kernel level. SeeFigure 9.32.For network-capable mobile devices (mobile phones and PDAs, forexample), short-link connections are also important for network access.Typically, they provide the connection alternative to using the onboardphone. In Symbian OS, short-link services act as bearers for higher-levelcommunications services, including both networking and telephony. Thisenables some interesting scenarios, for example, remote use of a phonein one Symbian OS device from another over a short-link connection.Although continuing to evolve to enable increased data rates, shortlink technologies are relatively mature and Symbian’s support for themis relatively mature.
RS232 serial has a long history and IrDA, Bluetoothand USB have all been standardized since the mid-1990s.However, there are interesting and significant evolutions in all thetechnologies. In terms of connection speeds, while serial cable is limitedto data transfer rates of 115 kbps, Bluetooth offers data rates closer to1 mbps with a range of 10 meters, while ‘newer’, ‘faster’ IrDA standardsincrease rates beyond 16 mbps and even up to 100 mbps. USB began as a12 mbps standard, before increasing 40-fold (with USB 2.0) to 480 mbps.The application possibilities are also interesting and extend beyondbasic data management and data synchronization.
After a slow start,Bluetooth has become ubiquitous on phones, in particular for hands-freeand headset peripherals, including stereo headsets. USB offers muchmore than just a physical link protocol. USB is both a link technology anda transport protocol definition with extras such as support for poweringunpowered devices and hot-plugging (‘plug and play’ notification to thehost). In a Symbian context, it allows a Symbian OS device to plug into aUSB host (for example, a desktop computer) and offer multiple services.Both IrDA and Bluetooth specify a complete protocol stack defininglink, transport and application layers, which offers significantly more thanjust serial-like setup for a simple physical link.Because Bluetooth allows ad hoc, ‘promiscuous’ connection betweenany devices within range, security is potentially an issue.
![](https://s.studizba.com/z.php?f=/templates/si/i/noavatar.png&w=100&h=100&t=1"){kind=avatar}
