[ Pobierz całość w formacie PDF ]
.8 COPS object header.Table 7.6COPS Object TypesC-NumNature of Object1Handle2Context3In interface4Out interface5Reason code6Decision7LPDP decision8Error9Client-specific information10Keep-alive timer11PEP identification12Report type13PDP redirect address14Last PDP address15Accounting timer16Message integrityThe c-type distinguishes between different types or versions of thec-num.A frequent distinction is the use of c-type 1 for IPv4 and c-type 2 for IPv6, but the decisions have several separate c-types.The client handle is used in most COPS operations and is selected bythe PEP to identify the request state of a particular client type.It is then used in requests, reports, and delete messages from PEP to PDP until deleted (forthe reason specified in the reason code of a DRQ).The context object is required for request messages and specifies thetype of event that triggered the request.The structure of this object is shown in Figure 7.9.164QoS in Integrated 3G NetworksR-typeM-typeFigure 7.9 Context object.Request type (r-type) flag• 0x01 = Incoming-Message/Admission Control request• 0x02 = Resource-Allocation request• 0x04 = Outgoing-Message request• 0x08 = Configuration requestMessage type (m-type)• Client-specific 16-bit values of protocol m-types• The key policy control objects are the decisions (c-nums 6 and 7)issued by the PDP or LPDP, respectively.There are three possibleoutcomes:1.Command-code 0 indicates a NULL decision (no configurationdata);2.Command-code 1 indicates INSTALL (accept request/installconfiguration);3.Command-code 2 indicates REMOVE (remove request/removeconfiguration).There are at least five c-types describing different types of decision data.Use of COPS with RSVPCOPS does not require the use of RSVP but can be combined with itthrough the use of the policy objects for RSVP as defined in an extensionto the RSVP definition [24].RSVP is potentially only one of many c-typesand corresponds to COPS c-type 1.COPS provides admission control, whileRSVP provides resource allocation for connection requests that have beenaccepted by COPS.Policy data is carried in the type 1 RSVP class 14 Policy_Data Objectfor c-type 1.After the RSVP object header there is a policy options list andProtocols165a set of policy elements, both of which are opaque to RSVP but used bypolicy-aware nodes along the route to ensure consistent policies.RFC2753[33] discusses principles for implementing PDPs and PEPs in conjunctionwith RSVP routers or in general, and these recommendations are followed inUMTS (see Section 8.1.3).7.4.7 Real-Time Transport ProtocolReal-Time Transfer Protocol (RTP) [34] was designed to provide end-to-end network transport functions suitable for real-time data transmission,especially audio and video, over both unicast and multicast network services.Unlike RSVP it does not reserve resources, nor does it guarantee QoS.Appli-cations usually run RTP over UDP in order to use the multiplexing andchecksum functions of the latter.Examples of applications likely to be usedover 3G networks that will run over RTP are given in Chapter 10.The fea-tures that RTP provides include payload identification, sequence numbering,time stamping, and delivery monitoring.It does not reorder out-of-sequencepackets nor provide timely delivery, but the sequence numbers and time-stamps enable the end application to perform this itself.RTP uses its ownReal-Time Transport Control Protocol (RTCP) to provide feedback on thequality of data distribution, carry a persistent name for the RTP source, and perform some multicast session control.Multimedia applications, such asvideo-conferencing, use separate RTP sessions for each media type.RTP adds a header to its payloads that has the structure shown inFigure 7.10 whereTEAMFLY1.Version (V ) is a 2-bit field defining the version of RTP.That forRFC1889 is 2.2.Padding bit (P) is set if one or more padding octets are added at theend of the payload where fixed block sizes are required for anotherprotocol.V P X CC MPTSequence numberTimestampSynchronization source (SSRC) identifierContributing source (CSRC) identifierFigure 7.10 RTP header.Team-Fly®166QoS in Integrated 3G Networks3.Extension bit (E ) is set if there is exactly one header extension afterthe fixed RTP header.4.CSRC count (CC ) is a 4-bit count of the number of CSRC identi-fiers that follow the fixed header.5.Marker bit (M ) can be used to mark important events, such asvideo frame boundaries, in the data stream.6.Payload type (PT ) is a 7-bit field to identify the type of payload bya standard code.7.Sequence number is a 16-bit identifier for individual RTP packetsthat is incremented by one for each RTP data packet sent.8.Time-stamp is a 32-bit time that indicates the sampling time of thefirst octet of the data packet.Packets that belong to the same videoframe typically have the same time-stamp.9 [ Pobierz całość w formacie PDF ]
  • zanotowane.pl
  • doc.pisz.pl
  • pdf.pisz.pl
  • agnieszka90.opx.pl