![]() ![]() For example, if a given traffic class is toreceive the highest supported priority, and this is a value of 3 in one domainand 7 in the next domain, packets with a priority 3 value traversing the firstdomain are re-marked as priority 7 when entering the second domain. Also, re-marking may be required atthe boundary between two DS domains. This may be done for packets that exceed the profile forexample, if a given throughput is guaranteed for a particular service class, anypackets in that class that exceed the throughput in some defined time intervalmay be re-marked for best-effort handling. ![]() Marker: Polices traffic by re-marking packets with a differentcodepoint as needed. Meter: Measures submitted traffic for conformance to a profile.The meter determines whether a given packet stream class is within or exceedsthe service level guaranteed for that class. A classifier mayseparate traffic only on the basis of the DS codepoint (behavior aggregateclassifier) or based on multiple fields within the packet header or even thepacket payload (multifield classifier). The traffic-conditioning function consists of five elements:Ĭlassifier: Separates submitted packets into different classes.This is the foundation of providing differentiated services. Theboundary node function can also be provided by a host system attached to thedomain, on behalf of the applications at that host system. Thus,interior routers have minimal functionality and minimal overhead in providingthe DS service, while most of the complexity is in the boundary nodes. The boundary nodes include PHB mechanisms but also more sophisticatedtraffic-conditioning mechanisms required to provide the desired service. This PHB must be available at allrouters, and typically PHB is the only part of DS implemented in interiorrouters. The DS specifications refer to the forwarding treatment provided ata router as per-hop behavior (PHB). This includes queuing discipline togive preferential treatment depending on codepoint value, and packet-droppingrules to dictate which packets should be dropped first in the event of buffersaturation. Routers in a DS domain are either boundary nodes or interior nodes.Typically, the interior nodes implement simple mechanisms for handlingpackets based on their DS codepoint values. Within adomain, the interpretation of DS codepoints is uniform, so that consistentservice is provided. ![]() A DS domain consists of a set of contiguous routers that is,it's possible to get from any router in the domain to any other router inthe domain by a path that does not include routers outside the domain. Learn More Buy DS Configuration and Operationįigure 2 illustrates the type of configuration envisioned in the DSdocuments. High-Speed Networks and Internets: Performance and Quality of Service, 2nd Edition ![]()
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