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ZYTRAX Router QoS features are concerned with managing traffic priority on communications links. This allows both control over latency for time sensitive applications such as VoIP and optimization of finite network resources baed on the user's required needs.
The user may configure the router to allocate a Priority rating to traffic types. The priority values (High, Medium and Low) will determine the order traffic is processed internally and dispatched to the remote network. Finally in a case of overload the Priority rating will determine the order in which traffic is discarded.
The 'service ratio' determines the number of times a priority queue is serviced before the router moves to the next priority level. This parameter may be used, among many others uses, to ensure that even low priority traffic receives some level of service and is not 'starved' even in high load situations.
To illustrate the use of the 'service ratio' parameter assume that High Priority traffic is given a 'service ratio' of 5, Medium 3 and Low 1. The router will service the High priority queue 5 times (e.g. send 5 blocks to the remote network) or until the queue is empty if sooner, then service the medium Priority queue 3 times or until empty if sooner, then service the Low Priority queue once if there are any items on it. By varying the 'service ratio' any level of granularity may be obtained.
The user may configure the priority value based on the IP address (source or destination) or IP address range (using a net mask), the traffic type (UDP, TCP, ICMP etc.) and the port number or port range. As many or as few values as necessary to identify the specific traffic may be defined e.g. UDP only, all traffic to this IP etc.
Up to 8 assignments may be defined and supported. Anything not explicity defined is defaulted to Low Priority, except traffic generated and destined for the router which is automatically assigned a special (High) value.
Certain protocols use secondary ports or 'spawn' additional ports in their normal operation. H.323 is one such protocol. If the router is configured to recognize port 1720 (the H.323 control port) then the priority rating assigned to this port is automatically allocated to all secondary or 'spawned' ports during that H.323 call sequence. SIP is handled similary.
Certain protocols use secondary ports or 'spawn' additional ports in their normal operation. FTP is one such protocol. If the router is configured to recognize port 21 (the FTP control port) then the priority rating assigned to this port is automatically allocated to all secondary or 'spawned' ports during that FTP session.