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Without a framework, it would be necessary to separately maintain each QoS policy on a perdevice basis If administrators must "touch" each device (probably via a Telnet logon), QoS within an internetwork would be both labor intensive and mistake prone Most couldn't imagine managing network devices or security in a large internetwork without the benefit of SNMP and RADIUS, and the same holds true for QoS Indeed, QoS presents a much tougher implementation proposition than do system management and security because, for end-to-end service quality, the policy must be implemented across autonomous systems Generally, this entails implementing QoS across ISPs, but extranets imply QoS between end-user enterprise internetworks also Manual implementation of any meaningful QoS is virtually impossible In a typical internetwork, requests for service and changes in operating conditions take place several times a minute It therefore follows that network teams will need to tweak fixed QoS policies with some frequency, probably at least weekly This suggests the need for a layer of abstraction between the content of the policy and its application devices For example, a router interface could have the role Priority Enforcer, but the actual rule of "give Gold packets 50% of available bandwidth" would be separately defined So if the network manager decided to reduce Gold's priority to 40%, the change would be implemented only in the policy server, not in every device assigned the Priority Enforcer role

1 Information gathering identify symptoms and problems 2 Identify the affected areas of the network

Binding rules to roles in real time would give a QoS system a lot more flexibility QoS needs the ability to self-operate in the way routing protocols can Routing protocols let routers update one another on topology changes, so each router can continually recalculate optimal routes to various destinations The Internet was able to scale to its gigantic size because routing protocols imbue the Internet with a degree of self-awareness and self-operation especially because of the Border Gateway Protocol (BGP) operating at the Internet peer routing level Specifically, QoS needs a way to continually account for finite bandwidth resources Also needed are automated mechanisms to make decisions between competing QoS requests, and to set up and tear down QoS assignments as connections come and go The mission of a QoS framework takes on high complexity as QoS services span autonomous systems

= e ln r +i ( +2 n ) = rei ei 2 n = rei (cos 2 n + i sin 2 n ) = rei EXAMPLE 110 Find the fourth roots of 2 SOLUTION We nd the nth roots of a number a by writing r n ein = a ei 0 and equating moduli and arguments, and repeating the process by adding 2 This may not be clear, but we ll show this with the current example First we start out with (rei )4 = 2ei 0 r = 21/ 4

3 Establish if anything has changed 4 Identify the most probable cause 5 Determine if escalation is necessary 6 Create an action plan and solution identifying potential effects 7 Implement and test the solution 8 Identify the results and effects of the solution 9 Document the solution and the entire process

All networking subsystems work by manipulating packets in one way or another Doing anything with a packet involves going through a CPU cycle While it's true that smart engineering can pack more instructions into a cycle, the fact remains that every QoS action requires additional tasks that come at a cost The trick is to get the most service-quality effect at the least processing-overhead cost Routers, switches, and other network devices don't need disks because their function is to forward traffic Packets are only stored temporarily, where DRAM is used to set up and manage one or more packet queues while the CPU figures out how to forward them Indeed, queuing is so important to router operations that most routers have separate DRAM called packet memory dedicated specifically to that purpose One of the primary tools used by QoS to influence service levels is queue manipulation Because virtually all routers use first-in/first-out (FIFO) ordering by default, queue manipulation mechanisms are often referred to as non-FIFO queuing The most common name for the practice, though, is class-based queuing (CBQ) CBQ works by somehow defining packets to a class by flow If, for example, a router is instructed to favor one type of traffic over another, it must intervene and influence the queue's default FIFO order to bump the favored class of traffic toward the front This process is shown in Figure 15-4, in which packet C is bumped to the front of the queue