et classification in advanced networks that provide service level agreements (SLAs) as well as quality of service (QoS) and class of service (CoS) guarantees. We will discuss these topics later when we cover issues such as Integrated Services (IntServ) and Differen- tiated Services (DiffServ). For example, deep packet classification could be based on the application of specific rules that require the simultaneous use of six bit fields. Those bit fields could potentially be the source and destination addresses (each 32 bits long), the source and destination port numbers (each 16 bits long), the type of service (TOS) field (8 bits long), and the type of protocol field (also 8 bits long). Deep packet classification sorts out the incoming unstructured packet stream in a series of flows. The flow is an artificial concept that may bear no relationship with tangible reality. It is just a subset of a packet stream that satisfies specific sorting criteria that we impose arbitrarily to reflect what we expect the network service provider to manage. The flow assignment of packets distinguishes the actual service that a packet will receive. At an age where we talk more about QoS, SLAs, and billing per usage, it is imperative that equipment at the disposal of service providers be able to take a peek inside all the packets in order to ensure that the appropriate session-related information is extracted Downloaded from Digital Engineering Library McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. CLASSIFICATION PROCESSORS CLASSIFICATION PROCESSORS 239 and fed into the SLA rules to ensure correct billing or to the QoS rules to ensure that the client obtains the service he or she expects. The following are examples of different uses of packet classification: To manage access control lists (ACLs) for specific applications For example, in a firewall, systems manager may be required to block (filter) packets c