QoS Application Classes

The transactional data class includes enterprise resource planning (ERP) applications such as Peoplesoft, SAP, Oracle, SQL server, and Citrix. The transactional data class is very similar to the mission critical data class, but the traffic in the transactional data class is normally of a slightly lower priority and not interactive in nature. The network management data class includes protocols like simple network management protocol (SNMP) and service assurance agent (SAA) probes. SAA probes have been associated with the IOP SLA measurement features of Cisco IOS 12.4. I have included a link to the documentation of the 12.4 IOS IP SLA Configuration guide. The SLA configuration guide provides a useful way to measure the delay, jitter, and packet loss of the 11 different application classes in QoS. Bulk data applications include bursty applications which transfer large amounts of data. Bulk data applications are TCP based which makes the traffic very resilient. Lost packets are retransmitted and out of order packets are reordered in the TCP/IP stack. The bulk data application class normally includes HTTP, E-Mail, FTP, and backup traffic. Backup traffic represents a traffic type that may be of high priority during non production hours, but not allowed during business hours. Time-based access control lists allow the administrator to distinguish backup applications based on the time of day and/or day of the week. The best effort data class will include all of the applications that have not been identified by other application classes. This traffic is normally sent on a best effort (BE) basis with or without a bandwidth guarantee. The modular QoS CLI (MQC) will only allow the administrator to provision 75% of the interface bandwidth by default to ensure applications not classified and marked by one of the other application classes receive a share of the bandwidth and the traffic streams are not starved. The 75% rule does not guarantee 25% bandwidth to the best effort class though. The best effort class will compete for the remaining 25% of bandwidth with all of the other application classes that need more bandwidth than that which was provisioned. The only exception to the 25% remaining bandwidth contention is the priority queue used for voice over IP media and videoconferencing. The priority queue traffic is implicitly policed to the amount of bandwidth provisioned and a 200ms burst which is based on the configured priority queue bandwidth. The Scavenger data class includes peer to peer file sharing applications, Internet worms, and other nasty stuff on the network. The scavenger class concept relies on policing technology at the access layer switches. Most networks have been, or are planning to upgrade to Gigabit Ethernet technology for desktop and laptop LAN connectivity. The average utilization of these connections is normally less than 5% or 5Mbps. Any traffic above 5Mbps that is not classified and marked by the access switch classification and marking policy should be marked into the scavenger class. The scavenger traffic includes suspect traffic that may be dangerous to the network. Scavenger traffic is given a very small bandwidth guarantee ensuring this traffic does not consume resources during periods of high congestion. The use of this data class represents a preemptive measure to protect your network before the signatures of viruses or worms have been identified by security vendors. We will continue our QoS coverage in the next blog with the topic of queuing. REFERENCES IP SLA Configuration Guide (IOS 12.4) http://www.cisco.com/en/US/docs/ios/12_4/ip_sla/configuration/guide/hsla_c.html

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