CoS on Application Services Modular Line Card Overview
The Application Services Modular Line Card (AS-MLC) is designed to run services for real-time traffic. It consists of three main components:
Application Services Modular Carrier Card (AS-MCC)
Application Services Modular Processing Card (AS-MXC)
Application Services Modular Storage Card (AS-MSC)
The AS-MLC supports CoS features to ensure quality of service (QoS) for real-time traffic that is sensitive to latency on a network. The AS-MLC supports the following CoS features:
Code-point Aliases—On the AS-MLC, you can use the code-point alias name for CoS components such as classifiers and drop-profile maps.
Classification—On the AS-MLC, the traffic flowing from the AS-MXC toward the AS-MCC supports three types of classification:
Behavior Aggregate (BA)—You can configure BA classifiers on the aggregated logical interfaces to classify traffic flowing from the AS-MXC toward the AS-MCC. With BA classification you can set the forwarding class and loss priority of a packet based on its code points. The AS-MLC only supports IP classification (classification based on ToS and DSCP) and classification is supported for the IPv4 family only. The Media Flow Controller application sets appropriate DSCP/ToS code-point in the packet that is evaluated by the BA classifier on the AS-MCC to classify the packet.
Multifield Classification—With multifield classifiers you can set the class and loss priority based on one or more of the following packet header fields: destination address, destination port, DSCP, IP protocol, and source address.
Fixed Classification—Fixed classification can be configured on logical interfaces by specifying a forwarding class to be applied to all packets received by the logical interface, regardless of the packet contents.
Scheduling—Schedulers enable you to define the buffer sizes, delay buffer size, drop profile map, excess priority, excess rate percentage, output-traffic-control profile, priority, scheduler-map, shaping rate, transmit rate, and RED drop profiles to apply to a particular queue for packet transmission.
The AS-MLC provides CoS features in the following deployment scenarios:
HTTP Reverse Proxy— In HTTP reverse proxy configurations, the service provider provides services to a set of domains (content providers) that buy content caching capability from the service provider. Clients connect to content providers through virtual IP (VIP) addresses. Service providers in the reverse proxy scenario generally deploy the routers with AS-MLC hardware to honor service requests (such as caching) from the domain users.
HTTP Transparent Proxy—In HTTP transparent proxy configurations, the service provider implements the AS-MLC to improve its own caching capability and reduce the load on its own network. Implementing caching on a router with an AS-MLC improves the retrieval speeds for data and optimizes the back-end network utilization.
Mixed Mode—In mixed mode both reverse proxy and transparent proxy are configured on the same router.
CoS Implementation in HTTP Reverse Proxy Scenario
In the reverse proxy configuration, the AS-MXC provides content to multiple domains. The Media Flow Controller application on an AS-MXC implements DiffServ by setting the DSCP or IP precedence value for the IP packets traversing from the AS-MXC to an AS-MCC on the AS-MLC hardware. The Modular Carrier Card uses these values to classify the packet and provide a suitable level of service.
The Media Flow Controller application detects the domain it serves and marks the DSCP values or the IP precedence bit value based on how important the traffic corresponding to that particular domain is. The service provider operator also sets a BA classifier on the aggregated interfaces on the AS-MCC.
Unlike a firewall, the Media Flow Controller application implemented on the AS-MLC hardware marks the DSCP/IP precedence values based on the application layer protocols. This feature ensures that important traffic flowing from the AS-MXC gets a higher priority and is processed accordingly. For example, if you implement MPEG on the egress, the drop preference for each frame can be different such that the P and B frames (which require more processing) are dropped before the I frames. This approach results in a better quality video for the end user.
End-to-end CoS policies ensure that traffic arriving at an interface has the right DSCP values and the traffic is prioritized based on the forwarding class and PLP values.
CoS Implementation in Transparent Proxy Scenario
In the HTTP transparent proxy configuration, the service provider deploys the AS-MLC hardware to reduce its own traffic instead of serving a particular domain. The Media Flow Controller application marks the DSCP bits based on its own requirements rather than the requirements of the domains. Besides this difference, the CoS implementation for the egress interface is similar to the reverse proxy configuration scenario. The incoming packets follow the CoS policies applied at the WAN interface.
CoS Implementation in Mixed-Mode Scenario
In mixed mode both reverse proxy and transparent proxy configuration coexist on the same AS MLC hardware. In such a scenario, reverse proxy is configured on an aggregated interface and transparent proxy is configured on a regular interface with the Media Flow Controller application marking the appropriate DSCP values for both the configurations. The individual CoS implementation in both the scenarios remains similar to the implementation discussed in CoS Implementation in HTTP Reverse Proxy Scenario and CoS Implementation in Transparent Proxy Scenario