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COS Feature Differences Between PTX Series Packet Transport Routers and T Series Routers

This topic provides a list of Class of Service features available on PTX Series routers and compares them with Class of Service features on T Series routers.

• T Series routers support VRF table labels for Layer 3 VPNs. On PTX Series routers, this feature is not supported.

• On T Series routers, IEEE 802.1 classifiers cannot co-exist with Layer 3 classifiers. On PTX Series routers, these classifiers can co-exist.

• On T Series routers, IEEE classifiers are supported on Ethernet IQ, IQ2 and IQ2-E interfaces. These interfaces have the flexibility of classifying traffic based on inner or outer VLAN tags. On PTX Series routers, IEEE classification is always based on outer VLAN tags.

• PTX Series routers do not support rewrite of both exp and inet-precedence fields using:
  • exp protocol mpls-any
  • exp protocol mpls-inet-both
  • exp protocol mpls-inet-both-non-vpn
• On T Series routers, the DSCP and DSCP IPv6 rewrite for protocol MPLS is not supported. PTX Series routers support rewrite of both DSCP and DSCP IPv6 for protocol MPLS.
• PTX Series routers support layer 2 rewrite of 802.1p and 802.1ad, to either the outer vlan tag, or both outer and inner vlan tags.

• On T Series routers, you can override the default fabric priority queuing of egress traffic by including the priority statement at the following hierarchy level: .
  [class-of-service forwarding-classes queue queue-number class-name] priority (high |low);

  On PTX Series routers, fabric priority queuing is not supported; therefore, the priority statement for forwarding-classes is not supported.

• On T Series routers, the copy-plp-all statement needs to be configured to support tricolor marking. On PTX Series routers, tricolor marking is enabled by default.

• T Series routers, which use egress queuing architecture, support chassis and fabric schedulers. Alternatively, PTX Series routers support a Virtual Output Queuing (VOQ) architecture that does not require fabric schedulers. With the VOQ architecture, packets are queued and dropped on ingress during congestion.
• On T Series routers, high priority queues have precedence to acquire excess bandwidth and may consume all excess bandwidth. On PTX Series routers, excess bandwidth is shared based on the ratio of the configured transfer rate. Therefore, all priority queues get a share of excess bandwidth.
• On T Series routers, strict-high priority queues and high priority queues are assigned the same hardware priority. On PTX Series routers, strict-high priority queues and high priority queues are assigned different hardware priorities.
• On T Series routers, if a strict-high priority queue is oversubscribed, it can block all other queues except high priority queues. On PTX Series routers, if a strict-high priority queue is oversubscribed, it can block all other queues including high priority queues.

  To restrict the bandwidth of strict-high priority queues, the transmit-rate rate-limit configuration statement has been implemented for PTX Series routers.

• On both T Series routers and PTX Series routers, if a strict-high priority queue is oversubscribed and results in oversubscription of the guaranteed bandwidth, the distribution of bandwidth that is not taken up by strict-high priority queues is undetermined. T Series routers and PTX Series routers distribute this unused bandwidth differently.

• On T Series routers, memory allocation dynamic (MAD) is enabled by default and can be disabled. On PTX Series routers, MAD cannot be disabled.
• On T Series routers, the maximum delay bandwidth buffering configured per queue is 50 ms. On PTX Series routers, the maximum delay bandwidth buffering configured per queue is 100 ms.
• On T Series routers, the maximum latency associated with a packet is fairly consistent and independent of the number of sources sending the traffic to an interface. On PTX Series routers, over-provisioning is possible. When traffic is sent from multiple Packet Forwarding Engines, the latency is about 10% to 15% higher than when traffic is sent from one Packet Forwarding Engine.
• On T Series routers, a high priority queue has lower latency than a low priority queue with the same configured transfer rate and same offered load. On PTX Series routers, there is no latency difference.

• The Queuing and Memory Interfaces ASIC does not support drop-profile assignments for a queue based on the protocol. As a consequence, the protocol option for the drop-profile-map configuration statement is treated as protocol any.

• On T Series routers, transmitted byte counters are computed using Layer 3 packet length. On PTX Series routers, transmitted byte counters are computed using Layer 2 packet length (excluding CRC).
• On T Series routers, the tail-dropped counters and the RED-dropped counters are displayed separately in the show interfaces queue output. On the PTX Series routers, tail-dropped counters are always zero. All the packet drops will be shown as RED-dropped in the show interfaces queue output.