FRF.12 in QoS

Unanswered Question
Jan 24th, 2010

Dear Friends,

It is just a thought process on Frame-Relay fragmentation FRF.12.

I know that by enabling FRF.12 on any PVC will change the FRTS FIFO Queueing Strategy to DUAL FIFO. It has 2 Priority Queues called HIGH & NORMAL. Packets with smaller size than Fragment value configured, will be placed in HIGH queue of DUAL FIFO and Packets that are fragmented will be placed in NORMAL Queue of DUAL FIFO. I hope everybody agrees with this.

My observation is below:

1. I am not able to apply 'frame-relay fragment" directly on the interface that is configured with "frame-relay traffic-shaping" .

2. Say for example if I have two PVC numbered 102 & 103. As soon as i configure 'frame-relay fragment" in PVC 102, the interface queue stratergy changes to DUAL FIFO

3. There is no Fragmentation parameters is seen in PVC 103. But where as I am seeing the Fragmentation parameters under PVC 102, if I issue the command show frame-relay pvc 102

Here I want to know where is the fragmentation is really happening. Whether the fragmentation is happening before moving to Interface DUAL FIFO or after moving to DUAL FIFO

Sources says that using IP RTP PRIORITY voice packets and smaller packets will be moved to DUAL FIFO HIGH Queue and not clearly saying about where the Larger packets are fragmented

I guess it should be  fragemented at the PVC level itself. Can you please reassure this understanding

Thanks in advance


  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3 (1 ratings)
Giuseppe Larosa Tue, 02/02/2010 - 06:21

Hello Sairam,

your understanding is correct.

what IOS image is running on the router? Because the configuration part may have changed with different image versions (using FRTS versus Modular QoS)

Hope to help


snarayanaraju Tue, 02/02/2010 - 11:21

Hello Giuseppe,

At the outset thanks for your courtesy. Because this query got response after a long days. I am very happy that you involved in this.

I am using 12.4 (25a) version.

I know generally people get bit irritated or do not show interest to know these subtle matters which is not going to help in real time. As I mentioned It is just a thought process only. If you get time let us discuss

Thanks and regards,



This Discussion