The Journey of a Network Engineer

Dec 7 2011   5:47AM GMT

How to traffic shape Frame-Relay? – part 1

Sulaiman Syed Profile: Sulaiman Syed

Frame-Relay Traffic shaping (FRTS) is one of the fundamental topics that is required to master before going to the CCIE lab exam. Since you never know which method will be required by the exam to do. There are four different types of methods, namely:

  • Generic Traffic Shaping
  • Legacy Frame-Relay Traffic Shaping
  • MQC  Frame-Relay Traffic Shaping
  • Class Based Generic Traffic Shaping
I would explain two methods in this entry, and the other two methods in the next entry.
Generic Traffic Shaping
This command syntax was one of the first few ones that were designed for QoS. It can be applied at any interface media, Ethernet, frame-relay, etc. With this, you can configure Bc, Be, and Queue size.  The syntax for this command is as follows:
traffic-shape {group|rate} Peak-Rate Bc Be Queue-size
traffic-shape group 100 256000 2560 2560 16
In the above example, i have used group 100 (access-list) with rate of 256000bps, Bc 2560bps, Be  2560 bps and queue size of 16 packets. Of course, these numbers are just randomly chosen. We have effectively set Tc to 10ms.  This can be re-calculated by knowing the equation
Bc = Rate * Tc (in seconds), Tc = Bc/Rate = 2560/256000 = 0.01 second
To enable the interface to react to BECN we would need to enable the adaptive shaping. follow the syntax
traffic-shape adaptive CIR
traffic-shape adaptive 128000
Know that you can apply multiple commands of traffic-shape group since the first packet matching the access list will be shaped according to the respective rate configured.
One of the things to note about this type of shaping is that it will be enabled for the whole interface. So if we have multiple PVCs, the same shaping parameters will be applied to all. If one BECN sent to one of the PVCs the interface will slow down all the other PVCs which is not desirable. Using point-to-point sub-interfaces could solve this issue.
Legacy Frame-Relay Traffic Shaping
This is method uses the map-class frame-relay name syntax. It is installed under the interface configuration mode frame-relay interface-dlci number . Lets see the options that we can use within the map-class for QoS
R1(config-map-class)#frame-relay ?
adaptive-shaping   Adaptive traffic rate adjustment, Default = none
bc                 Committed burst size (Bc), Default = 7000 bits
be                 Excess burst size (Be), Default = 0 bits
cir                Committed Information Rate (CIR), Default = 56000 bps
congestion         Congestion management parameters
custom-queue-list  VC custom queueing
end-to-end         Configure frame-relay end-to-end VC parameters
fair-queue         VC fair queueing
fecn-adapt         Enable Traffic Shaping reflection of FECN as BECN
fragment           fragmentation – Requires Frame Relay traffic-shaping to be configured at the interface level
holdq              Hold queue size for VC
idle-timer         Idle timeout for a SVC, Default = 120 sec
interface-queue    PVC interface queue parameters
ip                 Assign a priority queue for RTP streams
iphc-profile       Configure IPHC profile
mincir             Minimum acceptable CIR, Default = CIR/2 bps
priority-group     VC priority queueing
tc                 Policing Measurement Interval (Tc)
traffic-rate       VC traffic rate
voice              voice options
All these variables can be changed to reflect the QoS requirements for the frame-relay network. Let’s see example of configuring frame-relay with peak rate of 256kbps, bc 2560 bps, be 0,  and cir of 128kbps will be configured as following
map-class frame-relay TEST
frame-relay cir 256000
frame-relay mincir 128000
frame-relay be 0
frame-relay bc 2560
interface serial 1/0
frame-relay traffic-shaping
frame-relay interface-dlci 201
class TEST
This method could be considered the easiest and most implemented method for Frame-relay networks.

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