FRTS uses a mechanism called a Token BUCket. The Token Bucket regulates the amount of data that can be sent from the Frame Relay interface during a specific time period, 1/8th of a second by default. Data can be sent out the Frame Relay interface only if there are enough free tokens in the token bucket. If there are enough tokens, the data is sent and the apPRopriate amount of tokens are removed from the Token Bucket. If there are not enough tokens, the router will buffer the data until the Token Bucket has enough tokens to send the data and then remove the appropriate amount of tokens.
Before proceeding please note that there are two basic types of FRTS implementations.
(1) FRTS with only local concern to the Frame Network (2) FRTS configuration with remote concern for other routers on the network. For example, if you need to throttle bandwidth down on your T1 so that you so not overwhelm the remote router which is running at just 128k.
Frame Relay Terms and How They Apply to Cisco FRTS Implementations:
AR (access Rate) This is the depth of the token bucket. This is the physical circuit speed to your frame provider.
Local Example: If you have agreed to purchase a 128k circuit to your Frame Provider, your AR is 128k. Remote Example: If you have 128k physical circuit and you intend to lower the rate of data transmission to a remote site which only has a 64k AR, you would then set this to 64k.
Implementation: When configuring Cisco FRTS using the data from the Local Example above, this will be entered using "cir". frame-relay cir 128000.
CIR (Committed Information Rate) This is the average amount of data that you and your service provider have agreed that you will send per second. This is normally lower than your AR.
Local Example: Your Frame Relay Service Provider has stated that your CIR = 64k. You now have a 128k physical circuit to your provider with a CIR of 64k. Remote Example: If you have 64k CIR to your provider and you need to throttle bandwidth down so you don't overwhelm your you remote router which has a 32k CIR, you would set this to 32K CIR.
Implementation: When configuring Cisco FRTS using the data from the Local Example above, this will be entered using "mincir" frame-relay mincir 64000
Bc - (Committed Burst) This is the amount of data that can be sent during a time interval. That time interval is identified by "Tc", which by default is 1/8th of a second. Bc = AR/8
Local Example: In order to send traffic to meet your 128k AR, Bc = 16000bps. Remote Example: This would be set to 1/8th of the remote routers AR. Implementation: When configuring Cisco FRTS using the data from the Local Example above, this will be entered using "bc" frame relay bc 16000
Be - (Excess Burst) This is the difference between CIR and AR. Configure Be only if CIR is less than AR.
Local Example: If your CIR is 64k and your access rate is 128k, then your Be is 64k. Remote Example: The difference between cir and mincir. If cir = 128000 and mincir = 64000, then be = 64000 Implementation: When configuring Cisco FRTS using the data from the Local Example, this will be entered using "be". frame-relay be 64000
Tc (Time Interval) Time interval is the time measurement that works with Bc to control the amount of data that is allowed to be sent to the token bucket. The router calculates this value based on AR and Bc values that you enter. Tc = Bc/AR.
By default on a Cisco router, it is 0.125 (125ms). If Bc/AR. is greater than or equal to 125msec, it uses the internal Tc value of 125msec. If Bc/AR is less than 125 ms, it uses the Tc calculated from that equation. Why does this matter? A Tc should be adjusted to 10ms if you are running Voice across the Frame Relay circuit.
Before proceding, please once again note the difference in terminology:
FRAME RELAY TERMINOLOGY CISCO TERMINOLOGY USING FRTS AR - ACCESS RATE = CIR ? COMMITED INFORMATION RATE CIR - COMMINITED INFORMATION RATE = MINCIR - MINIMUM COMMITED INFORMATION RATE
Examples:
Single Site If you were to traffic shape to your Frame Relay provider, you would do the following. Let's say your provider has given you the following:
"Welcome to Global.Net WAN Services. Your 512k circuit has been installed. Per our agreement, you have a 384k CIR to our Frame Network. Thank you for using Global.Net."
Here is how you would configure your router:
int s0 frame-relay traffic-shaping int s0.1 Frame-relay class hub
map-class frame-relay hub frame-relay adaptive-shaping becn <-- notification if congestion Frame-relay cir 512000 <-- port speed Frame-relay mincir 384000 <-- committed rate from provider Frame-relay be 128000 <-- burst rate (port - committed rate) Frame-relay bc 64000 <-- port speed / 8
Hub and Spoke
Note: As soon as we begin to configure FRTS to adapt for other routers on our network, in most cases our Cisco map-class settings now begin to reflect the requirements put upon us by the remote router.
Scenario 1 You have a hub site with T1 port access and 128k cir from your provider. You are communicating to a remote site, which only has 64k port access and 32k cir to the same Frame network. You'll want to throttle the hub site down enough so that it does not overwhelm the remote site with traffic.
Hub Site
int s0 frame-relay traffic-shaping int s0.1 frame-relay class hub
map-class frame-relay hub frame-relay adaptive-shaping becn <-- notification if congestion frame-relay cir 64000 <-- remote site port speed frame-relay mincir 32000 <-- remote site cir from provider frame-relay be 32000 <-- initial burst, port speed of remote router frame-relay bc 8000 <-- remote port speed /8
Scenario 2 You have a hub site with 512 port access 256k cir from provider communicating with 2 spoke remote sites which also have 512k port access 256k cir from provider. You'll want to throttle the spoke sites down enough so that they do not overwhelm the hub router.
Spoke Sites
int s0 frame-relay traffic-shaping int s0.1 frame-relay class spoke
map-class frame-relay spoke frame-relay adaptive-shaping becn <-- notification if congestion frame-relay cir 256000 <-- = of remote site AR, read comment below frame-relay mincir 128000 <-- = of hub site cir from provider frame-relay be 128000 <-- initial burst frame-relay bc 32000 <-- 1/8th interval of AR which we have manually set to 256k above.
With CIR we have to share bandwidth for the hub with the other remote router, so our CIR is now set to 256000 which is = of the hub routers port speed.
BC should always be 1/8th of your CIR setting in the Cisco map class unless you are running voice.
