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Frame Relay

Dear all,

Please tell me the differences and relationship between Maximum Frame size of a Frame-relay and MTU .

In a Frame relay network here , framerelay maxframesize is 4000 and MTU is 1500. What is the logic behind this settings ?




Re: Frame Relay

Frame Relay frame size is one of the parameters in IWF equations used for converting Frame Relay traffic parameters to their equivalent ATM traffic parameters and vice-versa. The default configuration uses a constant frame size of 250 bytes in the IWF equations. For some Frame Relay network configurations this could cause problems such as:

Frames being dropped if actual frame size is less than 250 bytes

Wasted bandwidth if actual frame size is greater than 250 bytes

To overcome this problem you can configure the Frame Relay frame size.

If the incoming traffic is always a single frame length, then configure that frame size in the connection traffic table row (CTTR). However, if the incoming traffic has a varying frame-size, then configure the Frame Relay CTTR using the highest sustained cell rate (SCR) for a given committed information rate (CIR) in the corresponding ATM-CTTR.

To use the Frame Relay frame size feature, requires the following:

Create a Traffic table row (CTTR) using frame size

Use that CTTR row while creating a VC (PVC or Soft PVC)

A maximum transmission unit (MTU) is the largest size packet or frame, specified in octets (eight-bit bytes), that can be sent in a packet- or frame-based network such as the Internet. The Internet's Transmission Control Protocol uses the MTU to determine the maximum size of each packet in any transmission. Too large an MTU size may mean retransmissions if the packet encounters a router that can't handle that large a packet. Too small an MTU size means relatively more header overhead and more acknowledgements that have to be sent and handled. Most computer operating systems provide a default MTU value that is suitable for most users. In general, Internet users should follow the advice of their Internet service provider (ISP) about whether to change the default value and what to change it to.

In Windows 95, the default MTU was 1500 octets (eight-bit bytes), partly because this is the Ethernet standard MTU.

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