Packet Size Negotiation
Negotiated packet sizes are passed transparently from the originating DTE to the destination DTE. However, if the originating DTE does not specify the packet size parameter in the call request packet, the X.25 services inserts this facility at the destination. The following table shows the packet size negotiation that is implemented by the X.25 services.
| Originator's Request | Originator's Default Remote Packet Size | Originator's Default Local Packet Size | Action by the X.25 Services |
|---|
| No packet size specified | 256 bytes | 256 bytes | The destination Passport 4400 unit issues a call request with packet size negotiation parameters based on the originator's default local and remote packet sizes (in this case, 256, 256). |
| No packet size specified | 256 bytes | 128 bytes | The destination unit issues a call request with packet size negotiation parameters based on the originator's default local and remote packet sizes (in this case, 256, 128). |
| 128, 256 requested | 256 bytes | 128 bytes | The destination unit issues a call request using the packet size parameters requested by the originator (in this case, 128, 256). |
During call accept, the destination DTE may request that the specified packet size be negotiated to a lower value. If the originating DTE did not specify packet size negotiation, the negotiated size is not communicated to the originator. In this case, the Passport 4400 unit splits packets (using the M-bit) to ensure that negotiated packet sizes are enforced, as shown in the following diagram:
