User's Manual

Table Of Contents

MDS 05-2708A01, Rev. D MDS TransNET I&O Guide 53

Extended SAF Network

Below is an example of a multilevel network utilizing two repeaters—X

J,K

and X

K,L

. The example demonstrates the extensibility of the network. In this

case, messages directed to Remotes in the sub-network L will be relayed

through Extension radios X

J,K

and X

K,L

. Like the previous example, the

Extension radios will split their operating time equally between their Master

and Remote “personalities.” This multi-layered network can be extended

indefinitely without degradation in throughput, beyond that initially incurred

by placing the network in the SAF mode.

Invisible place holder

Figure 18. Extended SAF Network

Networks: J, K, L

Retransmission and ARQ Operation

Functionally, the sub-network side of an Extension behaves like a corre-

sponding connection between a Master and a Remote.

When an Extension is using its “Master personality” it sends acknowledg-

ments and performs unconditional retransmissions based on its REPEAT

count.

When an Extension is using its “Remote personality,” acknowledgments are

processed and retransmissions occur as needed, up to the number of times

specified by the

RETRY count value.

If data arrives from a new source prior to completion of retransmissions, it is

considered to be a violation of the polling model protocol. The new data takes

precedence over the old data, and the old data is lost. In such a situation, new

data is likely to be corrupted as it will have some old data mixed in with it.

SAF Configuration Example

Here is an outline for the configuration of a simple store-and-forward link.

K,L

J,KI

Sub-Network “J”

Sub-Network “K”

Sub-Network “L”