Avaya Configuring DLSw Services Manual do Utilizador descarregar pdf (Página 55)

DLSw Implementation Notes

2-17

LLC2 Flow Control

The LLC2 protocol interface provides a bidirectional window mechanism and a

SAP credit allocation mechanism that together manage ﬂow control on individual

LLC2 connections between the router and LAN-attached SNA or NetBIOS

systems.

The SAP window attempts to limit the number of outstanding frames queued for

transmission to a remote endstation from a local endstation at this SAP address, as

follows.

1. As frames are sent by the local endstation but not yet acknowledged by the

remote endstation, a counter on the remote DLSw switch increments.

2. When this counter reaches half the value speciﬁed in the SAP Window

parameter, the remote DLSw switch sends a ﬂow control indication back to

the local DLSw switch.

3. The local DLSw switch sends RNRs (Receiver Not Ready) to the local

endstation to control the ﬂow of the session.

4. As frames are acknowledged by the remote endstation, the counter on the

remote DLSw switch decrements.

5. After all outstanding frames have been acknowledged by the remote

endstation, the remote DLSw switch sends an end-ﬂow-control indication

back to the local DLSw switch.

6. The local DLSw switch then sends RR (Receiver Ready) to the local

endstation, thereby allowing it to send more frames.

TCP Flow Control

Each pair of TCP connections between DLSw peers carries data from many LLC2

sessions. When congestion occurs on the TCP/IP network between DLSw peers,

TCP

• Reduces or closes its transmit window

• Signals the local and remote LLC2 interfaces to assert ﬂow control on any

LLC2 connections associated with the congested TCP connections

1 2 ... 50 51 52 53 54 55 56 57 58 59 60 ... 203 204

Sem comentários

Avaya Configuring DLSw Services Manual do Utilizador Página 55