Example: Switched virtual circuit (SVC)
Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2
Example: Switched virtual circuit (SVC)
The following example shows in detail how an SVC connection is established in an ATM network.
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An ATM user, End station A, sends a SETUP message on the virtual channel connection reserved for signaling (VPI=0, VCI=5) to its directly connected ATM switch, ATM switch 1.
The SETUP message contains:
The 20-byte ATM address of End station B.
Quality of Service (QoS) parameters needed for connection.
ATM switch 1 analyzes the SETUP message to determine whether it can find a table entry for End station B's switch address and whether it can support the required QoS parameters for the requested connection.
If ATM switch 1 can find End station B's switch address and support the required QoS parameters for connection, a CALL PROCEEDING message is sent back to End station A.
If ATM switch 1 either cannot find End station B's switch address or accommodate the connection, a RELEASE message containing standard error codes is sent back to End station A and the call request is rejected.
ATM switch 1 sends the SETUP message (described in Step 1) on the virtual channel connection reserved for signaling (VPI=0, VCI=5) to the next switch in the network, ATM switch 2, on its way to the destination, End station B.
The SETUP message contains the same ATM address of End station B and all required QoS parameter information as included in Step 1. Additionally, the SETUP message now identifies a new VPI/VCI pair for use between ATM switch 1 and ATM switch 2.
ATM switch 2 receives the SETUP message. End station B is determined to be a directly connected endpoint registered to ATM switch 2. If the QoS required for the requested connection can be accommodated, ATM switch 2 sends a CALL PROCEEDING message back to ATM switch 1.
The SETUP message reaches its final destination, End station B. End station B can respond in either of two ways:
If End station B accepts the call, it sends a CALL PROCEEDING message, followed immediately by a CONNECT message back to ATM switch 2.
If End station B rejects the call, it sends a RELEASE message back to ATM switch 2. The RELEASE message is passed through the network back to the original source user (End station A) containing standard error codes that describe the reason for rejection.
ATM switch 2 sends a CONNECT ACK message back to End station B, then passes the CONNECT message to ATM switch 1.
ATM switch 1 sends a CONNECT ACK message back to ATM switch 2, then passes the CONNECT message to End station A.
End station A sends a CONNECT ACK message back to ATM switch 1.
The previous example demonstrates a simplified SVC connection using only two intermediate switches, ATM switch 1 and ATM switch 2. In practice, most SVC connections use many intermediate switches. When more intermediate switches are used, each switch forwards SETUP, CONNECT, and RELEASE messages to its downstream neighbor switch, while relaying acknowledgment messages (CONNECT ACK, RELEASE ACK) back to its upstream neighbor switch.
The result of this connection process is a virtual circuit (VC) in both directions between End stations A and B in which:
All intermediate switches and ATM user hardware at End stations A and B now support and protectively enforce the QoS communication parameters required for this connection.
All intermediate switches (in this case, ATM switches 1 and 2) have been programmed with switch table entries for mapping the series of VPI/VCI pairs used for routing ATM cells between End stations A and B.
If any intermediate switch cannot accommodate the requested QoS connection parameters, a RELEASE message is sent back in the direction of the source user. The RELEASE message contains the standard error codes and frees the resources being reserved at each device in the connection path and at the source.