Cabletron Systems CyberSWITCH CSX150 User Manual

Also see for CyberSWITCH CSX150: User guide Quick start guide

Contents

Small Office Remote Access Switch 189CONFIGURING A LTERNATE ACCESSESX.25 Accessesa virtual path, although it appears that a real circuit exits, in reality, the network routes the device’sinformation packets to the designated designation. Any given path may be shared by severaldevices.When the virtual circuit is established, a logical channel number is assigned to it at the originatingend. A logical channel number is also assigned to the virtual circuit at the destination end, such thatat each end there is a one to one correspondence between logical channel number and the virtualcircuit. However, the logical channel numbers at each end of a virtual circuit are different.Two types of virtual circuits can be used: a permanent virtual circuit (PVC) or a switched virtualcircuit (SVC). A PVC is similar to a dedicated line. At subscription time, the subscriber gives thenetwork the address to be associated with that virtual circuit. A logical channel is permanentlyassigned. From that point on, no call set up is needed. Data to be sent to that destination is simplysent in data packets using the assigned logical channel.A SVC is similar to a dial-up connection. A call origination packet called a Call Request packet,containing the address of the called party, must be given to the network to cause the establishmentof the virtual circuit.As is specified by X.25, multiple logical connections can be multiplexed over a single physicalchannel. In the case where an ISDN basic rate line is providing the physical channel to a PPSN,multiple X.25 virtual circuits can be present on a single B-channel. The following diagramillustrates that point.Note: In the illustration, the DTEs are all CyberSWITCH systems. Throughout the X.25 Accesssection, the term “DTE” can be interchanged with “CyberSWITCH”.Public Packet Switched Networks are typically more cost effective for users who transmit data inthe mid-traffic range. Low volume users can incur lower costs using public telephone dial-up thana comparable session in a packet network. At the other end of the spectrum, high volume users arebetter served with leased lines.Public PacketSwitched NetworkDTEDCEDCEDTED C ED T EDB1B2DB1B2D B1 B2= X.25 Virtual CircuitsCSX150 CSX150CSX150