Computer Network Unit 1 q what are the topologies in computer n/w ?

Setting the Data Link

Set the data-link protocol for each serial interface. The RBX 250 Series router in Figure, has three serial interfaces, two for X.25 and one for PPP.

Configuring IP

Before you configure the Concentrator router for XTP, you must define the IP address for the IP interface and the router.

Configuring X.25

Prior to configuring XTP, you must configure the X.25 parameters for each interface. This example configures the basic parameters for X.25, based on the topology in Figure, Configuring XTP

Configuring XTP

After you have configured X.25 and defined the IP address, you are ready to configure XTP.
Q 12. What is frame relay ? Compare frame relay and X-25 network.
Ans: Frame relay is a synchronous HDLC protocol based network. Data is sent in HDLC packets, referred to as "frames". The diagram below of an HDLC frame may be familiar, since without adding specific definitions of how the Address, Control and CRC is used, the diagram is applicable to IBM's SDLC, to X.25, to HDLC, to Frame Relay, as well as other protocols.
The Frame Relay frame structure is based on the LAPD protocol. In the Frame Relay structure, the frame header is altered slightly to contain the Data Link Connection Identifier (DLCI) and congestion bits, in place of the normal address and control fields. This new Frame Relay header is 2 bytes in length and has the following format:

Frame Relay header structure

DLCI
10-bit DLCI field represents the address of the frame and corresponds to a PVC.
C/R
Designates whether the frame is a command or response