 All rights reserved. Any use is subject to the Terms of Use as given at the website. PCUSN-to-SGSN Interface (Gb) Chapter 9 Inside the network, the same scheme is used although the Frame Relay switches need not maintain a strict virtual relationship in the network. Connectionless operations can be implemented to enable dynamic and robust routing between the Frame Relay switches. The only requirement is to make certain that the frame arrives sequentially at the port designated in the DLCI. Data Link Connection Flow The Frame Relay UNI enables multiple users to share the physical link. In Figure 9-11, users A and C are multiplexed onto the UNI by a router and the assigned DLCIs 499 and 506. The traffic is transported to the receiving Frame Relay switch, where it is presented to a router. Notice that the DLCIs are translated and mapped into DLCIs 700 and 530 at the re- mote UNI. Because Frame Relay is a connection-oriented technology and uses labels DLCIs to identify traffic, a router must be able to translate a con- nectionless address to a DLCI and vice versa. Although this operation is not complex, it does require the careful construction of mapping tables at the router. The Frame Relay standards do not describe how this mapping and address translation takes place. Typically, each router has a table that cor- relates IP addresses to DLCIs and vice versa. Figure 9-11 The translated mapping of the DLCI. Router 1 Router 2 Switches Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PCUSN-to-SGSN Interface (Gb) PCUSN-to-SGSN Interface (Gb) The FECN and BECN The congestion and flow control option is optional; vendors need not imple- ment this, and they will still comply with the standard. However, unless other flow control measures are implemented in the network, the use of this option is quite important. Two mechanisms are employed to (a) notify us