DATA COMMUNICATION Principles Multiple Connections Per Protocol Multiple

DATA COMMUNICATION Principles : Multiple Connections Per Protocol

Multiple Connections Per Protocol The figure also shows protocol number 1 in layer N+1 opening two connections together invoking the services of protocol number 1 in layer N. The PDUs for both of these connections from protocol 1 in layer N+1 could be traveling with or without a logical connection. Alternatively, there could be a single logical connection for both. An example of multiple connections from the same protocol without a logical connection is the connectionless user datagram protocol (UDP) protocol sending multiple PDUs (from different applications) through the IP protocol. An example of multiple PDU types from one layer using a single logical connection is a layer 2 point -to-point protocol (PPP) carrying multiple IP datagrams over a single PPP link.

The purpose of Figure 7 -8 is to demonstrate that there a variety of ways in which multiplexing is realized in upper layer. We have seen in Chapter 6 that the ATM cell provides multiplexing by defining a 16 bits virtual channel number (8 bit virtual path identifier VPI and 8 bit virtual circuit identifier VCI). A protocol above ATM can make use of many VCIs, or many VCIs can be used as a single VPI, thus providing multiplexing of many Virtual Circuits in a single Virtual Path. In fact, one way that the relationship between the VPI and VCI has been describes is as shown in Figure 7 -9. In this figure, VPI is the address of a data pipe carrying many thinner pipes, each labeled with a VCI. In turn, ATM is like a very thick pipe carrying many virtual paths. Multiplexing capability at a higher layer protocol is a powerful function and is essential for all future protocols, as we move towards links with hundreds of Gbps capacity and applications that require simultaneous delivery of many packets types, data, voice and video, between two or more stations located at various places in the world.

REFERENCES • Ahmad A. - Data Communication Principles. For Fixed and Wireless Networks • Cornelius T. Leondes - Database and Data Communication Network Systems, Three-Volume Set_. . -Academic Press