D) (i) What are two differences between how a virtual circuit packet switching n

Question

D) (i) What are two differences between how a virtual circuit packet switching network works and how a datagram based packet switching network works? (ii) What is the key difference between a virtual channel switch and a virtual path switch in an ATM network? (iii) Explain how the AAL 5 adaption layer protocol operates to send data packets from higher layers using ATM cells. (iv) Explain what a label stack is in MPLS (Multi Protocol Label Switching) networks. Describe how a label stack may be used to create a tunnel in an MPLS network.

Explanation / Answer

1)

et us see what are the highlighting differences between these two hot debated topics here:

Virtual Circuits-

Datagram Networks :

2)

VIRTUAL PATH AND VIRTUAL CHANNEL

Connection between two endpoints is accomplished through virtual paths and virtual circuits. The physical fiber between end points may consist of many virtual paths (VP). A VP provides a connection or a set of connections between two switches. VP is like a highway that connects two cities. Cell networks are based on Virtual circuits (VC). All cells belonging to a single message follow the same virtual circuit as the lanes of highway.

           Several virtual paths utilize/access the bandwidth of the media. Forexample if media bandwidth is B and there are N VPs, then each VP may have a bandwidth of B/N.

                    Each VP is divided into several Virtual Channels. The VP BW is then divided into the VCs. VPI (virtual path identifier) specifies the VP numberassigned to the user for that session.If it does not require the full VP BW then only some VCs may be allocated and the VCI (virtual circuit identifier)carries the VC number.

3)

10.3.2

ATM ADAPTATION LAYER

The purpose of the ATM Adaptation Layer (AAL) is to adapt the PDUs passed down from the higher layer onto ATM cells. As the higher level PDUs may in general be of an arbitrary size, so one of the two sublayers in the AAL is responsible for segmentation and reassembly (SAR) of the higher layer PDUs. The other sublayer, the convergence sublayer (CS), is responsible for pack aging the higher layer PDU with any additional information required for the adaptation necessary and offering an interface to the B-ISDN user.

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