(a) Why Frame Relay was originally designed for use across Integrated Services Digital Network (ISDN) interfaces? (b) A connectionless protocol, such as Ethernet, defines the route of a packet through...

(a)

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  Why Frame Relay was originally designed for use across Integrated Services Digital Network (ISDN) interfaces?
  

(b)

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  A connectionless protocol, such as Ethernet, defines the route of a packet through source and destination addresses. However, a connection-oriented protocol, such as ATM, defines the route of a cell through virtual connection identifiers (VPIs and VCIs). Could you explain this statement?
  

(c)

Transferring files from one system to another seems simple and straightforward, some problems must be dealt with first. For example, two systems may use different file name conventions. Two systems may have different ways to represent text and data. Two systems may have different directory structures. How to solve these issues in case of transferring of files from one system to another.