Answers to Chapter Review Questions

     

A1:	Because this appears to be a mission-critical application where it is crucial that data gets to the remote site as quickly as possible, the type of ATM service purchased would have to be a Constant Bit Rate ( CBR ) service.
A2:	No. The propagation delays will not change just because we increase the available bandwidth. Propagation delays include things like the internal circuitry in a switch and the speed of light; no matter how much bandwidth you have available, these costs will never diminish.
A3:	Data consistency is where the structure and format of the data is the same on two physically separate but paired devices. Data currency is where the same data records can be found on two physically separate but paired disks. The difference is that we could have consistency in that the application can understand the structure and format of the data on both disks but not currency, i.e., not all data records exist on both disks, possibly due to synchronization delays between the two disks. Conversely, the technology that keeps two physically separate but paired disks current needs to ensure that data arrives at its destination in the same format and structure (possibly using some form of packet/record tagging), hence ensuring that consistency is maintained . For an individual application, data consistency is normally more important because information that is unintelligible, i.e., inconsistent, is of no use to the application and might as well be not there. To say that currency is more important highlights the lack of understanding of the importance of consistency.
A4:	Hard zoning is where the switch and port numbers are used to identify individual members of the zone. Soft zoning is where individual Port WWN of attached devices is used to identify individual members of the zone. Where we were experiencing a large number of HBA failures, we would see an increased number of changes Port WWN addresses. As such, hard zoning would be preferable because the WWN is not used to configure the zone.
A5:	Devices in a VPN will use both symmetric and asymmetric cryptography. Initially, they will use asymmetric or public-key cryptography in order to exchange information securely. They will be the only devices that understand the information they exchange. The information exchanged will be the secret key, subsequently used for symmetric key cryptography. This key exchange is known as creating a session key. The session key can be used for a number of subsequent communications or can be recalculated after each transmission.