Validity period is an optional value that can be set on a per message basis to control how long an SMSC should attempt to deliver an SMS message. It is usually only useful when a destination recipient handset is turned off or out of coverage, and an SMS message is time critical. The value of the validity period is the “number of minutes” from the time the SMS message is submitted, until it should expire. The value may be specified as an absolute (date and time to the second) or relative (indicated in HHMMSS). When this time is reached, an SMSC would generally return an expired delivery report.
If no validity period is set, the SMSC default is used which is usually 7 days (10,080 minutes). For example - setting the validity period to 30 would result in an SMS message only being retried for delivery by an SMSC for a maximum of 30 minutes.
Visitor Location Register (VLR) is a database which stores information about mobile phones that have recently joined a particular area of a mobile operator’s network. It plays a vital role in keeping track of roamed mobile phone subscribers and co-ordinates with the HLR to determine whether the mobile is a permanent subscriber or a temporary one. Whenever a Mobile Switch Center (MSC) detects a new mobile in its network, in addition to creating a new record in the VLR, it also updates the HLR of the mobile subscriber, apprising it of the new location of that mobile (the MSC address). The MSC address received during an HLR lookup for a particular mobile number is useful for identifying numbers roaming in another country. The foreign network that the number is logged onto can also be identified using this data.
A Virtual Private Network extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network.