sms.bharti.com has no NS records.
NS records for this zone are defined at bharti.com.
NS records for this zone are defined at bharti.com.
Question and response
Question
dig sms.bharti.com. NS
Answer
The response has no answer records.
Authority
bharti.com. 86400 SOA infoblox.localdomain. root.dnsdel.mantraonline.com. 2014051015 3600 3600 1209600 86400
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0