Http links between ATS and SPG are fault.
1 Use ATS IP address to ping SPG IP address successfully..
2 Check the SPG data configuration, and all data configuration are normal.
3 Check the ATS data configuration, and find the ATS server type is as Client.
Regarding to ATS and SPG data configuration principle: when the ATS services are provisioned through the SPG, set this parameter to SERVER.
4 Remove the Http links and follow the data configuration principle to add Http links again. All Http links are UP.
May be they are affected as below:
1 IP between ATS and SPG are broken.
2 Data configuration are wrong between ATS and SPG.