Hi Pavan,
With 1GB for DMGR would need to be enough, but take in mind the size of your cell.
Review your hostname resolution in all the components (DMGR, NodeAgents, Servers), directly and reverse.
f.e if you do a dnslookup of DMGR_HOSTNAME you will get an IP address then if you do a dnslookup of the IP you need to get the SAME hostname.
Review if you get the same resolution from DMGR and from nodes.
I have use the next links several times:
Slow performance or hang in HostName lookup
www-01.ibm.com/support/docview.wss?rs=18... Hang/slowness in WebSphere Application Server Administrative console
www-01.ibm.com/support/docview.wss?uid=s... Finally if you have security enabled and is with some LDAP, is communication over SSL?
Slow Logon to Admin Console after implementing federated repository
www.websphereusergroup.org/go/thread/vie... Hope this helps.
regards