I have two sites connected by 256K leased line, each site has a cisco 2620 router connecting to PABX with 2 E&M module to fufill voip. The voip function good. but I find a strange issue, I call from one site to another through voip, the conversatio...

I have two site with cisco 2620 router & leased line connected. the function of voip through E&M module attached to PABX on each site. When I dial another site through voip, the phone call only keep ten minutes and dropped constrainedly. I check the...