[单选] Sun Stable is a global insurance company with headquarters located in Houston, Texas. The campus there is made up of a number of office buildings located within the same vicinity. In 2003, a new building, Building 331B was added. The additional building houses approximately 1000 employees. Rather than deploy a private branch exchange (PBX) in the new building, Sun Stable has decided to implement an IP telephony solution. External calls will be carried across a MAN link to another building, where a gateway connects into the worldwide PBX network of Sun Stable. Voice mail and unified messaging components are required and all IP phones and workstations should be on separate VLANs and IP subnets.Which IP telephony deployment best suits their need?（）

简述校风对儿童心理发展的影响。 水表必须在符合（）要求的装置上检定 原理。 规程。 数据。 条件。 以下事故类别属于按伤亡事故原因分类的有（） 电气。 物体打击。 不懂操作技术。 冒顶片帮。 中毒和窒息。 证券投资按投资目的分为股票投资、债券投资和基金投资。 水如何影响非水相中酶的特性：（）、（）、（）、（），（）。 Sun Stable is a global insurance company with headquarters located in Houston, Texas. The campus there is made up of a number of office buildings located within the same vicinity. In 2003, a new building, Building 331B was added. The additional building houses approximately 1000 employees. Rather than deploy a private branch exchange (PBX) in the new building, Sun Stable has decided to implement an IP telephony solution. External calls will be carried across a MAN link to another building, where a gateway connects into the worldwide PBX network of Sun Stable. Voice mail and unified messaging components are required and all IP phones and workstations should be on separate VLANs and IP subnets.Which IP telephony deployment best suits their need?（）