澳大利亚签证155是什么？
澳洲入境签证有3种，分别为676、600和155. 676和600是临时进入许可，一般给短期访问者，比如去澳洲参加教育活动的，或者探亲访友的；而155是给永久居民的延期居留签。持有该签证的人，已经取得了澳洲永居身份，只是现在不在澳洲境内，需要在一定时间之内回到澳洲，并且定居在这里。
在移民局网站上查到“155签证”的内容如下：
What does the visa allow？
The permanent residency (PR) visa allows you to live and work in Australia permanently， unless you are a citizen of Iran because this country is subject to special visa conditions. You can travel in and out of Australia as much as you like but if you leave it for more than two years you'll lose your PR rights while overseas. If you go abroad on business or official government business then there will be no time limit when returning. The main condition of holding an Australian PR is that you must hold a passport from another country and return home frequently enough. This means that although you may own property and have bank accounts in Australia， these cannot benefit anyone else such as members of your family who are not citizens of other countries. There is also a requirement that at least one parent should be an Australian Permanent Resident， Citizen or British Subject before birth. Children born outside Australia do not automatically become Australian citizens by virtue of birth alone. They need to apply for Australian Citizenship after reaching the age of 18 if they want this status. Please visit our citizenship page for further information about how this process works. Also see below the list of exceptions under Iranian nationality to understand why their visas are treated differently with regard to travel restrictions。
When applying for a Visa， which one shall I choose？ Do I need both？
You need either a '155' PR or a '157A' Provisional PR to come into Australia. A provisional PR gives the same rights and privileges as a full PR apart from being able to work， vote or study without restriction until three months before the end of five year validity period whereupon you would normally apply for a full PR. It also costs less money than a full PR and so if you intend to stay only for up to two years then you could save yourself thousands of dollars by doing this. When coming into the country on a temporary entry permit（6个月），