描述：
老大打算踢掉我的工作，让我找个能代替sip协议的开源程序。分两步走，第一步先找适合的java版本的sip server端程序；第二部用java重新开发原来的sip协议程序。
选型要求(2020)：
1.需要还在维护中,不能是那种已经不维护的。
2.使用范围广，用的人多的。
3.java开发的。
备选：
1.opensips:
git地址：https://github.com/OpenSIPS/opensips
官网：https://opensips.org/
提供能力：
OpenSIPS has to offer many important and interesting features. To mention some of the most important ones:
- SIP registrar server
- SIP router / proxy (lcr, dynamic routing, dialplan features)
- SIP redirect server
- SIP presence agent
- SIP back-to-back User Agent
- SIP IM server (chat and end-2-end IM)
- SIP to SMS gateway (bidirectional)
- SIP to XMPP gateway for presence and IM (bidirectional)
- SIP load-balancer or dispatcher
- SIP front end for gateways/asterisk
- SIP NAT traversal unit
- SIP application server
看了下，文档清晰，功能貌似强度，可惜是C开发的，只能放弃。
2.openims:
这个系统写的挺好的，不过已经不维护了。只能放弃，这个是java开发的，
基于java1.7。
http://openimscore.sourceforge.net/
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3.Asterisk
https://www.asterisk.org/
这是是顶顶大名了，非常专业，就是入手难度有点高，以下为他的功能列表。这个也是C语言开发的。
- Secure RTP (SRTP)
- IPv6 Support for SIP
- Connected Party Identification Support - COLP and CONP.
- Calendaring Integration for CalDAV, iCal, Exchange or EWS calendars
- A new call logging system, Channel Event Logging (CEL)
- Distributed Device State, including Message Waiting Indicator using Jabber/XMPP PubSub
- Call Completion Supplementary Services (CCSS) Support, including Call Completion on Busy Subscriber (CCBS) and Call Completion on No Response (CCNR)
- Advice of Charge, including AOC-S, AOC-D, and AOC-E Support
- Multicast RTP
- ISDN Q.SIG Call Rerouting and Call Deflection
- Google Talk and Google Voice integration
- Audio Pitch Shifting (for fun and profit)
4.clearwater
https://www.metaswitch.com/products/core-network/clearwater-ims-core
这个功能做的很全，不过没找到源码，应该是商业的。
