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In my experience, ASA works very well with the UC500. I am not even any special settings worked, and everything works OK.<br />
In any case, you can turn off the firewall and NAT in UC500
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In my experience, ASA works very well with the UC500. I am not even any special settings worked, and everything works OK.
In any case, you can turn off the firewall and NAT in UC500

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We have an ASA 5520 in place as firewall/rotuer/vpn. We will be adding a Cisco UC520 to our network. I am new ot the UC520 and VOIP . <br />
Can the UC520 stay behind the ASA and still use a SIP gateway service. Does that create issues down the road. I know the UC520 also has firewall/vpn/routing , but not sure if that is going to cause issues. <br />
What had to be done on the ASA and also the UC520 for them to work on the network? 
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We have an ASA 5520 in place as firewall/rotuer/vpn. We will be adding a Cisco UC520 to our network. I am new ot the UC520 and VOIP . 
Can the UC520 stay behind the ASA and still use a SIP gateway service. Does that create issues down the road. I know the UC520 also has firewall/vpn/routing , but not sure if that is going to cause issues. 
What had to be done on the ASA and also the UC520 for them to work on the network? 

Cisco UC520 phone system  Behind ASA firewall.

Voice over IP (VoIP) is a methodology and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. Other terms commonly associated with VoIP are IP telephony, Internet telephony, broadband telephony, and broadband phone service. The term specifically refers to the provisioning of communications services (voice, fax, SMS, voice-messaging) over the public Internet, rather than via the public switched telephone network (PSTN).  Examples of the VoIP protocols are H.323, Media Gateway Control Protocol (MGCP), Session Initiation Protocol (SIP), H.248 (also known as Media Gateway Control (Megaco)), Real-time Transport Protocol (RTP), Real-time Transport Control Protocol (RTCP), Secure Real-time Transport Protocol (SRTP), Session Description Protocol (SDP), and Inter-Asterisk eXchange (IAX).

Voice Over IP

Cisco PIX is a dedicated hardware firewall appliance; the Cisco Adaptive Security Appliance (ASA) is a firewall and anti-malware security appliance that provides unified threat management and protection the PIX does not. Other Cisco devices and systems include routers, switches, storage networking, wireless and the software and hardware for PIX Firewall Manager (PFM), PIX Device Manager (PDM) and Adaptive Security Device Manager (ASDM).

Cisco

IP telephony (Internet Protocol telephony) is a general term for the technologies that use the Internet Protocol's packet-switched connections to exchange voice, fax, and other forms of information that have traditionally been carried over the dedicated circuit-switched connections of the public switched telephone network (PSTN). Using the Internet, calls travel as packets of data on shared lines, avoiding the tolls of the PSTN. The challenge in IP telephony is to deliver the voice, fax, or video packets in a dependable flow to the user.