|
SIP differs from most other Internet protocols in that it carries absolute IP addresses
rather than relying on the lower layers to comunicate current addresses. Consequently, SIP traffic cannot traverse a
standard router or any other device that is performing Network Address Translation (NAT)
without special treatment WITHIN that device to adjust between internal and external IP addresses..
In the context of residential and
small business networks this incompatibility with NATed devices causes SIP devices to be
configured in the no-man's-land between the modem and the router. There are two variations
of this configuration; (1) using a dedicated IP address, usually with cost penalties, or
(2) intercepting Ethernet traffic to syphon off and inject SIP traffic while letting other
traffic pass through, as shown in the diagram above.
Configuring SIP equipment
outside the local area network introduces two management challenges. Most obviously, the
SIP device is itself difficult to monitor and manage in any meaningfull way other than by
making simple deductions by pinging. Perhaps less obvious, prior to deployment, are the
consequences of introducing another in-line component. Every time that there is a problem
in the local area network suspicion will fall on the SIP device.
The Gatespace solution is to address the underlying problem by providing special treatment
for SIP traffic in the Gateway (router) and moving SIP devices inside the local area network as shown below.
This moves the SIP devices out of the critical path while making it manageable in the same
way as all other devices in the residential/small business network.
The SIP Proxy residing in the gateway (CPE) examines all SIP traffic for IP
addresses and converts between external and internal IP addresses. 
The gateway SIP Proxy supports all styles of SIP device/end-point:
- Asynchronous Telephone Adapter (ATA)
- Free standing telephones
- Softphones
|
