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Technical Information on ProbeView and PVProxy

The ProbeView iPhone application uses ICMP pings (echo/response messages) and TCP port probes to test a user-defined set of locations, called 'targets'.   After a refresh, the overall state of the set of targets is displayed as well as detailed information for each target.

ProbeView Behavior

Basic (non-extended) ProbeView tests four types of targets: pings and TCP probes in both non-proxied and proxied mode.  It attempts to test every target as quickly as it can and returns results as the responses come in.

ProbeView can operate using either LTE/4G/3G or WiFi, but what is visible can change significantly based on the current connection.  Private (local network) servers and sites visible while using WiFi are not usually visible from the open internet under 4G because they lack unique, public IP addresses (see 'proxy' information below).  Both types of connection rely only on DNS information or IP addresses; neither Apple's Bonjour service nor Windows' NetBIOS/WINS services are used.

Groups of defined targets can be saved under user-given names.  It is common, for example, to have a set for use "at home" and another "away from home".  The primary difference is how local (non-public IP addresses) are treated. 

Non-Proxied Targets

By default, targets do not use proxies.  The two normal test types use standard TCP/IP protocols on whatever carrier the iPhone is using at the time (LTE, 4G or WiFi).  Unproxied targets, therefore, must either be known to your DNS server or defined by IPv4 address.  If a hostname cannot be resolved ProbeView will return that error.

A note of warning.  Some ISPs, including Comcast, are rerouting invalid (unknown) hostnames to special websites that claim to be help pages but in reality are advertising "pushers".  If you misspell a hostname in this situation, the host will erroneously appear to be available.  To test whether this applies to you, start your browser and type in a random string of characters (e.g. and see if you get a full-blown web page with spelling recommendations or a simple "domain name not found" error.  If the former appears, you may be able to disable this service by accessing your account details at your ISP's web site.

Users can set the number of retries and the timeout value for each attempt.

Proxied Targets

Using PVProxy, ProbeView can test targets behind firewalls (in private networks) using either of the two standard tests.  PVProxy is a simple web server running on a machine internal to the firewall.  A router 'pinhole' or port-forwarding rule usually needs to be set up to route HTTP requests on the chosen proxy port to the machine running PVProxy.

From the iPhone user's point of view, the only difference between a proxied and a non-proxied target is the need to specify the proxy.  ProbeView has pages that allow defining, choosing and testing proxies.

ProbeView handles proxied targets by sending a URL to the proxy server and receiving a reply.  Because timeout and retry characteristics for web site interaction are set by the iPhone itself and the 3G network, retry and timeout settings in ProbeView do not apply to proxied targets.

Evaluation Logic

ProbeView is designed to give you network status 'at a glance'.  A primary 'network condition' indicator button in the upper left-hand corner of the main page of ProbeView shows the status of the overall set.  This determination is based on characteristics you set for each of your targets.

Every target has two logic settings: 'ignore' and 'vital'.  If the target is marked as 'ignore', no test is performed.  This is typically used when the user knows in advance that a target is temporarily unavailable for some reason.  Targets are set as 'not ignored' by default.

Targets are marked 'vital' by default.  If a vital target is 'down' (unresponsive) during a refresh, the overall target set test is considered to have failed.

In other words, the overall state of the target set is considered 'successful' if no vital, non-ignored target is down.

In addition, tapping the network condition button shows a list containing every target, ordered by importance; that is, vital targets that failed are shown first.

How ProbeView and PVProxy Interact

If a target is proxied, ProbeView constructs a special URL with a set of query terms specifying the host, port and type of test to perform.  This URL is sent to the specified proxy and port, which performs the test as indicated and returns the result, packaged as a small XML document.

This type of interaction is based on the REST model.  The returned XML packet contains tags and attributes representing the target tested, the type of test performed, the status of the test, the round-trip time and an error message from the proxy.  For more details, download the document "Extending PVProxy".

ProbeView, PVProxy and PingView

Once you have PVProxy running on your server, you can test network connections from anywhere, even if they are behind firewalls.  You can also run the free PingView application on the server.  This program performs network testing in a manner similar to the ProbeView iPhone app.  More importantly, it is able to store and forward copies of its status information to other PingView applications or PVProxy.  The full version of ProbeView allows you to view this information.  For more information, see "Understanding Collection Storage".

Proxy Extensions

Because the interaction between ProbeView and a proxy is so simple, it is easy to extend the system to incorporate a wider variety of tests.  A 'proxy extension' is a small piece of code that is loaded into PVProxy and activated when the test type is something other than 'ping' or 'TCP open/close'.   Please see the page on Proxy Extensions for more information.

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