Category: Technical Posts

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Analyzing SIP and SIP calls 

This blog article will be dedicated to SIP and SIP calls. It is meant to provide an introduction for UC Engineers to the main headers and guide through the debugging of the most popular call scenarios that will be described in the next articles.

As we have seen in SIP and XMPP standards in Unified Communications and Media transfer in Unified Communications – SDP protocol, SIP (Session Initiation Protocol) and SDP-RTP have become the de facto replacement mode for traditional analog and digital lines provided by operators all over the world.

SIP is also the most popular signaling mode to handle VoIP calls.

Being able to understand SIP sessions has become for a Unified Communication Engineer as important as in the past for Telephony Experts to read signaling traces in Q.931 / Q.921 / DS1 / QSIG generated by T1 / E1 PRI – BRI ISDN lines.

Before Starting the Analysis

Continue reading “Analyzing SIP and SIP calls “

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RTP, RTCP and Jitter Buffer

jitter bufferIn this blog article we continue to analyze RTP and RTCP and we will see why Jitter Buffer is important and how it affects call quality.

As we saw in the previous article — SDP is not able to transfer media–this task is delegated to protocols such as RTP or RTSP.

RTCP (or Real Time Control Protocol) provides different levels of feedback about the ongoing RTP Stream.

The goal of RTCP is to provide information to the remote endpoint about the quality of service of the ongoing communication.

This is done by providing regular statistics about the amount of packets received, jitter, and packets lost (either via network or discarded by the jitter buffer). Continue reading “RTP, RTCP and Jitter Buffer”

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Media transfer in Unified Communications – SDP protocol

SDP-protocolMedia is another vital component of a Unified Communication system. Once signaling is in place and working between two endpoints, information about media capabilities can be transferred, eventually allowing for streaming audio, making video calls, or exchanging other information.

In this blog article we will analyze what technologies are used to transfer information about available media between endpoints.

SDP

SDP (Session Description Protocol) is a format for describing streaming media initialization parameters standardized by IETF in 1998.

What follows is the Session Description fields usage and an example:

Continue reading “Media transfer in Unified Communications – SDP protocol”

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Introducing BOSH and WebSocket Transport protocols

BOSH and WebSocket protocolsThis time we will talk about transport protocols over the web, in particular, about BOSH and WebSocket.

Besides TCP (XMPP/SIP) and UDP (SIP only) transports, two other transports, BOSH and WebSocket, are available which are embedded inside existing TCP/HTTP stacks.

BOSH

Bidirectional-streams Over Synchronous HTTP (BOSH) allows real-time communication between a browser and a web server. The browser connects to the server and will keep the connection open as long as it has no data to send. When data is available, the server sends it over the open HTTP connection and closes the connection itself. This reduces the number of requests, as the browser is not continuously polling the server. The server retains a cache of events that the client missed between reconnections.

Continue reading “Introducing BOSH and WebSocket Transport protocols”

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Slow your Roll

Slow your Roll
This is a phrase that we’re all familiar in the US. It means to slow down, relax or calm down. It means to think about things before you let your enthusiasm lead you too quickly down a path that can cause more harm than good. As a VAR, MSP, System Integrator or an ISP, we know that in the world of software updates this can simply mean… don’t blindly upgrade all systems at once. No matter how many developers there are or how many tests a company performs, new software releases can have issues that need to be addressed after the release. Perhaps it’s better to roll the software out in a controlled, planned and well thought out fashion. Continue reading “Slow your Roll”

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