AEQ
PHOENIX MERCURY
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ANNEXE C: Protocols associated with communications over IP networks.
Communication over IP networks differs notably from the communications traditionally used to
date in broadcast environments, whether they are POTS or ISDN, in that IP networks do not
have dedicated resources or qualities of service implemented in most systems, with the
associated problems this involves in terms of communication signaling, establishment,
maintenance and cleardown.
This set of problems originates in the technical characteristics that are intrinsic to the definition
and operation of communications systems based on IP protocols. The EBU-TECH 3326
standard developed by the N/ACIP working group provides certain tools for attempting to
simplify work by making use of many protocols associated with IP communication, and which
will be described below.
N/ACIP
•
Signaling, understood as connection initiating and finalizing procedures, as well as
negotiation of connection parameters (encoding algorithms, ports, etc.)
o
SDP (Session Description Protocol) to describe the parameters of the
connection
o
SAP (Session Announcement Protocol) for multicast type unidirectional links
o
SIP (Session Initiation Protocol) simulates the working system in traditional
telephone networks
•
Transport: defines the transport protocols over IP networks
o
RTP (Real-Time Transport Protocol) over UDP and IPv4
o
RTCP (Real-Time Control Transport Protocol) for synchronization and active
retrieval functions
o
IP ports defined:
5004 (RTP) and 5005 (RTCP)
While this appendix is not intended to be a reference document for all the relevant technical
matters, it should at least serve to give its readers an initial contact with these subjects that will
ease the assimilation of the new working method over IP networks for the PHOENIX MERCURY
user and, as a result, the use of this equipment. The user interested in expanding his or her
knowledge of some or all of these subjects is encouraged to turn to the extensive, excellent
technical material currently available regarding the IP realm and the technologies associated
with it.
C1. Circuit switching versus packet switching.
The communications systems traditionally used in the broadcast environment for applications
with portable codecs have been mostly telephone or ISDN networks—that is, circuit switching
networks; PHOENIX STUDIO, on the other hand, uses a packet switching network in its IP
interface.
C1.1. Circuit switching.
In a circuit switching network, the switching equipment must establish a physical path between
the communication media prior to the connection between users. This path remains active
during the communication between the users, and is cleared down or released when the
communication ends. Example: Switched telephone network.
Its operation passes through the following stages: request, establishment, file transfer and
connection cleardown.
C1.1.1. Advantages:
•
The transmission is made in real time.
•
Dedicated resources. The nodes that are involved in the communication use the
established circuit exclusively as long as the session lasts.
•
Once the circuit has been established, the parties can communicate with each other at
the highest speed that the medium allows, without having to share the bandwidth nor
the use time.
