[VoiceOps] GLBX soft switch
abalashov at evaristesys.com
Wed Aug 5 02:33:01 EDT 2009
Ric Messier wrote:
> Good question. I did mean IP PBX SIP connect trunking. I'd normally think of
> carrier to carrier as transport or something similar rather than trunking.
SIP trunking simply refers to a static arrangement of IP endpoints for
the purpose of setting up multiple sessions between them in order to
pass traffic. It can either be access (for a customer) or traffic of an
intra-industrial nature, such as private SIP peering between carriers or
Also, the endpoints of a trunk need to be network elements related to
service delivery rather than end-user handsets, ATAs and similar devices
designed for end-user access. Client-side equipment designed for
further switching - most notably, a PBX - qualifies under that
definition, insofar as a PBX is a micro-switch of sorts, but anything
that would be typically attached to that PBX as an extension does not.
Like many terms imported into VoIP from the TDM world by marketing
departments, the term "trunking" is neither precise nor astute. The
essence of its original meaning, which draws on key pieces of
electromechanical, digital and analog telephony history and heritage, is
lost when marshaled in a VoIP context. "Trunks" make most sense when
applied to physically distinctive bundles of circuitry intended to move
traffic in between distribution nodes in an intensely hierarchical
topology; most classically, the distribution nodes are central
offices/telephone exchanges containing some sort of switch, but more
recently, premise-based "miniature" switches like PBXs, which have the
distinction of "internal" lines (to handsets) versus "outside lines"
used for PSTN access, too.
"SIP trunking" is really no better than "virtual PRI" in this respect.
It's a transplanted figment of marketing imagination that otherwise
lacks conceptual integrity from an engineering perspective - in my
opinion, at least. Although, I suppose the notion of a VoIP "line"
really takes the cake. Even a SIP "channel" is really pushing it; SIP
does not establish "channels," it establishes sessions. Aside from
certain logical configuration parameters (network and transport-layer
reachability information) on equipment, there is no kind of intrinsic
"container" in which those sessions participate, so there's nothing to
"channelise" as with a T1 electrical or ISDN link-layer synchronous
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