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What is a trunk or line?

Viewing 6 posts - 16 through 21 (of 21 total)
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  • #32754

    In the USA the difference between a “line” and a “trunk” is basically this.
    A line is what you receive dial tone over when you pick up the receiver of your home phone. A line also has a unique number assigned to it so people can call you.

    A trunk is generally refferred to as an “inter-office” connection, that is telephone switch to telephone switch. Their is no unique number assigned or published, it can not be dialed or accessed in the normal sense and it is not dedicated generally to one subscriber.
    It can be shared by the “lines” to make a connection from one switch to another.

    Erlangs can be described as a unit or finite amount, for example 1 erlang may equal 1 hour of telephone traffic.
    If you have 10 lines, you can´t put 10 erlangs of traffic on them because call setup time, busies, abandons, etc would only allow for example 9.6 erlangs mathmatically.
    If you have 10 trunks you may put 9.8 erlangs of traffic because a trunk is controlled by the switching system computers, not a person with the phone in their hand thereby making the trunk more efficient.

    The various references to erlang b, erlang c, etc. refers to the type of calling attempts you expect on the line/trunk(s). Erlang b allows for better utilization because it assumes a % of the callers will retry their calls if not successful, the normal erlang chart does not assume retries.

    Hope this long winded explanation helped.. Ben B.

    Jade Clayton

    A Trunk……….
    In TDM technology a 64kbps DSO (one voice call). To telephone companies, all POTS lines are considered trunks, even ones that terminate to end user telephone sets. They assume all lines are trunks because they do not know what the user has connected on the other end (i.e. multiline telephones or key systems).
    To telephone/telecom/networking gear equipment manufacturers, a trunk is a connection resource between switches that can be utilized by any end user station, or network appliance. So in this aspect, a trunk could be a DS0 between central office switches or a PBX. It could also be a Gigabit Ethernet connection between two Ethernet switches, where they are referred to as VLAN trunks.

    In mobile wireless it is a little more complicated because you add codecs into the equation, and in many networks it also adds VoIP into the equation as well. So, your trunks then become G.711 (which is a packetized form of the TDM DS0 at 64kbps) or G.729, (which is 8kbps). For the VoIP part, packet header overhead needs to be added, which makes a G.711 packet voice stream (or packet voice Trunk) require 80kbps for G.711 and 12kbps for G.729. Though in the voice world G.729 is generally used, the IP Telephony manufacturers are now making their gear G.729 compatable as well.

    Ben’s explanation of how Erlangs fit into this was well done.

    Jade Clayton
    Author: McGraw-Hill Illustrated Telecom Dictionary


    I would also add to Ben’s comments is that on a line Erlang C is used to engineer lines. Here the caller waits until served withDial Tone.

    lovekesh mehta

    How is Erlang is calculated online in a GSM Switch?

    Ben B.

    GSM uses the same methods of calculating traffic as other telecomms networks however since the duration of the time used in in milli – erlangs ( 1000th of an erlang ).

    Richard Arcadi

    To Iovekesh mehta:

    The online Erlang calculation of a GSM switch (can be any other like Siemens EWSD 13 or 15)is performed
    by a simple algorithm:

    A counter/timer is assigned for every trunk group processor (or equivalent at any switch). This counter/timer adds every seizure time (conversation+signalling) and report the utilization ration within a period of 60 seconds, resetting after this.

    At the core processor, and reporting to the management system, an utility program add every reported time and divides it by the full available time across all line-trunk groups enabled at the switch. It’s an useful reference for ‘real time’ load at the switching matrix.

Viewing 6 posts - 16 through 21 (of 21 total)
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