Telos Zephyr Xstream User Manual page 369

USER'S MANUAL
Packet Switching Packet Switched networks are more commonly associated with Computers,
Local Area Networks, and the Internet. In a packet switched network the raw stream of data is
broken into individual pieces, called packets. Each packet is routed through the data network,
individually. This is somewhat analogous to taking the pages of a book and sending each page as
a letter through the postal system. The page numbers would allow reassembly of the book no
matter what order the pages were received at the far end. The end user does not know or care
that the packets may travel a variety of routes. If a given page did not arrive in a reasonable
length of time, one could request that this page be re‐ sent. Most packet switched systems allow
packets to be discarded if the network capacity is exceeded (the postal system is not supposed
to do this). This is accommodated by the higher‐ level protocol, which knows to request that a
packet be re‐ sent if it does not arrive. Therefore, the typical behavior of a packet switched
network when overloaded is that throughput decreases (i.e. the network "slows down") as the
percentage of discarded packets increases. In stark contrast to Circuit Switched networks. See
Circuit Switching.
PBX‐ Private Branch Exchange A privately owned switch. Basically, a PBX is a private "business"
telephone system which also interfaces to the telephone network. In some circles 'PBX' implies a
manual switchboard whereas 'PABX' (Private Automatic branch exchange) implies a PBX that
supports dialing by end users. Many PBX's can now offer ISDN BRI service, usually over the S
Interface. A few vendors are now offering BRI over the U interface as well. PRI over DSX‐ 1/T1 or
E1 is also offered in some cases. Be wary of these ISDN protocols since they have not been as
well tested as the versions running on "public" switches. They may or may not work with a given
piece of CPE.
PIC‐ Primary Interexchange Carrier (USA) This is your default "1+" carrier used for interLATA
calls. In some areas you may have two PICs, one for interLATA calls, and one for intraLATA long
distance calls (in which case it stands for Primary Intraexchange Carrier). In some areas
intraLATA long distance calls are still handled by your RBOC, in others you now have a choice.
You may be able to discover who you current PIC is by dialing 700 555‐ 4141.
PMP (USA) AT&T "Custom Point to Multi‐ Point" Custom ISDN Protocol. Not supported by the
Zephyr or ZephyrExpress. See Custom ISDN and ISDN Protocol.
POP ‐ Point Of Presence The local facility where your IEC maintains a switch. This is where your
long distance calls get routed so that your IEC can handle them. Also used to describe the local
access point of an Internet Service Provider.
Port This is a pretty general term. Newton's Telecom Dictionary 10th edition defines a port as
"An entrance to or an exit from a network". Many phone equipment vendors refer to ports as
the physical interface between a Switch and a Line or Trunk. Product literature often refers to
the number of ports on a phone system. In this context it refers to the number of phones or
lines (or sometimes the combination) the system supports.
POT‐ Plain Old Telephone A black, rotary‐ dial desk phone. Usually a Western Electric model
500 set. Outdated term.
POTS – Plain Old Telephone Service Regular old‐ fashioned analog loop start phone service.
PRI ISDN
Appendix 10 – Glossary 357