casbs@csli.stanford.edu (Lynn Gale) (02/28/90)
Is it known at this point in time what medium ISDN will run on? In particular, what number of wire pairs are necessary and do they need to be shielded or unshielded? (Thinking about wiring decisions with the future in mind...) If it takes, say, 4 pairs, what function(s) do each of the pairs perform? Will ISDN incorporate Fax functions? RS-232? What else besides voice? Thanks in advance. Lynn casbs@csli.stanford.edu x3.a37@stanford.bitnet
goldstein@carafe.enet.dec.com (Fred R. Goldstein) (03/01/90)
In article <4459@accuvax.nwu.edu>, casbs@csli.stanford.edu (Lynn Gale) writes... >Is it known at this point in time what medium ISDN will run on? In >particular, what number of wire pairs are necessary and do they need >to be shielded or unshielded? (Thinking about wiring decisions with >the future in mind...) The ISDN Basic Rate ("2B+D") interface at Reference Point U (Network Interface, in the US) is 2-wires, copper. At Reference Points S and T (intended for inside wiring), it's 4-wire copper. The two pairs are send and receive (balanced). Unshielded twisted pair is all you need. NOT quad, and no need to use fancy shielded wire. The Primary Rate Interface ("23B+D") is based on good old fashioned T1 (North America/Japan) and E1 (rest of Earth). That runs on two twisted pairs too. >Will ISDN incorporate Fax functions? RS-232? What else besides >voice? ISDN ships bits. It allows the bits to be handled raw (64 kbps circuit switched, and some multiples of that), or as X.25 packets, or as digitized voice (A-law and mu-law, with conversion as appropriate). FAX may be supported over the 64 kbps service, for which Group 4 was designed, although Group 3 can also use it. RS-232 is a physical layer not part of ISDN, though you can certainly have a Terminal Adapter (ISDNese for "modem function") that has RS-232 on one side and ISDN on the other. Essentially you can do with the 64 kbps as your imagination allows. Fred R. Goldstein goldstein@carafe.enet.dec.com or goldstein@delni.enet.dec.com voice: +1 508 486 7388
zweig@cs.uiuc.edu (Johnny Zweig) (03/01/90)
casbs@csli.stanford.edu (Lynn Gale) writes: >Will ISDN incorporate Fax functions? RS-232? What else besides voice? ISDN is lower level than Fax -- it's higher level than rs-232; think of it about the level of complexity of ethernet. Basically a way of moving bits. Fax will certainly be one of the first available applications since that involves moving many bits quickly. >Is it known at this point in time what medium ISDN will run on? In >particular, what number of wire pairs are necessary and do they need >to be shielded or unshielded? (Thinking about wiring decisions with >the future in mind...) >If it takes, say, 4 pairs, what function(s) do each of the pairs >perform? It's complicated. There are a couple of "reference points" which serve different points of your house/business. At the U-reference point which is where the phone-company's wires/fibers/whatever come into the building there are standards for 2- and 4-wires and for fiber (the 2-wire one would be most common for ISDN to your house since most houses only have one twisted pair in). At the S- and T-reference points, there are 4 wires used for balanced data transmission in each direction, with a dc-imbalance between the average voltages in each direction, so you can tap the centers of the send and receive transformers to get DC to power the equipment == extremely hip. Unshielded twisted pair pairs (i.e. ordinary telco 4-color cable) should be hip for that, at least according to this book I have. Johnny -- not-an-Electrical-Engineer-but-I-play-one-on-the-Net
tjrob@ihlpl.att.com (Thomas J Roberts) (03/01/90)
From article <4459@accuvax.nwu.edu>, by casbs@csli.stanford.edu (Lynn Gale): > Is it known at this point in time what medium ISDN will run on? In > particular, what number of wire pairs are necessary and do they need > to be shielded or unshielded? (Thinking about wiring decisions with > the future in mind...) ISDN is considerably more complicated than traditional analog phone service. This is reflected in its wiring. The following describes wiring for the ISDN Basic Rate Interface, which carries 2 Bearer (64 kb/s) and one Delta (16 kb/s signaling) channels (i.e. it can carry 2 simultaneous voice or data calls and up to 15 packet data calls aggregating 16 kilobits per second). This is the ISDN equivalent to the analog loop. Between the telco office and the subscriber's location, the U interface carries bidirectional digital data on 1 (unshielded) twisted pair. If no loading coils are present, existing wires can be used. Most Central Office switches can support the U interface up to 20,000 - 25,000 cable feet without repeaters (various equipments can be used to extend this, I don't know the details). Within the subscriber's building, the NT1 unit converts the 1-pair U interface into the (unshielded) 2-pair S interface, which carries unidirectional digital data on each pair. Most NT1s can support up to about 1000 cable feet. Note that because the S interface has very little protection (e.g. lightning), it is unsuitable to use between buildings. Unlike traditional analog service, ISDN cannot provide power to the station set (or the NT1) over the same wiring as the signaling and data. Most AT&T installations use 4-pair wiring within the building, with 2 pairs carrying the S interface signaling, 1 pair carrying power to the station set, and 1 pair is spare. In a typical (large office building) installation, on each floor a wiring closet is used to hold the NT1s and battery-supported power supplies for the NT1s and the station sets on the floor. The ISDN set uses a larger modular plug than traditional analog sets (it needs 4 pairs, not just 2 pairs). If you wire the building using 4 pairs between the wiring closet(s) and the station set locations, and use the larger modular jacks, you can still plug in the smaller analog plugs, using the middle two pairs (that is, the 2-pair plug will physically connect to the 4-pair jack, but will only connect to 2 of the pairs). When (if) you convert to ISDN, you will then only need to rewire the wiring closet(s), not the individual station wiring. I don't know part numbers for the various connectors. Tom Roberts AT&T Bell Laboratories att!ihlpl!tjrob
jason@cnd.hp.com (Jason Zions) (03/03/90)
Okay, so a B channel is raw 64kb/s. Is there any way to signal, end-to-end, the higher-level meaning imposed on those bits? For example, if I attach a Fax machine to an ISDN line and place a call, can the receiving end get some indication on the D channel that the incoming call is facsimile? If I place a call through ISDN, I understand that the dialing information goes across the D channel to do call setup and all that other junk. Is it possible to send other setup information end-to-end through D channel? The idea would be that the 2B+D line gets plugged into a really smart box. When a call comes in, the smart box knows what data is about to come in on the B channel; fax, voice, data, slow video, etc. It then connect the B channel to the appropriate device (if present) or rejects the call (if there's no such device present). Jazz