DDS and T1 (Where are the differences?)
Hugo Zambrano
HI,
May somebody out there tell me what are the tecnical differences
between DDS and T1 transmitions.
They both are digital comunication, they both use 4-wires, they both
need DSU/CSUs, so why DDS can only do 56 Kpbs and T1 1.544 Mbps?
How a single T1 line from one side of the cloud can communicate with
diferent lines (DDS or T1) in the other side of the cloud. I must
missing a concept here.
"The encyclopedia of networking" tells me that T1 uses D4 or ESF
frames, but It does not tell me what encoding DDS uses.
IF you know about a book that can answer this and similar question I
would apreciate you let me know. Hopefully it won't be too expensive.
May I ask for something else? What kind of framming or encoding ISD
uses. I know they could be 2B+D or 23B+D. It seems that they could be
use to transmit with differen channels other than 2 or 23. Let's say
16 19.2Kbps channes.
Cliff Liles
hzam...@synapse.net (Hugo Zambrano) wrote:
>HI,
> May somebody out there tell me what are the tecnical differences
>between DDS and T1 transmitions.
> They both are digital comunication, they both use 4-wires, they both
>need DSU/CSUs, so why DDS can only do 56 Kpbs and T1 1.544 Mbps?
Because they were designed to different things. DDS was a specific
service designed to run in the DS0 rate range (56/64 Kbps) T1 was
designed to carry the traffic from 24 DS0s (including DDS) in a
multiplexed format.
> How a single T1 line from one side of the cloud can communicate with
>diferent lines (DDS or T1) in the other side of the cloud. I must
>missing a concept here.
The transport network is composed of many types of devices. One is a
"Channel Bank" or time division multiplexor which combines 24 voice or
56/64 kbps data channels into a single T1. These devices can combine
the DDS signal and others into the T1 that can be transported across
the network and delivered by a T1 (as a fractional T1 segment) at
another location.
There is another important device in this scheme. It is a Digital
Cross Connect System (the term DACS is an AT&T Trademark for this
generic type of device). This device will allow channels from T1s to
be "cross connected" into others. These have a large number of T1
ports, and any channel in any T1 can end up in any other T1. This
allows the telco to conveniently map single channels (or channel
groups) across the network.
> "The encyclopedia of networking" tells me that T1 uses D4 or ESF
>frames, but It does not tell me what encoding DDS uses.
There isn't a similar frame overhead on DDS unless it is carrying or
multiplexing slower channels (DS0A or DS0B formats).
> IF you know about a book that can answer this and similar question I
>would apreciate you let me know. Hopefully it won't be too expensive.
Try "Digital Telephony and Network Integration" By Bernhard Keiser
and Eugene Strange ISBN 0-442-00901-1 (~$65)
> May I ask for something else? What kind of framming or encoding ISD
>uses. I know they could be 2B+D or 23B+D. It seems that they could be
>use to transmit with differen channels other than 2 or 23. Let's say
>16 19.2Kbps channes.
ISDN Basic Rate was designed to carry 2 dial up 64K channels and a 16K
signaling plus some overhead for maintenance etc. The same technology
has been proposed/used to provide alternate transport methods for a
variety of services including lower speed multiplexed lines. There is
a Belcore spec for that type of transport, but I don't remember the
number or name.
As far as Primary rate ISDN goes, it is an ESF T1, that has specific
designations for the channels and signaling messages. It goes through
a dial/switch, so the services are limited by the progrmming of the
switch as well as the Terminal Adapter at the customer's locaton. It
does have 384 Kbchannels defined, and I believe one other higher speed
channel. If you want to multiplex a bunch of lower speed signals
together, use an unswitched T1 service, not an ISDN primary rate
service.
CL
John Brothers
In article <51qa7b$diu$2...@piano.synapse.net>,
Hugo Zambrano <hzam...@synapse.net> wrote:
>HI,
> They both are digital comunication, they both use 4-wires, they both
>need DSU/CSUs, so why DDS can only do 56 Kpbs and T1 1.544 Mbps?
T1 requires more switch bandwidth than DDS. DDS can be stuck inside a DS0,
which makes it a lot cheaper for the telco to provide.
> How a single T1 line from one side of the cloud can communicate with
>diferent lines (DDS or T1) in the other side of the cloud. I must
>missing a concept here.
I don't think that you can intercommunicate between a T1 and a DDS line.
But I've been wrong before.
T1s intercommunicate with one other T1 'endpoint'. Those endpoints
are often routers, so the information can be sent on to a different
point-to-point T1 connection.
DDS lines are point-to-point as well. I suppose that the other end
of the DDS line could be a router, and it could intermix with T1 that
way.
> "The encyclopedia of networking" tells me that T1 uses D4 or ESF
>frames, but It does not tell me what encoding DDS uses.
I think it uses ESF. I haven't been down in the lab working with it
for a while, so I can't be sure.
> May I ask for something else? What kind of framing or encoding ISDN
>uses. I know they could be 2B+D or 23B+D. It seems that they could be
>use to transmit with differen channels other than 2 or 23. Let's say
>16 19.2Kbps channes.
ISDN basic-rate line cards are physically designed to send 2B+D. What
you do with that 2B is your own business - it could be split up into
several 19.2k channels if you have the right hardware and software. Of
course the other side of that connection would need to be using the
same configuration.
The same is true of primary rate I suppose.
John
--
John Brothers | Minds are just like parachutes. They...
!nortel.opinion | well, actually they're not at all like parachutes. *SPLAT*
Jim Sackman
In article <51qa7b$diu$2...@piano.synapse.net> hzam...@synapse.net (Hugo Zambrano) writes:
>Path: news.internetMCI.com!imci5!imci4!newsfeed.internetmci.com!in3.uu.net!ott.istar!istar.net!n3ott.istar!news.synapse.net!not-for-mail
>From: hzam...@synapse.net (Hugo Zambrano)
>Newsgroups: comp.dcom.telecom.tech
>Subject: DDS and T1 (Where are the differences?)
>Date: Thu, 19 Sep 1996 03:15:16 GMT
>Organization: Synapse Internet [www.synapse.net]
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>Message-ID: <51qa7b$diu$2...@piano.synapse.net>
>NNTP-Posting-Host: harp-06.synapse.net
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>HI,
> May somebody out there tell me what are the tecnical differences
>between DDS and T1 transmitions.
> They both are digital comunication, they both use 4-wires, they both
>need DSU/CSUs, so why DDS can only do 56 Kpbs and T1 1.544 Mbps?
> How a single T1 line from one side of the cloud can communicate with
>diferent lines (DDS or T1) in the other side of the cloud. I must
>missing a concept here.
> "The encyclopedia of networking" tells me that T1 uses D4 or ESF
>frames, but It does not tell me what encoding DDS uses.
> IF you know about a book that can answer this and similar question I
>would apreciate you let me know. Hopefully it won't be too expensive.
> May I ask for something else? What kind of framming or encoding ISD
>uses. I know they could be 2B+D or 23B+D. It seems that they could be
>use to transmit with differen channels other than 2 or 23. Let's say
>16 19.2Kbps channes.
There are many differences between DDS and T-1. At the physical level, T-1
extends to about 6000' without repeaters (3000' in some cases depending on how
you wish to do the loopbacks). DDS can go over 14000' without repeaters. In
both cases, the data is AMI encoded (yes, there is 0 suppression over the top
of the encoding). DDS is available in point to point or point, point to
network (Frame Relay), or multi-point arrangements. T-1 is point to point or
point to network (FT-1 is really point to network, unlike multi-drop DDS).
It is possible to provision a DS0 on a T-1 circuit as carrying many things
(voice, DDS, SW56, Frame Relay). The network (in this case) breaks apart the
T-1 into its 24 DS0s. One (or more) of these DS0s can be carried through the
network and terminated at the remote end in a channel bank with an OCU (Office
Channel Unit), thus providing DDS service.
There are in fact several versions of DDS. There is regular DDS which is
available in rates from 2.4K to 56K. There is also CC64 which allows for
clear 64K transport. There is also DDS-SC (Secondary Channel, aka DDS-2).
The latter services use a local loop rate of 72K. DDS uses a loop rate of
64K. The sub-rate channels are created in DS0A or DS0B formats (SRDM was an
option here). There are specific frame formats for each type of interface.
I would look at the AT&T pubs on the topics for the real deal (54016, 62411, I
can't remember the DDS #). There is also an ANSI spec or two (T1.403, T1.408)
that are quite handy.
There is a specific ISDN frame for 2B+D service over either an S or a U
interface (BRI). PRI (23B+D) is carried over a T-1, that uses ESF framing.
CPE attached to a PRI could certainly find a way to carry 16 x 19.2. However,
it seems to me that unless you are dialing leased services may be better.
Jim Sackman
Jim_S...@usa.racal.com
John Agosta
In article <Jim_Sackman...@usa.racal.com>, Jim_S...@usa.racal.com (Jim Sackman) says:
>
>I would look at the AT&T pubs on the topics for the real deal (54016, 62411, I
>can't remember the DDS #). There is also an ANSI spec or two (T1.403, T1.408)
>that are quite handy.
DDS specifications of interest include:
Digital Data System Channel Interface Specification - ATT 62310
Subrate Data Multiplexing - ATT TR 54075
-ja