Data Rates - or Speeds

(the tables are listed here also - but with descriptions included)

*** also see http://www.zytrax.com/tech/data_rates.htm 

*** this page explains the speeds - for detailed descriptions of the complex T-carrier system - see the T1 and T3 pages

Here the DSx or T-Carrier Table and the STS-STM-OC Table describe the families of data rates, or speeds.  In addition, we list most of the common data rates in a separate table.

There are two main, standardized Telecom families of data rates - and a number of other data rates (for example, Ethernet/Fast-Ethernet/ Giga-Ethernet, etc.).

• Digital Signal (DSx), also called the T-Carrier (Tx) & E-Carrier (Ex) System - based on multiples of the DS0 (which is 64kbps) - common speeds range from 64 Kbps up to 44.736 Mbps (DS0 to DS3) but can go as high as 274.176 (DS4).  Uses copper cables primarily.  standardized by the ANSI accredited Committee T1 

• Synchronous Transport (STS & STM), also called Optical Carrier (OC) - speeds range from 51.84 Mbps to 9953.28 Mbps (OC-1 to OC-192).  Uses optical fiber cables.

DSx vs Tx - yes, there is a slight difference between, for example, a DS1 and a T1.  They describe identical data rates - but DSx is at the equipment, and Tx is on the cable.  

The Tx Acronym - no one ever states what the "T" stands for (you can search the web, fruitlessly), but it sometimes is said to mean Terrestrial, and other times is said to mean Transmission.

Plesiochronous Systems (DSx/Tx/Ex) vs Synchronous Systems (STS/STM/OC)

SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media. It is the international equivalent of Synchronous Optical Network. Both technologies provide faster and less expensive network interconnection than the traditional PDH (Plesiochronous Digital Hierarchy) systems, such as the T-carrier.

Synchronous means the systems that connect to each other are running on a master clock (Stratum-1 clock, which is nuclear and therefore virtually exactly timed), and the data is timed perfectly.  

Plesiochronous means "almost (but not) synchronous," - this means the systems that connect to each other are running at the same data rate but are on separate clocks.  The clocks, of course, can be off slightly, which means the data is not timed perfectly.  To get around this, "stuff bits" are inserted by the faster of the two systems - the stuff bits are meaningless bits, inserted only for timing correction, and they must be marked as stuff bits so that the receiving end can remove them..

The following tables list the standard data rates for DSx/Tx/Ex systems, and the Synchronous Transport or Optical Carrier systems.  SONET bases it's data rates on the STS/STM/OC system.  

Speed & Data Rate  vs  Bandwidth & Capacity

• Speed and Data Rate define how fast data is flowing in one direction.
• Bandwidth and Capacity define how fast data can flow (the max) in one direction.  

Data can be any type of information.  But with computers and networks, the fundamental block of Data is the Bit (1 or 0) and the Byte (a group of eight bits).  Bits and Bytes are numeric information.  This numeric info can be encoded at the sending end and decoded (interpreted) at the receiving end to represent any type of info.  For example, alphabetic characters can be encoded/decoded into numbers using ASCII code.  

Speed, or Data Rate, is simply the speed that the data is flowing from one point to another, through some type of physical medium, or pipe.

The pipe or circuit, may be one channel or multiple channels.  For example, a DS0 is one channel at 64 Kbps - whereas a DS1 is 1.544 Mbps, but consists of 24 channels at 64 Kbps.

IMPORTANT - data is bidirectional (flows in both directions) .  The data rate or speed is the value of how fast data flows in one direction.  The aggregate data rate is 2 times that !!  For example, a T1 has data flowing at 1.544 Mbps, in one direction, and it has 1.544 Mbps flowing in the other direction as well.  This is a symmetric circuit since the speeds are the same.  Most circuits are symmetric.  However, there are examples of assymetric, such as ADSL (Asymmetric DSL).

Bandwidth or "capacity," describes how wide the pipe is - which corresponds to the maximum rate that the bits can be sent through pipe or the channels in the pipe. 

How Channels in a Pipe are Separated (TDM) - in telecom, channels are separated by TDM (Time Division Multiplexing).  This is where groups of bits (frames) take turns in entering the pipe for transmission.  Then at the receiving end these groups of bits are separated again.  For example, a DS1 is actually 24 DS0's being sent in alternating groups of bits, using TDM (see the T1 page).

The T-Carrier Standards

If you EVER find the official original T1 standards paper, that defines the basics - please email me.  Originally, ANSI came up with the first T1 standard document. But now there are tons of T-carrier standards documents !!!  A few common ones I have seen mentioned are ANSI T1.403-1998, T1.-107-1995, T1.107a-1990, etc

 If you are wealthy, all the ANSI and T1 Committee standards can be found and bought from https://www.atis.org/atis/docstore/searchform.asp (about $250 each).  Actually, the T1 Committee has been split up into several new groups.  The one that deals with T-carrier stuff the most is the T1X1 group (see http://www.t1.org/t1x1/_x1-prj.htm for a listing of all their documents).

DSx/Tx/Ex/Jx Data Rates

The following speeds include several DS levels (such as DS1C, DS2, and DS4) that you will rarely, if ever encounter.  The DS2 is a building block of the DS3 (7 DS2's = 1 DS3) - you won't see it as an available access speed for a circuit, but it's there.  

For a T1 if you multiply 24 x DS0 (64,000) you do NOT get 1.544 Mbps (that would be 24 * 64,000 = 1.536 Mbps). The extra bits are lost between 'frames' where a frame consists of one 8 bit sample for each of the 24 channels (remember the DS0 basics). So every 192 bits (24 x 8 = 192) we add a 'frame separator' bit to give 193 bits per frame. The final arithmetic is 193 bits x 8K samples = 1.544 Mbps. Easy really.

If you do the same arithmetic for DS1C, T2 etc. the above will not give the right answer. In short above T1 things get even messier with M-Frames and M-subframes. Its mind numbing stuff and if you really want to know you need ANSI T1.107-1995 and lots of coffee.

The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitized voice transmission. The original transmission rate (1.544 Mbps) in the T-1 line is in common use today in Internet service provider (ISP) connections to the Internet. Another level, the T-3 line, providing 44.736 Mbps, is also commonly used by Internet service providers. Another commonly installed service is a fractional T-1, which is the rental of some portion of the 24 channels in a T-1 line, with the other channels going unused.

Digital signal X is based on the ANSI T1.107 guidelines. The ITU-TS guidelines differ somewhat.  The T-carrier system is entirely digital, using pulse code modulation and time-division multiplexing. The system uses four wires and provides duplex capability (two wires for receiving and two for sending at the same time). The T-1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.

In the T-1 system, voice signals are sampled 8,000 times a second and each sample is digitized into an 8-bit word. With 24 channels being digitized at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T-1's 1.544 Mbps data rate. The signaling bits are the least significant bits in each frame.

OC/STS/STM Data Rates

These are standards that describe data rates.  Unfortunately the world did not agree on one standard, so we have two systems in place:   SONET (Synchronous Optical Network) for North America and SDH (Synchronous Digital Hierarchy) for the rest of the world.

North America Terms

• SONET - Synchronous Optical Network
• OC - Optical Carrier - a SONET-based data rate where OC-n = 51.84 Mbps x n 
• STS - Synchronous Transport Signal (standardized by ANSI) - a SONET-based data rate 

Europe and ROW Terms

• SDH - Synchronous Digital Hierarchy
• STM -  Synchronous Transport Module (standardized by the CCITT)

OC and STS speeds are part of the SONET (Synchronous Optical Network) United States system. Optical Carriers are typically known by their OC-xn number where n is a multiple of the OC-1 rate of 51.84 Mpbs

Conversion 
STM-n = STS-3n = OC-3n

For example:  STM-1 =  STS-3 = OC-3 = 155.52 Mbps

SDH vs SONET  -  Both systems are standards for synchronous data transmission on an optical media (fiber) - and their speeds are identical.  However, SDH is an international standard, while SONET is a North American standard.  Therefore, in the United States you will rarely hear speeds stated in STS-x or STM-x terms - instead they will be stated in OC-x terms.

North America uses an STS-x format for frames (packets) and Europe an STM-x (Synchronous Transport Module) format. 

*** four OC-3 or STM-1 circuits can be aggregated to form a 622.08 Mbps circuit designated as OC-12 or STM-4.

*** the current state of the art maximum data rate is the OC-192 or STM-64 circuit, which operates at rate of just under 10 Gbit/s.

• STS = Synchronous Transport Signal
• STM = Synchronous Transport Module
• OC = Optical Carrier

SDH uses the following Synchronous Transport Modules (STM) and rates: STM-1 (155 megabits per second), STM-4 (622 Mbps), STM-16 (2.5 gigabits per second), and STM-64 (10 Gbps).

Definitions

STS-1  Synchronous Transport Signal 1: SONET standard for transmission over OC-1 optical fiber at 51.84 Mbps.

STS-n  Synchronous Transport Signal "n" : (where n is an integer) SONET standards for transmission over OC-n optical fiber by multiplexing "n" STS-1 frames, (e.g., STS-3 at 155.52 Mbps STS-12 at 622.08 Mbps and STS-48 at 2.488 Gbps).

STS-nc  Synchronous Transport Signal "n" concatenated: (where n is an integer) SONET standards for transmission over OC-n optical fiber by multiplexing "n" STS-1 frames, (e.g., STS-3 at 155.52 Mbps STS-12 at 622.08 Mbps and STS-48 at 2.488 Gbps but treating the information fields as a single concatenated payload).

STM  Synchronous Transfer Module: STM is a basic building block used for a synchronous multiplexing hierarchy defined by the CCITT/ITU-T. STM-1 operates at a rate of 155.52 Mbps (same as STS-3).

STM-1  Synchronous Transport Module 1: SDH standard for transmission over OC-3 optical fiber at 155.52 Mbps.

STM-n  Synchronous Transport Module "n" : (where n is an integer) SDH standards for transmission over optical fiber (OC-'n x 3) by multiplexing "n" STM-1 frames, (e.g., STM-4 at 622.08 Mbps and STM-16 at 2.488 Gbps).

STM-nc  Synchronous Transport Module "n" concatenated: (where n is an integer) SDH standards for transmission over optical fiber (OC-'n x 3) by multiplexing "n" STM-1 frames, (e.g., STM-4 at 622.08 Mbps and STM-16 at 2.488 Gbps, but treating the information fields as a single concatenated payload).

RFC2615 - Table Comparing SONET and SDH entities

RFC2615 - the only currently supported SONET/SDH SPE/VCs 
(SONET SPE's = Synchronous Payload Envelopes, are basically the same thing as SDH VC's = Virtual Containers):

Virtual Tributaries and Virtual Containers

SONET:   SPE (Synchronous Payload Envelope)      VT (Virtual Tributary) 

SDH:    VC (Virtual Container - ROW)   AU (Administrative Unit)   TU = Tributary Unit (used in RoW)

SONET is designed to support a wide variety of payloads. The SONET node accepts these payloads and multiplexes them into a SONET envelope called an SPE (Synchronous Payload Envelope). These payloads are called virtual tributaries (VTs) in North America and virtual containers (VCs) in SDH. 

SDH/SONET defines a way or packaging capacity into Virtual Containers (VCs) which may be Higher Order Virtual Container (HVC) or Lower Order Virtual Containers (LVC). The term Tributary Unit (TU - used in RoW) or Virtual Tributary (VT - North America) describes a method of mapping PDH (e.g. T1) carriers onto SDH/SONET.

GigE Speeds

The standards for high-speed Ethernet are GbE, or GigE (Gigabit Ethernet at 1 Gbps which equals 1000 Mbps), and 10 GbE (10 Gbps).  GbE can use Cat6 copper cable but preferably fiber, while the 10 Gbps speed requires fiber.  As far as the circuit speed required, GbE (1 Gbps) requires an OC-24, and 10 GbE (10 Gbps) requires an OC-192.  Virtually no SONET network providers offer OC-24 circuits, so to transmit GbE across a fiber link, you would need to purchase either an OC-12 and just accept that you will only get 622 Mbps, or get an OC-48 and accept a huge amount of wasted bandwidth.  Or you could buy non-SONET dark fiber and run your GbE across it (although DF is expensive !!).

Common Data Rates

This table shows the stated data rates for the most important end-user and backbone transmission technologies.

 

Technology	Speed	Physical Medium	Application
GSM mobile telephone service	9.6 to 14.4 Kbps	RF in space (wireless)	Mobile telephone for business and personal use
High-Speed Circuit-Switched Data service (HSCSD)	Up to 56 Kbps	RF in space (wireless)	Mobile telephone for business and personal use
Regular telephone service (POTS)	Up to 56 Kbps	twisted pair	Home and small business access
Dedicated 56Kbps on frame relay	56 Kbps	Various	Business e-mail with fairly large file attachments
DS0	64 Kbps	All	The base signal on a channel in the set of Digital Signal levels
General Packet Radio System (GPRS)	56 to 114 Kbps	RF in space (wireless)	Mobile telephone for business and personal use
ISDN	BRI: 64 Kbps to 128 Kbps PRI: 23 (T-1) or 30 (E1) assignable 64-Kbps channels plus control channel; up to 1.544 Mbps (T-1) or 2.048 (E1)	BRI: Twisted-pair PRI: T-1 or E1 line	BRI: Faster home and small business access PRI: Medium and large enterprise access
IDSL	128 Kbps	Twisted-pair	Faster home and small business access
AppleTalk	230.4 Kbps	Twisted pair	Local area network for Apple devices; several networks can be bridged; non-Apple devices can also be connected
Enhanced Data GSM Environment (EDGE)	384 Kbps	RF in space (wireless)	Mobile telephone for business and personal use
satellite	400 Kbps (DirecPC and others)	RF in space (wireless)	Faster home and small enterprise access
frame relay	56 Kbps to 1.544 Mbps	Twisted-pair or coaxial cable	Large company backbone for LANs to ISP ISP to Internet infrastructure
DS1/T-1	1.544 Mbps	Twisted-pair, coaxial cable, or optical fiber	Large company to ISP ISP to Internet infrastructure
Universal Mobile Telecommunications Service (UMTS)	Up to 2 Mbps	RF in space (wireless)	Mobile telephone for business and personal use (available in 2002 or later)
E-carrier	2.048 Mbps	Twisted-pair, coaxial cable, or optical fiber	32-channel European equivalent of T-1
T-1C (DS1C)	3.152 Mbps	Twisted-pair, coaxial cable, or optical fiber	Large company to ISP ISP to Internet infrastructure
IBM Token Ring/802.5	4 Mbps (also 16 Mbps)	Twisted-pair, coaxial cable, or optical fiber	Second most commonly-used local area network after Ethernet
DS2/T-2	6.312 Mbps	Twisted-pair, coaxial cable, or optical fiber	Large company to ISP ISP to Internet infrastructure
Digital Subscriber Line (DSL)	512 Kbps to 8 Mbps	Twisted-pair (used as a digital, broadband medium)	Home, small business, and enterprise access using existing copper lines
E-2	8.448 Mbps	Twisted-pair, coaxial cable, or optical fiber	Carries four multiplexed E-1 signals
cable modem **	512 Kbps to 52 Mbps (see "explanation" below)	Coaxial cable (usually uses Ethernet); in some systems, telephone used for upstream requests	Home, business, school access
Ethernet	10 Mbps	10BASE-T (twisted-pair); 10BASE-2 or -5 (coaxial cable); 10BASE-F (optical fiber)	Most popular business local area network (LAN)
IBM Token Ring/802.5	16 Mbps (also 4 Mbps)	Twisted-pair, coaxial cable, or optical fiber	Second most commonly-used local area network after Ethernet
E-3	34.368 Mbps	Twisted-pair or optical fiber	Carries 16 E-l signals
DS3/ T-3	44.736 Mbps	Coaxial cable	ISP to Internet infrastructure Smaller links within Internet infrastructure
OC-1	51.84 Mbps	Optical fiber	ISP to Internet infrastructure Smaller links within Internet infrastructure
High-Speed Serial Interface (HSSI)	Up to 53 Mbps	HSSI cable	Between router hardware and WAN lines Short-range (50 feet) interconnection between slower LAN devices and faster WAN lines
Fast Ethernet	100 Mbps	100BASE-T (twisted pair); 100BASE-T (twisted pair); 100BASE-T (optical fiber)	Workstations with 10 Mbps Ethernet cards can plug into a Fast Ethernet LAN
Fiber Distributed-Data Interface (FDDI)	100 Mbps	Optical fiber	Large, wide-range LAN usually in a large company or a larger ISP
T-3D (DS3D)	135 Mbps	Optical fiber	ISP to Internet infrastructure Smaller links within Internet infrastructure
E-4	139.264 Mbps	Optical fiber	Carries 4 E3 channels Up to 1,920 simultaneous voice conversations
OC-3/SDH	155.52 Mbps	Optical fiber	Large company backbone Internet backbone
E-5	565.148 Mbps	Optical fiber	Carries 4 E4 channels Up to 7,680 simultaneous voice conversations
OC-12/STM-4	622.08 Mbps	Optical fiber	Internet backbone
Gigabit Ethernet	1 Gbps	Optical fiber (and "copper" up to 100 meters)	Workstations/networks with 10/100 Mbps Ethernet plug into Gigabit Ethernet switches
OC-24	1.244 Gbps	Optical fiber	Internet backbone
SciNet	2.325 Gbps (15 OC-3 lines)	Optical fiber	Part of the vBNS backbone
OC-48/STM-16	2.488 Gbps	Optical fiber	Internet backbone
OC-192/STM-64	10 Gbps	Optical fiber	Backbone
OC-256	13.271 Gbps	Optical fiber	Backbone

** Cable modem note:  rhe upper limit of 52 Mbps on a cable is to an ISP, not currently to an individual PC. Most of today's PCs are limited to an internal design that can accomodate no more than 10 Mbps (although the PCI bus itself carries data at a faster speed). The 52 Mbps cable channel is subdivided among individual users. Obviously, the faster the channel, the fewer channels an ISP will require and the lower the cost to support an individual user.