Twinaxial cabling, or twinax, is a type of cable similar to coaxial cable, but with two inner conductors in a twisted pair instead of one. [3] Due to cost efficiency it is becoming common in modern (2013) very-short-range high-speed differential signaling applications.
Historically, twinax was the cable specified for the IBM 5250 terminals and printers, used with IBM's System/34, System/36, System/38, and IBM AS/400 midrange hosts, and with IBM Power Systems machines running IBM i. The data transmission is half-duplex, balanced transmission, at 1 Mbit/s, on a single shielded, 110 Ω twisted pair. [4]
With twinax seven devices can be addressed, from workstation address 0 to 6. The devices do not have to be sequential.
Twinax is a bus topology that requires termination to function properly. Most twinax T-connectors have an automatic termination feature. For use in buildings wired with Category 3 or higher twisted pair there are baluns that convert Twinax to twisted pair and hubs that convert from a bus topology to a star topology.
Twinax was designed by IBM. Its main advantages were high speed (1 Mbit/s versus 9600 bit/s) and multiple addressable devices per connection. The main disadvantage was the requirement for proprietary twinax cabling with bulky screw-shell connectors.
Signals are sent differentially over the wires at 1 Mbit/s (1 μs/bit ± 2%), Manchester coded, with preemphasis. [5] The signal coding is only approximately differential and not completely differentially balanced. In general, one of the two signal lines is driven to −0.32 V ± 20%, while the other carries 0 V. This, itself, could be considered as two differential signals of ±0.16 V superimposed on a −0.16 V common mode level. However, to provide preemphasis, for the first 250 ns (1/4 bit time) after a signal is driven low, the negative signal line is driven to −1.6 V. During this time, the common-mode voltage is −0.8 V.
This signal is designed to provide a minimum of ±100 mV at the end of 152 m (500 feet) of cable.
The two wires are denoted A and B. To encode a 0 bit, A>B for the first half of the bit time, and A<B for the second half. A 1 bit is the opposite. Thus, each signal line is driven low for either 500 or 1000 ns at a time, of which the first 250 ns is emphasized.
The plug consists of two pins of the same gender. [1]
A message begins with five normal 1 bits (A driven low for 500 ns, then B driven low for 500 ns) for bit synchronization, followed by a special frame sync pattern, three bit times long, that violates the usual Manchester encoding rules. A is driven low for 1500 ns, then B is driven low for 1500 ns. This is like a 1 bit sent at 1/3 normal speed (although the preemphasis pulses remain 250 ns long). [5] [6]
This pattern is followed by up to 256 16-bit data frames. Each data frame consists of a start bit of 1, an 8-bit data field, a 3-bit station address, and an even parity bit (which includes the start bit, so it equivalent to odd parity over the data and address fields only). This is then followed by three or more fill bits of 0. Unusually for an IBM protocol, the bits within each frame are sent lsbit-first. [6]
All messages are sent between the controller (master) and one slave device. The first frame in a message from the controller contains the device's address, from 0 to 6. The address field of following frames can be any value from 0 to 6, although is usually set to the device's address as well. The final frame in a message includes an address of 7 (all ones) as an end-of-message (EOM) indicator. A single-frame message does not have an EOM indicator.
When a command calls for a response, the device is expected to respond in 30 to 80 μs. A device's response also consists of up to 256 frames, and includes its address in all frames but the last. In this case, a single-frame response includes the EOM address, and the controller assumes it comes from the device it most recently addressed.
Generally, the first frame in a message is a command byte, and following frames are associated data. [6] [7]
MIL-STD-1553 specifies that the data bus should have characteristic impedance between 70 and 85 ohms, while the industry has standardized on 78 ohms. Likewise the industry has generally standardized on the cable known as twinax cable that has a characteristic impedance of 78 ohms.
Direct-Attach Copper (DAC) is a type of standard cabling used in Small Form-factor Pluggable (SFP) Ethernet, initially defined with SFP+ Direct-Attach Copper (10GSFP+Cu), which provides 10 Gigabit Ethernet over either an active or passive twinax cable assembly and connects directly into an SFP+ housing. An active twinax cable has active electronic components in the SFP+ housing to improve the signal quality; a passive twinax cable is mainly just a straight "wire" and contains few components. Generally, twinax cables shorter than 7 meters are passive and those longer than 7 meters are active, but this may vary from vendor to vendor. SFP+ Direct Attach Copper (DAC) is a popular choice for 10G Ethernet reaches up to 10 m [8] due to low latency and low cost.
One major application is connecting network hardware through their SFP+ interfaces. This type of connection is able to transmit at 10 gigabits/second full duplex speed over 5 meter distances. Moreover, this setup offers 15 to 25 times lower transceiver latency than current 10GBASE-T Cat 6/Cat 6A/Cat 7 cabling systems: 0.1 μs for Twinax with SFP+ versus 1.5 to 2.5 μs for current 10GBASE-T specification. The power draw of Twinax with SFP+ is around 0.1 watts, which is also much better than 4–8 watts for 10GBASE-T.
As always with cabling, one of the consideration points is the bit error ratio (BER). Twinax copper cabling has a BER of better than 10−18 according to Cisco, and therefore is acceptable for applications in critical environments.
| AWG cable size | Sustained bend radius |
|---|---|
| 24 | 1.5 inches (38 mm) |
| 26 | 1.3 inches (33 mm) |
| 28 | 1.0 inch (25 mm) |
| 30 | 0.9 inches (23 mm) |
Cables must not be bent below their minimum bend radius, [9] [10] which depends upon cable size as expressed in AWG. The table on the right summarizes minimum values typically admitted for SFP+ sustained bend radiuses.
This SFP+ twinax DAC is also referred to as "10GBASE-CR" or "10GBASE-CR1" by some manufacturers, [11] even though there is no IEEE or other standard with that name.
A 40 Gbps QSFP+ (Quad SFP+) was defined in 2012. [12] 802.3ba-2010 defines 40 Gigabit Ethernet over this connection as "40GBASE-CR4" and a 100 Gigabit connection over three of these connections named 100GBASE-CR10 (now in phase out).
SFP28, which runs at 28 Gbps for 25 Gigabit Ethernet (25GBASE-CR1), was defined in 2014; a quad version (QSFP28) capable of running 100 Gbps was also defined. [13] The newer QSFP28 connection runs 100GBASE-CR4 Ethernet (802.3bj-2010).
SFP112 was defined in 2018, with 100 Gbps per pair. All these versions retain the same length limit.
Many manufacturers of DisplayPort cabling are also using twinax configurations to accommodate the strict insertion loss, return loss, and crosstalk requirements for the 2.7 Gbit/s signaling rate.
The cable used to connect the MIL-STD-1553 bus and stub devices has a characteristic impedance of 78 ohms at 1 MHz. A 2-conductor twisted-pair cable known as twinax is used to connect the bus and stub devices. The insulated pairs are balanced and have an overall shielding braid around the pairs. The twisting of the signal-carrying pairs theoretically cancels any random induced noise caused by the pair. The two internal dielectric fillers separate the braid from the pairs to minimize the leakage capacitance to ground. The fillers also assist in uniform twisting of the pairs. The 90% braid coverage protects the pair from external noise. The PVC outer jacket cable is suitable for laboratory use, while the high-temperature rated outer jacket cable is applicable for vehicle use.
A concentric bayonet plug known as "TRB" is used. [15]
Ethernet is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET.
Ethernet over twisted-pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. They are a subset of all Ethernet physical layers.
In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common.
In computer networking, Gigabit Ethernet is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use in 1999, and has replaced Fast Ethernet in wired local networks due to its considerable speed improvement over Fast Ethernet, as well as its use of cables and equipment that are widely available, economical, and similar to previous standards. The first standard for faster 10 Gigabit Ethernet was approved in 2002.
Fibre Channel (FC) is a high-speed data transfer protocol providing in-order, lossless delivery of raw block data. Fibre Channel is primarily used to connect computer data storage to servers in storage area networks (SAN) in commercial data centers.
XENPAK is a multisource agreement (MSA), instigated by Agilent Technologies and Agere Systems, that defines a fiber-optic or wired transceiver module which conforms to the 10 Gigabit Ethernet (10GbE) standard of the Institute of Electrical and Electronics Engineers (IEEE) 802.3 working group. The MSA group received input from both transceiver and equipment manufacturers during the definition process. XENPAK has been replaced by more compact devices providing the same functionality.
Small Form-factor Pluggable (SFP) is a compact, hot-pluggable network interface module format used for both telecommunication and data communications applications. An SFP interface on networking hardware is a modular slot for a media-specific transceiver, such as for a fiber-optic cable or a copper cable. The advantage of using SFPs compared to fixed interfaces is that individual ports can be equipped with different types of transceivers as required, with the majority including optical line terminals, network cards, switches and routers.
Power over Ethernet (PoE) describes any of several standards or ad hoc systems that pass electric power along with data on twisted-pair Ethernet cabling. This allows a single cable to provide both a data connection and enough electricity to power networked devices such as wireless access points (WAPs), IP cameras and VoIP phones.
The media-independent interface (MII) was originally defined as a standard interface to connect a Fast Ethernet medium access control (MAC) block to a PHY chip. The MII is standardized by IEEE 802.3u and connects different types of PHYs to MACs. Being media independent means that different types of PHY devices for connecting to different media can be used without redesigning or replacing the MAC hardware. Thus any MAC may be used with any PHY, independent of the network signal transmission medium.
MIL-STD-1553 is a military standard published by the United States Department of Defense that defines the mechanical, electrical, and functional characteristics of a serial data bus. It was originally designed as an avionic data bus for use with military avionics, but has also become commonly used in spacecraft on-board data handling (OBDH) subsystems, both military and civil, including use on the James Webb space telescope. It features multiple redundant balanced line physical layers, a (differential) network interface, time-division multiplexing, half-duplex command/response protocol, and can handle up to 31 Remote Terminals (devices); 32 is typically designated for broadcast messages. A version of MIL-STD-1553 using optical cabling in place of electrical is known as MIL-STD-1773.
Autonegotiation is a signaling mechanism and procedure used by Ethernet over twisted pair by which two connected devices choose common transmission parameters, such as speed, duplex mode, and flow control. In this process, the connected devices first share their capabilities regarding these parameters and then choose the highest-performance transmission mode they both support.
The physical coding sublayer (PCS) is a networking protocol sublayer in the Fast Ethernet, Gigabit Ethernet, and 10 Gigabit Ethernet standards. It resides at the top of the physical layer (PHY), and provides an interface between the physical medium attachment (PMA) sublayer and the media-independent interface (MII). It is responsible for data encoding and decoding, scrambling and descrambling, alignment marker insertion and removal, block and symbol redistribution, and lane block synchronization and deskew.
IEEE Standard 1355-1995, IEC 14575, or ISO 14575 is a data communications standard for Heterogeneous Interconnect (HIC).
The physical-layer specifications of the Ethernet family of computer network standards are published by the Institute of Electrical and Electronics Engineers (IEEE), which defines the electrical or optical properties and the transfer speed of the physical connection between a device and the network or between network devices. It is complemented by the MAC layer and the logical link layer. An implementation of a specific physical layer is commonly referred to as PHY.
Token Ring is a physical and data link layer computer networking technology used to build local area networks. It was introduced by IBM in 1984, and standardized in 1989 as IEEE 802.5. It uses a special three-byte frame called a token that is passed around a logical ring of workstations or servers. This token passing is a channel access method providing fair access for all stations, and eliminating the collisions of contention-based access methods.
40 Gigabit Ethernet (40GbE) and 100 Gigabit Ethernet (100GbE) are groups of computer networking technologies for transmitting Ethernet frames at rates of 40 and 100 gigabits per second (Gbit/s), respectively. These technologies offer significantly higher speeds than 10 Gigabit Ethernet. The technology was first defined by the IEEE 802.3ba-2010 standard and later by the 802.3bg-2011, 802.3bj-2014, 802.3bm-2015, and 802.3cd-2018 standards. The first succeeding Terabit Ethernet specifications were approved in 2017.
10 Gigabit Ethernet is a group of computer networking technologies for transmitting Ethernet frames at a rate of 10 gigabits per second. It was first defined by the IEEE 802.3ae-2002 standard. Unlike previous Ethernet standards, 10GbE defines only full-duplex point-to-point links which are generally connected by network switches; shared-medium CSMA/CD operation has not been carried over from the previous generations of Ethernet standards so half-duplex operation and repeater hubs do not exist in 10GbE. The first standard for faster 100 Gigabit Ethernet links was approved in 2010.
Dell Networking is the name for the networking portfolio of Dell. In the first half of 2013, Dell started to rebrand their different existing networking product brands to Dell Networking. Dell Networking is the name for the networking equipment that was known as Dell PowerConnect, as well as the Force10 portfolio.
IEEE 802.3bz, NBASE-T and MGBASE-T are standards released in 2016 for Ethernet over twisted pair at speeds of 2.5 and 5 Gbit/s. These use the same cabling as the ubiquitous Gigabit Ethernet, yet offer higher speeds. The resulting standards are named 2.5GBASE-T and 5GBASE-T.
AES50 is an Audio over Ethernet protocol for multichannel digital audio. It is defined in the AES50-2011 standard for High-resolution multi-channel audio interconnection (HRMAI).
{{cite web}}: CS1 maint: unfit URL (link)The signal cable wire consists of two twinax sections in a common outer sheath.