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Twinaxial cabling

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. Due to cost efficiency it is becoming common in modern (2013) very-short-range high-speed differential signaling applications.

Twinaxial plug (style used by IBM;[1] other designs exist[2])

Legacy applications Edit

IBM Edit

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.[3]

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.

Physical layer Edit

Signals are sent differentially over the wires at 1 Mbit/s (1 μs/bit ± 2%), Manchester coded, with preemphasis.[4] 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]

Data link layer Edit

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).[4][5]

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.[5]

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.[5][6]

MIL-STD-1553 Edit

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.

Current applications Edit

Networking (Direct-Attach Copper) Edit

 
A DAC cable has SFP+ plugs at each end integrated.

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 (twinaxial) 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[7] 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,[8][9] 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,[10] even though there is no IEEE or other standard with that name.

Higher rates Edit

A 40 Gbps QSFP+ (Quad SFP+) was defined in 2012.[11] 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.[12] 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.

SATA 3.0 cables Edit

 
Cross section of a SATA 3.0 cable, showing the dual Twinax conductors for the differential pairs.

SATA 3.0 cables are implemented using Twinax (twinaxial cable).

DisplayPort Edit

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.

MIL-STD-1553 Edit

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.[13]

See also Edit

References Edit

  1. ^ a b "IBM 4236482 Eq. - Stonewall Cable". www.stonewallcable.com.
  2. ^ Even among BNC-like bayonet connectors, there are at least three Twinax designs (IBM, "TRB" concentric with varying lug counts, and a polarized shape with one male & one female on each end). See drawings at "Twinax Connectors - RF Connectors | Amphenol RF". www.amphenolrf.com.
  3. ^ . NLynx. 2006. Archived from the original on October 6, 2007.
  4. ^ a b Quigley, Thomas J. (March 1988), (PDF), National Semiconductor, AN-516, archived from the original (PDF) on June 15, 2011
  5. ^ a b c Twinax Cable Information, Anzac Computer Equipment Corporation, 2004-07-22, from the original on March 4, 2011, retrieved 2009-01-30
  6. ^ Norcross, Thomas; Patchen, Paul J.; Quigley, Thomas J.; Short, Tim; Worsley, Debra; Johnson, Laura (April 1995), (PDF), National Semiconductor, AN-641, archived from the original (PDF) on March 5, 2012
  7. ^ . Archived from the original on 2009-03-08. Retrieved 2009-08-13.{{cite web}}: CS1 maint: unfit URL (link)
  8. ^ "Recommended minimum bend radii for QSFP+ and SFP+ cables". from the original on 2014-04-24. Retrieved 2014-04-24.
  9. ^ (PDF). Archived from the original (PDF) on 2014-04-24. Retrieved 2014-04-24.
  10. ^ "Arista Networks Transceivers & Cables". from the original on May 12, 2014. Retrieved 2012-03-28.
  11. ^ SFF SFF-8436
  12. ^ SFF SFF-8402
  13. ^ "TRB MIL-STD-1553B Twinax/Triax Connectors | Trompeter". www.belfuse.com.

External links Edit

  • Cisco 10GBASE SFP+ Modules
  • MIL-STD-1553B Concepts and Considerations from MilesTek Corporation ( February 24, 2012, at the Wayback Machine)

twinaxial, cabling, twinax, type, cable, similar, coaxial, cable, with, inner, conductors, twisted, pair, instead, cost, efficiency, becoming, common, modern, 2013, very, short, range, high, speed, differential, signaling, applications, twinaxial, plug, style,. 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 Due to cost efficiency it is becoming common in modern 2013 very short range high speed differential signaling applications Twinaxial plug style used by IBM 1 other designs exist 2 Contents 1 Legacy applications 1 1 IBM 1 1 1 Physical layer 1 1 2 Data link layer 1 2 MIL STD 1553 2 Current applications 2 1 Networking Direct Attach Copper 2 1 1 Higher rates 2 2 SATA 3 0 cables 2 3 DisplayPort 2 4 MIL STD 1553 3 See also 4 References 5 External linksLegacy applications EditIBM Edit 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 W twisted pair 3 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 Physical layer Edit Signals are sent differentially over the wires at 1 Mbit s 1 ms bit 2 Manchester coded with preemphasis 4 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 gt B for the first half of the bit time and A lt 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 Data link layer Edit 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 4 5 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 5 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 ms 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 5 6 MIL STD 1553 Edit 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 Current applications EditNetworking Direct Attach Copper Edit Main article Small Form factor Pluggable A DAC cable has SFP plugs at each end integrated 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 twinaxial 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 7 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 ms for Twinax with SFP versus 1 5 to 2 5 ms 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 radius24 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 8 9 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 10 even though there is no IEEE or other standard with that name Higher rates Edit A 40 Gbps QSFP Quad SFP was defined in 2012 11 802 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 12 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 SATA 3 0 cables Edit Cross section of a SATA 3 0 cable showing the dual Twinax conductors for the differential pairs SATA 3 0 cables are implemented using Twinax twinaxial cable DisplayPort Edit 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 MIL STD 1553 Edit 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 13 See also EditCoaxial cable IBM 5250 Triaxial cableReferences Edit a b IBM 4236482 Eq Stonewall Cable www stonewallcable com Even among BNC like bayonet connectors there are at least three Twinax designs IBM TRB concentric with varying lug counts and a polarized shape with one male amp one female on each end See drawings at Twinax Connectors RF Connectors Amphenol RF www amphenolrf com NLynx Technologies what is Twinax NLynx 2006 Archived from the original on October 6 2007 a b Quigley Thomas J March 1988 Interfacing the DP8344 to Twinax PDF National Semiconductor AN 516 archived from the original PDF on June 15 2011 a b c Twinax Cable Information Anzac Computer Equipment Corporation 2004 07 22 archived from the original on March 4 2011 retrieved 2009 01 30 Norcross Thomas Patchen Paul J Quigley Thomas J Short Tim Worsley Debra Johnson Laura April 1995 MPA II A Multi Protocol Terminal Emulation Adapter Using the DP8344 PDF National Semiconductor AN 641 archived from the original PDF on March 5 2012 10 gigabit Ethernet alphabet soup never tasted so good Archived from the original on 2009 03 08 Retrieved 2009 08 13 a href Template Cite web html title Template Cite web cite web a CS1 maint unfit URL link Recommended minimum bend radii for QSFP and SFP cables Archived from the original on 2014 04 24 Retrieved 2014 04 24 Temporary and Sustained Bend Radii for GORE SFP cables PDF Archived from the original PDF on 2014 04 24 Retrieved 2014 04 24 Arista Networks Transceivers amp Cables Archived from the original on May 12 2014 Retrieved 2012 03 28 SFF SFF 8436 SFF SFF 8402 TRB MIL STD 1553B Twinax Triax Connectors Trompeter www belfuse com External links EditCisco 10GBASE SFP Modules MIL STD 1553B Concepts and Considerations from MilesTek Corporation Archived February 24 2012 at the Wayback Machine Retrieved from https en wikipedia org w index php title Twinaxial cabling amp oldid 1167589626, wikipedia, wiki, book, books, library,

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