Twinaxial cabling

From Wikipedia, the free encyclopedia

Twinaxial cabling, or "Twinax", is a type of cable similar to coax, but with two inner conductors instead of one. Due to cost efficiency it is becoming common in modern very short range high speed differential signaling applications.

1 Legacy Applications
- 1.1 IBM
- 1.2 NEC
2 Current Applications
3 References
4 See also
5 External links

[edit] Legacy Applications

[edit] IBM

Historically, twinax was the cable specified for the IBM 5250 terminals and printers, used with IBM's midrange hosts, which are currently AS/400 (Application System 400) minicomputers (which are now called iSeries or i5), and also with its predecessors, such as the S/36. The data transmission is half-duplex, balanced transmission, at 1 Mbit/s, on a single shielded, 110 Ω twisted pair^[1].

With Twinax seven devices can be addressed, from workstation address 0 to 6. The devices do not have to be sequential.

Straight Twinax cables can go up to 5,000 feet or 1 mile (1.6 km). 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 as a replacement for RS-232 dumb terminals. Its main advantages were high speed (1Mbit/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.

[edit] NEC

NEC Astra system also uses this kind of cable for networking.^{[citation needed]}

[edit] Current Applications

One of major applications includes Cisco Systems implementation coupled with SFP+ modules. This type of connection is able to transmit at 10 Gigabit full duplex speed over 10 meter distances. Moreover this setup offers 15 to 25 times lower transceiver latency than current 10GBASE-T CAT6/CAT6a/CAT7 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 Bit error ratio or BER for short. Twinax copper cabling has BER better than 10^-18 according to Cisco, and therefore is acceptable for applications in critical environments.