FireWire can connect together up to 63 peripherals in an acyclic network structure (as opposed to SCSIs linear structure). It allows peer-to-peer device communication, such as communication between a scanner and a printer, to take place without using system memory or the CPU. FireWire also supports multiple hosts per bus, and through software IP networks can be formed between FireWire-linked computers. It is designed to support plug-and-play and hot swapping. Its six-wire cable is not only more convenient than SCSI cables but can supply up to 45 watts of power per port, allowing moderate-consumption devices to operate without a separate power cord. (Sony-inspired iLink usually deletes the power part of the cable/connector system and only uses a 4-pin connector.)
Provided a major technical improvement, namely new port specification that provides 800 Mbit/s over the same 8P8C (Ethernet) connectors with Category 5e cable, which is specified in IEEE 802.3 clause 40 (gigabit Ethernet over copper twisted pair) along with a corresponding automatic negotiation that allows the same port to connect to either IEEE Std 1394 or IEEE 802.3 (Ethernet) devices.Though the potential for a combined Ethernet and FireWire 8P8C port is intriguing, as of November 2008, no products or chipsets include this capability
Isochronous or asynchronous data transfers are possible. The isochronous data transport of the 1394 bus provides the guaranteed bandwidth and latency required for high-speed data transfer over multiple channels. On bus reset or when an isochronous node is added to the bus, the node requests a bandwidth allocation. If adequate bandwidth is not available, the requesting device is expected to repeat its request periodically. As an example of bus allocation, video acquisition for non-linear digital editing requires only a single isochronous channel, plus an asynchronous path for device control.
FireWire 800 was introduced by Apple in 2003, allows an increase to 786.432 Mbit/s with backwards compatibility to the slower rates and 6-pin connectors of FireWire 400. However, while the IEEE 1394a and IEEE 1394b standards are compatible, FireWire 800s connector, referred to as a beta connector, is different from FireWire 400s alpha connectors, making legacy cables incompatible. A bilingual cable allows the connection of older devices to the newer port. The full IEEE 1394b specification supports data rates up to 3200 Mbit/s (i.e., 400 megabytes/s) over beta-mode or optical connections up to 100 metres (330 ft) in length. Standard Category 5e unshielded twisted pair supports 100 metres (330 ft) at S100.
The 1394 cable standard defines three signaling rates: 98.304, 196.608, and 393.216 Mbps (megabits per second; MBps in this paper refers to megabytes per second.) These rates are rounded to 100, 200, and 400 Mbps, respectively, in this paper and are referred to in the 1394 standard as S100, S200 and S400. Consumer DV gear uses S100 speeds, but most 1394 PC adapter cards support the S200 rate. The signaling rate for the entire bus ordinarily is governed by the slowest active node; however, if a bus master (controller) implements a Topology_Map and a Speed_Map for specific node pairs, the bus can support multiple signaling speeds between individual pairs.
(*) Thomson/RCA receivers for DirecTV and USSB DSS satellite programming presently have an unused high-speed parallel data port intended to transmit MPEG-encoded video and audio to a digital tape recorder for time-shift recording. A Thomson/Hitachi digital VCR using JVC’s D-VHS 1/2-inch bitstream recording format was announced in 1994 for availability in early 1996, together with an upgraded version of the Thomson/RCA DBS receiver. Despite the press releases, this combination didn’t arrive. At the 1997 Winter Consumer Electronics show, Hitachi exhibited a prototype of its DX815 D-VHS recorder, which uses a non-standard implementation of 1394 to connect the recorder to a Hitachi DSS set-top box. Thomson did not display a D-VHS deck, but is expected to announce a similar product later in 1997. The R-4.1 ATV Receiver Interface Subcommittee of the Consumer Electronics Manufacturers Association (CEMA, formerly the Consumer Electronics Group) of the Electronic Industries Association is supporting a proposal to the IEC TC84 committee for a transport layer over fully-compliant 1394 to handle MPEG-2 and other digital data streams associated with Digital (Standard- and High-Definition) TV.
The 1394 cable standard defines three signaling rates: 98.304, 196.608, and 393.216 Mbps (megabits per second; MBps in this paper refers to megabytes per second.) These rates are rounded to 100, 200, and 400 Mbps, respectively, in this paper and are referred to in the 1394 standard as S100, S200 and S400. Consumer DV gear uses S100 speeds, but most 1394 PC adapter cards support the S200 rate. The signaling rate for the entire bus ordinarily is governed by the slowest active node; however, if a bus master (controller) implements a Topology_Map and a Speed_Map for specific node pairs, the bus can support multiple signaling speeds between individual pairs. The 1394 Trade Association’s 1394.1 working group presently are refining and clarifying the setup requirements for handling interconnected devices with multiple signaling speeds.
4 pin, 6 pin or 9 pin IEEE1394 (FireWire) plug connectors at the cable.
Each node usually has three connectors, although the standard provides for 1 to 27 connector per a device’s physical layer or PHY. Up to 16 nodes can be daisy-chained through the connectors with standard cables up to 4.5 m in length for a total standard cable length of 72 m. (Using higher-quality “fatter” cables permits longer interconnections.) Additional devices can be connected in a leaf-node configuration, as shown in figure 1. All 1394 consumer electronic devices announced as of early 1997 have only a single connector; there are no currently are digital camcorders or VCRs that correspond to the devices with ID 3 or ID 5 shown in figure 1. Physical addresses are assigned on bridge power up (bus reset) and whenever a node is added or removed from the system, either by physical connection/disconnection or power up/down. No device ID switches are required and hot plugging of nodes is supported. Thus 1394 truly qualifies as a plug-and-play bus.
*Note: Part 1 of the “General Specifications for Consumer-Use Digital Interface” (*Specifications’’) defines packet formats, data flow management, and connection management for DV and DA data over the 1394 bus, plus “general transmission rules” for control commands, which are “vendor-unique.” The Specifications define the concept of a logical input or output plug that corresponds to a single physical connector (or set of audio and video connectors) on a camcorder, VCR or related device. Input and output plug control registers determine the properties of plugs. As an example, a DV camcorder could have two logical output plugs, one for camera out and one for tape out, plus a logical input plug for DV dubbing, but only one physical connector. The Specifications also define a broadcast mode, over which an output plug continuously transmits “in the blind” on one channel, rather than to a particular input plug. Part 2 of the Specifications defines the SD-DVCR data stream for 525/60 and 625/50 systems, and Part 3 covers HD-DVCR streams for 1125/60 and 1250/50 high-definition formats. The DV recording format is defined by “Proposal for Digital Interface for Consumer Electronic Audio/Video Equipment,” authored by Philips, Matsushita, Thomson Multimedia, and Sony (sometimes called the “Big Four” of the DV standard), and presented at the 1394 Trade Association meeting in October 1995. Implementation of the consumer electronics device control protocol is the subject of “Specifications of AV/C Command and Transaction Set for Digital Interface,” by Sony Corp. and Matsushita Electric Industry Co., Ltd., presented to the January 1996 meeting of the 1394 Trade Association. This specification defines VCR-like commands, such as Play, Record, Rewind, etc.
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