Cisco Systems RJ-45-to-AUX manual Synchronous Transport Signal STS

The capability of broadband to carry multiple signals enables it to have a higher transmission speed. Table 3.2 displays the various broadband transmissions, which require more expensive and specialized transmitters and receivers.

Table 3.2: The different broadband transmission types and their bandwidth.

Transmission Type	Bit Rate
DS2	6.312Mbps
E2	8.448Mbps
E3	34.368Mbps
DS3	44.736Mbps
OC/STS−1	51.840Mbps
OC/STS−3	155.520Mbps
OC/STS−9	466.560Mbps
OC/STS−12	622.080Mbps
OC/STS−18	922.120Mbps
OC/STS−24	1.244Gbps
OC/STS−36	1.866Gbps
…	…
OC/STS−768	39.820Gbps

Digital signal 2 (DS2), E2, E3, and DS3 describe digital transmission across copper or fiber cables. OC/STS resides almost exclusively on fiber−optic cables. The OC designator specifies an optical transmission, whereas the STS designator specifies the characteristics of the transmission (except the optical interface). There are two types of fiber−optic media:

∙Single−mode fiber—Has a core of 8.3 microns and a cladding of 125 microns. A single light wave powered by a laser is used to generate the transmission. Single−mode can be used for distances up to 45 kilometers; it has no known speed limitation. Figure 3.2 shows an example of a single−mode fiber.

Figure 3.2: Single mode fiber.

∙Multimode fiber—Has a core of 62.5 microns and a cladding of 125 microns. Multiple light waves powered by a light−emitting diode (LED) are used to power the transmission. Multimode has a distance limit of two kilometers; it has a maximum data transfer rate of 155Mbps in WAN applications. (It has recently been approved for use for Gigabit Ethernet.) Figure 3.3 shows an example of a multimode fiber. The core and cladding boundary work as a mirror to reflect the light waves down the fiber.

Figure 3.3: Multimode fiber.

Synchronous Transport Signal (STS)

Synchronous transport signal (STS) is the basic building block of the Synchronous Optical Network (SONET). It defines the framing structure of the signal. It consist of two parts: STS overhead and STS payload. In STS−1, the frame is 9 rows of 90 octets. Each row has 3 octets of overhead and 87 octets of payload, resulting in 6,489 bits per frame. A frame occurs every 125 microseconds, yielding 51.84Mbps.

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