Question 152 of 250 from exam 400-201: Cisco CCIE Service Provider Written Exam

Question 152 of 250 from exam 400-201: Cisco CCIE Service Provider Written Exam


Based on the 802.3ae definition, which capability is a function of WIS?



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A. B. C. D.


The 802.3ae is a standard that defines the implementation of 10 Gigabit Ethernet (10GbE) over fiber optic networks. It specifies the physical layer specifications of 10GbE, including the Physical Medium Dependent (PMD) sublayer and the Physical Coding Sublayer (PCS).

The WIS (WAN Interface Sublayer) is a sublayer in the PCS that is responsible for adapting Ethernet MAC frames to be transmitted over a serial interface, such as a point-to-point optical link or a SONET/SDH network. The WIS performs three main functions:

  1. Interoperability with other WAN technologies: The WIS enables interoperability between Ethernet and other WAN technologies, such as POS (Packet-over-SONET/SDH). It does this by adapting the Ethernet MAC frames to be based on a serial protocol such as PPP (Point-to-Point Protocol), which is commonly used in WAN environments.

  2. Line Clocking: The WIS is responsible for generating the clock signal that synchronizes the transmission of data over the serial link. This clock signal is based on the synchronous nature of the POS requirements, either by clocking when the interface is connected back-to-back or external clocking when connected through DWDM (Dense Wavelength Division Multiplexing).

  3. Optical and Electrical Signal Conversion: The WIS also performs an important function in mapping the Ethernet frames onto the SONET/SDH network. It generates an equivalent POS optical and electrical signal on SONET/SDH protocols and APS (Automatic Protection Switching) to restore link failures in 50 ms.

Therefore, the correct answer to the given question is A, as interoperability with other WAN technologies is a primary function of the WIS. The other options, such as line clocking, signal conversion, and payload mapping, are important functions of other sublayers in the PCS, but they are not specifically attributed to the WIS.