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REVIEW DRAFT—CISCO CONFIDENTIAL
14-12
Cisco ONS 15454 SDH Reference Manual, R5.0
April 2008
Chapter 14 Ethernet Operation
14.3.2 E-Series IEEE 802.3z Flow Control
because the E1000-2-G has a maximum bandwidth of VC4-4c. Ethernet frame sizes up to 1522 bytes are
also supported, which allows transport of IEEE 802.1Q tagged frames. The larger maximum frame size
of Q-in-Q frames (802.1Q in 802.1Q wrapped frames) are not supported.
Figure 14-11 E-Series Mapping Ethernet Ports To SDH STM Circuits
Port-mapped mode disables Layer 2 functions supported by the E-Series in single-card and multicard
mode, including STP, VLANs, and MAC address learning. It significantly reduces the service-affecting
time for cross-connect and TCC2 card switches.
Port-mapped mode does not support VLANs in the same manner as multicard and single-card mode. The
ports of E-Series cards in multicard and single-card mode can join specific VLANs. E-Series cards in
port-mapped mode do not have this Layer 2 capability and only transparently transport external VLANs
over the mapped connection between ports. An E-Series card in port-mapped mode does not inspect the
tag of the transported VLAN, so a VLAN range of 1 through 4096 can be transported in port-mapped
mode.
Port-mapped mode does not inspect or validate the Ethernet frame header. The Ethernet CRC is
validated, and any frame with an invalid Ethernet CRC is discarded.
Port-mapped mode also allows the creation of STM-N circuits between any two E-Series cards; it does
not allow an E-Series cards to connect to the ML-Series or G-Series cards.
14.3.2 E-Series IEEE 802.3z Flow Control
The E100T-G card in any mode and the E1000-G card in port-mapped mode support IEEE 802.3z
symmetrical flow control and propose symmetric flow control when auto-negotiating with attached
Ethernet devices. For flow control to operate, both the E-Series port and the attached Ethernet device
must be set to auto negotiation (AUTO) mode. The attached Ethernet device may also need to have flow
control enabled. The flow-control mechanism allows the E-Series to respond to pause frames sent from
external devices and to send pause frames to external devices.
Flow control matches the sending and receiving device throughput to that of the bandwidth of the
STM-N circuit. For example, a router might transmit to the Gigabit Ethernet port on the E-Series card
in port-mapped mode. The data rate transmitted by the router can occasionally exceed 622 Mbps, but the
ONS 15454 SDH circuit assigned to the E-Series port in port-mapped mode is a maximum of VC4-4c
(622.08 Mbps). In this scenario, the ONS 15454 SDH sends out a pause frame and requests that the
router delay its transmission for a certain period of time.
SONET/SDH
ONS Node
ONS Node
1:1 Ethernet port to STS/VC circuit mapping
83497