23-3
Ethernet Card Software Feature and Configuration Guide, R7.2
January 2009
Chapter 23 E-Series and G-Series Ethernet Operation
G-Series Example
Software R4.0 and later identifies G1K-4 cards at physical installation. Software R3.4 and earlier
identifies both G1000-4 and G1K-4 cards as G1000-4 cards at physi cal installation.
G-Series Example
Figure 23-1 shows a G-Series application. In this example, data traffic from the Gigabit Ethernet port of
a high-end router travels across the ONS node’s point-to-point circuit to the Gigabit Ethernet port of
another high-end router.
Figure 23-1 Data Traffic on a G-Series Point-to-Point Circuit
The G-Series cards carry any Layer 3 protocol that can be encapsulated and transported over Gigabit
Ethernet, such as IP or IPX. The data is transmitted o n the Gigabit Ethernet fiber into the standard
Cisco Gigabit Interface Converter (GBIC) on an ONS 15454 or ONS 15454 SDH G-Series card or into
the standard Small Form-factor Pluggable (SFP) modules on an ONS 15327 G-Series card. The G-Series
card transparently maps Ethernet frames into the SONET/SDH payload by multiplexing the payload onto
an OC-N/STM-N card. When the payload reaches the destination node, the process is reversed and the
data is transmitted from the standard Cisco GBIC or SFP in the destination G-Series card onto the
Gigabit Ethernet fiber.
The G-Series cards discard certain types of erroneous Ethernet frames rather than transport them over
SONET/SDH. Erroneous Ethernet frames include corrupted frames with cycle redundancy check (CRC)
errors and under-sized frames that do not conform to the minimum 64-byte length Ethernet standar d. The
G-Series cards forward valid frames unmodified over the SONET/SDH network. Information in the
headers is not affected by the encapsulation and transport. For example, packet s with formats that
include IEEE 802.1Q information will travel through the process unaffected.
IEEE 802.3z Flow Control and Frame Buffering
The G-Series supports IEEE 802.3z flow control and frame buffering to red uce data traffic congestion.
To prevent over-subscription, 512 KB of buffer memory is available for the receive and transmit channels
on each port. When the buffer memory on the Ethernet port nears capacity, the G-Series uses
IEEE 802.3z flow control to transmit a pause frame to the source at the opposite end of the Gigabit
Ethernet connection.
The pause frame instructs the source to stop sending packets for a specific perio d of time. The sending
station waits the requested amount of time before sending m ore data. Figure 23-1 illustrates pause
frames being sent and received by G-Series cards and attached switches.
The G-Series cards have symmetric flow control. Symmetric flow control allows the G-Series cards to
respond to pause frames sent from external devices and to send pause frames to external devices. Prior
to Software R4.0, flow control on the G-Series cards was asymmetric, meaning that the cards sent pause
frames and discarded received pause frames.
Software Release 5.0 and later features separate CTC provisioning of autonegotiation and flow control .
A failed autonegotiation results in a link down.
67832
STS-N/VC-N
SONET/SDH
Pause Frames
Gig-E ONS Node ONS Node
Pause Frames
Gig-E