Cisco 15327 - Manual (Page 383)

23-3
Ethernet Card Software Feature and Configuration Guide, R7.2
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 physical 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 on 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 standard. 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, packets 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 reduce 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 period of time. The sending
station waits the requested amount of time before sending more 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