Cisco Cisco ONS 15454 SONET Multiservice Provisioning Platform (MSPP) Guía De Diseño

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MPLS and VLAN Trunking (also referred to as Q-in-Q) require frame lengths exceeding 1522 
bytes.  The E-Series cards cannot support these protocols.  However, a workaround is possible 
using an externally connected device.   
 
Large frame support makes it possible to provide MPLS Ethernet.  However, many Ethernet 
switches, including the existing E-Series cards, do not support large frames, thus forcing routers 
to compensate as a workaround.  The router that needs to put an over-sized MPLS frame onto an 
Ethernet interface must fragment the data and adjust for an MTU of 1500 bytes.  However, some 
IP packets may be marked as do-not-fragment (DF bit), which should trigger MTU negotiation via 
ICMP.  If the initiating host doesn't support MTU discovery, the DF bit can be cleared on the 
Cisco device and force fragmentation.  However, fragmentation may hurt routing performance, 
particularly on a core device. 
 

 
E-Series cards have a distributed, shared memory architecture.  So the aggregate buffer memory 
applies to all ports and STSs on the card.  The E100T-12-G has 32 Mb of physical buffer 
memory.  Of this, 8 Mb is addressable for forwarding frames.  The E1000-2-G has 24 Mb of 
physical memory, with 6 Mb that is addressable. 
 

 
The E-Series Ethernet cards support IEEE 802.3x flow control and frame buffering to reduce data 
traffic congestion.  Approximately 8MB on the E100T-12-G and 6MB on the E1000-2-G of total 
buffer memory is available for the transmit and receive channels to buffer over-subscription.  
When the Ethernet connected device nears capacity, it will issue an 802.3x flow control frame 
called a “pause frame” which instructs the E-Series card to stop sending packets for a specific 
period of time. 
 
E-Series Ethernet cards will only respond to 802.3x “pause frames” connected to 802.3x 
compliant stations.  E-Series Ethernet cards will not issue 802.3x “pause frames” to end stations. 
 

 
E-Series cards do not support fast or Gigabit EtherChannel. 
 

 
For E-Series Ethernet cards, you can specify a value of exactly 10 Mb/s, 100 Mb/s or 1000 Mb/s 
per port on the user-interface side or STS-1, STS-3c, STS-6c or STS-12c on the optical transport 
side.  If the STS-N circuit is shared by multiple ONS 15454 nodes, the bandwidth per node 
cannot be limited.   Also, if multiple ports on the same node share the STS-N, the bandwidth per 
port cannot be limited. 
 
There are work-around solutions available to limit the amount of bandwidth allocated to a port.   
For example, if you need Ethernet rate shaping, Cisco can provide a solution using a switch such 
as the Cisco Catalyst 3550.