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Cisco ONS 15600 SDH Reference Manual, Release 9.0
78-18400-01
Chapter 10 Ethernet Operation
10.3 Ethernet Rates and Mapping
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Valid pr synchronization
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Valid size
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Valid cyclic redundancy check (CRC)
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Valid interpacket gap
10.3 Ethernet Rates and Mapping
This section explains the Ethernet frame format, encapsulation methods, path and circuit configurations,
and oversubscription.
10.3.1 Frame Size
The IEEE 802.3 frame format is supported on the GE interfaces. The minimum frame size supported by
the system is 64 bytes; the interface drops smaller sized frames. The maximum frame size per interface
is 9600 bytes and can be provisioned independently. 9600 bytes is the maximum transmission unit
(MTU).
10.3.2 Encapsulations
The Ethernet ports can be provisioned for encapsulation in frame-mapped GFP (GFP-F) as per
ITU G.7041, Cisco HDLC/LEX as per RFC 1841, or Ethernet over Link Access Protocol over SDH
(LAPS) as per ITU X.86. LEX with CRC-32 is the default encapsulation, as it is supported by most Cisco
data cards.
The value of the C2 byte in a high-order SDH path is set to the following values for each encapsulation
type:
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0x1B for GFP-F
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0x18 for X.86
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0x05 for LEX with CRC-16
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0x01 for LEX with CRC-32
Note
Bridge Control Protocol (BCP), HDLC, LEX, and ITU X.86 are all variations of Point-to-Point Protocol
(PPP) in HDLC framing. To the Ethernet processor, the packets look essentially the same. GFP
encapsulation is drastically different.
10.3.3 Path and Circuit Sizes
GE interfaces can be mapped to all supported SDH paths of sizes VC3, VC4, VC4-2c, VC4-3c, VC4-4c,
VC4-8c, and VC4-16c.
Note
Mapping depends on the particular concatenation being supported on the card. It also depends on the
concatenation being supported on all of the network elements (NEs) that the end-to-end circuit is being
built through.
