Cisco 15327 - Manual (Page 339)

20-7
Ethernet Card Software Feature and Configuration Guide, R7.2
Chapter 20 POS on ONS Ethernet Cards
E-Series Proprietary
E-Series Proprietary
The E-Series uses a proprietary HDLC-like encapsulation that is incompatible with LEX, Cisco HDLC,
or PPP/BCP. This proprietary encapsulation prevents the E-Series from interoperating with other ONS
Ethernet cards.
In Release 5.0 and later, the ONS 15327 E-Series card, E10/100-4, supports LEX encapsulation with a
16-bit CRC as well as the original proprietary E-Series encapsulation.
POS Framing Modes
The framing mode is the type of framing mechanism employed by the ONS Ethernet card to frame and
encapsulate data packets into a POS signal. These data packets were originally encapsulated in Ethernet
frames that entered the standard Fast Ethernet or Gigabit Ethernet interfaces of the ONS Ethernet card.
All ONS Ethernet cards support HDLC framing. ML-Series and CE-Series cards also offer GFP-F
framing mode.
HDLC Framing
HDLC is one of the most popular Layer 2 protocols. The framing mechanism used by the HDLC
protocol, HDLC framing, is employed by a variety of other protocols, including POS on the ONS
Ethernet cards. The HDLC framing mechanism is detailed in the IETF’s RFC 1662, “PPP in HDLC-like
Framing.”
The HDLC frame uses the zero insertion/deletion process (commonly known as bit stuffing) to ensure
that the bit pattern of the delimiter flag does not occur in the fields between flags. The HDLC frame is
synchronous and therefore relies on the physical layer to provide a method of clocking and
synchronizing the transmission and reception of frames.
GFP-F Framing
GFP defines a standard-based mapping of different types of services onto SONET/SDH. The ML-Series
and CE-Series support frame-mapped GFP (GFP-F), which is the PDU-oriented client signal adaptation
mode for GFP. GFP-F maps one variable length data packet onto one GFP packet.
GFP is composed of common functions and payload specific functions. Common functions are those
shared by all payloads. Payload-specific functions are different depending on the payload type. GFP is
detailed in the ITU recommendation G.7041.
POS Characteristics of Specific ONS Ethernet Cards
The following sections list and illustrate the various framing and encapsulation options supported by
specific ONS Ethernet cards.