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Packet over SDH (POS)
POS Protocol Stack
POS Protocol Stack
POS technology can be found in the line cards of high speed routers. It is a layer 2
protocol that maps IP packets into the SONET/SDH frame. Data is first of all
segmented into an IP datagram that includes the 20-byte header. This datagram is
encapsulated via PPP packets and framing information is added with HDLC-like
framing. Gaps between frames are filled with flags (7E). The resulting data is
scrambled, and mapped octet synchronously into the SONET/SDH frame.
POS is described by the Internet Engineering Task Force (IETF) in the following
'Request for Comment' (RFC) documents:
RFC-1661 (Point- to- Point Protocol), RFC-1662 (PPP in HDLC-like framing) and
RFC-2615 (PPP over SONET/SDH).
Link Access
Control
HDLC
Framing
Payload
Scrambling
184
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IP
(RFC 791)
MPLS 'Shim' Headers (1-n)
*
*
IPCP
(RFC 1332)
LCP
PPP
(RFC 1661)
HDLC
Cisco HDLC
(RFC 1662,
RFC 2615)
Payload Scrambling: SSS (1+x
SONET
SDH
(GR-253-CORE)
(G.707)
155Mb/s
622Mb/s 2.5Gb/s
51Mb/s
*
MPLS supported on Rx but not on Tx
*
LCP, IPCP not supported
Layer 3 -
Network Layer
*
Layer 2 -
Link Layer
43
)
Layer 1 -
Physical Layer
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