SS2002-IP_over_SONET-4up

IP over SONET/SDH

ITU-T G.7041 Generic Framing Procedure

Broadband Network Technologies SS 2002 OKS/TKN 2

Table of Contents

•Introduction

•

Packet over SONET (PoS)

–Point-to-Point Protocol (PPP)

–High-level Data Link Control (HDLC)–Scrambling

•Simple Data Link (SDL) Protocol

•Multiple Access over SONET (MAPOS)•Generic Framing Procedure (GFP)

•

Link Capacity Adjustment Scheme (LCAS)

Introduction (cont.)

•

What do we need the whole protocol stack for?–Speed (up to the end of 1990ies):

wavelength>>SONET/SDH(40Gbit/s)>>ATM(2.4Gbit/s)>>IP(1Gbit/s)

–IP routers by now have become faster than ATM switches –IP routers implement QoS/CoS features •No need for an ATM layer anymore (?)•Other disadvantages of ATM:

–…Cell tax“ – an overhead of more than 10%

–Depending on the average IP packet size the overhead is around 25% in real IP over ATM networks

–ATM cells are too small for the backbone

•424 bit at 10 Gbit/s --> 40 ns per one cell

•Table lookup, header processing (VCI/VPI change, HEC), QoS monitoring /scheduling, all in 40 ns !?

•Maximum Receive Unit (default: 1500 octets)

•Authentication protocol: password, challenge handshake

•Quality protocol:

–Protocol field == 0xC025 -> will expect link reports

•Magic number

–Relates responses with requests

–Random number, used to detect looped back links

•Protocol field compression

–Only one field is used even for 2-byte protocols

•Address and Control field compression

–Address and control field are not transmitted

–Is recognized by the receiver, because protocol field is not allowed to

be 0xFF

Broadband Network Technologies SS 2002 OKS/TKN 9PPP over SONET (RFC 1619)

•

In PPP/LCP (RFC 1619) recommended:–Magic number

–No address and Control field compression –No protocol field compression

–32-bit FCS (Frame check sequence)•

In SONET/SDH

–PATH Signal Label (C2)=207 =0xCF –Originally, no scrambling of the payload

Broadband Network Technologies SS 2002 OKS/TKN 10

PPP over SONET

•

HDLC frame is written into SONET/SDH VC4–Starts directly after the Path Overhead (POH)–Write the frame row by row into the payload –Long frames can continue over payload borders

•Introduce a buffering delay of 125µs •Should not pose problems with STM-Nc

–When nothing is to be transmitted, send flags (0x7E) continuously –In point-to-point connections (PoS card to PoS card) less accurate clocks may be used

•…SONET/SDH light “

PPP over SONET

•

The SONET/SDH scrambler:

–Located in the PHOTONIC layer of SONET/SDH

–Designed to provide enough 1-to-0-changes in a byte-multiplexed environment

–Polynomial 1+x 6+x 7 , works similar to a CRC

–Seed 0xFF, restarted at each frame, only payload scrambled

•

When introducing ATM over SONET/SDH, an additional scrambler was needed

– A single user can control a larger part of the SONET frame and induce longer sequences of z eroes or ones

– A self-synchroni z ing 1+X 43 self synchronous scrambler was introduced

PPP over SONET -Scrambling

•

A malicious user could cause a desaster by introducing a pre-scrambled bit sequence of 1500 byte

–Only about 90 packets of 1500 byte guarantee that 13µs of z eroes will be transmitted

–SONET/SDH uses NR Z coding (1=light on, 0=light off)

–LOS (Loss Of Signal) timer defined between 2.3 and 100 µs with most of the implementations between 13 and 27µs –Bit synchronisation may be lost after 80 bits already !–LOS causes APS (Automatic Protection Switching)

•50 ms interruption plus the need for additional links

–The user could not even be tracked with normal management equipment and protocols