EoS

1
EoS

• Yaakov (J) Stein
• Chief Scientist
• RAD Data Communications

2
Course Outline

• 1) Introduction
• 2) Background - Ethernet
• 3) Background HDLC
• 4) Background - PPP
• 5) Background - SONET/SDH
• 6) VCAT
• 7) LCAS
• 8) POS (PPP over SONET/SDH RFC 1619/2615)
• 9) LAPS
• 10) GFP
• 11) Alternatives

3
Introduction
4
Motivation

• Assume that you are a traditional operator
• You have an extensive SONET/SDH network
• This network has cost you Millions-Billions to
  build
• This network is highly reliable
• Your staff is well trained to maintain it
• You may have not yet reached Return On Investment
• It supports the service that brings the most
  revenue voice
• It supports the service with the highest margin
  leased lines
• But suddenly customers are asking for something
  new
• Ethernet handoff
• And new competitors are willing to supply it!

5
Option 1 install new infrastructure

• You may choose to build a new IP/MPLS based
  network (BT 21CN approach)
• Yes this means significant investment, but this
  is definitely the future!
• But SONET/SDH has comparative advantages
• Reliable optical transport
• Well known technology and protocols
• Ubiquitous with present operators
• Many supported data rates (from 1 Mbps to many
  Gbps)
• Low overhead
• Strong OAM (MPLS isnt there yet )
• So if you replace the existing network
• How will you handle the service that brings your
  main income voice ?
• You may lose your existing leased line customers
• You will need to solve the timing distribution
  problem
• And if you keep your existing network
• You need to maintain two completely different
  networks !
• This sounds problematic !

6
Option 2 leased lines

• You can try to convince these customers to use
  leased lines
• The customer converts traffic into T1/E1 (e.g. by
  using frame relay)
• You can supply this service now
• The major expense is for the customer (who needs
  FRAD, CSU/DSU, etc.)
• Leased lines are profitable
• But this only worked before the new competitors
  appeared
• You will probably lose these customers !

7
Option 3 ATM

• You can offer ATM service
• The customer converts traffic into ATM (AAL5)
• You can supply this service now
• ATM is a well-known technology
• ATM is a reliable and high-quality service
• ATM maps efficiently onto SONET/SDH
• You may even be able to perform the conversion at
  your POP
• (but Ethernet is notoriously hard to
  transport over distances)
• But ATM has its disadvantages
• ATM has high overhead but you can only charge
  for user BW
• ATM is an additional network
• you will have to train and pay new staff
• maintain another operations center
• ATM usually carries IP, not native Ethernet
  traffic

8
Option 4 EoS

• A new choice is Ethernet over SONET/SDH (EoS)
• The customers Ethernet traffic is transported
  directly by SONET/SDH
• You build on your existing network
• You transport native Ethernet
• neednt route at network edges
• maintain all Ethernet features
• New SONET/SDH features make EoS highly efficient
• But EoS and related protocols are new
  technologies
• You may need to upgrade existing equipment
• Market hasnt yet stabilized on one technology
• So you will probably need to take this course !

9
Worlds Apart

• SONET/SDH is presently the most prevalent
  transport infrastructure
• Ethernet is by far the most popular user data
  interface
• So we need efficient methods for carrying
  Ethernet over SONET
• But Ethernet
• comes in bursty frames (packets)
• uses basic rates of 10, 100, 1000 Mbps
• While SONET/SDH
• is constant bit rate
• is designed for various rates such as 1.6, 2.176,
  6.784 Mbps
• So the job isnt easy !

10
Standards we will encounter

• IEEE 802.3 Ethernet
• ISO 3309 HDLC
• RFC1661 PPP (ex 1548)
• RFC1662 PPP in HDLC framing (ex 1549)
• RFC2615 PoS (ex 1619)
• G.707 SDH (especially the new section 11
  VCAT)
• G.709 OTN
• G.7041 GFP
• G.7042 LCAS for SDH
• G.7043 VCAT for PDH
• X.85 IP over SDH using LAPS
• X.86 Ethernet over SDH using LAPS

11
BackgroundEthernet
12
Ethernet frame

• For our purposes, Ethernet is any layer 2
  protocol
• using 1 of the following frame formats

13
Ethernet frame size

• Minimum frame is 64 bytes
• Maximum payload was 1500 bytes
• and maximum frame was 1522 bytes
• 802.3as lengthened maximum frame to 2000 bytes
• Various physical layer modulations and framing
• Rates 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps,

14
BackgroundHDLC
15
Packet to bit stream

• The first problem in converting Ethernet to TDM
• Ethernet consists of frames carrying packets
• TDM is a continuous bit stream
• We can convert a sequence of packets into a bit
  stream
• by using an idle code
• For example, we can use a sequence of 1s as idle
  indication
• The appearance of a 0 bit indicates that data
  follows

111111111111111111111110 packet 1
0111111111111111111110 packet 2
011111111111111111111110 01111110 packet 3
01111111111111111
16
Packet to bit stream (cont.)

• How does the receiver know when to return to
  idle?
• We use a specific flag (HDLC uses hex 7E
  01111110)
• We can use the flag as the idle code as well
• Some implementations allow zero sharing
• But the flag must not appear in valid data!
• If we have access to the physical layer we can
  mark there (violations)
• Otherwise (we only access bits) we must disallow
  the idle code
• by replacing it with something else

01111110 01111110 01111110 packet 1 01111110
01111110 01111110 packet 2 01111110 01111110
01111110 01111110 packet 3 01111110
0111111011111101111110 packet 1 011111101111110
01111110 packet 2 011111101111110 1111110 1111110
packet 3 011111101111110
17
HDLC flags

• ISO developed High level Data Link C based on
  IBMs SDLC
• HDLC inputs packets of bytes
• HDLC uses hex 7E as its idle code (flag)
  01111110
• So an idle HDLC stream repeats 7E
• Alternatively, 1s can be sent as idle, flags as
  delineators
• There are two methods of disallowing flags
• bit stuffing (zero insertion)
• byte (octet) stuffing

01111110 01111110 01111110 packet 1 01111110
01111110 01111110 packet 2 01111110 01111110
01111110 01111110 packet 3 01111110
11111111111111111 01111110 packet 1 01111110
111111111101111110 packet 2 01111110
11111111111111111101111110 packet 3 01111110
18
Bit stuffing / zero insertion

• ECMA-40
• Whenever the encoder sees 5 successive 1s it
  appends a 0
• thus there are never 6 successive 1s in the data
• When the decoder sees 5 successive 1s
• If the next bit is a 0 it is deleted
• If the next bit is a 1 then this is the closing
  flag
• Notes
• bit stream length is no longer necessarily
  divisible by 8
• bit stream length is not a priori predictable
• worst case expansion is 20
• encoding/decoding is easy in HW, hard in SW

19
Byte (octet) stuffing

• RFC1549
• Whenever the encoder sees hex 7E
• It replaces it with 7D 5E
• Whenever the encoder sees hex 7D
• It replaces it with 7D 5D
• Optionally other codes (e.g. some under hex 20)
  can be escaped
• Second byte is original with 6th bit complemented
  (xor with hex 20)
• e.g. Q hex 11? 7D 31 S hex 13 ? 7D 33
• When the receiver sees 7D xx
• It replaces it with the original byte
  (complementing 6th bit)
• Notes
• bit stream remains byte oriented
• length expansion is typically about 1, but can
  range from 0 to 100 !
• (there is also a consistent overhead
  algorithm but not in use)
• encoding/decoding is easy in SW

20
HDLC framing

• HDLC frame is bounded by flags, and has a
  particular structure
• Many variants (SDLC, ISO, LAPB, LAPD, LAPF, LAPS,
  SS7, PPP-HDLC, Cisco-HDLC, etc)
• Address
• There may be no address (e.g. SS7 HDLC)
• SDLC always had 8 bit addresses
• ISO 3309 HDLC has structured multibyte address
• Service Access Point Identifier (MSB of SAPI 1
  may indicate broadcast/multicast)
• EA1 means 8 bit, EA0 means extended address
• C/R1 for commands, C/R0 for responses
• The single byte hex FF is recognized as the
  broadcast address

EA
C/R
SAPI
EA
21
HDLC control

• HDLC networks can be configured
• Balanced all stations have equal responsibility
• Unbalanced primary and one or more secondary
  stations
• and HDLC can operate
• Best effort (datagram)
• uses Un-numbered (U) frames
• Reliable (Asynchronous Balanced Mode)
• uses frames with sequence numbers in control
  field
• Information (I) frames (data acknowledgement)
• Supervisory (S) frames (only acknowledgement)
• The various frame types are indicated by the
  control field
• which varies widely between different protocols

22
HDLC FCS

• HDLC uses a Frame Check Sequence to detect errors
• The FCS is implemented as a shift-register
• CRC-16 X16 X12 X5 1
• CRC-32 X32 X26 X23 X22 X16 X12 X11
  X10 X8 X7 X5 X4 X2 X 1
• Some HDLC-based protocols require 32 bit FCS
• others allow 16 bit but recommend 32 bit FCS

23
BackgroundPPP
24
Point to Point Protocol (RFC 1661)

• PPP is a method for transporting datagrams
  between 2 peers
• over full-duplex, point-to-point data links
• for example short lines, leased lines, dial-up
  modems
• PPP may be used to connect hosts to routers, and
  routers to routers
• PPP is made up of 3 components
• encapsulation method for (multiprotocol)
  datagrams
• Link Control Protocol for establishing,
  configuring,
• and testing data-link connections
• Network Control Protocols for establishing
• and configuring different network-layer
  protocols
• PPP is a suite containing many protocols
• ML-PPP, PPPoE, BAP, BCP, IPCP,

25
Basic PPP encapsulation (RFC 1661)

• Encapsulation enables demuxing of different
  network-layer protocols
• Only 1 field needs to be examined for protocol
  determination
• Protocol field obeys ISO 3309 rules
• protocol value must be odd (for EA1)
• if 16-bit, then the LSB of first byte must be
  zero (for EA0)
• PPP protocol values managed by IANA
• (http//www.iana.org/assignments/ppp-numbers)
• Padding may be used (e.g. to cause header to fall
  on 32-bit boundary)

26
PPP using HDLC framing (RFC 1662)

• When using PPP over synchronous links
• we use HDLC-like framing
• 1 byte Broadcast address is used by default
  (users may define alternative address)
• Synchronous Link may be bit-oriented or
  byte-oriented
• Basic PPP encapsulation is extended by 8 bytes
• Bit stuffing or byte stuffing allowed
• Escape mechanism
• allows transparent transfer of control data (e.g.
  S/Q)
• enables removal of spurious control data
  (inserted by intermediate boxes)

27
RFC1662 vs. X.85

• ITU-T X.85 defines IP over SDH using LAPS (will
  study later)
• Its encapsulation is similar to RFC1662 (but
  cant co-exist with it)
• Instead of the protocol ID it has a SAPI 21 for
  IPv4 57 for IPv6
• The FCS MUST be 32 bits and no padding is used
• No special escaping is defined

PPP frame
1662
flag 7E
address 04
ctrl 03
IP Packet
FCS (32b)
SAPI (16b)
flag 7E
X.85
28
BackgroundSONET/SDH
Note For more information see SONET/SDH course.
29
SONET architecture

• SONET (SDH) has at 3 layers
• path end-to-end data connection, muxes
  tributary signals path section
• there are STS paths Virtual Tributary (VT)
  paths
• line protected multiplexed SONET payload
  multiplex section
• section physical link between adjacent elements
  regenerator section
• Each layer has its own overhead to support needed
  functionality
• 
  SDH
  terminology

30
SONET STS-1 frame

• Synchronous Transfer Signals are bit-signals (OC
  are optical)
• Each STS-1 frame is 90 columns 9 rows 810
  bytes
• There are 8000 STS-1 frames per second
• so each byte represents 64 kbps (each column is
  576 kbps)
• Thus the basic STS-1 rate is 51.840 Mbps

31
SDH STM-1 frame

• Synchronous Transport Modules are the bit-signals
  for SDH
• Each STM-1 frame is 270 columns 9 rows 2430
  bytes
• There are 8000 STM-1 frames per second
• Thus the basic STM-1 rate is 155.520 Mbps
• 3 times the STS-1 rate!

32
SONET/SDH rates
SONET SDH columns rate
STS-1 90 51.84M
STS-3 STM-1 270 155.52M
STS-12 STM-4 1080 622.080M
STS-48 STM-16 4320 2488.32M
STS-192 STM-64 17280 9953.28M

• STS-N has 90N columns STM-M corresponds to
  STS-N with N 3M
• SDH rates increase by factors of 4 each time
• STS/STM signals can carry PDH tributaries, for
  example
• STS-1 can carry 1 T3 or 28 T1s or 1 E3 or 21 E1s
• STM-1 can carry 3 E3s or 63 E1s or 3 T3s or 84
  T1s

33
SONET/SDH tributaries
SONET SDH T1 T3 E1 E3 E4
STS-1 28 1 21 1
STS-3 STM-1 84 3 63 3 1
STS-12 STM-4 336 12 252 12 4
STS-48 STM-16 1344 48 1008 48 16
STS-192 STM-64 5376 192 4032 192 64

• E3 and T3 are carried as Higher Order Paths
  (HOPs)
• E1 and T1 are carried as Lower Order Paths (LOPs)

34
STS-1 frame structure
90 columns
Synchronous Payload Envelope
3 rows
9 rows
9 rows
6 rows
section line overhead

• Section overhead is 3 rows 3 columns 9 bytes
  576 kbps
• framing, performance monitoring, management
• Line overhead is 6 rows 3 columns 18 bytes
  1152 kbps
• protection switching, line maintenance,
  mux/concat, SPE pointer
• SPE is 9 rows 87 columns 783 bytes 50.112
  Mbps
• Similarly, STM-1 has 9 (different) columns of
  sectionline overhead !

35
STM-1 frame structure
270 columns

Transport Overhead TOH

• Similarly, STM-1 has 9 (different) columns of
  transport overhead !
• RS overhead is 3 rows 9 columns
• Pointer overhead is 1 row 9 columns
• MS overhead is 5 rows 9 columns
• SPE is 9 rows 87 columns

36
Scrambling

• SONET/SDH receivers recover clock based on
  incoming signal
• Insufficient number of 0-1 transitions causes
  degradation of clock performance
• In order to guarantee sufficient transitions,
  SONET/SDH employ a scrambler
• All data except first row of section overhead is
  scrambled
• Scrambler is 7 bit self-synchronizing X7 X6
  1
• Scrambler is initialized with ones
• A short scrambler is sufficient for voice data
• but NOT for data which may contain long stretches
  of zeros
• When sending data an additional payload scrambler
  is used
• modern standards use 43 bit X43 1
• run continuously on ATM payload bytes (suspended
  for 5 bytes of cell tax)
• run continuously on HDLC payloads

37
HOP SPE structure

• 2 bytes in the line overhead point to the STS
  path overhead POH
• pointer (floating) allows frequency/phase
  compensation
• (after re-arranging) POH is one column of 9 rows
  (9 bytes 576 kbps)

38
Path overhead
C2 (hex) Payload type
00 unequipped
01 nonspecific
02 LOP (TUG)
04 E3/T3
12 E4
13 ATM
16 PoS RFC 1662
18 LAPS X.85
1A 10G Ethernet
1B GFP
CF PoS - RFC1619

• POH is responsible for
• path performance monitoring
• status (including of mapped payloads)
• trace
• 2 bytes are of particular interest to us
• C2 is the signal label
• indicates path payload type
• H4 is the multiframe indication
• used by VCAT/LCAS (discussed later)

39
STS-1 HOP

• 1 column of SPE is POH
• 2 more (fixed stuffing) columns are reserved
• We are left with
• 84 columns 756 bytes 48.384 Mbps for payload
• This is enough for a E3 (34.368M) or a T3
  (44.736M)

40
LOP
VTG
1
87
59
30
1
2
3
4
5
6
7

• To carry lower rate payloads, divide 84 available
  columns
• into 7 12 interleaved columns, i.e. 7 Virtual
  Tributary (VT) groups
• VT group is 12 columns of 9 rows, i.e. 108 bytes
  or 6.912 Mbps
• VT group is composed of VT(s)
• There are different types of VT in order to carry
  different types of payload
• all VTs in VT group must be of the same type
• but different VT groups in same SPE can have
  different VT types
• A VT can have 3, 4, 6 or 12 columns

41
SONET/SDH VT/VC types
VT/STS VC column rate payload
VT 1.5 VC-11 3 1.728 DS1 (1.544)
VT 2 VC-12 4 2.304 E1 (2.048)
VT 3 6 3.456 DS1C (3.152)
VT 6 VC-2 12 6.912 DS2 (6.312)
STS-1 VC-3 48.384 E3 (34.368)
STS-1 VC-3 48.384 DS3 (44.736)
STS-3c VC-4 149.760 E4 (139.264)
4 per group
3 per group
LOP
2 per group
1 per group
HOP
standard PDH rates map efficiently into SONET/SDH
!
42
Payload capacity

• VT1.5/VC-11 has 3 columns 27 bytes 1.728 Mbps
  
• but 2 bytes are used for overhead
• so actually only 25 bytes 1.6 Mbps are
  available
• Similarly
• VT2/VC-12 has 4 columns 36 bytes 2.304 Mbps
• but 2 bytes are used for overhead
• So actually only 34 bytes 2.176 Mbps are
  available

43
VCATVirtual Concatenation
44
Concatenation

• Payloads that dont fit into standard VT/VC sizes
  can be accommodated
• by concatenating of several VTs / VCs
• For example, 10 Mbps doesnt fit into any VT or
  VC
• so w/o concatenation we need to put it into an
  STS-1 (48.384 Mbps)
• the remaining 38.384 Mbps can not be used
• We would like to be able to divide the 10 Mbps
  among
• 7 VT1.5/VC-11 s 7 1.600 11.20 Mbps or
• 5 VT2/VC-12 s 5 2.176 10.88 Mbps

45
Concatenation

• There are 2 ways to concatenate X VTs or VCs
• Contiguous Concatenation (G.707 11.1)
• HOP STS-Nc (SONET) or VC-4-Nc (SDH)
• or LOP 1-7 VC-2-Nc into a VC-3
• since has to fit into SONET/SDH payload
• only STS-Nc N3 4n or VC-4-Nc N4n
• components transported together and in-phase
• requires support at intermediate network elements
  
• Virtual Concatenation (VCAT G.707 11.2)
• HOP STS-1-Xv or STS-Nc-Xv (SONET) or VC-3/4-Xv
  (SDH)
• or LOP VT-1.5/2/3/6-Xv (SONET) or VC-11/12/2-Xv
  (SDH)
• HOP X 256 LOP X 64 (limitation due to
  bits in header)
• payload split over multiple STSs / STMs
• fragments may follow different routes
• requires support only at path terminations
• requires buffering and differential delay
  alignment

46
Contiguous Concatenation STS-3c
270 columns

9 rows
258 columns of SPE
STS-3
9 columns of section and line overhead
258 columns 0.576 148.608 Mbps
3 columns of path overhead
270 columns

9 rows
STS-3c
260 columns of SPE
9 columns of section and line overhead
1 column of path overhead
260 columns 0.576 149.760 Mbps
47
STS-N vs. STS-Nc

• Although both have raw rates of 155.520 Mbps
• STS-3c has 2 more columns (1.152Mbps) available
• More generally, For STS-Nc gains (N-1) columns
• e.g. STS-12c gains 11 columns 6.336Mbps vis a
  vis STS-12
• STS-48c gains 47 columns 27.072 Mbps
• STS-192c gains 191 columns 110.016 Mbps !
• However, an STS-Nc signal is not as easily
  separable
• when we want to add/drop component signals

48
Virtual Concatenation

H4

• VCAT is an inverse multiplexing mechanism
  (round-robin)
• VCAT members may travel along different routes in
  SONET/SDH network
• Intermediate network elements dont need to know
  about VCAT
• (unlike contiguous concatenation that is handled
  by all intermediate nodes)

49
SDH virtually concatenated VCs
VC Capacity (Mbps) if all members in one VC
VC-11-Xv 1.600, 3.200, 1.600X in VC-3 X 28 C 44.800 in VC-4 X 64 C 102.400
VC-12-Xv 2.176, 4.352, 2.176X in VC-3 X 21 C 45.696 in VC-4 X 63 C 137.088
VC-2-Xv 6.784, 13.568, , 6.784X in VC-3 X 7 C 47.448 in VC-4 X 21 C 142.464

• So we have many permissible rates
• 1.600, 2.176, 3.200, 4.352, 4.800, 6.400, 6.528,
  6.784, 8.000,

50
SONET virtually concatenated VTs
VT Capacity (Mbps) If all members in one STS
VT1.5-Xv 1.600, 3.200, 1.600X in STS-1 X 28 C 44.800 in STS-3c X 64 C 102.400
VT2-Xv 2.176, 4.352, 2.176X in STS-1 X 21 C 45.696 in STS-3c X 63 C 137.088
VT3-Xv 3.328, 6.656, 3.328X in STS-1 X 14 C 46.592 in STS-3c X 42 C 139.776
VT6-Xv 6.784, 13.568, 6.784X in STS-1 X 7 C 47.448 in STS-3c X 21 C 142.464

• So we have many permissible rates
• 1.600, 2.176, 3.200, 3.328, 4.352, 4.800, 6.400,
  6.528, 6.656, 6.784,

51
Efficiency comparison
rate w/o VCAT efficiency with VCAT efficiency
10 STS-1 21 VT2-5v VC-12-5v 92
100 STS-3c VC-4 67 STS-1-2v VC-3-2v 100
1000 STS-48c VC-4-16c 42 STS-3c-7v VC-4-7v 95

• Using VCAT increases efficiency to close to 100 !

52
PDH VCAT

• Recently ITU-T G.7043 expanded VCAT to
  E1,T1,E3,T3
• Enables bonding of up to 16 PDH signals to
  support higher rates
• Only bonding of like PDH signals allowed (e.g.
  cant mix E1s and T1s)
• Multiframe is always per G.704/G.832 (e.g. T1
  ESF 24 frames, E1 16 frames)
• 1 byte per multiframe is VCAT overhead (SQ, MFI,
  MST, CRC)
• Supports LCAS (to be discussed next)

53
PDH VCAT overhead octet

• There is one VCAT overhead octet per multiframe,
  so net rate is
• T1 (2424-1) 575 data bytes per 3 ms.
  multiframe 191.666 kB/s
• E1 (1630-1) 495 data bytes per 2 ms multiframe
  247.5 kB/s
• T3 and E3 can also be used
• We will show the overhead octet format later
• (when using LCAS, the overhead octet is called
  VLI)

54
Delay compensation

• 802.1ad Ethernet link aggregation cheats
• each identifiable flow is restricted to one link
• doesnt work if single high-BW flow
• VCAT is completely general
• works even with a single flow
• VCG members may travel over completely separate
  paths
• so the VCAT mechanism must compensate for
  differential delay
• Requirement for over ½ second compensation
• Must compensate to the bit level
• but since frames have Frame Alignment Signal
• the VCAT mechanism only needs to identify
  individual frames

55
VCAT buffering

• Since VCAT components may take different paths
• At egress the members
• are no longer in the proper temporal relationship
  
• VCAT path termination function buffers members
• and outputs in proper order (relying on POH
  sequencing)
• (up to 512 ms of differential delay can be
  tolerated)
• VCAT defines a multiframe to enable delay
  compensation
• length of multiframe determines delay that can be
  accommodated
• H4 byte in members POH contains
• sequence indicator (identifies component) (number
  of bits limits X)
• MFI multiframe indicator (multiframe sequencing
  to find differential delay)

56
Multiframes and superframes

• Here is how we compensate for 512 ms of
  differential delay
• 512 ms corresponds to a superframe is 4096 TDM
  frames (40960.125m512m)
• For HOS SDH VCAT and PDH VCAT (H4 byte or PDH
  VCAT overhead)
• The basic multiframe is 16 frames
• So we need 256 multiframes in a superframe
  (256164096)
• The MultiFrame Indicator is divided into two
  parts
• MFI1 (4 bits) appears once per frame
• and counts from 0 to 15 to sequence the
  multiframe
• MFI2 (8bits) appears once per multiframe
• and counts from 0 to 255
• For LOS SDH (bit 2 of K4 byte)
• a 32 bit frame is built and a 5-bit MFI is
  dedicated
• 32 multiframes of 16 ms give the needed 512 ms

57
LCASLink Capacity Adjustment Scheme
58
LCAS

• LCAS is defined in G.7042 (also numbered Y.1305)
• LCAS extends VCAT by allowing dynamic BW changes
• LCAS is a protocol for dynamic adding/removing of
  VCAT members
• hitless BW modification
• similar to Link Aggregation Control Protocol for
  Ethernet links
• LCAS is not a control plane or management
  protocol
• it doesnt allocate the members
• still need control protocols to perform actual
  allocation
• LCAS is a handshake protocol
• it enables the path ends to negotiate the
  additional / deletion
• it guarantees that there will be no loss of data
  during change
• it can determine that a proposed member is ill
  suited
• it allows automatic removal of faulty member

59
LCAS how does it work?

• LCAS is unidirectional (for symmetric BW need to
  perform twice)
• LCAS functions can be initiated by source or sink
• LCAS assumes that all VCG members are error-free
• LCAS messages are CRC protected
• LCAS messages are sent in advance
• sink processes messages after differential
  compensation
• message describes link state at time of next
  message
• receiver can switch to new configuration in time
• LCAS messages are in the upper nibble of
• H4 byte for HOS SONET/SDH
• K4 byte for LOS SONET/SDH
• VCAT overhead octet for PDH VCAT and LCAS
  Information
• LCAS messages employ redundancy
• messages from source to sink are member specific
• messages from sink to source are replicated

60
LCAS control messages

• LCAS adds fields to the basic VCAT ones
• Fields in messages from source to sink
• MFI MultiFrame Indicator
• SQ SeQuence indicator (member ID inside
  VCAT group)
• CTRL ConTRoL (IDLE, being ADDed, NORMal, End
  of Sequence, Do Not Use)
• GID Group Identification (identifies VCAT
  group)
• Fields in messages from sink to source (identical
  in all members)
• MST Member Status (1 bit for each VCG
  member)
• RS-Ack ReSequence Acknowledgement
• Fields in both directions
• CRC Cyclic Redundancy Code
• The precise format depends on the VCAT type (H4,
  K4, PDH)
• Note for H4 format SQ is 8 bits, so up to 256
  VCG members
• for PDH SQ is only 4 bits, so up to 16
  VCG members

61
H4 format
MFI1
MFI2 bits 1-4 0 0 0 0
MFI2 bits 5-8 0 0 0 1
CTRL 0 0 1 0
0 0 0 GID 0 0 1 1
0 0 0 0 0 1 0 0
0 0 0 0 0 1 0 1
CRC-8 bits 1-4 0 1 1 0
CRC-8 bits 5-8 0 1 1 1
MST bits 1 0 0 0
more MST bits 1 0 0 1
0 0 0 RS-ACK 1 0 1 0
0 0 0 0 1 0 1 1
0 0 0 0 1 1 0 0
0 0 0 0 1 1 0 1
SQ bits 1-4 1 1 1 0
SQ bits 5-8 1 1 1 1
reserved fields
16 frame multiframe
reserved fields
62
H4 format some comments

• CRC-8 (when using K4 it is CRC-3)
• covers the previous 14 frames (not synced on
  multiframe)
• polynomial x8 x2 x 1
• MST
• each VCG member carries the status of all members
• so we need 256 bits of member status
• this is done by muxing MST bits
• there are MST bits per multiframe
• and 32 multiframes in an MST multiframe
• no special sequencing, just MFI2 multiframe mod
  32
• GID
• single bit - cycles through 215-1 LFSR sequence

63
VLI format
MFI1
MFI2 bits 1-4 0 0 0 0
MFI2 bits 5-8 0 0 0 1
CTRL 0 0 1 0
0 0 0 GID 0 0 1 1
0 0 0 0 0 1 0 0
0 0 0 0 0 1 0 1
CRC-8 bits 1-4 0 1 1 0
CRC-8 bits 5-8 0 1 1 1
MST bits 1 0 0 0
more MST bits 1 0 0 1
0 0 0 RS-ACK 1 0 1 0
0 0 0 0 1 0 1 1
0 0 0 0 1 1 0 0
0 0 0 0 1 1 0 1
0 0 0 0 1 1 1 0
SQ 1 1 1 1
reserved fields
16 frame multiframe
reserved fields
64
LCAS adding a member (1)

• When more/less BW is needed, we need to
  add/remove VCAT members
• Adding/removing VCAT members first requires
  provisioning (management)
• LCAS handles member sequence numbers assignment
• LCAS ensures service is not disrupted
• Example to add a 4th member to group 1
• Initial state
• Step 1 NMS provisions new member
• source sends CTRLIDLE for new member
• sink sends MSTFAIL for new member

65
LCAS adding a member (2)

• Step 2 source sends CTRLADD and SQ
• sink sends MSTOK for new member
• if it has been provisioned
• if receiving new member OK
• if it is able to compensate for delay
• otherwise it will send MSTFAIL
• and source reports this to NMS
• Step 3 source sends CTRLEOS for new member
• new member starts to carry traffic
• sink sends RS-ACK
• Note 1 several new members may be added at once
• Note 2 removing a member is similar
• Source puts CTRLIDLE for member to be
  removed and stops using it
• All member sequence numbers must be adjusted

66
LCAS service preservation

• To preserve service integrity if sink detects a
  failure of a VCAT member
• LCAS can temporarily remove member (if service
  can tolerate BW reduction)
• Example Initial state
• Step 1 sink sends MSTFAIL for member 2
• source sends CTRLDNU (special
  treatment if EoS)
• and ceases to use member 2
• Note if EoS fails, renumber to ensure EoS is
  active
• Step 2 sink sends MSTOK indicating defect is
  cleared
• source returns CTRL to NORM
• and starts using the member again
• Note if NMS decides to permanently remove the
  member, proceed as in previous slide

67
PoSPacket over SONET
68
Packet over SONET

• Currently defined in RFC2615 (PPP over SONET)
  obsoletes RFC1619
• SONET/SDH path can provide a point-to-point
  byte-oriented
• full-duplex synchronous link
• PPP is ideal for data transport over such a link
• PoS uses PPP in HDLC framing to provide a
  byte-oriented interface
• to the SONET/SDH infrastructure
• SONET/SDH POH signal label (C2)
• indicates PoS as C216 (C2CF if no scrambler)

69
PoS architecture

• PoS is based on PPP in HDLC framing
• Since SONET/SDH is byte oriented, byte stuffing
  is employed
• A special scrambler is used to protect SONET/SDH
  timing
• PoS operates on IP packets
• If IP is delivered over Ethernet
• the Ethernet is terminated (frame removed)
• Ethernet must be reconstituted at the far end
• require routers at edges of SONET/SDH network

70
What happened to the Ethernet ?

• The conventional model
• Ethernet is a LAN technology
• last 100m
• 10s of hosts
• IP is a WAN technology
• data transported in native IP
• different L2 technologies for last segment
• But modern Ethernet wants to be more

71
PoS Details

• IP packet is encapsulated in PPP
• default MTU is 1500 bytes
• up to 64,000 bytes allowed if negotiated by PPP
• FCS is generated and appended
• PPP in HDLC framing with byte stuffing
• 43 bit scrambler is run over the SPE
• byte stream is placed octet-aligned in SPE
• (e.g. 149.760 Mbps of STM-1)
• HDLC frames may cross SPE boundaries

72
RFC2615 vs. RFC1619

• RFC1619 did not have the 43 bit scrambler
• Malicious users could generate packets
• containing frame alignment pattern
• deceiving framer into mis-syncing
• with low transition density
• degrading clock performance
• containing SONET/SDH reset scrambler pattern
• causing errors
• So RFC2615 added the scrambler
• scrambler does not reset during use
• hard to guess proper internal state

73
POS problems

• PoS is BW efficient
• but POS has its disadvantages
• BW must be predetermined
• HDLC BW expansion and nondeterminacy
• BW allocation is tightly constrained by SONET/SDH
  capacities
• e.g. GbE requires a full OC-48 pipe
• POS requires removing the Ethernet headers
• So lose RPR, VLAN, 802.1p, multicasting, etc
• POS requires IP routers

74
LAPSLink Access Protocol over SDHX.85 and X.86
75
LAPS

• In 2001 ITU-T introduced protocols for
  transporting packets over SDH
• X.85 IP over SDH using LAPS
• X.86 Ethernet over LAPS
• Built on series of ITU LAPx HDLC-based
  protocols
• Use ISO HDLC format
• Implement connectionless byte-oriented protocols
  over SDH
• X.85 is very close to (but not quite) IETF PoS

76
X.85 vs. X.86

• X.85 transports IP packets
• if delivered over Ethernet, the Ethernet is
  terminated
• X.86 transports Ethernet
• can transport all sorts of Ethernet traffic not
  only IP packets

77
X.85

• IP over SDH using LAPS
• address 04 (or FF for compatibility with PoS)
• SAPI 21 for IPv4 57 for IPv6 (changed to be
  like PoS)
• Scrambler always used
• Can use LOP VCs, HOP VCs or STMs

78
X.86

• Similar to X.85 (IP over SDH using LAPS)
• but transports the entire Ethernet frame
• Provides a virtual MII/GMII interface
• Transparent to all Ethernet features (VLAN, P
  bits, RPR, etc.)
• Rate adaptation by adding hex DD (after byte
  stuffing 7D DD)
• Ammendment specifies use of Ethernet PAUSE frames
  for rate limiting

79
LAPS drawbacks

• Only IP or Ethernet payloads
• Single bit errors (e.g. in flags) may cause
  misalignment
• Not very efficient
• HDLC BW expansion
• HDLC BW nondeterminacy

80
GFPGeneric Framing Procedure
81
GFP architecture

• Defined in ITU-T G.7041 (also numbered Y.1303)
• originally developed in T1X1 to fix ATM
  limitations
• (like ATM) uses HEC protected frames instead of
  HDLC
• GFP generically encapsulates client (e.g. IP,
  Ethernet)
• onto transport network (e.g. SONET/SDH, OTN)
• Client may be PDU-oriented (Ethernet MAC, IP)
• or block-oriented (GbE, fiber channel)
• GFP frames
• are octet aligned
• contain at most 65,535 bytes
• consist of a header payload area
• Any idle time between GFP frames is filled with
  GFP idle frames

82
GFP frame structure

• Every GFP frame has a 4-byte core header
• 2 byte Payload Length Indicator
• PLI 01,2,3 are for control frames
• 2 byte core Header Error Control
• X16 X12 X5 1
• entire core header is XORed with B6AB31E0
• so idle frames are B6AB31E0 (Barker-like
  codes)
• Idle GFP frames
• have PLI0
• have no payload area
• Non-idle GFP frames
• have 4 bytes in payload area
• the payload has its own header
• 2 payload modes GFP-F and GFP-T
• optionally protect payload with CRC-32
• payload is scrambled like PoS

83
GFP payload header

• GFP payload header has
• type (2B)
• type HEC (CRC-16)
• extension header (0-60B)
• either null or linear extension (payload type
  muxing)
• extension HEC (CRC-16)
• type consists of
• Payload Type Identifier (3b)
• PTI000 for client data
• PTI100 for client management (OAM dLOS, dLOF)
• Payload FCS Indicator (1b)
• PFI1 means there is a payload FCS
• Extension Header ID (4b)
• User Payload Identifier (8b)
• values for Ethernet, IP, PPP, FC, RPR, MPLS, etc.

PTI (3b)
EXI (4b)
PFI
type (2B)
UPI (8b)
tHEC (2B)
extension header (0-58B)
eHEC (2B)
84
GFP modes

• GFP-F - frame mapped GFP
• Good for PDU-based protocols (Ethernet, IP, MPLS)
• or HDLC-based ones (PPP)
• Client PDU is placed in GFP payload field
• GFP-T transparent GFP
• Good for protocols that exploit physical layer
  capabilities
• In particular
• 8B/10B line code
• used in fiber channel, GbE, FICON, ESCON, DVB,
  etc
• Were we to use GFP-F would lose control info,
  GFP-T is transparent to these codes
• Also, GFP-T neednt wait for entire PDU to be
  received (adding delay!)

85
GFP-T

• Main application Storage Area Networks (SAN)
• SANs use 8B/10B line code and are very delay
  sensitive
• 8B/10B line code maps each of the 256 values of
  the 8-bit input
• into 1 or 2 different 10 bit words
• Maintains a running 0-1 balance and when encoding
  an input with 2 possibilities, it chooses the one
  that improves the balance
• spare 10b symbols are used as control codes (e.g.
  start/end of frame)
• Were we to use GFP-F would lose control info,
  GFP-T is transparent to these codes
• Also, GFP-T neednt wait for entire PDU to be
  received (adding delay!)
• GFP-T maps 8B/10B line code into 64B/65B block
  code

86
GFP-F

• Client packet/frame without un-needed overhead
  (e.g. flags, preamble, etc)
• is placed in GFP payload field
• Interface is at link layer
• More BW efficient than GFP-T since idle periods
  are filtered out
• preambles, frame-start, etc are also not
  transported
• GFP-F must know the client protocol in order to
  detect frames
• Can mux different client protocols on a frame to
  frame basis
• If the client protocol has a good FCS, dont need
  to use GFPs FCS
• GFP-F is used for EoS
• Either IP in PPP or native Ethernet can be used

87
GFP advantages

• Supports multiple protocols (not just Ethernet
  and IP)
• For Ethernet, GFP can transparently transport
  entire frame
• Robust single bit errors do not cause loss of
  alignment
• Constant predictable overhead
• Good efficiency (similar to LAPS best case)
• GFP-T for SAN support
• Can run over OTN (G.709) as well as SONET

88
Alternatives
89
There are yet other ways

• Ethernet in the first mile (EFM)
• WAN-PHY (10GBASE-W)
• Ethernet over wavelengths (EoW) or OTN (G.709)
• Ethernet over Resilient Packet Rings (RPR)
• Ethernet pseudowires (PWs)

90
Ethernet in the First Mile

• IEEE 802.3ah task force produced the EFM
  definition
• Optical technologies
• point to point optical fiber _at_ 100Mbps 10 km
• Dual fiber duplex 100Base-LX10
• Single fiber simplex 100Base-BX10
• point to point optical fiber _at_ 1Gbps 10 km
• Dual fiber duplex 1000Base-LX10
• Single fiber simplex 1000Base-BX10
• point to multipoint optical fiber _at_ 1Gbps 10/20
  km (EPON )
• Single fiber simplex 1000Base-PX10/20
• Copper technologies
• point to point copper _at_ 10 Mbps 750 m (short
  reach PHY)
• VDSL 10PASS-TS
• point to point copper _at_ 2 Mbps 2.7 km (long
  reach PHY)
• SHDSL.bis 2Base-TL
• up to 45 Mbps by bonding
• OAM

91
WAN-PHY (10 GbE in STM-64)
10GBASE-W 802.3-2005 Clause 50 G.707 Annex F

• There is a special case where Ethernet and SDH
  bit-rates are close
• STM-64 is 9953.28Mbps
• GbE 10GBASE-R (64B/66B coding) can be directly
  mapped
• into a STM-64 (with contiguous concatenation)
  without need for GFP
• MAC creates "stretched InterPacket Gap" to
  compensate for rate being lt 10G
• This is the fastest connection commonly used for
  Internet traffic
• Complication SDH clock accuracy is ?4.6 ppm,
  GbE accuracy is ?20 ppm

64(270-9) 16704 columns
J1
63 columns of fixed stuff
92
Ethernet over Wavelengths

• Rather than muxing Ethernet flows using SONET
  mechanisms
• We can allocate a separate wavelength (lambda)
  per flow
• Wavelength Division Multiplexing (WDM)
• For example, each wavelength may support OC-48
  (2.5 Gbps)
• Up to 8 channels is called coarse CWDM
• More than 8 wavelengths (20 Gbps) is called dense
  DWDM
• Present DWDM technology allows about 80 channels
• Higher densities expected soon
• DWDMs tight channel spacing requires expensive
  cooled laser sources

93
Ethernet PWs
Pseudowire (PW) mechanism that emulates
essential attributes of a native service while
transporting over a PSN
Customer Edge (CE)
Customer Edge (CE)
MPLS network
Customer Edge (CE)
Provider Edge (PE)
Provider Edge (PE)
Customer Edge (CE)
Customer Edge (CE)
Ethernet
PseudoWires (PWs)
Ethernet