EoS by fjhuangjun



Yaakov (J) Stein
Chief Scientist
RAD Data Communications
                   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

                                               Y(J)S EoS Slide 2

               Y(J)S EoS Slide 3
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!

                                                                Y(J)S EoS Slide 4
         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 isn’t 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 !
                                                                              Y(J)S EoS Slide 5
                         Option 2: leased lines

         Ethernet    I      A            A      I
                                 SONET                 Ethernet
          Switch     W      D            D      W
                                  RING                  Switch
                     F      M            M      F

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 !

                                                                   Y(J)S EoS Slide 6
                                     Option 3: ATM
          Ethernet      A        A              A         A
                                      SONET                     Ethernet
           Switch       T        D              D         T
                                       RING                      Switch
                        M        M              M         M

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
                                                                           Y(J)S EoS Slide 7
                               Option 4: EoS
              Ethernet     I              I
                                 SONET            Ethernet
               Switch      W              W
                                  RING             Switch
                           F              F

A new choice is Ethernet over SONET/SDH (EoS)
The customer’s Ethernet traffic is transported directly by SONET/SDH
 You build on your existing network
 You transport native Ethernet
   – needn’t 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 hasn’t yet stabilized on one technology

So you will probably need to take this course !

                                                                 Y(J)S EoS Slide 8
                             World’s 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

   is constant bit rate
   is designed for various rates such as 1.6, 2.176, 6.784 Mbps

So the job isn’t easy !

                                                              Y(J)S EoS Slide 9
           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
                                                         Y(J)S EoS Slide 10


             Y(J)S EoS Slide 11
                                    Ethernet frame
For our purposes, “Ethernet” is any layer 2 protocol
   using 1 of the following frame formats :

                                    64 – 1518 B
         DA (6B)    SA (6B)   T/L (2B)   data (0-1500B)    pad (0-46)    FCS (4B)

                                     68 – 1522 B
DA(6B)     SA(6B)    VT(2B)   VLAN(2B)   T/L(2B)    data (0-1500B)      pad(0-46)   FCS(4B)

                                                                                Y(J)S EoS Slide 12
                  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, …

                                                     Y(J)S EoS Slide 13


             Y(J)S EoS Slide 14
                                          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”

                packet 1                     packet 2                 packet 3          packet 4

                packet 1                    packet 2                  packet 3          packet 4

For example, we can use a sequence of 1s as idle indication
111111111111111111111110 packet 1 0111111111111111111110 packet 2 011111111111111111111110 01111110 packet 3 01111111111111111

The appearance of a 0 bit indicates that data follows
                                                                                                                  Y(J)S EoS Slide 15
                                  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
01111110 01111110 01111110 packet 1 01111110 01111110 01111110 packet 2 01111110 01111110 01111110 01111110 packet 3 01111110

Some implementations allow “zero sharing”
0111111011111101111110 packet 1 011111101111110 01111110 packet 2 011111101111110 1111110 1111110 packet 3 011111101111110

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

                                                                                                                     Y(J)S EoS Slide 16
                                                          HDLC flags
ISO developed High level Data Link C based on IBM’s SDLC
HDLC inputs packets of bytes
HDLC uses hex 7E as its idle code (“flag”) 01111110
So an idle HDLC stream repeats 7E
01111110 01111110 01111110 packet 1 01111110 01111110 01111110 packet 2 01111110 01111110 01111110 01111110 packet 3 01111110

Alternatively, 1s can be sent as idle, flags as delineators
11111111111111111 01111110 packet 1 01111110 111111111101111110 packet 2 01111110 11111111111111111101111110 packet 3 01111110

There are two methods of disallowing flags
     bit stuffing (zero insertion)
     byte (octet) stuffing

                                                                                                                     Y(J)S EoS Slide 17
                 Bit stuffing / zero insertion
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

   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

                                                                Y(J)S EoS Slide 18
                                Byte (octet) stuffing
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)
   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
                                                                       Y(J)S EoS Slide 19
                                        HDLC framing
HDLC frame is bounded by flags, and has a particular structure

    flag (8)   address (0/8/16) ctrl (8/16)        data           FCS (16/32) flag (8)

Many variants (SDLC, ISO, LAPB, LAPD, LAPF, LAPS, SS7, PPP-HDLC, Cisco-HDLC, etc)
 There may be no address (e.g. SS7 HDLC)
 SDLC always had 8 bit addresses
 ISO 3309 HDLC has structured multibyte address

                   SAPI            C/R EA                              EA

     – Service Access Point Identifier (MSB of SAPI =1 may indicate broadcast/multicast)
     – EA=1 means 8 bit, EA=0 means extended address
     – C/R=1 for commands, C/R=0 for responses
   The single byte hex FF is recognized as the broadcast address
                                                                                 Y(J)S EoS Slide 20
                         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

                                                             Y(J)S EoS Slide 21
                                     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

                                                                                 Y(J)S EoS Slide 22


             Y(J)S EoS Slide 23
         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
                                                                  Y(J)S EoS Slide 24
     Basic PPP encapsulation (RFC 1661)
              protocol (8/16)    information         padding

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 EA=1)
    – if 16-bit, then the LSB of first byte must be zero (for EA=0)

PPP protocol values managed by IANA

Padding may be used (e.g. to cause header to fall on 32-bit boundary)

                                                                        Y(J)S EoS Slide 25
          PPP using HDLC framing (RFC 1662)
   flag   address   ctrl   protocol     information   padding       FCS       flag
    7E      FF      03     (8/16b)                    (optional)   (16/32b)   7E

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)

                                                                               Y(J)S EoS Slide 26
                                RFC1662 vs. X.85
   ITU-T X.85 defines IP over SDH using LAPS (will study later)
   Its encapsulation is similar to RFC1662 (but can’t 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
        flag   address   ctrl   protocol   information       padding       FCS           flag
         7E      FF      03      (8/16b)                     (optional)   (16/32b)        7E

        flag   address   ctrl    SAPI            IP Packet                 FCS           flag
         7E      04      03      (16b)                                     (32b)          7E

                                                                             Y(J)S EoS Slide 27


For more information – see SONET/SDH course.

                                               Y(J)S EoS Slide 28
                                      SONET architecture
                             ADM                    regenerator               ADM
       Path                    Line                    Section                  Line                    Path
    Termination             Termination              Termination             Termination             Termination

                   line                                 line                                line
                  section                 section                  section                 section

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
                                                                                                       Y(J)S EoS Slide 29
                           SONET STS-1 frame
                                    90 columns
9 rows

         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
                                                                         Y(J)S EoS Slide 30
                        SDH STM-1 frame
                             270 columns

9 rows

     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!
                                                                 Y(J)S EoS Slide 31
                         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
                                                              Y(J)S EoS Slide 32
                 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)

                                                          Y(J)S EoS Slide 33
                                      STS-1 frame structure
                                              90 columns
3 rows
          9 rows

                          Synchronous Payload Envelope
6 rows

         section + line
                           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 section+line overhead !
                                                                                         Y(J)S EoS Slide 34
                     STM-1 frame structure
                             270 columns


            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
                                                                        Y(J)S EoS Slide 35
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
                                             Xn                     Yn = Xn + Yn-43

                                                                          Y(J)S EoS Slide 36
                            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)

                                                                        Y(J)S EoS Slide 37
                               Path overhead
                                                   C2      Payload type

J1    POH is responsible for                       00       unequipped

        – path performance monitoring              01       nonspecific
        – status (including of mapped payloads)
C2      – trace                                    02       LOP (TUG)
G1                                                 04         E3/T3
F2    2 bytes are of particular interest to us:
                                                   12           E4
H4    C2 is the “signal label”                     13          ATM
F3       indicates path payload type               16     PoS – RFC 1662
K3    H4 is the “multiframe indication”            18       LAPS X.85
N1        used by VCAT/LCAS (discussed later)
                                                   1A      10G Ethernet
                                                   1B          GFP
                                                   CF     PoS - RFC1619

                                                                Y(J)S EoS Slide 38
                                 STS-1 HOP
      1                   30                 59       87

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)

                                                      Y(J)S EoS Slide 39
                                              LOP                            VTG
    1                      30                  59                  87    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
                                                                           Y(J)S EoS Slide 40
                 SONET/SDH : VT/VC types
         VT/STS     VC     column          payload
        VT 1.5    VC-11    3    1.728 DS1    (1.544)    4 per group
        VT 2      VC-12    4    2.304 E1      (2.048)   3 per group
        VT 3               6    3.456 DS1C (3.152)      2 per group
        VT 6      VC-2    12    6.912 DS2     (6.312)   1 per group
        STS-1     VC-3         48.384 E3     (34.368)

HOP     STS-1     VC-3         48.384 DS3    (44.736)

        STS-3c    VC-4     149.760 E4       (139.264)

  standard PDH rates map efficiently into SONET/SDH !
                                                         Y(J)S EoS Slide 41
                    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

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

                                                          Y(J)S EoS Slide 42

Virtual Concatenation

                        Y(J)S EoS Slide 43
Payloads that don’t fit into standard VT/VC sizes can be accommodated
   by concatenating of several VTs / VCs

For example, 10 Mbps doesn’t 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

                                                                 Y(J)S EoS Slide 44
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 : N=3 * 4
                                 n or VC-4-Nc : N=4n

     – 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
                                                                     Y(J)S EoS Slide 45
       Contiguous Concatenation: STS-3c
                                      270 columns

   9 rows

                                       258 columns of SPE
9 columns of    3 columns of    258 columns * 0.576 = 148.608 Mbps
  section and   path overhead
line overhead

                                      270 columns

   9 rows

                                       260 columns of SPE
9 columns of     1 column of    260 columns * 0.576 = 149.760 Mbps
  section and   path overhead
line overhead
                                                                          Y(J)S EoS Slide 46
                         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

                                                                Y(J)S EoS Slide 47
                           Virtual Concatenation


VCAT is an inverse multiplexing mechanism (round-robin)
VCAT members may travel along different routes in SONET/SDH network
Intermediate network elements don’t need to know about VCAT
   (unlike contiguous concatenation that is handled by all intermediate nodes)
                                                                                 Y(J)S EoS Slide 48
           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, …

                                                            Y(J)S EoS Slide 49
     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, …

                                                                  Y(J)S EoS Slide 50
               Efficiency comparison

   rate      w/o VCAT    efficiency   with VCAT      efficiency
    10        STS-1        21%         VT2-5v          92%

   100        STS-3c       67%        STS-1-2v        100%
               VC-4                    VC-3-2v

   1000      STS-48c       42%        STS-3c-7v        95%
             VC-4-16c                  VC-4-7v

Using VCAT increases efficiency to close to 100% !

                                                          Y(J)S EoS Slide 51
          overhead                     PDH VCAT

4 E1s

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. can’t 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)

                             each E1                        time

                                                                        Y(J)S EoS Slide 52
         overhead   PDH VCAT overhead octet

of an

 There is one VCAT overhead octet per multiframe, so net rate is
 T1: (24*24-1=) 575 data bytes per 3 ms. multiframe = 191.666 kB/s
 E1: (16*30-1=) 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)

                                                                     Y(J)S EoS Slide 53
                       Delay compensation
802.1ad Ethernet link aggregation cheats
   – each identifiable flow is restricted to one link
   – doesn’t 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

                                                          Y(J)S EoS Slide 54
                                   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 member’s POH contains :
 sequence indicator (identifies component) (number of bits limits X)
 MFI multiframe indicator (multiframe sequencing to find differential delay)

                                                                                Y(J)S EoS Slide 55
                Multiframes and superframes
Here is how we compensate for 512 ms of differential delay
512 ms corresponds to a superframe is 4096 TDM frames (4096*0.125m=512m)
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 (256*16=4096)
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

                                                                 Y(J)S EoS Slide 56

Link Capacity Adjustment Scheme

                            Y(J)S EoS Slide 57
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 doesn’t 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

                                                                          Y(J)S EoS Slide 58
                   LCAS – how does it work?
      LCAS is unidirectional (for symmetric BW need to perform twice)
      LCAS functions can be initiated by source or sink
J1    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
F2       – message describes link state at time of next message
H4       – receiver can switch to new configuration in time
F3    LCAS messages are in the upper nibble of
K3       – H4 byte for HOS SONET/SDH
N1       – 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
                                                                        Y(J)S EoS Slide 59
                   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
                                                                      Y(J)S EoS Slide 60
                                        H4 format
                       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
reserved fields

                                                          16 frame multiframe
                  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
reserved fields

                  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
                                                                        Y(J)S EoS Slide 61
              H4 format – some comments
CRC-8 (when using K4 it is CRC-3)
  – covers the previous 14 frames (not sync’ed on multiframe)
  – polynomial x8 + x2 + x + 1

   –   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
   – single bit - cycles through 215-1 LFSR sequence
                                                         Y(J)S EoS Slide 62
                                        VLI format
                       MFI2 bits 1-4     0   0    0   0
                       MFI2 bits 5-8     0   0    0   1
                           CTRL          0   0    1   0
reserved fields

                  0      0    0 GID      0   0    1   1

                                                          16 frame multiframe
                  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
reserved fields

                  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
                                                                        Y(J)S EoS Slide 63
                 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”
                 GID=g SQ=1 CTRL=NORM
Initial state:   GID=g SQ=2 CTRL=NORM
                 GID=g SQ=3 CTRL=EOS

Step 1: NMS provisions new member                GID=g SQ=1 CTRL=NORM
                                                 GID=g SQ=2 CTRL=NORM
         source sends CTRL=IDLE for new member
                                                 GID=g SQ=3 CTRL=EOS
         sink sends MST=FAIL for new member
                                                 GID=g SQ=FF CTRL=IDLE

                                                              Y(J)S EoS Slide 64
              LCAS – adding a member (2)
Step 2: source sends CTRL=ADD and SQ
       sink sends MST=OK for new member            GID=g SQ=1 CTRL=NORM
         if it has been provisioned
                                                   GID=g SQ=2 CTRL=NORM
         if receiving new member OK
                                                   GID=g SQ=3 CTRL=EOS
         if it is able to compensate for delay

                                                   GID=g SQ=4 CTRL=ADD
        otherwise it will send MST=FAIL
        and source reports this to NMS
                                                      GID=g SQ=1 CTRL=NORM
Step 3: source sends CTRL=EOS for new member
                                                      GID=g SQ=2 CTRL=NORM
        new member starts to carry traffic
                                                      GID=g SQ=3 CTRL=NORM
        sink sends RS-ACK                             GID=g SQ=4 CTRL=EOS
Note 1: several new members may be added at once
Note 2: removing a member is similar
        Source puts CTRL=IDLE for member to be removed and stops using it
        All member sequence numbers must be adjusted
                                                                      Y(J)S EoS Slide 65
                 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)
                            GID=g SQ=1 CTRL=NORM
                            GID=g SQ=2 CTRL=NORM
Example: Initial state
                            GID=g SQ=3 CTRL=NORM
                            GID=g SQ=4 CTRL=EOS

                                                              GID=g SQ=1 CTRL=NORM
Step 1: sink sends MST=FAIL for member 2
                                                              GID=g SQ=2 CTRL=DNU
        source sends CTRL=DNU (special treatment if EoS)
                                                              GID=g SQ=3 CTRL=NORM
        and ceases to use member 2
Note: if EoS fails, renumber to ensure EoS is active          GID=g SQ=4 CTRL=EOS

Step 2: sink sends MST=OK 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
                                                                               Y(J)S EoS Slide 66

Packet over SONET

                    Y(J)S EoS Slide 67
                        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 C2=16 (C2=CF if no scrambler)

                                                            Y(J)S EoS Slide 68
                        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
                                                          Y(J)S EoS Slide 69
         What happened to the Ethernet ?

                       Ethernet              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

                                                        Y(J)S EoS Slide 70
                       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

                                                    Y(J)S EoS Slide 71
                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

                                                 Y(J)S EoS Slide 72
                          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

                                                           Y(J)S EoS Slide 73

Link Access Protocol over SDH

        X.85 and X.86

                            Y(J)S EoS Slide 74

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

                                                            Y(J)S EoS Slide 75
                              X.85 vs. X.86
                    IP               IP              IP
          X.85     LLC             LAPS             LLC
                  MAC              SDH              MAC

                    IP               IP              IP
          X.86     LLC              LLC             LLC
                  MAC              MAC              MAC

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
                                                                Y(J)S EoS Slide 76
    flag   address   ctrl   SAPI        IP Packet          FCS       flag
     7E     (16b)    03     (16b)                          (32b)      7E

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

                                                                   Y(J)S EoS Slide 77

                   rate adaptation

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

 flag   address   ctrl       SAPI       Ethernet frame        FCS     flag
  7E     (16b)    03         FE01    DA SA T/L INFO PAD FCS   (32b)   7E
                                                                           Y(J)S EoS Slide 78
                     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

                                                           Y(J)S EoS Slide 79

Generic Framing Procedure

                            Y(J)S EoS Slide 80
                               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)
               Ethernet        IP      HDLC            other
                          GFP – client specific part
                            GFP – common part
               PDH          SDH       OTN              other
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

                                                                  Y(J)S EoS Slide 81
                             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                core        PLI (2B)
   – 2 byte core Header Error Control                   header      cHEC (2B)
      X16 + X12 + X5 + 1
   – entire core header is XOR’ed with B6AB31E0                   payload header
      so idle frames are B6AB31E0 (Barker-like codes)

Idle GFP frames                                         payload
     – have PLI=0                                         area        payload
     – have no payload area
Non-idle GFP frames                                               optional payload
   – have ≥ 4 bytes in payload area                                  FCS (4B)
   – 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
                                                                         Y(J)S EoS Slide 82
                         GFP payload header
GFP payload header has
   – type (2B)                        PTI (3b) PFI EXI (4b)
   – type HEC (CRC-16)                                            type (2B)
                                              UPI (8b)
   – extension header (0-60B)                                     tHEC (2B)
       either null or linear extension (payload type muxing)
                                                               extension header
   – extension HEC (CRC-16)                                        (0-58B)
type consists of                                                 eHEC (2B)
    – Payload Type Identifier (3b)
         PTI=000 for client data

         PTI=100 for client management (OAM dLOS, dLOF)

    – Payload FCS Indicator (1b)
         PFI=1 means there is a payload FCS

    – Extension Header ID (4b)
    – User Payload Identifier (8b)
         values for Ethernet, IP, PPP, FC, RPR, MPLS, etc.

                                                                      Y(J)S EoS Slide 83
                                    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 needn’t wait for entire PDU to be received (adding delay!)

                                                                         Y(J)S EoS Slide 84
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 needn’t wait for entire PDU to be received (adding delay!)
GFP-T maps 8B/10B line code into 64B/65B block code

                                                                            Y(J)S EoS Slide 85
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, don’t need to use GFP’s FCS

GFP-F is used for EoS
Either IP in PPP or native Ethernet can be used

                                                                     Y(J)S EoS Slide 86
                      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

                                                            Y(J)S EoS Slide 87

               Y(J)S EoS Slide 88
              There are yet other ways …

   Ethernet in the first mile (EFM)
   Ethernet over wavelengths (EoW) or OTN (G.709)
   Ethernet over Resilient Packet Rings (RPR)
   Ethernet pseudowires (PWs)

                                                     Y(J)S EoS Slide 89
                       Ethernet in the First Mile
IEEE 802.3ah task force produced the EFM definition
Optical technologies
   point to point optical fiber @ 100Mbps 10 km
     – Dual fiber duplex 100Base-LX10
     – Single fiber simplex 100Base-BX10
   point to point optical fiber @ 1Gbps 10 km
     – Dual fiber duplex 1000Base-LX10
     – Single fiber simplex 1000Base-BX10
   point to multipoint optical fiber @ 1Gbps 10/20 km (EPON )
     – Single fiber simplex 1000Base-PX10/20

Copper technologies
   point to point copper @ 10 Mbps 750 m (short reach PHY)
     – VDSL 10PASS-TS
   point to point copper @ 2 Mbps 2.7 km (long reach PHY)
     – SHDSL.bis 2Base-TL
     – up to 45 Mbps by bonding

                                                                 Y(J)S EoS Slide 90
                            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 < 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


63 columns of fixed stuff                                               Y(J)S EoS Slide 91
                 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
DWDM’s tight channel spacing requires expensive cooled laser sources

                                                               Y(J)S EoS Slide 92
                           Ethernet PWs
 Edge        Pseudowire (PW): mechanism that emulates essential
             attributes of a native service while transporting over a PSN
  (CE)                     MPLS network                          Customer
 Edge           Provider                   Provider               (CE)
                 Edge                       Edge
                  (PE)                      (PE)                 Customer
Customer                                                          Edge
           Ethernet      PseudoWires (PWs)                         (CE)
             MPLS                 PWE            Ethernet frame
                         PW      control
                         label                  (with or w/o FCS)
             stack                word
                                                                    Y(J)S EoS Slide 93

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