Transcript EoS - DSPCSP Pages

EoS
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
Introduction
Y(J)S EoS Slide 3
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!
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
Switch
I
W
F
A
D
M
SONET
RING
A
D
M
I
W
F
Ethernet
Switch
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
Switch
A
T
M
A
D
M
SONET
RING
A
D
M
A
T
M
Ethernet
Switch
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
Switch
I
W
F
SONET
RING
I
W
F
Ethernet
Switch
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
While SONET/SDH


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
Background
Ethernet
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
Background
HDLC
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
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
Y(J)S EoS Slide 18
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:
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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)
Address:
 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
CRC-32
X16 + X12 + X5 + 1
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
Background
PPP
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
ML-PPP, PPPoE, BAP, BCP, IPCP, …
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
(http://www.iana.org/assignments/ppp-numbers)
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
7E
FF
03
(8/16b)
information
padding
FCS
flag
(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
1662
X.85
flag
address
ctrl
protocol
7E
FF
03
(8/16b)
flag
address
ctrl
SAPI
7E
04
03
(16b)
information
padding
FCS
flag
(optional)
(16/32b)
7E
FCS
flag
(32b)
7E
IP Packet
Y(J)S EoS Slide 27
Background
SONET/SDH
Note:
For more information – see SONET/SDH course.
Y(J)S EoS Slide 28
SONET architecture
Path
Termination
ADM
regenerator
ADM
Line
Termination
Section
Termination
Line
Termination
Path
Termination
path
line
section
line
section
line
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

section – physical link between adjacent elements
multiplex section
regenerator section
Each layer has its own overhead to support needed functionality
SDH terminology
Y(J)S EoS Slide 29
SONET STS-1 frame
9 rows
90 columns
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
STS-1
columns
rate
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
STS-1
T1
T3
E1
E3
28
1
21
1
E4
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
9 rows
6 rows
3 rows
90 columns
Synchronous Payload Envelope
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 section+line overhead !
Y(J)S EoS Slide 34
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
Y(J)S EoS Slide 35
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


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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
Z-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
J1
B3
C2
POH is responsible for
– path performance monitoring
– status (including of mapped payloads)
– trace
G1
C2
(hex)
Payload type
00
unequipped
01
nonspecific
02
LOP (TUG)
04
E3/T3
12
E4
F2
2 bytes are of particular interest to us:
H4
C2 is the “signal label”
indicates path payload type
13
ATM
16
PoS – RFC 1662
H4 is the “multiframe indication”
used by VCAT/LCAS (discussed later)
18
LAPS X.85
1A
10G Ethernet
1B
GFP
CF
PoS - RFC1619
F3
K3
N1
POH
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
1
30
59
VTG
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
LOP
HOP
VC
column
rate
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
6
3.456 DS1C (3.152)
2 per group
6.912 DS2
1 per group
VT 3
VT 6
VC-2
12
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
(6.312)
(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
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
Y(J)S EoS Slide 42
VCAT
Virtual Concatenation
Y(J)S EoS Slide 43
Concatenation
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
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
n or VC-4-Nc : N=4n
 only STS-Nc : N=3 * 4
– 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
section and
line overhead
3 columns of
path overhead
258 columns * 0.576 = 148.608 Mbps
STS-3
270 columns
9 rows
…
260 columns of SPE
9 columns of
section and
line overhead
1 column of
path overhead
260 columns * 0.576 = 149.760 Mbps
STS-3c
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
…
H4
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
VC-11-Xv
Capacity (Mbps)
if all members in one VC
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)
VT1.5-Xv 1.600, 3.200, … 1.600X
If all members in one STS
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%
VC-12-5v
100
STS-3c
67%
VC-4
1000
STS-48c
VC-4-16c
STS-1-2v
100%
VC-3-2v
42%
STS-3c-7v
95%
VC-4-7v
Using VCAT increases efficiency to close to 100% !
Y(J)S EoS Slide 51
PDH VCAT
VCAT
overhead
octet
1st
frame
of
4 E1s
TS0
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
VCAT
overhead
octet
PDH VCAT overhead octet
frames
of an
E1
…
TS0
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
LCAS
Link Capacity Adjustment Scheme
Y(J)S EoS Slide 57
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 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
B3
C2
G1
F2
H4
F3
K3
N1
POH
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
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
reserved fields
0
0
0
0
0
0
0
MFI2 bits 1-4
MFI2 bits 5-8
CTRL
0
0 GID
0
0
0
0
0
0
CRC-8 bits 1-4
CRC-8 bits 5-8
MST bits
more MST bits
0
0 RS-ACK
0
0
0
0
0
0
0
0
0
SQ bits 1-4
SQ bits 5-8
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
MFI1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
16 frame multiframe
reserved fields
H4 format
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
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
Y(J)S EoS Slide 62
reserved fields
0
0
0
0
0
0
0
0
MFI2 bits 1-4
MFI2 bits 5-8
CTRL
0
0 GID
0
0
0
0
0
0
CRC-8 bits 1-4
CRC-8 bits 5-8
MST bits
more MST bits
0
0 RS-ACK
0
0
0
0
0
0
0
0
0
0
0
0
SQ
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
MFI1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
0
0
0
0
1
0
1
1
0
1
0
1
1
1
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
16 frame multiframe
reserved fields
VLI format
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
source sends CTRL=IDLE for new member
sink sends MST=FAIL for new member
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=NORM
GID=g SQ=3 CTRL=EOS
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
 if it has been provisioned
 if receiving new member OK
 if it is able to compensate for delay
otherwise it will send MST=FAIL
and source reports this to NMS
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=NORM
GID=g SQ=3 CTRL=EOS
GID=g SQ=4 CTRL=ADD
Step 3: source sends CTRL=EOS for new member
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=NORM
new member starts to carry traffic
sink sends RS-ACK
GID=g SQ=3 CTRL=NORM
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
Step 1: sink sends MST=FAIL for member 2
source sends CTRL=DNU (special treatment if EoS)
and ceases to use member 2
Note: if EoS fails, renumber to ensure EoS is active
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=DNU
GID=g SQ=3 CTRL=NORM
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
PoS
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
IP
PPP
HDLC
SONET/SDH
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
IP
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
LAPS
Link Access Protocol over SDH
X.85 and X.86
Y(J)S EoS Slide 74
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
Y(J)S EoS Slide 75
X.85 vs. X.86
X.85
X.86
IP
IP
IP
LLC
LAPS
LLC
MAC
SDH
MAC
IP
IP
IP
LLC
LLC
LLC
MAC
MAC
MAC
LAPS
SDH
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
X.85
flag
address
ctrl
SAPI
7E
(16b)
03
(16b)
IP Packet
FCS
flag
(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
MAC
X.86
reconciliation
MII/GMII
LAPS
rate adaptation
SDH
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
GFP
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
– 2 byte core Header Error Control
core
header
X16 + X12 + X5 + 1
– entire core header is XOR’ed with B6AB31E0
so idle frames are B6AB31E0 (Barker-like codes)
Idle GFP frames
– have PLI=0
– 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
payload
area
PLI (2B)
cHEC (2B)
payload header
(4-64B)
payload
optional payload
FCS (4B)
Y(J)S EoS Slide 82
GFP payload header
GFP payload header has
– type (2B)
PTI (3b) PFI EXI (4b)
– type HEC (CRC-16)
UPI (8b)
– extension header (0-60B)
either null or linear extension (payload type muxing)
– extension HEC (CRC-16)
type (2B)
tHEC (2B)
extension header
(0-58B)
eHEC (2B)
type consists of
– 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
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 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
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, 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
Alternatives
Y(J)S EoS Slide 88
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)
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
OAM
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
J1
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
Customer
Edge
Pseudowire (PW): mechanism that emulates essential
attributes of a native service while transporting over a PSN
(CE)
Customer
Edge
(CE)
Customer
Edge
Customer
Edge
MPLS network
Provider
Edge
Provider
Edge
(CE)
(PE)
(PE)
Customer
Edge
Ethernet
Ethernet
PseudoWires (PWs)
(CE)
(CE)
MPLS
label
stack
PW
label
PWE
control
word
Ethernet frame
(with or w/o FCS)
Y(J)S EoS Slide 93