Get documents about "EoS
Document Sample
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 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
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:
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 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
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 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
1662
7E FF 03 (8/16b) (optional) (16/32b) 7E
flag address ctrl SAPI IP Packet FCS flag
X.85
7E 04 03 (16b) (32b) 7E
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
ADM regenerator ADM
Path Line Section Line Path
Termination Termination Termination Termination Termination
path
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
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
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
C2 Payload type
(hex)
J1 POH is responsible for 00 unequipped
B3
– 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
POH
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
rate
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
LOP
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
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
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
STS-3
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
STS-3c
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
…
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 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%
VC-12-5v
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
VCAT
overhead PDH VCAT
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 PDH VCAT overhead octet
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 LCAS assumes that all VCG members are error-free
B3
– LCAS messages are CRC protected
C2
LCAS messages are sent in advance
G1
– 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
POH
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
MFI1
MFI2 bits 1-4 0 0 0 0
MFI2 bits 5-8 0 0 0 1
CTRL 0 0 1 0
0 0 0 GID 0 0 1 1
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
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
VLI format
MFI1
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
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 Ethernet
IP
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
IP IP IP
X.85 LLC LAPS LLC
MAC SDH MAC
IP IP IP
X.86 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 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
MAC
reconciliation
X.86
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 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)
(4-64B)
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
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) MPLS network Customer
Edge
Customer
Edge Provider Provider (CE)
Edge Edge
(CE)
(PE) (PE) Customer
Customer Edge
Ethernet
Edge
Ethernet PseudoWires (PWs) (CE)
(CE)
MPLS PWE Ethernet frame
label
PW control
label (with or w/o FCS)
stack word
Y(J)S EoS Slide 93
