Upload
jack-boone
View
235
Download
8
Tags:
Embed Size (px)
Citation preview
EoSEoS
Yaakov (J) Stein Chief ScientistRAD Data Communications
Y(J)S EoS Slide 2
Course OutlineCourse 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 3
IntroductionIntroduction
Y(J)S EoS Slide 4
MotivationMotivationAssume 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 5
Option 1: install new infrastructureOption 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 6
Option 2: leased linesOption 2: leased lines
You can try to convince these customers to use leased linesThe 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 !
IWF
IWF
Ethernet Switch
Ethernet Switch
SONETRING
ADM
ADM
Y(J)S EoS Slide 7
Option 3: ATMOption 3: ATM
You can offer ATM serviceThe 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
ATM
ATM
Ethernet Switch
Ethernet Switch
SONETRING
ADM
ADM
Y(J)S EoS Slide 8
Option 4: EoSOption 4: EoS
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 !
IWF
IWF
Ethernet Switch
Ethernet Switch
SONETRING
Y(J)S EoS Slide 9
World’s ApartWorld’s ApartSONET/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 10
Standards we will encounterStandards 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 11
BackgroundBackground
EthernetEthernet
Y(J)S EoS Slide 12
Ethernet frameEthernet frame
For our purposes, “Ethernet” is any layer 2 protocol using 1 of the following frame formats :
DA (6B) SA (6B) T/L (2B) data (0-1500B) pad (0-46) FCS (4B)
64 – 1518 B
DA(6B) SA(6B) T/L(2B) data (0-1500B) pad(0-46) FCS(4B)VT(2B) VLAN(2B)
68 – 1522 B
Y(J)S EoS Slide 13
Ethernet frame sizeEthernet 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 14
BackgroundBackground
HDLCHDLC
Y(J)S EoS Slide 15
Packet to bit streamPacket to bit streamThe first problem in converting Ethernet to TDM: Ethernet consists of frames carrying packets TDM is a continuous bit stream
We can convert a sequence of packets into a bit stream by using an “idle code”
For example, we can use a sequence of 1s as idle indication
The appearance of a 0 bit indicates that data follows
packet 1 packet 2 packet 3 packet 4
packet 1 packet 2 packet 3 packet 4
111111111111111111111110 packet 1 0111111111111111111110 packet 2 011111111111111111111110 01111110 packet 3 01111111111111111
Y(J)S EoS Slide 16
Packet to bit stream Packet to bit stream (cont.)(cont.)
How does the receiver know when to return to idle?
We use a specific “flag” (HDLC uses hex 7E = 01111110)
We can use the flag as the idle code as well
Some implementations allow “zero sharing”
But the flag must not appear in valid data!
If we have access to the physical layer we can mark there (“violations”)
Otherwise (we only access bits) we must disallow the idle code
by replacing it with something else
01111110 01111110 01111110 packet 1 01111110 01111110 01111110 packet 2 01111110 01111110 01111110 01111110 packet 3 01111110
0111111011111101111110 packet 1 011111101111110 01111110 packet 2 011111101111110 1111110 1111110 packet 3 011111101111110
Y(J)S EoS Slide 17
HDLC flagsHDLC flagsISO 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
Alternatively, 1s can be sent as idle, flags as delineators
There are two methods of disallowing flags
bit stuffing (zero insertion)
byte (octet) stuffing
01111110 01111110 01111110 packet 1 01111110 01111110 01111110 packet 2 01111110 01111110 01111110 01111110 packet 3 01111110
11111111111111111 01111110 packet 1 01111110 111111111101111110 packet 2 01111110 11111111111111111101111110 packet 3 01111110
Y(J)S EoS Slide 18
Bit stuffing / zero insertionBit stuffing / zero insertion
ECMA-40
Whenever the encoder sees 5 successive 1s it appends a 0thus 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 19
Byte (octet) stuffingByte (octet) stuffingRFC1549
Whenever the encoder sees hex 7E It replaces it with 7D 5E
Whenever the encoder sees hex 7DIt 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 20
HDLC framingHDLC framing
HDLC frame is bounded by flags, and has a particular structure
Many variants (SDLC, ISO, LAPB, LAPD, LAPF, LAPS, SS7, PPP-HDLC, Cisco-HDLC, etc)
Address: There may be no address (e.g. SS7 HDLC) SDLC always had 8 bit addresses ISO 3309 HDLC has structured multibyte address
– Service Access Point Identifier (MSB of SAPI =1 may indicate broadcast/multicast)
– 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
flag (8) flag (8)address (0/8/16) ctrl (8/16) data FCS (16/32)
EAC/RSAPI EA
Y(J)S EoS Slide 21
HDLC controlHDLC 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 fieldwhich varies widely between different protocols
Y(J)S EoS Slide 22
HDLC FCSHDLC 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 FCSothers allow 16 bit but recommend 32 bit FCS
Y(J)S EoS Slide 23
BackgroundBackground
PPPPPP
Y(J)S EoS Slide 24
Point to Point Protocol (RFC 1661)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 protocolsML-PPP, PPPoE, BAP, BCP, IPCP, …
Y(J)S EoS Slide 25
Basic PPP encapsulation (RFC 1661)Basic PPP encapsulation (RFC 1661)
Encapsulation enables demuxing of different network-layer protocols
Only 1 field needs to be examined for protocol determination
Protocol field obeys ISO 3309 rules:
– protocol value must be odd (for 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)
protocol (8/16) information padding
Y(J)S EoS Slide 26
PPP using HDLC framing (RFC 1662)PPP using HDLC framing (RFC 1662)
When using PPP over synchronous links we use HDLC-like framing
1 byte Broadcast address is used by default (users may define alternative address)
Synchronous Link may be bit-oriented or byte-oriented
Basic PPP encapsulation is extended by 8 bytes
Bit stuffing or byte stuffing allowed
Escape mechanism allows transparent transfer of control data (e.g. ^S/^Q)
enables removal of spurious control data (inserted by intermediate boxes)
flag
7E
address
FF
ctrl
03
information FCS
(16/32b)
protocol
(8/16b)
padding
(optional)
flag
7E
Y(J)S EoS Slide 27
RFC1662 vs. X.85RFC1662 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
flag
7E
address
04
ctrl
03
IP Packet FCS
(32b)
SAPI
(16b)
flag
7E
flag
7E
address
FF
ctrl
03
information FCS
(16/32b)
protocol
(8/16b)
padding
(optional)
flag
7E1662
X.85
PPP frame
Y(J)S EoS Slide 28
BackgroundBackground
SONET/SDHSONET/SDH
Note:
For more information – see SONET/SDH course.
Y(J)S EoS Slide 29
SONET architectureSONET architecture
SONET (SDH) has at 3 layers: path – end-to-end data connection, muxes tributary signals path section
– there are STS paths + Virtual Tributary (VT) paths
line – protected multiplexed SONET payload multiplex section section – physical link between adjacent elements regenerator section
Each layer has its own overhead to support needed functionality
SDH terminology
Path
Termination
Path
Termination
Line
Termination
Line
Termination
Section
Termination
path
line line line
ADM ADMregenerator
section section sectionsection
Y(J)S EoS Slide 30
SONET STS-1 frameSONET STS-1 frame
Synchronous Transfer Signals are bit-signals (OC are optical)
Each STS-1 frame is 90 columns * 9 rows = 810 bytes
There are 8000 STS-1 frames per secondso each byte represents 64 kbps (each column is 576 kbps)
Thus the basic STS-1 rate is 51.840 Mbps
90 columns
9 ro
ws
Y(J)S EoS Slide 31
SDH STM-1 frameSDH STM-1 frame
Synchronous Transport Modules are the bit-signals for SDH
Each STM-1 frame is 270 columns * 9 rows = 2430 bytes
There are 8000 STM-1 frames per second
Thus the basic STM-1 rate is 155.520 Mbps
3 times the STS-1 rate!
270 columns
9 ro
ws
…
Y(J)S EoS Slide 32
SONET/SDH ratesSONET/SDH rates
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
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
Y(J)S EoS Slide 33
SONET/SDH tributariesSONET/SDH tributaries
E3 and T3 are carried as Higher Order Paths (HOPs)
E1 and T1 are carried as Lower Order Paths (LOPs)
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
Y(J)S EoS Slide 34
Synchronous Payload Envelope
STS-1 frame structureSTS-1 frame structure9
row
s
section + lineoverhead
6 ro
ws
3 ro
ws
Section overhead is 3 rows * 3 columns = 9 bytes = 576 kbpsframing, performance monitoring, management
Line overhead is 6 rows * 3 columns = 18 bytes = 1152 kbpsprotection 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 !
90 columns
9 ro
ws
Y(J)S EoS Slide 35
STM-1 frame structureSTM-1 frame structure
TransportOverhead
TOHSimilarly, 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
…
270 columns
Y(J)S EoS Slide 36
ScramblingScramblingSONET/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
Z-43
Xn Yn = Xn + Yn-43
Y(J)S EoS Slide 37
HOP SPE structureHOP SPE structure
2 bytes in the line overhead point to the STS path overhead POHpointer (floating) allows frequency/phase compensation
(after re-arranging) POH is one column of 9 rows (9 bytes = 576 kbps)
Y(J)S EoS Slide 38
Path overheadPath overhead
POH is responsible for – path performance monitoring– status (including of mapped payloads)
– trace
2 bytes are of particular interest to us:
C2 is the “signal label” indicates path payload type
H4 is the “multiframe indication” used by VCAT/LCAS (discussed later)
J1
B3
C2
G1
F2
H4
F3
K3
N1
POH
C2 (hex)
Payload type
00 unequipped
01 nonspecific
02 LOP (TUG)
04 E3/T3
12 E4
13 ATM
16 PoS – RFC 1662
18 LAPS X.85
1A 10G Ethernet
1B GFP
CF PoS - RFC1619
Y(J)S EoS Slide 39
STS-1 HOPSTS-1 HOP
1 column of SPE is POH
2 more (“fixed stuffing”) columns are reserved
We are left with84 columns = 756 bytes = 48.384 Mbps for payload
This is enough for a E3 (34.368M) or a T3 (44.736M)
1 875930
Y(J)S EoS Slide 40
LOPLOP
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
1 875930 1 2 3 4 5 6 7VTG
Y(J)S EoS Slide 41
SONET/SDH : VT/VC typesSONET/SDH : VT/VC types
VT/STS VC column
rate
payload
VT 1.5 VC-11 3 1.728 DS1 (1.544)
VT 2 VC-12 4 2.304 E1 (2.048)
VT 3 6 3.456 DS1C (3.152)
VT 6 VC-2 12 6.912 DS2 (6.312)
STS-1 VC-3 48.384 E3 (34.368)
STS-1 VC-3 48.384 DS3 (44.736)
STS-3c VC-4 149.760 E4 (139.264)
LOP
HOP
standard PDH rates map efficiently into SONET/SDH !
4 per group
3 per group
2 per group
1 per group
Y(J)S EoS Slide 42
Payload capacityPayload 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 43
VCATVCAT
Virtual ConcatenationVirtual Concatenation
Y(J)S EoS Slide 44
ConcatenationConcatenation
Payloads that don’t fit into standard VT/VC sizes can be accommodatedby concatenating of several VTs / VCs
For example, 10 Mbps doesn’t fit into any VT or VCso 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 or5 VT2/VC-12 s = 5 * 2.176 = 10.88 Mbps
Y(J)S EoS Slide 45
ConcatenationConcatenationThere 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 * 4n 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 46
Contiguous Concatenation: STS-3cContiguous Concatenation: STS-3c270 columns
9 ro
ws …
9 columns of section and
line overhead
3 columns of path overhead
258 columns of SPE STS-3
270 columns
9 ro
ws …
9 columns of section and
line overhead
1 column of path overhead
260 columns of SPE STS-3c
258 columns * 0.576 = 148.608 Mbps
260 columns * 0.576 = 149.760 Mbps
Y(J)S EoS Slide 47
STS-N vs. STS-NcSTS-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) columnse.g. STS-12c gains 11 columns = 6.336Mbps vis a vis STS-12STS-48c gains 47 columns = 27.072 MbpsSTS-192c gains 191 columns = 110.016 Mbps !
However, an STS-Nc signal is not as easily separablewhen we want to add/drop component signals
Y(J)S EoS Slide 48
Virtual ConcatenationVirtual 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)
…
H4
Y(J)S EoS Slide 49
SDH virtually concatenated VCsSDH virtually concatenated VCs
So we have many permissible rates
1.600, 2.176, 3.200, 4.352, 4.800, 6.400, 6.528, 6.784, 8.000, …
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
Y(J)S EoS Slide 50
SONET virtually concatenated VTsSONET 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 51
Efficiency comparisonEfficiency comparison
Using VCAT increases efficiency to close to 100% !
rate w/o VCAT efficiency with VCAT efficiency
10 STS-1 21% VT2-5v
VC-12-5v
92%
100 STS-3c
VC-4
67% STS-1-2v
VC-3-2v
100%
1000 STS-48c
VC-4-16c
42% STS-3c-7v
VC-4-7v
95%
Y(J)S EoS Slide 52
PDH VCATPDH VCAT
Recently ITU-T G.7043 expanded VCAT to E1,T1,E3,T3
Enables bonding of up to 16 PDH signals to support higher rates
Only bonding of like PDH signals allowed (e.g. 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)
TS0
1st frameof4 E1s
VCAToverhead
octet
timeeach E1
Y(J)S EoS Slide 53
PDH VCAT overhead octetPDH VCAT overhead octet
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)
TS0
frames of an E1
VCAToverhead
octet
…
Y(J)S EoS Slide 54
Delay compensationDelay 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 pathsso 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 Signalthe VCAT mechanism only needs to identify individual frames
Y(J)S EoS Slide 55
VCAT bufferingVCAT 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 membersand 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 56
Multiframes and superframesMultiframes 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 57
LCASLCAS
Link Capacity Adjustment SchemeLink Capacity Adjustment Scheme
Y(J)S EoS Slide 58
LCASLCAS
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 59
LCAS – how does it work?LCAS – how does it work?LCAS is unidirectional (for symmetric BW need to perform twice)
LCAS functions can be initiated by source or sink
LCAS assumes that all VCG members are error-free
– LCAS messages are CRC protected
LCAS messages are sent in advance – sink processes messages after differential compensation– message describes link state at time of next message– receiver can switch to new configuration in time
LCAS messages are in the upper nibble of– H4 byte for HOS SONET/SDH– K4 byte for LOS SONET/SDH– VCAT overhead octet for PDH – VCAT and LCAS Information
LCAS messages employ redundancy– messages from source to sink are member specific– messages from sink to source are replicated
J1
B3
C2
G1
F2
H4
F3
K3
N1
POH
Y(J)S EoS Slide 60
LCAS control messagesLCAS 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 61
H4 formatH4 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 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1
CRC-8 bits 1-4 0 1 1 0CRC-8 bits 5-8 0 1 1 1
MST bits 1 0 0 0more MST bits 1 0 0 1
0 0 0 RS-ACK 1 0 1 0 0 0 0 0 1 0 1 1 0 0 0 0 1 1 0 0 0 0 0 0 1 1 0 1
SQ bits 1-4 1 1 1 0SQ bits 5-8 1 1 1 1
16 frame m
ultiframeMFI1
rese
rved
fie
lds
rese
rved
fie
lds
Y(J)S EoS Slide 62
H4 format – some commentsH4 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 63
VLI formatVLI 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 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 1
CRC-8 bits 1-4 0 1 1 0CRC-8 bits 5-8 0 1 1 1
MST bits 1 0 0 0more MST bits 1 0 0 1
0 0 0 RS-ACK 1 0 1 0 0 0 0 0 1 0 1 1 0 0 0 0 1 1 0 0 0 0 0 0 1 1 0 1 0 0 0 0 1 1 1 0
SQ 1 1 1 1
16 frame m
ultiframeMFI1
rese
rved
fie
lds
rese
rved
fie
lds
Y(J)S EoS Slide 64
LCAS – adding a member (1)LCAS – adding a member (1)When more/less BW is needed, we need to add/remove VCAT members
Adding/removing VCAT members first requires provisioning (management)
LCAS handles member sequence numbers assignment
LCAS ensures service is not disrupted
Example: to add a 4th member to group “1”
Initial state:
Step 1: NMS provisions new member
source sends 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=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 65
LCAS – adding a member (2)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=FAILand source reports this to NMS
Step 3: source sends CTRL=EOS for new member
new member starts to carry traffic
sink sends RS-ACK
Note 1: several new members may be added at once
Note 2: removing a member is similar
Source puts CTRL=IDLE for member to be removed and stops using it
All member sequence numbers must be adjusted
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=NORM
GID=g SQ=3 CTRL=EOS
GID=g SQ=4 CTRL=ADD
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=NORM
GID=g SQ=3 CTRL=NORM
GID=g SQ=4 CTRL=EOS
Y(J)S EoS Slide 66
LCAS – service preservationLCAS – service preservationTo preserve service integrity if sink detects a failure of a VCAT member
LCAS can temporarily remove member (if service can tolerate BW reduction)
Example: Initial state
Step 1: sink sends MST=FAIL for member 2 source sends CTRL=DNU (special treatment if EoS) and ceases to use member 2Note: if EoS fails, renumber to ensure EoS is active
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
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=NORM
GID=g SQ=3 CTRL=NORM
GID=g SQ=4 CTRL=EOS
GID=g SQ=1 CTRL=NORM
GID=g SQ=2 CTRL=DNU
GID=g SQ=3 CTRL=NORM
GID=g SQ=4 CTRL=EOS
Y(J)S EoS Slide 67
PoSPoS
Packet over SONETPacket over SONET
Y(J)S EoS Slide 68
Packet over SONETPacket 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 interfaceto 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 69
PoS architecturePoS 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
IP
PPP
HDLC
SONET/SDH
Y(J)S EoS Slide 70
What happened to the Ethernet ?What happened to the Ethernet ?
The conventional model:
Ethernet is a LAN technology – last 100m– 10s of hosts
IP is a WAN technology– data transported in native IP– different L2 technologies for last segment
But modern Ethernet wants to be more
IPEthernet Ethernet
Y(J)S EoS Slide 71
PoS DetailsPoS 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 72
RFC2615 vs. RFC1619RFC2615 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 scramblerscrambler does not reset during usehard to guess proper internal state
Y(J)S EoS Slide 73
POS problemsPOS 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 74
LAPSLAPS
Link Access Protocol over SDHLink Access Protocol over SDH
X.85 and X.86X.85 and X.86
Y(J)S EoS Slide 75
LAPSLAPS
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 76
X.85 vs. X.86X.85 vs. X.86
X.85 transports IP packets if delivered over Ethernet, the Ethernet is terminated
X.86 transports Ethernetcan transport all sorts of Ethernet traffic – not only IP packets
IP
LLC
MAC
IP
LLC
MAC
IP
LLC
MAC
LAPS
SDH
X.86
IP
LLC
MAC
IP
LLC
MAC
IP
LAPS
SDH
X.85
Y(J)S EoS Slide 77
X.85X.85
IP over SDH using LAPS
address = 04 (or FF for compatibility with PoS)
SAPI = 21 for IPv4 =57 for IPv6 (changed to be like PoS)
Scrambler always used
Can use LOP VCs, HOP VCs or STMs
flag
7E
address
(16b)
ctrl
03
IP Packet FCS
(32b)
SAPI
(16b)
flag
7E
Y(J)S EoS Slide 78
X.86X.86
Similar to X.85 (IP over SDH using LAPS)but transports the entire Ethernet frame
Provides a virtual MII/GMII interface
Transparent to all Ethernet features (VLAN, P bits, RPR, etc.)
Rate adaptation by adding hex DD (after byte stuffing 7D DD)
Ammendment specifies use of Ethernet PAUSE frames for rate limiting
MAC
LAPS
SDH
reconciliation
rate adaptation
MII/GMII
flag
7E
address
(16b)
ctrl
03
Ethernet frame
DA SA T/L INFO PAD FCS
FCS
(32b)
SAPI
FE01
flag
7E
Y(J)S EoS Slide 79
LAPS drawbacksLAPS 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 80
GFPGFP
Generic Framing ProcedureGeneric Framing Procedure
Y(J)S EoS Slide 81
GFP architectureGFP architectureDefined in ITU-T G.7041 (also numbered Y.1303)
originally developed in T1X1 to fix ATM limitations(like ATM) uses HEC protected frames instead of HDLC
GFP generically encapsulates client (e.g. IP, Ethernet)onto transport network (e.g. SONET/SDH, OTN)
Client may be PDU-oriented (Ethernet MAC, IP) or block-oriented (GbE, fiber channel)
GFP frames– are octet aligned– contain at most 65,535 bytes– consist of a header + payload area
Any idle time between GFP frames is filled with GFP idle frames
Ethernet IP other
GFP – client specific part
GFP – common part
SDH OTN other
HDLC
PDH
Y(J)S EoS Slide 82
GFP frame structureGFP frame structure
Every GFP frame has a 4-byte core header– 2 byte Payload Length Indicator PLI = 01,2,3 are for control frames
– 2 byte core Header Error Control X16 + X12 + X5 + 1
– entire core header is 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
PLI (2B)
cHEC (2B)
payload header (4-64B)
payload
optional payloadFCS (4B)
coreheader
payloadarea
Y(J)S EoS Slide 83
GFP payload headerGFP payload header
GFP payload header has– type (2B)– type HEC (CRC-16)– extension header (0-60B)
either null or linear extension (payload type muxing)
– extension HEC (CRC-16)
type consists of– Payload Type Identifier (3b)
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.
type (2B)
tHEC (2B)
extension header (0-58B)
eHEC (2B)
UPI (8b)
PTI (3b) EXI (4b)PFI
Y(J)S EoS Slide 84
GFP modes 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 particular8B/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 85
GFP-T 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 inputinto 1 or 2 different 10 bit wordsMaintains 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 86
GFP-F 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 outpreambles, 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 87
GFP advantagesGFP 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 88
AlternativesAlternatives
Y(J)S EoS Slide 89
There are yet other ways …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 90
Ethernet in the First MileEthernet in the First MileIEEE 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 91
WAN-PHY WAN-PHY (10 GbE in STM-64)(10 GbE in STM-64)
There is a special case where Ethernet and SDH bit-rates are closeSTM-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
10GBASE-W 802.3-2005 Clause 50 G.707 Annex F
Y(J)S EoS Slide 92
Ethernet over WavelengthsEthernet over WavelengthsRather 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 93
Ethernet PWsEthernet PWs
ProviderEdge
(PE)Customer
Edge
(CE)
CustomerEdge
(CE)
CustomerEdge
(CE)
Ethernet
MPLS network
PseudoWires (PWs)
CustomerEdge
(CE)
CustomerEdge
(CE)
ProviderEdge
(PE)Ethernet
Pseudowire (PW): Pseudowire (PW): mechanism that emulates essential mechanism that emulates essential attributes of a native service while transporting over a PSNattributes of a native service while transporting over a PSN
MPLS labelstack
PW label
PWEcontrolword
Ethernet frame(with or w/o FCS)