Download - GFP Eth Frame
-
8/8/2019 GFP Eth Frame
1/89
Connection-Oriented Networks - Harry Perros 1
Chapter 2:SONET/SDH and GFP
TOPICS
T1/E1
SONET/SDH - STS 1, STS -3 frames
SONET devices
Self-healingrings
Generic frame protocol, and Data over SONET
-
8/8/2019 GFP Eth Frame
2/89
Connection-Oriented Networks - Harry Perros 2
T1/E1
Time division multiplexing allows a link
to be utilized simultaneously by many
users
M
U
X
D
E
M
U
X
N inputlinks N outputlinks
link
1
2
N
1
2
N
-
8/8/2019 GFP Eth Frame
3/89
Connection-Oriented Networks - Harry Perros 3
The transmission is organized into frames. Each frame contains a fixed number of time slots.
Each time slot is pre-assigned to a specific inputlink. The duration of a time slot is either a bit or a
byte. If the buffer of an input link has no data, then its
associated time slot is transmitted empty.
A time slot dedicated to an input link repeats
continuously frame after frame, thus forming achannelor a trunk.
-
8/8/2019 GFP Eth Frame
4/89
Connection-Oriented Networks - Harry Perros 4
Pulse code modulation
TDM is used in telephony
Voice analog signals are digitized at the
end office using Pulse Code Modulation.
A voice signal is sampled 8000 times/sec,
or every 125 sec.
A 7-bit or 8-bit number is created every
125 sec.
-
8/8/2019 GFP Eth Frame
5/89
-
8/8/2019 GFP Eth Frame
6/89
Connection-Oriented Networks - Harry Perros 6
T carrier / E carrier The DS signal is carried over a carrier system
known as the T carrier.
T1 carries the DS1 signal,
T2 carries the DS2 signal etc
The ITU-T signal is carried over a carrier systemknown as theE carrier.
The DS and ITU-T hierarchy is known as the
plesiochronous digital hierarchy (PDH). (Plesionmeans nearly the same, and chronos meanstime in Greek).
-
8/8/2019 GFP Eth Frame
7/89
Connection-Oriented Networks - Harry Perros 7
Digital signal number Voice channels Data Rate (Mbps)DS0 1 0.064DS1 24 1.544
DS1C 48 3.152DS2 96 6.312DS3 672 44.736
DS3C 1344 91.053DS4 4032 274.176
Table 2.1: The North American Hierarchy
Level number Voice channels Data Rate (Mbps)0 1 0.0641 30 2.0482 120 8.4483 480 34.3684 1920 139.2645 7680 565.148
Table 2.2: The international (ITU-T) hierarchy
-
8/8/2019 GFP Eth Frame
8/89
Connection-Oriented Networks - Harry Perros 8
The DS1 signal
24 8-bit time slots/frame Each time slot carries 8 bits/ 125 sec, or the channel
carries a 64 Kbps voice.
Every 6th successive time slot (i.e, 6th, 12th, 18th,24th, etc), the 8 bit is robbed and it is used for
signaling. F bit: Used for synchronization. It transmits the
pattern: 10101010
FTime
slot 1
Time
slot 2
Time
slot 3
Time
slot 24. . .
-
8/8/2019 GFP Eth Frame
9/89
Connection-Oriented Networks - Harry Perros 9
T1: Total transmission rate: 24x8+1 = 193 bits per 125
sec, or 1.544 Mbps
E1 30 voice time slots plus 2 time slots for
synchronization and control
Total transmission rate: 32x8 = 256 bits per 125 sec,or 2.048 Mbps
-
8/8/2019 GFP Eth Frame
10/89
Connection-Oriented Networks - Harry Perros 10
Fractional T1/E1
Fractional T1 or E1 allows the use of only
a fraction of the T1 or E1 capacity. For example: if N=2, then only two time
slots are used per frame, which corresponds
to a channel with total bandwidth of 128
Kbps.
-
8/8/2019 GFP Eth Frame
11/89
-
8/8/2019 GFP Eth Frame
12/89
Connection-Oriented Networks - Harry Perros 12
The synchronous optical network(SONET)
Proposed by Bellcore (Telecordia).
It was designed to multiplex DS-n signals andtransmit them optically.
ITU-T adopted the synchronous digitalhierarchy (SDH), as the international
standard. It enables the multiplexing of level 3 signals
(34.368 Mbps)
-
8/8/2019 GFP Eth Frame
13/89
Connection-Oriented Networks - Harry Perros 13
STS, STM, OC
The electrical side of the SONET signal is
known as the synchronous transport signal
(STS)
The electrical side of the SDH is known as
the synchronous transport module (STM).
The optical side of a SONET/SDH signal isknown as the optical carrier(OC).
-
8/8/2019 GFP Eth Frame
14/89
Connection-Oriented Networks - Harry Perros 14
The SONET/SDH hierarchyOptical
level
SONET
level
(electrical)
SDH
level
(electrical)
Data rate
(Mbps)
Overhead
rate
(Mbps)
Payload
rate
(Mbps)
OC-1 STS-1 - 51.840 1.728 50.112
OC-3 STS-3 STM-1 155.520 5.184 150.336
OC-9 STS-9 STM-3 466.560 15.552 451.008
OC-12 STS-12 STM-4 622.080 20.736 601.344
OC-18 STS-18 STM-6 933.120 31.104 902.016
OC-24 STS-24 STM-8 1244.160 41.472 1202.688
Oc-36 STS-36 STM-12 1866.240 62.208 1804.932
OC-48 STS-48 STM-16 2488.320 82.944 2405.376
OC-96 STS-96 STM-32 4976.640 165.888 4810.752
OC-192 STS-192 STM-64 9953.280 331.776 9621.504
OC-768 STS-768 STM-256 39813.120 1327.104 38486.016
OC-N STS-N STM-N/3 N*51.840 N*1.728 N*50.112
-
8/8/2019 GFP Eth Frame
15/89
Connection-Oriented Networks - Harry Perros 15
SONET/SDH is channelized.
STS-3 consists of 3 STS-1 streams, and each STS-1 consists of a number of DS-1 and E1signals.
STS-12 consists of 12 STS-1 streams
Concatenated structures (OC-3c, OC-12c, etc) The frame of the STS-3 payload is filled with
ATM cells or IP packets packed in PPP or HDLC
frames.
Concatenated SONET/SDH links are commonlyused to interconnect ATM switches and IP routers
(Packets over SONET).
-
8/8/2019 GFP Eth Frame
16/89
Connection-Oriented Networks - Harry Perros 16
The STS-1 frame structure
1 2 3 4 5 6 90
1 1 2 3 4 5 6 90
2 91 92 93 94 95 96 180
3 181 182 183 184 185 186 270
4 271 272 273 274 275 276 360
5 361 362 363 364 365 366 450
6 451 452 453 454 455 456 560
7 561 562 563 564 565 566 630
8 631 632 636 634 635 636 720
9 721 722 723 724 725 726 810
-
8/8/2019 GFP Eth Frame
17/89
Connection-Oriented Networks - Harry Perros 17
Main features
The frame is presented in matrix form and it is
transmitted row by row.
Each cell in the matrix corresponds to a byte
The first three columns contain overheads The remaining 87 columns carry the
synchronous payload envelope (SPE), which
consists of user data, and additional overheads
referred to as thepayload overhead(POH)
-
8/8/2019 GFP Eth Frame
18/89
Connection-Oriented Networks - Harry Perros 18
An SPE may straddle between
two successive frames
Frame i
Frame i+1
1 2 3 4 5 6 . . . 90
1
2
3
4
5
6
7
8
9
276
276275
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
. . .
1
2
3
4
5
6
7
8
9
-
8/8/2019 GFP Eth Frame
19/89
Connection-Oriented Networks - Harry Perros 19
The section, line, and path overheads
Section
Line
STS-1 STS-1
A B
regeneratorregeneratorSTS-1
A1
A12
STS-12
. . .
STS-1
B1
B12
STS-12
. . .
Section Section Section Section
LineLine
Path
-
8/8/2019 GFP Eth Frame
20/89
Connection-Oriented Networks - Harry Perros 20
Section: a single link with a SONET deviceor a regenerator on either side of it.
Line: A link between two SONET devices,
which may include regenerators The section overhead in the SONET frame
is associated with the transport of STS-1
frames over a section, and the line
overhead is associated with the transport ofSPEs over a line.
-
8/8/2019 GFP Eth Frame
21/89
Connection-Oriented Networks - Harry Perros 21
The SONET stack
Section
Line
Path
Photonic
Section
Line
Path
Photonic
Section
Line
Photonic
Section
Photonic
Section
Photonic
Section
Line
Photonic
Ai
A Regenerator Regenerator Bi
B
-
8/8/2019 GFP Eth Frame
22/89
Connection-Oriented Networks - Harry Perros 22
STS-1: Section and line overheads
SOH
LOH
Column
1 2 3
1 A1 A2 J0
2 B1 E1 F1
3 D1 D2 D3
4 H1 H2 H3
5 B2 K1 K2
6 D4 D5 D6
7 D7 D8 D9
8 D10 D11 D12
9 Z1 Z2 E2
-
8/8/2019 GFP Eth Frame
23/89
Connection-Oriented Networks - Harry Perros 23
The following are some of the bytes in the
section overhead (SOH) : A1 and A2: These two bytes are called the
framing bytes and they are used for framealignment. They are populated with the value
1111 0110 0010 1000 or 0xF628, whichuniquely identifies the beginning of an STS-frame.
J0: This is called the section trace byte and itis used for to trace the STS-1 frame back to itsoriginating equipment.
-
8/8/2019 GFP Eth Frame
24/89
Connection-Oriented Networks - Harry Perros 24
B1: This byte is the bit interleaved parity byteand it is commonly referred to as BIP-8. It isused to perform an even-parity check on theprevious STS-1 frame after the frame has beenscrambled. The parity is inserted in the BIP-8field of the current frame before it is scrambled
E1: This byte provides a 64 Kbps channel canbe used for voice communications by fieldengineers.
-
8/8/2019 GFP Eth Frame
25/89
Connection-Oriented Networks - Harry Perros 25
The following are some of the bytes in the line
overhead (LOH) that have been defined:
H1 and H2: These two bytes are known as thepointer
bytes, and they contain a pointer that points to the
beginning of the SPE within the STS-1 frame. The
pointer gives the offset in bytes between the H1 andH2 bytes and the beginning of the SPE.
B2: This is similar to the B1 byte in the section
overhead and it is used to carry the BIP-8 parity check
performed on the line overhead section and the
payload section. That is, it is performed on the entire
STS-1 frame except the section overhead bytes.
-
8/8/2019 GFP Eth Frame
26/89
Connection-Oriented Networks - Harry Perros 26
The path overhead bytes
J1
B3
C2
G1
F2
H4
Z3
Z4
Z5
J1
B3C2
G1
F2
H4
Z3
Z4
Z5
Location of the POH The POH bytes
-
8/8/2019 GFP Eth Frame
27/89
Connection-Oriented Networks - Harry Perros 27
The following are some of the bytes that have
been defined:
B3: This byte is similar to B1 used in the section
overhead and B2 used in the line overhead. It is used to
carry the BIP-8 parity check performed on the payload
section. That is, it is performed on the entire STS-1frame except the section and line overhead bytes.
C2: This byte is known as the path signal labeland it
indicates the type of user information carried in the
SPE, such as, virtual tributaries (VT), asynchronous
DS-3, ATM cells, HDLC-over-SONET, and PPP over
SONET.
-
8/8/2019 GFP Eth Frame
28/89
Connection-Oriented Networks - Harry Perros 28
The STS-1 payload
The payload consists of user data and the
path overhead.
User data: Virtual tributaries: sub-rate synchronous data
streams, such as DS-0, DS-1, E1, and entire
DS-3 frames
ATM cells and IP packets
-
8/8/2019 GFP Eth Frame
29/89
Connection-Oriented Networks - Harry Perros 29
Virtual tributaries
The STS-1 payload is divided into seven
virtual tributary groups (VTG).
Each VTG consists of 108 bytes (12 columns)
Each VTG may carry a number ofvirtual
tributaries, i.e., sub-rate streams.
-
8/8/2019 GFP Eth Frame
30/89
Connection-Oriented Networks - Harry Perros 30
The following virtual tributaries have beendefined:
VT1.5:This virtual tributary carries one DS-1
signal and it is contained in three columns, that
take up 27 bytes. Four VT1.5s can betransported in a single VTG.
VT2: This virtual tributary carries an E1 signal
of 2.048 Mbps. VT2 is contained in four
columns, that is it takes up 36 bytes. ThreeVT2s can be carried in a single VTG.
-
8/8/2019 GFP Eth Frame
31/89
Connection-Oriented Networks - Harry Perros 31
VT3: This virtual tributary transports theunchannelized DS-1 signal. A VT3 iscontained in 6 columns that takes up 54 bytes.This means that a VTG can carry two VT3s.
VT6: This virtual tributary transports a DS-2signal, which carries 96 voice channels. VT6 iscontained in 12 columns, that is it takes up 108bytes. A VTG can carry exactly one VT2.
-
8/8/2019 GFP Eth Frame
32/89
Connection-Oriented Networks - Harry Perros 32
ATM cells
Mapped directly onto the SPE. An ATMcells may straddle two SPEs.
10
Cell 1 Cell 2
Cell 2 Cell 3
Cell 14 Cell 15
Cell 15
904
1
9
2
8
3
POH
-
8/8/2019 GFP Eth Frame
33/89
Connection-Oriented Networks - Harry Perros 33
IP packet over SONET
IP packets are first encapsulated in HDLC andthe resulting frames are mapped into the SPE
payload row by row as in the case above forATM cels.10 904
1
9
2
8
3
POH
7E 7E 7E
7E7E7E
-
8/8/2019 GFP Eth Frame
34/89
Connection-Oriented Networks - Harry Perros 34
IP packets can also be encapsulated in PPPinstead of HDLC.
A frame may straddle over two adjacent SPEs, asin the case of ATM.
The interframe fill 7E is used to maintain acontinuous bit tstream
-
8/8/2019 GFP Eth Frame
35/89
Connection-Oriented Networks - Harry Perros 35
The STS-3 frame structure
Overhead section Payload section
1 2 3 4 5 6 7 8 9 10 11 12
270
.
.
.
1st
S TS
-1
1stSTS-1
1stSTS-1
1stSTS-1
1stSTS-1
2ndS
TS-1
2ndS
TS-1
2ndS
TS-1
2ndS
TS-1
2ndS
TS-1
3rd
STS-1
3rd
STS-1
3rdS
TS-1
3rdS
TS-1
3rd
STS-1
-
8/8/2019 GFP Eth Frame
36/89
Connection-Oriented Networks - Harry Perros 36
The channelized STS-3 frame is constructed by
multiplexing byte-wise three channelized STS-1frames. As a result:
Byte 1, 4, 7, , 268 of the STS-3 frame contains byte1, 2, 3, , 90 of the first STS-1 frame.
Byte 2, 5, 8, , 269 of the STS-3 frame contains byte
1, 2, 3, , 90 of the second STS-1 frame Byte 3, 6, 9, , 270 of the STS-3 frame contains byte
1, 2, 3, , 90 of the third STS-1 frame.
This byte-wise multiplexing, causes the columnsof the three STS-1 frames to be interleaved in theSTS-3 frame
-
8/8/2019 GFP Eth Frame
37/89
Connection-Oriented Networks - Harry Perros 37
The first 9 columns of the STS-3 framecontain the overhead part and the
remaining columns contain the payload
part. Error checking and some overhead bytes
are for the entire STS-3 frame, and they are
only meaningful in the overhead bytes of
the first STS-1 frame.
-
8/8/2019 GFP Eth Frame
38/89
Connection-Oriented Networks - Harry Perros 38
SONET/SDH devices
Several different equipment exist: Terminal multiplexer (TM)
Add/drop multiplexer (ADM)
Digital cross connect(DCS)
-
8/8/2019 GFP Eth Frame
39/89
Connection-Oriented Networks - Harry Perros 39
It multiplexes a number of DS-n or E1 signalsinto a single OC-N signal
It consists of a controller, low-speed interfaces
for DS-n or E1 signals, an OC-N interface, and atime slot interchanger (TSI)
It works also as a demultiplexer
. . .
DS-n
OC-N
DS-n
TM
The terminal multiplexer (TM):
-
8/8/2019 GFP Eth Frame
40/89
Connection-Oriented Networks - Harry Perros 40
It is a more complex version of the TM
It receives an OC-N signal from which it candemultiplex and terminate (i.e., drop) anynumber of DS-n or OC-M signals, where M
-
8/8/2019 GFP Eth Frame
41/89
Connection-Oriented Networks - Harry Perros 41
SONET rings
ADM
1
ADM
2
ADM
3
ADM
4
OC3
OC3
OC3
OC3
SONET/SDH ADM devices are typically connected toform a SONET/SDH ring.
SONET/SDH rings are self-healing, that is they canautomatically recover from link failures.
-
8/8/2019 GFP Eth Frame
42/89
Connection-Oriented Networks - Harry Perros 42
An example of a connection
A
B
TM
1
TM
2
ADM
1ADM
2
ADM
3
ADM
4
DS1
OC12
DS1
OC12
OC12
OC12
OC3
OC3
-
8/8/2019 GFP Eth Frame
43/89
Connection-Oriented Networks - Harry Perros 43
A transmits a DS-1 signal to TM 1
TM 1 transmits an OC-3 signal to ADM 1 ADM 1 adds the OC-3 signal into the STS-
12 payload and transmits it out to the nextADM.
At ADM 3, the DS-1 signal belonging to Ais dropped from the payload andtransmitted with other signals to TM 2.
TM 2 in turn, demultiplexes the signals andtransmits As DS-1 signal to B.
-
8/8/2019 GFP Eth Frame
44/89
Connection-Oriented Networks - Harry Perros 44
Connection setup: Using network management procedures the
SONET network is provisioned appropriately.This is an example of apermanent connection.
It remains up for a long time. The connection is dedicated to user A
whether the user transmits or not.
-
8/8/2019 GFP Eth Frame
45/89
Connection-Oriented Networks - Harry Perros 45
A digital cross connect (DCS)
Ring 1 Ring 2ADM
ADM
ADM
ADM
ADM
ADM
DCS
It is used to interconnect multiple SONET rings
It is connected to multiple incoming and outgoing OC-N
interfaces. It can drop and add any number of DSn and/or
OC-M signals, and it can switch DSn and/or OC-M
signals from an incoming interface to any outgoing one.
-
8/8/2019 GFP Eth Frame
46/89
Connection-Oriented Networks - Harry Perros 46
Self-healing SONET/SDH rings
SONET/SDH rings have been specially
architected so that they are available 99.999% of
the time (6 minutes per year!) Causes for ring failures:
Fiber link failure due to accidental cuts, and
transmitter/receiver failure
SONET/SDH device failure (rare)
-
8/8/2019 GFP Eth Frame
47/89
Connection-Oriented Networks - Harry Perros 47
Automatic protection switching (APS)
SONET/SDH rings are self-healing, that is, the
rings services can be automatically restored
following a link failure or degradation in thenetwork signal.
This is done using the automatic protection
switching (APS) protocol. The time to restore the
services has to be less than 50 msec.
-
8/8/2019 GFP Eth Frame
48/89
Connection-Oriented Networks - Harry Perros 48
Protection schemes: point-to-point
Schemes for link protection
dedicated 1+1
1:1
Shared 1:N
ADM
Working
Protection
ADM
-
8/8/2019 GFP Eth Frame
49/89
Connection-Oriented Networks - Harry Perros 49
Working/protection fibers The working and protection fibers have to
be diversely routed. That is, the two fibers
use separate conduits and different physicalroutes.
Often, for economic reasons, the two fibers
use different conduits, but they use the
same physical path. In this case, we saythat they are structurally diverse.
-
8/8/2019 GFP Eth Frame
50/89
Connection-Oriented Networks - Harry Perros 50
Classification of self-healing rings Various ring architectures have been
developed based on the following threefeatures:
Number of fibers
2 or 4 fibers
Direction of transmission:
Unidirectional bidirectional
Line or path switching
-
8/8/2019 GFP Eth Frame
51/89
Connection-Oriented Networks - Harry Perros 51
Number of fibers: 2- or 4-fiber rings
Two-fiber ring: fibers 1, 2, 3, and 4 areused to form the workingring (clockwise),
and fibers 5, 6, 7, and 8 are used to formtheprotection ring (counter-clockwise).
1
2
3
4
5
6
7
8
ADM 1 ADM 2
ADM 3ADM 4
ADM 1 ADM 2
ADM 3ADM 4
-
8/8/2019 GFP Eth Frame
52/89
Connection-Oriented Networks - Harry Perros 52
In another variation of the two-fiber ring, each set of fibersform a ring which can be both a working and a protectionring. In this case, the capacity of each fiber is divided intotwo equal parts, one for working traffic and the other for
protection traffic. In a four-fiber SONET/SDH ring there are two working
rings and two protection rings, one per working ring.
1
2
3
4
5
6
7
8
ADM 1 ADM 2
ADM 3ADM 4
ADM 1 ADM 2
ADM 3ADM 4
-
8/8/2019 GFP Eth Frame
53/89
Connection-Oriented Networks - Harry Perros 53
Direction of transmission
Unidirectional ring:
signals are only transmitted in one
direction of the ring. Bidirectional ring:
signals are transmitted in both directions.
-
8/8/2019 GFP Eth Frame
54/89
Connection-Oriented Networks - Harry Perros 54
Line and path switching
Path switching: Restores the traffic on the
paths affected by a link failure (a path is an
end-to-end connection between the pointwhere the SPE originates and the point where
it terminates.)
Line switching: Restores all the traffic that
passes through a failed link.
-
8/8/2019 GFP Eth Frame
55/89
Connection-Oriented Networks - Harry Perros 55
Based on these three features, we have thefollowing 2-fiber or 4-fiber possible ringarchitectures:
Unidirectional Line Switched Ring(ULSR) Bidirectional Line Switched Ring(BLSR)
Unidirectional Path Switched Ring(UPSR)
Bidirectional Path Switched Ring(BPSR)
-
8/8/2019 GFP Eth Frame
56/89
Connection-Oriented Networks - Harry Perros 56
Of these rings the following three areused:
Two-fiber unidirectional path switched ring(2F-UPSR)
Two-fiber bidirectional line switched ring(2F-BLSR)
Four-fiber bidirectional line switched ring(4F-BLSR)
-
8/8/2019 GFP Eth Frame
57/89
Connection-Oriented Networks - Harry Perros 57
Two-fiber unidirectionalpath switched ring (2F-UPSR)
ADM 1 ADM 2
ADM 3ADM 4
5
264 8
3
7
A
Protection ring
Working ring
1
B
-
8/8/2019 GFP Eth Frame
58/89
Connection-Oriented Networks - Harry Perros 58
Features:
Working ring consists of fibers 1, 2, 3 and 4,
and the protection ring of fibers 5, 6, 7, and 8.
Unidirectional transmission means that traffic
is transmitted in the same direction. Atransmits to B over fiber 1 of the working ring,
and B transmits over fibers 2, 3, and 4 of the
working ring.
Used as a metro edge ring to interconnectPBXs and access networks to a metro core ring
-
8/8/2019 GFP Eth Frame
59/89
Connection-Oriented Networks - Harry Perros 59
Self-healing mechanism:
Path level protection using the 1+1 scheme. Thesignal transmitted by A is split into two. One
copy is transmitted over the working fiber 1, and
the other copy is transmitted over the protection
fibers 8, 7, and 6.
During normal operation, B receives two
identical signals from A, and selects the one
with the best quality. If fiber 1 fails, B will
continue to receive As signal over theprotection path. The same applies if there is a
node failure.
-
8/8/2019 GFP Eth Frame
60/89
Connection-Oriented Networks - Harry Perros 60
Two-fiber bidirectional line switchedring (2F-BLSR)
ADM 1 ADM 2 ADM 3
ADM 4
7
396 12
5
11
A B
1
8
4
2
10
ADM 5ADM 6
C
-
8/8/2019 GFP Eth Frame
61/89
Connection-Oriented Networks - Harry Perros 61
Features:
Used in metro core rings.
Fibers 1, 2, 3, 4, 5, and 6 form a ring, call it ring 1, onwhich transmission is clockwise. Fibers 7, 8, 9, 10, 11,and 12 form another ring, call it ring 2, on which
transmission is counter-clockwise. Both rings 1 and 2 carry working and protection traffic.
This is done by dividing the capacity of each fiber onring 1 and 2 to two parts. One part is used to carryworking traffic and the other protection traffic.
A transmits to B over the working part of fibers 1 and2 of ring 1, and B transmits to A over the working partof fibers 8 and 7 of ring 2.
-
8/8/2019 GFP Eth Frame
62/89
Connection-Oriented Networks - Harry Perros 62
Self-healing mechanism:
The ring provides line switching. If fiber 2 fails
then the traffic that goes over fiber 2 will be
automatically switched to the protection part of
ring 2.
That is, all the traffic will be re-routed to ADM
3 over the protection part of ring 2 using fibers
7, 12, 11, 10, and 9. From there, the traffic for
each connection will continue on following the
original path of the connection.
-
8/8/2019 GFP Eth Frame
63/89
Connection-Oriented Networks - Harry Perros 63
Four-fiber bidirectional line switched
ring (4F-BLSR)
Working rings
ADM 1 ADM 2 ADM 3
ADM 4
A B
ADM 5ADM 6
Protection rings
-
8/8/2019 GFP Eth Frame
64/89
Connection-Oriented Networks - Harry Perros 64
Features
Two working rings and two protection rings.The two working rings transmit in opposite
directions, and each is protected by a
protection ring which transmits in the same
direction. The advantage of this four-fiber ring is that it
can suffer multiple failures and still function.
In view of this, it is deployed by long-distance
telephone companies in regional and nationalrings.
-
8/8/2019 GFP Eth Frame
65/89
Connection-Oriented Networks - Harry Perros 65
Self-healing operation (span switching):
If a working fiber fails, the working traffic willbe transferred over its protection ring. This isknown as span switching.
ADM 1 ADM 2 ADM 3 ADM 1 ADM 2 ADM 3
Normal operation Span switching
-
8/8/2019 GFP Eth Frame
66/89
Connection-Oriented Networks - Harry Perros 66
Self-healing operation (ring switching):
Often, the working and protection fibers arepart of the same bundle of fibers. When thebundle is cut the traffic will be switched to theprotection fibers. This is known as ringswitching.
B
ADM 1 ADM 2 ADM 3
ADM 4
A
ADM 5ADM 6
Working
Protection
ADM 1 ADM 2 ADM 3
ADM 4
A
B
ADM 5ADM 6
Working
Protection
B
-
8/8/2019 GFP Eth Frame
67/89
Connection-Oriented Networks - Harry Perros 67
Generic Framing Procedure (GFP)
This is a light-weight adaptation scheme
that permits the transmission of differenttypes of traffic over SONET/SDH and in
the future, over G.709.
-
8/8/2019 GFP Eth Frame
68/89
Connection-Oriented Networks - Harry Perros 68
GFP permits the transport of
a) frame-oriented traffic, such as Ethernet, andb) block-coded data for delay-sensitive storage
area networks (SAN) transported by networks
such as Fiber Channel, FICON, and ESCON
over SONET/SDH and G.709.
GFP is a result of joint standardizationeffort by ANSI committee T1X1.5 and ITU-T.
It is described in ITU-T recommendationG.7041
-
8/8/2019 GFP Eth Frame
69/89
Connection-Oriented Networks - Harry Perros 69
Private
linesEthernet ESCON FICON
Fiber
Channel
Frame Relay POS
ATM
SONET/SDH
WDM/OTN
GFP
Voice Data (IP, MPLS, IPX) SAN
DM
Video
Existing and GFP-based transport options
for end-user applications
HDLC
-
8/8/2019 GFP Eth Frame
70/89
Connection-Oriented Networks - Harry Perros 70
The GFP stack
GFP
GFP client-dependent aspects
GFP client-independent aspects
SONET/SDH G.709
Ethernet IP over PPP SAN data
-
8/8/2019 GFP Eth Frame
71/89
Connection-Oriented Networks - Harry Perros 71
GFP frame structure
Payload
Core header
Payload length
Payload length
Core HEC
Core HEC
Payload header
Payload
Payload FCS
GFP core header
Payload length indicator
(PLI) - 2 bytes. It gives the
size of the payload.
Core HEC (cHEC) - 2bytes. It protects the PLI
field. Standard CRC-16
enables single bit error
correction and multiple bit
error detection.
-
8/8/2019 GFP Eth Frame
72/89
-
8/8/2019 GFP Eth Frame
73/89
Connection-Oriented Networks - Harry Perros 73
GFP payload headervariable-length area from 4 to 64 bytes.
Payload type - 2 bytes
Payload type identifier (PTI) - 3 bits.
Identifies the type of frame:
User data frames , Client mgmt frames
Payload FCS indicator (PFI) - 1 bit.
Identifies if there is a payload FCS
Extension header identifier (EXI) - 4 bits.Identifies the type of extension header.
User payload identifier (UPI) - 8 bits.
Identifies the type of payload
Frame-mapped Ethernet
Frame-mapped PPP (IP, MPLS)
Transparent-mapped Fiber Channel
Transparent-mapped FICON
Transparent-mapped ESCON
Transparent-mapped GbE
Type HEC (tHEC) - 2 bytes. It protects the
payload header. Standard CRC-16.
Payload type
Payload type
Type HEC
Type HEC
0-60 bytes
Of
Extension header
PTI
UPI
PFI EXI
-
8/8/2019 GFP Eth Frame
74/89
Connection-Oriented Networks - Harry Perros 74
GFP payload trailer
Payload header
Payload
Payload FCS
Payload FCS
Payload FCS
Payload FCS
Payload FCS
Optional 4-byte FCS.
CRC-32
Protects the contents ofthe payload
information field.
-
8/8/2019 GFP Eth Frame
75/89
Connection-Oriented Networks - Harry Perros 75
GFP-client independent functions
The client independent sublayer supports
the following functions:
Frame delineation
Client/frame multiplexing
Payload scrambler
Client managment
-
8/8/2019 GFP Eth Frame
76/89
Connection-Oriented Networks - Harry Perros 76
Frame delineation
The frame
delineation
mechanism is similarto the one used in
ATM.
The cHEC is used to
assure correct frameboundary
identification
hunt
Presync
Sync
Correct
cHEC2nd
cHEC match
Non-correctable
core header error
No 2ndcHEC
-
8/8/2019 GFP Eth Frame
77/89
Connection-Oriented Networks - Harry Perros 77
Operation:
Under normal conditions, the GFP receiver
operates in the Sync state. The receiver
examines the PLI field, validates the cHEC,
and extracts the framed higher-level PD. It
then moves on to the next GFP header.
When an uncorrectable error in the core
header occurs (i.e., cHEC fails and more than
one bit error is detected), the receiver enters
theHuntstate.
-
8/8/2019 GFP Eth Frame
78/89
Connection-Oriented Networks - Harry Perros 78
Hunt state:
Using the cHEC it attempts to locate the
beginning of the next GFP PDU, moving one
bit at a time (Same as in ATM - see Perros An
introduction to ATM networks, Wiley 2001.
Once this is achieved it moves to the Pre-Sync
state, where it verifies the beginning of the
boundary of the next N GFP PDUs.
If successful, it moves to the Sync state,otherwise it moves back to the hunt state.
-
8/8/2019 GFP Eth Frame
79/89
Connection-Oriented Networks - Harry Perros 79
Frame multiplexing
Client data frames and client management
frames are multiplexed, with client data
frames having priority over clientmanagement frames.
Idle frames are inserted to maintain a
continuous bit flow (rate coupling
)
-
8/8/2019 GFP Eth Frame
80/89
Connection-Oriented Networks - Harry Perros 80
GFP client-specific functions
The client data can be carried in GFP
frames using on of the two adaptation
modes: Frame-mapped GFP (GFP-F) applicable to
most packet data types
Transparent-mapped GFP (GFP-T) applicable
to 8B/10B coded signals
-
8/8/2019 GFP Eth Frame
81/89
Connection-Oriented Networks - Harry Perros 81
Frame-mapped GFP
Variable length frames such as:
Ethernet MAC frames,
PPP/IP packets HDLC-framed PDUs
can be carried in the GFP payload.
One frame per GFP payload.
Max. size: 65,535 bytes
-
8/8/2019 GFP Eth Frame
82/89
Connection-Oriented Networks - Harry Perros 82
Transparent-mapped GFP
Fiber Channel, ESCON, FICON, GigabitEthernet high-speed LANs use 8B/10B
block-coding to transport client data andcontrol information.
Rather than transporting data on a frame-by-frame basis, the GFP transparent-mapped
mode, transports data as a stream ofcharacters.
-
8/8/2019 GFP Eth Frame
83/89
Connection-Oriented Networks - Harry Perros 83
Specifically, the individual characters are
de-mapped from their client 8B/10B blockcodes and then mapped into periodic fixed-length GFP frames using 64B/65B blockcoding.
This reduces the 25% overhead introducedby the 8B/10B block-coding.
Also, transparent mapping reduces latency,
which is important for storage relatedapplications
-
8/8/2019 GFP Eth Frame
84/89
Connection-Oriented Networks - Harry Perros 84
The first step, is to decode the 8B/10B
codes. The 10 bit code is decoded into itsoriginal data or control codeword value.
The decoded characters are then mappedinto 64B/65B codes. A bit in the 65-bit
code indicates whether the 65-bit blockcontains only data or control characters arealso included
8 consecutive 65-bit blocks are grouped
together into a single superblock. A GFP frame contains N such superblocks.
-
8/8/2019 GFP Eth Frame
85/89
Connection-Oriented Networks - Harry Perros 85
Data over SONET/SDH (DoS)
The DoS architecture provides an efficientmechanism to transport data coming from
interfaces such as: Ethernet, Fiber Channel,ESCON/FICON over SONET/SDH.
It relies on a combination of
GFP,
Virtual concatenation, andLink capacity adjustment scheme (LCAS)
-
8/8/2019 GFP Eth Frame
86/89
Connection-Oriented Networks - Harry Perros 86
Virtual concatenation
This procedure maps an incoming traffic streaminto a number of individual sub-rate payloads.
The sub-rate payloads are switched through the
SONET/SDH network independently of eachother
At the destination, they are used to reconstruct theoriginal traffic stream.
-
8/8/2019 GFP Eth Frame
87/89
Connection-Oriented Networks - Harry Perros 87
Example
Let us consider the case of transporting the
1 GbE signal over SONET/SDH.
According to the specifications, an STS-
48c (2,488 Gbps) has to be used, thusleaving a lot of unused capacity.
Using the virtual concatenation scheme, 7
independent STS-3c (7x155,520 = 1,088)
can be employed to carry the 1 GbE signal
at full rate.
-
8/8/2019 GFP Eth Frame
88/89
Connection-Oriented Networks - Harry Perros 88
This works as follows:
At the transmitter the incoming stream isde-multiplexed and distributed in somefashion over 7 different payloads, each anSTS-3c.
Intermediate SONET/SDH nodes only seedifferent payloads and they are not awareof the concatenation
At the destination, the seven flows getmultiplexed into the single original GbEstream.
-
8/8/2019 GFP Eth Frame
89/89
Connection-Oriented Networks - Harry Perros 89
Link capacity adjustment scheme
(LCAS)
This scheme permits to dynamically adjust
the number of sub-rate payloads allocated
to a traffic stream, whose transmission ratemay vary over time.
LCAS can be also used when re-routing
traffic due to a failure.