G805 Introduction
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Transcript G805 Introduction
Introduction
to
G.805
Yaakov (J) Stein
Chief Scientist
RAD Data Communications
The classical model (OSI, X.200)
once upon a time networks were exclusively described by
the OSI model
however
few networks actually work only that way
highly inflexible (always need more layers!)
some features only in one place (security, mux)
missing features (OAM)
doesn’t help to design transport networks
APPLICATION
PRESENTATION
SESSION
TRANSPORT
NETWORK
LINK
PHYSICAL
LayerNet
Slide 2
Simple telephony counter-example
voice channel
voice channel
E1 (TDM)
E1 (TDM)
E3 (PDH)
E3 (PDH)
VC3 (SDH)
there are actually
2 STM layers here:
• multiplex section
• regenerator section
OSI application layer
?
STM1 (SDH)
OC3 (OTN)
VC3 (SDH)
STM1 (SDH)
OSI physical layer
OC3 (OTN)
this type of scenario important to carriers, and thus to ITU-T
not captured by ISO layering model
there can be an arbitrary large number of intervening layers
all intermediate layers fulfill the same function -- transport
LayerNet
Slide 3
Packet network counter-example
application
OSI application layer
application
TCP
TCP
IP
IP
MPLS
MPLS
Ethernet
?
Ethernet
MPLS
MPLS
SDH
SDH
OTN
OSI physical layer
OTN
here as well, there may be multiple layers
many of the layers are equivalent in functionality
LayerNet
Slide 4
The new model (G.805)
a more generally applicable model for transport
(infrastructure) networks
a transport network is solely responsible for transfer of information from place to place
(no “value added” services)
a transport network is usually operated by a service provider for a client
unlimited client/server layering (recursion)
partitioning decomposes network into atomic functions
treatment of OAM
support for interworking
convenient diagrammatic technique
References:
G.805 CO networks
G.705 PDH
I.326 ATM
G.806 equipment
G.781 timing
G.8010 Ethernet
G.809 CL networks
G.783 SDH
G.8110 MPLS
G.800 Unified functional architecture
G.872 OTN
G.8110.1 T-MPLS
LayerNet
Slide 5
Network Modes
Circuit Switched
Packet Switched
(CS)
(PSN)
Connection Oriented
Connectionless
(CO)
(CL)
many native network types (technologies) for each mode
– CS: TDM, PDH, SDH, OTN
– CO: ATM, FR, MPLS, TCP/IP, SCTP/IP
– CL: UDP/IP, IPX, Ethernet, CLNP
can layer any mode over any mode
– but some layerings may involve performance loss
– CL over CO over CS is easy
– CO over CL, or CS over CO is harder
– CS over CL is very hard
LayerNet
Slide 6
G.805
we will focus here on CO networks
these are described by G.805
CO networks transfer information over connections
CL networks do not have connections but may have flows
CL networks are described in G.809
CS networks are described in G.705 (PDH) and G.783 (SDH)
New unified approach described in G.800
LayerNet
Slide 7
Characteristic Information
the purpose of communications is to move information
each application and network has its own information format
examples:
E1 with CAS
HDLC
SYNC
TS1
TS2
flag(7E) address control
IP packet
in
Ethernet frame
Ethernet header
IP header
TCP header
payload
Ethernet CRC
TS3
…
signaling
bits
data
…
CRC
TSn
flag(7E)
<HTML>
<BODY>
web page
html
</BODY>
</HTML>
this is called characteristic information (CI)
LayerNet
Slide 8
Layer Networks
in the new framework, each layer is an independent network
we call such a network a layer network
because it exists at one layer
because it is a network unto itself
we will first describe features of a layer network
afterwards we discuss the relationships of neighboring layers
LayerNet
Slide 9
Layer Networks (cont.)
network
inputs
outputs
a layer network has inputs and outputs
CI is input to the network at an input
and is transported to an output with no (or minimal) degradation
the association of an input with an output is called a connection
in CO networks connections are changed by setup and tear-down procedures
in CL networks connections are transient (for a single packet)
or longer lived (for a flow)
LayerNet
Slide 10
Network Connection
a network connection matches one output to one input
often we want to have a bidirectional connection
+
like a transceiver or a modem,
=
is a
colocated with a
LayerNet
Slide 11
Network Connection Types
a link connection (LC) is a fixed connection between 2 “ports”
unidirectional link connection
ports
the LC is the smallest unit
of manageable capacity
bidirectional link connection
a subnetwork connection (SNC) is a flexible connection
for CO networks SNCs are changed by network management functions
unidirectional subnetwork connection
bidirectional subnetwork connection
the simplest subnetwork is a network element (NE)
such as a matrix, switch, or crossconnect
LayerNet
Slide 12
Transport and Topology
a transport entity transfers information from point to point
and a transport processing function performs some information processing
but at a high level of abstraction
only the possible connections between inputs and outputs is important
the geographical location of the endpoints
the data rate
the type of physical connection
etc.
are ignored
G.805 defines a topological component that relates inputs to outputs
layer networks and subnetworks are topological components
SNCs and LCs are transport entities
we will see processing functions later, e.g. to adapt format from layer to layer
LayerNet
Slide 13
Reference Points
unidirectional input or output point
=
bidirectional input/output point
we concatenate connections by binding the output of one connection
to the input of the next connection
we can do the same thing with bidirectional connections
we thus create reference points called connection points (CP)
unidirectional connection point
bidirectional connection point
LayerNet
Slide 14
Connection Points
we can concatenate link connections
CP
CP
LC
LC
CP
similarly, we use link connections to connect
subnetwork connections
SNC
CP
LC
CP
SNC
CP
LC
CP
SNC
we will mostly focus on bidirectional connections
but remember this merely hides the functionality
LayerNet
Slide 15
Partitioning
if we can zoom in on an SNC we discover
that it too is made up of SNCs connected by LCs
SNC
LC
SNC
LC
SNC
LC
SNC
SNC
we can continue recursively zooming in until we are left
with LCs and flexible connections internal to NEs
different degrees of detail are useful for different purposes
partitioning may be used to delineate:
routing domains
administrative boundaries between different operators
service provider/customer networks
LayerNet
Slide 16
Layer Network Partitioning
the whole layer network can be recursively decomposed
into connections internal to NEs and link connections
network
NE
NE
NE
NE
NE
NE
NE
NE
NE
LayerNet
Slide 17
OAM
analog channels and 64 kbps digital channels
did not have mechanisms to check signal validity and quality
thus
major faults could go undetected for long periods of time
hard to characterize and localize faults when reported
minor defects might be unnoticed indefinitely
as PDH networks evolved, more and more overhead was dedicated to
Operations, Administration and Maintenance (OAM) functions
including:
monitoring for valid signal
defect reporting
alarm indication/inhibition
when SONET/SDH was designed
overhead was reserved for OAM functions
today service providers require complete OAM solutions
LayerNet
Slide 18
Trails
since OAM is critical to proper network functioning
OAM must be added to the concept of a connection
a trail is defined as a connection along with integrity supervision
clients gain access to the trail at access points (AP)
trail terminations are
denoted by triangles
a trail termination (TT) source accepts CI
and adds trail overhead information
a trail termination (TT) sink
supervises integrity of trail
and removes trail overhead
the triangle always points
towards the supervised connection
reference points where trail terminations binds to connections
are called termination connecting points (TCP)
LayerNet
Slide 19
Trails (cont.)
for bidirectional trails
there is a shorthand notation
for colocated termination source and sinks
=
bidirectional trail termination
a trail is considered to run
from the input to the trail termination source
to the output of the trail termination sink
so the access points are
trail
AP
AP
before the trail termination source
after the trail termination sink
TCP
A
TCP
sometimes we specify the network
inside the triangle
LayerNet
Slide 20
Trail Termination Functions
what precise functionality does the trail add to the connection itself?
continuity check (e.g. LOS, periodic CC packets)
connectivity check (detect misrouting)
signal quality monitoring (e.g. error detection coding)
alarm indication/inhibition (e.g. AIS, RDI)
source termination function:
generates error check code (FEC, CRC, etc)
returns remote indications (REI, RDI)
inserts trail trace identification information
sink termination function:
detects misconnections
detects loss of signal, loss of framing, AIS instead of signal, etc.
detects code violations and/or bit errors
monitors performance
LayerNet
Slide 21
Defects, Faults, etc.
G.806 defines:
anomaly (n):
smallest observable discrepancy
between desired and actual characteristics
defect (d):
density of anomalies that interrupts some required function
fault cause (c): root cause behind multiple defects
failure (f):
persistent fault cause - ability to perform function is terminated
action (a):
action requested due to fault cause
performance parameter (p): calculatable value representing ability to function
for example:
dLOS = loss of signal defect
cPLM = payload mismatch cause
aAIS = insertion of AIS action
equipment specifications define relationships
e.g.
aAIS <= dAIS or dLOS or dLOF
alarms are human observable failure indications
LayerNet
Slide 22
Supervision Flowchart
performance
monitoring
anomaly
pX
statistics
gathering
nX
defect
correlation
defect filter
N.B. this is a greatly simplified picture
cX
persistence
monitoring
fX
dX
consequent
action
aX
more generally there are external
signals, time constants, etc.
LayerNet
Slide 23
Layering
another lesson learned as the PSTN evolved
was the importance of layering
each layer network is an independent network in its own right
all layer networks are described using the same tools
each layer network is independently designed and maintained
one should be able to add/modify layer networks
without changing neighboring layer networks
there is a client/server relationship between neighboring layers
in order for layering to be clean
server layer should transparently carry the client layer’s CI
each layer network needs its own OAM mechanisms
in order to guarantee QoS for its client
LayerNet
Slide 24
Some Layer Network Types
PDH (G.705)
P0
P11
P12
P21
P22
P31
P32
=
=
=
=
=
=
=
DS0
DS1
E1
DS2
E2
DS3
E3
P1 = P11 or P12
Eq is electric level equivalent
e.g. E11 is T1
P2 = P21 or P22
P3 = P31 or P32
SDH (G.783)
ESn STM-N Electrical Section (n = 1)
OSn STM-N Optical Section (n = 1, 4, 16, 64, 256)
RSn STM-N Regenerator Section (n = 1, 4, 16, 64, 256)
MSn STM-N Multiplex Section (n = 1, 4, 16, 64, 256)
Sn LO (n=11, 12, 2, 3) or HO (n=3,4) VC-n
LayerNet
Slide 25
Some Layer Network Types
ATM
VP and VC layer networks
Ethernet
ETH (MAC) and ETY (PHY) layer networks
ETY1: 10BASE-T (twisted pair electrical; full-duplex only)
ETY2.1: 100BASE-TX (twisted pair electrical; full-duplex only; for further study)
ETY2.2: 100BASE-FX (optical; full-duplex only; for further study)
ETY3.1: 1000BASE-T (copper; for further study)
ETY3.2: 1000BASE-LX/SX (long- and short-haul optical; full duplex only)
ETY3.3: 1000BASE-CX (short-haul copper; full duplex only; for further study)
ETY4: 10GBASE-S/L/E (optical; for further study)
ETH-m VLAN multiplexed
MPLS
stack of multiple MPLS layer networks
LayerNet
Slide 26
Some client/server Relationships
telephony
ISDN
IP
DS0
ATM VC
E1/T1
ATM VP
E3/T3
LOP SDH
HOP SDH
STM-N
OTN
LayerNet
Slide 27
Adaptation
unfortunately, although all layer networks are created equal
the format of their CI is different
so in order to put the client information into a server format
we have to adapt it
this is done by an adaptation function
CI
an adaptation source accepts client CI
and encapsulates it for transfer over the server trail
creating adapted information (AI)
CI
an adaptation sink accepts the AI
AI
adaptations are
denoted by trapezoids
and recovers the client layer CI
AI
the trapezoid always points
towards the server layer
LayerNet
Slide 28
Adaptation (cont.)
for bidirectional trails
there is a shorthand notation
for colocated adaptation source and sinks
=
client CI
CP
adaptation function
server trail
AP
trail termination function
A
B/A
B
server layer connection
TCP
sometimes we specify the layer networks
inside the trapezoid
order - server/client
LayerNet
Slide 29
Adaptation Functions
what precise functionality does the adaptation perform?
source adaptation may include:
bit scrambling
encoding
framing
encapsulation
bit-rate adaptation
multiplexing, inverse multiplexing
etc.
sink adaptation:
descrambling
decoding
deframing
decapsulation
bit-rate adaptation
demultiplexing
timing recovery
monitoring for AIS
etc.
LayerNet
Slide 30
Muxing and Inverse Muxing
there may be a many-to-one relationship between clients and server
one server layer trail simultaneously multiplexing many client layer
networks
the client layer networks could be of the same or of different types
there may be a one-to-many relationship between a client and servers
multiple server layer trails simultaneously inverse multiplex a client layer
network
the server layer networks could be of the same or of different types.
LayerNet
Slide 31
The BIG Picture
a link connection in the client layer
is supported by a trail in the server layer
CP
client LC
CP
AP
server trail
AP
TCP
TCP
N.B. the flexibility of the server layer connections
is unavailable to the client layer
LayerNet
Slide 32
Shorthand notation
it is often convenient to combine
adaptation and trail terminations
=
AP
and we obtain the simpler diagram:
CP
CP
trail
but AP is hidden
TCP
TCP
LayerNet
Slide 33
More and more layers
..
.
trail
each layer has
its own OAM
each client/server pair
has its own adaptation
trail
TCP
TCP
LayerNet
Slide 34
Simple Example: SAToP-MPLS
TDM trail
TDM AP
TDM
TDM
CP
CP
MPLS/TDM
MPLS/TDM
MPLS trail
MPLS AP
TDM AP
MPLS
MPLS AP
MPLS
MPLS network
MPLS TCP
MPLS TCP
LayerNet
Slide 35
More Complex Example
PDH over SDH
E1
SDH MUX
VC12 ADM
VC4 CC
SDH MUX
low order
path sections
G.703
interface
E1
G.703
interface
high order
path sections
multiplex
sections
regenerator
sections
LayerNet
Slide 36
Layering vs. Partitioning
each layer network may be separately partitioned
reflecting its management requirements
layering and partitioning are thus orthogonal analyses
layering is vertical
– client layer network is “above” the server layer network
partitioning is horizontal
– subnetworks and links belong to same layer network
a trail in a server layer network
supports a LC in its client layer network
LayerNet
Slide 37
Layering vs. Partitioning (cont.)
layer network
layer network
links
layer network
AGs
AGs
layering
subnetworks
layer network
partitioning
Access Groups (AG) are colocated APs that belong to the same client
LayerNet
Slide 38
Service Interworking
A>B
we have seen how to carry traffic
from network A over network B
client/server relationship
=
A<>B
A<B
layer network interworking (service interworking - SI)
there is a special symbol when we need to
terminate network A and carry its client over network B
peer to peer relationship
Example: SI of ATM with MPLS
N.B. SI is usually limited
to a specific client type
client trail
ATM layer network
MPLS layer network
LayerNet
Slide 39
Permissible Bindings
inputs and outputs may be bound together iff share CI or adapted information
connection points (CP)
connection - adaptation
adaptation - adaptation
SI - adaptation
termination connection points (TCP)
TT - connection
TT - TT
access points (AP)
TT - adaptation
TT - SI
the difference between a LNC and a SNC:
network connections are delineated by TCPs
SNCs are delineated by CPs
adaptation - TT
LayerNet
Slide 40
Expansions
new functionality is formally introduced
by inserting a new layer network
to do this one can expand a CP or a TT
CP expansion
TT expansion
CP
TCP
CP
TCP
we will show one example of each of these expansions:
CP expansion to monitor SNC
TT expansion for trail protection
LayerNet
Slide 41
Example - tandem monitoring
if we need to separately monitor subnetworks
for example, in order to provide defect localization
we can expand a CP to make them into full layer networks
CP
CP
CP
CP
SNC
CP
CP
CP
CP
adaptation adds overhead room
TT adds supervision information
SNC
LayerNet
Slide 42
Example - trail protection
to add 1+1 protection for a trail, we can expand a TT
we use a special transport processing function - the protection switch
unprotected
trail
protected trail
the unprotected TTs report status
to the protection switch
LayerNet
Slide 43
G.809
CL networks can be partitioned and layered just like CO ones
but in CL networks there are no connections
instead we have a new concept - a flow
(there are link flows, flow domain flows, and network flows)
once monitored, adapted CI is transported on a
connectionless trail
G.809 diagrams are similar to G.805 ones
but shading indicates CL components
LayerNet
Slide 44
CL client / CO server
connectionless trail
flow
TFP
TFP
trail
TCP
TCP
LayerNet
Slide 45
CL traffic conditioning
CL networks have some unique requirements
For example, G.8010 defines a traffic conditioning function
This transport processing function classifies packets
and then meters / polices within each class
You can add the TC function by expanding a FP
FP expansion
FP
FP
FP
LayerNet
Slide 46