Introduction%20to%20G.805

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IntroductiontoG.805

• Yaakov (J) Stein
• Chief Scientist
• RAD Data Communications

2
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)
• doesnt help to design transport networks

3
Simple telephony counter-example
OSI application layer
?

• there are actually 2 STM layers here
• multiplex section
• regenerator section

OSI physical layer

• 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

4
Packet network counter-example
OSI application layer
?
OSI physical layer

• here as well, there may be multiple layers
• many of the layers are equivalent in functionality

5
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.872 OTN
• G.806 equipment G.781 timing G.8010
  Ethernet
• G.809 CL networks G.783 SDH G.8110 MPLS
  G.8110.1 T-MPLS
• G.800 Unified functional architecture

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Network Modes
Circuit Switched (CS)
Packet Switched (PSN)
Connection Oriented (CO)
Connectionless (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

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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

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Characteristic Information

• the purpose of communications is to move
  information
• each application and network has its own
  information format
• examples
• this is called characteristic information (CI)

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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

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Layer Networks (cont.)
network
outputs
inputs
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)
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Network Connection

• a network connection matches one output to one
  input

often we want to have a bidirectional connection
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Network Connection Types

• a link connection (LC) is a fixed connection
  between 2 ports
• unidirectional link connection
• 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

the LC is the smallest unit of manageable capacity
ports
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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

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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
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Connection Points
we can concatenate link connections
similarly, we use link connections to connect
subnetwork connections
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Partitioning

• if we can zoom in on an SNC we discover
• that it too is made up of SNCs connected by LCs
• 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

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Layer Network Partitioning

• the whole layer network can be recursively
  decomposed
• into connections internal to NEs and link
  connections

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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

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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)
• 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
• reference points where trail terminations binds
  to connections
• are called termination connecting points (TCP)

trail terminations are denoted by triangles
the triangle always points towards the
supervised connection
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Trails (cont.)

• for bidirectional trails
• there is a shorthand notation
• for colocated termination source and sinks
• 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
• before the trail termination source
• after the trail termination sink

bidirectional trail termination
sometimes we specify the network inside the
triangle
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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

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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
• alarms are human observable failure indications

equipment specifications define
relationships e.g. aAIS lt dAIS or dLOS or dLOF
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Supervision Flowchart
N.B. this is a greatly simplified picture more
generally there are external signals, time
constants, etc.
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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 layers CI
• each layer network needs its own OAM mechanisms
• in order to guarantee QoS for its client

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Some Layer Network Types

• PDH (G.705)
• P0 DS0
• P11 DS1
• P12 E1
• P21 DS2
• P22 E2
• P31 DS3
• P32 E3
• 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 (n11, 12, 2, 3) or HO (n3,4) VC-n

Eq is electric level equivalent e.g. E11 is T1
P1 P11 or P12
P2 P21 or P22 P3 P31 or P32
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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

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Some client/server Relationships
telephony
ISDN
IP
DS0
ATM VC
E1/T1
ATM VP
LOP SDH
E3/T3
HOP SDH
STM-N
OTN
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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
• an adaptation source accepts client CI
• and encapsulates it for transfer over the server
  trail
• creating adapted information (AI)
• an adaptation sink accepts the AI
• and recovers the client layer CI

adaptations are denoted by trapezoids
the trapezoid always points towards the server
layer
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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
server layer connection
TCP

• sometimes we specify the layer networks
• inside the trapezoid
• order - server/client

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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.

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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.

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The BIG Picture
a link connection in the client layer is
supported by a trail in the server layer
N.B. the flexibility of the server layer
connections is unavailable to the client layer
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Shorthand notation
it is often convenient to combine adaptation and
trail terminations
and we obtain the simpler diagram
but AP is hidden
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More and more layers
each layer has its own OAM
each client/server pair has its own adaptation
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Simple Example SAToP-MPLS
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More Complex ExamplePDH over SDH
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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

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Layering vs. Partitioning (cont.)
layer network
layer network
layer network
Access Groups (AG) are colocated APs that belong
to the same client
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Service Interworking

• we have seen how to carry traffic
• from network A over network B
• client/server relationship
• 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
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Permissible Bindings
inputs and outputs may be bound together iff
share CI or adapted information
connection points (CP)
termination connection points (TCP)
access points (AP)
the difference between a LNC and a SNC network
connections are delineated by TCPs SNCs are
delineated by CPs
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Expansions

• new functionality is formally introduced
• by inserting a new layer network
• to do this one can expand a CP or a TT

• we will show one example of each of these
  expansions
• CP expansion to monitor SNC
• TT expansion for trail protection

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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

adaptation adds overhead room
TT adds supervision information
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Example - trail protection

• to add 11 protection for a trail, we can expand
  a TT
• we use a special transport processing function -
  the protection switch

the unprotected TTs report status to the
protection switch
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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

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CL client / CO server
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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