Wide Area Networking

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Wide Area Networking
Asynchronous Transfer Mode (ATM) Networks
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ATM applications services

• Classical IP over ATM
• Circuit Emulation Serice
• Lan Emulation Service

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Classical IP over ATM (CLIP) (1)

• Main differences between ATM and IP
• ATM - first of all quality
• Connection oriented
• Switching and routing are performed in separation
• Advanced traffic control functions allowing for
  QoS guarantees
• IP - first of all connectivity
• Connectionless oriented
• Switching and routing performed together
• Only best-effort service

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Classical IP over ATM (CLIP) (2)

• CLIP
• is a basic model of interworking between IP and
  ATM (RFC 2225)
• assumes the same model as in case of LAN networks
• forms a logical LIS (Logical IP Sub-network).
  Data transfer between LISs requires an IP router
• defines methods for
• address translation between IP and ATM
• handling connectionless traffic (ATM connection
  establishing and releasing)
• IP packet encapsulation using AAL5
• handling of broadcast i multicast traffic
• Main advantage
• Possibility of handling IP traffic with quality
  of service

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Classical IP over ATM (CLIP) (3)

• How it works?
• Each LIS has implemented an ATM ARP (ATM Address
  Resolution Protocol) server which performs a
  mapping between ATM and IP addresses.
• Client before transmission asks the ATM ARP
  server for the ATM address of destination host
  and then it establishes ATM connection
• Connection is controlled by client
• Transmission between LIS is performed using IP
  routers

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Classical IP over ATM (CLIP) (4)

• CLIP advantages
• Full compatibility with IP architecture (from
  application point of view there is no difference)
• CLIP drawbacks
• Direct connections can only be established in a
  single LIS
• The whole traffic between a given pair of hosts
  is served by a single connection (there is no
  possibility to differentiate service)
• The broadcast and multicast transmission requires
  additional mechanism (e.g. MARS server)

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Classical IP over ATM (CLIP) (5)

• Next Hop Resolution Protocol (NHRP) as an
  extension of CLIP allowing for establishing
  connections between hosts belonging to a
  different LISs (called shortcut)
• Each LIS has defined Next Hop Server (NHS) which
  is responsible for looking for addresses of host
  which do not belong to home LIS. NHS changes
  information between them using standard IP
  routing protocols.

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Classical IP over ATM (CLIP) (6)

• NHRP advantages
• Eliminate the need for employing routers between
  different LIS by establishing direct connections
  between hosts
• NHRP drawbacks
• The whole traffic between a given pair of hosts
  is served by a single connection (there is no
  possibility to differentiate service)
• The stable routing loops can occur (this problem
  is still not solved)
• Additional software is required in hosts and
  switches.
• The multicast and broadcast transmission is not
  possible

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Circuit Emulation Service (CES)
Emulates PDH connections over ATM network E1, E3

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Unstructured service

• The E1/DS1, E3/DS3, J2 stream (bit by bit) is
  encapsulated in the AAL1 frame and transmitted
  via ATM network
• The internal structure of the PDH signal is not
  considered by the ATM network
• Any PDH framing can be supported
• Clock recovery methods
• Syncronous
• asynchronous

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Structured service

• Nx64 kbps channels can be transmisted via the ATM
  network
• Up to 30 in case of E1 interface canbe transmited
• Up 24 in case of DS1 interface can be transmited
• Clock recovery method synchronous
• The PDH framing must comply with G.704 standard
• Two service types
• Without signalling
• With Channel Associated Signalling (wCAS )

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AAL1 protocol (1)
CSI bit
Sequence number
Sequence number SN 4 bits
Payload    47 bytes
Checksum 4 bits
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AAL1 protocol (2)
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CES interworking model unstructured mode
ATM wirtual connection (CBR)
CESIWF
CESIWF
ATM network
TDM device
TDM device
ATM interface
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CES interworking model structured mode
ATM wirtual connection (CBR)
TDM interface( E1 ot T1)
TDM interface( E1 ot T1)
CESIWF
CESIWF
ATM network
TDM device
TDM device
ATM access interfaces
TDM interface( E1 ot T1)
CESIWF
TDM device
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Payload field
Unstructured mode
CES payload (48 bytes)
Structured mode


Pointer (byte) CES payload CES
payload CE payload
pading
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Structured service without CAS
Wskaznik AAL1
First TDM channel (one byte form first
transmitted TDM slot) Second TDM channel Next TDM
channel

• The bytes form selected TDM slots are mapped to
  the ATM cell byte by byte
• AAL1 pointer (bit CSI 1) is added every 8
  AAL1-PDU
• AAL1 pointer is used to detect the beginning of
  TDM frame and to recover form loss of frame
  synchronizatuion (due to the cell loss)

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Structured service with CAS
AAL1 pointer
First TDM frame
First TDM channel Second TDM channel Third TDM
channle
Second TDM Frame
Last TDM frame (from superframe)
Signalling bits for first TDM channel
Signalling block
Signalling bits for third TDM channel
Signalling bits for second TDM channel
Block structure N3
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Clock recovery

• Synchronous ATM IWF must be synchronized to the
  PRC clock
• Asynchronous
• Synchronous Residual Time Stamp (STRS) the
  sender clock is recovered in the receiver with
  the use of SRTS timestamp
• Adaptive Clock Recovery (ACR) Adaptive clock
  recovery based on the receiver buffer occupancy

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Synchronous method

• All network device must be synchronized to the
  common reference (PRC clock)
• ATM switches must be synchronized to the PDH clock

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SRTS method

• ATM network is synchronized to different clock
  (probably of lower quality)
• The clock difference is transmitted in the SRTS
  bits

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ACR method

• ATM switches are not synchronized to common
  reference clock
• Internal switch clocks may be used

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ATM Signalling (1)

• ATM signalling is responsible for
• connections establishing/releasing
• addressing
• routing

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ATM Signalling (2)

• There are defined different types of signalling
  each of specific purposes, which are
• User-Network Interface (UNI), used between
  terminal and network
• ITU-T Q.2931, Q2731 public
• ATM Forum UNI 3.0, 3.1, 4.0 private
• Network-Network Interface (NNI), used between two
  ATM networks/switches
• ATM Forum PNNI - private
• ATM Forum B-ICI public
• ITU B-ISUP - public
• ...

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ATM Signalling (3)

• Types of signalling
• Common associated signalling, signalling entity
  is responsible for all virtual circuits (VC)
• Signalling channel VPI0, VCI5
• VP associated signalling, signalling entity is
  responsible only for VCs on its own path
• Signalling channel VPIpath no., VCI5

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ATM Signalling (4)
Model of signalling layers
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ATM Signalling (5)
Signalling AAL (SAAL)
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ATM Signalling (6)

• UNI signalling standards
• ITU Q.2931
• point-to-point (p2p) connections only
• for each direction of connection QoS class is
  specified
• only a single connection per request
• signalling is sent out-of-band, the VCI5 is used
• UNI 3.1
• fulfils Q.2931
• allows for point-to-multipoint (p2m) connections
• UNI 4.0
• enhances UNI 3.1 by
• QoS parameters for each direction
• support for ABR service

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ATM Signalling (7)

• UNI signalling messages (p2p connections)
• SETUP - request for establishing connection
• CALL PROCEEDING - denotes that all information
  necessary for call admission are received
• ALERTING - ringing tone
• CONNECT - call accepted
• CONNECT ACK - confirmation of call acceptance
• RELEASE - request for releasing the connection
• RELEACE COMPLETE - confirmation of releasing call

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ATM Signalling (8)
Example of establishing p2p connection
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ATM Signalling (9)

• UNI signalling messages (p2m connections)
• ADD PARTY - adding a new user to p2m connection
• ADD PARTY ACK - acceptance confirmation of a new
  user in p2m connection
• PARTY ALERTING - ringing tone
• ADD PARTY REJECT - discarding of a p2m connection
  by a new user
• DROP PARTY - releasing of a user in p2m
  connection
• DROP PARTY ACK - confirmation of releasing the
  p2m connection

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ATM Signalling (10)
Phase 1 of establishing p2m connection Root to
Leaf 1
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ATM Signalling (11)
Phase 2 of establishing p2m connection Root to
Leaf 2
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ATM Signalling (12)

• Information elements of signalling messages
• calling/called subscriber number
• calling/called subscriber sub-number
• reason for signalling message (type of message)
• type of signalling (common / VP associated)
• Descriptor of connection class (CBR,
  rtVBR,nrtVBR, ABR, GFR, UBR)
• Traffic descriptor (PCR, SCR, MBS, CDVT)
• QoS parameters (maxCTD, CVD, CLR)
• VPI/VCI number
• type of AAL (AAL1, AAL2, AAL3/4, AAL5)
• ...

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ATM Signalling (13)

• Private-Network-Network-Interface (PNNI)
  signalling is used between ATM switches or ATM
  networks
• PNNI standard (ATM Forum) is based on ITU-T
  recommendations Q.2931, Q.2971
• PNNI defines
• addressing scheme
• routing (hierarchical routing with elements of
  OSPF, IS-IS, IDRP)
• signalling procedures
• PNNI enables extremely scalable, full function,
  dynamic, multi-vendor ATM networks (global ATM
  internet)

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ATM Signalling (14)

• ATM End System Addresses (AESA)
• ATM address has length of 20 bytes
• Address prefix (13 bytes)
• ESI (End System Identifier) (6 bytes)
• SEL (1 byte)
• Hierarchical addressing
• 1 to 104 levels

Inter Domain Part
Domain Specific Part
Address prefix
ESI
SEL
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ATM Signalling (15)

• Aggregation of ATM addresses

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ATM Signalling (16)

• PNNI routing is hierarchical!
• Each switch is (manually) initialised with a full
  20-byte address
• Routing hierarchy is then defined recursively
• Neighbouring nodes form Peer Groups based on
  their longest prefix in common
• Each peer group then behaves as a Logical Group
  Node (LGN) , to form (next level) peer group,
  etc.

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ATM Signalling (17)

• PNNI routing assumes
• Topology state routing at a given hierarchy level

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ATM Signalling (18)

• 2.Source Routing between hierarchy stages
• Ingress nodes choose a complete path to the
  destination
• Ingress node then adds full path to the message
  itself
• Transit nodes simply follow the given path

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ATM Signalling (19)

• Such approach allows for aggregation of routing
  information and each node has complete
  information so called Designated Transient List
  (DTL).

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ATM Signalling (21)

• PNNI allows for QoS routing, which takes into
  account QoS parameters
• Maximum Cell Transfer Delay (maxCTD)
• Cell Delay Variation (CDV)
• Cell Loss Rate
• Link weights and capacity

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ATM Signalling (22)

• Call Admission Control (CAC)
• Generic Call Admission Control (GCAC)
• Run by a switch choosing a source route
• Determines if a path can (probably) support the
  call
• Actual Call Admission Control (ACAC)
• Run by each switch in the chosen path
• Determines whether or not the switch can support
  the call

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Network management (1)

• Network management concerns the following areas
• Configuration Management How do I set up the
  correct parameters consistently?
• Fault Management What broke? Where did it
  break? Did it recover? d
• Performance Management Is service degrading? Is
  something going to break? Do I need to upgrade my
  network?
• Accounting Management Who is using the
  network? How much are they using? When do I need
  to re-engineer the network?
• Security Management Is the network being used
  properly? Do I have illegal users?

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Network management (2)

• Network Management functionality occurs in areas
• Network Management Model used for total
  management of ATM networks and services,defines 5
  points (M1-M5)
• Integrated Local Management Interface (ILMI)
  Used primarily for configuration alarms of ATM
  interfaces More precisely getting 2 adjacent
  devices to interface to one another
• Layer Management used primarily for end to end
  circuit management and checking a user circuit
  through a complete network
• Signalling replaces some Network Management
  functions

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Network management (3)
M3
M5
Managementsystem
Managementsystem
Managementsystem
M1
M4
M2
Private ATMNetwork
Public ATMNetwork
Public ATMNetwork
BICI
UNI
UNI/PNNI
Management Functions at UNI Physical link
Performance Fault Layer Management Fault
ILMI Configuration, Fault
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Network management (4)

• Integrated Local Management Interface (ILMI)
• ILMI provides status, configuration and control
• information for an ATM interface
• specifically the link and physical layers of a
  UNI or PNNI
• Address registration can also occur
• UNI ILMI attributes are organized in a standard
  SNMP MIB
• One MIB instance per ATM device link
• An ATM device may contain more than 1 UNI/PNNI
• ILMI very useful when you do not control the
  device on the other end of the ATM link
  information is read only across UNI or PNNI

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Network management (5)

• Layer management performs
• Alarm Surveillance at VP (OAM cells)
• Connectivity Verification at VP,VC (OAM cells))
• Invalid VPI/VCI detection (VPI/VCI)
• Operation, Administration and Maintenance Cells
  (OAM) allows for monitoring of functions
  performed by physical and ATM layer
• Alarm Indication Signal (AIS)
• Far End Receive Failure (FERF)
• Remote Defect Indicator (RDI)
• Loopback
• Allows connectivity checking
• Allows fault isolation to subnetworks

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Network management (6)

• OAM procedures are related with different levels
• Flow F1 regeneration section
• Flow F2 digital section
• Flow F3 path
• Flow F4 virtual path
• End-to-end VP VP/VCI100
• segment VP VP/VCI011
• Flow F5 - virtual circuit
• End-to-end VCCPTI101
• segment VCCPTI100