CSC 600 Internetworking with TCP/IP

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CSC 600InternetworkingwithTCP/IP

• Unit 9 TCP/IP over ATM
• (ch. 18)
• Dr. Cheer-Sun Yang
• Spring 2001

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William StallingsData and Computer Communications
Most of the slides were taken from William
Stallings Book.

• Chapter 11
• Asynchronous Transfer Mode
• and Frame Relay

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Protocol Architecture

• Similarities between ATM and packet switching
• Transfer of data in discrete chunks
• Multiple logical connections over single physical
  interface
• In ATM flow on each logical connection is in
  fixed sized packets called cells
• Minimal error and flow control
• Reduced overhead
• Data rates (physical layer) 25.6Mbps to 622.08Mbps

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Protocol Architecture
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Protocol Architecture
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Reference Model Planes

• User plane
• Provides for user information transfer
• Control plane
• Call and connection control
• Management plane
• Plane management
• whole system functions
• Layer management
• Resources and parameters in protocol entities

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Control Plane

• Between subscriber and network
• Separate logical channel used
• Similar to common channel signaling for circuit
  switching services
• Data link layer
• LAPD (Q.921)
• Reliable data link control
• Error and flow control
• Between user (TE) and network (NT)
• Used for exchange of Q.933 control signal messages

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User Plane

• End to end functionality
• Transfer of info between ends
• LAPF (Link Access Procedure for Frame Mode Bearer
  Services) Q.922
• Frame delimiting, alignment and transparency
• Frame mux and demux using addressing field
• Ensure frame is integral number of octets (zero
  bit insertion/extraction)
• Ensure frame is neither too long nor short
• Detection of transmission errors
• Congestion control functions

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ATM Hardware
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Large ATM Networks
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The Logical View of an ATM Network
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The Logical View of an ATM Network

• The goal of ATM is an end-to-end communication
  system.
• ATM hides the details of physical hardware.
• ATM hardware provides attached computers with the
  appearance of a single, physical network.

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ATM Logical Connections

• Virtual channel connections (VCC)
• Analogous to virtual circuit in X.25
• Basic unit of switching
• Between two end users
• Full duplex
• Fixed size cells
• Data, user-network exchange (control) and
  network-network exchange (network management and
  routing)
• Virtual path connection (VPC)
• Bundle of VCC with same end points

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ATM Connections

• ATM provides connection-oriented interface to
  attached hosts using two paradigms
• Permanent Virtual Circuits
• Switched Virtual Circuits

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ATM Connections

• ATM assigns each circuit a virtual circuit
  identifier (VCI).

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ATM Connection Relationships
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Advantages of Virtual Paths

• Simplified network architecture
• Increased network performance and reliability
• Reduced processing
• Short connection setup time
• Enhanced network services

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Call Establishment Using VPs
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Virtual Channel Connection Uses

• Between end users
• End to end user data
• Control signals
• VPC provides overall capacity
• VCC organization done by users
• Between end user and network
• Control signaling
• Between network entities
• Network traffic management
• Routing

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VP/VC Characteristics

• Quality of service
• Switched and semi-permanent channel connections
• Call sequence integrity
• Traffic parameter negotiation and usage
  monitoring
• VPC only
• Virtual channel identifier restriction within VPC

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Control Signaling - VCC

• Done on separate connection
• Semi-permanent VCC
• Meta-signaling channel
• Used as permanent control signal channel
• User to network signaling virtual channel
• For control signaling
• Used to set up VCCs to carry user data
• User to user signaling virtual channel
• Within pre-established VPC
• Used by two end users without network
  intervention to establish and release user to
  user VCC

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Control Signaling - VPC

• Semi-permanent
• Customer controlled
• Network controlled

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ATM Cells

• Fixed size
• 5 octet header
• 48 octet information field
• Small cells reduce queuing delay for high
  priority cells
• Small cells can be switched more efficiently
• Easier to implement switching of small cells in
  hardware

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ATM Cell Format
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Header Format

• Generic flow control
• Only at user to network interface
• Controls flow only at this point
• Virtual path identifier
• Virtual channel identifier
• Payload type
• e.g. user info or network management
• Cell loss priority
• Header error control

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Transmission of ATM Cells

• 622.08Mbps
• 155.52Mbps
• 51.84Mbps
• 25.6Mbps
• Cell Based physical layer
• SDH based physical layer

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Cell Based Physical Layer

• No framing imposed
• Continuous stream of 53 octet cells
• Cell delineation based on header error control
  field

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ATM Adaptation Layer

• Support for information transfer protocol not
  based on ATM
• PCM (voice)
• Assemble bits into cells
• Re-assemble into constant flow
• IP
• Map IP packets onto ATM cells
• Fragment IP packets
• Use LAPF over ATM to retain all IP infrastructure

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Adaptation Layer Services

• Handle transmission errors
• Segmentation and re-assembly
• Handle lost and incorrectly inserted cells
• Flow control and timing

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Supported Application types

• Circuit emulation
• VBR voice and video
• General data service
• IP over ATM
• Multiprotocol encapsulation over ATM (MPOA)
• IPX, AppleTalk, DECNET)
• LAN emulation

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AAL Protocols

• Convergence sublayer (CS)
• Support for specific applications
• AAL user attaches at SAP
• Segmentation and re-assembly sublayer (SAR)
• Packages and unpacks info received from CS into
  cells
• Four types
• Type 1
• Type 2
• Type 3/4
• Type 5

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AAL Protocols
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AAL Type 1

• CBR source
• SAR packs and unpacks bits
• Block accompanied by sequence number

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AAL Type 2

• VBR
• Analog applications

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AAL Type 3/4

• Connectionless or connected
• Message mode or stream mode

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AAL Type 5

• Streamlined transport for connection oriented
  higher layer protocols

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CPCS PDUs
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Example AAL 5 Transmission
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Segmentation and Reassembly PDU
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Datagram Encapsulation and IP MTU Size

• IP uses AAL5 to transfer datagrams across an ATM
  network.
• Before data can be sent, a virtual circuit (PVS
  or SVC) must be in place and both ends must agree
  to use AAL5 on the circuit.

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Datagram Encapsulation and IP MTU Size

• To transfer a datagram, the sender passes it to
  AAL5 along with the VPI/VCI identifying the
  circuit.
• AAL5 generates a trailer, divides the datagram
  into cells, and transfers the cells across the
  network.
• At the receiving end, AAL5 reassembles the cells,
  checks the CRC to verify that no bits were lost
  or corrupted, extracts the datagram, and passes
  it to IP.

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Datagram Encapsulation and IP MTU Size

• When TCP/IP sends data across an ATM network, it
  transfers an entire datagram using ATM Adaptation
  Layer5. Although AAL5 can accept and transfer
  packets that contain up to 64K octets, IP must
  fragment any datagram larger than 9180 octets
  before passing it to AAL5 according to TCP/IP
  standard.

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Packet Type and Multiplexing

• The two computers at the end of a virtual circuit
  agree a priori that the circuit will be used for
  a specific protocol (e.g., the circuit will only
  be used to send IP datagram).
• The two computers at the ends of a VC agree a
  priori that some octets of the data area will be
  reserved for use as a type field.

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IP Address Binding

• IP address binding in a non-broadcast multiple
  access (NBMA) environment can be difficult.

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Difficulties RE IP Address Binding

• ATM physical address is larger than an IP address
• ATM hardware does not support broadcast ARP
  cannot be used to resolve address mapping.

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Difficulties RE IP Address Binding

• An ATM network manager manually configures each
  PVC, a host only knows the circuits VPI/VCI
  pair. Software on this host may not know the IP
  address of the remote host.
• Switched connection-oriented technologies further
  complicate address binding because they require
  two levels of binding. First, when creating a
  virtual circuit, the dest. IP address must be
  mapped to an ATM endpoint address. Second, when
  sending a datagram, the dest IP address must be
  mapped to the VPI/VCI pair for the circuit.

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Logical IP Subnet Concept

• Although no protocol has been proposed to solve
  the general case of address binding, a protocol
  has been devised for a restricted form.
• The case aries when a group of computers uses an
  ATM network in place of a LAN. The group formss a
  Logical IP Subnet (LIS).
• Multiple LISs can be defines among a set of
  computers that all attached to the same ATM
  hardware network.

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Logical IP Subnet Concept

• ATM allows a subset of computers attached to an
  ATM network to operate like an independent LAN.
• Computers in the same LIS share a single IP
  network prefix.
• A computer must use a router to communicate with
  a computer in another LIS.

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Unanswered Questions

• How can switching hardware be exploited to
  forward IP traffic at higher speeds?
• How does Label Switching work?
• How can IP forwarding be optimized?

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Suggested Reading

• Stallings Chapter 11
• ATM Forum Web site
• Newman et. al.April 1998 IP Switching
• Laubach and Helpern RFC 2225 logical IP
  subnet, ATMARP, default MTU