IS516 Computer Communication and Networks Lecture 12

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IS516 ?????????????????????????????????
(Computer Communication and Networks)
Lecture 12 ????????????????????????????
?????????????????

• ??.????????? ????????

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????????????????????(???? Mid-term)
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????????????? (Network System)

• ?????????????????????????? X.25
• ?????????????????????????? Frame Relay
• ?????????????????????????? ATM

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?????????????????????????? X.25

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X.25

• ????????? CCITT ???? ?.?. 2531????????????????????
  ???????????????????????????????? Packet Switched
• ?????????????????????????? (Connection-Oriented)
  ?????????????????????????????????? Switched
  Virtual Circuit ?????? Permanent Virtual Circuit
• Switched Virtual Circuit ?????????????????????????
  ?????????????????????????????? ??? packet
  ????????????????????????????????????????
  ???????????????????????????????? packet
• Permanent Virtual Circuit ????????????????????????
  ????????????????????????????????????????????????
  ? ???????????????????? (Leased Line)
  ???????????????????????????????????
• PAD (Packet Assembler Disassembler) ??? x.3, x.28
  ??? x.29 ????????Terminal ??? ????????????????????
  ????????? x.25 ???
• X.3 ?????????????????????????? PAD
• X.28 ???????????????????????????????? PAD ???
  Terminal
• X.29 ???????????????????????????????? PAD ???
  ?????????????

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X.25

• The first public data network deployed in the
  1970s
• A connection-oriented network that supports
  switched virtual circuit and permanent virtual
  circuit like Leased Line
• Were replaced by a new kind of network called
  Frame Relay in the 1980s

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X.25

• X.25 is an ITU-T standard protocol suite for wide
  area networks using the phone or ISDN system as
  the networking hardware
• X.25 is a packet switched data network protocol
• defines an international recommendation for the
  exchange of data as well as control information
  between
• - user device (host), called Data Terminal
  Equipment (DTE)
• - network node, called Data Circuit Terminating
• Equipment (DCE)

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X.25 Equipment Terminology

• DTE (Data-Terminal Equipment.) A computer that
  uses a network for communications.
• DCE (Data Circuit-Terminating Equipment.) A
  device at the point of access to a network.
• DSE (Data-Switching Equipment.) A switching node
  in a packet-switched data network.
• X.25 utilizes a Connection-Oriented service which
  insures that packets are transmitted in order.

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The X.25 Network
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To use X.25

• First establish a connection to the remote
  computer, (i.e. placed a telephone call). This
  connection was given a connection number to be
  used in data transfer.
• Data packet consists of 3-byte header and up to
  128 bytes of data
• Header consists of 12-bit connection number,
  packet sequence number, and acknowledgement
  number, and a few miscellaneous bits

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X.25 Protocol
X.25 comes with three levels based on the first
three layers of the Open Systems Interconnection
(OSI) seven layers architecture as defined by the
International Standard Organization (ISO).
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Three Levels of X.25

• The Physical Level describes the interface with
  the physical environment. It is similar to the
  Physical Layer in the OSI model.
• The Link Level responsible for the reliable
  communication between the DTE and the DCE. It is
  similar to the Data Link Layer in the OSI model.
• The Packet Level describes the data transfer
  protocol in the packet switched network. It is
  similar to the Network Layer in the OSI model.

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Protocols used in the link level

• Link Access Protocol, Balanced (LAPB)
• - the most commonly used
• - enables to form a logical link connection
• Link Access Protocol (LAP)
• - an earlier version of LAPB and is seldom used
  today
• Link Access Procedure, D Channel (LAPD)
• - enables data transmission between DTEs
  through D
• channel, especially between a DTE
  and an ISDN node
• Logical Link Control (LLC)
• - an IEEE 802 Local Area Network (LAN) protocol
  which
• enables X.25 packets to be transmitted
  through a LAN
• channel

http//www.raduniversity.com/networks/1996/x25/x25
.htm
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Obsolescence of X.25

• With the widespread introduction of "perfect"
  quality digital phone services and error
  correction in modems, the overhead of X.25 was no
  longer worthwhile
• Frame Relay, essentially the X.25 protocol with
  the error correction systems removed, and
  somewhat better throughput as a result

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?????????????????????????? Frame Relay

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??????????????????? Frame Relay

• ????????????????? Connection-Oriented
• ??????????????????????????????????????????????????
  ?
• ??????????????????????????????????????????????????
  ?????????????????? ????????????????????????
  ??????????????????????????????????????????????
• ? ???????????????????????????????????????
  ??????????????????????????????????????????????????
  ???
• ??????????????????????????????????? (Virtual
  leased line) ????????????????? Permanent Virtual
  Circuit ?????????????????????????????????
• ????????????? 1,600 byte/packet ?????????????
• ????????????????????????????????????????????????
• ??????????????????????????????????????????????????
  ?
• ?????????????? x.25 ??? Permanent Virtual Circuit
  ??? Frame Relay ??????????????????? 1.5 Mbps
  (???????? x.25 ??? 23 ????)

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Frame Relay

• Frame Relay is a high-performance WAN protocol
  that operates at the physical and data link
  layers of the OSI reference model
• was designed for use across Integrated Services
  Digital Network (ISDN) interfaces
• Frame relay has its technical base in the older
  X.25 packet-switching
• frame relay offers a fast packet technology,
  which means that the protocol does not attempt to
  correct errors

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Frame Relay Devices
DTEs generally are considered to be terminating
equipment for a specific network and typically
are located on the premises of a customer. In
fact, they may be owned by the customer. Examples
of DTE devices are terminals, personal computers,
routers, and bridges.
DCEs are carrier-owned internetworking devices
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Frame Relay Virtual Circuits

• Frame Relay provides connection-oriented data
  link layer communication
• Frame Relay virtual circuits are identified by
  data-link connection identifiers (DLCIs)
• A Single Frame Relay Virtual Circuit Can Be
  Assigned Different DLCIs on Each End of a VC

Click for more information
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Simple Frame Relay Network
A Simple Frame Relay Network Connects Various
Devices to Different Services over a WAN
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Frame Relay versus X.25

• The elimination of functions and fields, combined
  with digital links, enables frame relay to
  operate at speeds 20 times greater than X.25
• X.25 specifies processing at layers 1, 2 and 3 of
  the OSI model, while frame relay operates at
  layers 1 and 2 only. This means that frame relay
  has significantly less processing to do at each
  node, which improves throughput by an order of
  magnitude.
• X.25 prepares and sends packets, while frame
  relay prepares and sends frames. X.25 packets
  contain several fields used for error and flow
  control, none of which frame relay needs
• X.25 has a fixed bandwidth available. Frame relay
  can dynamically allocate bandwidth during call
  setup negotiation at both the physical and
  logical channel level.

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(No Transcript)
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?????????????????????????? ATM

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??????????????????? ISDN ???????????????? (B-ISDN)

• ??????????????????????????????????????????????
• ??????????????????????????????????? ?????????????
  ???????????????????? ????????????????????????????
  ??????????????????? ??????????????????????????????
  ? ???
• ????????? B-ISDN ???????? ATM (Asynchronous
  Transfer Mode)
• ??????
• ???????????????????????????????? ???????? cell
• ????? cell ????????? 53 ????
• ?????????????????(????????????????????)???????????
  ?????????????????????
• ??????????? Cell Relay ??????????????????? Frame
  Relay

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ATM (Asynchronous Transfer Mode )

• ??????????????????????????????????????????????????
  Packet ????????????????????? X.25 ???????? LAN
  ???? ? ???? Ethernet, Token Ring
  ???????????????????????????????????????
  ??????????????????????????????????????????????????
  ?????
• ATM ?????????????? Packet Switching ???? ? ???
  ???????????????????? Packet ?????? Packet
  ??????????????????????????????????? Cell
  ?????????? 53 ???? ???? Header
  ???????????????????????????? 5 ????
  ??????????????????????? 48 ????
• ???????????? Cell ????????????????????????????????
  ????????????????????????? ? ??????????????????????
  ?? ??????????????? ????? ????????????????? ?
  ?????????????????????????????????????????
• ??????????????? ATM ??????????????????????????????
  ? ? ??????? 64 Kbps, 45 Mbps, 155 Mbps, 622 Mbps
  ???? ???????????? ?????????????? LAN ????
  Ethernet ?????????????? 10 Mbps ????Token
  Ring?????? 16 Mbps

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????????? ATM

• ????????? ATM ????????????????????????????????????
  ? ??????? LAN ???? WAN ???????????????????????????
  ?????????????????? ???????????????????????????????
  ?????????????????????????????????? ATM Switch
  ?????????????????????????????????????????????????

???????????????????? ATM ??????????????????
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????????? ATM ??? WAN

• ?????????????????????????????????????????????????
  ????????? ATM ????????????????????????????????????
  ??? WAN ???? ?????????????????????????????????????
  ???????????????? ????????? WAN ???????????????????
  ?????????????????????? ATM ??????????

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ATM uses the following features

• Fixed-size cells, permitting more efficient
  switching in hardware than is possible with
  variable-length packets
• Connection-oriented service, permitting routing
  of cells through the ATM network over virtual
  connections, sometimes called virtual circuits,
  using simple connection identifiers
• Asynchronous multiplexing, permitting efficient
  use of bandwidth and interleaving of data of
  varying priority and size

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ATM Network Device
An ATM network is made up of one or more ATM
switches and ATM endpoints. An ATM endpoint (or
end system) contains an ATM network interface
adapter. Workstations, routers, data service
units (DSUs), LAN switches, and video
coder-decoders (CODECs) are examples of ATM end
systems that can have an ATM interface
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Virtual Paths and Virtual Channels
ATM virtual connections

• - Virtual path connections (VPCs), identified by
  a VPI.
• Virtual channel connections (VCCs), identified
  by the combination of a VPI and a VCI.

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Virtual Path Switching
VP switching is often used when transporting
traffic across the WAN. VPCs, consisting of
aggregated VCCs with the same VPI number, pass
through ATM switches that do VP switching
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Common ATM Physical Interface Types
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Service Categories and Characteristics
ATM provides five standard service categories
that meet these requirements by defining
individual performance characteristics, ranging
from best effort (Unspecified Bit Rate UBR) to
highly controlled, full-time bandwidth (Constant
Bit Rate CBR).
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Virtual Path/Virtual Channel Switching
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Frame Relay to ATM Migration

• Why do businesses migrate from frame relay
  service to ATM?
• Two main drivers
• The need for greater capacity than frame relay
  can handle.
• The need to support mixed-media traffic,
  especially voice and video.

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Frame Relay/ATM Network Interwoking Topology
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ATM versus Frame Relay
The following diagrams compare the headers for
Frame Relay and ATM respectively. Notice that
they are actually very similar.
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ATM vs Frame Relay
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ATM versus LAN Technologies
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ATM versus IP

• ATM is connection oriented, IP is connectionless

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