Chapter 12 Frame Relay

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Chapter 12 Frame Relay Powered By Docstoc
					Chapter 12
Frame Relay



              1
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           2
Frame Relay Standards and Equipments

    Frame Relay is a packet-
    switching             and
    encapsulation technology
    that function at the
    Physical and Data Link
    layers of the OSI model.

                                   3
Frame Relay Standards and Eq. (cont.)

      The data rate for the
     Frame Relay can be from
     56 Kbps to 45.736 Mbps,
     or higher.



                                   4
Frame Relay Standards and Eq. (cont.)

     ITU-T and ANSI define
    Frame    Relay    as    a
    connection between the
    data terminal equipment
    (DTE)      and       data
    communications
    equipment (DCE) .
                                   5
Frame Relay Standards and Eq. (cont.)

        DCE    is    switching
    equipment supplied by a
    telecom.   provider   that
    serves as a connection to
    the public data network
    (PDN).

                                   6
Frame Relay Standards and Eq. (cont.)

    DTE is also known as
   custom premises equipment
   (CPE), because it is the
   equipment that belongs to,
   and is maintained by, the
   PDN customer.

                                   7
Frame Relay Standards and Eq. (cont.)

      For example, if you
    connect your Cisco router
    to a Frame Relay switch,
    the Cisco router is the CPE
    and the Frame Relay switch
    is the DCE. (see Fig. 12-1)

                                   8
Frame Relay Standards and Eq. (cont.)
     In Fig. 12-2, you can see a
    CSU/DSU that is used with a
    Cisco 2501 router to make the
    connection. The CSU/DSU is at
    the customer location.
    The unit is used for encoding,
    filtering,   and    translating
    communications to and from
                                      9
Frame Relay Standards and Eq. (cont.)

    Some routers have built-in
    cards that allow them to
    make WAN connections.
    Fig. 12-3 indicates a T1
    CSU/DSU cards built into
    the router.

                                  10
Frame Relay Standards and Eq. (cont.)

   A typical example Frame
   Relay   connection   was
   shown in the figure.




                                  11
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           12
    Virtual Circuits
 You can use Frame Relay
with nearly any serial
interface. It operates by
multiplexing, which means
that it combines multiple
data streams onto one
physical link.
                            13
  Virtual Circuits (cont.)
Frame Relay separate each
data streams into logical
(software-maintained)
connections called virtual
circuits, which carry the
data transferred on the
connection.
                             14
   Virtual Circuits (cont.)
Two types of virtual circuits,
switched virtual circuits
(SVC) and permanent virtual
circuits  (PVC),     connect
Frame Relay ports.


                                 15
   Virtual Circuits (cont.)
   The     SVC      software
automatically    dials   the
WAN, establishing and
terminating the connection
as required to transfer data
over Frame Relay service.

                               16
   Virtual Circuits (cont.)
PVCs remain permanently
connected to the WAN. The
administrator     manually
defines the PVC; it remains
until      the      network
administrator removes it.

                              17
   Virtual Circuits (cont.)
DLCI
  Frame Relay connections
 identify virtual circuits by
 Data Link Connection
 Identifier (DLCI) number.



                                18
   Virtual Circuits (cont.)
DLCI (cont.)
  The DLCI number map
 virtual circuits to layer 3
 protocol addresses.
   For example, a DLCI
 number associates an IP
 address with a specific
 virtual circuits.             19
   Virtual Circuits (cont.)
Frame Relay Map
    DLCI      numbers   are
 mapped, or assigned, to a
 specific interface.
  Each router that supports
 Frame Relay will have a
 Frame Relay map, which
 is a table in RAM.           20
 Virtual Circuits (cont.)

Fig. 12-4 shows a sample
Frame Relay configuration.
 Notice that the Frame
Relay switching table is
configured to map its
ports to the correct DLCI
numbers for the virtual
connection.                  21
   Virtual Circuits (cont.)
 The switching table in this
example      is     simplified.
Remember        that       DLCI
numbers are only locally
significant, so it would be
possible both routers use
the same DLCI numbers to
specify a virtual circuit.        22
  Virtual Circuits (cont.)
Subinterfaces
  A single router serial
 interface can service
 multiple PVCs through a
 single physical serial
 interface.

                             23
   Virtual Circuits (cont.)
Subinterfaces (cont.)
   To allow a single serial
  interface    to    support
  multiple PVCs, the IOS
  divides the interface into
  logical subinterface.

                               24
   Virtual Circuits (cont.)
Subinterfaces (cont.)
  For example, if Serial 0
 (s0)        had       three
 subinterfaces,         they
 would be referenced as
 s0.1, s0.2, and s0.3.

                               25
   Virtual Circuits (cont.)
Subinterfaces (cont.)
   Subinterfaces are not
 real physical interfaces;
 they are virtual interfaces
 associated       with     a
 physical interface.

                               26
   Virtual Circuits (cont.)
Subinterfaces (cont.)
  With subinterfaces, the
 cost of implementing
 multiple Frame Relay
 virtual circuits is reduced
 because      one port is
 required on the router.
                               27
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           28
           LMI
  The Local Management
Interface (LMI) is used only
locally, between the Frame
Relay DTE (e.g., a router)
and Frame Relay DCE (e.g.,
a switch), as shown in the
figure.
                               29
        LMI (cont.)
 The LMI basically extend
the functionality of Frame
Relay by:
    Making     the    DLCIs
 globally significant rather
 then locally significant

                               30
       LMI (cont.)

  Creating a signaling
mechanism between the
routers and Frame Relay
switch, which could report
the status of the link.
Supporting multicasting

                             31
        LMI (cont.)

 Providing DLCI numbers
that      are     globally
significant        makes
automatic configuration of
Frame Relay map possible.


                             32
        LMI (cont.)
   LMI   uses    keepalive
packets to verify the
Frame Relay link and to
ensure the flow of data.
The Frame Relay switch in
turn provides the status of
all    VCs    and     their
respective DLCI numbers.      33
          LMI (cont.)
  Each virtual circuit,
represented by its DLCI
number, can have one of
three connection states:
 Active
 Inactive
 Deleted
                           34
        LMI (cont.)
 Without LMI, the Frame
Relay map must be built
statically in the router.
By making DLCIs globally
significant, LMI facilitates
dynamic Frame Relay map
tables through the use of
inverse ARP protocol.          35
        LMI (cont.)
Inverse ARP
   In multipoint config.,
 routers use the protocol
 inverse ARP to send a
 query using DLCI number
 to find a remote IP
 address.
                            36
         LMI (cont.)
Inverse ARP (cont.)
   As other routers respond
  to the inverse ARP
  queries, the local routers
  can build its Frame Relay
  map automatically.

                               37
        LMI (cont.)
Inverse ARP (cont.)
   To maintain Frame Relay
  map, routers exchange
  inverse ARP messages
  every 60 sec by default.
    LMI is required for
  inverse ARP to work.
                             38
         LMI (cont.)
Inverse ARP (cont.)
  Do not confuse inverse
 ARP with reverse ARP
 (RARP); RARP is used
 primarily on LANs to
 provide hosts that only
 have MAC address with IP
 address.                   39
        LMI (cont.)
Encapsulation Types
  Different Frame Relay
 switches, CPE, and Frame
 Relay        connectivity
 equipment        support
 different types of LMI
 encapsulation.
                             40
          LMI (cont.)
Encapsulation Types (cont.)
   Cisco routers support
 theses types of LMI
 encapsulation:
    cisco
   ansi
   q933a
                              41
         LMI (cont.)
Split Horizon
  Split horizon is a routing
 technique that reduces
 the chance of routing
 loops on a network.



                               42
          LMI (cont.)
Split Horizon (cont.)
       A      split     horizon
 implementation       technique
 preventing routing update
 information received on one
 physical interface from being
 rebroadcast to other devices
 through that same physical
 interface.                       43
         LMI (cont.)
Split Horizon (cont.)
  People also refer to this
 rule as nonbroadcast
 multiaccess (NBMA).
  NBMA is a term used to
 describe WAN networks
 that   use    VCs   for
 connectivity.                44
        LMI (cont.)
Split Horizon (cont.)
  Fig. 12-5 shows a split
 horizon problem. RouterA
 would not be able to send
 route updates received
 from RouterB to RouterC,
 and vice versa.
                             45
         LMI (cont.)
Split Horizon (cont.)
  The best solution is to
 configure separate point-
 to-point subinterfaces for
 each virtual connection.
 (see Fig. 12-6)

                              46
         LMI (cont.)
Split Horizon (cont.)
 Point-to-point connections
 allow you to divide a single
 serial     interface     into
 multiple       subinterfaces,
 each supporting a separate
 virtual connection.
                                 47
          LMI (cont.)
Split Horizon (cont.)
 In a multipoint configurations,
 the network administrator can
 configure a single serial
 interface or subinterface to
 support multiple connections
 to    physical    or    logical
 interfaces on other routers.
                                   48
         LMI (cont.)
Split Horizon (cont.)
   A single subinterface
 configured for multiple
 connection is still subject
 to the spit horizon rule.



                               49
          LMI (cont.)
Split Horizon (cont.)
  The only benefit to the
 multiple configuration is
 that it allows you to use a
 single network for all of
 your routers, as shown in
 Fig. 12-7.
                               50
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           51
Performance Parameters
Terms that appear in the
contract may include:
  Access rate: The speed
 of    the    line,   which
 indicates transfer rate.
 Access rate is also known
 as the local access rate.
                              52
Performance Parameters (cont.)

    Committed Information
  Rate (CIR): The minimum
  transfer rate that the
  Frame Relay customer
  negotiates with Frame
  Relay service provider.

                             53
Performance Parameters (cont.)

    CIR (cont.): The service
   provider agrees to always
   allow the customer to
   transfer information at no
   less than the transfer rate
   specified by the CIR.

                                 54
Performance Parameters (cont.)

    Committed Burst Size
  (CBS): The maximum
  amount of data bits that
  the    service    provider
  agrees to transfer in a set
  time period under normal
  conditions.
                                55
Performance Parameters (cont.)

  Excess Burst Size (EBS):
 The amount of excess
 traffic (over the CBS) that
 the network will attempt to
 transfer during a set time
 period. The network can
 discard     EBS   data,   if
 necessary.                     56
Performance Parameters (cont.)

  Oversubscription: When the
 sum of the data arriving over
 all virtual circuits exceeds
 the access rate, the situation
 is called oversubscription.
 Oversubscription results in
 dropped packets.
                                  57
Performance Parameters (cont.)
    Two      features     of
 oversubscription are:
     Fewer T1 lines:     less
   infrastructure;
    Win-win concept: huge
   saving for both customers
   and providers.
                                58
  Performance Parameters (cont.)
         The figure shows an
      example of how the Frame
      Relay traffic parameters
 (excess
      affect the data rate of a VC.
burst rate)
(committed
burst rate)



                                      59
Performance Parameters (cont.)

   As long as the data rate of
  VC is below the CIR/BC
  values, the Frame Relay
  switch allows the frames
  into the Frame Relay
  network.

                                 60
Performance Parameters (cont.)

  However, those frames (4
  and 5) that exceed the VC
  value will have their
  Discard Eligible bits set,
  which allows the carrier to
  drop these frames in times
  of internal congestion.
                                61
Performance Parameters (cont.)

   Also,   any frames that
  exceed the BE are dropped,
  in this example, frames 6
  and 7 are dropped.




                               62
Performance Parameters (cont.)
  Congestion
    When the Frame Relay
   switch         recognizes
   congestion, it send a
   forward             explicit
   congestion     notification
   (FECN) message to the
   destination router.            63
Performance Parameters (cont.)
  Congestion (cont.)
    In addition, the switch
   sends a backward explicit
   congestion    notification
   (BECN) message to the
   transmitting, or source
   router.
                                64
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           65
     Frame Format
Frame Relay devices can
use different Frame Relay
frame format. Fig. 12-8
shows       the     Cisco
proprietary Frame Relay
frame format.

                            66
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           67
Frame Relay Topologies

 Frame Relay can use all
of the WAN technologies
discussed in Ch. 5: peer
(point-to-point), star (hub-
and-spoke), partial mesh,
or full mesh physical
topology. (see Fig. 12-9),
                               68
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           69
  Frame Relay Configuration
Basic Multipoint Config. With 2 Routers
    In Fig. 12-10, RouterA is a
   Cisco router running IOS ver.
   11.2, so it has ability to
   autosense LMI type. In
   addition,    it automatically
   receives the DLCI information
   by querying the network.      70
Frame Relay Configuration (cont.)
  Config. With 2 Routers (cont.)
     Table 12-1 lists the Cisco
    router    prompts       and
    commands that you need
    to        complete      this
    configuration.

                                   71
Frame Relay Configuration (cont.)
  Config. With 2 Routers (cont.)
    If RouterB is running IOS
   release ver. 11.0, the
   configuration commands
   for the router are shown in
   Fig. 12-11.

                                   72
Frame Relay Configuration (cont.)
    Another     example      of
  configuring with 2 routers




                                  73
Frame Relay Configuration (cont.)
    Multipoint    Configuration
  Using Subinterfaces
       To     configure    a
   multipoint subinterfaces,
   you map it to multiple
   remote routers using the
   same subnet mask, but
   different DLCI number.       74
Frame Relay Configuration (cont.)
    Multipoint   Configuration
  Using Subinterfaces (cont.)
      Table 12-2 outlines
     the steps to configure
     RouterA.
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                                 75
Frame Relay Configuration (cont.)


  (config-subif)# frame-relay
              interface-dlci 102
  (config-subif)# frame-relay
              interface-dlci 103
  (config-subif)# frame-relay
              interface-dlci 10476
Frame Relay Configuration (cont.)
  Point-to-Point Configuration
  Using Subinterfaces
    In Fig. 12-13, RouterA will
   be configured for three
   point-to-point connections
   to remote routers B, C,
   and D.
                                  77
Frame Relay Configuration (cont.)
  Point-to-Point Configuration
  Using Subinterfaces (cont.)
               Point-to-point
    connections        Frame
    Relay configurations do
    not support Inverse ARP.


                                 78
Frame Relay Configuration (cont.)
  Point-to-Point Configuration
  Using Subinterfaces (cont.)
    You have to configure each
   subnet separately and use
   the frame-relay interface-
   dlci command to associate
   the DLCI number with a
   specific subinterface.
                                 79
Frame Relay Configuration (cont.)
  Point-to-Point Configuration
  Using Subinterfaces (cont.)
      These remote routers
    configurations          will
    resemble the earlier basic
    multipoint    configuration
    with two routers.
                                   80
Frame Relay Configuration (cont.)
  Point-to-Point Configuration
  Using Subinterfaces (cont.)
       The    commands      to102
    configure RouterA for the
                              103
    point-to-point    example
    are shown in Fig. 12-14. 104

                                    81
Frame Relay Configuration (cont.)
  Frame Relay Static Mapping
     You statically configure
   your DLCI entries in the
   following situation:
     The remote router doesn’t
     support Inverse ARP.

                                 82
Frame Relay Configuration (cont.)
 Frame Relay Static Mapping (cont.)
     You need to assign
    specific subinterfaces to a
    specific DLCI connections.
      You want to        reduce
    broadcast traffic.

                                  83
Frame Relay Configuration (cont.)
 Frame Relay Static Mapping (cont.)
     You are configuring
    OSPF over Frame Relay.




                                84
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           85
Monitoring Frame Relay

You can check your Frame
Relay configurations by
using show commands.




                           86
Monitoring Frame Relay (cont.)
  The most common show
  commands for monitoring
  Frame Relay operations are:
     show interface
     show frame-relay pvc
     show frame-relay map
     show frame-relay lmi
                                87
Monitoring Frame Relay (cont.)

   Figs. 12-15~18 show
  these commands with
  their output.




                             88
     Contents
Frame Relay Stand. & Eq.
Virtual Circuits
LMI
Performance Parameters
Frame Format
Frame Relay Topologies
Frame Relay Config.
Monitoring Frame Relay
Review Questions           89
    Review Questions
Which protocol is used to
automatically build the Frame
Relay map along with LMI?
 A. ARP
 B. RARP
 C. Inverse ARP
 D. DLCI
 E. None of the above
 Ans: C                      90
   Review Questions (cont.)
   What is the purpose of
  keepalive packets?
A. To reduce data transfer rates
B. To keep PVCs active
C. To increase data transfer rate
D. To negotiate connection speed
E. None of the above
  Ans: B                       91
  Review Questions (cont.)
Which of the following layers do
WAN     specifications    typically
define? (Choose all that apply.)
 A. Physical
 B. Data Link
 C. Network
 D. Transport
 E. Presentation
 Ans: A, B                        92
Review Questions (cont.)
In Frame Relay, what would
be considered the DCE?
 A. Customer’s router
 B. Terminal adapter
 C. PPP
 D. Frame Relay switch
 E. None of the above
 Ans: D                    93
 Review Questions (cont.)
Which of the following is a
type   of    virtual    circuit?
(Choose all that apply.)
 A. MVC
 B. PVC
 C. SVC
 D. QVC
 E. RVC
 Ans: B, C                      94
 Review Questions (cont.)
Which of the following are LMI
encapsulation types supported
by Cisco routers? (Choose all
that apply.)
 A. LMI 2
 B. cisco
 C. ansi
 D. q923i
 E. q923a
                                 95