Frame%20Relay - PowerPoint PPT Presentation

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Frame%20Relay

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Frame Relay. Advantages. High data rates & access rates ... Maximum frame size 9000 bytes. Less expensive technology ... Frame Relay. Topology virtual ... – PowerPoint PPT presentation

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Title: Frame%20Relay


1
Frame Relay
  • Nirmala Shenoy
  • Information Technology Department
  • Rochester Institute of Technology

2
Frame Relay
  • Purpose
  • Faster transmission
  • Virtual circuit technology
  • Data rates up to 2.048 Kbps to the end user
  • Network Data rates 44.376 Mbps T3 lines
  • Assumes smart end systems reliable media
  • No error flow control in the network
  • High data rates at low costs

3
Frame Relay
  • Purpose
  • Replacement for a number of leased T1 lines
  • Virtual private networks
  • Lower costs for similar resources
  • Wide Area coverage interconnect LANs
  • Ideally suited to bursty traffic

4
Frame Relay
  • Purpose
  • Bursty traffic

5
Frame Relay
  • Advantages
  • High data rates access rates
  • Lower 2 layers- ideal for backbone networks
  • Support bursty data
  • Maximum frame size 9000 bytes
  • Less expensive technology
  • Can be used on lease or on requirement basis

6
Frame Relay
  • Disadvantages
  • Not high enough data rates
  • Variable length frames
  • Not suited to time sensitive applications

7
Frame Relay
  • Topology

8
Frame Relay
  • Topology virtual circuits

9
Frame Relay
  • Topology virtual circuits
  • At the Data link layer
  • DLCI Data Link Connection Identifier
  • PVCs and SVCs
  • Different connections get different DLCI
  • Local significance
  • DLCIs within the network

10
Frame Relay
  • Route table at FR switch

11
Frame Relay
  • Layers
  • Core data link function LAPF
  • Simplified HDLC

12
Frame Relay
  • LAPF PDU
  • Flag
  • Address field
  • DLCI
  • C/R (command response bit) not used
  • EA extended address bit
  • FECN
  • BECN
  • DE - Drop eligibility bit

13
Frame Relay
  • LAPF PDU
  • Information
  • FCS Frame check sequence
  • Flag

14
Frame Relay
  • LAPF PDU
  • EA bit useful for extended address capability
  • 0 signifies another address byte to follow
  • FECN
  • Forward explicit congestion notification
  • Warning to receiver of message that there is
    congestion along the direction of flow

15
Frame Relay
  • LAPF PDU
  • BECN
  • Notify sender that there is congestion in a
    direction opposite to the information flow
  • Use response frames going in reverse direction
  • Use predefined DLCI connection 1023
  • FECN BECN inform end systems of network
    congestion

16
Frame Relay
  • FECN BECN

17
Frame Relay
  • Discard Eligibility bit
  • This frame can be dropped during congestion
  • A congestion control mechanism

18
Frame Relay
  • Traffic Control - Attributes
  • Committed burst size Bc
  • Eg 400kbs for 4 seconds
  • During the 4 second period max traffic 400kbs
  • Committed information rate
  • Average rate
  • Bc/T (T predefined period for burst)
  • CIR 400/4 100kbs/sec

19
Frame Relay
  • Traffic Control - Attributes
  • Excess burst size Be
  • Bits in excess of Bc that can be sent in T
  • May not be transferred under congestion

20
Frame Relay
  • Traffic Control

21
Frame Relay
  • Traffic Control
  • Forwarding of traffic
  • Fast forward
  • Leaking CIR
  • Traffic control via leaky bucket

22
Frame Relay
  • Traffic Control
  • Control of output from leaky bucket leak rate
  • Timer (?T) and counter for counting bits sent

23
Frame Relay
  • Traffic Control leaky bucket

24
Frame Relay
  • Traffic Control
  • Use of the DE bit
  • User setting
  • Network setting, based on Bc, Be
  • May not be used
  • Policing Traffic shaping

25
Frame Relay
  • Service class categorization
  • Be only all data can be dropped on congestion
  • CIR and Bc,
  • User sets DE flag, network will discard these
    frames under severe network congestion if
    exceeding Bc
  • CIR, Bc and Be
  • Network will tag Be traffic and drop if severe
    congestion

26
Frame Relay
  • UNI NNI inter-working
  • ANSI T1.617

27
Frame Relay
  • UNI NNI inter-working
  • Messages
  • SE - Status Enquiry
  • S Status
  • FS full status on all PVCs
  • Use of Unnumbered Information frames of HDLC
    DLCI 0

28
Frame Relay
  • NNI operations
  • Adding a PVC notification
  • Detection of PVC deletion
  • UNI, NNI failures
  • PVC segment availability
  • Link verification
  • Node verification

29
Frame Relay
  • Typical Bellcore PVC service
  • Exchange Access Frame Relay XA-FR
  • Defined between LEC (Local Exchange Carrier) and
    IC(Interchange Carrier)
  • FR-ICI interface
  • Consistent service end-to-end PVC, UNI to UNI

30
Frame Relay
  • XA-FR topology

31
Frame Relay
  • XA-FR
  • Service parameters at FR-ICI compliant frames
  • Performance objective
  • Delay
  • Accuracy
  • Availability

32
Frame Relay
  • XA-FR delay
  • FR-UNI access rate
  • FR-ICI access rate
  • Frame size
  • Time the first bit placed on the UNI, till the
    last bit received at ICI lt specified value for
    95 of the frames

33
Frame Relay
  • XA-FR accuracy
  • Number of errored frames
  • Number of lost frames
  • Number of extra frames
  • Compute
  • Frames not delivered ratio
  • Errored frames ratio
  • Extra frames ratio

34
Frame Relay
  • XA-FR availability
  • Scheduled hours of service
  • Service availability
  • MTTSR mean time to service restoration
  • MTBSO mean time between service outages
  • Fraction of time in non-congestion notification
    state
  • Mean time between congestion notification st

35
Frame Relay
  • DLCI Values two octet field
  • 0 in channel signaling
  • 1-15 reserved
  • 16- 991 assigned by FR connections
  • 992-1007 layer management for bearer service
  • 1008-1022 reserved
  • 1023 in-channel layer management

36
Frame Relay
  • DLCI Values
  • Global addressing unique destination address
  • Semi-broadcast copied to multiple routers

37
Frame Relay
  • Frame Relay SVC operation

38
Frame Relay
  • Frame Relay SVC operation
  • Set up information
  • DLCI
  • An explicit address
  • Requested end-to-end delay
  • Max frame size
  • Requested throughput (incoming outgoing)
  • Requested Bc (incoming outgoing)
  • Requested Be (incoming outgoing)

39
Frame Relay
  • Quality of service options
  • Residual Error rate
  • Frame related
  • Switched virtual call establishment delay
  • Clearing delay
  • Premature disconnect

40
Frame Relay
  • Features of emerging technologies?
  • Bursty data high bit rate (not so high?!)
  • Quality of Service addressed
  • Frame based real time suitability?
  • Flow control implicit minimal
  • Drop traffic on congestion
  • Error control no
  • Drop traffic on error
  • Payload integrity management no
  • Band width on demand

41
Frame Relay
  • Summary
  • Extended use of HDLC technology
  • High speed WAN
  • Ideal to interconnect high speed LANs
  • Limitations
  • Speed
  • Frame size
  • Good backbone technology

42
Frame Relay
  • Summary
  • Lower costs
  • Operational
  • End user
  • Better sharing of resources
  • New service offering
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