Matakuliah
Tahun
Versi
: H0174/Jaringan Komputer
: 2006
: 1/0
Pertemuan 25
High Speed Network
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menunjukkan Teknik High Speed transmission
2
Outline Materi
• Frame Relay
• xDSL
3
Frame Relay
• Frame Relay is a packet-switched, connectionoriented, WAN service.
• Frame Relay operates at the data link layer of
the OSI reference model.
• Frame Relay uses a subset of the high-level
data-link control (HDLC) protocol called Link
Access Procedure for Frame Relay (LAPF)
• Designed to be more efficient than X.25
4
Frame Relay
• Call control carried in separate logical connection
• Multiplexing and switching at layer 2
– Eliminates one layer of processing
• No hop by hop error or flow control
• End to end flow and error control (if used) are
done by higher layer
• Single user data frame sent from source to
destination and ACK (from higher layer) sent
back
5
Frame Relay Mesh
6
Advantages and Disadvantages
• Lost link by link error and flow control
– Increased reliability makes this less of a
problem
• Streamlined communications process
– Lower delay
– Higher throughput
• ITU-T recommend frame relay above 2Mbps
7
Terminology
• The connection through the Frame Relay
network between two DTEs is called a virtual
circuit (VC).
• Generally, permanent virtual circuits (PVCs)
that have been preconfigured by the carrier are
used.
• Virtual circuits may be established dynamically
by sending signaling messages to the network.
In this case they are called switched virtual
circuits (SVCs).
8
Frame Relay Functions
1.
2.
3.
Frame Relay receives a packet from the
network layer protocol, such as IP.
Frame Relay wraps it with a layer 2 address
field which contains the DLCI.
The frame is then passed to the physical
layer and transmitted on the wire.
9
Frame Relay Features
• Based on packet (frame) switching
• Frames of variable length - up to 4096 bytes,
typically 1600 bytes
• Connection oriented - PVC
• High data rates at user-network interfaces 2Mbps, ultimately up to 45 Mbps
• Bandwidth on demand
• No flow control mechanisms (nearly)
• No retransmission mechanisms
• All protocol functions implemented at 2nd level
(data link) of OSI model
• Physical interface: X.21, V.35, G.703, G.704
10
Frame Relay network
VCIs in Frame Relay are called DLCIs
11
Parameters of a UNI interface
• Physical speed - just clock rate
• Guaranteed bandwidth parameters
– CIR: Committed Information Rate
– BC: Committed Burst Size
• Extended bandwidth parameters
– EIR: Extended Information Rate
– BE: Extended Burst Size
• TC: Measurement Interval
192kbps
User
traffic
EIR
256kbps
64kbps CIR
time
12
Frame Relay frame
• Flag - Frame marker (1 byte: 01111110)
• Address field - two bytes
• FCS: Frame Check Sequence (Control Sum)
13
Link Management Interface (LMI)
• For DTE to dynamically acquire information
about the status of the network to help
verify the integrity of logical and physical
links.
• LMI messages are exchanged between the
DTE and DCE using reserved DLCIs
• Three types of LMI:
– Cisco
– ANSI (T1.617 Annex D
– ITU standard Q933 Annex A
14
Flow and congestion control
• There is no explicit flow control in FR; the network
informs a user about congestion
• Congestion: FR frames are discarded from overflowed
buffers of switching devices
• Congestion information:
• FECN - Forward Explicit Congestion Notification
• BECN - Backward Explicit Congestion Notification
• There are recommendations for access devices what to
do with FECN and BECN (usually not implemented)
Transmission direction
FRAD
BECN
FRAD
FECN
15
DSL Access Technology
• Why is DSL attractive?
• Shannon limit of data rate is 30,000 bps
(3-KHz, 30 dB S/N channel)
• Digital transmission over loop (DSL) improves
data rate
• T1/DS1 (1.544Mbps) 18,000 feet
• T2/DS2 (6.312 Mbps) 12,000 feet
16
DSL Limitations
• Loop conditions with no direct copper to the house
• Loaded coils in loop (used to increase analog
distance) cannot carry digital signal
• Modern subdivisions have fiber to the
neighborhood or curb with digital mux
• Operating company inventory dated (administrative
issue)
17
ADSL Network
Broadband
Network
ADSL
Loop
ATU-C
Splitter
Splitter
Voice
Voice
ATU-R
• ADSL .. Asymmetric Digital Subscriber Line
• ATU-C ADSL transmission unit - central office
• ATU-C ADSL transmission unit - remote/residence
• Splitter separates voice and data
18
ADSL Network
Private
Network
Public
Network
Premises
Network
ADSL Access Network
OS
Service
Systems
OS
Broadband
Network
Narrowband
Network
Access
Node
Packet
Network
ATU-C
ATU-R
ADSL
ADSL
PDN
SM
Settop
TE
TV
SM
PC I/O
TE
PC
SM
ISDN
TE
ISDN
STM
Packet
ATM
STM
Packet
ATM
ATM
Transport Modes
ADSL
ATM
STM
TE
OS
PDN
SM
Asynchronous Digital Subscriber Line
Asynchronous Transfer Mode
Synchronous Transfer Mode
Terminal Equipment
Operations System
Premises Distribution Network
Service Module
19