OSI VI

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30 Οκτ 2013 (πριν από 3 χρόνια και 5 μήνες)

64 εμφανίσεις

Instructor: Sam Nanavaty

ISDN

Instructor: Sam Nanavaty

ISDN


The Original Digital Service


Technology was defined in the mid
-
80s


Uses circuit switched technology to
support


D (Delta) channels are used for signaling


Data is transported over 64 Kbps B
(Bearer) channels


Channels may carry voice, packet data,
video, and fax


Instructor: Sam Nanavaty

ISDN basics


BRI (Basic Rate Interface)




Targeted at home and small business users




Provides 2 B channels over a single twisted
pair


• PRI (Primary Rate Interface)




Targeted at larger corporate customers




Provides 23 B channels over T1 in North
America




Provides 30 B channels over E1 in Europe


Instructor: Sam Nanavaty

Instructor: Sam Nanavaty

Advantages


ISDN provides more bandwidth than a traditional 56
kbps dialup connection.


ISDN uses bearer channels, also called B channels, as
clear data paths.


Each B channel provides 64 kbps of bandwidth.


An ISDN connection with two B channels would provide
a total usable bandwidth of 128 kbps.


ISDN can be used for backup connections or for
implementing Bandwidth on demand.


Each ISDN B channel can make a
separate

serial
connection to any other site in the ISDN network.


Instructor: Sam Nanavaty

Disadvantages


BRI is slower than DSL and cable


More expensive than DSL and cable


PRI is still used as a backup mechanism
or for load balancing.

Instructor: Sam Nanavaty

ISDN Protocol Stack

Instructor: Sam Nanavaty

Dial
-
on
-
demand routing (DDR)
is triggered when traffic that matches

a predefined set of criteria is queued to be sent out a DDR
-
enabled

interface.

• The traffic that causes a DDR call to be placed is referred to as

interesting traffic
.

• Once the router has transmitted the interesting traffic, the call is

terminated.

ISDN applications

Instructor: Sam Nanavaty

ISDN applications


ISDN is also used for the following
purposes:



Backup for the network and the access
links


Load balancing

Instructor: Sam Nanavaty

Homework 2


What are the different types of ISDN
Interfaces?


What is V.120?


What Protocols are supported over B
channels?

Instructor: Sam Nanavaty

Frame Relay

Instructor: Sam Nanavaty

Frame Relay


Modern telecommunications networks are
characterized by relatively error
-
free digital
transmission and highly reliable fiber
infrastructures.


Frame Relay relies on upper
-
layer protocols to
detect and recover from errors.


Frame Relay does
not

have the
sequencing,
windowing, and retransmission mechanisms
that are used by X.25
.


The network providing the Frame Relay service
can be
either a carrier
-
provided public
network or a privately owned network.

Instructor: Sam Nanavaty


Most popular service today that replaces
existing leased line and X.25
infrastructures.


Why


Better control of bandwidth,
scalability, low latency, congestion control
and efficiency


Used in private and public networks

Instructor: Sam Nanavaty

Frame Relay Network

Instructor: Sam Nanavaty

FRAME RELAY PROTOCOL FORMAT

Instructor: Sam Nanavaty

Field definitions


Flag: Beginning or end of frame


Address/ control


2 bytes


DLCI is a 10 bit address field


Congestion control


3 bits [FECN,BECN, DE]


Information field


variable length


FCS


Frame Check sequence for error control


Flag: End of frame


Instructor: Sam Nanavaty

Data Link Connection Identifier


Identifies a logical circuit between a router
and a frame relay switch


DLCI s normally have local significance
(exception global DLCIs)


Think of DLCI as the equivalent of MAC
address in LAN domain.


The FR switch maps DLCIs between each
pair of routers to build a Permanent Virtual
Connection (PVC).


Instructor: Sam Nanavaty

Instructor: Sam Nanavaty

CIR, Bc, Be


Committed Information Rate (CIR) is a guaranteed rate,
in bits per second that a service provider commits to
providing


Committed Burst (Bc) is the maximum number of bits
that the switch agrees to transfer during any Committed
rate measurement interval


Excess Burst (Be) is the maximum number of
uncommitted bits that a FR switch attempts to transfer
beyond CIR. (Be) is limited to the port speed of the Local
Access. Network treats (Be) data as discard eligible.


CIR

Bc

Be

time

Instructor: Sam Nanavaty

Forward Explicit Congestion Notification/
Backward Explicit Congestion
Notification


FECN


Upon encountering congestion in
the network, a FR switch sends FECN to
the destination device indicating that the
congestion has occurred


BECN


Upon encountering congestion in
the network, a FR switch sends BECN to
the source device instructing it to reduce
the rate at which it is sending the packets.

Instructor: Sam Nanavaty

Discard Eligibility (DE)


DE bit is set by the switch at the ingress
for all the Frame Relay traffic that exceeds
the Committed Information Rate


Upon detecting heavy congestion, the
Switch is authorized to drop the traffic
marked DE

Instructor: Sam Nanavaty

ATM

Asynchronous Transfer Mode

Instructor: Sam Nanavaty

ATM Facts


Worldwide ATM switch market for 2004
was about $5.23 Billion



Roughly 80% of Service Providers use
ATM in their core networks



Instructor: Sam Nanavaty

Where is ATM deployed?



ATM workgroup in campus networks


ATM in Core Network


Content Delivery Networks (CDNs)


Internet backbones


Carrier infrastructures

Instructor: Sam Nanavaty

ATM switches

Instructor: Sam Nanavaty

ATM


Cell switching



•ATM breaks up streams of data, video,
and voice into fixed size units called “cells”


•A fixed size cell allows switching
decisions to be done at the hardware level


•Hardware Level switching implies high
speed!


•ATM networks switch and multiplex all
information using these fixed length cells


Instructor: Sam Nanavaty

ATM over SONET


ATM cells are transported over long
distances via SONET


Please note that SONET does not “switch”
the ATM cells. The switching is
accomplished by ATM switches.


Instructor: Sam Nanavaty

Physical Layer

ATM

Adaptation module

Voice

Video

Data

Instructor: Sam Nanavaty

VCI



Virtual Channel Identifier: Have same QOS
requirements as the VPI and multiple VC’s are
multiplexed within a single VP.

GFC
-

Generic Flow
Control: Control traffic
flow at the User
network Interface

VPI



Virtual Path Identifier: bundle of virtual
channels switched transparently across the
ATM network on the basis of the common VPI

PT
: Indicates the type of
information in the Payload
field

CLP
: Cell Loss Priority: when set to 1,
the cell is discard eligible

Source: Warren Hioki

Telecommunications,

Fourth Edition

ATM User to
Network
Interface
(UNI) header

Instructor: Sam Nanavaty

Transmission Path

Virtual Path

Virtual Channels

Relationship between the TP, VP and VC

Instructor: Sam Nanavaty

CBR

Constant Bit Rate service provides constant bandwidth with a
fixed timing relationship, which requires clocking synchronization.
Because CBR traffic reserves a fixed amount of bandwidth, some trunk
bandwidth might go unused. CBR is typically used for circuit emulation
services to carry real
-
time voice and video.


VBR
-
RT

Variable Bit rate


Real Time service provides only a partial
bandwidth guarantee. Cell delay is controlled in this case due to real
time requirements. Typical applications include packetized voice and
video, and interactive multimedia. Supports statistical multiplexing


VBR
-
NRT

Variable Bit rate


Non Real Time
service provides a
partial bandwidth guarantee, but with a higher cell delay than VBR
-
RT.
This service category is suitable for bursty applications (i.e. applications
with unpredictable traffic patterns). Supports statistical multiplexing.
E.g., Web browsing


Service Types supported by ATM

Instructor: Sam Nanavaty

Service Types supported by ATM


ABR

provides a best effort service, in which feedback
flow control within the network is used to increase
bandwidth when no congestion is present, maximizing
the use of the network. ABR does guarantee a minimum
cell rate (MCR). Applications include Database Archival,
File Transfers etc.



UBR

service provides no bandwidth guarantee, but
attempts to fill bandwidth gaps with bursty data. Used for
low bandwidth applications or the applications where end
user experience is not impacted by latency variations.