Transcript Business Data Communications

Business Data Communications
Chapter Seven
Wide Area Networking
Fundamentals
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Primary Learning Objectives
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Understand the need for varying WAN connectivity
options
Define the term switching network
Describe circuit switching networks
Describe packet switching networks
Differentiate X.25, Frame Relay, and ATM
Explain Point-to-point protocol
Identify common trunk carrier services
Distinguish between symmetric and asymmetric Digital
Subscriber Line services
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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WAN Connectivity Options
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There are several ways in which WAN connections
can be established
Many connection options are provided by common
carrier infrastructures (AT&T, MCI, Sprint, for
example)
WAN connectivity options include:
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Circuit switching
Packet switching: X.25, Frame Relay, ATM
Point-to-point protocols
Trunk carrier services
Digital subscriber lines
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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WAN Connectivity Options
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Switching Networks
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Composing a switching network are switches, which:
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Are a series of interlinked devices
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Interlinks between two communicating devices are temporary
Can be hardware, software, or a combination of both
Can be connected to multiple links
The switching network infrastructure is referred to, and
graphically illustrated as, a “cloud”
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Edge switches and edge routers connect the enterprise
to the cloud
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Switching Network
Cloud
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Circuit Switching
Networks
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Are well-suited for voice, but not data, communications
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Create a direct connection between two communicating
devices:
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Voice communications are continuous; data
communications are bursty
This direct connection is referred to as a “path”
While established, no two other devices can use the
circuit path
The circuit path uses a constant rate determined by the
slower of the two devices
Circuit-switched paths can be temporary or permanent
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Circuit Switching
Networks
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Temporary paths:
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Permanent paths:
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Require a call setup
Are less expensive than permanent paths
Do not guarantee that a circuit will always be available
Do not require a call setup
Are more expensive than temporary paths
Guarantee that a circuit will always be available
Neither temporary nor permanent circuit switching
prioritizes communications
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Break data into units called “packets”:
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Packets traverse the packet switching cloud through a
series of links
Links are connected by packet switching nodes
Improve line efficiently significantly because many
packet streams, from differing communications, can use
the same links between packet switching nodes
Deliver packets even when the network is busy,
although the packets may be delayed
Provide for data-rate link conversion between packet
switching nodes
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Data-Rate Link Conversion
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Use the network implementation to determine
packet size
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Packets contain not only core data, but control
information as well
Temporarily store and then forward packets as they
pass through the packet switching cloud
Allow for prioritization of communications
May be based on datagram or virtual circuit delivery
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Datagram delivery:
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Is best for small messages
Treats each packet independently
Does not guarantee packet delivery
Does not sequence packets
Permits packets to be dynamically rerouted
Does not require a setup procedure between sender and
receiver
Requires little overhead
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Virtual circuit delivery:
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Is best for data-sensitive messages
Requires a set-up procedure between sender and receiver
Requires all packets in a message to take the same route
Guarantees packet delivery
Sequences packets
Cannot dynamically reroute packets
Has significant overhead
Takes one of two forms:
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Switched virtual circuit
Permanent virtual circuit
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Switched virtual circuits:
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Are similar in concept to a dial-up circuit switched
connection
Temporarily set up the route of links a circuit takes,
meaning only for the duration of the communication
Require a setup procedure for each communication
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Permanent virtual circuits:
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Are similar in concept to a leased circuit switched
connection
Once defined, require no additional set-up procedures,
meaning that the route of links does not have to be
recreated
Are always available as they are permanent
Require virtual circuit identifiers for each communication
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Packet Switching
Networks
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Three common forms of packet switching network are:
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X.25 – The oldest
Frame Relay
ATM – The newest
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X.25
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Uses data terminal equipment and data-circuit
terminating equipment
Uses virtual circuits and statistical time division
multiplexing
Supports variable length packets
Has a three-layer design: physical, frame, and packet
Uses Link Access Procedure-Balanced protocol (based
on HDLC) at the frame layer
Provides for significant error checking, a drawback given
today’s much improved transmission media
Was not designed with multimedia data in mind
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Frame Relay
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Utilizes two layers: physical and data link
Supports variable length packets
Requires Frame Relay Access Devices (FRADs) to
disassemble and reassemble packets
Requires that subscribers negotiate a committed
information rate with a common carrier
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A committed burst rate can also be negotiated
Uses the Link Access Procedure-Function protocol
(based on HDLC)
Does not provide for flow and error control
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These are left to higher-level services
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ATM –
Asynchronous Transfer Mode
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Is a universal integrated carrier of voice, data, audio,
and video
Has a significant implementation cost and high degree
of configuration complexity
Utilizes two layers: physical and data link
Is a point-to-point solution
Uses virtual path and virtual channel identifiers
Requires fixed-length packets, called cells, of 53 bytes
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5 bytes of header, 48 bytes of data
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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ATM –
Asynchronous Transfer Mode
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Point-to-Point Protocol
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Was developed by the IETF
Creates a physical serial link between two devices
Is inexpensive, but provides limited bandwidth capacity
Is the most common protocol used by dial-up modems
Replaced Serial Link Internet Protocol (SLIP)
Requires no media access control
Uses protocols such as PAP and CHAP for authentication
Has a five-phase sequence
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Point-to-Point Protocol –
Five Phases
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Trunk Carrier Services
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Most commonly used forms include: T-1, T-3, and
Fractional T-1; the “T” stands for trunk services
The higher the “T” level designation, the greater the
possible number of communication channels
Significantly more costly than point-to-point protocol,
but offers much higher bandwidths
Digital leased lines have a range of bandwidths referred
to as digital signal (DS) speeds
Subscribers negotiate with common carriers the level of
service quality, for a cost
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Trunk Carrier Services
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Trunk Carrier Services
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Usually used in conjunction with a:
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Channel service unit (CSU):
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The end-point of the digital link
Keeps the link open and active
Data service unit (DSU):
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Converts signals from a connecting device into the type of
signal required by the leased line
Connecting devices may be switches, routers, or Private
Branch Exchanges
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Trunk Carrier Services
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Usually used in conjunction with a:
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Private Branch Exchange (PBX):
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A common connecting device used with a CSU and a DSU
An on-site switching facility used to interconnect telephones
to a Public Switched Telephone Network
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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Trunk Carrier Services
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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DSL –
Digital Subscriber Line
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Supports simultaneous voice and data communications
Has a relatively low cost, with high transmission speeds
Is technically referred to as “xDSL”, whereby the “x”
indicates the type of DSL service provided, for example:
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ADSL
HDSL
SDSL
IDSL
VDSL
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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DSL –
Digital Subscriber Line
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Two terms associated with DSL are Downstream and
Upstream:
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Downstream describes the transmitting of data from a
remote location to a local device
Upstream describes the transmitting of data from a local
device to a remote location
Most users of DSL primarily utilize downstream
transmission
Downstream and upstream transmission rates can vary or
be the same, depending on the DSL service
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Asymmetric versus Symmetric DSL
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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DSL –
Digital Subscriber Line
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The most common form of DSL is ADSL, or Asymmetric
Digital Subscriber Line
With ADSL, downstream transmissions are faster than
upstream transmission, for example:
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Up to 1 Mbps downstream
Up to 512 Kbps upstream
Users located less than 18,000 feet from a local
provider’s point-of-presence are good candidates for
ADSL
DSL users also need to select between static and
dynamic IP addresses
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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DSL –
Digital Subscriber Line
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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DSL – Digital Subscriber Line
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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In Summary
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There are a variety of WAN connectivity solutions
Circuit switched networks are most appropriate for voice
Packet switched networks are most appropriate for data
Common packet switched networks include X.25, Frame
Relay, and ATM
Point-to-Point Protocol, while inexpensive, offers low
bandwidth
Trunk services, particularly T-1, T-3, and Fractional T-1,
are popular business WAN solutions
Forms of Digital Subscriber Line are becoming
increasingly implemented as home and business
solutions
Business Data Communications, by Allen Dooley, (c) 2005 Pearson Prentice Hall
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