Transcript CHABOT COLLEGE CISCO NETWORKING ACADEMY Semester 4 Chapter 2 WANs CHABOT COLLEGE CISCO NETWORKING ACADEMY Table of Contents • • • • • 2.1 WAN Service Providers 2.2 WAN Devices 2.3 How.

CHABOT COLLEGE CISCO NETWORKING ACADEMY
Semester 4
Chapter 2
WANs
CHABOT COLLEGE CISCO NETWORKING ACADEMY
Table of Contents
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2.1 WAN Service Providers
2.2 WAN Devices
2.3 How WANs relate to the OSI Model
2.4 WAN Encapsulation Formats
2.5 WAN Link Options
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WAN Services
• A WAN is a Data Communications Network
operating beyond a LAN's geographic scope.
• You must subscribe to a WAN service provider,
such as a regional Bell operating company
(RBOC) to use WAN carrier network services.
• A WAN connects the locations of an
organization to:
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each other
locations of other organizations
external services (such as databases)
remote user
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WAN Services
• A WAN uses data links, such as Integrated
Services Digital Network (ISDN) and Frame
wide-area geographies
• WANs carry many types of traffic, such as:
– voice
– data
– video
• WAN technologies function at three layers of the OSI model:
– physical
– data link
– Network
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WAN Services
• Telephone and data services are the most commonly
used WAN services.
• Telephone and data services are connected from the
building POP to the WAN provider's central office (CO).
• The CO is the local telephone company office to which all
local loops in that area connect
• The services offered by the WAN provider are of 3 main
types:
– Call setup (also called signalling)
– Time Division Multiplexing (TDM)
– Frame Relay
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WAN Services
• Call setup (also called signalling):
– Sets up and clears calls between telephone
users. Most commonly used call setup is
Signaling System 7 (SS7)
• Time Division Multiplexing (TDM):
– Information from many sources has bandwidth
allocation on a single medium. Basic telephone
service and ISDN use TDM circuits.
• Frame Relay:
– Data contained in frames shares bandwidth with
other WAN Frame Relay subscribers. Uses
statistical multiplexing (STDM)
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CPE, demarc, "last mile", CO switch, toll
network
• The most commonly used terms associated with the main
parts of WAN services:
– Customer premises equipment (CPE) -- Devices physically
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located on the subscriber's premises.
Demarcation (or demarc) -- The point at which the CPE ends
and the local loop portion of the service begins. Often
occurs at the POP of a building.
Local loop (or "last-mile") -- Cabling (usually copper wiring)
that extends from the demarc into the WAN service
provider's central office.
CO switch -- A switching facility that provides the nearest
point of presence for the provider's WAN service.
Toll network -- The collective switches and facilities (called
trunks) inside the WAN provider's cloud.
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CPE, demarc, "last mile", CO switch, toll
network
CHABOT COLLEGE CISCO NETWORKING ACADEMY
CPE, demarc, "last mile", CO switch, toll
network
• A key interface is between the data terminal equipment (DTE)
and the data circuit-terminating equipment (DCE).
– Typically, the DTE is the router, and the DCE is the device used to
convert the user data from the DTE into a form acceptable to the
WAN service's facility (eg. MODEM, CSU/DSU, TA/NT1).
• The WAN path between the DTEs is called the
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link
circuit
channel
line
• The DTE/DCE interface describes the physical layer
standards. It uses various protocols (such as HSSI and V.35)
that establish the codes that DTEs and DCEs use to
communicate with each other.
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WAN Virtual Circuits
• A virtual circuit is a pathway through a packet-switched network that
appears to be a dedicated, physically-connected circuit (as opposed
to an actual, physical, circuit-switched pathway through a network).
• Virtual circuits are connection oriented
• Two types of virtual circuits exist:
– switched virtual circuits (SVCs)
– permanent virtual circuits (PVCs).
• In a PVC, the customer and the carrier have negotiated the
endpoints and characteristics of the virtual circuit ahead of time, and
they are constantly available.
– The end points and a stated bandwidth called a Committed
Information Rate (CIR) constitute a PVC, which is defined to the
frame relay network devices
• In a SVC, the virtual circuit is available only "on-demand".
– circuit establishment, data transfer, and circuit termination.
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PVC and SVC
• SVCs are used in situations where data transmission between
devices is sporadic.
– Disadvantage = increased bandwidth due to the circuit
establishment and termination phases
– Advantage = decreased costs compare with constant virtualcircuit availability.
• A PVC is a permanently established virtual circuit that
consists of one mode:
– data transfer.
• PVCs are used in situations where data transfer between
devices is constant.
– Advantage = PVCs decreased bandwidth use because there
are no establishment and termination phases
– Disadvantage = increased costs due to constant availability.
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WAN Line Types
OC-768 now exists running at 40Gbps
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Fundamental WAN Devices
• The router is the essential WAN device, but it is
also considered a LAN device.
– It offers many services, including LAN and
WAN interface ports
• WAN switches connect to WAN bandwidth for
voice, data, and video communication.
• Modems interface voice-grade services
(telephone lines). They include:
– CSUs/ DSUs devices that interface T1/E1 lines
– TA/NT1 devices that interface ISDN services.
• Communication servers concentrate dial-in and
dial-out user communication.
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Routers and WAN Switches
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Routers provide interfaces for a wide range of links and
subnetworks at a wide range of speeds.
Routers are active and intelligent network devices and can
participate in managing the network by:
– providing dynamic control over resources
– supporting the tasks and goals for networks such as:
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Connectivity
Reliable performance
Management control
Flexibility
Security
A WAN switch is a multiport networking device that operates at the data
link layer of the OSI reference model. A WAN switch typically switches
traffic such as:
– Frame Relay
– X.25
– Switched Multimegabit Data Service (SMDS)
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Routers and WAN Switches
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Describe modems on a WAN
• A device that interprets digital and analog signals
by modulating and demodulating the signal, which
enables data to be transmitted over voice-grade
telephone lines.
• At the source, digital signals are converted to a
form suitable for transmission over analog
communication facilities. That is digital signals are
converted into analog signals. At the destination,
these analog signals are returned to their digital
form.
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CSU/DSUs on a WAN
• A CSU/DSU is :
– A digital-interface device that connects a T1/E1
– Sometimes two separate digital devices
– Sometimes it is integrated into the router
• Adapts the physical interface on a DTE device
(such as a terminal or router) to the interface of
a DCE device (such as a switch) in a switchedcarrier network
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ISDN Terminal Adapters on a WAN
• An ISDN Terminal Adapter (TA) is a device used to
connect ISDN Basic Rate Interface (BRI) connections to
other interfaces
• Its is an adapter that allows non ISDN devices (terminals
or routers) to communicate on an ISDN network
• The ISDN TA can be either a standalone device or a
board inside the TE2.
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Organizations that deal
with WAN Standards
• WANs use the OSI model layered approach to
encapsulation, just as LANs do
• WANs mainly focus on the physical and data-link layers
– Physical layer includes delivery of data
– Data-link requirements include addressing, flow control,
encapsulations
• WAN standards are defined and managed by:
– International Telecommunication Union-Telecommunication
Standardization Sector (ITU-T)
– International Organization for Standardization (ISO)
– Internet Engineering Task Force (IETF)
– Electronic Industries Association (EIA)/ Telecommunications
Industries Association (TIA)
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WAN Physical Layer Standards
• WAN physical-layer protocols describe how to
provide electrical, mechanical, operational, and
functional connections for WAN services.
• Also describes the interface between the DTE and
the DCE
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WAN Physical Layer Standards
• Physical layer standards define the rules for the DTE/DCE
interface:
– EIA/TIA-232: developed by TIA/EIA, supports signal speeds of up
to 64kbps, formerly called RS-232
– EIA/TIA-449: a faster version of EIA/TIA-232 (up to 2 Mbps),
capable of longer cable runs.
– EIA/TIA-612/613: A standard describing HSSI, which provides
access to services at T3 (45 Mbps), E3 (34 Mbps), SONET (51.84
Mbps) rates.
– V.35 : An ITU-T standard describing a synchronous, physical-layer
protocol used for communications between a network access device
and a packet network. For speeds up to 48kbps
– X.21 -- An ITU-T standard for serial communications over
synchronous digital lines.
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Name and describe 6 data-link encapsulations
• The WAN data link layer defines how data is encapsulated for
transmission to remote sites
– Frame Relay: uses simplified encapsulation with no error correction over
high-quality digital facilities. A very fast protocol compared to the other
WAN protocols.
– Point-to-Point Protocol (PPP): developed by the IETF. PPP contains a
protocol field to identify the network-layer protocol.
– ISDN: a set of digital services that transmits voice and data over existing
phone lines.
– Link Access Procedure, Balanced (LAPB): For packet-switched networks
used to encapsulate packets at Layer 2 of the X.25 stack. Provides reliability
and flow control on a point-to-point basis.
– Cisco/IETF: Used to encapsulate Frame Relay traffic. The Cisco option is
proprietary and can be used only between Cisco routers.
– High-Level Data Link Control (HDLC): an ISO standard, HDLC not
compatible between different vendors because of the way each vendor has
chosen to implement it. HDLC supports both point-to-point and multipoint
configurations.
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Serial line frame fields
• The two most common point-to-point WAN
encapsulations are HDLC and PPP
• All the serial line encapsulations share a
common frame format, which has the following
fields
• The choice of encapsulation protocol depends on
the WAN technology and the communicating
equipment.
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PPP and HDLC
• PPP is a standard serial-line encapsulation method
– This protocol can check for link quality during connection
establishment.
– Provides authentication through Password Authentication Protocol
(PAP) and Challenge Handshake Authentication Protocol (CHAP).
• HDLC is Cisco's default encapsulation for serial
lines
– No windowing or flow control
– Address field is 11111111, just like PPP
– A proprietary type code is inserted in the frame which means that
HDLC framing is not interoperable with other vendors' equipment.
– Used when both ends of a dedicated-line connection are routers
running Cisco IOS
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Two basic WAN link options
• Dedicated lines are physical circuits that involve no
switching
• Switched lines are broken up into 2 categories:
– Circuit-switched: A physical circuit is established for the duration
of the data transfer
– Packet-switched: Packets may take different physical routes
through the cloud on the way to the destination
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Dedicated Lines
• Dedicated lines, also called leased lines, provide full-time
service. Typically are used to carry:
– Data
– Voice
– Video
• Generally provide core or backbone connectivity between
major sites or campuses, as well as LAN-to-LAN connectivity.
• The following are required for dedicated line connections:
– A router port
– CSU / DSU
– An actual circuit from the service provider.
• Most important dedicated lines are T1, E1, and J1 depending
on where in the world you are located
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Leased Lines
• Leased lines are a form of dedicated lines.
• Dedicated lines also are referred to as point-to-point links because their
established path is permanent and fixed for each remote network
reached through the carrier facilities.
• Connections are made using the router's synchronous serial ports with
typical bandwidth use of up to 2 Mbps (E1) available through the use
of a CSU/DSU.
• Point-to-point links provide a single, pre-established WAN
communications path from the subscriber through a carrier network
(such as a telephone company), to a remote network
• The service provider reserves point-to-point links for the private use of
the customer.
• Point-to-point is used for direct physical links or for virtual links
consisting of multiple physical links.
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Packet-Switched Connections
• Network devices share a (PVC) permanent virtual circuit to transport
packets from a source to a destination across a carrier network,
• Switched networks can carry variable-size frames or fixed-size cells.
• The most common packet-switched network type is Frame Relay.
Others include X.25 and SMDS
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Frame Relay
• Designed to be used over high-speed, high quality digital facilities
• Does not offer much error checking or reliability, but expects upperlayer protocols to attend to these issues
• Connect multiple network devices on a multipoint WAN
• Frame Relay access is typically at 56 kbps, 64 kbps, or 1.544 Mbps
• Each site can be connected to every other by a virtual circuit.
• Frame Relay service is offered through a PVC.
• A data-link connection identifier (DLCI) identifies a PVC
• The DLCI number is a local identifier between the DTE and the DCE
• The DLCI identifies the logical circuit between the source and
destination devices.
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Frame Relay
• Two common topologies can be used in a
Frame Relay solution:
– Fully meshed topology: Every Frame Relay
network device has a PVC to every other device
on the multipoint WAN.
– Partially meshed topology: also often called a
star topology or hub-and-spokes topology. In a
partially meshed topology, not every device on
the Frame Relay cloud has a PVC to every other
device.
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Circuit-switched connections
• A dedicated physical circuit is established,
maintained, and terminated through a carrier
network for each communication session.
• Operates much like a normal telephone call
• Connections from one site to another are brought up
when needed and generally require low bandwidth
• ISDN connections are limited to 64 or 128 kbps
• Used primarily:
– to connect remote users and mobile users to corporate LANs
– as backup lines for higher-speed circuits like Frame Relay
and T1 lines.
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DDR
• Dial on Demand Routing is a technique that routers use to initiate and
close circuit-switched sessions when transmitting end stations need
them.
• DDR means that the connection is brought up only when a specific type
of traffic (interesting traffic) initiates the call or when you need a
backup link.
• DDR is a substitute for dedicated lines when full-time circuit
availability is not required.
• DDR can be used to provide backup load sharing and interface backup
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Describe ISDN
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Terminal Equipment 1 (TE1): Designates a device that is compatible with the
ISDN network. A TE1 connects to an NT of either Type 1 or Type 2.
Terminal Equipment 2 (TE2): Designates a device that is not compatible with
ISDN and requires a TA.
TA: Converts standard electrical signals into the form used by ISDN so that nonISDN devices can connect to the ISDN network.
NT Type 1 (NT1): Connects four-wire ISDN subscriber wiring to the conventional
two-wire local loop facility.
NT Type 2 (NT2): Directs traffic to and from different subscriber devices and the
NT1. The NT2 is an intelligent device that performs switching and concentrating.
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ISDN
ISDN BRI operates mostly over the copper twisted-pair
telephone wiring in place today.
ISDN BRI delivers a total bandwidth of a 144 kbps line
into three separate channels.
Two of the channels, called B (bearer) channels, operate at
64 kbps and are used to carry voice or data traffic.
The third channel, the D (delta) channel, is a 16-kbps
signalling channel used to carry instructions that tell
the telephone network how to handle each of the B
channels.
ISDN BRI often is referred to as 2B+D.
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Good luck on the test !!!