wans. table of contents wan technology & devices wans & the osi model wan encapsulation...

Table of Contents

WAN Technology & Devices

WANs & The OSI Model

WAN Encapsulation Formats

WAN Link Options

Go There!

Go There!

Go There!

Go There!

WAN Technology & Devices

Table of Contents

WAN Services

A WAN is the communications network that connects LANs through a WAN Service Provider (e.g. RBOC)

WANs operate at the first three layers of the OSI, but focus mainly on the physical and data link layers.

Examples of WAN Services include….

Call-setupSS7 used for telephone calls

ISDNA circuit-switched service using TDM, which allocates bandwidth to different

sources on the same media

Frame RelayA packet-switched service using statistical multiplexing

WAN Physical Structure

Toll Network – collection of switches/trunks in WAN cloud

CO Switch – nearest point of presence for the WSP’s service

Local loop – extends from the CPE (at the demarc) to the CO

CPE – devices located on premises, either owned or leased

DTE/DCE Interface

The transfer of responsibility for service between the ISP and the customer occurs at the DTE/DCE interface.

The DTE generates the data and passes them, along with any necessary control characters to a DCE.

The DCE converts the signal to a format appropriate to the transmission medium and introduces it into the network link.

(Reverse process at the receiving end)

WAN Virtual Circuits

Switched Virtual Circuits (SVCs) are WAN paths to the destination established and terminated on demand.

Three phases:Circuit establishment – creates the virtual circuitData transfer – sending and receiving user dataCircuit termination – tearing down the virtual circuit

Telephone service and ATM use SVCsIncreased use of bandwidth but decreased cost

Permanent Virtual Circuits (PVCs) are permanently established circuits with one mode: data transfer

X.25 and Frame Relay use PVCsDecreased use of bandwidth but increased cost

Link Types & Bandwidth

Line Type Signal Standard Bit Rate Capacity56 DS0 56 kbps64 DS0 64 kbpsT1 DS1 1.544 MbpsE1 ZM 2.048 MbpsE3 M3 34.064 MbpsJ1 Y1 2.048 MbpsT3 DS3 44.736 MbpsOC-1 SONET 51.84 MbpsOC-3 SONET 155.54 MbpsOC-9 SONET 466.56 MbpsOC-12 SONET 622.08 MbpsOC-18 SONET 933.12 MbpsOC-24 SONET 1.21 GbpsOC-36 SONET 1.82 GbpsOC-48 SONET 2.43 Gbps

WAN Devices

In order to connect to a leased line, the customer must have…

Access to the service provider’s circuitAn appropriate router port availableAn a CSU/DSU, modem or ISDN Terminal Adapter

Routers

Routers offer many services including:

InternetworkingWAN serial interfaces

Routers can operate as...

Internal RoutersBackbone Routers Area Border RoutersAutonomous System Boundary Routers

Modems

Also called CSU/DSUs (channel service units/digital service units)

Interface with voice-grade connection in order to convert analog signal to digital.

Represents the DCE side of the DTE/DCE connection.

Leased line

Router RouterCSU/DSU CSU/DSU

WANs & The OSI Model

Table of Contents

WAN Standards

What layers of the OSI model do WAN standards describe?

Physical and Data Link Layers

WAN Physical Layer

Protocols that describe how to provide electrical, mechanical, operational, and functional connections for WAN services.

These services are most often obtained from WAN service providers such as RBOCs, alternate carriers, post, telephone and telegraph (PTT) agencies.

Describes the interface between the data terminal equipment (DTE) and the data circuit-terminating equipment (DCE).

WAN Physical Layer

Typically, the DCE is the service provider and the DTE is the attached device.

In this model, the services offered to the DTE are made available through a modem or a CSU/DSU.

WAN Physical Layer

Several physical layer standards specifying this interface between the DTE & DCE are...

EIA/TIA-232 EIA/TIA-449 V.24 V.35 X.21 G.703 EIA-530

WAN Data-Link Layer

WAN data link protocols describe how frames are carried between systems on a single data link.

They include protocols designed to operate over dedicated point-to-point, multipoint, and multi-access switched services.

WAN standards are defined and managed by a number of recognized authorities, including the following agencies: ITU-T, ISO, IETF, & EIA

WAN Encapsulation Formats

Table of Contents

WAN Data-Link Encapsulations

PPP (Point-to-Point Protocol)

Developed by IETF; replacing SLIPContains a field to identify the network layer protocolPPP can check for link quality during connection establishmentSupports PAP (Password Authentication Protocol) & CHAP (Challenge Handshake Authentication Protocol)


High-Level Data Link Control (HDLC)

Cisco default encapsulation; typically used between routers running Cisco IOS; replacing SDLCStreamlined: no windowing or flow control may not be compatible with different vendors because of the way each vendor has chosen to implement it. HDLC supports both point-to-point and multipoint configurations with minimal overhead


Frame Relay

uses high-quality digital facilities; uses simplified framing with no error correction mechanisms (connectionless!!);it can send Layer 2 information much more rapidly than other WAN protocols

WAN Link Options

Table of Contents

• T1, E1, T3, E3• xDSL• SONET

Switched

• POTS• ISDN

• X.25• Frame Relay• ATM (cell)• SMDS (cell)

WAN Link Options

Circuit Switched

Packet/Cell Switched

Dedicated

Dedicated Digital Services

T series in U.S. and E series in Europe

Uses time division multiplexing to “slice up” data and assign time slots for transmissions T1 = 1.544 Mbps T3 = 44.736 Mbps E1 = 2.048 Mbps E3 = 34.368 Mbps

•Uses twisted pair & fiber•Extremely popular•Moderate cost

Dedicated Digital Services provide full-time connectivity through a point-to-point link


Digital Subscriber Lines (xDSL); the x stands for a family of technologies

WAN Technology for home use; decreasing bandwidth with increasing distance from the phone companies CO.Data rates as high as 51.84 Mbps but more common to be in the 100s of KbpsVarieties include HDSL, SDSL, ADSL, & VDSLModerate expense and getting cheaper


Synchronous Optical Network (SONET)

Specialized high bandwidth technology for use at various Optical Carrier speeds (OC) ranging from 51.84 Mbps (OC-1) to 9,952 Mbps (OC-192)Uses lasers to divide the wavelength of the light into sections that can carry large amounts of data (Wave Division Multiplexing)Very expensive; used by large ISPs and other Internet backbone entities.


Switched

• POTS• ISDN


WAN Link Options

Circuit Switched


Dedicated

Circuit Switched Services

Plain Old Telephone System (POTS)

Not a computer data service but... POTS is an important component of our communication

infrastructure and It is still the standard for designing reliable networks


Integrated Services Digital Network (ISDN)Historically important--first dial-up digital serviceProvides both voice & data transmission over existing phone linesCost is moderate; max. bandwidth = 128 kbps for BRI (Basic Rate Interface)2 B channels @ 64kps and 1 D channel @ 16kpsB channels are voice/data channels; D for signaling

B

B

D


Switched

• POTS• ISDN


WAN Link Options

Circuit Switched


Dedicated

Packet Switched Services

X.25 (Connection-oriented)

Older WAN technology developed in 1970sReliable--X.25 has been extensively debugged and is now very stable--literally no errors in modern X.25 networksStore & Forward--Since X.25 stores the whole frame to error check it before forwarding it on to the destination, it has an inherent delay (unlike Frame Relay) and requires large, expensive memory buffering capabilities.


Frame Relay (Connectionless)

More efficient and much faster than X.25Packet switched version of ISDN (which is circuit switched); data rates up to 44.736Mbps with 56kbps and 384kbps being the most popularUsed mostly to forward LAN IP and IPX packets but can be used to forward other types of trafficPrimary competitive advantage is its low cost

Cell Switched Services

Asynchronous Transfer Mode (ATM)Relatively new WAN Technology related to broadband ISDN; max. bandwidth = 622 MbpsDeveloped in order to provide one technology for both WANs and LANs to transport data, video, and voice. (High Cost)Key Benefits: One network for all traffic--voice, data, video Compatible with current wiring infrastructure (cable plant) Very flexible and scalable Simplifies network management


Switched Multimegabit Data Service (SMDS)

Closely related to ATM; SMDS is the MAN (Metropolitan Area Network) implementation of ATMHigh Cost with max. bandwidth 44.736 Mbps

Acronym Name Max. Bandwidth Comments

T1, T3 T1, T3 1.544 & 44.736 Mbps Widely used telecommunicationsxDSL Digital Subscriber Line 384 kbps New technology over phone lines

SONETSynchronous Optical Network

9,992 Mbps Very fast optical fiber transmission

POTSPlain Old Telephone Service

4 kHz Analog The Standard for Reliability

ISDNIntegrated Services Digital Network

128 kbps Data and Voice Together

X.25 X.25 An Old Reliable, WorkhorseFrame Relay Frame Relay up to 44.736 Mbps A flexible new workhorse; son of ISDN

ATMAsynchronous Transfer Mode

622 Mbps High powered Networks

SMDSSwitched Multimegabit Data Service

1.544 & 44.736 Mbps MAN variant of ATM





WAN Link Options Review

Table of Contents

End Slide Show

wans. table of contents wan technology & devices wans & the osi model wan encapsulation...

Documents

wan devices

wan service providers

wan standards

wan cloud

wan paths

wan virtual circuits

leased slide

examples of wan services