Wan Protocols Iccnwan002

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WAN PROTOCOLS

MODULE ID: ICCNWAN002

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Topics Covered

1. WAN Terminology

2. WAN & OSI

3. WAN Technologies

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WAN Standardization

Organizations that create standards: International Organization for Standards (ISO) American National Standards Institute (ANSI) Electronic Industries Alliance (EIA) Internet Engineering Task Force (IETF) International Telecommunications Union-

telecommunication (ITU-T)

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Defining WAN TermsCustomer premises equipment (CPE)

owned by/located at subscribers premises.Demarcation point

It is spot where the service provider gives freedom to the customer to use his own cable from CPE

Local loop loop to the closest CO (central office)

Central office (CO) This point connects the customers to the providers

switching network. Toll network

Is a trunk line inside a WAN providers network .(is a collection of switches and facilities owned by the ISP)

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WAN Connection Methods

Connection methods Dedicated point-to-point (Known as Leased lines) Circuit-switched (PSTN / ISDN) Packet-switched (X.25,ATM,FR)

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ISDN/LAPD

ISDN/LAPD Circuit-switched technology Dedicated circuit for the length of the

transmissionTwo types of ISDN

Basic rate interface (BRI) Primary rate interface (PRI)

Bandwidth BRI 128 Kbps PRI 1.544 Mbps / 2.048 Mbps

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ISDN/LAPD (continued)

B-channels (bearer channels) 64-kbps

D-channel (delta or data channel) BRI 16 kbps PRI 64 kbps

BRI Two B channels One D channel

PRI 23 B for T1/30 B Channels for E1 One D channel for T1/2 D Channels for E1

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ISDN Components

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ISDN Terminals

Terminal adapter: A converter device that allows non-ISDN devices to operate on an ISDN network.

Terminal Equipment 1 (TE1): A device that supports ISDN standards.

Terminal Equipment 2 (TE2): A non-ISDN device. Network Termination 1 (NT1): A device that is

attached to ISND BRI lines to provide power. It also terminates the 2-wire connection from CO and connects to the 4-wire customer network.

Network Termination 2 (NT2): A provider equipment.

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Reference Points

U The U-interface is the actual two-wire cable which connects the customers equipment to the telecommunications provider

R The R-interface is the wire or circuit that connects TE2 to the TA

S The S-interface is a four-wire cable from TE1 or TA to the NT1 or NT2

T The point between NT1 and NT2, which is also called the T-interface

S/T The interface between NT1 & TA or NT1 & TE

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Connecting to the Provider

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ISDN Switch Types

Interfaces Basic Rate Interface (BRI) Primary Rate (Interface)

Potential Switch Types To Be Obtained from ISDN Providers basic-5ess, basic-dms100, basic-ni,....

Service Profile Identifiers (SPIDs) Reference number assigned to ISDN channels Functions like a phone number Frequently referred to as ISDN phone numbers Most modern ISDN systems now have a feature

called AutoSPID

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ATM: Used within and between LAN connections Based on Frame Relay technology Cell-switched technology Circuit-oriented in the sense that ATM cells follow

the same path for the duration of the connection Cell are fixed length of 53 bytes Provides high-speed data transmission No error correction like X.25 Bandwidth up to 10 Gbps

Asynchronous Transfer Mode (ATM)

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ATM is a cell relay protocol developed by ATM Forum and adopted by ITU-T

A cell is a small data unit of fixed size 53 Bytes long (5 Bytes of header and 48 Bytes of

payload) In a cell network the smallest unit is a cell This

distinction makes the network operation efficient and cheaper

Switching and multiplexing can be implemented in H/W

ATM is created for time-sensitive traffic, providing simultaneous transmission of voice, video, and data.

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Asynchronous Transfer Mode instead of predefined TDM slots, tag each slot with a virtual connection ID ( VCI )

Small packets are used to allow real time data transfer

Fixed sized packets (cells 53 bytes) support fast switching

VCIVCI datadata

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Virtual Circuit Switching

Signaling establishes mapping from (Portin, VCIin) to (Portout, VCIout) at each switch on path.

VCI remapping Cells in a VC arrive in order.

swsw

swswswsw

swsw

P0 P11

P6 P8

P7 P12

P1 P5VCI=4 VCI=3 VCI=27

VCI=3 VCI=16

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WAN Physical Layer

WAN CONNECTION DEVICES

PSTN CO SWITCH

PSTN CO SWITCH

CSU / DSU (DCE)

CSU / DSU (DCE)

ROUTER (DTE) ROUTER (DTE)

LAN LAN

TOLL NETWORK

DEMARCATION LINE

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WAN Physical Standards

Physical WAN serial interface standards EIA/TIA-232 EIA/TIA-449 EIA-530

High-Speed Serial Interface (HSSI) standards V.24 V.35 X.25 X.21 G.703

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Emerging WAN Connection Methods

Broadband access Two new WAN connection methods

Digital subscriber lines (DSL) Cable access with cable modem

DSL Two types of DSL

Asynchronous DSL Symmetric DSL

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Emerging WAN Connection Methods

DSL (continued) Modulates voice and data over existing copper

phone lines Download speeds vary 256 kbps to faster than T1 (1.544 Mbps) or

E1( 2.048 Mbps) Upload speeds are typically slower than download

speeds Speed and cost are attractive Distance limitations to CO

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Emerging WAN Connection Methods (continued)

Cable access and cable modems Uses existing cable TV infrastructure Shared bandwidth Distance limitation not an issue like DSL Need VPN!

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High-Level Data-Link Control Protocol

HDLC specifies an encapsulation method for data on synchronous serial data links using frame characters and checksums.

Default encapsulation used by CISCO. Everyone has its own proprietary HDLC. If your are connecting a CISCO router with another

type router, you must specify an encapsulation type (protocol).

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HDLC FRAME FORMAT

FLAG ADDRESS CONTROL INFORMATION FCS FLAG

8 bits 8 bits 8 / 16 bits variable 8 8 bits

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PPP

PPP is an Internet standard protocol to provide point-to-point, router-to-router, and host-to-host connections.

It supports network layer protocols IP Novell IPX Apple Talk

It can be used over several different physical interfaces Asynchronous serial ISDN synchronous serial High-speed Serial Interface

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PPP Frame Format

0 4 8 12 16 20 24 28 32

Flag(binary 01111110)

Address(binary 11111111)

Control(binary 00000011)

Protocol1st byte

Protocol 2nd byte Information

Information

Information Padding

Padding Frame Check Sequence (FCS)(may also be 4 bytes)Flag

(binary 01111110)

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Establishing PPP Communication

Communication process is established in three steps: Link Establishment Authentication Password Authentication (PAP) Challenge Authentication Protocol (CHAP) Network Layer Protocol negotiation

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Point-to-Point Protocol (PPP)

The basic purpose of PPP is to transport layer 3 packets across a Data Link layer point-to-point link.

It is non-proprietary, PPP can encapsulate several layer 3 routed protocols

and provide authentication, dynamic addressing, and callback

PPP contains four main components: EIA/TIA-232-C, V.24, V.35, and ISDN A Physical layer

international standard for serial communication. HDLC A method for encapsulating datagrams over

serial links.

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Point-to-Point Protocol (PPP)

LCP: A method of establishing, configuring, maintaining, and terminating the point-to-point connection.

NCP: A method of establishing and configuring different Network layer protocols.

NCP is designed to allow the simultaneous use of multiple Network layer protocols.

Examples of protocols here are IPCP (Internet Protocol Control Protocol) and IPXCP (Internetwork Packet Exchange Control Protocol).

PPP protocol stack is specified at the Physical and Data Link layers only.

NCP is used to allow communication of multiple Network layer protocols by encapsulating the protocols across a PPP data link.

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Link Control Protocol (LCP) Options

(LCP) offers different PPP encapsulation options, Authentication Compression Error detection Multilink PPP callback

Authentication: It tells the calling side of the link to send

information that can identify the user. The two methods are PAP and CHAP.

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Link Control Protocol (LCP) OptionsCompression:

It is used to increase the throughput of PPP connections by compressing the data or payload prior to transmission

PPP decompresses the data frame on the receiving end

Error: detection PPP ensures a reliable, loop-free data link

Multilink: This option allows several separate physical paths to

appear to be one logical path at layer 3 For example, two T1s running multilink PPP would

appear as a single 3Mbps path to a layer 3 routing protocol

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Features of PPP

Point-to-Point Protocol (PPP) is an industry-standard protocol.

It uses a Network Control Protocol field in the Data Link header to identify the Network layer protocol.

Allows authentication and multilink connections Can be run over asynchronous and synchronous

links.

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PPP callback

PPP callback can be configured to call back after successful authentication.

A calling router (client) will contact a remote router (server) and authenticate

Both routers must be configured for the callback feature.

Once authentication is completed, the remote router will terminate the connection and then re-initiate a connection to the calling router from the remote router

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PPP Session Establishment

Three phases of session establishment, Link-establishment phase LCP packets are sent by

each PPP device to configure and test the link. Authentication phase If required, either CHAP or

PAP can be used to authenticate a link. Network layer protocol phase PPP uses the

Network Control Protocol (NCP) to allow multiple Network layer protocols to be encapsulated and sent over a PPP data link.

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PPP session establishment

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PPP Authentication Methods

Password Authentication Protocol (PAP): The Password Authentication Protocol (PAP) is

the less secure of the two methods. Passwords are sent in clear text, PAP is only performed upon the initial link

establishment. When the PPP link is first established, the remote

node sends back to the originating router the username and password until authentication is acknowledged.

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PPP Authentication Methods

Challenge Handshake Authentication Protocol (CHAP): CHAP is used at the initial startup of a link and at

periodic checkups on the link to make sure the router is still communicating with the same host.

After PPP finishes its initial link-establishment phase, the local router sends a challenge request to the remote device.

The remote device sends a value calculated using a one-way hash function called MD5.

The local router checks this hash value to make sure it matches.

If the values dont match, the link is immediately terminated.

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Configuring PPP on Cisco Routers

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Frame Relay

Frame Relay provides connection-oriented, Data Link layer communication via virtual circuits. ANSI defines Frame Relay as a connection between the data terminal equipment (DTE) and the data communication equipment (DCE) over high speed digital medium. CSU/DSU is located at customer location and used for encoding, filtering, and translating communication to and from the digital line.

CSU/DSU (channel service unit/digital service unit)

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Frame Relay

Supports many protocols, IP, Novell IPX, Decnet, AppleTalk, ....

Efficient and fast (56Kps to 44.736Mbps) since it does not perform error checking.

Uses both permanent virtual circuits (PVC) and switched virtual circuits (SPC).

Virtual circuits are maintained by a software and multiplexed on onto physical channels.

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Data Link Connection IdentifierFrame Relay virtual circuits are identified by DLCIs. IP address need to be mapped DLCI

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FRAME RELAY FRAME FORMAT

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How Frame Relay works

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WAN Technologies & OSI Layers

OSI Layers WAN Specifications

Network Layer X.25 PLP

Data-link Layer LAPB

Frame Relay HDLC PPP SDLC

MACSub-layer

SMDS

Physical Layer X.21 bis

EIA/TIA-232EIA/TIA-449

V.24 V.35HSSI G703

EIA-530

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Bit Transmission

WAN serial connectors use serial transmission, [one bit at a time over a single channel.]

Parallel transmission pass 8 bits at a time, but all WANs use serial transmission.

Cisco routers use a proprietary 60-pin serial connector/smart-serial, connector

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X.25

An ITU-T standard protocol that defines how connections between user devices and network devices are established and maintained, and that operates effectively regardless of the type of systems connected to the network.

X.25 connections contain both SVCs and PVCs within the physical circuit. X.25 uses the following three protocols, which map to the bottom three layers of the OSI reference model: PLP, which maps to the network layer LAPB, which maps to the data link layer X.21bis, EIA/TIA-232, EIA/TIA-449, EIA-530, and

G.703, which map to the physical layer

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X.25 PLP Frame Format

General Format Indicator: (4 bits) Identifies packet parameters, such as whether the packet carries user data or control information, what kind of windowing is being used, and whether delivery confirmation is required

Logical Channel Identifier: (12 bits) Identifies the virtual circuit (1-4095) across the local DTE to DCE interface. This field consists of a 4-bit Logical Channel Group Number (LCGN) and an 8-bit Logical Channel Number (LCN)

Packet Type Identifier: (8 bits) Identifies one of 17 different packet types

User Data: (varies is size but typically 128 bits) Contain encapsulated user data for data packets or additional control information for other packets

GFI LIC PTI User Data

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LAPB Frame Format

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X.121 Address

The X.121 Address field includes the International Data Number (IDN), which consists of two fields:

Data Network Identification Code (DNIC) and the National Terminal Number (NTN).

DNIC is an optional field that identifies the exact PSN in which the destination DTE device is located.

This field is sometimes omitted in calls within the same PSN. The DNIC has two subfields: Country and PSN. The Country subfield specifies the country in which the destination PSN is located. The PSN field specifies the exact PSN in which the destination DTE device is located.

The NTN identifies the exact DTE device in the PSN for which a packet is destined. This field varies in length.

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Frame Relay

Frame Relay (early 90s) is a Data Link and Physical layer specification that provides high performance.

Frame Relay is a successor to X.25, Frame Relay provides features for dynamic

bandwidth allocation and congestion control

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Frame Relay

Frame Relay is a packet-switched technology. Frame Relay is classified as a non-broadcast

multi-access (NBMA) network, It does not send any broadcasts, such as RIP

updates, across the network by default. Frame Relay is based on X.25. Frame Relay incorporates the components of

X.25 relevant to todays reliable and relatively clean telecommunications networks and leaves out the error-correction components that arent needed anymore.

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Summary

WAN Terminology

Circuit Switched WAN Links

Packet Switched WAN Links

WAN Protocols

WAN Frame Formats

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References

Books: Internetworking Technology Hand Book by Cisco Press

URL: http://www.networkdictionary.com/protocols/wan.php http://www.cisco.com/en/US/docs/internetworking/techn

ology/handbook/Intro-to-WAN.pdf

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Wan Protocols Iccnwan002