CCNA -A Short Notes - 9 - WAN Protocols

Part IX – WAN Protocols

Protocol	Meaning	Type	Layer	Characteristics
X25		Packet Switched	Data-link and Physical	ITU-T standard (International Telephone Union – Telecommunications Standardization Sector) Addresses expressed in decimal numbers in the following format:
Frame Relay		Packet Switched	Data-link and Physical	Connection-oriented and similar to X.25 with less overhead but does not provide error correction. More cost-effective than PPP. Uses Permanent Virtual Circuits (PVC) mostly but also Switched Virtual Circuits (SVC)
HLDC	High-Level Data Link Control	Dedicated Connection Bit Oriented	Data-link	peer-to-peer HDLC not intended to encapsulate multiple Network layer protocols across the same link, which prompted vendors to have their own proprietary HDLC protocol. No authentication is provided by HDLC. Default encapsulation of serial links, which have a default bandwidth of 1.54 Mbps (T1).
SDLC	Synchronous Data Link Control	Bit Oriented	Data-Link	Full-Duplex non peer-to-peer bit oriented serial protocol created by IBM.
ISDN	Integrated Services Digital Network	Circuit Switching	Physical, Data-link and Network, typically used with PPP.	Set of digital services that transmit voice and data over existing phone lines. The Basic Rate Interface (BRI) consists of two B channels at 64 kbps and one D channel at 16 kbps. PRI (Primary Rate Interface) T1 is 23 X 64kbps B channels and 1X 64 kbps D channel, and the PRI E1 is 30 X 64 kbps B channels and 1 X 64kbps D channel.
ATM	Asynchronous Transfer Mode			53-byte cell that allows fast hardware base switching. LANE (LAN Emulation) was created to hite ATM and look like 802.3 Ethernet.
PPP	Point-to-Point Protocol	Dedicated Connection	Data-link	Can be used to create point-to-point links between different vendors’ equipment. Allows authentication and multilink connections and can be run over asynchronous (dial-up) and synchronous (ISDN) links. Created to replace SLIP (Serial Line Internet Protocol) which could only run IP at the Network Layer but was also a dedicated connection protocol. Stacker and Predictor compression methods are supported.
LAPB	Link Access Procedure, Balanced		Data-link	Connection-oriented, has tremendous amount of overhead for links that are error-prone. Defined by X.25 at the data-link layer

Pint-to-Point protocol (PPP): 

Protocol Stack:

OSI Layer	PPP Protocol Stack
3	Upper Layer Protocols such as IP, IPX, AppleTalk
2 LLC	Network Control Protocol (NCP)	Specific to the Network Protocol used. Examples are IPCP (IP Control Protocol) and IPXCP (IPX Control Protocol)
2 MAC	Link Control Protocol (LCP)	Provides authentication with PAP (Password Authentication Protocol) or CHAP (Challenge Authentication Protocol), compression, error detection (with Quality and Magic Number) and multilink (splits the load for PPP over several parallel circuits.)
	High-Level Data Link Control Protocol (HDLC)
1	Physical Layer (such as EIA/TIA-232, V.24, V.35, ISDN

To enable PPP and authentication:

config t 

 hostname hostname

username username password password: password must be the same on both routers, and username corresponds to remote hostnam.e

int s0

encapsulation ppp

ppp authentication chap/pap: PAP is only performed upon the initial link estb and passwords are sent in clear. CHAP forces periodic checks.

sh int s0: verifies the PPP encapsulation.

debug ppp authentication: allows you to verify the PPP authentication configuration. 

Frame Relay: 

Uses the DLCI (Data Link Connection Identifier) which also identify the type of circuit (PVS or SVC) in order to allow two internet devices to communicate end-to-end through the frame relay cloud.

CIR (Committed Information Rate): Metric used when purchasing bandwidth, determining the guaranteed flow of traffic by the service provider. Traffic flow exceeding the CIR will not be guaranteed and retransmissions may occur. 

DE (Discard Eligibility): When a Frame Relay router detects congestion on the network, the DE bit is turned on in. A congested switch will first discard these packets. A CIR of zero will have the DE bit always turned on. 

FECN (Forward-Explicit Congestion Notification): When the Frame Relay network detects congestion in the cloud, this bit is turned on and the destination DTE (Data Terminal Equipment) is informed the path traversed is congested. 

BECN (Backward-Explicit Congestion Notification): When the switch detects congestion in the network, the BECN bit is set and the packet sent to the source router, telling it to slow down the transmitting rate.

To enable Frame Relay. IARP (Inverse-ARP) or static frame-relay maps must also be defined for the Frame Relay devices to talk together:: 

config t 

 int s0 

encapsulation frame-relay [ietf]: Cisco encapsulation is default, use ietf (Internet Engineering Task Force) to connect to non-Cisco devices. 

frame-relay interface-dlci number: number is between 16-1007. 

frame-relay lmi-type cisco/ansi/q933a: Local Management Interface. used only between router and service provider’s switch. Provides information about the local or global significance of the DLCI value and the status of virtual circuits. cisco is default. 

To create subinterfaces once the interface is configured: 

int s0.subintnumber multipoint/point-to-point

To create maps which provide the DLCI to IP address conversion, if inverse-arp cannot be used, static maps must be defined: 

no inverse-arp: inverse-arp, a different and dynamic method for converting DLCI to IP addresses. It must be turned off to enable frame relay maps. 

frame-relay map ip ip dlci [ietf/cisco] [broadcast]: frame relay maps is the only way to mix both cisco and ietf encapsulation types. 

Other commands: 

sh frame-relay ip/lmi/map/pvc [number]/route/traffic: sh frame pvc and sh running-config will indicate DLCI number. 

sh interface: displays LMI information and bandwidth as well as sh frame lmi and DLCI type but not the DLCI number. 

debug frame-relay lmi 

ISDN: Designed to run over existing telephone lines, can support both voice and data and sets up faster than conventional dial-up. Supports virtually every upper-layer protocol and you can choose PPP, HDLC, or LAPD (Link Access Procedure on the D Channel) as your encapsulation protocol. 

TE1: Terminal Eqpt Type 1 understands ISDN standards and plug directly into the U or through a NT1 device in North-America. 

TE2: devices that predate the ISDN standard and require a TA to connect to an NT1. 

NT1: Network Termination 1 implements the ISDN physical layer specifications and connects users to the ISDN network. 

NT2: is a provider’s equipment such as a switch or PBX. Provides Data-Link (Q921) and Network Layer (Q931) implementations. 

TA: converts TE2 wiring to TE1 wiring, and connects to an NT1.

Interface Connection: 

A router’s U interface allows you to connect directly into the local loop (with the conventional two wires) and has a built-in NT1 connector. A S/T interface is a four-wire interface that needs a NT 1 converter from the two-wire ISDN specification and will connect to a TE1 device or to a TE2 device with a TA. 

To enable ISDN: 

config t 

isdn switch-type basic-nil: contact your service provider to find out what switch to use. Can be configured globally or for each BRI.

int bri0 

encap ppp (optional) 

isdn spid1 086506610100 8650661: Service Profile Identifier similar to a phone number.

isdn spid2 086506610100 8650662: one for each channel.