WAN technologies are Analogue Dialup, ISDN DSL, Cable, Frame Relay, ATM, Leased Lines and X.25. These operate at layer 2 of the OSI model.
Analogue Dialup: Uses regular telco lines to transmit analogue data at 56Kbps
ISDN: Digital transmission using two different channels.
-B or Bearer channel for voice and data
-D or delta channel for setting up and terminating the call.
Types of ISDN.
Basic Rate Interface (BRI). Two 64kbps B (voice & data) channels and one 16kbps D (call setup & termination) channel. 1 DS0
Primary Rate Interface (PRI). 23 64kbps B channel and 1 64kbps channel ( speed of a T1 line). 24 DSO which equals to DS1 . (1.544Mbps)
Leases lines are point to point lines to an ISP and paid monthly. Speeds range from 56kbps. A router serial port is required for each leased line connection. A CSU/DSU and the
actual circuit from the service provider are also required.
Uses PVC and SVC to provide connectivity between two locations
ATM. (Asynchronous Transfer Mode). Operates at high bandwidths using a cell technology. Data is split into 53 byte cells for faster transmission. Minimizes delay and jitter over the line.
DSL. Uses a regular telephone line to transmit data at higher frequencies above 4kHz, thereby improving the speed of transmission. It provides an always on- connection for instant connectivity. Multiple DSL connections are terminated or multiplexed at the ISP using the DSLAM( DSL Access Multiplexer.. DSL uses TDM technology to aggregate many subscriber lines.
Types of DSL
Asymetric DSL. Higer download than upload
Symetric DSL. Same download and upload capacity
Other variations of ADSL include
CDSL (Consumer DSL also known as G.Lite or G.992.2
VDSL (Very-righ-rate DSL)
CABLE uses coax cable to provide an always-on connection
Common WAN line Types and connection speed
Line Signal speed
56K DS0 56Kbps
64 DS0 64Kbps
T1 DS1 1.544Mbps
E1 ZM 2.048Mbps
E3 M3 34.064 Europe
T3 DS3 44.736Mbps
OC-1,- 48 SONET 51.84Mbps to 2488.32Mbps
Operates at Layers 1 & 2 of the OSI
Layer1 1 is concerned with the Physical Addressing and Flow Control. Layer 2 takes care of the encapsulation methods.
Layer 1 connection media
A 25 pin D connector. Signal speed is 64Kbps over short distances
A 36 pin D connector. Signal speed is 2Mbps over long distances
EIA/TIA-612/613. HSSI (High Speed Serial Interface).
A 60 pin D connector with signal speed of 52Mbps
An ITU-T standard for synchronous communication between network access devices and packet network at speeds of 48Kbps. A 34 pin rectangular connector
An ITU-T standard for synchronous digital communication. A 15 pin D connector
Layer 2 WAN Protocols
Frame Relay, HDLC, PPP, ATM
A circuit-switched network establishes a dedicated circuit (or channel) between nodes and terminals before the users may communicate. PSTN & IDN are circuit-switched technologies.
Packet switching splits traffic data into packets that are routed over a shared network. Packet-
switching networks do not require a circuit to be established, and they allow many pairs of nodes to communicate over the same channel. Packets are routed based on the connection type:
Connectionless or Connection-oriented
This method carries full addressing information in each packet. Each switch must check the
address to determine where to send the packet.
predetermines the route for a packet, and each packet only has to carry an identifier. The switch determines the onward route by looking up the identifier in tables held in memory. The set of entries in the tables identifies a particular route or circuit through the system. If this circuit is only physically in existence while a packet is
traveling through it, it is called a virtual circuit (VC)
Packet-switched networks may establish routes through the switches for particular end-to-end connections. These routes are called virtual circuits. A VC is a logical circuit created within a shared network between two network devices. Two types of VCs exist
Permanent Virtual Circuit (PVC)
A permanently established virtual circuit only for data transfer.PVCs are used in situations in which data transfer between devices is constant.. PVCs decrease the bandwidth use associated with establishing and terminating
VCs, but they increase costs because of constant virtual circuit availability. PVCs are generally
configured by the service provider when an order is placed for service.
Switched Virtual Circuit (SVC)
SVC is a VC that is dynamically established on demand and terminated when transmission is complete. Communication over an SVC consists of three phases: circuit establishment, data transfer, and circuit termination
The establishment phase creates the VC between the source and destination devices.
Data transfer involves transmitting data between the devices over the VC, and the circuit termination phase
involves tearing down the VC between the source and destination devices.
SVCs are used in situations in which data transmission between devices is intermittent, largely to save costs. SVCs
release the circuit when transmission is complete, which results in less expensive connection charges than those incurred by PVCs, which maintain constant virtual circuit availability.
Examples of packet- or cell-switched connections include:
Private WAN connections include both Dedicated and switched
Dedicated connections are required when point-to-point lines are used with various
capacities that are limited only by the underlying physical facilities and the willingness of users to
pay for these dedicated lines. A point-to-point link provides a pre-established WAN communications
path from the customer premises through the provider network to a remote destination. Point-to-
point lines are usually leased from a carrier and are also called leased lines
Switched communication links.
In packet-switched networks, the data is transmitted in labelled frames, cells, or packets. Packet-switched
communication links include Frame Relay, ATM, X.25, and Metro Ethernet
Dynamic switching that establishes a dedicated virtual connection for voice or data between a sender and a receiver.
PSTN & ISDN
Serial Point-To-Point Links
A fundamental part of a WAN is the link used in transmission. A popular WAN transmission method over a serial link is TDM (Time-division multiplexing).
TDM can send more data by using time slots. Multiple devices can transmit at the same time using TDM.
A second aspect is the demarcation points or demarc. This is the meeting point of responsibility or the provider and customer.
The DTE is the device that provides the WAN or internet connection. The DTE (Data Terminal Equipment) is the customer using the device.
The DCE sets the rate at which the link operates (synchronously). Encapsulation is then required for the data to be sent.. Any of the following WAN protocols can be used to encapsulate the data:
Frame Relay, HDLC, PPP or ATM
Customer Premises Equipment (CPE)
The devices and inside wiring located at the premises of the subscriber, connected with a telecommunication
Channel of a carrier. The subscriber either owns or leases the CPE. A subscriber, in this context, is a company that arranges for WAN services from a service provider or carrier.
Data Communications Equipment (DCE)
Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.
Data Terminal Equipment (DTE)
The customer devices that pass the data from a customer network or host computer for transmission over the WAN. The DTE connects to the local loop through the DCE.
The copper or fiber cable that connects the CPE at the subscriber site to the central office (CO) of the service provider. The local loop is sometimes called the “last mile.”
A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop. It is usually placed for easy access by a technician. The demarcation point is the place where the responsibility for the connection changes from the user to the service provider. This is very important, because when problems arise, it is necessary to determine whether the user or the service provider is responsible for troubleshooting or repair.
Central office (CO)
A local service provider facility or building where local cables link to long-haul, all-digital, fiber-optic
communications lines through a system of switches and other equipment.