 Introduction to Wide Area Networks 2 nd semester

Outline  Why do we need a WAN?  What is A wide-area network ?  How do WANs and LANs differ?  WAN and OSI model  WAN Devices  WAN Terms  WAN Physical Layer Standards

For the purpose of communication and sharing resources. Computer networks LAN

Why do we need a WAN? Distributed organizational structures Business needs Remote access Individual user needs

Why do we need a WAN?

 Without WANs, LANs would be a series of isolated networks.  WANs allow the information exchange, communication and collaboration between branches, organizations and among employees effectively.  Regional or branch offices of an organization  Organizations need to share information with other customer organizations  Employees ( home or mobile worker)  Home computer users

WAN  A wide-area network (WAN) is a data communications network that extends across a large geographic area.  It interconnects LANs that are usually separated by large geographic areas.

WAN  who own the WAN ?  Is it cost effective for an organization to install its own cable and connect all LANs?  WAN networks often use transmission facilities provided by a service provider, for example, telephone companies.

WAN The major characteristics of WANs are as follows:  They connect networks that are separated by wide geographical areas.  They use the services of common carriers/ service provder such as a telephone network, cable company, or satellite service.  They use serial connections of various types to access bandwidth over large geographic areas.  The world’s most popular WAN is the internet ( our course!)

WAN and LAN What is the difference between WAN and LAN? WANs differ from LANs in several ways:  LAN  a single building or other small geographic area.  WAN  greater geographic distances.  LANs  typically are owned by the company that uses them.  WAN  use services of a WAN service provider.

WAN and OSI model  WAN operations focus primarily on the physical layer (Layer 1) and the data link layer (Layer 2) of the OSI reference model.

WAN Standards  WAN access standards typically describe both physical layer delivery methods and data link layer requirements, including physical addressing, flow control, and encapsulation.  WAN access standards are defined and managed by a number of recognized authorities, including the  Telecommunication Industry Association and the Electronic Industries Alliance (TIA/EIA)  International Organization for Standardization (ISO)  Institute of Electrical and Electronics Engineers (IEEE)

WAN Standards  Unlike Ethernet LAN standards, which define both Layer 1 and Layer 2 details, most WAN standards focus on either Layer 1 or Layer 2  WAN physical layer protocols describe how to provide electrical, mechanical, operational, and functional connections to the services of a communications service provider.  WAN data-link protocols describe how data is encapsulated for transmission toward a remote location, and the mechanisms for transferring the resulting frames.

WAN Physical Layer Concepts  The WAN access physical layer describes the physical connection between the company network and the service provider network.  The WAN physical layer includes several devices and terms specific to wide-area networks.  In the following slides:  WAN Devices  WAN Physical Layer Terminology

WAN Devices  The following devices are used in WANs

Router  Offer many services, including internetworking and WAN interface ports used to connect to the service provider network.  With some types of WAN interfaces, an external device, such as a DSU/CSU or modem is required to connect the router to the service provider.  The routers that reside within the service provider WAN backbone called Core router

WAN Switches  A multiport internetworking device used in service provider networks.  These devices typically switch traffic and operate at Layer 2.

Modem  A modem is a device that interprets digital and analog signals, enabling data to be transmitted over voice-grade telephone lines ( analog lines).  Modulating and demodulating signals ( Modem).

CSU/DSU  For digital lines, a channel service unit (CSU) and a data service unit (DSU) are required.  We won’t go into the differences here.  The CSU/DSU provides signal timing for communication between devices.  The two are often combined into a single piece of equipment, called the CSU/DSU.  The CSU/DSU may be  Separate device like a modem ( External CSU/DSU)  Built into the interface card in the router.

nalhareqi©2015 To routerTo T1 circuit

Access Server  An access server acts as a concentration point for dial-in and dial-out connections

WAN Devices  The type of devices used depends on the WAN technology implemented

WAN Terms  To understand WAN technologies, you need to understand the different WAN terms and connection types that can be used to connect your networks together.

WAN Terms

Customer Premises Equipment (CPE)  The devices and inside wiring located at the premises of the subscriber, connected with a telecommunication channel of a services provider.  The subscriber either owns or leases the CPE.  A subscriber: is a company that arranges for WAN services from a service provider or carrier.

WAN Terms Local loop  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.” Central office (CO)  A local service provider facility or building where local cables link to long-haul fiber-optic communications lines through a system of switches and other equipment.

WAN Terms

Data Communications Equipment (DCE)  Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. ( CSU/DSU )  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. ( Router)  The DTE connects to the local loop through the DCE.

WAN Terms

nalhareqi©2015

WAN Terms Demarcation point  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. nalhareqi©2015

WAN Terms nalhareqi©2015

WAN Physical Layer Standards  WAN physical-layer protocols describe how to provide electrical, mechanical, operational, and functional connections for WAN services.  The WAN physical layer also describes the interface between the DTE and DCE. nalhareqi©2015

WAN Physical Layer Standards  Choosing a protocol is largely determined by the service provider’s method of facilitation  The EIA and ITU-T develops the standards that allow DTEs to talk to DCEs

WAN Physical Layer Standards The DTE/DCE interface for a particular standard defines the following specifications  Mechanical/physical - Number of pins and connector type  Electrical - Voltage levels for 0 and 1  Functional - Specifies the functions that are performed by assigning meanings to each of the signaling lines in the interface  Procedural - Specifies the sequence of events for transmitting data nalhareqi©2015

WAN Physical Layer Standards nalhareqi©2015

Review  Are WANs Necessary?  How do WANs and LANs differ?  Where do WANs operate on the OSI model?  What devices are used in WANs?  WAN terms  WAN Physical Layer standards

Outline  WAN Switching Concepts  Circuit and Packet Switching  WAN Connection Options  Point-to-point Connection  Circuit-switched Connection  Packet-switched Connection  Public WAN connection

WAN Switching Concepts  WAN switching technologies form the carrier backbone based on which it delivers communications services.  WAN switched networks are categorized as either circuit- switched or packet-switched

Circuit Switching  A circuit-switched network is one that establishes a dedicated circuit (or channel) between nodes before the users may communicate.

Packet Switching  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.

Packet Switching  The routers in a packet-switched network determine the links that packets must be sent over based on the addressing information in each packet.  The following are two approaches to this link determination: Connectionless or Connection-oriented

Packet Switching  Connectionless networks:  Full addressing information must be carried in each packet.  Each router must evaluate the address to determine where to send the packet.  An example of a connectionless system is the Internet.  Each packet is treated independently  The destination needs to reorder the packets, and to take care of lost ones

Packet Switching  Connection-oriented networks:  The network predetermines the route for a packet, and each packet only has to carry an identifier.  The router determines the onward route by looking up the identifier in tables held in memory.  All the packets to follow the same route in order of submission.

Circuit and Packet Switching  The cost of packet switching is lower than that of circuit- switching:  Because the links are shared between many users.  Delays (latency) and variability of delay (jitter) are greater in packet-switched networks than in circuit-switched networks.  Because the links are shared and  Because packets must be entirely received at one switch before moving to the next.

WAN Connection Options  There are different WAN connection options to interconnect LANs  These WAN access options differ in technology, speed, and cost. Each has distinct advantages and disadvantages.

Dedicated Connection  Typically referred to as a point-to-point.  It is a pre-established connection from the customer premises through the provider network to a remote destination.  The established path is permanent and fixed for each remote network reached through the carrier facilities which allow communication at any time.  Since point-to-point lines usually are leased from a carrier, it also called leased lines.

Dedicated Connection  Leased lines are available in different capacities.  They generally are priced based on the bandwidth required and the distance between the two connected points.

Dedicated Connection  It uses synchronous serial lines.  Serial transmission means that the bits of a frame are transmitted one at a time over the physical medium.  In WANs, the serial connections are preferred because  Serial cables can be longer than parallel cables.  Synchronization easier than parallel connections.  Simpler wiring and less cost.

Dedicated Connection  A router serial port and a CSU/DSU is required for each leased-line connection.  Synchronization is preserved end to end.  HDLC and PPP Data-link protocols are frequently used on them.

Dedicated Connection Pros  They provide high bandwidth and constant data rate for data transfer.  The dedicated connections removes latency and jitter between the endpoints.  The private nature of a dedicated connection allows a corporation better control over the WAN connection

Dedicated Connection Cons Cost:  Because the line is not shared, dedicated connections tend to be more costly.  Each endpoint needs a separate physical interface on the router, which increases equipment costs. Limited flexibility:  WAN traffic is often variable, and leased lines have a fixed capacity, so that the bandwidth of the line seldom matches the need exactly.

Dedicated Connection  As a general rule, dedicated connections are most cost- effective in the following situations:  Long connect times  Short distances  Critical traffic requirements that must be guaranteed

Circuit-switched Connection  A dedicated physical circuit through a carrier network is established, maintained, and terminated for each communication session.  It establishes a data connections when needed and then terminates it when communication is complete.  In circuit-switched networks, the resources along the path are reserved for the duration of the communication session.

Circuit-switched Connection  It normally provides low bandwidth for data transfer.  The advantage of this WAN service is low cost, where subscribers only pay for the duration of the usage.  The two most common types of circuit-switched WAN technologies are the public switched telephone network (PSTN) and the Integrated Services Digital Network (ISDN).

Circuit-switched Connection PSTN (Dialup)  Transporting binary computer data through the voice telephone network using a modem.  It is an option for WAN connection when no other WAN technology is available.  It is suitable when intermittent, low-volume data transfers are needed.

Circuit-switched Connection PSTN (Dialup)  The advantages of modem and analog lines are simplicity, availability, and low implementation cost.  The disadvantages are :  The low data rates and a relatively long connection time.  The dedicated circuit has little delay or jitter for point-to-point traffic, but voice or video traffic does not operate adequately at these low bit rates.

Circuit-switched Connection ISDN  is a circuit-switching technology that enables the local loop of a PSTN to carry digital signals, resulting in higher-capacity switched connections.  ISDN changes the internal connections of the PSTN from carrying analog signals to time-division multiplexed (TDM) digital signals.  TDM allows two or more signals or bit streams to be transferred as subchannels in one communication channel.

ISDN turns the local loop into a TDM digital connection. This change enables the local loop to carry digital signals that result in higher-capacity switched connections

Packet-switched Connection  Packet switching connection is a technology based on the transmission of data in packets.  Packets are routed through a carrier network based on the destination address contained within each packet.  Examples of Packet switched communication links :Frame Relay and X.25.

Packet-switched Connection  Dividing a data into packets enables data from one or more sources to one or more destinations to share the communication channels within the carrier network.  In this technology, a customer network uses a single point- to-point link to a service provider to transport packets intended for one or more destinations across a carrier network

Packet-switched Connection  The carrier then create virtual circuits between customers’ sites by which packets of data are delivered from one to the other through the network.

Packet-switched Connection  This WAN service allows the sharing of bandwidth with other companies to save money.  It only works well for data transfer in bursty nature; hence leased lines would be the better choice if constant data transfer is required.

Public WAN connection  Public connections use the global Internet infrastructure.  Service provider offers broadband Internet access using digital subscriber line (DSL), cable, and satellite access.  Broadband connection options are typically used to connect small offices and telecommuting employees to a corporate site over the Internet.  Data traveling between corporate sites over the public WAN infrastructure should be protected using VPNs.

Outline  The Hierarchical Model  Core Layer  Distribution Layer  Access Layer

The Hierarchical Model  The Hierarchical internetworking model is a three-layer model for network design first proposed by Cisco.  It divides company networks into three layers: core, distribution, and access layer, each layer focuses on specific functions

The Hierarchical Model

Core Layer  The core layer is a high-speed, highly-redundant switching and routing backbone that move packets between distribution-layer devices in different regions of the network.  It should be designed to pass network traffic as fast as possible.  Core switches and routers are usually the most powerful, in terms of raw forwarding power.

Core Layer  This layer of the network should not perform any frame or packet manipulation, such as access lists and filtering, which would slow down the switching of traffic and in turn result in less than a "high-speed" environment.

Distribution Layer  Distribution layer is the isolation point between the network’s access layer and core layers.  The distribution layer is used for policy base services. It is the smart layer in the three-layer model. Routing, filtering, and QoS policies are managed at the distribution layer.

Access Layer  The access layer is the point at which local end users are allowed into the network.  It responsible for providing access to different network resources.  Access layer includes shared LAN, switched LAN and VLAN

CH1 Learning Outcomes (LOC)  WAN overview  WAN terms, WAN devices, WAN PHY Layer  WAN Switching Concepts  WAN connection types: Dedicated leased lines, Circuit switched, Packet switched, public connections  WAN design including core, distribution, and access layers.