1. Introduction to Wide Area Networks

2. Outline WAN Switching Concepts WAN Connection Options
Circuit and Packet Switching
WAN Connection Options
Point-to-point Connection
Circuit-switched Connection
Packet-switched Connection
Public WAN connection
The WAN Hierarchical Model
Core Layer
Distribution Layer
Access Layer

3. Outline WAN Switching Concepts WAN Connection Options
Circuit and Packet Switching
WAN Connection Options
Point-to-point Connection
Circuit-switched Connection
Packet-switched Connection
Public WAN connection
The WAN Hierarchical Model
Core Layer
Distribution Layer
Access Layer

4. 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

5. Circuit Switching
A circuit-switched network is one that establishes a dedicated circuit (or channel) between nodes before the users may communicate.
circuit switching dynamically establishes a dedicated virtual connection for voice or data between a sender and a receiver. Before communication can start, it is necessary to establish the connection through the network of the service provider. It is important to note that the circuit must remain established and never change or communication will be terminated.
If the circuit carries computer data, the usage of this fixed capacity may not be efficient. For example, if the circuit is used to access the Internet, there is a burst of activity on the circuit while a web page is transferred. This could be followed by no activity while the user reads the page, and then another burst of activity while the next page is transferred. This variation in usage between none and maximum is typical of computer network traffic. Because the subscriber has sole use of the fixed capacity allocation, switched circuits are generally an expensive way of moving data.
The two most common types of circuit-switched WAN technologies are the public switched telephone network (PSTN) and the Integrated Services Digital Network (ISDN).

6. 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.

8. 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

9. 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

10. 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.

11. 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.

12. Outline WAN Switching Concepts WAN Connection Options
Circuit and Packet Switching
WAN Connection Options
Point-to-point Connection
Circuit-switched Connection
Packet-switched Connection
Public WAN connection
The WAN Hierarchical Model
Core Layer
Distribution Layer
Access Layer

13. 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.
There are several WAN access connection options that ISPs can use to connect the local loop to the enterprise edge.

14. Corporate networks can be interconnected using private WAN infrastructures and public WAN infrastructures.
As summarized in Figure 2-10, an enterprise can get WAN access over a
Private WAN infrastructure: Service providers may offer dedicated point-to-point leased lines, circuit-switched links, such as PSTN or ISDN, and packet-switched links, such as Ethernet WAN, ATM, or Frame Relay.
Public WAN infrastructure: Service provider may offer 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.

15. 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.
connects two devices over a WAN
with no setup procedures before transmitting data.
Leased lines give the devices on each end (typically routers) the ability to send data to each other at the same time. Leased lines are also permanently installed, meaning that the devices can send data to each other at any time.
hence a circuit does not need to be established before data transmission).
Point-to-point lines usually are leased from a carrier and are also called leased lines.

16. To create a point-to-point WAN link, a company must use the services of a telephone company (telco) or other company that sells WAN services.
To install a new leased line, a company must order the leased line from a telco or other company that sells such services. The order form for the leased line lists the street address of each site, the exact location inside the building to which the telco should install its cables, and the speed at which the leased line should run. The telco then can physically install cables into the buildings, to the correct floor and room, to provide a physical link over which bits can be sent between the two devices.
Additionally, the telco requires a special type of networking device to be attached to the end of the leased line. This device, called a channel service unit/data service unit (CSU/DSU) , helps protect the telco’s equipment electrically and provides many other functions to make the leased line work.
The leased line from the telco acts as if it were a single cable, with two twisted pairs: one for transmission in each direction.
However, the telco does not actually run a cable between the two routers, but instead uses other technology that is beyond the scope of this book and the related course. So, the telco cloud and lightning-bolt line represent the fact that the details are hidden and unimportant for this discussion.

17. 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.

18. 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 .
Serial cables can be longer than parallel cables, because there is much less interaction (crosstalk) among the conductors in the cable
cost of cable and synchronization difficulties make parallel connections impractical.

19. 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.
Leased line serial connections typically connect to a transport service provider through a data communications equipment (DCE) device, which both provides a clock and transforms the signal to the channelized format used in the service provider network
The CSU connects to the service provider network, while the DSU connects to the network device serial interface. It is a device (or sometimes two separate digital devices) that adapts the media format from a serial data terminal equipment (DTE) device, such as a router, to the media format of the service provider equipment, such as a WAN switch, in a switched carrier network. The CSU/DSU also provides signal clocking for synchronization between these devices

20. 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 connections are ideal for high-volume environments with steady rate traffic patterns or high peak demands of critical traffic.
The advantages of leased lines include
Simplicity: Point-to-point communication links require minimal expertise to install and maintain.
Quality: Point-to-point communication links usually offer high service quality, if they have adequate bandwidth. The dedicated capacity removes latency or jitter between the endpoints.
Availability: Constant availability is essential for some applications, such as e-commerce. Point-to-point communication links provide permanent, dedicated capacity, which is required for VoIP or Video over IP.

21. 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.
Leased lines have a fixed capacity; if WAN traffic is variable, some of the capacity is unused
The disadvantages of leased lines include
Cost: Point-to-point links are generally the most expensive type of WAN access. The cost of leased line solutions can become significant when they are used to connect many sites over increasing distances. In addition, each endpoint requires an 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. Any change to the leased line generally requires a site visit by ISP personnel to adjust capacity.

22. 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

23. 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 switching Sets up line like a phone call. No data can transfer before the end-to-end connection is established.

25. 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) .
Because of the switching operation used to establish the circuit, the telephone system is called a circuit-switched network. If the telephones are replaced with modems, then the switched circuit is able to
carry computer data.

26. 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.
Dialup WAN access may be required when no other WAN technology is available. For example, a remote location could use a m
Traditional telephony uses a copper cable for the local loop to connect the telephone handset in the subscriber premises to the CO. The signal on the local loop during a call is a continuously varying electronic signal that is a translation of the subscriber voice into an analog signal.
Traditional local loops can transport binary computer data through the voice telephone network using a modem.
The modem modulates the binary data into an analog signal at the source and demodulates the analog signal to binary data at the destination. The physical characteristics of the local loop and its connection to the PSTN limit the rate of the signal to less than 56 Kbps.
odem and analog dialed telephone lines to provide low-capacity and dedicated switched connections.

27. 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.

28. 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.
The signals appear to transfer simultaneously, but physically they take turns on the channel.

29. ISDN turns the local loop into a TDM digital connection
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

30. 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.
Many WAN users do not make efficient use of the fixed bandwidth that is available with dedicated or switched circuits, because the data flow fluctuates.
Communications providers have data networks available to more appropriately service these users.
In packet-switched networks, the data is transmitted in labeled frames, cells, or packets.

31. 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.
the bandwidth is sharing with other companies 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.
In a packet switching set-up, networks have connections into the carrier’s network, and many customers share the carrier’s 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
The carrier then create virtual circuits between customers’ sites by which packets of data are delivered from one to the other through the network.
Because this allows the carrier to make more efficient use of its infrastructure, the cost to the customer is generally much better than with point-to-point lines.
Packet-switched networks offer an administrator less control than a point-to-point connection, and the bandwidth is shared statistically. However, the cost is generally less than a leased line. With WAN speeds comparable to those of leased lines, packet-switched networks are generally suitable for links between two large sites that require high link utilization or present high peaks of critical traffic.

32. 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.
Until recently, the Internet was not a viable networking option for many businesses because of the significant security risks and lack of adequate performance guarantees in an end-to-end Internet connection.

33. Outline WAN Switching Concepts WAN Connection Options
Circuit and Packet Switching
WAN Connection Options
Point-to-point Connection
Circuit-switched Connection
Packet-switched Connection
Public WAN connection
The WAN Hierarchical Model
Core Layer
Distribution Layer
Access Layer

34. 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

35. The Hierarchical Model

36. 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.
Since core layer is the backbone of any network and providing services to other layers therefore this layer is reliable and have availability, also must be Redundant and have load balancing between its different links. Cisco recommends that Core layer should have mesh topology and there should be no stuff like ACL, packet handling etc.

37. 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.

38. 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.
is the point in the network at which packet manipulation can take place. The distribution layer is where access lists and filtering (based on Layer 2 MAC or Layer 3 network addresses) will take place, providing network security. The distribution layer is also where broadcast domains are defined and traffic between VLANs is routed. If there is any media transition that needs to occur, such as between a 10-Mbps Ethernet and 100-Mbps Fast Ethernet network segment, this transition also happens at the distribution layer.
Distribution is normally a boundary between mediums in network.

39. 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

40. 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.