Network knowledge: WAN hardware

The WAN hardware you use depends on the WAN service you want to connect to. Each WAN protocol has different specifications and requirements for hardware and transmission media. However, with your choice, there are many hardware that can be compatible with many different WAN services.

The WAN service provider is responsible for the WAN and provides the local loop connection (Local loop) to the Boundary Point (Demarc) (see the Internet as simple as 2/2004). The terminal cable is usually copper cable, the same type of wire used for telephone service.

Set up phone lines

Many households and businesses now use 4-wire cables with 2 twisted-pair pairs: the first pair is used for phones and the second pair is for backup. This allows new businesses to be ready to connect to the WAN without having to install new line systems. A similar signal line using two copper wires and a digital signal line can use two wires or all four end-connected copper cables depending on the type of WAN connection. Phone companies need to modify line switching at the central office to be able to transmit digital signals on the terminal cable.

Copper conductors are classified by bandwidth. The bandwidth, in turn, determines the amount of data you can send and the transmission signal is the same or the digital signal. Below we will study two methods of bandwidth classification on copper cables.

Plain Old Telephone Service (POTS)

The analog phone system only sends an analog signal on each pair of wires: each of these separate signals is considered a channel. Using POTS and modems to send analog signals gives you a 64Kbit / s channel, of which only 56Kbit / s of bandwidth is available for data transmission. Traditional modems and telephone lines are quite suitable for the purpose of using the Internet to send email and some other common tasks. However, if you need to send and receive large amounts of data, it will take a long time.

POTS services have the following characteristics:

- The current lines only use two twisted pairs
- Signal on the terminal cable is the same signal.
- Need modem to convert digital signal into analog signal
- Network knowledge: WAN hardware Picture 1 The effective speed of the line is limited to 56 Kbit / s


Figure 1: Internal WAN connection via telephone line

T-Carries

The physical layer of many US WAN systems is based on T-Carrier technology developed by Bell / AT & T. T-1 lines use all four copper wires: one for sending and one for receiving data. They do not use additional wires but establish virtual channels. Fiber optic cables and other types of transmissions are used for the End-to-End Cables allowing higher data transfer rates.

T-carrier technology has the following characteristics:

- Use two pairs of twisted copper wire cables
- Use digital signals
- Support multiple 64 Kbit / s channels on one wire

T-carrier lines are classified based on the number of channels it can support

+ T1 (24 channels, used in the US)
+ E1 (31 channels, used in Europe)

T-carrier lines are also classified according to the type of data that will be transmitted on the line (eg pure data, digital audio, digital images .). Moreover, users can register a part of T1 line service and use some of its available channels.

Note : T-carrier lines separated for bandwidth descriptive purposes, this is not WAN protocols. For example, ISDN is a WAN service that uses digital signal transmission via four wires. The bandwidth of ISDN depends on how much capacity of the T1 line is used.

ISDN Basic Rate (BRI)

ISDN Basic Rate consists of 2 channels of 64Kbit / s (called B channels) and a 16 Kbit / s channel (called D channel). So it is also called 2B + D. B channels transmit data, audio and digital images. Channel D is the service channel used for both data and control information. ISDN BRI is reasonable for households and small businesses that need higher data transfer rates than traditional modems.
Network knowledge: WAN hardware Picture 2
Figure 2: BRI

Here are the two most typical cases of using ISDN BRI:

- A B channel is used for voice, the other channel is used for data
- Both channels are used for data transmission at a total speed of 128 Kbit / s

Note : The total bandwidth of ISDN BRI is 144 Kbit / s (2 B channels and 1 D channel) while [/ i] the data transfer rate is 128 Kbit / s in total (data is only sent over 2 channel B)

ISDN Primary Rate (PRI)

In the US, Primary Rate ISDN uses all T1 lines, supports 23 B 64 Kbit / s B channels and a 64 Kbit / s D channel, so it is called 23B + D. ISDN PRI used in businesses requires a high speed connection, which is frequently turned on.

In Europe, Primary Rate is often called 30B + D because it uses the entire E-1 line to support 30 B channels and 1 D1 channel.

In addition to the line, you need hardware to connect to the WAN and correctly format the signal for the type of connection you use. For example, hardware may be modems that convert digital signals to analog signals. You will use one or two types of t Network knowledge: WAN hardware Picture 3 The hardware device below for fully digital networks.

Figure 3: PRI

Multiplexer (Multiplexer)

As shown in the figure below, the multiplexer operates at both ends of the transmission line. At the signal sender, multiplexer is a device that combines signals from two or more other devices to transmit on a transmission line. At the receiving end, a multiplexer with a channel solver will separate the combined signal into the original signal as the original. Many routers on the WAN have built-in multiplexers.
Network knowledge: WAN hardware Picture 4
Figure 4: Multiplexer

Statistical multiplexer: Use separate virtual channels on the same physical path to send different signals simultaneously. (signals are transferred at the same time on the line)

Time-division multiplexer: Send data packets of different signals at different time intervals. Instead of dividing the physical transmission line into channels, it allows data streams to use the transmission line at specified time 'slots' (signals are used in turn for short periods of time).

CSU / DSU (Chanel Service Unit / Data Service Unit)

This is a device that connects networks with high-speed transmission like T-1. This device formats the data streams into framing formats and determines the transmission code for the digital transmission lines. Some CSU / DSU are also multiplexers, or built-in routers. You may also hear about CSU / DSU as a digital modem but this is not entirely accurate. Modem converts data from analog to digital and vice versa while CSU / DSU only reformats existing digital form data.
Network knowledge: WAN hardware Picture 5
Figure 5: CSU / DSU

- CSU receives the signal and transmits the received signal to the WAN line, reflecting the response signal when the telephone company needs to check the device and prevent electromagnetic interference.

- DSU is similar to a modem between DTE and CSU. It converts data frames from the LAN format to the T-1 format and vice versa. It also manages lines, time division errors and signal reproduction.

Interface protocols

There are different types of 'interface' protocols for WAN connectivity. The 'interface', in this context, involves the format of physical layer frames or methods of establishing bit signals (format of electromagnetic pulses).

Synchronous Serial Protocols

Synchronous serial protocols use accurate clock signals between DCE and DTE to transmit data over time. In synchronous communication, a large number of data frames are sent when the clock is synchronized and the data transfer rate is set in advance. This is a very effective method of communication using bandwidth.
Network knowledge: WAN hardware Picture 6
Figure 6: Synchronous transmission

Synchronous signaling protocols include:

- V.35
- RS -232 (EAI / TIA)
- X.21
- RS-449
- RS-530

Although each 'interface' protocol uses a separate connector type, most connectors can be used for different interfaces. Usually, the type of hardware you have will determine which connectors are used. In fact, check the number of connectors in the connector to make sure it matches the serial port of the device. Common types of connectors include (numbers showing the number of pins in the connector):

- DB60
- DB25
- DB15
- DB9

Asynchronous protocols

Asynchronous transfer protocols add additional start bits and stop bits to each packet to transmit thinly, instead of forcing the sending device and receiving device to use the prior agreement. about the clock beat. Asynchronous signal transmission is commonly used between 2 modems. However, this is a transmission method with a surcharge because the extra bits will slow down the data transfer rate.
Network knowledge: WAN hardware Picture 7
Figure 7: Synchronous transmission

Asynchronous protocols are used to set the standard for communications of similar modems. A modem you purchase may support one or more different asynchronous communication standards. Asynchronous communication protocols include:

- V.92
- V.45
- V.35
- V.34
- V.32, V.32 bis, V.32 turbo
- V.22

Asynchronous signal transmission uses standard phone lines and jacks. Connectors can be:

- RJ-11 (2 seconds)
- RJ-45 (4 wires)
- RJ-48

Methods of data packaging in the WAN

The physical layer protocols of the WAN determine the hardware and the bit signal transmission method. Protocols of the data link layer will control the following functions:

- Check and fix errors
- Set up links
- Organization of fields (fields) of data frames
- Control point-to-point flow control

Physical link layer protocols also define the method of encapsulating data or the format of data frames. The method of encapsulating data in a WAN is often called HDLC (high-level data link control). The term is both a common name for Data Link protocols and a protocol name in the WAN protocol and service suite. Depending on the WAN service and the connection method, you can use one of the following data encapsulation methods:

- Cisco HDLC for synchronous, point to point connection with other Cisco routers.
- LAPB for X.25 network
- LAPD, used in conjunction with other protocols for B channels in ISDN network.
- Cisco / IETF for Frame Relay networks
Network knowledge: WAN hardware Picture 8
Figure 8: Methods of data packaging in the WAN

The figure below shows the most common data encapsulation methods and how to use them for typical WAN connection types. As can be seen in the figure, PPP is a flexible method that can be used for many types of WAN connections. In general, using any method will depend on the type of WAN service, such as Frame Relay or ISDN, and also the method of packing data of the network service provider.