---
# System prepended metadata

title: '<center><i class="fa fa-edit"></i> Network Fundamentals: WAN Technologies </center>'
tags: [Internship]

---

# <center><i class="fa fa-edit"></i> Network Fundamentals: WAN Technologies </center>
###### tags: `Internship`
:::info
**Goal:**
To gain a basic understanding of the components behind network technologies. Focus on vocabulary and systems overview.
- [x] WAN Technologies

**Resources:**
[Juniper Online Learning Modules](https://learningportal.juniper.net/juniper/user_activity_info.aspx?id=769)
[Pre-Internship Notes by Jessica Chen](https://hackmd.io/@j-chen/SyfRATOmD)
[Daily Report by Lin Yen-Ting](https://hackmd.io/@8KbRc796SnuYA2Dvsvk_BA/SJU_CawIL)
:::
## Module 5: WAN Technologies

### Overview
 - Operate at Layer 1 and 2 (Physical and Data Link Layers)
 - Multiprotocol Label Switching (MPLS, or Layer 2.5): NOT WAN technology, but WAN service. Operates between Layer 2 and 3
 - Network Cloud: the WAN or Internet through which data travels
 - Customer Premises Equipment (CPE): any communications equipment located on the customer's premises that is used to connect to the service providers network
 - Central Office (CO): service provider's nearest exchange
 - Local Loop ("Last Mile"): A copper or fiber cable that connects the CPE to the nearest CO
     - Analog Line: typically camies voice traffic, or a continuous series of electrical pulses that vary over time (ex: voice-grade phone line coming into the house)
         - Modem: converts or modulates the digital signal into a format for the analog phone line and vice versa
     - Digital Line: binaries (ex: used by companies)
         - Channel Service Unit/Data Service Unit (CSU/DSU): Device requireed to prepare data traffic for digital lines
             - CSU: Provides termination for the digital signal and ensures connection integrity through error correction and line monitoring
             - DSU: Converts digital frames used in service providers network into a frame format that the router can understand and vice versa
 - Data Terminal Equipment (DTE): Device generating the data 
 - Data Communications Equipment (DCE): Device that puts data on the local loop

### WAN Layer 1 Technologies
- T1 Lines (point-to-point connection): High-speed digital telephone line that transfers data at 1.54 Mbps; used to transmit voice and data between devices in NA and Japan
    - Time Division Multiplexing (TDM): A system that combines voice and data signals from different devices within a location 
    - Divides a single line into 24 different channels Digital Signal 0 (DS0 or timeslots) operating at 64 Kbps
        - Each timeslot gets a turn to transmit 8 bits at a time. Once all 24 received a turn, a bit is stuffed in for framing and synchronization, and the process is repeated 8,000 times per second
    - Customers can:
        1. Allocate all time slots for data
        2. Allocate all time slots for voice
        3. Allocate time slots for any combo of voice and data 
![](https://i.imgur.com/mdbWxmw.png)
![](https://i.imgur.com/YaiOWBl.png)
- T3 Lines (DS3): Is 28 DS1s or 672 DS0s bundled together. Electrical signal running at 44.74 Mbps including soeme overhead bits to provide bit stuffing, alignment, error checking, and in band management
![](https://i.imgur.com/QyPpZsX.png)
- E1: Used in most other places in the world; differs slightly from a T1 since data rate is 2.05 Mbps and is comprised of 32 DSOs instead
- DS3 bundles 28 DS1’s whereas E3 bundles 16 E1s or 512 DS0S and has as a data rate of 34.37 Mbps
- T1 and E1 services are incompatible though both use the DS0 as the base signal rate
- Copper Cable vs Fiber Cable
![](https://i.imgur.com/Rs9mqaa.png)
- Fiber Optic Lines 
    - Synchronous Optical Network (SONET): Developed first and deployed in NA
    - Sychronous Digitical Hierarchy (SDH): Developed later and deployed inrest of the world 
    - Both define basic frame format and hiearchy of signaling speeds
    - Not compatible 
    - To keep costs down, most SONET/SDH hardware can be configured to support either standard
![](https://i.imgur.com/2Vi2PUp.png)
- SONET
    - Synchronous Transport Signal (STS): Frame format used by SONET. Lowest or base-level signal is STS-1 but barely used
        - STS-3: 3 STS-1 links multiplexed
        - STS-3c: Concatenated version of STS-3 and viewed as a single pipleline
        - Not necessarily carried on a fiber optic line
![](https://i.imgur.com/eancXZf.png)
    - Optical Carrier (OC): SONET signal being carried over a fiber optic network. Expressed the speed of an OC-n line (Speed = n * 51.84 Mbps)
        - OC-1 signal: bit rate of 51.84 Mbps 
        - OC-3-signal: bit rate of 51.84 times 3 Mbps, or a 155.52 Mbps
- SDH
    - Synchronous Transport Module (STM): Frame format used by SDH. Base-level signal at 155 Mbps (= STS-3c or OC-3 in terms of speed)
        - Can be multiplexed (i.e. STM-4)
- Optical Transport Network (OTN): Successor to traditional SONET and SDH networks for transport of data over optical networks
    - Wavelength Divsion Multiplexing (WDM): Transmits incoming signals simultaneously over fiber optic line by putting each signal into a different wavelength of light. On the receiving end, the de-multiplexer recognizes each different wavelength and turns it back into the signal it received
        - Better than SONET and SDH, which both use time-division multiplexing 
        - Can transport MANY more signals at a time
        - Can easily integrate with existing systems (SONET, SDH, Ethernet, native OTN
        
### WAN Layer 2 Technologies 
- Point-to-Point Protocol (PPP Frame Relay)
    - Router receives a packet with destination and performs route lookup to determine that the next hop is across the WAN
    - Encapsulates the data into a PPP frame (same as Ethernet)
        - Can be encapsulated using different technologies at different points along the path to its destination
        - Can then be re-encapsulated in an Ethernet frame for routing over a LAN
    - Designed in later 1980s to support communication between devices over leased-lines 
    - PPP vs Ethernet
        - PPP: Two devices can be end-user devices, routers, Network Access Servers, or others
        - Ethernet: Has no idea if the device is ready to receive
### Establising a PPP connection 
- Step 1( sometimes called a "handshake")
![](https://i.imgur.com/DrgNuNM.png)
    - How LCP Establishes and Negotiates a Connection
![](https://i.imgur.com/tqUvbyc.png)
- Step 2
![](https://i.imgur.com/Tnd3d3V.png)
- Desgined to work over a variety of links, such as dedicated point-to-point links, dial-up connections, and Digital Subscriber Line (DSL) connections
- If authentication fails PPP terminates the link
- Authentication Protocols
    - Password Authentication Protocol (PAP)
    - Challenge Handshake Authentication Protocol (CHAP)
    - Microsoft Challenge Handshake Authentication Protocol (MS-CHAP)
    - Extensible Authentication Protocol (EAP)
- Step 3
![](https://i.imgur.com/ZuzjkN6.png)
- Devices in an IP-based network use IPCP to configure, enable, and disable the IP protocol on both ends of the point to-point link
- WAN devices running PPP use IPCP to configure the IP addresses in use and optionally request the use of a compression protocol
- Keepalives: Period messages sent to maintain the PPP connection
- PPP frame
![](https://i.imgur.com/tegxUv4.png)
    - Flag
    ![](https://i.imgur.com/lcji1ft.png)
    - Address
    ![](https://i.imgur.com/4LArCpu.png)
    - Control
    ![](https://i.imgur.com/TcKlMfI.png)
    - Protocol 
    ![](https://i.imgur.com/FmoJW2a.png)
    - Data 
    ![](https://i.imgur.com/UG0FJqI.png)
    - Frame Check Sequence (FCS)
    ![](https://i.imgur.com/GY9Ahmh.png)

- Limitations of PPP
    - Requires a dedicated circuit, or "leased lines" between each location. No other devices can send info across that circuit. Tend to be expensive
- Frame Relay: Customers have a leased line only until they reach the service provider's network -> Can establish multiple virtual connections running over a single leased line and reduces costs
    - Example of a Virtual Private Network (VPN): A private network built across a public network such as the service provider's network or the Internet
    - Does not make network faster
    - Network congestion problems can easily occur
- Asynchronous Transfer Mode (ATM)
![](https://i.imgur.com/KQNRSux.png) 
![](https://i.imgur.com/XS0QnOy.png)
- Both Frame Relay and ATM require specialized network experts to run the network and are not frequently used today
- Carrier Ethernet: Ethernet interfaces as fast as 100 Gbps
- Ethernet solves for WAN problems 
![](https://i.imgur.com/0BgJ41A.png)
- Challenges in Ethernet WAN
    - Service-Level Agreements (SLAS): Ensures quality of service to customer from service provider. Usually covers frame delay and frame loss 
    - Need to: 
![](https://i.imgur.com/QMvFK33.png)
- Organizations 
    - Work to solve problems that Ethernet poses in WAN 
    -  Metro Ethernet Forum
    -  Institute of Electrical and Electronics Engineers
    -  International Telecommunication Union
        -  provides a series of recommendations for camera Ethernet including:
            -  The G series of recommendations for transmission systems and media digital systems, and networks
            -  The Y series of global information infrastructure, IP aspects and next-generation networks
![](https://i.imgur.com/ERgBnKl.png)
- MEF 3 Layer Model: Somewhat collapsed version of the 5 Layer Network Model 
    - Application Services Layer: Supports end user applications
- Ethernet Services Layer: Carries the applications (main focus of the Metro Ethernet Forum)
    - Carrier Ethernet 
- Transport Services Layer: Uses various networking and media types to deliver the Ethernet services
    - Includes provider backbone bridging, Virtual Private LAN Service (VPLS), SONET, SDH, and OTN
![](https://i.imgur.com/jzAyZ9P.png)
- Multiprotocol Label Switching (MPLS): Provides the privacy and security of a Frame Relay or ATM network, yet allows for the inherent any-to-any connectivity and flexibility typical of an IP-based network
    - Can have a single physical connection to its WAN service provider, send IP packets, and get VPN services—regardless of the provider’s Layer 2 protocol
    - Many customers are transitioning their old Frame Relay or ATM-based VPNs to MPLS VPN
- Packet in IP routing domain 
![](https://i.imgur.com/3ESEtx8.png)
- Packet in MPLS domain 
![](https://i.imgur.com/7sVX5Jy.png)
- MPLS Header 
![](https://i.imgur.com/12A2T3o.png)
    - MPLS Label 
    ![](https://i.imgur.com/0DMez2T.png)
    - CoS EXP
    ![](https://i.imgur.com/B5lEMMB.png)
    - S
    ![](https://i.imgur.com/f3Mq0dY.png)
    - TTL
    ![](https://i.imgur.com/L4JP0NC.png)
 - MPLS Serives
     - MPLS Layer 2 VPNs
     - MPLS Layer 3 VPNs (aka IP VPNs)
     - Virtual Private LAN Services(VPLS)
     - Generalized MPLS(GMPLS)
     - MPLS Traffic Engineering
     - MPLS Network Management

:::success
### Module 5 Summary 
- PPP
![](https://i.imgur.com/RNPIgFt.png) 
- MPLS
![](https://i.imgur.com/NqkUyPi.png) 
- ATM
![](https://i.imgur.com/o8stZLg.png) 
- Carrier Ethernet
![](https://i.imgur.com/UjByayV.png) 
- Frame Relay
![](https://i.imgur.com/yFZuE3o.png)
:::