# <center><i class="fa fa-edit"></i> Network Fundamentals: WAN Technologies </center>
###### tags: `Internship`
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**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)
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## 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
- 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
- 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
- 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
- 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
- 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")
- How LCP Establishes and Negotiates a Connection
- Step 2
- 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
- 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
- Flag
- Address
- Control
- Protocol
- Data
- Frame Check Sequence (FCS)

- 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)
- 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
- 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:
- 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
- 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
- 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
- Packet in MPLS domain
- MPLS Header
- MPLS Label
- CoS EXP
- S
- TTL
- 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
- MPLS
- ATM
- Carrier Ethernet
- Frame Relay
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