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- Leased line WANs, a type of WAN link that has been part of enterprise networks since 1960s
- How Ethernet can be used to create WAN services by taking advantage of the longer cable length possibilities of modern fiber-optic Ethernet standards
- Common WAN technology used to access the Internet
- WAN is something given by a provider.
- Usually, we would contact ISP and ask for WAN connection and choose which technology to use (MPLS, DSL, VPN, PPP…)
Leased Line WANs
- Leased line WANs do forwarding data between two routers.
- Business branches communicate (LANs) by using services and technologies of WANs and have to communicate over WANs.
- WAN technologies include a large number of options for physical links and data-link protocols that control those links.
- You don’t share bandwidth as with the broadband
- Upload and download speeds are the same
- Uses analog circuits
- Uses the same path for a destination
- Charges are fixed, whether use lease line or not, you pay the same
- Permanent connection for the destination
- Not scalable
- ISPs put their equipment in buildings called central offices (CO)
- ISP installs cables from the CO to almost every other building in the city, expecting to sell services there, one day.
- Each site has customer premises equipment (CPE) which includes a router, serial interface card, and CSU/DSU.
- Serial interface card on a router, acts as a NIC on a PC, sending and receiving data over a physical link.
- Speeds are fixed (64kbps to 1.5Mbps)
- Because leased lines are layer 1 service, people have come to an idea to control data-link details of leased lines. Therefore, they created HDLC and PPP protocols.
- Data-link protocols perform a similar role: to control the correct delivery of data over a physical link!
- For example, Ethernet data-link protocol uses the destination address field to identify the correct device that should receive data.
- HDLC has less work to do because of the simple Point-to-Point topology of a point-to-point leased line.
- When one router sends HDLC frame, it can go only on the other side of the leased line, to the other router.
Ethernet as a WAN technology
- At first, Ethernet was only appropriate for LANs
- Restrictions on cable lengths and devices might allow a LAN that stretched a kilometer or two, to support campus LAN, and that was the limit.
- As time passed, IEEE improved Ethernet standards.
- Now, Ethernet is reasonable WAN technology.
- For example, 1000BASE-LX supports 5km cable length, 1000BASE-ZX supports up to 70km cable length.
- In the 21st century, many ISPs offer WAN services using Ethernet.
- Different WAN technologies exist using Ethernet, but at the core, they all use the same technology (packets and Ethernet)
- The picture explains how ISP create leased lines nowadays.
- Customer connects to Ethernet link using router interface
- Fiber Ethernet link leaves customer building and connects to nearby ISP location called a point of presence (PoP)
- Inside ISP’s network, ISP uses any technology it wants to create Ethernet WAN services.
- It is important to say that it uses Ethernet standards, packet-switched networks, and Ethernet router and switches together with IEEE Ethernet physical mediums.
WAN over Ethernet
- Ethernet WAN service goes by two names: ethernet emulation and Ethernet over MPLS (EoMPLS).
- Ethernet emulation means that the service acts like one Ethernet link
- EoMPLS refers to Multiprotocol Label Switching MPLS. MPLS is technology used inside ISP’s cloud.
Digital subscriber line (DSL):
- Creates short high speed link WAN between customer and ISP.
- To do so, uses same telephone line.
- Voice cabling concept, without DSL
- DSL on the other hand splits the line.
- Voice switch at Telco CO forwards voice through the worldwide voice network, called Public Switched Telephone Network PSTN
- A new DSL modem now connects to a phone outlet instead of a telephone in image before.
- DSL modem follows physical and data-link standards to send data to/from the telco.
- This is now a small LAN network, with SOHO router (switch, router, AP)
- In order for router to send data to/from the Internet, ISP uses DSL access multiplexer (DSLAM).
- DSLAM splits out the data over to the router at the lower right side of the image, which completes the connection to the Internet.
- DSLAM also splits out voice data and sends them over PSTN
- Has many similarities with DSL.
- Cable Internet takes full advantage of existing cabling, using the existing cable TV to send data.
- Uses asymmetric speeds, sending data faster (download), than upload speeds
- Uses coaxial cable from CATV company
- A DSL modem is replaced with a cable modem.
- Difference in CATV side, where here we don’t have DSLAM, but we have a splitter that splits Ethernet data, and video data through a satellite dish.