Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 History

A closer look at network structure: network edge: applications and hosts access networks, physical media: wired, wireless communication links network core: interconnected routers network of networks

The network edge: end systems (hosts): client/server model run application programs e.g. Web, email at “edge of network” peer-peer client/server client/server model client host requests, receives service from always-on server e.g. Web browser/server; email client/server peer-peer model: minimal (or no) use of dedicated servers e.g. Skype, BitTorrent

Access networks and physical media Q: How to connect end systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated?

Residential access: point to point access Dialup via modem up to 56Kbps direct access to router (often less) Can’t surf and phone at same time: can’t be “always on” DSL: digital subscriber line deployment: telephone company (typically) up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) dedicated physical line to telephone central office

Access networks There are three ways to provide access to the internet to home Over the telephone ADSL-based modems Over the television plant Cable-based modems Over an optical fiber Passive Optical Networks (APON or EPON)

The ADSL-based access network is one of the access technologies that Can be used to convert the telephone line into a high-speed digital link is a part of a family of technologies called The x-type digital subscriber line (x-DSL) Where x takes on different values

X-DSL data rates ADSL modem is the most commonly used Rates Downstream: 8 Mbps Upstream: 800 Kbps – 1 Mbps

Bandwidth vs. distance VDSL ADSL 52 Mbps/6.4 Mbps up to 1000 feet (300 m) 13 Mbps/1.6 Mbps up to 5000 feet (1.5 km) ADSL Downstream 2 Mbps up to 5.4 Km 8 Mbps up to 2.7 Km Upstream 64 Kbps to 800 Kbps

Bandwidth vs distance

Digital subscriber line Some of the key features DSL allows analog voice signals and digital data To be sent over the same local loop wiring The local loop must be connected to sthg besides A traditional voice switch at the end office A device called DSL access multiplexer (DSLAM) is used Provides high speed access to end users DSL was designed to provide high speed access.

ADSL: equipment configuration

ADSL equipment A telephone company technician must install a Network Interface Device on the customer’s permises. This small plastic box marks the end of the telephone company’s property and the start of the customer’s property. Close to the NID is a splitter, that separates the 0-4000 Hz band used by the POTS from data. The POTS signal is routed to the existing telephone or fax machine and the data signal is routed to an ADSL modem.

ADSL deployment: at the customer’s permise ADSL Transmission Unit at the customer premises end ADSL + POTS signals Travel together down the twisted pair Using filter you will be isolating each signal

ADSL access multiplexer Transmission between the end office and customer is done using the ADSL layer Speeds are limited to 1.5 Mbps

Discrete multi-tone technique The twisted pair bandwidth extends to 1.1 Mbps is divided into 256 sub-channels Each occupying 4.3125 KHz Sub-channel 0 is reserved For the voice band region Sub-channels 1-5 separate data and POTS signal The remaining sub-channels are used by ADSL

Upstream and upstream data In ADSL Both the upstream and downstream data Are sent over the same twisted pair This can be implemented using Frequency division multiplexing (FDM) Up to 32 sub-channels for the upstream direction Up to 218 downstream sub-channels

Discrete multi-tone technique What it does is to divide the available 1.1 Mhz spectrum on the local loop into 256 independent channels of 4 Khz each. Channel 0 is used for POTS (Plain Old Telephone Service). Channels 1-5 are not used to keep the voice signal and data signals from interfering. The rest are available for user data. In its ADSL version 32 channels are used for upstream and the rest downstream. The ADSL standard allows speeds of as much as 8 Mbps downstream and 1 Mbps in the upstream ADSL 8 Mbps in the downstream 1 Mbps in the upstream

The ADSL reference model architecture DSLAM can support Up to 64 homes

Residential access: cable modems HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps upstream network of cable and fiber attaches homes to ISP router homes share access to router deployment: available via cable TV companies

Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Cable Network Architecture: Overview Typically 500 to 5,000 homes cable headend home cable distribution network (simplified)

Cable Network Architecture: Overview server(s) cable headend home cable distribution network

Cable Network Architecture: Overview cable headend home cable distribution network (simplified)

Cable Network Architecture: Overview FDM (more shortly): Channels V I D E O A T C N R L 1 2 3 4 5 6 7 8 9 cable headend home cable distribution network

Company access: local area networks company/univ local area network (LAN) connects end system to edge router Ethernet: 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet modern configuration: end systems connect into Ethernet switch LANs: chapter 4

Physical Media Twisted Pair (TP) two insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet Category 5: 100Mbps Ethernet Bit: propagates between transmitter/rcvr pairs physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio

Physical Media: coax, fiber Fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10’s-100’s Gps) low error rate: repeaters spaced far apart ; immune to electromagnetic noise Coaxial cable: two concentric copper conductors bidirectional baseband: single channel on cable legacy Ethernet broadband: multiple channels on cable HFC

The Network Core mesh of interconnected routers the fundamental question: how is data transferred through net? circuit switching: dedicated circuit per call: telephone net packet-switching: data sent thru net in discrete “chunks”