Communication Networks (1-2)

https://birkhoffg.github.io/blog/posts/networking-what-is-networking/

Internet

Internet: “network of networks”

• Interconnected ISPs

Protocols control sending,receiving of messages

• e.g., TCP, IP, HTTP, Skype, 802.11 (WiFi)

Internet standards

• RFC: Request for comments
• IETF: Internet Engineering Task Force
• ISO, IEEE

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Internet Structure

Network edge:

• hosts: clients and servers
• servers often in data centers
• access networks, physical media: wired, wireless
  communication links

Network core:

• interconnected routers
• network of networks

Connect end systems to edge routers

• residential access nets
• institutional access networks (school, company)
• mobile access networks
• shared or dedicated?

Access Network: Digital Subscriber Line (DSL)

=

• Use existing telephone line to central office DSLAM.
• dedicated access to central office
• < 2.5 Mbps upstream transmission rate (typically < 1 Mbps)
• < 24 Mbps downstream transmission rate (typically < 10 Mbps)

Access Network: Cable Network

• Frequency division multiplexing: different channels transmitted in different frequency bands
• HFC: hybrid fiber coax up to 30Mbps
• Network of cable, fiber attaches homes to ISProuter
• homes share network to cable headend

Access Network: Home Network

Enterprise Access Networks (Ethernet)

• 10 Mbps,100Mbps,1Gbps, 10Gbps transmission rates
• Today, end systems typically connect into Ethernet switch

Wireless Access Networks

• Shared wireless access to base station aka “access point”

Wireless LANs (WiFi):

• 
• 11, 54, 450 Mbps rate

Wide-area wireless accesss

• 
• cellular operator, 10’s km
• 1 to 10 Mbps
• 3G, 4G, LTE

Host: Sends Packets of Data

Host sending function:

• breaks appilication layer messages into smaller chunks (packets), of length $L$ bits
• transmits packet into access network at transmission rate $R$
• link transmission rate / link capacity / link bandwidth:

$$\frac{L \text{ (bits)}}{R\text{ (bits/s)}}$$

Physical Media

guided media:

• signals propagate in solid media: copper,fiber,coax

unguided media:

• signals propagate freely
  e.g., radio

twisted pair (TP)：

• two insulated copper Wires
• Category 5:100 Mbps1，Gbps Ethernet / Category 6: 10Gbps

Coaxial Cable:

• multiple channels

Fiber optic cable:

• high-speed point-to-point transmission (e.g.,10’s-100’s Gbps transmission rate)

Network-core

2 key functions:

• routing
• forwarding