Internetwork, Exams of Local Area Network (LAN)

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Internetwork

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• recursive definition → point-to-point and multi-access: internetwork → composition of one or more internetworks

Additional complications to deal with:

• addressing necessary → LAN addresses may suffice → additional addressing structure: e.g., IP
• protocol translation: internetworking → e.g., Ethernet and WLAN speak different languages
• path selection between sender/receiver: routing → within and across organizations
• how fast to send: congestion control → not-too-fast, not-too-slow
• location management: e.g., Mobile IP

Myriad of different LAN technologies co-existing in a WAN. For example:

• Fast Ethernet (100 Mbps)
• Gigabit Ethernet (1000 Mbps); 10 and 100 GigE → Purdue CS backbone: 10 Gbps → AT&T (tier-1 provider): 10+ Gbps
• WLAN (11, 54, 300 Mbps)
• 4G cellular (100 Mbps mobile, 1 Gbps stationary) → today: pre-4G → ITU-R
• WiMAX (tens of Mbps up to 1 Gbps) → wider area: several miles
• modem/DSL (cable and dial-up) → 12 Mbps (down)/2 Mbps (up), 50/10, higher

Note: WAN is a collection of LANs

→ ultimately: everything happens at LANs

Each LAN, in general, speaks a different language

→ message format (syntactic) → behavioral (semantic)

Internetworking handles this problem by translating ev- erything to IP (Internet Protocol)

→ technical definition of Internet

→ collection of interconnected LANs speaking IP

IP provides naming flexibility:

→ IP: v4 32-bit, v6 128-bit → in addition to 48-bit LAN addresses are hardwired and unique address per NIC

→ IP provides additional configurability

Common practice: assign similar addresses to network devices belonging to same organization

→ ARIN in the U.S. → blocks of contiguous addresses: makes routing easier

→ e.g.: Purdue 128.10.∗.?, 128.210.∗.? → LWSN B158: sslab01.cs.purdue.edu 128.10.25. → CS web server: www.cs.purdue.edu 128.10.19.

→ router bottleneck: table look-up speed

Naming: IP or LAN addresses are not enough

Communicating entities are processes running on host/router operating systems (Linux, Windows, IOS, etc.)

→ IP only specifies host/server/router

→ more accurately: one of the NICs attached to a device → host with multiple NICs: multiple IP addresses → multi-homed

Hence:

A name/address must also identify which process a mes- sage is destined for on a host

→ OS/network convention: port number abstraction

→ 16-bit → address: pair (host IP, port number) → well-known server port numbers (e.g., 80 for HTTP)

→ is client app’s port number important?

Three yardsticks of performance:

• bandwidth: bps (bits-per-second) → throughput: includes software processing overhead → e.g., 802.11b WLAN: nominal bandwidth 11 Mbps, throughput around 6 Mbps
• latency: msec (millisecond) → signal propagation speed

→ approximately: speed of light → delay: includes software processing overhead and waiting time at routers (queueing)

→ delay at high speed routers: very small (μsec) → delay at WLAN AP: up to hundreds of millisecond

• jitter: delay variation → not good for real-time content (video, audio, voice)

Bandwidth vs. throughput:

bandwidth—maximum data transmission rate achiev- able at the hardware level; determined by sig- nalling rate of physical link and NIC

throughput—maximum data transmission rate achiev- able at the software level; overhead of network pro- tocols inside/outside OS is accounted for

reliable throughput—maximum reliable data trans- mission rate achievable at the software level; effect of recovery from transmission errors and packet loss accounted for

−→ networks tend to be “leaky”

• thus: a single bit cannot go faster

→ can only increase “bandwidth”

→ analogous to widening highway, i.e., more lanes → simulatenous transmission of multiple bits

→ hence “broadband” is a more accurate term

• interpretation: “high-speed” ⇔ “many lanes”

→ what does it buy?

→ completion time of large files faster → in this sense, “higher” speed

Some units:

Tbps, Gbps, Mbps, Kbps:

1012 , 10^9 , 10^6 , 10^3 bits per second; indicates data transmission rate; influenced by clock rate (MHz/GHz) of signaling hardware

−→ communication rate: factors of 1000 −→ data size: 1 KB means 1024 bytes

Level3 backbone network: www.level3.com

→ 10 Gbps backbone (green): same speed as Purdue

→ outdated pic: faster backbone speeds now

What is traveling on the wires?

Mixture of:

bulk data (data, image, video, audio files), voice, streaming video/audio, real-time interactive data (e.g., games), etc. → around 90% of Internet traffic is TCP file traffic → HTTP web and P2P

Multimedia (video/audio) streaming: on the rise

→ a minority but share is increasing → non-real-time: e.g., youtube, netflix

→ real-time: e.g., VoIP, video conferencing, games