Chap 3. Networking and Internetworking Road map: 3.1. Intro 3.2. - - PowerPoint PPT Presentation

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Chap 3. Networking and Internetworking

Road map: 3.1. Intro 3.2. Types of network 3.3. Network principles 3.4. Internet protocols 3.5. Case studies

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3.1. Intro

As an infrastructure for DS Distributed computing rely on existing networks: LANs,

MANs, WANs (including internetworks) that use wired and/or wireless technologies

Hence such characteristics as: performance, reliability,

scalability, mobility, and QoS of DS are impacted by the underlying network technology and the OS

Principles of computer networking Every network has:

An architecture or layers of protocols Packet switching for communication Route selection and data streaming

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3.1. Intro

• Comm Subsystems (network technologies rest on):

Transmission media: wires, cables, fiber, wireless (sat, IR, RF,

µwave)

Hardware devices: routers, switches, bridges, hubs, repeaters,

network interfaces/card/transceivers

Software components: protocol stacks, comm handlers/drivers,

OS primitives, network-focus APIs

• Hosts

The computers and end-devices that use the comm subsystem Subnet: A single cluster or collection of nodes, which reach

each other on the same physical medium and capable of routing outgoing and incoming messages

The Internet is a collection of several subnets (or intranets)

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3.1. Intro

• Networking issues for distributed systems

Initial requirements for DS applications: ftp, rlogin, email, newsgroup Subsequent generation of DS applications.: on-line shared resources Current requirements: performance, reliability, scalability, mobility,

security, QoS, multicasting

• Performance

Key: time to deliver unit(s) of messages between a pair of

interconnected computers/devices – point-to-point latency (delay) from sending out of outgoing-buffer and receiving into incoming- buffer

Usually due to software overheads, traffic load, and path selection Data transfer/bit rate: speed of data transfer between 2 computers

(bps). Usually due to physical properties of the medium

• Message trans time = latency + length/bit-rate

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3.1. Intro

• Bandwidth vs. bit-rate

The total system bandwidth (volume of data sent and received in a

unit time, e.g., per sec.) is a measure of its throughput

Bit rate or transfer rate is restricted to the medium’s ability to

propagate individual bits/signals in a unit time

In most LANs, e.g., Ethernet’s, when full transmission capacity is

devoted to messaging (with little or no latency), then bandwidth and bit-rate are same in measure

Local memory vs. network resources: Applications access to shared resources on same network usually

under msec

Applications access to local memory usually under µsec (1000x

faster)

However, for high speed network web-server, with caches, the

access time is much faster (than local disk access due to hard disk latency)

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3.1. Intro

• Scalability (Internet and DSs)

Future growth of computing nodes of Internet (hosts, switches) in 109’s (100’s

• f 106 hosts alone)

Requires substantial changes to routing and addressing schemes Current traffic (load) on Internet approx. measured by the latencies (see

www.mids.org), which seem to have reduced (with advances in medium and protocol types)

Future growth and sustainability depend on economies of use, charge rate,

locality/placement of shared resource

• Reliability

Failures are typically, not due to the physical medium, but at the end-end (at

host levels) software (application-level), therefore, error detection/correction is at the level

Suggesting that the communication subsystem need not be error-free (made

transparent/hidden to user) because reliability is somewhat guaranteed at the send/receiver ends (where errors may be caused by, e.g., buffer overflow, clock drifts causing premature timeouts)

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3.1. Intro

• Security

Most intranets are protected from external (Internet-wide) DSs by firewall A firewall protects all the resources of an organized from unlawful/malicious

access by external users, and control/monitoring of use of resources outside the firewall

A firewall (bundle of security software and network hardware) runs on a

gateway – the entry/exit point of the corporate intranet

A firewall is usually configured based on corporate security policy, and filters

incoming and outgoing messages

To go beyond firewalls, and grant access to world- or Internet-wide

resources, end-to-end authentication, privacy, and security (Standards) are needed to allow DSs to function

E.g., techniques are Cryptographic and Authentication – usually implemented

at a level above the communication subsystem

Virtual Private Network (VPN) security concept allows intranet-level protection

• f such features/devices as local routers and secure links to mobile devices

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3.1. Intro

• Mobility

Need wireless to support portable computers and hand-held devices Wireless links are susceptible to, e.g., eavesdropping, distortions in medium,

• ut-of-sight/range transmitters/receivers

Current addressing and routing schemes are based on ‘wired’ technologies,

which have been adapted and, therefore, not perfect and need extensions

• QoS (Quality of Service)

Meeting deadlines and user requirements in transmitting/processing streams

• f real-time multimedia data

E.g., QoS requirements: guaranteed bandwidth, timely delivery or bounded

latencies, or dynamic readjustments to requirements (more later in Chp 15)

• Multicasting

Most transmissions are point-to-point, but several involve one-to-many (either

• ne-to-all – broadcast or selective broadcast – multicast)

Simply sending the same message from one node to several destinations is

inefficient

Multicasting technique allows single transmission to multiple destination

(simultaneously) by using special addressing scheme

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3.2. Type of Networks

LANs: (confined to smaller, typically, 2.5km diameter spread)

higher speed, single medium for interconnection (twisted pair, coax,

• pt), no routing within ‘segments’ – all point-to-point (from hub), inter-

segment connections via switches/hubs, low latency, low error rate

E.g., Ethernet, token ring, slotted ring protocols, wired. (1) Ethernet:

1970 with bandwidth of 10Mbps, with extended versions of 100/1000Mbps, lacking latency and bandwidth QoS for DSs: (2) ATM – using frame cells and optical fills the gap but expensive for LAN, newer high-speed Ethernets offer improvement and cost-effective

MANs: (confined to extended, regional area, typically, up

to 50km spread)

Based on high-bandwidth copper and fiber optics for multimedia

(audio/video/voice),

E.g., technologies: ATM, high-speed Ethernet (IEEE 802.6 –

protocols for MANs), DSL (digital subscriber line) using ATM switches to switch digitized voice over twisted pair @ 0.25-6Mbps within 1.5km, cable modem uses coax @ 1.5Mpbs using analog signaling

• n TV networks and longer distances than DSL

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3.2. Type of Networks

• WANs: (worldwide, lower speeds over sets of varying types of circuits with routers)

High latency (due to switching and route searching) between 0.1-0.5s,

signaling speed around 3x105km/s (bounds latency) plus propagation delay (round-trip) of about 0.2s if using satellite/geostationary dishes; generally slower at 10-100kbps or best 1-2Mbps

• Wireless: (connecting portable, wearable devices using access points)

Common protocol – IEEE 802.11 (a, b, and now g) (WaveLAN) @ 2-11Mbps

(11g’s bandwidth near 54Mbps) over 150m creating a WLANs, some mobiles connected to fixed devices – printers, servers, palmtops to create a WPANs (wireless personal area networks) using IR links or low-powered Bluetooth radio network tech @ 1-2Mbps over 10m.

Most mobile cell phones use Bluetooth tech. e.g., European GSM standard

and US, mostly, analog-based AMP cellular radio network, atop by CDPD – cellular digital packet data communication system, operating over wider areas at lower speed 9.6-19.2kbps.

Tiny screens of mobiles and wearables require a new WAP protocol

• Internetworks

Building open, extendible system for DSs, supporting network heterogeneity,

multi-protocol system involving LANs, MANs, WLANs, connected by routers and gateways with layers of software for data and protocol conversions – creating a ‘virtual network’ using underlying physical networks

E.g., the Internet using TCP/IP (over several other physical protocols)

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3.2. Type of Networks

• Comparisons

Range of performance characteristics: Frequency and types of failures, when used for DS applics Packet delivery/loss, duplicates (masked at TCP level to guarantee some

reliability and transparency to DSs; but may use UDP – faster but less reliable and DS applic’s responsibility to guarantee reliability)

Example Range Bandwidth (Mbps) Latency (ms) Wired: LAN Ethernet 1-2 kms 10-1000 1-10 WAN IP routing worldwide 0.010-600 100-500 MAN ATM 250 kms 1-150 10 Internetwork Internet worldwide 0.5-600 100-500 Wireless: WPAN Bluetooth (802.15.1) 10 - 30m 0.5-2 5-20 WLAN WiFi (IEEE 802.11) 0.15-1.5 km 2-54 5-20 WMAN WiMAX (802.16) 550 km 1.5-20 5-20 WWAN GSM, 3G phone nets worldwide 0.01-02 100-500

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3.3. Network principles

• Packet Transmission

Packet transmission superseded telephone/telegraph switched

network

Messages are packetized and packets are queued, buffered (in local

storage), and transmitted when lines are available using asynchronous transmission protocol

• Data Streaming

Multimedia data can’t be packetized due to unpredicted delays. AV

data are streamed at higher frequency and bandwidth at continuous flow rate

Delivery of multimedia data to its destination is time-critical / low

latency – requiring end-to-end predefined route

E.g. networks: ATM, IPv6 (next generation – will separate ‘steamed’

IP packets at network layer; and use RSVP (resource reserv. protocol) resource/bandwidth prealloc and RTP play-time/time-reqs (real-time transp protocol) at layers 3 & 1, respectively) to work

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3.3. Network principles

• Switching Schemes – 4 Kinds of switching methods typically used

Broadcast – no switching logic, all nodes ‘see’ signals on circuits/cells (e.g.,

Ethernet, wireless networks)

Circuit Switching – Interconnected segments of circuits via

switches/exchange boxes, e.g., POTS (Plain Old Telephone System)

Packet Switching – Developed as computing tech advanced with processors

and storage spaces using store-and-forward algorithms and computers as

• switches. Packets are not sent instantaneously, routed on different links,

reordered, may be lost, high latency (few µsec – msecs). Extension to switch audio/video data brought integration of ‘digitized’ data for computer comm., telephone services, TV, and radio broadcasting, teleconferencing

Frame Relay – PS (not instantaneous, just an illusion!), but FR, which

integrates CS and PS techniques, streams smaller packets (53 byte-cells called frames) as bits at processing nodes. E.g., ATM

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3.3. Network principles

• Protocols –
• Protocols – implemented as pairs of software modules in send/receive

nodes,

• Specify the sequence of messages for transmission
• Specify the format of the data in the messages
• Protocols Layers – layered architecture, following the OSI suite
• packets are communicated as peer-to-peer transmission but effected

vertically across layers by encapsulation method over a physical medium Layer n Layer 2 Layer 1 Message sent Message received Communication medium Sender Recipient

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3.3. Network principles

• Protocols Layers – layered architecture, following the OSI suite

each protocol type is included in headers to help protocol stack at receiver

end to unpack the encapsulated packets

Presentation header Application-layer message Session header Transport header Network header

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3.3. Network principles

• Protocols Suites – The 7-layered architecture of the ISO-OSI
• Each layer provides service to the layer above it and extends the service

provided by the layer below it

A complete set of protocol layers constitute a suite or stack Layering simplifies and generalizes the software interface definitions, but

costly overhead due to encapsulations and protocol conversions

Application Presentation Session Transport Network Data link Physical Message sent Message received Sender Recipient Layers Communication medium

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3.3. Network principles

Layer Description Examples Application Protocols that are designed to meet the communication requirements of specific applications, often defining the interface to a service. HTTP,

FTP, SMTP,

CORBA IIOP Presentation Protocols at this level transmit data in a network representation that is independent of the representations used in individual computers, which may

• differ. Encryption is also performed in this layer, if required.

Secure Sockets (SSL),CORBA Data Rep. Session At this level reliability and adaptation are performed, such as detection of failures and automatic recovery. Transport This is the lowest level at which messages (rather than packets) are handled. Messages are addressed to communication ports attached to processes, Protocols in this layer may be connection-oriented or connectionless. TCP, UDP Network Transfers data packets between computers in a specific network. In a WAN

• r an internetwork this involves the generation of a route passing through
• routers. In a single LAN no routing is required.

IP, ATM virtual circuits Data link Responsible for transmission of packets between nodes that are directly connected by a physical link. In a WAN transmission is between pairs of routers or between routers and hosts. In a LAN it is between any pair of hosts. Ethernet MAC, ATM cell transfer, PPP Physical The circuits and hardware that drive the network. It transmits sequences of binary data by analogue signalling, using amplitude or frequency modulation

• f electrical signals (on cable circuits), light signals (on fibre optic circuits)
• r other electromagnetic signals (on radio and microwave circuits).

Ethernet base- band signalling, ISDN

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3.3. Network principles

Underlying network Application Network interface Transport Internetwork Internetwork packets Network-specific packets Message Layers Internetwork protocols Underlying network protocols

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3.3. Network principles

• Protocols

Packet Assembly: Decomposing messages (packetizing) into packets,

transmitting, and reassembling using sequence #s at delivery- switch to receiving host in the transport layer. Applied to messages that exceed MTU (Max. transfer unit) of the switch. E.g., Ethernet MTU is 1518 bytes and Internet MTU is 8kbyes (min) to 64kbytes (max).

Ports:

Software-defined transmission/delivery points for network-

independent transport service on a host computer. Processes are typically attached to ports for pair-wise communication

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3.3. Network principles

• Protocols
• Addressing: Transport layer addressing scheme, composed of network

address (of host), I.e., the IP address, and the port number. The combined address is typically called a socket or transport address of the Transport

• Layer. Each host may have several port #s for different kinds of protocols

(e.g., for HTTP, FTP) or services. Hosts send port numbers to clients to establish, e.g., TCP, connection. Finding port # on server hosts in DS for arbitrary services requires RMI/RPC type of schemes

• Packet Delivery (at network layer):
• Datagram – one-at-a-time, hop-by-hop transmission of packets with no storing
• f copies at switches, no setup of paths, unreliable and failures are handled by

hosts, each packet contains full network address of source-to-destination, e.g., Internet IP datagram in network layer and some wireless networks

• Virtual circuits – set up of end-to-end path/address held in switch tables, no

network address in packets except VC #, switching at intermediate nodes, more reliable, latency depends on time to use the links/path segments, unlike POTS voice-links VC links can be shared and used/entered in multiple tables, e.g., ATM [Note: At transport layer, connection-oriented TCP is like virtual circuits, and connection-less UDP is like datagram]

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3.3. Network principles

• Routing

Routing is necessary in MANs and WANs, rarely in LANs since

point-to-point is typically used in LANs. Adaptive/dynamic routing is usually used – adapting to traffic patterns, topological changes, etc. Switching is done by multiple switches/routers in the subnet for host-to-host delivery using available routing algorithm

Algorithms depends on: 1) Either using VC or datagram -

depends on network type, e.g., ATM uses VC connection-

• riented and Internet uses datagram connectionless packet-

switching; and 2) dynamics of the network – topologically, traffic patterns

Routing decision is made hop-by-hop, with period update and

distribution of traffic data, e.g., the distance-vector, dynamic, distributed algorithm

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3.3. Network principles

Hosts Links

• r local

networks A D E B C 1 2 5 4 3 6 Routers

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3.3. Network principles

• The Routing Table – matrix/graph construction, reflecting topology of network

Routings from D Routings from E To Link Cost To Link Cost A B C D E 3 3 6 local 6 1 2 2 1 A B C D E 4 4 5 6 local 2 1 1 1

Routings from A Routings from B Routings from C To Link Cost To Link Cost To Link Cost A B C D E local 1 1 3 1 1 2 1 2 A B C D E 1 local 2 1 4 1 1 2 1 A B C D E 2 2 local 5 5 2 1 2 1

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3.3. Network principles

• The RIP algorithm for dynamic update and distribution of routing table info

Prepare RIP packets containing change-info and send to active links and update

table if the new cost to a neighboring node is lower/better

Send: Each t seconds or when Tl changes, send Tl on each non-faulty outgoing link. Receive: Whenever a routing table Tr is received on link n: for all rows Rr in Tr { if (Rr.link | n) { Rr.cost = Rr.cost + 1; Rr.link = n; if (Rr.destination is not in Tl) add Rr to Tl; // add new destination to Tl else for all rows Rl in Tl { if (Rr.destination = Rl.destination and (Rr.cost < Rl.cost or Rl.link = n)) Rl = Rr; // Rr.cost < Rl.cost : remote node has better route // Rl.link = n : remote node is more authoritative } } }

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3.3. Network principles

• Congestion Control

Link overload and queue overflows Packet dropping – manageable at network layer using retransmission

up to a threshold/limit (when throughput starts to decline)

Congestion control methods arrest overload problem early (at higher

nodes – closer to hosts) or buffering of packets for longer times at intermediate nodes, or hosts throttle application programs and/or queue packets in hard-drives –

Example: In datagram/IP/Internet connectionless networks, where host is

responsible for network problems, choke packets are used to throttle senders

In ATM, using connection-oriented protocol, congestion control

schemes depend on the QoS specified in the service

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3.3. Network principles

• Internetworking

Network technologies (or subnets):

LANs: Ethernet, ATM networks using different physical, data link, and network

layers

WANs: Internet, using analog and digital POTS switched technologies,

satellite links and wide-area ATM networks, and relying on underlying LANs and MANs

Internetworking:

Integrated network of subnets using

• 1) unified internetworking addressing scheme for communication between host and

any subnet

• 2) PDU (protocol data unit) format and conversion/handling protocols
• 3) standards/protocols and devices/switches for interconnecting and addressing

component subnets and hosts

Network (hardware) components: routers, bridges, hubs, switches Tunneling: Internetworking protocol, e.g., IPv6, for bridging a variety of

physical subnets using ‘packet encapsulation’ techniques. E.g., IPv6 protocol packets encapsulated inside IPv4, IP, ATM PDU’s and transported across a sea of IPv4, IP, ATM networks. Another, e.g., MobileIP transmits IP packets to

• ther mobiles by encapsulating IP packets over other networks, Another, e.g.,

PPP for transmitting IP packets.

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3.3. Network principles

file compute dialup

hammer henry hotpoint 138.37.88.230 138.37.88.162 bruno 138.37.88.249

router/

sickle 138.37.95.241 138.37.95.240/29 138.37.95.249 copper 138.37.88.248

firewall web

138.37.95.248/29

server desktop computers

138.37.88.xx subnet subnet Eswitch 138.37.88

server server server

138.37.88.251 custard 138.37.94.246

desktop computers

Eswitch 138.37.94

hub hub

Student subnet Staff subnet

• ther

servers router/ firewall

138.37.94.251

• 1000 Mbps Ethernet

Eswitch: Ethernet switch 100 Mbps Ethernet file server/ gateway printers Campus router Campus router

138.37.94.xx

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3.3. Network principles

A B IPv6 IPv6 IPv6 encapsulated in IPv4 packets Encapsulators IPv4 network

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3.4. Network protocols

Messages (UDP) or Streams (TCP) Application Transport Internet UDP or TCP packets IP datagrams Network-specific frames Message Layers Underlying network Network interface

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3.4. Network protocols

Internet Protocols

History: 1970’s research results. TCP – Transport control protocol, IP

– Internet protocol

Forms a single ‘internetworking’ protocol (using IP datagram

‘encapsulation’ methods)

Many existing application-specific/layer protocols are based on /

using TCP/IP i.e., built on top of TCP/IP – (e.g., Web (HTTP), SMTP, POP, FTP, Telnet)

When TCP is not enough additional higher-level protocol, e.g., SSL

(secure socket protocol) for security, can be built atop TCP

Internet protocols were initially developed for simple ftp and e-mails Exceptional networks not using TCP/IP – WAP and protocols for

multimedia

Internet protocols usually layered over existing ‘physical’ networks,

e.g., over Ethernets and over telephone serial lines via PPP for modem connection

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3.4. Network protocols

• Encapsulation
• ‘Tags’ in the encapsulation help in determining and conversion (packing /

unpacking packets) among protocol types

Application message TCP header IP header Ethernet header Ethernet frame

port TCP IP

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3.4. Network protocols

Conceptual (user view) architecture of TCP/IP over transmission networks

IP Application Application TCP UDP

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3.4. Network protocols

7 24 Class A: Network ID Host ID 14 16 Class B: 1 Network ID Host ID 21 8 Class C: 1 1 Network ID Host ID 28 Class D (multicast): 1 1 1 Multicast address 27 Class E (reserved): 1 1 1 1 unused

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3.4. Network protocols

• ctet 1
• ctet 2
• ctet 3

Class A: 1 to 127 0 to 255 0 to 255 1 to 254 Class B: 128 to 191 Class C: 192 to 223 224 to 239 Class D (multicast): Network ID Network ID Network ID Host ID Host ID Host ID Multicast address 0 to 255 0 to 255 1 to 254 0 to 255 0 to 255 0 to 255 0 to 255 0 to 255 0 to 255 Multicast address 0 to 255 0 to 255 1 to 254 240 to 255 Class E (reserved): 1.0.0.0 to 127.255.255.255 128.0.0.0 to 191.255.255.255 192.0.0.0 to 223.255.255.255 224.0.0.0 to 239.255.255.255 240.0.0.0 to 255.255.255.255 Range of addresses

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3.4. Network protocols

data IP address of destination IP address of source header up to 64 kilobytes

Source address (128 bits) Destination address (128 bits) Version (4 bits) Traffic class (8 bits) Flow label (20 bits) Payload length (16 bits) Hop limit (8 bits) Next header (8 bits)

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3.4. Network protocols

Sender Home Mobile host MH Foreign agent FA Internet agent First IP packet addressed to MH Address of FA returned to sender First IP packet tunnelled to FA Subsequent IP packets tunnelled to FA

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3.4. Network protocols

Internet Router/ Protected intranet a) Filtering router Internet b) Filtering router and bastion filter Internet R/filter c) Screened subnet for bastion R/filter Bastion R/filter Bastion web/ftp server web/ftp server web/ftp server

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3.5. Network case studies

IEEE No. Name Title Reference 802.3 Ethernet CSMA/CD Networks (Ethernet) [IEEE 1985a] 802.4 Token Bus Networks [IEEE 1985b] 802.5 Token Ring Networks [IEEE 1985c] 802.6 Metropolitan Area Networks [IEEE 1994] 802.11 WiFi Wireless Local Area Networks [IEEE 1999] 802.15.1 Bluetooth Wireless Personal Area Networks [IEEE 2002] 802.15.4 ZigBee Wireless Sensor Networks [IEEE 2003] 802.16 WiMAX Wireless Metropolitan Area Networks[IEEE 2004a]

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3.5. Network case studies

LAN Server Wireless LAN Laptops Base station/ access point Palmtop radio obstruction A B C D E

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3.5. Network case studies

Physical Application ATM layer Higher-layer protocols ATM cells ATM virtual channels Message Layers ATM adaption layer

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3.5. Network case studies

Flags Data Virtual channel id Virtual path id 53 bytes Header: 5 bytes VPI in VPI out 2 3 4 5 VPI = 3 VPI = 5 VPI = 4 Virtual path Virtual channels VPI = 2 VPI : virtual path identifier VP switch VP/VC switch VP switch Host Host