Chap 3. Networking and Internetworking · 2005/9/11 5 3.1. Intro n Bandwidth vs. bit-rate u The total system bandwidth (volume of data sent and received in a unit time, e.g., per

2005/9/11 1

Chap 3. Networking and Internetworking

n Road map:n 3.1. Intron 3.2. Types of networkn 3.3. Network principlesn 3.4. Internet protocolsn 3.5. Case studies

2005/9/11 2

3.1. Intro

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

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

u Hence such characteristics as: performance, reliability, scalability, mobility, and QoS of DS are impacted by the underlying network technology and the OS

n Principles of computer networkingu 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

n Comm Subsystems (network technologies rest on):u Transmission media: wires, cables, fiber, wireless (sat, IR, RF,

µwave)u Hardware devices: routers, switches, bridges, hubs, repeaters,

network interfaces/card/transceiversu Software components: protocol stacks, comm handlers/drivers,

OS primitives, network-focus APIs

n Hostsu The computers and end-devices that use the comm subsystemu 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

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

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3.1. Intro

n Networking issues for distributed systemsu Initial requirements for DS applications: ftp, rlogin, email, newsgroupu Subsequent generation of DS applications.: on-line shared resourcesu Current requirements: performance, reliability, scalability, mobility,

security, QoS, multicastingn Performance

u 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

u Data transfer/bit rate: speed of data transfer between 2 computers (bps). Usually due to physical properties of the medium

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

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3.1. Intro

n Bandwidth vs. bit-rateu The total system bandwidth (volume of data sent and received in a

unit time, e.g., per sec.) is a measure of its throughputu Bit rate or transfer rate is restricted to the medium’s ability to

propagate individual bits/signals in a unit timeu 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

u 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

n Scalability (Internet and DSs)u Future growth of computing nodes of Internet (hosts, switches) in 109’s (100’s

of 106 hosts alone)u Requires substantial changes to routing and addressing schemesu 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)

u Future growth and sustainability depend on economies of use, charge rate, locality/placement of shared resource

n Reliabilityu 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

u 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

n Securityu Most intranets are protected from external (Internet-wide) DSs by firewallu 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

u A firewall (bundle of security software and network hardware) runs on a gateway – the entry/exit point of the corporate intranet

u A firewall is usually configured based on corporate security policy, and filters incoming and outgoing messages

u 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

u E.g., techniques are Cryptographic and Authentication – usually implemented at a level above the communication subsystem

u Virtual Private Network (VPN) security concept allows intranet-level protection of such features/devices as local routers and secure links to mobile devices

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3.1. Intro

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

out-of-sight/range transmitters/receiversu Current addressing and routing schemes are based on ‘wired’ technologies,

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

n QoS (Quality of Service)u Meeting deadlines and user requirements in transmitting/processing streams

of real-time multimedia datau E.g., QoS requirements: guaranteed bandwidth, timely delivery or bounded

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

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

one-to-all – broadcast or selective broadcast – multicast)u Simply sending the same message from one node to several destinations is

inefficientu Multicasting technique allows single transmission to multiple destination

(simultaneously) by using special addressing scheme

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3.2. Type of Networks

n LANs: (confined to smaller, typically, 2.5km diameter spread)u higher speed, single medium for interconnection (twisted pair, coax,

opt), no routing within ‘segments’ – all point-to-point (from hub), inter-segment connections via switches/hubs, low latency, low error rate

u 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

n MANs: (confined to extended, regional area, typically, up to 50km spread)u Based on high-bandwidth copper and fiber optics for multimedia

(audio/video/voice), u 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 on TV networks and longer distances than DSL

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3.2. Type of Networksn WANs: (worldwide, lower speeds over sets of varying types of circuits with routers)

u 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

n Wireless: (connecting portable, wearable devices using access points)u 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.

u 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.

u Tiny screens of mobiles and wearables require a new WAP protocoln Internetworks

u 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

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

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3.2. Type of Networksn Comparisons

u Range of performance characteristics:u Frequency and types of failures, when used for DS applicsu 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 1-10WAN IP routing worldwide 0.010-600 100-500MAN ATM 250 kms 1-150 10Internetwork Internet worldwide 0.5-600 100-500Wireless:WPAN Bluetooth (802.15.1) 10 - 30m 0.5-2 5-20WLAN WiFi (IEEE 802.11) 0.15-1.5 km 2-54 5-20WMAN WiMAX (802.16) 550 km 1.5-20 5-20WWAN GSM, 3G phone nets worldwide 0.01-02 100-500

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3.3. Network principlesn Packet Transmission

u Packet transmission superseded telephone/telegraph switched network

u Messages are packetized and packets are queued, buffered (in local storage), and transmitted when lines are available using asynchronous transmission protocol

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

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

u Delivery of multimedia data to its destination is time-critical / low latency – requiring end-to-end predefined route

u 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 principlesn Switching Schemes – 4 Kinds of switching methods typically used

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

u Circuit Switching – Interconnected segments of circuits via switches/exchange boxes, e.g., POTS (Plain Old Telephone System)

u 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

u 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 principlesn Protocols –

u 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

u 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

Communicationmedium

Sender Recipient

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3.3. Network principlesn Protocols Layers – layered architecture, following the OSI suite

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

provided by the layer below itu A complete set of protocol layers constitute a suite or stacku 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

Communicationmedium

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3.3. Network principlesLayer Description ExamplesApplication 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 isindependent of the representations used in individual computers, which maydiffer. Encryption is also performed in this layer, if required.

Secure Sockets(SSL),CORBA DataRep.

Session At this level reliability and adaptation are performed, such as detection offailures 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 WANor an internetwork this involves the generation of a route passing throughrouters. In a single LAN no routing is required.

IP, ATM virtualcircuits

Data link Responsible for transmission of packets between nodes that are directlyconnected by a physical link. In a WAN transmission is between pairs ofrouters 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 ofbinary data by analogue signalling, using amplitude or frequency modulationof electrical signals (on cable circuits), light signals (on fibre optic circuits)or other electromagnetic signals (on radio and microwave circuits).

Ethernet base- bandsignalling, ISDN

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3.3. Network principles

Underlying network

Application

Network interface

Transport

Internetwork

Internetwork packets

Network-specific packets

MessageLayers

Internetworkprotocols

Underlyingnetworkprotocols

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3.3. Network principlesn Protocols

u Packet Assembly:u 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).

u 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 principlesn Protocols

u 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

u Packet Delivery (at network layer): • Datagram – one-at-a-time, hop-by-hop transmission of packets with no storing

of 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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n Routingu 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

u Algorithms depends on: 1) Either using VC or datagram -depends on network type, e.g., ATM uses VC connection-oriented and Internet uses datagram connectionless packet-switching; and 2) dynamics of the network – topologically, traffic patterns

u 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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Hosts Linksor local networks

A

D E

B

C

1

2

5

43

6

Routers

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3.3. Network principlesn The Routing Table – matrix/graph construction, reflecting topology of network

Routings from D Routings from ETo Link Cost To Link CostABCDE

336

local6

12201

ABCDE

4456

local

21110

Routings from A Routings from B Routings from CTo Link Cost To Link Cost To Link CostABCDE

local1131

01212

ABCDE

1local

214

10121

ABCDE

22

local55

21021

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3.3. Network principlesn The RIP algorithm for dynamic update and distribution of routing table info

u 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 Tlelse 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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n Congestion Controlu Link overload and queue overflows

u Packet dropping – manageable at network layer using retransmission up to a threshold/limit (when throughput starts to decline)

u 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 –

u 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 principlesn Internetworking

u 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

u 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 other mobiles by encapsulating IP packets over other networks, Another, e.g., PPP for transmitting IP packets.

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file

compute

dialup

hammer

henry

hotpoint

138.37.88.230

138.37.88.162

bruno138.37.88.249

router/sickle

138.37.95.241138.37.95.240/29

138.37.95.249

copper138.37.88.248

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

custard138.37.94.246

desktop computers

Eswitch

138.37.94

hubhub

Student subnetStaff subnet

otherservers

router/firewall

138.37.94.251

%

1000 Mbps EthernetEswitch: Ethernet switch

100 Mbps Ethernet

file server/gateway

printers

Campusrouter

Campusrouter

138.37.94.xx

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A BIPv6 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

MessageLayers

Underlying network

Network interface

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3.4. Network protocolsn Internet Protocols

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

u Forms a single ‘internetworking’ protocol (using IP datagram ‘encapsulation’ methods)

u 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)

u When TCP is not enough additional higher-level protocol, e.g., SSL (secure socket protocol) for security, can be built atop TCP

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

multimediau Internet protocols usually layered over existing ‘physical’ networks,

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

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3.4. Network protocolsn Encapsulation

u ‘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 protocolsConceptual (user view) architecture of TCP/IP over transmission networks

IP

Application Application

TCP UDP

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7 24

Class A: 0 Network ID Host ID

14 16

Class B: 1 0 Network ID Host ID

21 8

Class C: 1 1 0 Network ID Host ID

28

Class D (multicast): 1 1 1 0 Multicast address

27

Class E (reserved): 1 1 1 1 unused0

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octet 1 octet 2 octet 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 254240 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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dataIP address of destinationIP 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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Sender

Home

Mobile host MH

Foreign agent FAInternet

agent

First IP packet addressed to MH

Address of FAreturned to sender

First IP packettunnelled to FA

Subsequent IP packetstunnelled to FA

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Internet

Router/Protected intraneta) Filtering router

Internet

b) Filtering router and bastion

filter

Internet

R/filterc) Screened subnet for bastion R/filter Bastion

R/filter Bastion

web/ftpserver

web/ftpserver

web/ftpserver

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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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LAN

Server

WirelessLAN

Laptops

Base station/access point

Palmtop

radio obstruction

A B C

DE

2005/9/11 40


Physical

Application

ATM layer

Higher-layer protocols

ATM cells

ATM virtual channels

MessageLayers

ATM adaption layer

2005/9/11 41


Flags DataVirtual channel idVirtual path id

53 bytes

Header: 5 bytes

VPI in VPI out

23

45

VPI = 3

VPI = 5

VPI = 4

Virtual path Virtual channels

VPI = 2

VPI : virtual path identifier

VP switch VP/VCswitch

VP switch

Host

Host

Documents

Chap 3. Networking and Internetworking · 2005/9/11 5 3.1. Intro n Bandwidth vs. bit-rate u The total system bandwidth (volume of data sent and received in a unit time, e.g., per