Weiqiang Sun 一些数据 从 1978 年到 2007 年，通信业年业务收入一直保持两位数增长并一直领 先于 GDP...

Weiqiang Sun

一些数据• 从 1978 年到 2007 年，通信业年业务收入一直保持两位数增长并一直

领先于 GDP 增幅。业务总量和业务收入年同比增长率均保持了两位数，年收入规模从 7.3 亿元扩张到 7280 亿元，年均增长率达到 26.9%– 78 ～ 87 年，电信业务收入年平均增长率达到 21.1%, 7.3 亿 -> 41.1 亿– 88 ～ 97 年，电信业务收入年复合增长率达到 42.2%, 59.6 亿 1421.3 亿– 98 ～ 07 年，电信业务收入年平均增长率达到 16.6%, 1828.4 亿 7280

亿– 2007 年，电信业务收入增长 11.2%, GDP 增速 13.0%– 2008 年，电信业务收入增长 9.0%, GDP 增速 6.6%– 2009 年上半年，电信业务收入增长 2.3% ，不到 GDP 的 1/3

• 电信业的转型– 话务运营阶段– 转型阶段– 信息运营阶段

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Weiqiang Sun

机会在哪里？• 3G 与宽带！

• 2009 年上半年，电信运营商资本开支投向主要是 3G 、传输网 ( 光传输 ) 、和宽带 (FTTx)– 3G

• 中国移动计划 2009 年底前 3G 覆盖 238 个城市， 2011 年覆盖所有地级市

• 中国联通 3G 网络覆盖城市已由年初计划的 284 个扩大到年内的 335个， 2010 年将近一步扩大覆盖面

– 宽带业务具有高 ARPU 值，现金流稳定的特征• 宽带提速• 有线宽带和无线宽带的融合发展和无缝连接

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Weiqiang Sun

NETWORK LAYER IN PRACTICE: IP AND ATM

Weiqiang Sun

The TCP/IP protocol suite

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• Transmission Control Protocol / Internet Protocol• Developed by DARPA to connect universities and research labs

Applications

Transport

Network

Link

Telnet, FTP, email etc

TCP, UDP

IP, ICMP, IGMP

Device drivers, interface cards

TCP: Transmission Control ProtocolUDP: User Datagram ProtocolIP: Internet Protocol

The Internet Layered model

Weiqiang Sun

Internetworking with TCP/IP

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application

transport

IP

Data link and lower layer

application

transport

IP

Data link and lower layer

IP

Ethernet Token ring

Token ringEthernet

Ethernet

IP protocol

IP protocol

TCP/UDP protocol

FTP, HTTP, SMTP…

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The TCP/IP suite

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PING telnet & rlogin FTP SMTP X Trace

route DNS TFTP BOOTP SNMP RPC

TCP UDP

ICMP IP IGMP

DATA LINKARP RARP

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Internet sub-layer

• A sub-layer between the transport and network layers is required when various incompatible networks are joined together– This sub-layer is used at gateways between the different networks– In the internet this function is accomplished using the Internet Protocol (IP)

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IP

DLC LayerLink 1

DLC LayerLink 1

DLC LayerLink 1

DLC LayerLink 1

DLC LayerLink 1

DLC LayerLink 1

On a gateway connecting different types of networks, IP is the protocol to realize inter-operability

Weiqiang Sun

IP addresses

• 32 bit address written as four decimal numbers– One per byte of address (202.120.39.134)

• IP Address classes

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10 Net ID Host ID

0 Net ID Host ID

8 32

16 32

110 Net ID Host ID

16 32

Class A Address

Class B Address

Class C Address

11100000

16 32Class D Address, (For multicast only)

Weiqiang Sun

IPv4 address classes

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Weiqiang Sun

Routing a packet in the network

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1

2

5

3

6

4

11

22

1122

33

11 33

22

11 22

33

44

11

22 33

11

22 33

Routing table in 5

Dest Next Hop Out Intf

1 3 2

2 2 1

3 3 2

4 3 2

6 6 3

Routing table in 3

Dest Next Hop Out Intf

1 1 1

2 5 4

6 6 3

4 4 2

5 5 4

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Weiqiang Sun

IP router architecture

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3 generations of IP routers

Bus based router

Bus based router with dist. routing

Switch-based router with multi. Forwarding eng.

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Host name

• Each host has a unique name• Domain name system (DNS): a distributed

database that provides a mapping between IP addresses and host names

• E.g., 202.120.39.134 FRONT.SJTU.EDU.CN

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Weiqiang Sun

Internet standards

• Internet Engineering Task Force (IETF)– Development on near term internet standards– Open body– Meets 3 times a year

• Request For Comments (RFCs)– Official internet standards– Available from IETF web page: http://www.ietf.org/

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Weiqiang Sun

The Internet protocol (IP)

• Routing packets across the network• Unreliable service

– Best effort delivery– Recovery from lost packet must be done at higher layers

• Connectionless– Packets are delivered independently– Can arrive out of order– Re-ordering must be done at higher layers

• Current version V4, IPv4• Future IPv6

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Weiqiang Sun

IP header

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0 bit Version Header length Type of Service Total Length

32 bit Identification Flags Fragment Offset

64 bit Time To Live Protocol Header Checksum

96 bit Source IP Address

128 bit Destination IP Address

160 bit Options

160or192+ Data

Note that the minimum header size is 20 bytes, or 160 bits

Weiqiang Sun

IP header

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Weiqiang Sun

Dynamic Host Configuration (DHCP)

• Automated method for assigning network numbers– IP addresses, default routers

• Computer contact DHCP server at Boot-up time• Server assigns IP address• Allows sharing of address space

– More efficient use of address space– Adds scalability

• Addresses are “leased” for some time– Not permanently assigned

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Weiqiang Sun

Address Resolution Protocol (ARP)

• The role of the IP routing is to deliver the packet to its destination subnet– To the last hop router

• Addressing inside a subnet, or a LAN, is based on local addresses, such as Ethernet addresses

• ARP provides a mapping between IP addresses and LAN addresses• RARP provides mapping from LAN addresses to IP addresses• Both accomplished by sending out a broadcast message• An ARP cache is maintained at each node with recent mappings to avoid

frequent address resolution (for better performance)

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Weiqiang Sun

ARP at source subnet

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R1

S

(4) I am here at 00-01-21-32-32-32

(3) Hi all~ Where is my lovely router R1?

(1) Computer S is configured to have a default router R1(2) S wants to send a message to D, and D is outside of the same LAN(3) S sends an ARP request for Ethernet Address of R1(4) R1 sends ARP responds to S(5) S sends the message to R1 with Ethernet addressing(6) R1 routes the packet to the next hop in the internet and the message

will be subsequently routed further toward D

Weiqiang Sun

ARP at destination subnet

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R2

D

(3) Hi all~ I got a message for 202.120.39.134. Where is

he?

(4) Hi R2~ I am here at 00-01-01-11-AB-

ED

(1) An IP packet is delivered by the network from its source subnet to router R2.

(2) Router R2 realizes that the packet has reached its destination subnet by comparing the destination address in the IP packet and its local interface configurations (subnet address and mask)

(3) Router R2 sends an ARP request on the interface to the subnet(4) Destination node D responses to the request(5) Packet is delivered to D with Ethernet addressing

Weiqiang Sun

Routing in the multi-AS Internet

• The Internet is divided into sub-networks, each under the control of a single authority known as an Autonomous Systems (AS)

• Routing algorithms are divided into two categories– Interior protocols (within an AS)– Exterior protocols (between ASs)

• Interior protocols use shortest path algorithms– Distance vector proto. Based on Bellman-Ford– Link state proto. Based on Dijkstra’s algorithm

• Exterior protocols route packets across ASs– Issue: no single cost metric, policy routing, etc– Hierarchical routing based on “peering” agreements– Example: Exterior Gateway Protocol (EGP) and Border Gateway Protocols

(BGP)

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Weiqiang Sun

Border Gateway Protocol (BGP)

• Routing between Autonomous systems– Find a path (no optimality) to destination (AS)– Path must satisfy policy criteria

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AS corporation

AS Large service

provider

AS Large service

provider

AS Small ISP

AS corporation

AS corporation

AS Small ISP

AS Small ISP

Transit AS

Multi-homed AS(No transit traffic)

Stub AS

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BGP overview• BGP speaker – one per AS

– Establishes (TCP) sessions with other “speakers” to exchange reachability information

• Border “gateways” – routers that interface between AS’s• BGP advertises complete paths to destination AS

– Avoid loop problems– Enable policy decisions (e.g. avoid certain ASs)– AS numbers – centrally assigned 16 bit numbers for transit ASs

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128.64.3128.61.2

192.12.2Path to 128.64.2: (AS-144, AS-367)

AS - 12 AS - 144

AS - 367

AS - 298

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Relationship between ASs

• ISP “tiers”– Tier-1 ISPs – provide global reachability– Tier-2 ISPs – regional/country– Tier-3 ISPs – local

• Provider-customer relationship (transit)– Smaller ASs purchase internet access from

larger ones

• Peering– ISPs of similar size are “peers” and

forward each other’s traffic at no charge– Paid peering: a small ISP may purchase

the right to peer with a larger provider

• Policy issue– Which route would an ISP advertise?

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Tier-1 ISP

Tier-2 ISP Tier-1 ISP

Tier-2 ISP

Tier-3 ISP

Weiqiang Sun

IPv6

• Effort started in 1991 as IPng• Motivation

– Need to increase IP address space– Support for real-time applications – QoS– Security, mobility and auto-configuration

• Major changes– Increased address space (128bit)– Support for QoS via Flow Label field– Simplified header– Security

• Transition to IPv6– Cannot be done at once; must support co-existance– Dual-stack: routers run both IPv4 and IPv6– Tunneling: IPv6 packets carried in payload of IPv4 packets, or vice versa

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Weiqiang Sun

QoS in the Internet

• Quality of Service parameters– Dropped packets– Delay– Jitter– Out-of-order delivery– Error

• Applications that require QoS– Multimedia streaming – IPTV– IP telephony, or VoIP– Video conferencing– Online game– Remote control– …

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Weiqiang Sun

QoS mechanisms

• IntServ: integrated services– best-effort service, real-time service, and

controlled link sharing– Resource reserved prior to data transfer– Resource released after transfer completes

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request

grant

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QoS mechanisms (cont.)

• DiffServ: differentiated services– Tagging on ingress edge node– Un-tagging on egress edge node– Routed/processed in network according to the tag/label– Realizes service differentiation through per-hop behavior (PHB)

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Weiqiang Sun

DiffServ and MPLS

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• MPLS: Multi-Protocol Label Switching

Weiqiang Sun

ATM - Asynchronous Transfer Mode

• 1980’s effort by the phone companies to develop an integrated network standard (B-ISDN) that can support voice, data, video, etc.

• ATM uses small (53 Bytes) fixed size packets called “cells” – Why cells?

• Cell switching has properties of both packet and circuit switching Easier to implement high speed switches

– Why 53 bytes? • Small cells are good for voice traffic (limit sampling delays) For 64Kbps voice it takes 6 ms to fill

a cell with data

• ATM networks are connection oriented – Virtual circuits

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Weiqiang Sun

ATM Reference Architecture

• Upper layers – Applications – TCP/IP

• ATM adaptation layer – Similar to transport layer – Provides interface between upper layers

and ATM – Break messages into cells and

reassemble • ATM layer

– Cell switching – Congestion control

• Physical layer – ATM designed for SONET – Synchronous optical network – TDMA transmission scheme with 125 μs

frames

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Weiqiang Sun

ATM Cell format

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Weiqiang Sun

VPI/VCI

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Weiqiang Sun

ATM cell switches

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Weiqiang Sun

ATM summary

• ATM is mostly used as a “core” network technology • ATM Advantages

– Ability to provide QoS – Ability to do traffic management – Fast cell switching using relatively short VC numbers

• ATM disadvantages – It not IP -most everything was design for TCP/IP – It’s not naturally an end-to-end protocol

• Does not work well in heterogeneous environment • Was not design to inter-operate with other protocols • Not a good match for certain physical media (e.g., wireless)

• Many of the benefits of ATM can be “borrowed” by IP– Cell switching core routers – Label switching mechanisms

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Weiqiang Sun

Project #1

• Try to identify at least 3 applications that use plaint text password/identification method– Use Wireshark to capture the plaint text password– Write a report to describe the problem

– Due date: Oct. 28

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