Transcript 32 bit - FRONT!

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%
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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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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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NETWORK LAYER IN PRACTICE: IP AND ATM
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The TCP/IP protocol suite
• Transmission Control Protocol / Internet Protocol
• Developed by DARPA to connect universities and research labs
The Internet Layered model
Applications
Telnet, FTP, email etc
Transport
TCP, UDP
Network
IP, ICMP, IGMP
Link
Device drivers, interface cards
TCP: Transmission Control Protocol
UDP: User Datagram Protocol
IP: Internet Protocol
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Internetworking with TCP/IP
FTP, HTTP, SMTP…
application
TCP/UDP protocol
transport
IP
protocol
IP
Data link and
lower layer
Ethernet
Ethernet
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application
IP
protocol
IP
Ethernet
transport
Token
ring
IP
Data link and
lower layer
Token ring
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The TCP/IP suite
PING
telnet &
rlogin
FTP
SMTP
X
Trace
route
TCP
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DNS
TFTP
BOOTP
SNMP
RPC
UDP
ICMP
IP
IGMP
ARP
DATA
LINK
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)
On a gateway connecting different types of networks,
IP is the protocol to realize inter-operability
IP
DLC Layer
Link 1
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DLC Layer
Link 1
DLC Layer
Link 1
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IP addresses
• 32 bit address written as four decimal numbers
– One per byte of address (202.120.39.134)
• IP Address classes
8
0
32
Net ID
Class A Address
Host ID
16
10
Net ID
32
Host ID
16
110
Net ID
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Class C Address
Host ID
16
11100000
Class B Address
32
Class D Address,
(For multicast only)
8
IPv4 address classes
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Routing a packet in the network
1
3
4
1
1
2
2
1
1
3
4
2
2
Routing table in 2
1
1
5
Next Hop
Out Intf
1
1
1
3
1
1
Dest
Next Hop
4
5
2
1
5
5
2
6
5
2
Dest
Next Hop
Out Intf
1
1
1
2
1
1
3
3
2
5
3
2
6
6
3
Routing table in 3
3
Dest
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3
6
2
2
Routing table in 4
2
3
4
3
Dest
Next Hop
Out Intf
Out Intf
1
1
1
3
2
2
5
4
2
2
1
6
6
3
3
3
2
4
4
2
4
3
2
5
5
4
6
6
3
Routing table in 5
10
IP router architecture
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3 generations of IP routers
Bus based router
Switch-based router with multi. Forwarding eng.
Bus based router with dist. routing
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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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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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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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IP header
0 bit
Version
32 bit
64 bit
Header
length
Type of Service
Total Length
Identification
Time To Live
Flags
Protocol
Fragment Offset
Header Checksum
96 bit
Source IP Address
128 bit
Destination IP Address
160 bit
Options
160or
192+
Data
Note that the minimum header size is 20 bytes, or 160 bits
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IP header
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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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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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ARP at source subnet
(4) I am here at
00-01-21-32-32-32
(3) Hi all~ Where is
my lovely router R1?
S
R1
(1)
(2)
(3)
(4)
(5)
(6)
Computer S is configured to have a default router R1
S wants to send a message to D, and D is outside of the same LAN
S sends an ARP request for Ethernet Address of R1
R1 sends ARP responds to S
S sends the message to R1 with Ethernet addressing
R1 routes the packet to the next hop in the internet and the message
will be subsequently routed further toward D
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ARP at destination subnet
(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
D
R2
(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
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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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Border Gateway Protocol (BGP)
• Routing between Autonomous systems
– Find a path (no optimality) to destination (AS)
– Path must satisfy policy criteria
AS
corporation
AS
Large service
provider
AS
Large service
provider
AS
Small ISP
AS
Small ISP
AS
corporation
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AS
corporation
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
AS - 367
AS - 12
Path to 128.64.2:
(AS-144, AS-367)
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128.64.3
128.61.2
AS - 144
AS - 298
192.12.2
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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
Tier-1 ISP
Tier-2 ISP
Tier-1 ISP
• 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
Tier-2 ISP
Tier-3 ISP
• Policy issue
– Which route would an ISP advertise?
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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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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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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
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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DiffServ and MPLS
• MPLS: Multi-Protocol Label Switching
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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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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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ATM Cell format
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VPI/VCI
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ATM cell switches
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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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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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