1. TCP/IP
陳彥文

2. 傳統上，人們將數據或文件等視為資料(Data)；當通信技術成為日常生活的一部份後，發現除了語音可通信外，數據及視訊通信也是重要的應用。
何謂資料？
IEEE對Data的定義為 -- A representation of facts, concepts, or instructions in a formalized manner suitable for communication, interpretation, or processing by human or automatic means.
傳統上，人們將數據或文件等視為資料(Data)；當通信技術成為日常生活的一部份後，發現除了語音可通信外，數據及視訊通信也是重要的應用。
資訊 --- 包含 Voice, Data, Fax, Video, etc.

3. 資訊需依據各中種不同處理及應用的需要，做適當的格式(Format)轉換以另一種方式表達(Representation)。
Functions, Works, ----> Program
Program ----> Assembly code, Machine code (Processor-dependent)
流水帳 ----> 各種有意義的報表
非標準格式資料(資訊) ----> 共通、標準且易於處理的格式
任何資訊要在通信網路上傳送，也必須將資訊Represent成適合通信的格式。

4. 對目前網路而言，資訊大都先轉為Digital(0與1的信號)後，再在網路上傳送。
數位傳送的資訊對不同的應用，各有不同的意義及格式。例如：數據資料用的ASCII, EBCDIC碼、語音的A-Low、u-Low、視訊的MPEG等。
0與1在傳輸線上的表現方式：
+Voltage
0 Volts
較常用的表現方式則包括Unipolar, Bipolar, RZ, 及NRZ幾種

5. Data
Conversion
Compres.
Dagital
Transmission
Data
Conversion
Uncompres.
Sampling
ADC
Data conv./
Compres.
Analog
Transmission
Filter
DAC
Data conv./
Uncompres.

6. Conversion from analog into Digital
Conversion: Sampling (rate) --> Quantization (bit)
If a signal is to be reconstructed as the original signal it must sampled at a rate defined by the Nyquist criterion:
The sampling rate must be twice the highest frequency of the signal

7. Compression Methods Lossless compression: 資料保持正確性
Lossy compression: 分析重要影響資訊與不重要影響資訊, -- Voice, Video
e.g. 24-bit color information (16.7 million colors) v.s. 10-bit color information (1024 colors) are only a little dofference to eye.

8. 網路概念 Packet Switch (分封交換) v.s. Circuit Switch (電路交換)
電路交換 - 網路提供一條Dedicate的通路(Channel)專供收/送兩端專用。
例如： 電話網路等
分封交換 - 網路提供通信資源(通路、頻寬等)給大家共用，並未專屬於任一使用者使用者將資料切成符合網路標準的資料封包(Packet)，由網路送到收端
----> Virtual Circuit。
例如： Internet, X.25網路等

9. Connection oriented v.s. Connectionless
Connection oriented -- 送端要送資料前先通知(by signalling或人工)網路，建立收/送端的通道。
---> 電路交換一定是Connection oriented。
Connectionless -- 送端要送資料前，毋須先行建立收/送端的通道，但在每一送出之封包，均要註明收端住址(Address)，網路依其收端住址將資料送達目的地。 ----> 分封交換有可能是Connection oriented也可能是Connectionless。

10. 電路交換
B, A B, C
A, B A, C B
Network A
C, B C
分封交換

11. 電話網路(Public Switch Telephone Network, PSTN)
傳送的資料分 (1) User Information
(2) Signalling
Trunk 1 (Analogue)
Trunk 2 (Analogue)
4 lines: 2 for communication
2 for A-->B and B-->A supervision signal

12. 網路上傳送的訊息，包括 Signaling User Information Supervision Signal (監視網路及用戶狀態)
Control and Registration Signal (Addressing and Handshaking)
User Information
End-to-end message (對網路為透通性)
Network

13. 利用語音125us取樣一次(每次8個Bit)，及多工的方式可將多個Channel收容在一對線上傳送
125us us us ‧‧
n-1 n
Frame
n個channels的多工

14. ※ 北美標準PCM第一級多工(T1 or DS1)為24個Channels，即
每一Frame(125us duration)含24channels，8bits/ch，但每一Frame均
有一個bit做為Framing bit (added bit framing)，因此，
每一Frame共有 8x24+1= 193 bits
T1的速率：193bits/125us = 1544K bits/sec = 1.544Mbps
※歐洲標準PCM第一級多工(E1)為32個Channels，即
每一Frame(125us duration)含32channels，8bits/ch，每一Frame的
第0個Time slot (channel)做Synchronization，沒有Framing bit
(added channel framing)，因此
每一Frame共有 8x32 = 256 bits
E1的速率：256bits/125us = 2048K bits/sec = 2.048Mbps

15. Signalling Channels T1/DS1: E1:
“盜取”每第6個及第12個Frame的最右邊Bit (Least Significant Bit, LSB)
----> 每一channel由64KBps減為56KBps
E1:
第16個channel固定做為Signalling Channel
----> 真正提供給User使用為30channels

16. Why Chop a Message/File into Small Units
Error control
Congestion/flow control
Resource sharing
Buffer management
Scheduling management
Chop a message/file into packets/frames

17. Integrated Services Digital Networks
ISDN is a circuit switched network.
Multiplexing technique for the integration of ISDN channels
B channel: 64kbps
D channel: 16kbps or 64kbps
H channel: 384kbps (for H0); 1536kbps (H11); 1920kbps (H12)
Interface
Basic rate interface (BRI): 2B+D
Primary rate interface (PRI): 23B+D; 30B+D

18. Packet v.s. Frame
Packet  more logical or software view on the concept of small block of data
Frame more hardware or network dependent

19. Open System Interconnection (OSI) Model-- Seven Layers
應用層(Application Layer)
表達層(Presentation Layer)
會議層(Session Layer)
傳輸層(Transport Layer)
網路層(Network Layer)
鏈結層(Data Link Layer)
實體層(Physical Layer)

20. Basic Functions of Protocols
Encapsulation/Decapsulation
Segmentation/Reassembly
Connection Establishing
Flow Control
Error Control
Multiplexing

21. Layering Protocols 應用層 應用層 表達層 表達層 會議層 會議層 傳輸層 傳輸層 網路層 網路層 鏈結層 鏈結層 實體層
系統 B
應用軟體 X
應用軟體 Y
應用層
應用層通訊協定
應用層
表達層
表達層通訊協定
表達層
會議層
會議層通訊協定
會議層
傳輸層
傳輸層通訊協定
傳輸層
網路層
網路層通訊協定
網路層
鏈結層
鏈結層通訊協定
鏈結層
實體層
實體層通訊協定
實體層
傳輸媒介

22. 網路的基本概念(續)

23. Encapsulation/Decapsulation Mechanisms
往下送時訊框包裝
往上送時訊框拆裝
應用軟體 X 資料
應用軟體 Y
應用層 AH 資料
應用層
表達層 PH 資料
表達層
會議層 SH 資料
會議層
傳輸層 TH 資料
傳輸層
網路層 NH 資料
網路層
鏈結層
鏈結層
F A C 資料
FCS F
實體層
位元串
實體層
通訊路徑

24. Connections Multiplexing
Upward Multiplexing: Several layer N connections should be
multiplexed into a layer N-1 connection.
Downward Multiplexing: a layer N connection uses several
layer N-1 connections.
通訊軟體
通訊軟體
通訊軟體
通訊軟體
服務點
向上多工
向下多工
一對一
第 N 層
第 N-1 層

25. Physical Medium Twisted Pair 同軸電纜 光纖(Optical Fiber) Wireless
Shield twisted pair (STP)
Unshield twisted pair (UTP)
同軸電纜
光纖(Optical Fiber)
Wireless

26. 光纖通信基本概念 光纖通信特點 不受電磁干擾 低傳輸損失 體積小、重量輕、耐熱/水性佳 頻寬大 (10^13 ~ 10^16 Hz)
低原料成本
適用於數位傳輸
光纖通信缺點：饋電問題、線路分岐、接續、切割

27. 光纖通信系統基本架構 Decoder Out 一般通信系統架構 Decoder Out In 驅動電路 信號放大 光纖 感測器 光纖通信架構
Encoder
Decoder In
Out
Transmission Media
Modulator
Demodulator
一般通信系統架構
Encoder
Decoder
Out In
驅動電路
信號放大 光纖 光源
感測器
光纖通信架構

28. 光纖通信主要元件 光源種類：發光二極體(LED)、雷射二極體(LD) LED較適用於短距離、小容量光纖通信系統(e.g.用戶迴路)
LD較適用於長距離、大容量光纖通信系統(e.g. 長途中繼系統)
LED常用於短波長(0.8~1.0um)、LD則常用於長波長(1.3~1.5um) ---> depends on 材質
目前LED壽命較LD為長，但LD的輸出功率較大

29. 光纖通信主要元件(續) 光纖原理與結構 光纖基本上由兩部份組成：核心(Core)與纖殼(Cladding)
Core部份直徑約5~100um, 材質折射率大於Cladding
Cladding部份直徑約100~300um
光纖傳輸原理係利用幾何光學中介質不同折射率之全反射原理(Snell定律)
光纖分單模(Single-mode)與多模(Multi-mode)兩種，而依核心折射率的分佈，又可分為Step Index及Graded Index兩種
單模光纖較不會產生波形失真/損失，但核心直徑小，接續耦合時易造成損失

30. 光纖通信主要元件(續)
光感測器(檢光元件)之基本原理是將Diode的PN介面施以反向偏壓形成空乏區(無自由電子)，此時若接受到入射光的光子能量大於電子能隙時，便會激發自由電子的移動
常見之光感測器有PIN檢光二極體與瀉光二極體(Avalanche Photo Diode, APD)兩種
PIN大約只產出數奈安培(nA)的電流(APD約uA)
APD的缺點：複雜、成本高、外加偏壓大、易受溫度影響

31. 光纖的損失原因 固有損失 吸收損失 光散亂(Dispersion) 外部加力產生的損失 光纖畸變、彎曲等 人為因素 光元件耦合
連接損失：端面不平、有切角、核心面積不對稱、沒對準等

32. 網際網路之功能 Internet - 網際網路(Internet)是網路所構成的網路 (Network of Networks)
- 透過網際網路可達到資源/資料共享、訊息交換的目的
LAN
Internet
LAN

33. Definition of Local Area Network
IEEE: A LAN is a data communication system allowing a number of independent devices to communicate directly with each other, within a moderately sized geographic area over a physical communications channel of moderate dada rates .

34. Network Topologies Star Single Star (IEEE 802.12 100VG-AnyLAN, ATM)
Multiple Star (Snowflake) (ATM)
Bus
Single Bus (IEEE CSMA/CD, IEEE Token-Bus)
Dual Bus (IEEE DQDB)
Tree
Ring
Single Ring (IEEE Token Ring)
Dual Ring (FDDI, FDDI-II)
Mesh

35. Access Control Methods
Network Topologies
Star Topology
Bus/Tree Topology
Ring Topology
Mesh Topology
Transmission Control
Random Transmission Control
Distributed Transmission Control
Centralized Control

36. Transmission Control Random Transmission Control
ALOHA Network, Wireless LAN
Carrier Sense multiple access with collision detection (CSMA/CD)
Slotted Ring
Register Insertion Ring
Distributed Transmission Control
Token Passing : Token-Ring (FDDI), Token-Bus (GM, MAP)
Carrier Sense multiple access with collision avoidance (CSMA/CA)
Distributed Queue Dual Bus (DQDB)
Centralized Control
Polling
Circuit Switching (X.25, Frame-Relay, ATM network)
Time-division Multiple Access (TDMA)
Frequency-division Multiple Access (FDMA)
Wavelength-division Multiple Access (WDMA)
Code-division Multiple Access (CDMA)

37. IEEE Project 802 Standards
IEEE High Level Interface
IEEE 802.1D Local Bridge (Spanning Tree Algorithm)
IEEE 802.1G Remote Bridge
IEEE LLC (Logical Link Control)
IEEE CSMA/CD (Carrier Sense Multiple Access with Collision Detection; Fast Ethernet/Gigabit Ethernet
IEEE Token-Bus
IEEE Token-Ring
IEEE DQDB (Distributed Queue Dual Bus)
IEEE Broadband Technical Advisory Group
IEEE Fiber Optic Technical Advisory Group
IEEE Integrated Voice and Data LAN Working Group
IEEE LAN Security Working Group
IEEE Wireless LAN
IEEE Demand-Priority (100VG-AnyLAN)
ATM Basic

38. Bus Topology - Ethernet

39. Ring Topology – Token Ring

40. Ring Topology - FDDI

41. Star Topology - ATM
ATM Switch

42. Layer 2 v.s. Layer 3 LAN LAN LAN R R R R R R End to end Link by link
Routing Routing Routing Routing
End to end
Link by link
LAN
LAN
LAN R R R R R R

43. Unique Flag (Pattern) in bit oriented protocol
Flag Address Control Information FCS Flag
Flag
Zero bit insertion technique - <i> Flag pattern為單一
<ii> 的資訊能順利傳送
，不會混淆
方法 - 傳送資料時，逢五個連續1則插入一個0

44. Layer 2 – EtherFrame Format

45. Layer 2 – Ethernet Frame Type
Frame type value
Meaning DC
Reserved
0800
Internet Protocol
0805
X.25
6559
Frame Relay
Novell IPX
0806
Address Resolution Protocol (ARP)
…..

46. Major Technologies in Layer 2
Technology
CO/CL
LAN
WAN
Token Ring CL X
FDDI
Ethernet
ATM CO
Frame Relay
SMDS

47. Internet Overview Various Applications IP IP IP MAC MAC MAC PHY PHY
TCP/UDP
TCP/UDP IP IP IP
MAC
MAC
MAC
PHY
PHY
PHY
Internet

48. TCP and UDP TCP ---> Connection oriented connection
Connection establishment and release
Sequence number
UDP ---> Connectionless connection
Datagram services

49. 應用 Transport TCP UDP Net. IP Data link IEEE 802系列 Phy.
Ping, Telnet, FTP, Rlogin, … RPC, SNMP, ...
Transport
TCP
UDP
Net. IP
Data link
IEEE 802系列
Phy.

51. IPv6與IPv4之比較 IPv4 Packet Header IPv6 Packet Header 32 bits 32 bits
Ver.
32 bits
32 bits
Service
Type
Pri-
ority
IHL
Total Length
Ver.
Flow Label
Identification
Frag Offset
Payload Length
Flags
Next Header
Hop Limit
Protocol
Type
Source Address
Time to Live
Header Checksum
Source Address
Source Address
Destination Address
Source Address
Options + Padding
Source Address
Destination Address
Destination Address
Destination Address
Destination Address

52. Routing -- Routing table in Router
Eth 2
Eth 0
Router R
Eth 3
Eth 1 R R
Destination
Interface
Eth0
Eth1
Eth2 R R

53. Routing --Address Classes
3 Address Classes in Internet
Class A
Class B
Class C
Use network number to route a packet to the destination 10
110

54. Max. of Hosts per Network
IP Address
Address Class
Bits in Prefix
Range of Values
Max. of Networks
Max. of Hosts per Network A 7
0~127
128 B 14
128~191
16384
65536 C 21
192~223
256 D 20
224~239 -- E
240~255

55. IP Address
The IP address is not only an identify for a specific device in internet, it also identifies a connection between the device and a network.
Each port of a router shall be assigned one IP address.

56. Routers and IP Addressing

57. IP Networks and Routing
Interior Routing Protocols
RIP (Routing Information Protocol)
OSPF (Open Shortest Path First)
Other Protocols
Exterior Routing Protocols
EGP (Exterior Gateway Protocol)
BGP (Border Gateway Protocol) v.s. CIDR (Classless Inter Domain Routing)
Policy Routing

58. RIP
RIP is a simple protocol based on “Bellman Ford” protocol  distance vector
Overview of distance vector routing
Start up
Link breaks
Bouncing effect
Counting to infinity
Improvement schemes  split horizon; triggered updates
Decrease the time to converge

59. Comparison of RIPv1(rfc-1058, 1988) and RIPv2 (rfc-2453, 1998)
Subnet routing – support subnet mask information
Authentication – simple password protection defined in 2453, and MD5 is defined in rfc-2082
Next hop indication
Multicasting – define IP class D address for information advertisement.

60. OSPF Link state routing v.s. distance vector routing
Link state routing protocols are based on the “distributed map” concept
Changing information of the network is achieved by flooding protocol
Main issue – to maintain a synchronized copy of the link state database in all nodes of the network  secure map updates
Shortest path first  Dijkstra algorithm

61. Why is a link state protocol better?
Fast, loopless convergency
Support of precise/multiple metrics
The largest throughput; the lowest delay; the lowest cost; the best reliability; …
Metric per system v.s. metric per packet (OSPFv2)
Support multiple paths to a destination
Traffic splitting
Separate representation of external routes

62. Protocols within RIP and OSPF
RIP packets are carried over UDP/IP with port 520
Packets are sent every 30 seconds, or faster when triggered updates
If a route is not refreshed within 180 seconds (6x30), the distance is set to infinity
Each entry (one route) of RIP message is encoded over 20 bytes long (reservation part is used in RIPv2 for authentication, and etc.)

63. Protocols within RIP and OSPF
OSPF runs on top of of the IP layer with protocol type 89
Composes of 3 subprotocols
Hello: for checking the operation of the link and elect the designated/backup routers
Exchange: master/slave operation for exchange the routing information in DB
Flooding: to maintain the synchronization of the two databases

64. Other Routing Protocols
Intermediate System to Intermediate System (IS-IS)
Defined by ISO in 1980s for DECnet (especially in the Backbone) and many concepts of IS-IS were adopted by OSPF
IGRP (Internet Group Management Protocol)
Similar to ICMP and is a proprietary protocol defined by Cisco
Distance vector family protocol
Composite metrics: delay (D), bandwidth (B), reliability (R), load (L)

65. Exterior Routing Protocols
Splitting the internet into autonomous systems (AS)
Concept of AS
The minimum AS is composed of exactly one router directly connecting one LAN to Internet
An As can “self-routing” within its local network
Hierarchical (two) level routing
Exterior routing is to exchange routing information among ASs

66. Exterior Gateways’ Protocol (EGP)
EGP is run over IP with protocol type number 8
EGP Messages
Neighbor acquisition: to determine two adjacent gateways agree to become neighbors
Neighbor reachability: to monitor the links
Network reachability: exchange the reachability information

67. EGP Protocol NA  NR  NetR
Neighbor acquisition is a two-way handshake procedure; while the partner may refuse
Neighbor reachability uses “hello” and “I heard you” (I-H-U) packets to check the link
“Dual threshold” procedure is used to avoid oscillation
A reachable link is declared to be unreachable if fewer than “I-H-U”s have been received for the last “hello”s.
An unreachable link is declared to be reachable only if at least “I-H-U”s have been received for the last “hello”s.

68. EGP Protocol
AS “Z”
(transit)
AS “X” A B E F
AS “Y” D C

69. BGP
The main issue of BGP: large routing information and memory/CPU power requirement – “BGP-4 Protocol Analysis, “rfc-1774, March, 1995.
History of BGP:
BGP-1 (rfc-1105, 1989); BGP-2 (rfc-1163, June, 1990); BGP-3 (rfc-1267, Oct., 1991); BGP-4 (rfc-1654, 1994, rfc-1771, 1995)
BGP v.s. Calssless Inter-Domain Routing (CIDR) – CIDR was proposed in 1993~1995
Reduce routing table size
Route aggregation

70. BGP BGP is run over TCP/IP (with port number 179) Packet types of BGP
TCP provides a reliable data transmission link (with fair flow/congestion control), however,
Routing update packet to cure network congestion,…
Security issue (rfc-2385, 1998 – Protection of BGP Sessions via TCP MD5 Signature Option”)
Packet types of BGP
OPEN
UPDATE
NOTIFICATION
KEEPALIVE

71. BGP Initial exchange Updates
Use OPEN packet to check the BGP version and the “hold time” (the number of seconds used by the “keep alive procedure”)
Use UPDATE packet to exchange (list of) “withdrawn routes” and metrics information of each path
Updates
Loop protection
Stable – the path shall not oscillate too rapidly between reachable and unreachable

72. BGP Keep alive Error Notifications
According to the “hold time” value, and the keep alive messages will not exchanged for zero hold time.
Error Notifications
Message header error
OPEN message error
UPDATE message error
Hold time expired
Finite state machine error
Cease (terminate the association)

73. IPv4 Header 32 bits Source Address Destination Address
Service
Type
Ver.
IHL
Total Length
Identification
Flags
Frag Offset
Protocol
Type
Time to Live
Header Checksum
Source Address
Destination Address
Options + Padding
Version: IP protocol version (currently, 4)
IHL: Internet Header Length (in 4-byte unit, value=5 if no option)
Service Type: 3-bit for precedence, 3-bit flags for (D)elay, (T)hroughput, (R)eliability)
Total Length: Total length of the packet (including header and payload)
Identification: Packet ID, used with fragmentation
Time to live: Packet live time (original in seconds, currently, number of hops)
Header Checksum: Error check for IP header

74. IP Fragmentation and Reassembly
Concept of Maximum Transmission Unit (MTU)
Each hardware (physical network) specifies the maximum amount of data that a frame can be carried.
The hardware is not designed to accept or transmit frames that carry more data than the MTU allows.
The internet contains heterogeneous networks, and therefore, the frames shall be fragmented when its frame size can not fit into the MTU size of the network to be transmitted

75. IP Fragmentation and Reassembly

76. IP Fragmentation and Reassembly
All fragmented packets have the same packet identification with the original packet.
The total length and header checksum shall be re-calculated.
The fragmentation offset is used to determine the fragmented packets when they arrived the destination
Two flags
DF: De-fragment
MF: More fragment

77. IP Fragmentation and Reassembly
The fragmented packets are reassembled at the end destination:
Reduce the amount of state information in routers
Allow routes to be changed dynamically (remember that the
IP network is connectionless)

78. IP Fragmentation and Reassembly
Fragment Loss
IP network does not guarantee the reliable packet forwarding  fragment may loss
The receiver can not hold some fragments of a packet for an arbitrary long time.  timer starts when the first fragment received.
If all fragments of a packet can not received before timer expired, all fragments are discarded and this packet is lost.
There is no mechanism for a receiver to tell the sender which fragments have arrived

79. IP Header – Protocol Type
The protocol type specifies the protocol used in transport layer
ICMP 1 IP 4
TCP 6
UDP 17
EGP 8
RSVP 46
…..

80. Frame, IP, TCP/UDP TCP/UDP datagram IP Packet (datagram) LAN Frame
LAN IP TCP/UDP Data LAN
Header Header Header (Higher Layer PDU) Trailer
TCP/UDP datagram
IP Packet (datagram)
LAN Frame

81. Hardware Address v.s. IP (Software) Address
IP Address (S, D)
Network Layer
MAC
(S, D)
MAC
(S, D)
MAC
(S, D)
MAC
(S, D)
MAC
(S, D)
MAC
(S, D)
Link Layer
LAN
LAN
LAN R R R R R R

82. Address Resolution Protocol
Address Resolution Techniques
Table lookup: centralized
Closed-from computation: configured address
Message exchange: distributed computing

83. Address Resolution Protocol

84. Address Resolution Protocol
ARP message format is sufficiently general to allow arbitrary protocol
and hardware address. The following format is used in Ethernet
Operation: value 1 for request and value 2 for response

85. Address Resolution Protocol
In order to reduce the network traffic, ARP extracts and saves the information from a response so it can be used for subsequence packets.  Caching
The caching table is maintained by the ARP software – normally, the oldest entry is replaced whenever a response arrival.
The address information is valid for a predefined period of time (e.g. 20 minutes)

86. Internet Control Message Protocol
ICMP is designed for the error detection and information reporting during the transferring of IP packets.
ICMP can be used as a passive tool to gather the network information, it can also applied as the “active” tool to assist the packet forwarding.

87. Internet Control Message Protocol
Examples of ICMP message types:
Source Quench (type=4): To indicate that the router has no more available buffer space available.
Destination Unreachable (type=3): A router determines that a datagram cannot be delivered to its destination (due to various causes, e.g. DF)
Echo request (type=8)
Echo reply (type=0)
Time exceed (type=11): For packets whose TTL=0
Traceroute (type=30)

88. Internet Control Message Protocol
Applications of ICMP
Test the reachability: the “ping” program uses the “echo request” and “echo reply” messages.
Trace route: the “traceroute” message may set the TTL field for route tracing.
MTU discovery: to find the MTU of a route by sending various-size packets with DM=1

89. Transport Layer Protocols
TCP
UDP IP
Network
Layer

90. TCP Source Port Destination Port Sequence Number
Acknowledgement Number
THL Reserved Flags Window
Checksum Urgent Pointer

91. UDP
Source Port Destination Port
Length Checksum
Data

92. TCP/UDP
Port number: specify the end-point (e.g. application, service) of a connection
The IP address and the port number form a 48-bit TSAP (Transport Service Access Point)
Sequence number (TCP): specify the sequence of the current datagram
Acknowledgement number (TCP): specify the “expected” number of datagram to be received
UDP length: the length of the UDP datagram (including the 8-byte UDP header)

93. Flags in TCP Header
URG: to indicate that the “Urgent Pointer” is in use. The urgent pointer is used to indicate a byte offset from the current sequence number at which urgent data are to be found.
ACK: to indicate the acknowledgement number field is valid.
PSH: to request the receiver to push the data to the application (not to buffer it).
RST: to reset a connection that has become confused due to a host crash or some other reason.
SYN: to establish a connection (SYN=1, ACK=0)
FIN: to release a connection.

94. Some TCP/UDP Port Numbers
ftp-data 20
telnet 23
smtp 25
login 49
www-http 80
DNS 53
BGP
179
SNMP
161
…… ……….

95. TCP Characteristics of TCP services Connection oriented
Point-to-point communication
Reliable communication
Full duplex communication
Reliable connection start up
Graceful connection shutdown

96. TCP Connection Establishment
S/R S/R
S R
SYN(SEQ=x)
SYN(SEQ=x)
SYN(SEQ=y)
SYN(SEQ=y, ACK=x+1)
SYN(SEQ=y, ACK=x+1)
(SEQ=x+1, ACK=y+1)
SYN(SEQ=x, ACK=y+1)
Three-way
Handshake
(SEQ=x+1, ACK=y+1)

97. TCP Connection Sequence/Ack Number Establishment Data Transfer Release
SYN Packet
SYN/Ack
Establishment
Ack
Sequence/Ack
Number
Data Transfer
FIN
FIN/Ack
Release
Ack

98. Retransmission in TCP

99. TCP Congestion/Flow Control
Timer is important in reliable (acknowledgement) communication
If timer is too short  enable duplicate packet transmission
If timer is too long  ineffective and waste network resources

100. TCP Flow Control Functions of flow control: Actions of flow control
To control the packet delay
To control the packet loss
Speed matching (flow control v.s. congestion control)
Actions of flow control
Call blocking, packet discarding, packet blocking, packet scheduling

101. Transmission Delay v.s. Window
Consider that the sender transmits a packet to the destination and waits for the ack. Message.  Sender and network are idle during this time
 Consecutive sending packets  window (limited traffic volume) control is required for traffic regulation.

102. TCP Congestion/Flow Control
TCP applies the “window” to regulate the packet flow.
TCP is an end-to-end flow control. Thus, the flow control operation is performed at the end system.
The network condition will affect the window size.

103. TCP Congestion/Flow Control
In TCP, the window size is controlled by the received.
Theoretically, the window size may be larger as the round-trip delay is longer.
The network condition is changeable, therefore, a better way is to make the “window size” dynamically adjustable according to the network condition.

104. TCP Congestion/Flow Control

105. TCP Congestion/Flow Control
Larger
Window
Size
Long Round-Trip
Time
If network
Congested
 Packet loss
More packets
on the way

106. TCP Congestion/Flow Control
Dynamic window size adjustment in TCP
The TCP connection transmits packet from slow start (e.g. single message containing data), if ack. Received, then doubles the window size.  exponential incremental until the half of the advertised window size, at which linear incremental is applied.
The window size is backing off quickly if congested. – Fast recovery

107. TCP Congestion/Flow Control
Initial send: 64K –fail
threshold is set to be half (32K)
Transmission 13 is time out
backing of and threshold set to
be half of 40K

108. Threats in TCP Protocols
SYN flooding attack: Exhaust the system resources (memory, computing power, etc.) by sending huge SYN packets for connections and without ack. for system’s SYN/ack.
Session hijacking: intercept the connection by “de-synchronization” and “re-synchronization” the sequence number.

109. Threats in TCP Protocols – SYN Flooding

110. Threats in TCP Protocols - Hijacking
Hacker
Reject
Server
Disturb Sequence Number
Client

111. Future IP Network – IPv6 and QoS

112. ‘97 Q2
‘99 Q3
‘99 Q4
‘00 Q1
‘00 Q2
‘00 Q3
‘00 Q4

113. !!! 2005! IPv6 您或許知道現在所用的Internet 通信協定是IPv4!
Total
Time
Volume
2005!
!!!

114. IPv6 v.s. IPv4 IPv4 PDU ... IPv6 PDU IPv4 Header Data Field
maximum
65535 octets
minimum
20 octets
IPv4 Header
Data Field
IPv4 PDU
maximum
65535 octets
Fixed
40 octets
0 or more
Extension
Header
...
Extension
Header
IPv6 Header
Data Field
IPv6 PDU

115. IPv6 Header IPv6 Packet Header 32 bits Source Address Source Address
Pri-
ority
Ver.
Flow Label
Payload Length
Next Header
Hop Limit
Source Address
Source Address
Source Address
Source Address
Destination Address
Destination Address
Destination Address
Destination Address

116. IPv6 v.s. IPv4 -- overview Main Changes in Protocol Header
Five fields are suppressed
IP Header length --> due to fixed header size
Header check sum --> performed in the lower (MAC) layer
Identification, Flags, and Fragment offset --> fragment will not support inside the network (only end-to-end)
Type of service --> replaced by Priority
Three fields are renamed
Length --> Payload length
Payload type --> Next Header
Time to live --> Hop limit
Two new fields
Priority, and Flow label --> support QoS

117. IPv6 v.s. IPv4 -- overview
Header Size is fixed and the optional fields are replaced by the Extension Headers (e.g. hop-by-hop header, authentication header, etc.)
12 fixed + options -----> 8 fixed + extension
Enhanced Functionality
Scoping in multicast address
Anycast address
Single interface with multiple address
Use “flow” concept for QoS management

118. Internet QoS – The big picture
Internet QoS service categories
Best-effort services
Provided in current internet
Relied on the end-to-end TCP-like congestion control
Controlled load service: a service that is close to a lightly loaded best-effort network
Guaranteed service: provides deterministic worst-case delay bound through strict admission control and fair queuing scheduling