Internet Protocol Stack Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012

What’s the Internet: “nuts and bolts” view  millions of connected computing devices: hosts = end systems  running network apps Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points  communication links  fiber, copper, radio, satellite  transmission rate = bandwidth  routers: forward packets (chunks of data)

What’s the Internet: “nuts and bolts” view  protocols control sending, receiving of msgs  e.g., TCP, IP, HTTP, Skype, Ethernet  Internet: “network of networks”  loosely hierarchical  public Internet versus private intranet  Internet standards  RFC: Request for comments  IETF: Internet Engineering Task Force Home network Institutional network Mobile network Global ISP Regional ISP

What’s the Internet: a service view  communication infrastructure enables distributed applications:  Web, VoIP, , games, e-commerce, file sharing  communication services provided to apps:  reliable data delivery from source to destination  “best effort” (unreliable) data delivery

The topology structure Star Tree Bus Ring Mesh Network Node + communication lines, reflecting the network structure of the inter-entity relations

What’s a protocol? human protocols:  “what’s the time?”  “I have a question”  introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols:  machines rather than humans  all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

What’s a protocol? a human protocol and a computer network protocol: Q: Other human protocols? Hi Got the time? 2:00 TCP connection request TCP connection response Get time

关于网络协议的中文说明  计算机网络中的数据交换必须遵守事先约定好 的规则。  这些规则明确规定了所交换的数据的格式以及 有关的同步问题（同步含有时序的意思）。  网络协议 (network protocol) ，简称为协议， 是为进行网络中的数据交换而建立的规则、标 准或约定。

网络协议的组成要素  语法 数据与控制信息的结构或格式 。  语义 需要发出何种控制信息，完成何种动 作以及做出何种响应。  同步 事件实现顺序的详细说明。

Physical Media  Bit: propagates between transmitter/rcvr pairs  physical link: what lies between transmitter & receiver  guided media:  signals propagate in solid media: copper, fiber, coax  unguided media:  signals propagate freely, e.g., radio Twisted Pair (TP)  two insulated copper wires  Category 3: traditional phone wires, 10 Mbps Ethernet  Category 5: 100Mbps Ethernet

Physical Media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable  legacy Ethernet  broadband:  multiple channels on cable  HFC Fiber optic cable:  glass fiber carrying light pulses, each pulse a bit  high-speed operation:  high-speed point-to-point transmission (e.g., 10’s- 100’s Gps)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise

Physical media: radio  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects:  reflection  obstruction by objects  interference Radio link types:  terrestrial microwave  e.g. up to 45 Mbps channels  LAN (e.g., Wifi)  11Mbps, 54 Mbps  wide-area (e.g., cellular)  3G cellular: ~ 1 Mbps  satellite  Kbps to 45Mbps channel (or multiple smaller channels)  270 msec end-end delay  geosynchronous versus low altitude

The Network Core  mesh of interconnected routers  the fundamental question: how is data transferred through net?  circuit switching: dedicated circuit per call: telephone net  packet-switching: data sent thru net in discrete “chunks”  (message-switching)

Network Core: Circuit Switching End-end resources reserved for “call”  link bandwidth, switch capacity  dedicated resources: no sharing  circuit-like (guaranteed) performance  call setup required

Network Core: Circuit Switching network resources (e.g., bandwidth) divided into “pieces”  pieces allocated to calls  resource piece idle if not used by owning call (no sharing)  dividing link bandwidth into “pieces”  frequency division  time division

Circuit Switching: FDM and TDM FDM frequency time TDM frequency time 4 users Example:

Numerical example  How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?  All links are Mbps  Each link uses TDM with 24 slots/sec  500 msec to establish end-to-end circuit Let’s work it out!

Network Core: Packet Switching each end-end data stream divided into packets  user A, B packets share network resources  each packet uses full link bandwidth  resources used as needed resource contention:  aggregate resource demand can exceed amount available  congestion: packets queue, wait for link use  store and forward: packets move one hop at a time  Node receives complete packet before forwarding Bandwidth division into “pieces” Dedicated allocation Resource reservation

Packet switching versus circuit switching  1 Mb/s link  each user:  100 kb/s when “active”  active 10% of time  circuit-switching:  10 users  packet switching:  with 35 users, probability > 10 active at same time is less than.0004 Packet switching allows more users to use network! N users 1 Mbps link Q: how did we get value ?

Packet switching versus circuit switching  great for bursty data  resource sharing  simpler, no call setup  excessive congestion: packet delay and loss  protocols needed for reliable data transfer, congestion control  Q: How to provide circuit-like behavior?  bandwidth guarantees needed for audio/video apps  still an unsolved problem (chapter 7) Is packet switching a “slam dunk winner?” Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?

Protocol “Layers” Networks are complex!  many “pieces”:  hosts  routers  links of various media  applications  protocols  hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

Why layering? Dealing with complex systems:  explicit structure allows identification, relationship of complex system’s pieces  layered reference model for discussion  modularization eases maintenance, updating of system  change of implementation of layer’s service transparent to rest of system  e.g., change in gate procedure doesn’t affect rest of system  layering considered harmful?

计算机网络的体系结构  计算机网络的体系结构 (architecture) 是计算 机网络的各层及其协议的集合。  体系结构就是这个计算机网络及其部件所应完 成的功能的精确定义。  实现 (implementation) 是遵循这种体系结构的 前提下用何种硬件或软件完成这些功能的问题 。  体系结构是抽象的，而实现则是具体的，是真 正在运行的计算机硬件和软件。

Internet protocol stack  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  PPP, Ethernet  physical: bits “on the wire” application transport network link physical

Network Software Protocol Hierarchies Layers, protocols, and interfaces

Notions  Entity: any hardware of software process that can send or receive message; the active elements of every layer.  Peer entities: two entities that locate at the same layer of different system. Protocol is used between peer entities.  Interface: the interface between the contiguous layers.  Service: the function of one layer and its underlying layers, services are provided to the contiguous above layer through interface.  Protocol Stack: the set of protocols of a system.  Network Architecture: the layer structure and the protocols.

Services to Protocols Relationship The relationship between a service and a protocol.

ISO/OSI reference model  presentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine- specific conventions  session: synchronization, checkpointing, recovery of data exchange  Internet stack “missing” these layers!  these services, if needed, must be implemented in application  needed? application presentation session transport network link physical

ISO/OSI reference model

A Critique of the OSI Model and Protocols  Why OSI did not take over the world Bad timing Bad technology Bad implementations Bad politics

Bad Timing  The apocalypse of the two elephants.

TCP/IP RM

Example of TCP/IP 4-layer protocol Application Transport Internet Interface AB router network 2network 1 Application Transport Internet Interface Internet Interface

A Critique of the TCP/IP Reference Model  Problems: Service, interface, and protocol not distinguished Not a general model Host-to-network “layer” not really a layer No mention of physical and data link layers Minor protocols deeply entrenched, hard to replace

Hybrid Model  TCP/IP Model: Five-layer structure  Internet protocol stack  The hybrid reference model to be used in this book.

Node 1 sends data to Node Computer 1 AP 2 AP 1 Computer 2 pass data to the application layer add the application head, becomes msg

Computer 1 AP 2 AP 1 Computer 2 pass the msg to transport layer add the transport head

Computer 1 AP 2 AP 1 Computer 2 pass the segment to network add the network head, becomes datagram

Computer 1 AP 2 AP 1 Computer 2 pass the datagram to the data link layer add the link head and tail, becomes frame

Computer 1 AP 2 AP 1 Computer 2 pass the frame to the physical layer physical layers passes the bit stream to the media

physical media Computer 1 AP 2 AP 1 electronic signal is transmitted in physical media from the sender PHY to the receiver PHY Computer 2

Computer 1 AP 2 AP 1 Computer 2 the physical layer receives the bit stream, and hands over frame to the above data link layer

Computer 1 AP 2 AP 1 Computer 2 data link layer picks out the datagram and hands over to the network layer

Computer 1 AP 2 AP 1 Computer 2 network layer picks out the segment and hands over to the transport layer

Computer 1 AP 2 AP 1 Computer 2 transport layer picks out the msg and hands over to the application layer

Computer 1 AP 2 AP 1 Computer 2 application layer picks out the data and hands over to the application

Computer 1 AP 2 AP 1 Computer 2 I received the data sent by AP1 ！

Computer 1 AP 2 AP 1 Computer 2 application data app head H5H bit stream application data H5H5 H4H4 H5H5 H3H3 H4H4 H5H5 H4H4 trans head H3H3 net head H2H2 link head T2T2 link tail

Computer 1 AP 2 AP 1 Computer bit stream After receiving the bit stream, the physical layer of computer 2 hands it over to the link layer H2H2 T2T2 H3H3 H4H4 H5H5 application data

H3H3 H4H4 H5H Computer 1 AP 2 AP 1 Computer 2 After removing the head and tail of the frame, link Layer hands over the data to the network layer. H2H2 T2T2 H3H3 H4H4 H5H5 application data

H4H4 H5H5 H3H3 H4H4 H5H Computer 1 AP 2 AP 1 Computer 2 After removing the head, the network layer hands over the data to the transport layer.

H5H5 application data H4H4 H5H Computer 1 AP 2 AP 1 Computer 2 After removing the head, the transport layer hands over the data to the application layer.

application data H5H Computer 1 AP 2 AP 1 Computer 2 After removing the head, the application layer hands over the data to the application.

Computer 1 AP 2 AP 1 Computer 2 I received the data sent by AP1 ！

source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch Encapsulation message M HtHt M HnHn frame

Functions of each layer physical layer establish, maintain and release physical connection between two entities of data link layer. prescribe the electronic parameter of the physical layer. prescribe the connector bit To transfer bit stream

data link establish, maintain and release data link, show a right link to the network layer dividing and synchronizatio n of frames error detection and control access control frame Functions of each layer To transfer data from one node to its adjacent node

network forwarding datagram Functions of each layer Host-to-host data transmission routing

transport provide logical communication between app processes error control sequence control flow control segment Functions of each layer Process-to-Process (end2end) data transmission

application provide interface for users Functions of each layer message

Protocols and networks  Protocols and networks in the TCP/IP model initially.

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Introduction: Summary Covered a “ton” of material!  Internet overview  what’s a protocol?  network edge, core, access network  packet-switching versus circuit-switching  performance: loss, delay, throughput  layering, service models  Internet trends