IT Basic Concept
2016-09-02 17:24:26 0 举报AI智能生成
Internet Technology Architecture
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大纲/内容
OSI
1. Physical (Bits)
2. Data Link (Frames)
Handling transmission errors
CRC
Data flow regulation
3. Network (Packets)
Routing
Connectionless Network Protocol (CLNP)
does not perform connection setup or termination because paths are determined independently for each packet that is transmitted through a network.
best-effort delivery, which means that no guarantee exists that data will not be lost, corrupted, misordered, or duplicated
relies on transport-layer protocols to perform error detection and correction.
Connectionless Network Service (CLNS). CLNP and CLNS
Connection-Oriented Network Protocol (CONP)
Connection-Mode Network Service (CMNS)
Connectionless Network Protocol (CLNP)
Connectionless Network Service (CLNS)
does not perform connection setup or termination because paths are determined independently for each packet that is transmitted through a network.
provides best-effort delivery, which means that no guarantee exists that data will not be lost, corrupted, misordered, or duplicated.
relies on transport-layer protocols to perform error detection and correction
4. Transport (TPDU)
Combine data into segments
Segments are smaller than packets so they will be wrapped inside packets
connection-oriented transport service
this service is provided to session layer so must be connection-oriented
5. Session (SPDU)
Validate access
Data Transmission Control
6. Presentation (PPDU)
Data Encrypt/Decrypt
Data Decode/Encode/TransCode
Data Compression/Decompression
7. Application (APDU)
Questions
Why it does not take over the world?
Principles of Design
1. A layer should be created where a different abstraction is needed.
2. Each layer should perform a well-defined function.
3. The function of each layer should be chosen with an eye toward
defining internationally standardized protocols.
Basic Terms
Network
Type of Networks
Personal Area Network
Local Area Network
Transmission Technology
Physically connected network
Topology
Bus
Only 1 machine can transmit at any pointing time, need to resolve conflicts, Ethernet is the most common practice
Ring
Each transmission bit is propagated individually, FDDI is the most common practice
Metropolitan Area Network
Internt
World Wide Web
Telnet
Euronet
Bitnet
Mechanism
Inherently it is a network of networks
Type of Services
Connection-oriented
Reliable message stream
Sequences of pages
Reliable byte stream
Remote login
Unreliable connection
Digitised voice
Connectionless
Unreliable datagram
Junk mail
Acknowledged datagram
Registered mail
Request reply
Database query
Packet
IP Address
Network Tranmission
Broadcast Link
Broadcasting is a mode of operation which allows a packet to be transmitted that every machine must process.
Multicast Link
Multicasting is a mode of operation which allows a subset of machines to process a given packet.
Point to Point Link
Point to point networks consist of many connections between individual pairs of machines.
Service Primitives
Set of primitives that a layer provides to a layer above it
At the start of the discussion on each layer we talked about the services that the layer provides to the upper layer.
Types
LISTEN
CONNECT
ACCEPT
RECEIVE
SEND
DISCONNECT
Protocol
Rules which govern the format and meaning of packets that are exchanged by peers within a layer
Model
TCP/IP
OSI
Overhead
Categories
Headers for each packet
Establishing and ending the connection
Re-transmitted packets
Usage
The overheads/headers are used to allow each layer in the networking architecture perform their particular service.
These headers are part of how data is transferred between the networking layers, as is what we call ENCAPSULATION, and keeps networking functions separate and modular between the layers.
HTTP GET EXAMPLE
SYN and SYN ACK packets at the beginning which establishes a reliable connection between two hosts
the RST or FIN packet at the end when the connection is closed.
The packets in the middle are the transferring of the actual web page.
Between every two or three packets that are received, our computer sends an ACK or acknowledgement packet to communicate to the remote host that the packets sent were successfully received.
Why keep overhead with layering architecture?
A non-layered architecture may be more efficient (less or even zero protocol overhead), but at the cost of flexibility and modularity.
ADV: Information hiding (i.e. if you were a network engineer, you would not need to know detailed information on the physical layer or link layer – remember the interface?)
ADV: Flexibility (the ability to change protocols in a certain layer, without affecting the operation of other layers).
Network Architecture Design Issues
LAN
ADV of LAN over simply using a big time-sharing system
The LAN can be grown INCREMENTALLY. If the the LAN is just a long cable, it cannot be brought down by a single failure (if the servers are replicated). It is probably cheaper. It provides more computing power and better interactive interfaces.
Layering Architecture/Protocols
Breaking up the design problem into smaller, more managable pieces, and layering means that the protocols can be changed without affecting higher to lower ones.
International Standards
One advantage is that if everyone uses the standard, everyone can talk to everyone. Another is the widespread use of any standard will give its economies of scale, as with VLSI chips.
A disadvantage is that the political compromises necessary to achieve standardisation frequently lead to poor standards. Another disadvantage is that once a standard has been widely adopted, it is difficult to change, even if new and better techniques or methods are dicovered.
OSI and TCP/IP Models
Similarities
Stacking of layered protocols
Similar functionalities in each of the layers
Layers above transport layer relate to applications
Differences
TCP/IP does not distinguish between services interfaces and protocols
TCP/IP does not clearly separate physical and data link functions
OSI supports connectionless and connection-oriented at the network layer, while TCP/IP supports only connectionless at the IP layer
OSI supports only connection-oriented at the transport layer while TCP/IP supports both connectionless and connection-oriented at the transport layer(at TCP layer, each packet should receive ACK to finish transmission, while at IP layer it only takes packets as independent segment of data)
Topologies
Linear
Links: N-1 (N is number of nodes)
Ring
Links: N
Full Mesh
Used for connecting military centres, cost not important, reliability is the top priority
Links: C(2)(N)
Quality of Services(QoS)
reliability
delay
jitter
bandwidth
Good QoS Techniques
Over-provisioning
more than adequate buffer, router CPU, and bandwidth
Buffering
buffer received flows before delivery-increases delay, but smoothes out jitter, no effect in reliability or bandwidth
Traffic Shaping
regulate the average rate of transmission and burstiness of transmission
Buckets
leaky bucket: finite internal queue (in a buffer), regulates outbound flow as well as inbound flow
token bucket: finite internal queue (in buffer), variable to maximum outbound flow
Admission Control
routers can decide based on traffic patterns whether to accept new flows, or reject/reroute them
Server
Client
Network Device
PC
Router
Switch
Phone
TCP/IP
1. Host-to-Network Layer
2. IP or Internet Layer(this layer = network layer + datalink layer in OSI)
3. TCP or Transport Layer
TCP is a connection-oriented transport protocol that sends data as an unstructured stream of bytes
Three-way handshakes
4. Application Layer
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
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