First, the composition of the Internet
From the look works can be divided into two
- Edge portion: composed of all the hosts connected to the Internet. This is part of the user directly used for communications and resource sharing
- Core components: a large number of networks and routers connecting the network components. This section is provided for the edge portion (Interconnecting and exchange)
1.1 edge Internet
All hosts edge portion of the Internet that is connected to the Internet, also known as end system
client system may function in very different
meaning from end-system: "host A and host B communicate" actually means running a program running on the host a and the host B on another program to communicate, i.e., another process is a process and a host B communicate with host a, referred to as "communication between computers"
Communication between end systems
1, client - server approach
- Refers to two users and server applications are designed in-process communication
- Client - server described the relationship between the service and the service of process
- Customers are the service requester , the server is a service provider
- Service requestor and the service provider must use the services provided by the network core part
Features client software
- After the operation is called user , and then intends to initiate communication to a remote server communication. Therefore, the client must know the address of the server program
- It does not require special hardware and complex operating system
Features of the server software
- A specialized program for providing a certain service may process a plurality of local or remote client requests
- The system automatically calls after the start and has been continuously running, waiting passively and accept communication requests from customers around the country. Therefore, the client does not have to know the address of the server program
- Generally require powerful hardware and advanced operations support systems
After establishing the relationship between client and server communication, the communication may be bidirectional, client and server can send data
2, on the other connections
- Refers to two peer to peer connections in the host does not distinguish which is the communication service provider or a service requester
- As long as both hosts running peer to peer connectivity software, they will be able to communicate peer to peer connection
- Both sides can download other shared documents already stored in the hard disk
Features: In essence still use client - server mode, only peer connections per host both a client and a server , such as Host C Host D service requests, customer C, D is the server; if C simultaneously to host F to provide services, then C also plays a role in server
Peer connections can support large numbers of users simultaneously, etc.
1.2 core part of the Internet
The core part of the Internet network by a number of routers and interconnecting them composition, the Internet is the most complex part
between the core portion are generally high-speed routers link connection, the host edge portion generally at a relatively low rate link connection
1, the router
is not directly between the input and output ports to connect
to forward the packet, i.e. packet-switched
during the processing of the packets:
- The first group received income cache (temporary storage)
- Find forwarding table to find a destination port forwarding which should address
- Forwarding the packet to the appropriate port.
A router is a key component to achieve packet switching, packet forwarding its mission is to receive, which is the core of the network some of the most important functions
2, hosts and routers
host user information processing, and transmits a packet network, the network receives a packet from the
router to forward packets stored last packet delivery to the destination host
Second, the performance index
2.1 rate
The amount of bits of data in a computer unit, the unit amount of information used in information theory is
the most important performance indicators, referring to the data transmission rate, also known as the data rate or bit rate
Unit: bit / s, kbit / s , Mbit / s , Gbit / s. 4 * 10 ^ 10bit / s referred to as 40Gbit / s
rate often refers to the nominal rate or nominal rate, not the actual operating speed
2.2 Bandwidth
Definition: The ability of a data channel transmission network, i.e. the maximum data rate per unit time (bit / s) in the network can be a channel through
on the time axis, with the width of the signal increases the bandwidth is narrowed
2.3 Throughput
Definition: the amount of data per unit time through a network (or channel, interface)
is limited by the bandwidth of the nominal rate of the network or networks
2.4 Delay
Definition: data (a packet or packets, even bits) transmitted from one network (or link) to the other end of the desired time delay also called delay or
consists of the following components
2.4.1 sending delay
Also called transmission delay
when transmitting data, the data frames entering the time required for the transmission medium from the junction, i.e., the first bit from the transmitted data frame, the time of the last bit of the frame has been sent required: definition of
the transmission extension data frame length = (bit) / transmission rate (bit / s)
2.4.2 propagation delay
Definition: the electromagnetic wave propagation a distance spent in the channel time
and the propagation delay is substantially different
transmission rates and signals in the propagation rate of the channel is completely different
propagation delay = channel length (m) / signal propagation rate channel ( m / s)
2.4.3 processing delay
Time host or router receives the packet, processing the packet (e.g., header analysis, data extraction, error checking) takes Definitions:
2.4.4 queuing delay
Definition: the router delays the input packet output queue are queued for experienced process
often depends on the network traffic was
attached: where four kinds of delay produced
prone misconception
- For high-speed network links, only to increase the transmission rate of the data transmission bit rate instead of the link
- Link bandwidth is reduced to improve the data transmission delay
We can not say "a bit on the high-speed link (or high-bandwidth links) will be transmitted faster."
2.5 delay-bandwidth product
Also referred to in bits length link
delay propagation delay bandwidth product = Bandwidth *
2.6 round trip time RTT
Definition: starts data transmission from the sender to the sender receives acknowledgment from the recipient of the total elapsed time
on the Internet, the round trip time comprises a processing delay of each further intermediate nodes, queuing delay and transmission delay of forwarding data
2.7 Utilization
Into channel utilization and network utilization
channel utilization noted that a few percent of the channel time is utilized (with data)
network utilization is a weighted average channel utilization of the channel network-wide
channel utilization is not more high as possible. When a channel utilization increases, the delay caused by the rapid increase in channel
D0: when the network idle time delay D: Current Delay Network U: network utilization
are: D = D0 / (1 - U)