Protocol Hierarchy
高雄大學資工系
嚴力行
Protocol Hierarchies
•Most networks are organized as a series
of layers or levels.
–Each layer offers certain services to the
higher layers
•Protocol
–an agreement between the communicating
parties on how communication is to proceed.
–Layer n protocol
Peers and Interfaces
•Peers
–The entities comprising the corresponding
layers on different machines
•Interface
–between each pair of adjacent layers
–defines which primitive operations and
services the lower layer offers to the upper
one.
Entities and Peer Entities
•An entity
–an active element in a layer
–can be a software entity (a process), a
hardware entity (an I/O chip), or both (an I/O
chip with its driver).
•Peer entities
–entities in the same layer on different
machines
Protocol Stacks
•A protocol stack.
–A list of protocols used by a certain system,
one protocol per layer
•Network architecture
–A set of layers and protocols
Protocol Hierarchy -- Example
•Protocol
– 中西式信封格式, 投遞方式,
寄 件 人
收 件 人
寄 件 人
收 件 人
4
郵
件
服務人員
郵
件
服務人員
3
分封打包
服務人員
分封打包
服務人員
2
運
輸
服務人員
1
運
輸
服務人員 Layer
etc.
•Peers
– 寄件人, 收件人
– 郵筒收件人員(窗台收件人員),
郵差(窗台服務人員)
•Layer 3/4 Interface
–Services
‧平信, 掛號信, 雙掛號信
–Primitives
‧郵筒投遞, 郵局窗台掛號
Layers at An Interface
SAP = Service Access Point
ID U = Int erface D ata Unit
SD U = Service D at a U nit
PD U = Protocol D ata Unit
ICI
= Int erface Cont rol Informat ion
ID U
Layer N + 1
ICI
SD U
SAP
Int erface
Layer N
ICI
SD U
SD U
N -PD U
Header
Layer N ent it ies
exchange N -PD Us
in t heir layer N
prot ocol
Example: SAPs in LLC
Higher Layer
Higher Layer
LLC
LLC
SAP
MAC
MAC
PHY
PHY
Medium
L2
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.
Connections Multiplexing
Application
Application
Application
Application
SAP
Upward
Multiplexing
One-to-one
Downward
Multiplexing
Layer N
Layer N-1
Connection-Oriented and
Connectionless Services
•connection-oriented
–Establish a connection first, use the
connection, and then release the connection.
–Example: the telephone system
•connectionless
–No connection is established.
–Example: the postal system
Service Primitives
• Request
– layer n+1 to layer n
• Indication
– layer n to layer n+1
– signal an event
• Response
Layer N+1
Layer N+1
1
3
4
Layer N
2
Layer N
– layer n+1 to layer n
– respond to the previous
indication
• Confirm
– layer n to layer n+1
– confirm the previous request
1. CONNECT.request
2. CONNECT.indication
3. CONNECT.response
4. CONNECT.confirm
Reference Models
•The OSI Reference Model
–based on a proposal developed by the
International Standards Organization (ISO)
–a first step toward international
standardization of the protocols used in the
various layers.
•The TCP/IP Reference Model
The OSI Reference Model
7
Application
6
Presentation
5
Session
4
Transport
Application Protocol
Presentation Protocol
Session Protocol
Transport Protocol
Application
APDU
Presentation PPDU
Session
SPDU
Transport
TPDU
Network
Packet
Frame
3
Network
Internal Subnet Protocol
Network
Network
2
Data Link
Data Link
Data Link
Data Link
1
Physical
Physical
Physical
Physical
Layer
Host A
Router
Router
Host B
Bit
Encapsulation/Decapsulation
Mechanisms
往下送時訊框包裝
往上送時訊框拆裝
應用軟體 X
應用層
AH
表達層
TH
網路層
鏈結層
實體層
NH
F A C
Data
應用層
表達層
會議層
Data
SH
傳輸層
應用軟體 Y
Data
PH
會議層
Data
傳輸層
Data
網路層
Data
Data
Bitstream
通訊路徑
FCS F
鏈結層
實體層
The TCP/IP Reference Model
7
6
5
4
3
2
1
Application
Application
Presentation
Not present
in the model
Session
Transport
Transport
Network
Internet
Data Link
Physical
Host-tonetwork
OSI
TCP/IP