1 kyung hee university prof. choong seon hong x.25
DESCRIPTION
3 Kyung Hee University X.25 패킷 교환망 (cont’d) 1974 년 ITU-T 가 개발 광역 통신망에서 사용되는 패킷 교환 프로토콜 연결설정, 데이터 교환, 확인응답, 흐름제어, 데이터 제어 등에 필요한 절차 패킷교환 (SVC, PVC) – 가상회선방식 이용 다중패킷 – 비동기식 TDM 방식이용TRANSCRIPT
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11Kyung Hee Universit
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Prof. Choong Seon HONG
X.25X.25
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22Kyung Hee Universit
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1717 장 장 X.25 X.25 패킷 교환망패킷 교환망
17.1 X.25 계층 구조 17.2 패킷 계층 프로토콜
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33Kyung Hee Universit
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X.25 X.25 패킷 교환망패킷 교환망 (cont’d)(cont’d)
1974 년 ITU-T 가 개발
광역 통신망에서 사용되는 패킷 교환 프로토콜
연결설정 , 데이터 교환 , 확인응답 , 흐름제어 , 데이터 제어 등에 필요한 절차
패킷교환 (SVC, PVC) – 가상회선방식 이용
다중패킷 – 비동기식 TDM 방식이용
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44Kyung Hee Universit
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X.25 X.25 패킷 교환망 패킷 교환망 (cont’d)(cont’d)
DCE : Data Circuit EquipmentDTE : Data Terminal Equipment
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55Kyung Hee Universit
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17.1 X.25 17.1 X.25 계층 구조계층 구조 X.25 Layers in Relation to the OSI Layers
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66Kyung Hee Universit
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X.25 X.25 계층 구조 계층 구조 (cont’d)(cont’d)
X.25 계층구조• 물리층 : ITU-T X.21(X.21bis)
• 데이터 링크층 : LAPB(link access procedure, balanced)
• Frame layer
• 네트워크층 : PLP(packet layer protocol)
• X.25 requires error detection and correction in both the
data link and network layers
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77Kyung Hee Universit
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Frame LayerFrame Layer
Format of a Frame
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88Kyung Hee Universit
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Frame Layer (cont’d)Frame Layer (cont’d)
Addressing at the Frame Layer
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99Kyung Hee Universit
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Frame Layer (cont’d)Frame Layer (cont’d) Three Phases of the Frame Layer
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1010Kyung Hee Universit
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Packet LayerPacket Layer
Network layer in X.25 is called the Packet Layer Protocol (PLP)
It is responsible for establishing the connection, transferring the data and terminating the connection
Virtual circuit : VCs in X.25 are created at the network layer
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1111Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
Frame layer and packet layer domain
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1212Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
Virtual circuit in X.25
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1313Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
Virtual Circuit Identifier (VCI)논리채널번호 (LCN: Logical Channel Number)LCN 의 영역은 지역 (Local) 에 국한 사용
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1414Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d) LCN 할당
최대 4096(212) 까지 허용one-way LCN : simplex 통신에 사용two-way LCN : duplex 통신에 사용
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1515Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
PLP 패킷
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1616Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
PLP 패킷 필드GFI(General Format Identifier) : 4 bit 필드
LCN(Logical Channel Number) : 12bit 필드 4 bit : LGCN(Logical Group Channel Number) 8 bit : LCN (Logical Channel Number)
PTI (Packet Type Identifier) 패킷 유형 식별자
Q D 순서번호0: PLP1: 다른 상위 프로토콜
0: Local DCE1: Remote DTE
순서번호 크기01: 3 bit10: 7 bit
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1717Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
Categories of PLP packets
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1818Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
Data Packets in PLP Layer
사용자 데이터 전송에 사용
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1919Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
RR, RNR, and REJ packets
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2020Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
Other control packets
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2121Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d) 제어 패킷 유형
000010
000011
000100
000101
001000
001001
000110
000111
111110
111111
111100
111101
Incoming call
Call connected
Clear indication Clear confirm
Interrupt
Interrupt confirm
Reset indication
Reset confirm
Restart indication
Restart confirmation
Registration confirm
Call request
Call accepted
Clear request
Clear confirm
Interrupt
Interrupt confirm
Reset request
Reset confirm
Restart request
Restart confirmation
Registration request
Code DCE to DTE DTE to DCE
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2222Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
제어 패킷 형식 Optional services - contractual call basis : incoming calls barred, outgoing calls barred, etc - per call basis : flow control negotiation, reverse charging, etc
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2323Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
제어 패킷 형식 (cont’d)
Reset : using an existing VC
Restart : using a new VC
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2424Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
연결 설정
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2525Kyung Hee Universit
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Packet Layer (cont’d)Packet Layer (cont’d)
연결 해제
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2626Kyung Hee Universit
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Other Protocol Related to X.25Other Protocol Related to X.25
X.121 Protocol 공중망 또는 사설망에 연결되는 DTE 들의 광역 주소 지정
14 디지트 : 4 디지트 : 데이터 네트워크 식별 코드
10 디지트 : 국가 단말 번호
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2727Kyung Hee Universit
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Other Protocol Related to X.25 (cont’d)Other Protocol Related to X.25 (cont’d) Triple-X 프로토콜
X.3 PAD : Packet Assembler/Disassembler 문자중심 (dumb) 단말 연결에 사용
X.28 : X.25 기능이 없는 단말 (dumb terminal) 과 PAD 간의 통신규약
X.29 : PAD 와 원격 단말 간의 관계 정의