Summary of Data Communications

Transcription

1 Summary of Data Communications Nixu Oy PL 21 A REFRESHING TOUR - INCLUDES PICTURES (Mäkelänkatu 91) Helsinki, Finland tel fax info@nixu.fi

2 Network models TCP/IP Application TCP, UDP IP Data link Physical OSI Application Presentation Session Transport Network Data link Physical Copyright 2000 Nixu Oy1/20

3 How to retrieve a web page URL: HTML: <H1>Homepage</H1> HTTP: GET /index.html TCP: port 80, ACK 4378 IP: to: Ethernet: to: 00:00:00:12:56:A7 Browser open IP: routing ETH ATM Display WWW server HTML HTTP TCP IP ATM Copyright 2000 Nixu Oy2/20

4 A Data Packet on Ethernet Application data TCP Application data IP TCP Application data IP TCP Application data IP TCP Application data ETH IP TCP Application data CRC ETH IP TCP Application data CRC PPP IP TCP Application data Host Router Copyright 2000 Nixu Oy3/20

5 The Link Layer Transports data over physical media Often limited by the constraints of the physical media Ethernet > limited to short range connections (100 m - 1 km) > different cabling options (coaxial cabling, twisted pair etc.) Several common alternatives Ethernet ATM PPP In the TCP/IP world actually consits of many layers and services Copyright 2000 Nixu Oy4/20

6 IP IP = The Internet Protocol Defined in RFC-791 IP sends simple datagrams over network. It provides unreliable and connectionless delivery service. unreliable = no guarantees, best effort only connectionless = each packet is routed separately Copyright 2000 Nixu Oy5/20

7 Routing Router Default x x Router x.x x.x x.x Router... Router Default Default x x WWW-server WWW-client Copyright 2000 Nixu Oy6/20

8 TCP TCP = Transmission Control Protocol Defined in RFC-793 Connection-oriented, reliable, byte-stream service Application data is broken into segments, which are sent as IP datagrams. Features: checksums, timeouts and flow control segment reassembly in correct order, discarding duplicate packets Copyright 2000 Nixu Oy7/20

9 Reliable TCP operation Receiver sends acknowledgment for each segment. If a packet gets lost, timeout will ensure it s retransmitted Sender Packets in transit Receiver packet 1 packet gets lost waiting for acknowledgment retransmission Normally a sliding window technique Sender packet 1 packet 2 packet 3 waiting for ACK Packets in transit packet arrives acknowledgment sent Receiver Copyright 2000 Nixu Oy8/20

10 Application Level Protocol Sample 220 tcm.hut.fi SMTP/smap Ready. helo jalopeno.nixu.fi 250 (jalopeno.nixu.fi) pleased to meet you. mail from: 250 Sender Ok rcpt to: 250 OK data 354 Enter mail, end with "." on a line by itself From: kiravuo@jalopeno.nixu.fi To: kiravuo@hut.fi Subject: terveisiä Heipparallaa. 250 Mail accepted quit 221 Closing connection Copyright 2000 Nixu Oy9/20

11 What Protocols do? A protocol shall be: Completely and unambiguously defined Free of dead-locks and live-locks Able to recover from all error conditions Some possible functions of protocols Addressing Connections Error detection and correction Flow control Priorization Multiplexing/splitting Segmentation/concatenation Copyright 2000 Nixu Oy10/20

12 Network relations The network entities use different behavioral models on all protocol layers Client-Server Store and Forward Push Pull Poll Master-Slave Connection (Stateful) Connectionless (Stateless) Copyright 2000 Nixu Oy11/20

13 Copyright 2000 Nixu Oy12/20 OSI Model Two (N)-level entities in different systems communicate using (N)-level protocol The services give by layer (N) to layer (N+1) are realized in (N)-level protocol by encapsulation and decapsulation Encapsulation means embedding each layer s Service Data Units (SDU) into the Protocol Data Units (PDU) of the layer immediately below it, decapsulation is the reverse process Entities at the same level in separate systems are called peer entities (N+1)-level entities are using (N)-level services through (N)-level Service Access Points ((N)-SAPs) One (N+1)-entity can be simultaneously connected to one or more (N)-SAPs One (N)-SAP is connected to one (N)-entity

14 Socket Service Interface Protocols are usually internationally standardized Service interface implementations are usually operating system specific Different implementations can communicate, with common protocol Application programs need to be modified to use different interfaces Unix socket interface example: 1. open socket 2. parse address 3. connect to server 4. write request 5. read response 6. close socket Copyright 2000 Nixu Oy13/20

15 Network design and management The art and science of creating and maintaining working network that provide services The design starts at the requirements specification Design without clear requirements is usually pointless Major constraints are: Services required Performance and reliability Money Copyright 2000 Nixu Oy14/20

16 The FCAPS Model Fault Management Configuration Management Accounting Performance Management Security Management Part of Telecommunications Management Network (TMN) standard from ITU Here used more as a conceptual framework and checklist Copyright 2000 Nixu Oy15/20

17 Distributed Computing Generally a view of shared computing and data resources, transparent communications between programs and access to objects located in other hosts Sun RPC the first popular protocol CORBA and Jini currently interesting Advantages are access to shared resources, transparent communications and flexibility Disadvantages are added complexity and security risks Copyright 2000 Nixu Oy16/20

18 IPv6 Features 128-bit address space Lasts to foreseeable future (even if allocated badly) Header format simplification To reduce the common-case processing cost of packet handling and to limit the bandwidth cost of the IPv6 header. E.g. no IPv6 header checksum (routers win big time) Improved support for extensions and options Flow Labelling Capability Capability to enable the labelling of packets belonging to particular traffic "flows" for which the sender requests special handling. > Quality of Service Copyright 2000 Nixu Oy17/20

19 Mobile IP home net A remote network A Copyright 2000 Nixu Oy18/20

20 Quality of Service (RSVP) 1. Path message 2. Resv message Copyright 2000 Nixu Oy19/20

21 Network Security Internet & Threats DMZ Firewall Internal network Protected off-site network VPN gateway WWW server VPN server Copyright 2000 Nixu Oy20/20